app h--evaluation of sludge dryer and dewatering facilities

77
Western Wake RWRF Sludge Dryer and Dewatering Evaluation TM Page: 1/77 TECHNICAL MEMORANDUM To: Copies: Western Wake Project Partners Western Wake Design Team File From: Date: ARCADIS/CH2M HILL March 10, 2008 Subject: Evaluation of Sludge Dryer and Dewatering Facilities at the Western Wake Regional Water Reclamation Facility 1 Introduction 1.1 Purpose of Evaluation This evaluation is a continuation of the process of determining the most appropriate solids handling process for the Western Wake regional Water Reclamation Facility (WWRWRF). ARCADIS/CH2M HILL prepared a Technical Memorandum (TM), in September 2007, along with an associated Addendum in November 2007, which compared the current design to an alternative that included primary clarifiers and anaerobic digestion. Having reviewed that TM and revisited the operational cost of their existing dryer, the Project Partners asked that biosolids dryer technology be considered as an alternative solids handling process. The Project Partners also asked that available sludge dewatering technologies be assessed to determine whether solid-bowl centrifuges as currently proposed are the most suitable dewatering equipment for the WWRWRF. The purpose of this TM is to provide design development discussion and recommendations on dewatering and drying technologies, and to provide more detailed criteria and a design data summary for the modified aerated sludge holding facility. 1.2 Background to Dryer Alternative Several factors went into the development of the dryer alternative as an option for evaluation. It had previously been considered that the operation of a dryer was more costly than contract composting at a nearby merchant composting facility. Recent evaluations by the Project Partners demonstrated that a biosolids heat-drying facility as currently conceived provides lower operational costs than contract composting, although there is a significant capital investment to consider. The Alternative WWRWRF Design, with primary clarifiers and anaerobic digestion, had introduced the need to add metal salt and methanol to achieve the same level of biological nutrient removal as the Current WWRWRF Design. Town of Cary staff considered that the original process configuration, without primary clarifiers or anaerobic digestion, would yield the best biological nutrient removal performance for the WWRWRF.

Upload: rajan-bhosale

Post on 24-Oct-2014

65 views

Category:

Documents


11 download

TRANSCRIPT

Page 1: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM

Page: 1/77

TECHNICAL MEMORANDUM

To: Copies:

Western Wake Project Partners Western Wake Design Team File

From: Date:

ARCADIS/CH2M HILL March 10, 2008 Subject:

Evaluation of Sludge Dryer and Dewatering Facilities at the Western Wake Regional Water Reclamation Facility

1 Introduction 1.1 Purpose of Evaluation

This evaluation is a continuation of the process of determining the most appropriate solids handling process for the Western Wake regional Water Reclamation Facility (WWRWRF). ARCADIS/CH2M HILL prepared a Technical Memorandum (TM), in September 2007, along with an associated Addendum in November 2007, which compared the current design to an alternative that included primary clarifiers and anaerobic digestion.

Having reviewed that TM and revisited the operational cost of their existing dryer, the Project Partners asked that biosolids dryer technology be considered as an alternative solids handling process.

The Project Partners also asked that available sludge dewatering technologies be assessed to determine whether solid-bowl centrifuges as currently proposed are the most suitable dewatering equipment for the WWRWRF.

The purpose of this TM is to provide design development discussion and recommendations on dewatering and drying technologies, and to provide more detailed criteria and a design data summary for the modified aerated sludge holding facility.

1.2 Background to Dryer Alternative

Several factors went into the development of the dryer alternative as an option for evaluation.

It had previously been considered that the operation of a dryer was more costly than contract composting at a nearby merchant composting facility. Recent evaluations by the Project Partners demonstrated that a biosolids heat-drying facility as currently conceived provides lower operational costs than contract composting, although there is a significant capital investment to consider.

The Alternative WWRWRF Design, with primary clarifiers and anaerobic digestion, had introduced the need to add metal salt and methanol to achieve the same level of biological nutrient removal as the Current WWRWRF Design. Town of Cary staff considered that the original process configuration, without primary clarifiers or anaerobic digestion, would yield the best biological nutrient removal performance for the WWRWRF.

Page 2: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 2/77

Sludge Dryer and Dewatering Evaluation TM

With anaerobic digestion there would be a release of phosphorus and ammonia, which would be removed from the digested biosolids during dewatering and returned back to the BNR basins in the dewatering recycle stream. With the dryer alternative and no digestion, the anaerobic digesters are not required and there would be minimal to no release of phosphorus and ammonia during dewatering. The nutrients would mostly be retained in the dewatered cake and the dried product, and would not require treatment as a side stream or in the main plant.

One of the principal aims of including a sludge dryer at the WWRWRF is to produce Class A biosolids per EPA requirements with the flexibility for beneficial use or disposal that brings. A primary advantage of a Class A product is that it can be land applied with very few restrictions. Under the Current and Alternative WWRWRF Designs, unclassified or Class B sludge would be composted off site at a commercial facility. In the emergency situation where it were not possible for the contractor to accept the product for composting, then the options open to the Project Partners would be land application (if Class B standards could be attained) or hauling to landfill, neither of which the Project Partners are currently prepared or equipped to handle.

The dryer option can provide the Project Partners proven technology, more flexibility given the Class A product, and reduced volume of product for beneficial use or disposal. Among the factors that make the dryer alternative attractive for the Project Partners are:

• The Town of Cary and the Project Partners have a preference for controlling the ultimate use or disposal of biosolids, to the extent that it is practical and affordable.

• Dependence on outside contractors for biosolids processing places the Project Partners in a vulnerable position in the event of an emergency or change in the outside contractor’s business.

• Class A certification provides a positive public perception as compared to an unclassified or even a Class B product.

• The emergence of phosphorus loading as a controlling factor on potential land application sites will impact land application (whether Class A or Class B) as a potential backup plan for composting. Compost and dried biosolids are impacted to a much lesser extent by nutrient limits because those products have a considerably larger marketplace that will distribute nutrients over a much larger area.

• The utilization of outside contractors for biosolids disposal places an added obligation on the Project Partners to overbuild some facilities, such as aerobic digestion and dewatered cake storage processes, to accommodate unavailability on the part of an outside contractor.

• Reduced volume for onsite biosolids storage makes containment more practical and helps limit odor concerns. Reduced volume also minimizes hauling and disposal costs.

• Class A dried biosolids may be applied in locations such as forested land, parks and golf courses where dewatered cake, or liquid, digested biosolids, would not be acceptable, regardless of whether it is a Class A product. Among potential biosolids products, only heat-dried biosolids and compost are typically accepted for use on areas other than farmland.

• Several days inventory of Class A dried biosolids can be stored onsite in cases where they cannot be removed on a regular schedule. Safety measures to prevent re-heating of stored product are still required.

On the basis of these considerations, the dryer alternative was developed, assuming no sludge digestion other than the minimal aerobic digestion that would occur during several days of aerated sludge holding prior to dewatering (see below).

Page 3: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 3/77

Sludge Dryer and Dewatering Evaluation TM

2 Definitions 2.1 Definition of Treatment Alternatives

In the September 2007 Evaluation TM the current and alternative WWRWRF project are defined and the components of each are briefly summarized as follows:

Current WWRWRF Design - Preliminary Treatment with Odor Control, Biological Reactor Basins, Secondary Clarifiers, Effluent Filters, Ultraviolet (UV) Disinfection, Post Aeration, WAS Thickening, Aerated Sludge Holding with Partial-Stabilization, Solids Dewatering.

Alternative WWRWRF Design – Preliminary Treatment with Odor Control, Primary Treatment with Odor Control, Biological Reactor Basins, Secondary Clarifiers, Effluent Filters, UV Disinfection, Post Aeration, Waste Activated Sludge (WAS) Thickening and Aerated TWAS Holding, Blending Tank, Anaerobic Digestion, Digested Solids Dewatering with Odor Control.

The Dryer Alternative essentially preserves the features of the Current WWRWRF Design but adds a biosolids dryer to reduce the volume for disposal and to provide a Class A product. An additional change is in the Aerated Sludge Holding tank size. For the Current WWRWRF Design, the aerated sludge holding tank provides 20-days of hydraulic residence time (HRT) to give partial stabilization. That HRT is reduced to 5 days HRT for the Dryer Alternative evaluation.

For the purposes of this screening level evaluation, the dryer alternative design option for the WWRWRF is defined as follows:

• Primary clarifiers will not be provided. • The current design for liquid treatment facilities, as described in the most recent

(December 2007) Final Design deliverables, is maintained. • Aerated sludge holding tank facilities will provide for a 5-day HRT at design conditions.

The ultimate HRT would be determined during detailed design, but is assumed to be 5 days for the purpose of this analysis.

• Two dewatering alternatives will be compared: centrifuges and rotary presses. • Two biosolids management alternatives will be compared: biosolids heat-drying and

hauling dewatered biosolids cake to an off-site contracted composting operation. • Three alternative biosolids dryer options will be considered in the analysis. The biosolids

dryer would be fueled by natural gas. Truck loading and on-site dried biosolids silo storage will be provided.

• A design alternate will be investigated which includes additional equipment to accommodate use of dried biosolids pellets as a supplemental fuel source.

• Appropriate odor control and dryer emissions control facilities will be included in the alternative to handle the solids handling facilities and dryers.

• The Current and Alternative WWRWRF Designs will include composting via an outside contractor as the ultimate biosolids disposal process.

Page 4: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 4/77

Sludge Dryer and Dewatering Evaluation TM

2.2 Design Criteria/Facility Sizing

The design criteria for the sludge dryer options are presented in Table 1. These values were used by equipment manufacturers to base their proposals.

TABLE 1 – DESIGN CRITERIA PROVIDED TO VENDORS

Design Criteria Phase I Phase II

Dry Sludge Load (dry ton/year) 5,500 10,530

Dry Solids in Sludge Cake (%) 18% 17%

Sludge Cake Load (ton/year) 30,600 61,900

Solids Mass Load (lb/day) 30,100 57,700

Water Mass Load (ld/day) 137,300 281,700

Operation Time (hr/year)1 6,240 6,240

Minimum Dry Solids in dried sludge (%) 90% 90%

Discharge Product Temperature after product cooling (degrees F) 90 90

1 Based on 24 hr/day, 5 day/wk

The above sludge quantities were based on a review of the sludge production at the South Cary WRF, which averaged 1,650 lbs/MG, and the design flows for each phase.

Sludge quantities were also estimated using the process models, as shown in Table 2. These differ from the values above; the values in Table 1 are based on what the Town of Cary has found in terms of sludge loading at their existing water reclamation facilities (WRFs). The values in Table 2 are derived from the process models for the WWRWRF and predict a 10-15 percent reduction in solids generation per unit of wastewater treated, compared to Cary’s existing treatment facilities. This is due to predicted higher efficiencies of treatment and lower solids generation for the WWRWRF as compared to Cary’s two existing treatment facilities. Nevertheless, the drying facilities have been sized based on the Table 1 values because they are more conservative than Table 2.

As the dryer equipment included in the evaluation was sized based on the slightly more conservative values in Table 1, there is a certain amount of contingency capacity built into the equipment sizing.

Page 5: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 5/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 2 – ESTIMATED SLUDGE QUANTITIES FROM PROCESS MODELING

Start Up Phase I Phase II Description Annual

Average Maximum

Month Annual Average

Maximum Month

Annual Average

Maximum Month

Flow (MGD) 8.3 9.9 15.3 18.0 25.4 30.0

Thickened WAS

Flow. gpd 57,900 68,100 75,200 88,500 133,000 155,000

Solids Mass Load, lb/day 14,500 17,000 25,100 29,500 44,300 51,800

Concentration, % 3 3 4 4 4 4

Dewatered Sludge

Flow. gpd 6,300 7,400 13,500 15,800 23,000 27,200

Solids Mass Load, lb/day 11,100 13,200 20,200 23,800 34,600 40,800

Water Mass Load, lb/day 50,400 60,200 92,100 108,400 157,600 185,900

Concentration, % 18 18 18 18 18 18

Dry Sludge Load (dry ton/year) 2,020 2,410 3,690 4,340 6,310 7,450

3 Sludge Holding and Thickening Facility 3.1 Aerated Sludge Holding Tank and Aeration Equipment

The role of the Aerated Sludge Holding Tank is slightly different for each of the design scenarios. For the current design, the Aerated Sludge Holding tank provides 20 days of detention time and allows for substantial aerobic digestion of waste activated sludge. For the alternative design, the aerated holding tank primarily serves to buffer the feed rates and times to the anaerobic digester facility. For the dryer alternative, the aerated holding tank provides some minimal VSS reduction prior to drying, allows continuous wasting from the activated sludge process, and provides a storage area during times the dewatering and drying operations are inactive.

For the dryer alternative, the aerated sludge holding tanks have been designed to provide 5 days detention time with one tank out of service at the design flow of 18 MGD and a solids concentration of 3.5 percent. Waste activated sludge is pumped directly from the clarifiers to the aerated sludge holding tanks, thus sludge wasting can occur continuously. The sludge will be concentrated using Rotary Drum Thickeners, described later in this TM. The contents of the aerated sludge holding tanks are mixed and aerated using jet aeration equipment, which is also designed for a solids concentration of 3.5 percent. Jet aeration equipment is preferred rather than conventional fine or course bubble diffusers for the following reasons:

• Jet aeration utilizes a recirculation pump for mixing of the tank contents. This provides independent control of mixing and oxygen transfer

• Better oxygen transfer efficiency in concentrated sludges • Limited need to access the equipment or drain the basins for maintenance

The specifics of the tanks and the jet aeration equipment are shown in Table 3.

Page 6: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 6/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 3 – AERATED SLUDGE HOLDING TANKS SUMMARY

Description Phase I (18 MGD) Phase II (30 MGD)

Type of Tank Aerated, Covered

Number of Tanks 3 5

Volume, Each Tank 365,000 Gallons

Dimensions, Each Tank 74’ x 30’ x 25’ (3’ freeboard)

Aeration Equipment Jet Header

Blower Type Positive Displacement

Number of Units 3 5

Design Airflow Rate, each 2300 scfm

Recirculation Pump Type Screw Centrifugal

Number of Pumps 3 5

Pump Capacity, each 11,000 gpm

In order to reduce odor potential, the tanks are covered and the exhaust air is sent to odor control facilities.

The tanks are rectangular in shape for several reasons. Using rectangular tanks allows common wall construction, allows one wall to be common with the sludge processing building, and easily lends itself to the installation of Rotating Drum Thickeners (RDTs) on the top. The rectangular shape is also best suited to the header type jet aeration system which is proposed. The width of the tank (30 feet) matches up with the suggested optimum throw of the jet system in thickened sludges of 15 feet (each side of the header). Concrete is the preferred material for the tanks, both in terms of durability, corrosion resistance, and ease of providing wall penetrations.

The oxygen demand is based on typical aerobic digestion requirements for solids concentrations of 3.5 to 4 percent solids, with 80 percent influent VSS concentration. The resulting ratio of air to tank volume is approximately 47 cfm/1000 cubic feet, compared to recommended ratios of 20 to 40 cfm/1000 cubic feet (M&E). Positive displacement blowers are recommended for this application, as the reduced size of the tank and the resulting reduced oxygen demand does not justify the single stage centrifugal blowers. The blowers are to be located on top of the tanks, under a canopy, with sound attenuating enclosures. Given the grading of the site in this area, the top of the AHT is close to ground level. This would allow for easy access for maintenance.

In a typical aerobic digestion facility, the goal is to reduce the volatile suspended solids (VSS) by 38 percent in order to meet vector attraction reduction requirements. The VSS concentration can be an indicator of the odor potential in the aerobic digesters. For the dryer evaluation, however, it is not considered necessary to meet typical values for VSS reduction. The goal is only to reduce VSS and odor potential to a degree such that nuisance odors are prevented and the feed concentrations to the dryer are consistent. Figure 1 shows theoretical VSS reduction versus time assuming a 20oC digester liquid temperature, and Figure 2 shows theoretical VSS residue versus time, for conventional aerobic digestion. Note that the most rapid VSS reduction comes in the first 5 to 7 days, then the rate of reduction then decreases. Note that neither of these graphs takes into account any prior VSS reduction that may have occurred in the activated sludge process.

Page 7: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 7/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 1 - VSS REDUCTION

VSS Reduction v.s. Sludge Age in Aerobic Digester

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Sludge Age, days

Vola

tile

Solid

s R

educ

tion,

%

Page 8: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 8/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 2 - VSS RESIDUE

The oxygen demand over time follows a similar curve. As the total VSS concentration is reduced, the overall oxygen demand is reduced (See Figure 3).

VSS Residue v.s. Sludge Age in Aerobic Digester

30

40

50

60

70

80

90

100

110

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Sludge Age, days

VSS

Res

idue

, %

Page 9: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 9/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 3 - PLOT OF OXYGEN DEMAND VERSUS TIME

Based on the theoretical VSS reduction, oxygen demand, and past experience, we consider 5 days storage to be adequate preceding thermal drying, provided the market for dried biosolids remains restricted to agricultural or forested application sites. If the product were to be marketed to the general public, then a longer retention time would be recommended, in order to reduce VSS and potential for odor in the product. We recommend that the tanks be operated in series, such that fresh waste activated sludge is continuously fed into a full or almost full tank. Feed to the dewatering operations is to be from the second or third tank, depending upon plant flow. Piping and valves will be provided to allow parallel operation, which may be required for maintenance reasons.

3.2 Waste Activated Sludge Thickening

3.2.1 WAS Thickening

Both the current and alternative designs used gravity belt thickeners (GBTs) for thickening of waste activated sludge. The GBTs were located in the solids processing building, and were sized for shift operations with a 5-day work week. For the dryer alternative, the GBTs have been replaced using Rotary Drum Thickeners (RDTs), which are to be located directly on top of the aerated sludge holding tanks. The RDT unit is fed from the aerated sludge holding tank, and acts more as a tank concentrator than a thickener. Several advantages of this strategy include:

• The RDTs require less operator attention, and can run on a continuous basis. This allows units of smaller hydraulic capacity to be utilized

• The RDTs are enclosed by stainless steel and therefore not required to be located inside a building.

Oxygen Requirement v.s. Sludge Age in Aerobic Digester

30,000

40,000

50,000

60,000

70,000

80,000

90,000

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Sludge Age, days

Oxy

gen

Req

uire

men

t, lb

/day

Page 10: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 10/77

Sludge Dryer and Dewatering Evaluation TM

• Locating the RDTs on top of the aerated sludge holding tank allows the thickened sludge to be dropped directly into the tank

The aerated sludge holding tanks are fed directly from the activated sludge process; therefore the feed sludge to the holding tank is at a lower solids concentration (thus reducing the initial oxygen demand). By concentrating a blend of fresh sludge with the existing tank contents, the overall oxygen demand is decreased. When the aerated sludge holding tanks are operated in series, the solids concentrations can be increased in succeeding tanks, since oxygen demands are decreasing.

A schematic of the proposed aerated holding tanks with RDTs is shown in Figure 4.

FIGURE 4 – PROPOSED AHT SCHEMATIC

A photograph of a RDT is shown in Figure 5.

WAS

RDT RDT RDT

AEROBIC

HOLDING

AEROBIC

HOLDING

AEROBIC

HOLDING

CENTRIFUGE

TRUCK

P P P

Page 11: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 11/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 5 – ROTARY DRUM THICKENER PHOTOGRAPH

The specifics of the RDT application are shown in Table 4.

TABLE 4 – ROTARY DRUM THICKENER – SUMMARY OF WWRWRF APPLICATION

Description Phase I (18 MGD) Phase II (30 MGD)

Type of Thickener Rotary Drum

Number of Units 3 5

Capacity, Each Unit 300 gpm

Feed pump type Screw Centrifugal

Ancillary equipment for the RDT installation includes feed pumps, polymer storage and feed systems, and if desired, a distribution conveyor.

4 Technology Evaluations 4.1 Dewatering Technologies

Two different dewatering technologies were considered for the Dryer alternative – rotary presses and centrifuges. The rotary press technology was introduced as a possible lower cost alternative to the centrifuge technology during follow up activities after the Value Engineering Review. Descriptions of the technologies follow.

Centrifugation is widely used in the wastewater treatment industry for dewatering of waste biosolids. This is the dewatering technology currently used at the South Cary WRF. Waste sludge is conditioned using polymer or other chemicals, and is then fed at a constant rate into the rotating bowl of the centrifuge. The high speed rotation of the bowl causes the solids to settle on the bowl inner wall. A scroll or conveyor,

Page 12: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 12/77

Sludge Dryer and Dewatering Evaluation TM

rotates in the same direction as the bowl, but at a different speed. This differential speed creates torque in the solids discharge section to provide additional water removal. The differential speed also provides the conveying capability to discharge the cake. Typical values for solids concentrations of centrifuged sludge range from 15 to 30 percent. The feed solids concentrations for a thermal dryer installation range from 10 to 30 percent. The lower the percentage of solids, the more thermal energy that must be supplied by the dryer to evaporate water so the desired feed is at least greater than 15%, and preferably above 18%. A photograph of a dewatering centrifuge installation is shown in Figure 6.

FIGURE 6 – DEWATERING CENTRIFUGE

The rotary press is a relatively new entrant into the wastewater treatment industry. However, this technology has been widely used in the mining and pulp and paper industries. Several utilities have installed rotary presses for dewatering of municipal sludges, including the Orange Water and Sewer Authority and the Charleston (SC) Water Utility.

The rotary press operates primarily by using the forces of friction to dewater sludge. Sludge is conditioned using polymer, then fed into a rectangular channel and rotated between two parallel revolving perforated screens. The filtrate passes through the screens as the flocculated sludge advances within the channel. The sludge continues to dewater as it travels around the channel, eventually forming a cake near the outlet side of the press. The frictional force of the slow moving screens, coupled with an outlet restriction, results in the extrusion of a cake. A photograph of a rotary press is shown in Figure 7.

Page 13: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 13/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 7 - ROTARY PRESS

4.2 Pilot Testing

As part of the evaluation, on site pilot tests of the rotary press technologies were performed at the North Cary WRF.

Fournier Industries pilot tested their RDT unit at the North Cary WRF from December 4 until December 7, 2007. Various feed sludge ages were tested, including fully digested, partially digested, and undigested. Results of this testing are shown in Table 5.

TABLE 5 – FOURNIER ROTARY PRESS PILOT RESULTS

Date Sludge Age, days

Feed Concentration,

%

Capture Rate, % TSS

Filtrate TSS Concentration,

%

Cake Solids Concentration,

%

12/4,5 2-9 0.1 87.6 0.25 12.02

12/5,6 20-30 0.1 84.2 0.33 12.06

12/6,7 2-9 0.1 89.9 0.23 11.93

12/7 From Clarifier 0.1 91.6 0.05 12.68

Prime Solutions, Inc. tested their rotary press at the North Cary WRF on December 11 and 12, 2007. Although less data from the test is available, the range of cake solids for these tests was from 11.8 to 14.6 percent solids.

Page 14: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 14/77

Sludge Dryer and Dewatering Evaluation TM

Waste sludge samples were also shipped to two potential centrifuge vendors for bench testing. Results of these tests are presented below.

A 5-gallon sludge sample from the North Cary WRF was shipped to Andritz and received on January 3, 2008. Laboratory centrifuge testing indicates that a solids concentration of 18 percent (+/- 2 percent) can be achieved with a polymer dosage of 12 lbs/dry ton. A second sample from the North Cary WRF was shipped to Westfalia Separator. Test results from Westfalia indicate solids concentrations of 15.2 to 16.5 percent, using various polymers at reduced dosages. Onsite pilot testing of both manufacturers equipment is currently being arranged.

Since the preferred feed solids concentrations for all the drying technologies being evaluated is 18 to 30 percent (although 30% may be considered by some operators to be too dry), the rotary press is not a viable technology for the WWRWRF. Therefore, it is our recommendation to proceed with the original concept of using centrifuges for waste sludge dewatering.

4.3 Sludge Drying Technologies

Heat drying technology is based on removal of water from sludge generated during wastewater treatment. Typically, dewatered sludge of 15 to 30 percent dry solids concentration (i.e. 70-85 percent water content) is delivered to the heat drying system. In the heat drying system the temperature of the sludge is raised sufficiently to evaporate and remove most of the entrained water. By removing most of the water from the sludge, heat drying results in a significant reduction in both sludge volume and mass. Material produced in the heat drying process typically has a dry solids content of 90% to 96%, with an optimum range of 92% to 95% dry solids.

A variety of heat drying systems are currently offered by equipment manufacturers. Heat drying systems are generally divided into two main categories: direct and indirect. This classification is based on how the thermal energy is delivered to the sludge in the drying process.

In direct heat dryers, wet sludge comes into direct contact with hot air. Typically, hot air flows through a process vessel and comes into contact with the wet sludge. The contact between the hot air and the cold sludge allows the transfer of thermal energy, which causes an increase in sludge temperature that is needed for evaporation of water. The predominant method of heat transfer in direct drying systems is convection. Examples of direct drying equipment are rotary drum dryers, flash dryers, fluidized-bed dryers, and belt dryers.

In indirect heat dryers, materials with high heat-conducting capacity such as steel separate the wet sludge from the heat transfer medium (steam, hot water, or hot oil). Thermal energy is transferred from the hot transfer medium into the metal wall and then from the metal wall into the cold sludge. The sludge is heated by contact with the hot metal surfaces and never comes into contact with the heating medium. The predominant method of heat transfer is by conduction. Indirect heat drying equipment includes multiple-hearth dryers, paddle dryers, and disk dryers.

This dryer technology evaluation reviews alternative technologies, and compares performance and net present worth for rotary drum dryers, belt dryers, and paddle dryers. The rotary drum and belt dryers are direct-type dryers, while the paddle dryer is an indirect type.

4.3.1 Dryer Evaluation Criteria

The evaluation of the biosolids dryer option for WWRWRF is based upon both cost and non-cost criteria. A comparison of estimated construction costs for several different dryer alternatives, and estimated 20-year and 30-year net present value (NPV) cost incorporating operation costs for the dryer option compared

Page 15: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 15/77

Sludge Dryer and Dewatering Evaluation TM

with the current design and the previous primary clarifier/anaerobic digester alternative, is provided in Section 5.

In addition to construction cost and operating cost, non-cost criteria are also considered in evaluating dryer equipment. Discussion on these factors is provided in Section 4.5.

4.3.2 Dryer Options

(a) Rotary Drum Dryer

Direct type, rotary drum drying technology is based on evaporation of water by direct contact of material with a stream of hot air. The major components of the rotary drum dryer system are the wet cake bin, recycle bin, mixer, furnace, drying drum, air/solids separator, screen, crusher, cooler, main fan, saturator, and storage silos. A schematic for a direct type, rotary drum system is shown in Figure 8:

FIGURE 8 - DIRECT TYPE, ROTARY DRUM DRYER PROCESS FLOW DIAGRAM

The dewatered cake entering the drying system passes through a wet cake bin and is then mixed with recycled dry product in the mixer to create an approximately 70 percent dry mixture. The hot air required for the heat drying process is produced in a furnace that is usually gas-fired (other types of fuel are sometimes used). The furnace produces a stream of hot air/exhaust at temperatures between 800 and 1,000 °F. The evaporation process takes place in a horizontally mounted, slowly rotating drying drum. The dried

Page 16: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 16/77

Sludge Dryer and Dewatering Evaluation TM

material is conveyed through the drum where the hot air stream comes in direct contact with wet biosolids, heats the material, and evaporates the water contained in the biosolids. Dried pellets and the moisture-laden air stream leave the drying drum at temperatures between 190 and 220 °F. Both dried solids and hot air pass together through the air/solids separator, where solid particles fall out and separate from the air stream.

Dry solids are separated into oversized, product, and undersized (fine) fractions on vibrating screens. Product size pellets (1 to 4 mm diameter pellets are typically most desirable) are cooled and then pneumatically conveyed to storage silos for storage and loading onto trucks or railroad cars. Large size pellets are crushed in the crusher, combined with fine size pellets and passed through the recycle bin into the mixer for mixing with dewatered cake. The hot, moisture-laden air is forced by main fan into the saturator, where the air is cooled and water vapor condensed by a counter-current flow of hot process air and cold cooling water. Plant re-use water can be used as the cooling water, and the condensate is returned to treatment. In the case of Western Wake, condensate would pass to the filtrate/centrate pump station. Most of the cooled air is recycled back to the drying drum, while approximately 10 to 30 percent of the flow is treated in the air emissions control system and discharged to the atmosphere.

The direct type, rotary drum drying system is generally capable of producing well-sorted, semi-round pellets with approximate size of 1 to 4 mm. Systems with full product recycle and mixing produce pellets with hardness and dust characteristics that are typically better than those produced by other heat drying technologies. Direct dried product rarely requires additional processing to make it marketable.

Direct type, rotary drum dryers are the most prevalent type of dryer found in United States, with more facilities in operation drying biosolids than any other type of dryer. They are available from Andritz, Berlie, NEFCO, and Siemens (formerly Sernagiotto).

A photograph of the rotary drum installation at the South Cary WRF (Andritz Model DDS 40) is shown in Figure 9.

FIGURE 9 – ROTARY DRUM DRYER

Page 17: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 17/77

Sludge Dryer and Dewatering Evaluation TM

(b) Belt Dryer

Belt dryers use direct contact of circulating hot air with wet sludge that is pumped onto and conveyed by a slowly moving horizontal belt enclosed in a metal enclosure. The wet material moves through several drying chambers, where the moisture is released into the circulating air. After passing through the drying chambers, the dried cake falls off from the belt onto a hopper and is conveyed to a loading or storage facility.

Each drying zone has its own circulating fans and air temperature control. Excess moisture is removed from the air stream in a saturator. Heat for the air circulation loop in each zone is provided in a heat exchanger by indirect contact with steam, hot water, thermal oil, or hot air serving as the heat source. The drying temperatures are controlled at approximately 300°F at the belt entry and at 210°F at the belt discharge. The sludge is heated to approximately 170°F in its dried state. The lower drying temperature is claimed to produce a less odorous exhaust stream, and the drying process is less prone to accidental combustion than rotary drum dryers, which operate at much higher temperatures.

Dried material produced by the dryer is composed of larger fragments, non-uniform in shape, with sizes between 1 and 10 mm. A pelletizer must be added if smaller pellets of uniform size are desired. Since the sludge is not excessively moved in this system, dust formation is reduced in the dryer itself, although dust may form in subsequent handling of the dried product.

Belt dryers are available from Andritz, Kruger, and Huber. Kruger belt dryers were first installed in Europe in 1995, and Andritz’s first was installed in 2002. At present there are 15 Kruger and 20 Andritz belt dryers either in operation or development worldwide. Of these Kruger has 4 US installations, and Andritz has no US belt dryer installation. A schematic of the belt dryer technology is shown in Figure 10.

FIGURE 10 - DIRECT TYPE, BELT DRYER PROCESS FLOW DIAGRAM

DewateredBiosolids Cake

Feed Hopper

Biosolids Mixer / Conveyor

Biosolids Belt Dryer Product Screen

Product Cooler

Condenser Air Heat

Exchanger

Storage

Silo

Condensate

Cooling Water

Recycle Air

Recycled Dried Solids

Dried Biosolids

Dried Biosolids

Natural Gas

Hot Air

Air Exhaust to Air Pollution Control

Page 18: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 18/77

Sludge Dryer and Dewatering Evaluation TM

A photograph of a belt dryer (Andritz BDS 0.75) is shown in Figure 11.

FIGURE 11 – BELT DRYER

(c) Paddle Dryer

Paddle-type heat dryers are based on raising the temperature of dried biosolids above 220°F by contact with hot metal surfaces. The evaporation process takes place within an enclosed, insulated vessel that is usually mounted in a horizontal position. The vessel is fitted with two rotating shafts fitted with self-cleaning paddles that rotate in the opposite direction, much like in a pug mill mixer. Shaft and paddles are internally heated by thermal oil or steam circulating through their hollow interior and allow transfer of heat energy from steam to sludge by conduction. Rotation of shafts provides for good mixing and thorough contact of sludge with heated metal surfaces. Wet sludge enters the dryer at one end and dried material exits at the other end. Evaporated moisture is exhausted from the dryer and there is headspace above the drying screws is to provide a plenum to allow the evaporated moisture to be absorbed by the exhaust air and removed.

Paddle dryers have high thermal efficiency and produce less odorous air than direct dryers. Due to continuous break up of the dried material by the paddles in the vessel, paddle-dryers produce pellets of a smaller size, and a higher potential for dust formation in the product.

Nara Machinery of Japan was the original patent holder and developer of the paddle dryer. Komline-Sanderson acquired the rights to market the paddle dryer in North America and has about 25 industrial paddle dryers and 12 municipal paddle dryers in operation at present. The same paddle dryer technology is being applied by GMF-Gouda of the Netherlands, who have 30 installations worldwide, but none in North America at present. Both Komline-Sanderson and GMF-Gouda have continued to refine their respective versions of the paddle dryer, so there are various differences between the two even though they both operate using the same basic technology. GMF-Gouda is beginning to market its paddle dryer as a competitor to Komline-Sanderson in the US.

A photograph of a paddle dryer (Komline-Sanderson Model 13W 2000) is shown in Figure 12.

Page 19: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 19/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 12 – PADDLE DRYER

4.3.3 Vendor Information

Three representative manufacturers of each type of dryer (Kruger, Andritz, and Komline-Sanderson) have provided information on their dryer equipment and this is summarized in the following table and sections.

Table 6 presents the vendor provided sizing and equipment summary for Phase I requirements. Where information for Phase II has been provided that will be summarized under the discussion of each vendor’s proposal.

Page 20: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 20/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 6 – VENDOR INFORMATION SUMMARY (FOR PHASE I)

Description Kruger Belt Andritz Belt Andritz Drum Komline-

Sanderson Paddle

Design Data

Sludge Load (dry ton/year) 5,500 5,500 5,500 5,500

Dry Solids is sludge cake (%) 18 18 18 18

Sludge cake load (wet ton/year) 30,556 30,556 30,556 30,556

Vendor Data

Number of Trains 2 1 1 1

Model DR1500SAZN BDS 4.0 DDS 40 13W-2200

Drying System, Design Evaporative Rate (lb water/hr) 7,835 8,034 8,034 7,900

Drying System, Evaporative Capacity (lb water/hr)4 8,260 8,800 8,800 9,080

Required Evaporative Energy (BTU/lb water evaporated)5 1,530 1,400 1,500 1,440

Drying System, Sludge Cake Load (lb/hr) 9,793 9,988 9,988 9,815

Operating Time (hr/yr)2 6,240 6,120 6,120 6,120

Dry Solids in Dry Sludge (%) 906 92 92 92

Dried Sludge (lb/hr) 1,959 1,954 1,954 1,920

Fuel Consumption (MMbtu/hr)1 12 11.25 12.05 11.3

Natural Gas Utilization (million cf/yr)8 74.8 68.8 73.8 69.4

Electrical Load (kW)7 184 330 328 200

Vendor Quoted Cost ($m)3 $5.0m $5.7 m $5.7 m $4.1 m

1 1 MMbtu/hr = 1,000,000 btu/hr 2 Operating time based on 5 days per week at 24 hours per day. Kruger based on 52 weeks, others on 51

weeks. The difference in total hours does not affect the economic analysis. 3 Andritz Belt cost provided excludes concrete tank (included in capital cost estimates). 4 Komline evaporative load capacity based on 15% safety factor 5 These values were provided by the vendors as being representative of values they would be expected to

provide as a guarantee with their bids. In the economic analyses all have been assumed to be 1500 BTU/lb water evaporated.

6 A minimum of 92% solids would be required with vendor bids and guarantees. 7 Electrical load values were provided by the vendors and would need to be evaluated more closely when

provided with bids. 8 When corrected for 1,500 BTU/lb water evaporated, 1,000 BTU/cf for NG, and 92% dry solids in product, these

values all become 73.8 million cf/yr

Page 21: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 21/77

Sludge Dryer and Dewatering Evaluation TM

Table 7 summarizes the main features of the different dryers, based on the information provided by the vendors.

TABLE 7– DRYER FEATURE COMPARISON

Feature Kruger Belt Andritz Belt Dryer Andritz Rotary Drum

Komline-Sanderson Paddle

Installations Approx. 15 worldwide including 11 in Europe and 4 in U.S. (Operational or in development)

1st in world 1995

1st in US 2006

20 in Europe. None in US. (Operational or in development)

1st in world 2002

70 worldwide including 21 in US (operational or in development)

1st in world 1974 (Switzerland)

1st in US 1995

Approx 78 industrial and municipal worldwide

1st in world early 1970’s (Japan, by Nara Machinery)

1st US municipal 1992

Cake Storage 24 hour cake bin 4 hours. Live bottom bin

4 hours. Live bottom bin

8 hour, 50 cu yd

Live bottom bin

Cake Feed Progressive cavity pump to oscillating nozzle depositors

Screw and distribution coil

Mix of wet cake and dried product. Dosing screw with variable speed drive

Progressive Cavity Pump for even feed

Energy Source Natural Gas Natural Gas Natural Gas Natural Gas

Heat Source Direct – Heated Air Direct – Heated Air Direct – Heated Air Indirect - Thermal Oil

(High pressure steam also an option)

Operating Temperature

350 F zone and 210 F zone over belt

Feed temp. 250 – 300 F

265 F over belt

Feed temp 800 – 900oF

Exit air at 195-205 F

Oil at 350 – 400 F

Product 250 – 260 F at discharge

Product Classification

None None Vibrating screen Vibrating screen

Product Recycle No Yes, for granulation

Approx 50% recycled

Under-sized and over-sized particle (crushed) as all/part of recycle to obtain non-sticky feed

Particles > ½” to roll-off container;

Particles < 0.5mm returned to dryer

Product Cooling Dried product cools within dilute phase transport system

Cooled using ambient air.

Cools product to <100oF

Parallel plate, non-contact heat exchanger using plant effluent.

Cools product to 90 – 100 F

Two coolers, one before and one after product handling.

Cools product to 120 F

Product Characteristics

Granular Granular Pellet. Typically 1 – 4 mm

Granular. 0.5 mm to ½”

Page 22: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 22/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 7– DRYER FEATURE COMPARISON

Feature Kruger Belt Andritz Belt Dryer Andritz Rotary Drum

Komline-Sanderson Paddle

Class A Product Yes, with PFRP assessment

Yes with Pasteurization Tower

Yes Yes

Product Transport

Pneumatic. Dilute phase.

Dilute phase allows for cooling within transport system.

Pneumatic. Dense phase

Dense phase uses less air than dilute. Less product degradation

Pneumatic. Dense phase

Dense phase uses less air than dilute. Less product degradation

Pneumatic. Dense phase

Dense phase uses less air than dilute. Less product degradation

Dryer Safety Temperature detectors linked to SCADA

Water sprinkler

Air temperature well below ignition temperature of approx 350oF when biosolids are dry. Does not provide favorable conditions for fires and explosions.

Monitor CO and dust concentration

Auto shut off

Water sprinkler

Air temperature well below ignition temperature of approx 350oF when biosolids are dry. Does not provide favorable conditions for fires and explosions.

Thermocouples for high/low temperatures alarms

Inert atmosphere in drying loop

Explosion vents on recycle bin

Monitor O2, CO and dust concentration

Auto shut off

Water sprinkler

Well establish SOPs

Thermocouples to monitor temperature throughout dryer

Pressure relief panels

Water deluge interlocked to high temperature switch

Material left in dryer during shut-down. This can lead to CO formation and potential ignition during start up if purging no adequate.

Loose SOPs

Product Storage Level indicators

Nitrogen purge

Thermocouple ropes

Ultrasonic level detector

Nitrogen purge

Thermocouple ropes

Ultrasonic level detector

Nitrogen purge

CO monitor

Two temperature trees

Level indicators

Nitrogen purge

Exhaust Handling

Condenser to scrub air using plant effluent.

Majority of air returned to dryer. Remainder exhausted.

Saturator/wash for particulate removal

Impingent tray Condenser/sub-cooler to remove moisture and particles

Single Stage barometric condenser/cooler

Odor Control Combustion/vacuum fan exhaust used as combustion air of sent to facility’s odor control.

Biofilter odor control 15% off gas to venturi scrubber and RTO

Off-gas from air/solids separation sent to aeration basin (or AHT) via coarse bubble diffusers (external

Page 23: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 23/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 7– DRYER FEATURE COMPARISON

Feature Kruger Belt Andritz Belt Dryer Andritz Rotary Drum

Komline-Sanderson Paddle

system)

I&C SCADA, which can be integrated into plant SCADA

Modem link to Kruger for operational monitoring and advice

PLC with OIT PLC with OIT and PC based software

PLC with OIT for control, monitoring and alarm

Stop/Start Notes

Automated 0.5 - 1 hr “Quick Start” – 5 mins

“Quick Stop” – 15 mins

RTO requires 1-2 hr preheat before dryer starts. Then ½ -1 hour dryer startup. Shutdown about 1 hour.

Leave dried product (cooled) in dryer for easier start-up

Use of Product as Fuel

Yes Yes Yes No experience

Kruger Belt Dryer

The Kruger belt dyer operates with a twin belt system. The sludge is dried to 55% solids on the first belt and to above 90% on the second belt. The maximum air temperature is 350 deg F, where the wet sludge enters the dryer. Oscillating depositors distribute the sludge as thin strings onto the interlocking wire link mesh belt constructed of stainless steel.

Energy is provided by an air-to-air heat exchanger such that the drying air is heated indirectly via an air heater. The energy is transferred from the heat exchanger via a recirculation fan. A portion of the circulation air is sent through a condenser to remove water vapor that is absorbed from the sludge drying process.

The manufacturer claims that “no specialized or advanced technical skills” are required to operate the dryer and that the SCADA system simplifies monitoring and control operations. The system is designed to minimize operator oversight during normal working hours. Outside normal working hours, it is suggested that the system can be operated without an operator if the dryer is connected to the WWTP alarm system. The Town of Cary has noted that they would not likely operate a belt dryer in this mode, and would have staff present continuously.

The Kruger belt dryer produces a granulate product that meets Class A requirements, and has a minimum of 90% solids. The product is irregular in nature and is the least likely to be readily marketable of all the dryers.

Page 24: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 24/77

Sludge Dryer and Dewatering Evaluation TM

Kruger provided a number of options for different scenarios and these are summarized in Table 8 below.

TABLE 8 –KRUGER PROVIDED INFORMATION

SCENARIO 1 2 3

Belt Dryer Phase I Phase II Phase II

Sludge Load (dry ton/year) 5,500 10,526 10,526

Dry Solids is sludge cake (%) 18 173 17

Sludge cake load (wet ton/year) 30,556 61,916 61,916

Number of Trains 2 3 4

Model DR1500SAZN DR3000SAZN DR1500SAZN

Drying System, Design Evaporative Rate (lb water/hr) 7,835 16,097 16,097

Drying System, Sludge Cake Capacity (lb/hr) 9,793 19,845 19,845

Operating Time (hr/yr)1 6,240 6,240 6,240

Dry Solids in Dry Sludge (%) 904 90 90

Dried Sludge @ 90% (lb/hr) 1,959 3,748 3,748

Sludge Furnace and Energy Recovery System No No No

Heat Value of Dried Sludge (Btu/lb DS) N/A N/A N/A

Fuel Consumption (MMbtu/hr)2 12 24 24

Cost ($m) $5.0 m $10.3 m $9.8 m

1 Based on 24 hours/day and 5 days/week operation 2 1 MMbtu/hr = 1,000,000 btu/hr 3 17% based on data provided to vendors. Would be based on 18% ultimately. 4 Would be required to be a minimum of 92% ultimately.

For Phase I, 2 units are required, while at Phase II there is some flexibility. The two scenarios presented for Phase II suggested either 3 larger units or 4 smaller units. However, the capital cost of the 4 smaller units is lower. The dryer required under the 4 unit scenario is the same size at those required at Phase I, so would be most appropriate for future expansion.

Andritz Belt Dryer

Andritz’ belt dryer has a single fabric belt on which the sludge is dried. Dewatered biosolids are stored in a tank and fed continuously to a mixing screw. A portion of the previously dried product is also fed into the mixing system along with the wet feed. The mixed biosolids are spread onto the belt using a distribution screw, which is intended to assure a homogenous layer across the width of the belt. The biosolids are dried while it passes through the dryer on the belt. The desired over-belt temperature is 265 deg F; the maximum temperature is 284 deg F, which is lower than that reported for the Kruger belt dryer.

Page 25: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 25/77

Sludge Dryer and Dewatering Evaluation TM

In order to guarantee a Class A biosolids, the Andritz system adds a pasteurization tower after drying. The passage of dried solids through this vessel in plug-flow mode demonstrates that every particle of dried solids meets the time-temperature criterion of pathogen-reduction Alternative 1 from the EPA Part 503 sewage sludge regulation.

A high proportion of the drying air is recirculated and re-heated with a view to achieving the best possible thermal efficiency. Part of the drying air is exhausted from the system and fed to a saturator/washer. The proposal includes for treatment of exhaust air in a biofilter. Exhaust air could be treated in other devices if necessary.

The dryer is controlled and monitored using PLC and an operator interface is provided via a touch screen monitor. The system can run in un-manned operation by continuous measurement of the dry substance in the final product. System data can also be transmitted to a central system via an interface or modem to an external user. In a similar approach to the South Cary dryer, limit values are used to automatically shut-down the system should the limit values be exceeded.

One Andritz dryer can meet Phase I biosolids projections, unlike the Kruger belt dryer which requires two units to meet Phase I biosolids loads. In order to process Phase II biosolids production, a second BDS 4.0 would be required.

As with the Kruger system, the Andritz belt dryer can be equipped with a furnace and energy recovery system (termed the “Eco-Dry” system), which would heat the drying air and use dried product as a fuel.

Larger Andritz belt dryers, such as the one proposed, require the construction of reinforced concrete tank to form the base of the dryer. This base is not included in the vendor proposal, but has been included in the cost estimate used in the economic analysis.

Andritz Drum Dryer

The drum dryer model proposed for the Western Wake facility (DDS 40) is the same as that the Town of Cary operates at their South Cary WRF. The dryer is a triple-pass drum which produces a dry, hard pellet, which meets Class A biosolids requirements.

The system includes product classification to separate and return over-sized and under-sized product and produce even sized pellets in the 1 – 4 mm range. Recycled dried product is required by the system to mix with the dewatered cake and produce a feed that is a non-sticky phase mixture (that is, with a 50% - 70% dry solids content).

As with the Andritz Belt dryer, the proposed drum dryer recirculates a high proportion of the drying air. 85% of the air is recirculated and 15% is exhausted through a Venturi-type scrubber and regenerative thermal oxidizers (RTOs) for thermal destruction of odor compounds, carbon monoxide (CO) and volatile materials (VOMs).The RTOs would be multi-chamber type with monolithic packing. Thermal efficiency is quoted by the vendor as approximately 93%, and destruction and removal efficiency would be approximately 98%. The RTO would allow odor/air pollution control during start-up, regular operations and shut-down. The cleaned air is vented 10 feet above dryer system building (60 feet above ground) and no traditional stack is required.

The system is operated using PLC based controls with operator interface terminal (OIT) and personal computer (PC)-based software. The operational system in use at the South Cary WRF appears to be well understood and liked by the staff there.

One Andritz DDS 40 dryer will meet Phase I biosolids drying criteria. To meet Phase II biosolids drying requirements a second DDS 40 unit would be required.

Page 26: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 26/77

Sludge Dryer and Dewatering Evaluation TM

Komline-Sanderson Paddle Dryer

The indirect paddle dryer proposed (Komline-Sanderson Model 13W-2200) uses thermal oil as the heating medium, and the paddles and the dryer trough are heated by the oil. The proposed system includes product classification, which will classify all particles over ½” and below 0.5mm. The over-sized particles are discharged to roll-off containers for disposal while the under-sized particles are returned to the dryer. No other recycle is required as the paddle drive motor is sized to handle the increased torque of sticky-phased material. The product of paddle dryers is typically prone to dust problems, although the return of under-sized particles would help to minimize that issue. It has been reported from the Mason, OH treatment plant that oversized particles form only a small proportion and are readily handled using totes. Odor control is provided by passing exhaust gas through a condenser and then, typically, through aeration basins (or in the case of the Western Wake RWRF, through the aerated holding tanks) using a coarse bubble diffuser. It is strongly recommended that a separate blower, air piping, and air diffuser system be provided for the exhaust air from the drying process, due to its potentially corrosive properties that standard air piping is not likely to accommodate.

One Komline-Sanderson Model 13W-2200 dryer will meet Phase I biosolids drying criteria. To meet Phase II biosolids drying requirements a second 13W-2200 unit would be required.

4.3.4 Use of Dried Biosolids as a Fuel Source

When digester gas (from anaerobic digesters) is not available, biosolids dryers typically use natural gas as a fuel source. One of the potential uses of dried biosolids product is to supplement the use of natural gas as the fuel in the drying process. Both Kruger and Andritz offer incineration equipment that can be used in conjunction with their direct dryers to burn the dried pellets and use the heat generated for fuel. The heat generated in the oven is used to heat the drying air via a heat exchanger. Any residual energy requirements are provided by natural gas. Table 9 compares data provided by Kruger for their belt dryer with and without their Energy Recovery System (ERS) biosolids-fueled furnace. At the time of writing, no equivalent information had been provided by Andritz. Komline-Sanderson does not offer a biosolids-fueled furnace for the paddle dryer.

Page 27: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 27/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 9 – KRUGER PROVIDED DATA ON BELT DRYER WITH ENERGY RECOVERY SYSTEM (ERS)

Description Belt Dryer Belt Dryer with ERS

Sludge Load (dry ton/year) 5,500 5,500

Dry Solids is sludge cake (%) 18 18

Sludge cake load (wet ton/year) 30,556 30,556

Number of Trains 2 2

Model DR1500SAZN IN1500SAZN

Drying System, Design Evaporative Rate (lb water/hr) 7,835 7,835

Required Evaporative Energy (BTU/lb water evaporated) 1,530 1,750

Drying System, Sludge Cake Capacity (lb/hr) 9,793 9,793

Operating Time (hr/yr) 6,240 6,240

Dry Solids in Dry Sludge (%) 90 90

Dried Sludge @ 90% (lb/hr) 1,959 1,959

Ash for Disposal (lb/hr)2 N/A 440

Heat Value of Dried Sludge (Btu/lb DS) N/A 6,990

Fuel Consumption (MMbtu/hr)1 12 1.4

Percentage of Fuel Requirements provided by Dried Product (%)3 N/A 90

Cost ($m) $5.0 m $7.35 m

1 1 MMbtu/hr = 1,000,000 btu/hr 2 Assumes 75% volume reduction in furnace 3 Assumes 75% volatile solids, and 18% dry solids in cake

Assuming 75% volatile solids in the dewatered cake, there would be a reduction in volume of 55% from dewatered cake to dried product in the dryer alone, and close to 95% volume reduction from cake to ash from the furnace.

The cost-effectiveness of a dryer system that accommodates dried biosolids pellets as a supplemental fuel source is dependent on the present value of the savings in natural gas being greater than the additional capital cost of the furnace and energy recovery facilities.

Both vendors suggest that the cost of the biosolids furnace and energy-recovery equipment is at least equal to that of the dryer equipment itself, so potentially an additional $4m to $6m in capital outlay at Phase I will be required.

The economic analysis of the energy recovery option has been performed on the same basis as set out in Section 5 for the dryer analysis, but including appropriate additional cost factors such as ash disposal. There are potential uses in road construction as well as brick manufacturing, but in the economic assessment of the dryer it has been assumed that all of the ash would have to be disposed of. Based on

Page 28: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 28/77

Sludge Dryer and Dewatering Evaluation TM

information from a number of existing biosolids incineration facilities, the disposal rate has been assumed to be $40/ton (which includes ash handling, hauling, and ultimate disposal in a landfill).

The economic analysis considers a 30-year period, and assumes that the plant would expand with additional dryer capacity being provided. At the time this TM was prepared, information on the furnace and energy recovery operation is only available for the Kruger Energy-Recovery System (ERS) option.

The capital cost of Phase I of the plant with dryer and ERS is approximately $5.5 m (including contingency) higher than the cost of an equivalent-capacity facility with the dryer alone. The additional cost is in the energy recovery equipment and the associated building. The costs include 10 days of dried product storage for the dryer alone option, and half of that with the ERS option. The ERS option also includes an ash bagging station. The quoted cost of the ERS equipment itself assumes there will be two belt dryers and one ERS, which has the capacity for to incinerate the entire Phase I sludge production. The expansion is also $3.4 m more costly than the dryer option alone.

Table 10 compares the present worth of the Current design, the Kruger belt dryer option, and the Kruger ERS option, using the operation and maintenance escalation factors as described above, that is 3% annual escalation on all O&M costs except natural gas, which is assumed to escalate at 6% annually.

TABLE 10 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Kruger Belt Kruger Belt with ERS

Initial Construction Cost Sum ($m) 123.1 124.9 130.4

PV of Plant Expansion ($m) 37.8 43.6 47.0

NPV Operating Cost Sum ($m) 76.9 71.3 60.2

Total Present Worth ($m) 237.8 239.8 237.7

Present Worth Difference from Current ($m) - (2.0) 0.1

Present Worth Difference from Dryer Option($m) - - 2.1

The ERS option has reduced operational costs when compared to the dryer alone. The dryer alone has a much higher gas requirement, but the ERS option has higher electrical costs, and maintenance requirements. The ERS option also requires disposal of ash. These elements are offsetting but result in the present value of the operating cost being $11.1m less for the ERS option, which is sufficient to offset the additional capital cost of $5.5 m when compared to the dryer only option. The assumed heat value of the dried sludge, which is a function of the volatile solids content of the sludge, has a large impact on the predicted operating cost. Based on the value used, the dried sludge provides 90% of the heat requirement. Should the volatile solids content of the sludge be less, then more natural gas would be required to supplement the heat energy provided by the ERS. 75% volatile solids is considered to be a reasonable figure, based on the plant having no primary clarifiers, and only 5 days of aerated sludge holding.

The values in Table 10 assume that the Project Partners would pay for the disposal of ash. All four biosolids furnace facilities in North Carolina have provided information on their ultimate disposal of ash. WSACC collects ash in on-site ponds and then periodically contracts for disposal. Buncombe County MSD currently stores all ash on site. High Point has two disposal options: delivery to a brick

Page 29: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 29/77

Sludge Dryer and Dewatering Evaluation TM

manufacturer; and use as a soil amendment for the City’s landscaping. They have no disposal costs, and pay only for handling. High Point’s neighbor Greensboro, on the other hand, report handling and disposal costs for their furnace ash in the range of $35 to $40 per ton of ash.

If it is assumed that a beneficial use for the ash could be found and there is no cost for disposal, then the present value of the operating cost reduces by $1.1m. Due to the reduction in volume associated with drying and incineration, the volume of material for disposal is much lower for the ERS option than for the Current design and disposal costs are not a significant factor in the overall operating cost of the ERS option. When included at $40/ton (as presented in Table 11), the cost for ash disposal is approximately 5% of the cost for dewatered sludge disposal in the Current design.

The price of natural gas is subject to some significant volatility, as will be described in the discussion of present worth analysis sensitivity in Section 5. To reflect this the above comparison presented in Table 10 has been repeated in Table 11 using a higher rate of escalation for natural gas and sludge disposal (12% and 6% respectively, compared to 6% and 3% in the tables above). Ash disposal is included at $40/ton.

TABLE 11 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS WITH INCREASED NATURAL GAS AND SLUDGE DISPOSAL ESCALATION

30-Year Analysis Current Kruger Belt Kruger Belt with ERS

Initial Construction Cost Sum ($m) 123.1 124.9 130.4

PV of Plant Expansion ($m) 37.8 43.6 47.0

NPV Operating Cost Sum ($m) 91.5 106.0 66.0

Total Present Worth ($m) 252.3 274.4 243.4

Present Worth Difference from Current ($m) - (21.9) 9.1

Present Worth Difference from Dryer Option($m) - - 31.0

Under this scenario the ERS option has a present worth over $10m lower than the current design. The increase in natural gas price escalation increased the operational cost or the ERS option by close to the same amount that the sludge disposal escalation increased the operational cost of the current design. The combined effect was to give little change in the present worth differential.

However, with the higher gas price escalation, the ERS option performs favorably when compared to the dryer alone option, with a $31.0 m lower present worth. In this scenario, the saving in operational cost is sufficient to pay back the additional cost of the ERS facilities.

In order to quantify the time taken for the savings in operational cost to pay for the additional capital cost of the ERS facilities, a comparison of the annual operating cost of dryer and ERS options has been made. With the escalation factors of the first scenario above (Table 10), the additional capital cost is paid back in 27 years. Under the second scenario (Table 11), the additional capital cost is paid back in Year 17 and by the end of the analysis period in Year 30, there is a $32m benefit to providing the ERS unit.

It should be noted that the capital and operating cost estimates assume that additional drying and incineration capacity will be provided when the plant expands. A simplified analysis assuming no

Page 30: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 30/77

Sludge Dryer and Dewatering Evaluation TM

expansion of the drying and incineration facilities was completed. With no expansion of those facilities there would be a $9.7 m reduction in capital cost of the expansion, and an increase of $6.3 m in operating costs, resulting in a reduction in present worth of $3.4 m compared to the values in Table 10. The additional operating cost is associated with disposal of the dewatered sludge that is in excess of the dryer capacity. In this scenario, payback of the additional cost of the ERS equipment is achieved in year 20.

4.3.5 Cake Receiving Facilities

The proposed dryer facility and solids handling building would include a sludge cake receiving facility. This would allow cake from the Project Partners other facilities to be dried at the Western Wake RWRF. The Town of Cary currently hauls thickened waste activated sludge from the North Cary WRF to the South Cary WRF at solids concentrations of less than 4 percent. Distinct disadvantages of hauling thickened sludge rather than dewatered sludge include:

• Due to the low solids concentrations, the number of trucks required is much greater. This not only results in high transportation costs, but also increases heavy truck traffic both through residential neighborhoods and on both WRF sites.

• Biological phosphorus removal processes concentrate the removed phosphorus in the waste solids. After some period of time, the phosphorus is released back into solution. Hauling liquid sludge between facilities results in the majority of the phosphorus load being transferred to the receiving facility, thus taxing that facilities ability to meet effluent phosphorus limits.

• The required storage volume at the receiving facility is greatly increased.

The Solids Processing Building floor plans indicate a cake receiving facility located adjacent to the building. This facility would consist of a covered receiving hopper with a live bottom, a vertical conveyor to transport the cake to an elevated storage hopper (shown outside the building, but could be moved inside), and feed equipment to the dryer. Sludge cake from the dewatering operation would also be conveyed into the same elevated hopper. This allows common feed systems to the dryer operations and provides flexibility in dewatering operations versus drying operations.

The sizing of the cake receiving station is dependant upon the dewatered solids transportation mode chosen by the Project Partners. To effectively reduce heavy truck traffic, it may be desirable for the cake receiving facility to accommodate the contents of a tandem axle dump trailer. To provide maximum flexibility, the elevated hopper should be able to contain the solids produced by several hours’ operation of the dewatering facility.

The location of the cake receiving station must provide both good vehicular access and the ability to provide odor control. Details of the cake receiving facility will be determined during the final design of the facility. A photograph of a cake receiving station is shown in Figure 13.

Page 31: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 31/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 13 – CAKE RECEIVING STATION

4.3.6 Biosolids Storage and Disposal

Several options are available for the disposal of biosolids. Biosolids can be disposed of by composting (either onsite or by an outside contractor), landfilling, and land application.

Class A biosolids have several advantages over Class B biosolids; importantly, they can be land applied without site or use restrictions, so are suitable for use on places such as parks and golf courses.

Biosolids drying reduces the volume of biosolids to be disposed of and stored, and heat dried municipal sludge has qualities and characteristics that make it suitable for land application.

The beneficial use options for dewatered, composted biosolids and dried biosolids are largely the same markets, except that dried biosolids typically have nutrient values equivalent to many fertilizers, while composted biosolids have low fertilizer potential and is regarded as a soil amendment more than a fertilizer.

The design storage time for dried biosolids is typically between 2 and 4 weeks. In the case that on-site, emergency storage is required when the product cannot be removed from site, the options are the same for dried biosolids as they are for dewatered biosolids, except that dried pellets are typically only about 20% of the volume of compost, so require only a fifth of the storage capacity.

4.3.7 Implications With Regard to Part 503 Regulations

Heat dried municipal sludge that is applied on land is subject to federal and state regulations and statutes that regulate its use. The most important federal regulation that applies to heat dried material is the

Page 32: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 32/77

Sludge Dryer and Dewatering Evaluation TM

Standards for the Use or Disposal of Sewage Sludge (Title 40 of the Code of Federal Regulations, Part 503). Any heat dried material must meet the requirements of the Part 503 if “bulk sludge is applied to agricultural land, forest, a public contact site, or a reclamation site,” and when “bulk sewage sludge is applied to home lawn or garden,” and when “sewage sludge is sold or given away in a bag or other container for application to the land.” The rule was mandated by the Clean Water Act and applies to “any person who prepares sewage sludge and applies sewage sludge to the land.” In addition to Part 503 Rule, state and local regulations may apply to the use of heat dried material.

Quality parameters imposed by the Part 503 Standards include pathogen density, vector attraction reduction, and pollutant (metal) concentration requirements.

(a) Pathogen Density Reduction Requirements

Heat dried material must meet Class A pathogen density criteria (bacteria, viruses, protozoa, helminths), if it is to be applied to land as Class A product. Heat drying processes may meet part of the Class A pathogen requirements either through the time-temperature criteria of Class A, Alternative 1 by being defined as one of the processes listed in Part 503 as “Processes to Further Reduce Pathogens,” as further described below. However, analyses of dried sludge must also demonstrate that the concentration of fecal coliform bacteria is less than 1000 most probable number (MPN) per gram of total solids on a dry weight basis, or the concentration of Salmonella sp. are less than 3 MPN per 4 grams of total solids on a dry weight basis.

Pathogen destruction typically takes place in heat drying by exposing the feed solids to high temperatures. The temperatures in the drying system, combined with residence time of the solids in the drying vessel and dryness of the final product, virtually assure that all of pathogenic organisms are destroyed in the process. There are two commonly accepted ways of meeting the Class A pathogen-reduction criteria during the heat drying process:

• The time-temperature equation for heat-drying as specified in 503.32(a)(3)(ii)(B), also known as Class A Alternative 1, which is stated as follows:

o D = 131,700,000 / 100.14t

o Where D = contact time in days at or above temperature = t in degrees Celsius (C), with minimum contact time of 15 seconds and minimum temperature of 50 degrees C.

• Compliance with the heat-drying criteria for EPA’s Process to Further Reduce Pathogens (PFRP), in which biosolids are dried by direct or indirect contact with hot gases to reduce the moisture content of the biosolids to 10 percent or lower. Either the temperature of the biosolids particles exceeds 80 °C or the wet bulb temperature of the gas in contact with the biosolids as the biosolids leave the dryer exceeds 80 °C.

In both cases of Class A heat-drying process compliance above, periodic samples of the heat-dried biosolids must be taken and analyzed for either Fecal Coliform or Salmonella as specified above.

Of the equipment reported on in this TM, the Kruger belt dryer and Komline-Sanderson paddle dryer demonstrate Class A compliance via the PFRP route (Class A, Alternative 5), while Andritz belt (with pasteurization tower), and the Andritz drum dryers make use of the time and temperature approach (Class A, Alternative 1).

Page 33: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 33/77

Sludge Dryer and Dewatering Evaluation TM

(b) Vector Attraction Reduction Requirements

Heat dried material cannot be attractive to vectors (insects, rodents, etc). The heat drying process meets the following Part 503 vector attraction reduction requirement: “The percent solids of sewage sludge that contains unstabilized solids generated in a primary wastewater treatment process shall be equal to or greater than 90 percent based on the moisture content and total solids prior to mixing with other materials.” To meet the vector attraction reduction requirements, the water content in the dried material has been reduced to less than 10 percent content, which is typical for all heat drying systems evaluated in this TM.

(c) Regulated Metals (Part 503 Pollutants)

Heavy metals present in heat dried sludge must not exceed pollutant ceiling concentrations and loading rates tabulated in Part 503. Pollutants listed in Part 503 include nine metals: arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc. Typically, dried biosolids produced at municipal treatment plants treating mainly domestic wastewater do not exceed Part 503 metal concentration limits, and they usually do not exceed the “Clean Sludge” pollutant limits specified in Table 3 of Part 503. Analyses of dried biosolids produced to date at the South Cary WRF have always resulted in pollutant concentrations safely below the Table 3 “Clean Sludge” limits.

Heat drying technology is treated favorably by the Part 503 Rule and heat dried sludge is usually classified as Class A biosolids. By meeting the pathogen requirements, vector attraction requirements, and “Clean Sludge” pollutant limits simultaneously, the heat drying process produces dried material that is classified as Exceptional Quality (EQ) Biosolids under the Part 503 Rule. The EQ biosolids can be used virtually anywhere without regulation unless more stringent state requirements are in effect.

Heat dried material that is land filled at a regulated landfill or incinerated is subject to regulations that apply to landfills or incinerators. Heat-dried biosolids have been readily accepted by landfills nationwide when landfill disposal is used, and heat-dried biosolids also have fuel value in furnaces due to their dryness and high carbon content.

Modeling of MBR sludge thickening and dewatering show results which are comparable with conventional activated sludge. Therefore, if MBR treatment is selected at the Phase 2 30-MGD expansion, no changes in solids handling would need to be implemented solely because of the switch to MBR technology.

4.3.8 Air Quality Permitting Issues

(a) Types of Emissions

Heat drying systems emit a continuous stream of exhaust process air. The volume and characteristics of the exhaust air vary significantly depending on size and type of heat drying system used. The type of sludge that is processed in the heat drying system also impacts the characteristics of exhaust air. Generally, the volumetric flow of exhaust process air is a function of the equipment, while the emission loading rates and characteristics depend on characteristics of sludge processed.

The process air that is exhausted from the heat drying system may include regulated air pollutants. Depending on the mass and type of air pollutants, a heat drying system is likely to require air permitting and the installation of air pollution control devices.

Page 34: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 34/77

Sludge Dryer and Dewatering Evaluation TM

The air emissions are generated in the heat drying system by the combustion process and in the drying process itself. Air emissions present in the process air exhausted from heat drying systems typically include the following (some constituents are in very low concentrations):

• Carbon monoxide CO • Oxides of nitrogen NOx

• Volatile organic compounds VOC • Hydrogen sulfide H2S • Ammonia NH3

• Particulate matter (PM10) • Sulfur dioxide SO2

• Heavy metals The combustion process involves oxidation of fuel (natural gas, digester gas, heating oil, or any other fuel) in a burner. The burner is needed to generate heat for the heat drying system. The flue gas from the burner is discharged directly to the drying system, or can be forwarded onto a heat exchanger. In both cases, air emissions such as carbon monoxide (CO) and oxides of nitrogen (NOx) are exhausted by the system. Carbon dioxide (nonregulated to date, although the potential exists for future regulation) is also generated in the combustion process.

The drying process is based on contact of wet sludge with hot air or hot surface, during which the sludge is exposed to high temperatures. In the drying process, volatile compounds (VOCs) present in the sludge may be converted into a vapor phase and then picked up by exhaust air. Dissolved hydrogen sulfide or ammonia present in the sludge may be also converted into gaseous phase in the drying process. Last, significant amounts of particulate matter (dust) are created in the drying system. The particulate matter may contain heavy metals, depending on characteristics of the raw sludge. Accordingly, air emissions that are generated by the drying process may include volatile organic compounds, hydrogen sulfide, ammonia, particulate matter, sulfur dioxide, and heavy metals.

Amount of carbon monoxide and NOx emissions is primarily a function of burner operation. The type of drying system used and characteristics of sludge processed have little impact on carbon monoxide and NOx emissions.

Heat drying systems that use direct contact between hot air and high temperatures (flash dryers, direct dryers) tend to drive off volatile matter from the sludge more easily. Other heat drying systems (indirect dryers) use more “gentle” process and produce lesser amounts of volatile emissions. Thus, direct dryers tend to create higher VOC, H2S, and NH3 emissions than indirect dryers. Drying systems with higher operating temperatures such as drum dryers also tend to create higher VOC emissions as compared with belt dryers, which operate at significantly lower temperatures.

Emissions of particulate matter are primarily a function of heat dryer system used and air velocities in the system. Emissions of sulfur dioxide may be significant if hydrogen sulfide is present in the processed sludge or if digester gas with high hydrogen sulfide content is used as a fuel. Emissions of heavy metals are a function of sludge characteristics and amount of particulate matter emitted by the system.

Total volume of exhaust air emitted by heat dryers is typically higher for direct type dryers, as compared to indirect dryers.

(b) Air Pollution Control System

Components of a typical heat drying system may remove some of the air pollutants from the air stream. Most drying systems include a saturator/condenser that is designed to remove moisture from the air

Page 35: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 35/77

Sludge Dryer and Dewatering Evaluation TM

stream. A side effect of the saturator is the removal of particulate matter and heavy metals from the exhaust air. The heat drying system may also include a downstream baghouse or water-based Venturi scrubber or centrifugal separator to further reduce particulate and metal emissions.

Air pollution control system should be designed based on site specific project requirements and can range from no treatment to Venturi scrubbing systems to regenerative thermal oxidizers or other after-burners or oxidizers. Chemical scrubbers may also be employed to remove ammonia of hydrogen sulfide.

(c) Odors

Some of the compounds present in process air exhausted from the heat drying system may be odorous (ammonia, hydrogen sulfide, VOCs, and others). Some heat drying plants experience significant odor problems.

Some air pollution control systems remove odorous compounds. Where air pollution control is not required but the client wishes to prevent releases of odors, an odor control system can be designed using standard methods and approaches.

(d) Permitting

While heat drying does not attract the permitting scrutiny given to incinerators, it almost always requires permits by local or state regulators. Depending on the type and amount of regulated emissions that are expected to be emitted, the authorities may require installation of an air pollution control system. Larger heat drying systems may fall under the Title V Permit requirements.

The South Cary WRF dryer permit has conditions and limitations that include:

• allowable emissions rate, • limits on sulfur dioxide • limits on visible emissions, • reporting of excess emissions, • Bagfilter and particulate matter scrubber inspection, maintenance, and recordkeeping requirements, • Control and prohibition of odorous emissions. And • Toxic Air pollutant limitations.

(e) Air Emissions Permitting Issues for Incineration Alternate

The Project Partners are considering an incineration alternative using dried solids from the biosolids dryer being evaluated in this TM. The purpose of this review is to better understand from an air quality perspective the permitting requirements that would be expected as a result of the use of incineration at the WWRWRF. This review is general and preliminary in nature and will serve as an introduction to a more detailed future analysis of the air permitting requirements.

The North Carolina Division of Air Quality (DAQ) will use emissions estimates as a basis for issuing an air permit along with the determination of the appropriate type of permit and the resulting language therein. An air permit must be issued prior to the construction of any sources of air pollution beyond any land clearing and grading activities.

Based upon preliminary emissions data submitted from the vendors (Andritz and Kruger have provided emission data), it appears that the site could operate as a small source, even with the presence of an

Page 36: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 36/77

Sludge Dryer and Dewatering Evaluation TM

furnace for the purposes of burning dried sludge. Subject to the review and receipt of additional emissions information, it appears likely that Compliance Assurance Monitoring (CAM) may be applicable since control devices will be needed to keep WWRWRF out of non-Attainment New Source Review (NNSR).

To address the need for CAM, the vendors will have to issue clarity on how their uncontrolled emissions are being calculated. It appears the vendors do not understand that abatement devices built within the incinerator itself are viewed as pollution control equipment subject to regulatory review and scrutiny. There are some significant differences in similar emissions reported by the vendors, these discrepancies will have to be investigated in detail and reconciled as the project moves forward. Potential roadblocks:

• The public review due to the focus of environmental groups scrutinizing any sources with the potential to release mercury.

• The EPA is trending towards waiting until the public comments and looking at what the public is saying before issuing their own comments

Approach

The approach taken to perform this review is as follows:

• Using the available information, perform emissions estimates to determine the type and quantity of pollutants. The emissions estimates are needed on a controlled and an uncontrolled basis. (i.e., controlled means that technology is in place to reduce the quantities of regulated air pollutants.)

• The pertinent regulations as it pertains to this operation were looked at. The emission estimates are used as a basis to either exclude specific regulations or include them as potential regulations under which emission from the WWRWRF will be monitored.

Emissions Estimates

Tables 12 and 13 show the emissions estimates developed for this analysis for Kruger’s and Andritz’ belt dryers with biosolids furnaces. Upon taking into account the efficiency, Andritz reports an uncontrolled emission rate of 109.2 tons per year (tpy) of particulate matter (PM). Kruger reports for the same parameter 27.4 tpy of PM. While PM does not appear to pose any regulatory concerns to the WWRWRF, this difference in the emissions rate for PM is sizable.

New Source Review and Title V

Based upon the preliminary emissions estimates, it appears the project will not be subject to New Source Review (NSR). At this point, the Wake County area is non-attainment for ozone. This means that emissions in excess of 100 tpy of either NOx or VOC [separately] will trigger NSR. The preliminary emission estimates (controlled) do not exceed 100 tpy on a potential to emit basis (operation at 8,760 hours per year). This means that not only will the project avoid NSR, but also the Title V requirements since no other criteria pollutants exceed 100 tpy. In all likelihood, the project will be considered as a small source. As a result, the permit will be issued by the Raleigh Regional Office of DAQ.

Other regulations that may be applicable to WWRWRF:

• 40 CFR 503 – Standards for the Use or Disposal of Sewage Sludge • 40 CFR 60 – Standards of Performance for Sewage Treatment Plants (NSPS) (Also included is the

NSPS General Provisions 40 CFR 60 Subpart A) • 40 CFR 61, Subpart E – National Emission Standard for Mercury (NESHAP) (Also included is the

NESHAP General Provisions 40 CFR 61 Subpart A)

Page 37: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 37/77

Sludge Dryer and Dewatering Evaluation TM

• 40 CFR 64 – Compliance Assurance Monitoring (CAM) - Required for all equipment located at a major facility that have pre-controlled emissions above the major source threshold, and use a control device to meet an applicable standard. A complete emissions estimate table will enable a determination as to whether CAM will apply.

• 15A NCAC 02D .1204 – Sewage Sludge and Sludge Incinerators • 15A NCAC 2Q .0702 (a)(18) - State Air Toxics Requirements – Regulation calling for the control of

state-only toxics as defined by this regulation. Applicable sources will be subject to specific monitoring, recordkeeping, and recording requirements. The applicability of this regulation can be determined upon the submission of a complete emissions inventory.

Page 38: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM

Page: 38/77

TABLE 12 – EMISSIONS ESTIMATE – Kruger Belt Dryer

Pollutant Uncontrolled (tpy) Controlled (tpy) Comments (if any) Kruger Comments

Dryer Incinerator Tot.

Dryer

Incinerator

Total

Particulate Matter (PM) 0.26 27.4 27.

7 0.26 2.41 2.6

7

Need uncontrolled emissions; assume the control device for PM is a bag filter

Kruger calculates our PM emissions to be larger than CH2MHill estimate of 1.14 tons/yr. This is based upon the baghouse emission rate of 0.015 grains/dscf. The baghouse porosity is less than 1 micron, therefore the expected emission distribution should all be less than 2.5 microns.

Particulate Matter less than 10 microns (PM-10)

0.25 15.1 15.3

0.25 2.41 2.6

6 Need uncontrolled emissions and total PM-10

Kruger calculates our PM emissions to be larger than CH2MHill estimate of 1.14 tons/yr. This is based upon the baghouse emission rate of 0.015 grains/dscf. The baghouse porosity is less than 1 micron, therefore the expected emission distribution should all be less than 2.5 microns.

Particulate Matter less than 2.5 microns (PM-2.5)

0.25 4.1 4.4 0.25 2.41 2.6

6 Need uncontrolled emissions and total PM-2.5

We currently do not have PM2.5 vs PM10 distribution for the dryer only. As worst case we can assume all of the PM is 2.5 or less. Distribution for the Incineration portion is based upon EPA AP-42 Section 2.2.

SOx 0.02 44.9 44.92

0.02 3.51 3.5

3

Need uncontrolled emissions; assume control device for SOx is lime injection

Uncontrolled emissions are based upon our combustion test and an average uncontrolled emissions rate of 240 ppm SOx. Emissions will vary upon sulfur concentration of the biosolids. We are testing the sulfur content of the North Cary Sludge. Removal will depend upon the lime consumption. Kruger estimates the controlled emission to be less than 50 mg/m3

NOx 1.15 23.85 25 0.46 23.85 25

Need uncontrolled emissions; the control device for NOx at the dryer is a low NOx burner with a 60 percent efficiency

NOX emissions are a function of the afterburner residence time, operating temperature, and nitrogen in the biosolids. The furnace is equipped with an integral afterburner chamber which does not facilitate the measurement of NOX as an uncontrolled emission.

VOC 0.41 0.55

to 13.7

0.91 to 14.1

0.41 0.99 1.4

Need uncontrolled emissions; assume control device for VOCs is a secondary combustion chamber

The VOC emissions are a function of the integral furnace design and operation, as well as the biosolid inlet characteristics. Kruger has assumed a range of 0.2 to 5.2 lbs of VOC per ton of dry solids based upon the EPA AP42 section 2.2.

CO 0.06 3.51 3.57

0.06 3.51 3.5

7 Need uncontrolled emissions

Emissions rates are based upon the emissions limit of 50 mg/m3 of CO out the stack. Emissions are a function of the operation of the furnace. There is not a treatment device for CO but the furnace will be operated to ensure the limits are less.

Mercury 0 0.00352

0.0035

2 0 0.0035

2

0.0035

2

Data taken from recent sampling events and is based upon 5500 dry tons/yr of sludge

Kruger will warrant an emissions level. Removal at lower inlet concentration level will not always be the same percentage as higher inlet concentration.

Note 1 - Year round operation is assumed (24 hours per day; 365 days per year) Note 2 - Uncontrolled mean that a control device is not present prior the release of stack gases to atmosphere; controlled means that a control device is present Note 3 - Assume all dryer emissions will be vented to the atmosphere without passing through a control device. For the purposes of this evaluation, it is assumed the dryer will be permitted as a separate emissions point. Note 4 - Kruger input supplied based upon 5500 DT/yr from 18% solids input. Data Supplied by CH2MHill Revised data by Kruger

Page 39: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 39/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 13 – EMISSIONS ESTIMATE – Andritz Belt Dryer Pollutant Uncontrolled (tpy) Controlled (tpy) Comments (if any)

Dryer Incinerator Total Dryer Incinerator Total

Particulate Matter (PM) 0.26 109.2 0.26 5.46 The control device for PM is a condenser

Particulate Matter less than 10 microns (PM-10) 0.25 85.2 0.25 4.26

The control device for PM is a condenser

Particulate Matter less than 2.5 microns (PM-2.5)

Need uncontrolled emissions and total PM-2.5

SOx 0.02 0.13 0.02 0.13 No controls

NOx 1.15 0.46 4.59

Andritz says "No controls" this needs to be clarified since you can have NOx control devices within the furnace itself.

VOC 0.41 49 0.41 0.98 Control device is a RTO CO 0.06 91.2 0.06 9.12 Control device is a RTO

Mercury

0 0.00352 0.00352 0 0.00352 0.00352 Data taken from recent sampling events and is based upon 5500 dry tons/yr of sludge

Note 1 - Year round operation is assumed (24 hours per day; 365 days per year)

Note 2 - Uncontrolled mean that a control device is not present prior the release of stack gases to atmosphere; controlled means that a control device is present

Note 3 - Assume all dryer emissions will be vented to the atmosphere without passing through a control device. For the purposes of this evaluation, it is assumed the dryer will be permitted as a separate emissions point.

Page 40: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM

Page: 40/77

Incineration Facility Permit

A permit to operate a furnace may have to be obtained from the Solid waste Section – Permitting Branch. Thought on the Belt Dryer

A review of the listed emissions for the belt dryer indicates that the belt dryer can be permitted as a small source. From DAQ Guidance on Air Permitting

Nothing beyond land clearing and grading can be undertaken prior to the issuance of an air permit when a new source of air emissions is to be built on a site. Other Considerations

• Incinerators and power plants are being targeted by environmental groups as a result of mercury emissions. Any potential negative feedback from these groups could hold up the issuance of a permit.

• EPA is trending towards waiting until the public issues comments prior to issuing theirs so they can see what the public is saying.

(f) Approximate Permitting Process for a Small or a Synthetic Minor Source

This process is applicable to both the dryer alone and the dryer with furnace and energy recovery system. • Prepare Air Permit Application • Consistency determination from local government • DAQ Review for Completeness (if not complete DAQ will ask for more information) • DAQ Review for Technical Information (if technical information is missing, DAQ will ask for more

information) • Draft permit • Review of Draft permit by applicant • Public notice and/or hearing at the Discretion of the Director of the Division of Air Quality • Issue or deny permit

4.4 Site Layout

The proposed site layout for the Phase 1 and Phase 2 solids management and dryer facilities is shown in Figure 14. Figures 15 and 16 illustrate the layout of lower and upper floors of the solids building, including the dryer facilities. The dryer building sizes estimated for this evaluation were based on existing installations of similar sized equipment. Only one option is presented in the figures below.

Page 41: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM

Page: 41/77

FIGURE 14 – SITE PLAN

Page 42: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 42/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 15 – SOLIDS BUILDING LOWER PLAN

Page 43: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 43/77

Sludge Dryer and Dewatering Evaluation TM

FIGURE 16 – SOLIDS BUILDING UPPER PLAN

Page 44: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM Page: 44/77

4.5 Non-Cost Factor Comparison

4.5.1 Comparison of Non-Cost Factors

In addition to capital, and operating and maintenance costs there are many non-cost criteria that can be considered in the evaluation of dryer technology. In this section there is a discussion of the relative pros and cons of each dryer when considering the following criteria. These criteria were agreed with the Project Partners as important in dryer selection:

• Regulatory Permitting & Compliance – the ability to obtain and comply with relevant federal, state, and local regulatory requirements through use of the indicated alternative.

• Quality of Biosolids Product – Product quality is often a significant factor when comparing biosolids dryers, particularly when marketing to the general public. For the Western Wake RWRF it is not expected that the dried product will be marketed to the public, so product quality is less of a factor. However, the characteristics of the different dried products may be more suitable to different end users, and having a variety of product types may increase the Town’s ability to market the product.

• Odor Protection & Control – the typical severity of odors associated with the indicated alternative.

• Worker Health & Safety – worker exposure to the biosolids process and the level of concern associated with exposure to the indicated biosolids product.

• O&M Simplicity –the relative complexity of operation and maintenance tasks associated with the indicated alternative.

• Energy Efficiency –the relative energy consumption for the indicated alternative.

• Contingency Capacity – the availability of other processes for biosolids handling should the processes in the indicated alternative temporarily become unavailable for use.

• Constructability – the anticipated complexity of construction.

The following tables, 14a to 14d, summarize the pros and cons for each dryer.

Page 45: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 45/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 14a – NON-COST FACTOR SUMMARY

Dryer Relative Strength Relative Weakness

Kruger Belt Dryer

As with other belt dryers, operates at a relatively low temperature compared to some other types of dryer. Lower temperatures result in reduced potential for fires or explosions.

The feed extrusion device requires frequent cleaning.

There is process redundancy. The proposed system has two units, so one unit could be out of service without total loss of drying capacity.

The product is friable and subject to dust creation.

Belt dryers are a less complex operation than rotary drum dryers.

There is some debate over the dryness of the granule center and whether the product meets the 90% dry solids standard throughout.

Kruger has US operating experience with dryer, and ERS, systems

Different type of product (compared to existing South Cary WRF drum) may provide alternative outlets for disposal.

Stainless steel belt does not require frequent replacement

TABLE 14b – NON-COST FACTOR SUMMARY

Dryer Relative Strength Relative Weakness

Andritz Belt Dryer

As with other belt dryers, operates at a relatively low temperature compared to some other types of dryer. Lower temperatures result in reduced potential for fires or explosions.

Large concrete box required. Adds to capital cost.

Screw feed device is simpler than Kruger Belt

Product recycle loop adds to complexity of operation

Good granular product Large volume of hot air flow

Belt requires replacement every few years

Page 46: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 46/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 14c – NON-COST FACTOR SUMMARY

Dryer Relative Strength Relative Weakness

Andritz Drum Dryer

A number of operating facilities in US High operating temperatures

Pelletized, uniform product Mechanically complex (recycle loops, etc.)

Town of Cary experience with Andritz Drum

TABLE 14d – NON-COST FACTOR SUMMARY

Dryer Relative Strength Relative Weakness

Komline-Sanderson Paddle Dryer

Large number of installations in a variety of settings worldwide

Depends on a different material (oil or steam) as heating medium. Oil has ignited and caused damage in some locations

Mechanical simplicity Dustiness of product.

Relatively low operating temperature

Adding a furnace would increase the permitting, construction and operating complexity. The quantity of ash to be disposed of would be less than the quantity of dried biosolids, but ash is not as marketable and consequently, would cost more to dispose.

On the basis of the non-cost factors, the Kruger belt and Andritz drum dryers are considered the most appropriate technologies for the Western Wake RWRF. The Andritz belt does not add any benefit compared to the Kruger belt dryer to justify the additional capital cost. The paddle dryer is the least favored due to the dustiness of the product and safety issues of thermal oil as a heating medium.

Page 47: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 47/77

Sludge Dryer and Dewatering Evaluation TM

5 Construction and Operating Cost Assessment Capital and operating costs have been estimated for the Current, Alternative and Dryer Alternative Designs. These estimates have been used to compare the alternatives in terms of present worth.

5.1 Capital Cost

Capital and operating cost estimates were generated for the Current and Alternative WWRWRF Designs as part of the November 2007 Evaluation Addendum. These estimates have been used as a basis of the Dryer Alternative cost assessment. In addition, vendor quotes and data from previous project experience have been used to generate order of magnitude costs for the dryer facilities.

The dryer option includes the same liquid train process as the Current WWRWRF design. It added dryer equipment and an associated building as part of the solids handling process. The dryer alternative also includes a reduced aerated sludge holding tank (assumed to be 5 days for the purposes of this evaluation). The solids handling building required for the dryer alternative was found to be smaller than that required for the Current design.

The change in the Phase I cost estimate for the 4 dryer alternatives is summarized on Table 15 and further detail on cost estimates is included in Appendix C.

TABLE 15 – CONSTRUCTION COST COMPARISON

Facility Change in Cost ($m)

Kruger Belt Andritz Belt Andritz Drum Komline-Sanderson

Paddle

Solids and dryer building (2.2) (2.6) (2.9) (2.2)

Solids building equipment 1.1 1.1 1.1 1.1

Dryer equipment 6.2 7.5 7.0 5.1

Aerated Holding Tanks (3.6) (3.6) (3.6) (3.6)

Sub-Total Additional Base Cost 1.6 2.4 1.6 0.4

Contingency Allowance (based on 15%) 0.2 0.4 0.2 0.1

Total Additional Cost 1.8 2.7 1.8 0.5

The cost comparison shows that there is a range of $5.1m to $7.5m in dryer equipment cost. The additional cost of the dryer is largely offset by a reduced solids handling building footprint, even given the inclusion of a building for the dryer, and the reduced size of the aerated holing tanks. Each of the dryer options have a higher capital cost estimate than the current design. The total cost change for the dryer alternatives as defined is up to $2.7m more than the $123m cost of the Current design, or + 2%.

The $3.6m savings in aerated holding tanks (AHT) is relative to the Current design, which includes aerated holding tanks that can store 20 days worth of WAS produced at design conditions. If the Current design were pursued, then it is likely that the size of the AHT would be reduced in this case also, and

Page 48: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 48/77

Sludge Dryer and Dewatering Evaluation TM

some, or all, of this savings realized without a dryer. Additionally, were the current design to be pursued, further changes may be made, such as replacing the GBT’s with RDT’s. This would also reduce the cost of the current design.

The economic evaluation has used 20 and 30-year analysis period, and the cost of expansion of the facilities has been included.

5.2 Operation & Maintenance Cost

The present value of operating costs has been estimated for both 20 and 30 year analysis periods. The operating costs have been developed based on the following variables: electrical power consumption; natural gas usage; sludge disposal; dewatering polymer; chemical requirements; and maintenance. All other operational and maintenance (O&M) costs, including labor, have been estimated to be equal between the two cases. The belt dryer vendors suggest that it is possible to operate the dryers un-staffed, at least overnight, but the Project Partners do not expect that this is how they would operate the equipment, so labor was discounted as a differentiating factor, and is not included in the O&M estimates. This is consistent with the previous analysis of the primary clarifiers and anaerobic digesters alternative.

The flow at the plant has been assumed to vary linearly between an Annual Average Flow of 8.5 mgd at start-up to an Annual Average of 15.3 mgd in year 2020. This corresponds to the design capacity of 18 mgd on a Maximum Month basis for Phase 1. Beyond the anticipated year of plant expansion, it has been assumed that O&M costs increase linearly at the same rate as before the expansion.

Annual electrical costs for the Current WWRWRF Design were calculated using the existing plant electrical load list. This load list was amended to reflect the equipment loads required for the Alternative WWRWRF Design and the annual electrical cost calculated for that design. For the Dryer Alternative, the electrical load list for the current design was adjusted to take account of the electrical requirements for the dryer, and for the reduced aeration requirements of the aerated sludge holding tank.

Natural gas requirements were determined based on the data provided by the vendors, which was adjusted to ensure the values were on a consistent basis.

The sludge disposal and dewatering polymer rates have been adjusted from that used in the Primary Clarifier Evaluation, based on data provided by the Town of Cary. It is assumed that the dried product from each dryer will be of sufficient quality that the Project Partners will be able to, at least, dispose of the product at no cost.

Although two of the manufacturers included an estimate of annual maintenance costs based on differing percentages of the capital cost of the equipment, the ARCADIS/CH2M HILL design team has assumed that the annual maintenance should be based on the same percentage for each (2% of dryer capital cost). There is not sufficient data available to support the variable percentages quoted.

For the base analysis, it has been assumed that all O&M costs except natural gas will escalate at 3% per year. Is has been assumed that natural gas will escalate at 6%, to reflect the recent volatility in price. A sensitivity analysis has assessed the impact of changes in rate of escalation.

For the analysis, the values presented in Table 16 have been used as initial costs.

Page 49: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 49/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 16 – PRESENT WORTH ANALYSIS PARAMETERS

Parameter Rate

Electrical Power Analysis run using both $0.045/kWhr and $0.07/kWhr as initial costs

Natural Gas $8/1000 cf

Sludge Disposal $41/wet ton

Polymer $1/lb polymer

Ferric Chloride $0.18/lb

Methanol $1.50/gallon

Annual Maintenance 2% of dryer capital cost

Annual Escalation Rate for power, chemical, and sludge disposal O&M Costs

3%

Annual Escalation Rate for natural gas O&M Costs 6%

Polymer requirements for dewatering are included in the analysis at 30 lb/dry-ton for anaerobic digestion and 40 lb/dry-ton for aerobic digestion. These values reflect actual values used at existing WWTPs and are consistent with our experience that aerobically-digested solids typically have a higher polymer requirement in dewatering than anaerobically digested solids.

For reasons discussed in the beginning of this TM, Ferric Chloride and methanol are required to meet effluent limits with the Alternative Design configuration.

A summary of the O&M costs for the current, alternative, and dryer option designs is included in Appendix D. The data presented below is for the 30-year analysis, with an initial power cost of $0.07/kWhr.

5.3 Present Worth Analysis

The present worth (PW) analysis was prepared for 20 and 30 year time periods with a discount rate of 5.5%. O&M costs were escalated as described above. In order for above assumption of a linear increase in O&M costs to be valid in the present worth analysis, it is necessary to include the expansion based on conventional technology and not a conversion to membrane bioreactor (MBR) technology. The O&M profile of a converted plant would be very different, although a similar comparison based on an expansion as an MBR plant would be expected to produce similar results.

The results of the present worth analysis are presented in Table 17 for the 30-year analysis with an initial electrical cost of $0.07/kWhr. The Alternative design is included in this table for reference, since a decision has been made not to proceed with that alternative.

Similar tables for an initial electrical cost of $0.045/kWhr and for a 20-year analysis period are included in Appendix B.

Page 50: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 50/77

Sludge Dryer and Dewatering Evaluation TM

TABLE 17 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alt. Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson Paddle

Kruger Belt with

ERS

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5 130.4

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8 47.0

NPV Operating Cost Sum ($m) 76.9 66.8 71.3 73.5 73.5 71.0 60.2

Total Present Worth ($m) 237.8 233.0 239.8 242.5 242.0 237.3 237.7

Present Worth Difference from Current ($m) - 4.7 (2.0) (5.7) (4.2) 0.5 0.1

As described in the cost estimation section above, the initial capital cost of the dryer alternatives are all within $2.7m of the Current design. There is a more pronounced difference at the plant expansion, when expanded drying facilities and equipment would have to be provided. All dryer alternatives are less costly to operate than the Current design. This is largely due to the assumption that there will be no cost for disposal of the dried biosolids, whereas there will be significant disposal costs for dewatered sludge for the Current design.

The analysis indicates that the Komline-Sanderson paddle dryer has the lowest PW, some $0.5m lower than the current design. Both the Andritz belt and drum systems are shown to have a higher present worth than the current design. It should be noted that the variability in the present worth values, from paddle to Andritz Belt dryer, is approximately $6.2m in $238m, or a little over 2.5%.

When the analysis is run with a $0.045/kWhr electrical cost, or over 20 years, then the Komline-Sanderson paddle still has a lower PW than the current design, but each of the other three dryers has a higher PW than the current design. The shorter the analysis period, or the lower the electrical power cost, the more favorable the current design is when compared to the dryer option. In a similar way to the data presented above, the total present worth for these other scenarios is within 2.5% of the PW of the current design.

All of these base analyses show the following order in total present worth (from lowest to highest) Komline-Sanderson paddle; Kruger belt; Andritz Drum; and Andritz Belt. The paddle dryer has both the lowest capital cost, and the lowest NPV of operating cost, although the variation is within the level of accuracy of the analysis.

The ERS option, which is described in more detail in Section 4.3.4, has a similar PW to the Current design, but has a higher capital cost. The ERS has the lowest operating cost of all of the options evaluated.

Page 51: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 51/77

Sludge Dryer and Dewatering Evaluation TM

5.3.1 Revised Contract Composting Fees

The above analyses include the contract biosolids disposal rate that is currently being provided to the Town of Cary by a local contract composting facility for dewatered solids from the South Cary WRF. The contract composting facility that is used by the Town of Cary proposed reduced rates for biosolids disposal for the Western Wake RWRF. The revised rate excluded the existing transportation fee of $6/ton, and capped the escalation in disposal fee at 2.6% annually for 20 years. An additional amount was added for a $2 m performance bond, which increased the disposal rate by $1.80 in 2011 and $0.62 in 2030. The revised disposal rate proposed is $36.8/ton in 2011 rising to $57.61 in 2030, though these rates have not been accepted by the Town. With these revised cake disposal rates, the operating cost of the Current scenario reduces, and becomes more favorable compared to the dryer options from a present worth perspective. The values in Table 18 reflect the impact of the revised disposal rates, which reduce the present worth of operating costs of the Current design by $4.2 m.

TABLE 18 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

REVISED COMPOSTING RATE FOR CURRENT ALTERNATIVE

30-Year Analysis Revised Current Alt.

Kruger Belt

Andritz Belt

Andritz Drum

Komline-Sanderson Paddle

Kruger Belt with

ERS

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5 130.4

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8 47.0

NPV Operating Cost Sum ($m) 72.7 66.8 71.3 73.5 73.5 71.0 60.2

Total Present Worth ($m) 233.6 233.0 239.8 242.5 242.0 237.3 237.7

Present Worth Difference from Current ($m) - 0.6 (6.2) (8.9) (8.4) (3.7) (4.1)

The reduced disposal rate reduces the operating cost of the Current design sufficiently to make its total present worth about the same as the alternative design and less than all of the drying alternatives, but it leaves the Project Partners reliant on a third party for biosolids management and more vulnerable to influences outside their control.

5.4 Sensitivity Analysis

5.4.1 Natural Gas Price Escalation

The base data compared above included the assumption that natural gas prices would escalate at 6% annually, to reflect price volatility. That volatility is represented in Figure 17 below, which shows natural gas prices over the 2007 calendar year. If a factor of 1000 BTU/cf of natural gas is assumed (the normally-accepted rate for the energy value of natural gas), then the $/MMBTU shown in the chart can also be read

Page 52: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 52/77

Sludge Dryer and Dewatering Evaluation TM

as $/1000 cf. The Town of Cary has an agreement with PSNC that gas provided will have a minimum of 1000 BTU/cf, so the conversion factor is appropriate.

Historical data for natural gas prices going back to 2000 show a minimum of below $4/1000 cf (prior to September 11, 2001) and a maximum of $16/1000 cf, which occurred shortly after Hurricane Katrina in 2005. Natural gas prices have settled somewhat since 2006, but still have fluctuated within the range of $5.50 to $9.00 per MMBTU over the past year and averaging about $9.00 per MMBTU currently, as shown in Figure 17 below, so there remains a high degree of volatility in natural gas pricing because they are subject to world commodity markets. Natural gas prices are expected to remain volatile in the short term, while increasing at rates above general inflationary trends in the long term.

FIGURE 17 – NATURAL GAS PRICES 2007

To test the sensitivity, the analyses were re-run with natural gas escalating at 3%, as the other O&M costs. With the lower escalation is natural gas prices, there was a dramatic increase in the PW differential between the dryer options and the current design. Reducing the increase in future natural gas prices reduced the NPV of operating costs by approximately $5.9m to $7m when compared to the 30-year values presented above. For example, for the Komline-Sanderson paddle dryer option the total PW decreased by $6.8m. That is to say, the difference in total PW compared to the current design increased from $0.5m to $7.3m.

A second sensitivity analysis was run using a higher rate of escalation. In looking at recent trends in gas prices, a 13% escalation was noted in the last 5 years. A rate of 12% (or double the base escalation

Page 53: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 53/77

Sludge Dryer and Dewatering Evaluation TM

assumption of 6%) has been used in the sensitivity analysis. It is considered that such a rate increase would not happen in isolation. In this sensitivity scenario, an increase in sludge disposal rate has been included at 6% to reflect general fossil fuel price rises that would be seen in diesel fuel and gasoline.

Higher rates of increase in natural gas price will increase the total present worth of the dryer options and make them less favorable when compared to the Current design. The effect of the increase in sludge disposal escalation is to offset some of that increase in present worth from rising natural gas prices. The sludge disposal increase affects only the Current and Alternative designs, as it is assumed that there will be zero net cost for disposal of the dried product.

The results when considering 12% natural gas escalation, which are included in Appendix B, show that the dryer alternatives have significantly higher total present worth values than the Current design. The Komline-Sanderson paddle dryer option is closest to the Current design, but still suggests an increase in present worth of over $19.5m. The other three dryers have increases in present worth compared to the Current design of between $22m and $26m.

The calculated rate at which natural gas prices increase is very dependent on the particular period of estimation. For example, in addition to the 13% rate increase calculated above, separate estimates ranged from a 0.2% to a 35% annual increase based on different start and end points of the calculation. The 13% value is considered to be a reasonable, upper-bound estimate of average escalation since 2000.

The same price data used to assess the rate of increase also shows that the rate for natural gas was close to $8/1000 cf in 2000, and then dropped below that rate until towards the end of 2004. Since then the rate has been above $8/1000 cf, but is now returning to around $8/1000 cf. It could be taken that this shows that, while there is significant year-on-year volatility in natural gas prices, long-term trends are not as marked.

5.4.2 Sludge Disposal Escalation

The base data compared above included an escalation in sludge disposal costs of 3% annually. To test the sensitivity of sludge disposal costs, which are strongly linked to gasoline prices, the analyses were re-run with sludge disposal escalating at 6%.

This change was significant. The NPV of operating costs for the dryers remained fixed when compared to the values tabulated above, but the NPV of operating costs for the Current design increased by close to $15m. To illustrate the effect of the change, the difference in PW for the Komline-Sanderson paddle dryer option compared to the Current design increased from $0.5m to $15.2m. A similar impact occurs for the other dryer alternatives.

Page 54: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 54/77

Sludge Dryer and Dewatering Evaluation TM

5.4.3 Sensitivity Summary

Additional sensitivity analysis results are presented in Appendix B, and a summary is shown in Table 19.

TABLE 19 – 30-YEAR TOTAL PRESENT WORTH VALUES - $0.07/KWHR INITIAL ELECTRICAL COSTS

Escalation Rates Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

6% gas, 3% sludge disposal 237.8 233.0 239.8 224.5 242.0 237.3

3% gas, 3% sludge disposal 237.8 233.0 232.9 236.6 235.0 230.5

6% gas, 6% sludge disposal 252.5 245.2 239.8 243.5 242.0 237.3

12% gas, 6% sludge disposal 252.5 245.2 274.4 278.1 276.6 272.0

These sensitivity analyses show that variables that are outside of the control of the Project Partners, and are subject to significant volatility, have a major effect on the outcome of the cost analysis.

6 Summary and Recommendation 6.1 Dewatering Evaluation

The evaluation of dewatering technologies has shown that the rotary press is not an appropriate device for dewatering sludge for the Western Wake RWRF because it cannot achieve the 18% dry solids concentration that is the basis of the heat-drying design criteria. It is recommended that the design incorporates centrifuges for dewatering sludge. Centrifuges have been shown to consistently achieve 18% dry solids concentration on similar biosolids in operation at the South Cary WRF.

It is also recommended that RDTs be used to thicken waste activated sludge rather than the GBTs currently proposed. RDTs are more cost effective than GBTs at the WW WRF for a number of reasons, and they can reliably achieve 3-4% dry solids concentration as sludge thickeners, which is sufficient for the intended application of thickening prior to sludge holding and dewatering at the WWR WRF.

6.2 Dryer Evaluation

This evaluation has shown that a biosolids dryer is a viable option for the Western Wake RWRF. The capital cost, when taking into account future expansion, is marginally greater than for the Current design, but the cost to operate the plant with a biosolids dryer has been estimated to be lower than the cost to operate the plant as currently designed under most future scenarios.

The economic and sensitivity analyses summarized in Section 5 indicate that for the base case assumptions the Total Present Worth of the WWRWRF is slightly higher than the current design. In scenarios where natural gas prices escalation is reduced, or sludge disposal escalation is increased, then the dryer has a lower PW than the current design. As might be expected, a higher escalation in natural gas prices would favor the current design. In the scenario with 12% annual natural gas escalation in conjunction with 6%

Page 55: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 55/77

Sludge Dryer and Dewatering Evaluation TM

annual sludge disposal cost escalation does the Net Present Worth of all heat-drying alternatives significantly exceed the Current Design. Since sludge disposal costs are dependent on the general commodity prices for fossil fuels, similar to natural gas prices, it is more likely that natural gas price escalation will tend to track general price escalation including sludge disposal costs.

Based on the findings of this evaluation, a preliminary ranking of the four dryers has been made. It is considered that, because of the closeness of the present worth of the four dryer options (that is, they are within 2.5% of each other), the ranking of the dryers should be based on non-cost factors. Given that, the order of preference based on current criteria weights and rankings would be:

1 Kruger Belt Dryer and Andritz Rotary Drum Dryer (tied)

2 Andritz Belt Dryer

3 Komline-Sanderson Paddle Dryer

Furnace and Energy Recovery

On the basis of this evaluation, it is concluded that providing furnace capacity for both Phase I and Phase II is a viable option. Under the base assumption of a 6% rise in natural gas prices, the furnace and energy recovery equipment would take 27 years of operation analysis period to recover the additional cost of construction. Incineration becomes a more favorable option if the escalation of natural gas price is substantially higher than general price escalation. With a 12% natural gas price escalation (as compared to a 3% general price escalation) the additional capital cost of a furnace is estimated to be recovered in 17 years. A furnace and energy recovery system would provide some contingency against natural gas price fluctuations, but would not completely replace dependency on natural gas for heat drying at the WWRWRF. It should be noted that the analysis is sensitive to natural gas price escalation and the replacement of natural gas, which is a function of sludge volatile solids content.

If the dryer option is to be considered further, several issues should be taken into account.

• Consideration of alternative sludge disposal options when the plant is expanded. The current evaluation assumes that all sludge will be dried when the plant is expanded. Therefore additional drying facilities would be provided upon plant expansion. It may be appropriate to dry only a part of the total sludge produced, with the remainder being composted, landfilled, or land applied.

• The cost of fuel to operate the dryer is significant. If a dryer is included in the initial construction, it is recommended that price fluctuations be monitored during the early years of operating a dryer. It may be appropriate to find a lower cost source of dryer fuel as a contingency against natural gas price fluctuation, potentially through negotiated rates or longer-term contracts.

• When considering the next plant expansion, it will be worthwhile to re-evaluate the construction of primary clarifiers and anaerobic digestion, which will create digester gas as a more cost effective source of fuel for the dryer to offset the reliance on natural gas.

A more thorough investigation of operational heat-drying facilities of the rotary-drum, belt, and paddle types is recommended before making technology decisions regarding the type or types of heat-drying equipment to procure. This would include additional site visits, discussions with existing dryer facilities, and more detailed evaluations of preliminary design and price quotes provided by the different drying systems under consideration.

Page 56: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 56/77

Sludge Dryer and Dewatering Evaluation TM

Appendices

A Present Worth Analysis Results

B Present Worth Sensitivity Analysis Results

C Construction Cost Summary

D Operating Costs Summary

E Natural Gas Usage

F Sludge Quantities and Dryer Operations

Page 57: App H--Evaluation of Sludge Dryer and Dewatering Facilities

WESTERN WAKE REGIONAL WRF

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM Page: 57/77

APPENDIX A – Present Worth Tables

TABLE A.1 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 76.9 66.8 71.3 73.5 73.5 71.0

Total Present Worth ($m) 237.8 233.0 239.8 242.5 242.0 237.3

Present Worth Difference from Current ($m) - 4.7 (2.0) (5.7) (4.2) 0.5

TABLE A.2 – 30-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 58.9 53.4 54.7 56.3 56.3 54.4

Total Present Worth ($m) 219.9 219.6 223.2 226.3 224.8 220.7

Present Worth Difference from Current ($m) - 0.2 (3.3) (6.4) (4.9) (0.8)

Page 58: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 58/77

Sludge Dryer and Dewatering Evaluation TM

TABLE A.3 – 20-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 46.1 41.4 41.7 43.0 43.0 41.4

Total Present Worth ($m) 207.0 207.6 210.2 212.9 211.5 207.7

Present Worth Difference from Current ($m) - (0.6) (3.1) (5.9) (4.4) (0.7)

TABLE A.4 – 20-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 35.3 33.0 31.6 32.6 32.6 31.3

Total Present Worth ($m) 196.2 199.2 200.0 202.5 201.0 197.6

Present Worth Difference from Current ($m) - (3.0) (3.8) (6.3) (4.8) (1.4)

Page 59: App H--Evaluation of Sludge Dryer and Dewatering Facilities

WESTERN WAKE REGIONAL WRF

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM Page: 59/77

APPENDIX B – Sensitivity Analyses

Natural Gas Increases at 3% annually

TABLE B.1 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 76.9 66.8 64.4 66.6 66.6 64.2

Total Present Worth ($m) 237.8 233.0 232.9 236.6 235.0 230.5

Present Worth Difference from Current ($m) - 4.7 4.9 1.1 2.7 7.3

TABLE B.2 – 30-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 58.9 53.4 47.8 49.4 49.4 47.5

Total Present Worth ($m) 219.9 219.6 216.3 219.4 217.9 213.8

Present Worth Difference from Current ($m) - 0.2 3.6 0.5 2.0 6.1

Page 60: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 60/77

Sludge Dryer and Dewatering Evaluation TM

TABLE B.3 – 20-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 46.1 41.4 39.3 40.6 40.6 39.1

Total Present Worth ($m) 207.0 207.6 207.7 210.6 209.0 205.4

Present Worth Difference from Current ($m) - (0.6) (0.7) (3.5) (2.0) 1.6

TABLE B.4 – 20-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 35.3 33.0 31.6 30.2 30.2 28.9

Total Present Worth ($m) 196.2 199.2 200.0 200.1 198.6 195.2

Present Worth Difference from Current ($m) - (3.1) (3.8) (3.9) (2.4) 1.0

Page 61: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 61/77

Sludge Dryer and Dewatering Evaluation TM

Natural Gas Increases at 12% annually, Sludge Disposal Increase at 6% annually

TABLE B.5 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 91.6 78.9 106.0 108.2 108.2 105.7

Total Present Worth ($m) 252.5 245.2 274.4 278.1 276.6 272.0

Present Worth Difference from Current ($m) - 7.2 (21.9) (25.6) (24.1) (19.5)

TABLE B.6 – 30-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 73.7 65.6 89.4 91.0 91.0 89.0

Total Present Worth ($m) 234.6 231.8 257.9 260.9 259.4 255.3

Present Worth Difference from Current ($m) - 2.7 (23.3) (26.3) (24.8) (20.7)

Page 62: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 62/77

Sludge Dryer and Dewatering Evaluation TM

TABLE B.7 – 20-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 51.3 45.7 50.2 51.5 51.5 50.0

Total Present Worth ($m) 212.2 211.9 218.7 221.5 220.0 216.3

Present Worth Difference from Current ($m) - 0.2 (6.5) (9.3) (7.8) (4.1)

TABLE B.8 – 20-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 40.5 37.3 40.1 41.1 41.1 39.8

Total Present Worth ($m) 201.4 203.5 208.6 211.0 209.5 206.1

Present Worth Difference from Current ($m) - (2.2) (7.2) (9.6) (8.1) (4.8)

Page 63: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 63/77

Sludge Dryer and Dewatering Evaluation TM

Sludge Disposal Rate Increases at 6%

TABLE B.9 – 30-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 91.6 78.9 71.3 73.5 73.5 71.0

Total Present Worth ($m) 252.5 245.2 239.8 243.5 242.0 237.3

Present Worth Difference from Current ($m) - 7.2 12.7 9.0 10.5 15.2

TABLE B.10 – 30-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

30-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 73.7 65.6 54.7 56.3 56.3 54.4

Total Present Worth ($m) 234.6 231.8 223.2 226.3 224.8 220.7

Present Worth Difference from Current ($m) - 2.7 11.4 9.3 9.8 13.9

Page 64: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum Evaluation of Sludge Drying and Dewatering Facilities

at the Western Wake Water Reclamation Facility

Western Wake RWRF 64/77

Sludge Dryer and Dewatering Evaluation TM

TABLE B.11 – 20-YEAR PRESENT WORTH ANALYSIS - $0.07/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 51.3 45.8 41.7 43.0 43.0 41.5

Total Present Worth ($m) 212.2 212.0 210.2 213.0 211.5 207.8

Present Worth Difference from Current ($m) - 0.2 2.0 (0.8) 0.7 4.4

TABLE B.12 – 20-YEAR PRESENT WORTH ANALYSIS - $0.045/KWHR INITIAL ELECTRICAL COSTS

20-Year Analysis Current Alternative Kruger

Belt Andritz

Belt Andritz Drum

Komline-Sanderson

Paddle

Initial Construction Cost Sum ($m) 123.1 127.3 124.9 125.8 124.8 123.5

PV of Plant Expansion ($m) 37.8 38.9 43.6 44.2 43.6 42.8

NPV Operating Cost Sum ($m) 40.5 37.4 31.6 32.6 32.6 31.3

Total Present Worth ($m) 201.4 203.6 200.1 202.5 201.0 197.6

Present Worth Difference from Current ($m) - (2.2) 1.3 (1.1) 0.3 3.7

Page 65: App H--Evaluation of Sludge Dryer and Dewatering Facilities

WESTERN WAKE REGIONAL WRF

Western Wake RWRF

Sludge Dryer and Dewatering Evaluation TM

Page: 65/77

Appendix C.1 - Capital Costs ($m) for Current Design, Alternative Design & Dryer Alternative Designs, 18 MGD

Facility Description Current Design

Alternative Design Kruger Belt Andritz Belt

Andritz Drum

Komline-Sanderson

Paddle Kruger Belt

w/ERS

Preliminary Treatment Facility 3.2 3.2 3.2 3.2 3.2 3.2 3.2

Primary Influent Structure - 0.7 - - - - -

Primary Treatment - 5.0 - - - - -

Primary Sludge Pump Station - 1.6 - - - - -

Secondary Influent Structure 0.7 0.7 0.7 0.7 0.7 0.7 0.7

BNR Process Tanks and Related Pumping Facilities 27.2 24.1 27.2 27.2 27.2 27.2 27.2

Secondary Clarifiers and RAS/WAS Pumping Station 13.3 13.1 13.3 13.3 13.3 13.3 13.3

RAS/WAS and Blower Building 5.2 5.2 5.2 5.2 5.2 5.2 5.2

Effluent Filters 3.7 3.7 3.7 3.7 3.7 3.7 3.7

Effluent Disinfection (UV) 2.9 2.9 2.9 2.9 2.9 2.9 2.9

Post Aeration 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Solids Facilities (excluding Equipment) 11.0 10.0 8.8 8.4 8.1 8.8 10.2

Solids Building Dewatering Equipment 3.6 2.7 4.7 4.7 4.7 4.7 4.7

Dryer Equipment - - 6.2 7.5 7.0 5.1 9.8

Page 66: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 66/77

Sludge Dryer and Dewatering Evaluation TM

Facility Description Current Design

Alternative Design Kruger Belt Andritz Belt

Andritz Drum

Komline-Sanderson

Paddle Kruger Belt

w/ERS

Centrate/Filtrate Treatment Facilities 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Truck Loading Structure 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Solids Receiving/Aerated Sludge Holding Tanks 5.3 - 1.6 1.6 1.6 1.6 1.6

Anaerobic Digester Complex - 6.2 - - - - -

Chemical Storage and Feed Facilities, & Reuse Water 3.3 3.3 3.3 3.3 3.3 3.3 3.3

Plant Drain Pump Station 1.4 1.4 1.4 1.4 1.4 1.4 1.4

Electrical Building 2.1 2.1 2.1 2.1 2.1 2.1 2.1

Generator Set 3.9 3.9 3.9 3.9 3.9 3.9 3.9

Odor Control Facilities 2.2 2.8 2.3 2.2 2.2 2.2 2.2

Operations/Maintenance Buildings/Equipment Building 5.4 5.4 5.4 5.4 5.4 5.4 5.4

Site Electrical 4.3 4.1 4.3 4.3 4.3 4.3 4.3

Sitework 3.9 4.1 3.9 3.9 3.9 3.9 3.9

Yard Piping 3.1 3.1 3.1 3.1 3.1 3.1 3.1

Subtotal Construction Cost (excludes escalation) 107.0 110.7 108.6 109.4 108.6 107.4 113.4

Construction Contingency (15% of subtotal) 16.1 16.6 16.3 16.4 16.3 16.1 17.0

Total WRF Construction Cost 123.1 127.3 124.9 125.8 124.8 123.5 130.4

Page 67: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 67/77

Sludge Dryer and Dewatering Evaluation TM

Appendix C.2 - Breakdown of Phase I Solids Handling Facilities Capital Costs ($m)

Facility Description Current Design

Alternative Design

Kruger Belt

Andritz Belt

Andritz Drum

Komline-Sanderson

Paddle

Kruger Belt

w/ERS

Aerated Holding Tanks 5.3 - 1.6 1.6 1.6 1.6 1.6

Anaerobic Digester Complex - 6.2 - - - - -

Solids Building 11.0 10.0 8.8 8.4 8.1 8.8 10.2

Dryer Building Portion - - 2.4 2.0 1.7 2.4 3.8

Dryer Equipment - - 6.2 7.5 7.0 5.1 9.8

Solids Equipment 3.6 2.7 4.7 4.7 4.7 4.7 4.7

Truck Scale and Solids Receiving - - 0.7 0.7 0.7 0.7 0.7

RDT (GBT for Current and Alt) 0.4 0.4 0.7 0.7 0.7 0.7 0.7

Centrifuges 1.7 1.4 1.7 1.7 1.7 1.7 1.7

TOTAL 19.9 18.9 21.4 22.2 21.4 20.2 26.3

Page 68: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 68/77

Sludge Dryer and Dewatering Evaluation TM

Appendix D - Operating Costs TABLE D.1 - CURRENT WWRWRF DESIGN ESCALATED DOLLARS

YEAR POWER SLUDGE DISPOSAL CHEMICAL MAINTENANCE GAS TOTAL TOTAL (PV)

1 $1,000,000 $400,000 $70,000 $0 $0 $1,470,000 $1,390,0002 $1,150,000 $470,000 $80,000 $0 $0 $1,700,000 $1,530,0003 $1,300,000 $540,000 $90,000 $0 $0 $1,940,000 $1,650,0004 $1,470,000 $620,000 $110,000 $0 $0 $2,190,000 $1,770,0005 $1,640,000 $700,000 $120,000 $0 $0 $2,460,000 $1,880,0006 $1,820,000 $790,000 $140,000 $0 $0 $2,740,000 $1,990,0007 $2,010,000 $880,000 $150,000 $0 $0 $3,040,000 $2,090,0008 $2,210,000 $970,000 $170,000 $0 $0 $3,350,000 $2,180,0009 $2,420,000 $1,070,000 $190,000 $0 $0 $3,680,000 $2,270,00010 $2,640,000 $1,180,000 $210,000 $0 $0 $4,020,000 $2,350,00011 $2,870,000 $1,290,000 $220,000 $0 $0 $4,380,000 $2,430,00012 $3,110,000 $1,400,000 $240,000 $0 $0 $4,760,000 $2,500,00013 $3,370,000 $1,530,000 $270,000 $0 $0 $5,160,000 $2,570,00014 $3,630,000 $1,650,000 $290,000 $0 $0 $5,580,000 $2,640,00015 $3,920,000 $1,790,000 $310,000 $0 $0 $6,020,000 $2,690,00016 $4,210,000 $1,930,000 $340,000 $0 $0 $6,480,000 $2,750,00017 $4,520,000 $2,080,000 $360,000 $0 $0 $6,960,000 $2,800,00018 $4,840,000 $2,230,000 $390,000 $0 $0 $7,460,000 $2,850,00019 $5,180,000 $2,390,000 $420,000 $0 $0 $7,990,000 $2,890,00020 $5,530,000 $2,560,000 $450,000 $0 $0 $8,540,000 $2,930,00021 $5,900,000 $2,740,000 $480,000 $0 $0 $9,120,000 $2,960,00022 $6,290,000 $2,930,000 $510,000 $0 $0 $9,730,000 $3,000,00023 $6,700,000 $3,120,000 $540,000 $0 $0 $10,370,000 $3,030,00024 $7,120,000 $3,330,000 $580,000 $0 $0 $11,030,000 $3,050,00025 $7,570,000 $3,540,000 $620,000 $0 $0 $11,720,000 $3,070,00026 $8,030,000 $3,770,000 $660,000 $0 $0 $12,450,000 $3,090,00027 $8,510,000 $4,000,000 $700,000 $0 $0 $13,210,000 $3,110,00028 $9,020,000 $4,240,000 $740,000 $0 $0 $14,000,000 $3,130,00029 $9,550,000 $4,500,000 $780,000 $0 $0 $14,830,000 $3,140,00030 $10,110,000 $4,770,000 $830,000 $0 $0 $15,700,000 $3,150,000

TOTAL $137,600,000 $63,400,000 $11,100,000 $0 $0 $212,100,000 $76,900,000

Assumes $0.07/kWhr initial electrical cost.

Page 69: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 69/77

Sludge Dryer and Dewatering Evaluation TM

TABLE D.2 - ALTERNATIVE WWRWRF DESIGN ESCALATED DOLLARS

YEAR POWER SLUDGE DISPOSAL CHEMICAL MAINTENANCE GAS TOTAL TOTAL (PV)

1 $920,000 $380,000 $250,000 $0 $0 $1,550,000 $1,470,0002 $1,020,000 $440,000 $280,000 $0 $0 $1,730,000 $1,560,0003 $1,120,000 $500,000 $310,000 $0 $0 $1,930,000 $1,640,0004 $1,240,000 $560,000 $340,000 $0 $0 $2,130,000 $1,720,0005 $1,350,000 $630,000 $370,000 $0 $0 $2,350,000 $1,800,0006 $1,480,000 $700,000 $400,000 $0 $0 $2,580,000 $1,870,0007 $1,610,000 $770,000 $440,000 $0 $0 $2,810,000 $1,930,0008 $1,740,000 $850,000 $470,000 $0 $0 $3,060,000 $2,000,0009 $1,890,000 $930,000 $510,000 $0 $0 $3,320,000 $2,050,00010 $2,040,000 $1,010,000 $550,000 $0 $0 $3,600,000 $2,110,00011 $2,190,000 $1,100,000 $590,000 $0 $0 $3,890,000 $2,160,00012 $2,360,000 $1,190,000 $640,000 $0 $0 $4,190,000 $2,200,00013 $2,530,000 $1,290,000 $690,000 $0 $0 $4,510,000 $2,250,00014 $2,710,000 $1,400,000 $730,000 $0 $0 $4,840,000 $2,290,00015 $2,900,000 $1,500,000 $780,000 $0 $0 $5,190,000 $2,320,00016 $3,100,000 $1,620,000 $840,000 $0 $0 $5,560,000 $2,360,00017 $3,310,000 $1,740,000 $890,000 $0 $0 $5,940,000 $2,390,00018 $3,530,000 $1,860,000 $950,000 $0 $0 $6,340,000 $2,420,00019 $3,750,000 $1,990,000 $1,010,000 $0 $0 $6,760,000 $2,440,00020 $3,990,000 $2,130,000 $1,080,000 $0 $0 $7,200,000 $2,470,00021 $4,240,000 $2,270,000 $1,140,000 $0 $0 $7,650,000 $2,490,00022 $4,500,000 $2,420,000 $1,210,000 $0 $0 $8,130,000 $2,500,00023 $4,770,000 $2,580,000 $1,290,000 $0 $0 $8,630,000 $2,520,00024 $5,060,000 $2,740,000 $1,360,000 $0 $0 $9,160,000 $2,530,00025 $5,350,000 $2,910,000 $1,440,000 $0 $0 $9,710,000 $2,550,00026 $5,660,000 $3,090,000 $1,530,000 $0 $0 $10,280,000 $2,560,00027 $5,990,000 $3,280,000 $1,610,000 $0 $0 $10,880,000 $2,560,00028 $6,330,000 $3,470,000 $1,700,000 $0 $0 $11,500,000 $2,570,00029 $6,680,000 $3,680,000 $1,800,000 $0 $0 $12,160,000 $2,570,00030 $7,050,000 $3,890,000 $1,900,000 $0 $0 $12,840,000 $2,580,000

TOTAL $100,400,000 $52,900,000 $27,100,000 $0 $0 $180,400,000 $66,900,000

Assumes $0.07/kWhr initial electrical cost.

Page 70: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 70/77

Sludge Dryer and Dewatering Evaluation TM

TABLE D.3 - KRUGER BELT WWRWRF DESIGN ESCALATED DOLLARS

YEAR POWER SLUDGE DISP. CHEMICAL MAINT. GAS TOTAL TOTAL (PV)

1 $970,000 $0 $70,000 $100,000 $190,000 $1,330,000 $1,260,0002 $1,110,000 $0 $80,000 $100,000 $230,000 $1,510,000 $1,360,0003 $1,250,000 $0 $90,000 $110,000 $270,000 $1,710,000 $1,460,0004 $1,390,000 $0 $110,000 $110,000 $320,000 $1,930,000 $1,550,0005 $1,550,000 $0 $120,000 $110,000 $370,000 $2,150,000 $1,650,0006 $1,710,000 $0 $140,000 $120,000 $420,000 $2,390,000 $1,730,0007 $1,890,000 $0 $150,000 $120,000 $490,000 $2,650,000 $1,820,0008 $2,070,000 $0 $170,000 $120,000 $560,000 $2,920,000 $1,900,0009 $2,260,000 $0 $190,000 $250,000 $630,000 $3,330,000 $2,060,00010 $2,460,000 $0 $210,000 $260,000 $710,000 $3,640,000 $2,130,00011 $2,670,000 $0 $220,000 $270,000 $800,000 $3,960,000 $2,200,00012 $2,890,000 $0 $240,000 $270,000 $900,000 $4,310,000 $2,270,00013 $3,120,000 $0 $270,000 $280,000 $1,010,000 $4,680,000 $2,330,00014 $3,360,000 $0 $290,000 $290,000 $1,120,000 $5,070,000 $2,390,00015 $3,620,000 $0 $310,000 $300,000 $1,250,000 $5,480,000 $2,450,00016 $3,880,000 $0 $340,000 $310,000 $1,390,000 $5,920,000 $2,510,00017 $4,160,000 $0 $360,000 $320,000 $1,540,000 $6,380,000 $2,570,00018 $4,460,000 $0 $390,000 $330,000 $1,700,000 $6,870,000 $2,620,00019 $4,760,000 $0 $420,000 $340,000 $1,880,000 $7,390,000 $2,670,00020 $5,080,000 $0 $450,000 $350,000 $2,070,000 $7,950,000 $2,720,00021 $5,420,000 $0 $480,000 $360,000 $2,280,000 $8,530,000 $2,770,00022 $5,770,000 $0 $510,000 $370,000 $2,500,000 $9,150,000 $2,820,00023 $6,140,000 $0 $540,000 $380,000 $2,740,000 $9,810,000 $2,860,00024 $6,520,000 $0 $580,000 $390,000 $3,010,000 $10,500,000 $2,910,00025 $6,930,000 $0 $620,000 $400,000 $3,300,000 $11,240,000 $2,950,00026 $7,350,000 $0 $660,000 $420,000 $3,610,000 $12,020,000 $2,990,00027 $7,780,000 $0 $700,000 $430,000 $3,940,000 $12,850,000 $3,030,00028 $8,240,000 $0 $740,000 $440,000 $4,300,000 $13,730,000 $3,070,00029 $8,720,000 $0 $780,000 $450,000 $4,700,000 $14,660,000 $3,100,00030 $9,220,000 $0 $830,000 $470,000 $5,120,000 $15,640,000 $3,140,000

TOTAL $126,800,000 $0 $11,100,000 $8,600,000 $53,300,000 $199,700,000 $71,300,000

Assumes $0.07/kWhr initial electrical cost.

Page 71: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 71/77

Sludge Dryer and Dewatering Evaluation TM

TABLE D.4 - ANDRITZ BELT WWRWRF DESIGN ESCALATED DOLLARS

YEAR POWER SLUDGE DISP. CHEMICAL MAINT. GAS TOTAL TOTAL (PV)

1 $1,000,000 $0 $70,000 $110,000 $190,000 $1,370,000 $1,300,0002 $1,140,000 $0 $80,000 $120,000 $230,000 $1,560,000 $1,410,0003 $1,290,000 $0 $90,000 $120,000 $270,000 $1,770,000 $1,510,0004 $1,440,000 $0 $110,000 $120,000 $320,000 $1,990,000 $1,610,0005 $1,600,000 $0 $120,000 $130,000 $370,000 $2,220,000 $1,700,0006 $1,770,000 $0 $140,000 $130,000 $420,000 $2,470,000 $1,790,0007 $1,950,000 $0 $150,000 $140,000 $490,000 $2,730,000 $1,880,0008 $2,140,000 $0 $170,000 $140,000 $560,000 $3,010,000 $1,960,0009 $2,340,000 $0 $190,000 $290,000 $630,000 $3,450,000 $2,130,00010 $2,550,000 $0 $210,000 $300,000 $710,000 $3,760,000 $2,200,00011 $2,770,000 $0 $220,000 $310,000 $800,000 $4,100,000 $2,270,00012 $3,000,000 $0 $240,000 $320,000 $900,000 $4,460,000 $2,340,00013 $3,240,000 $0 $270,000 $330,000 $1,010,000 $4,830,000 $2,410,00014 $3,490,000 $0 $290,000 $330,000 $1,120,000 $5,230,000 $2,470,00015 $3,750,000 $0 $310,000 $340,000 $1,250,000 $5,660,000 $2,530,00016 $4,030,000 $0 $340,000 $360,000 $1,390,000 $6,110,000 $2,590,00017 $4,320,000 $0 $360,000 $370,000 $1,540,000 $6,590,000 $2,650,00018 $4,630,000 $0 $390,000 $380,000 $1,700,000 $7,090,000 $2,700,00019 $4,940,000 $0 $420,000 $390,000 $1,880,000 $7,620,000 $2,760,00020 $5,280,000 $0 $450,000 $400,000 $2,070,000 $8,190,000 $2,810,00021 $5,630,000 $0 $480,000 $410,000 $2,280,000 $8,790,000 $2,860,00022 $5,990,000 $0 $510,000 $420,000 $2,500,000 $9,430,000 $2,900,00023 $6,370,000 $0 $540,000 $440,000 $2,740,000 $10,100,000 $2,950,00024 $6,770,000 $0 $580,000 $450,000 $3,010,000 $10,810,000 $2,990,00025 $7,190,000 $0 $620,000 $460,000 $3,300,000 $11,570,000 $3,030,00026 $7,630,000 $0 $660,000 $480,000 $3,610,000 $12,370,000 $3,070,00027 $8,090,000 $0 $700,000 $490,000 $3,940,000 $13,220,000 $3,110,00028 $8,560,000 $0 $740,000 $510,000 $4,300,000 $14,110,000 $3,150,00029 $9,060,000 $0 $780,000 $520,000 $4,700,000 $15,060,000 $3,190,00030 $9,580,000 $0 $830,000 $540,000 $5,120,000 $16,070,000 $3,220,000

TOTAL $131,500,000 $0 $11,100,000 $9,800,000 $53,300,000 $205,700,000 $73,500,000

Assumes $0.07/kWhr initial electrical cost.

Page 72: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 72/77

Sludge Dryer and Dewatering Evaluation TM

TABLE D.5 - ANDRITZ DRUM WWRWRF DESIGN ESCALATED DOLLARS

YEAR POWER SLUDGE DISP. CHEMICAL MAINT. GAS TOTAL TOTAL (PV)

1 $1,000,000 $0 $70,000 $110,000 $190,000 $1,370,000 $1,300,0002 $1,140,000 $0 $80,000 $120,000 $230,000 $1,560,000 $1,410,0003 $1,290,000 $0 $90,000 $120,000 $270,000 $1,770,000 $1,510,0004 $1,440,000 $0 $110,000 $120,000 $320,000 $1,990,000 $1,600,0005 $1,600,000 $0 $120,000 $130,000 $370,000 $2,220,000 $1,700,0006 $1,770,000 $0 $140,000 $130,000 $420,000 $2,470,000 $1,790,0007 $1,950,000 $0 $150,000 $140,000 $490,000 $2,730,000 $1,880,0008 $2,140,000 $0 $170,000 $140,000 $560,000 $3,010,000 $1,960,0009 $2,340,000 $0 $190,000 $290,000 $630,000 $3,450,000 $2,130,00010 $2,550,000 $0 $210,000 $300,000 $710,000 $3,760,000 $2,200,00011 $2,760,000 $0 $220,000 $310,000 $800,000 $4,100,000 $2,270,00012 $2,990,000 $0 $240,000 $320,000 $900,000 $4,450,000 $2,340,00013 $3,230,000 $0 $270,000 $330,000 $1,010,000 $4,830,000 $2,410,00014 $3,490,000 $0 $290,000 $330,000 $1,120,000 $5,230,000 $2,470,00015 $3,750,000 $0 $310,000 $340,000 $1,250,000 $5,660,000 $2,530,00016 $4,030,000 $0 $340,000 $360,000 $1,390,000 $6,110,000 $2,590,00017 $4,320,000 $0 $360,000 $370,000 $1,540,000 $6,580,000 $2,650,00018 $4,620,000 $0 $390,000 $380,000 $1,700,000 $7,090,000 $2,700,00019 $4,940,000 $0 $420,000 $390,000 $1,880,000 $7,620,000 $2,760,00020 $5,270,000 $0 $450,000 $400,000 $2,070,000 $8,190,000 $2,810,00021 $5,620,000 $0 $480,000 $410,000 $2,280,000 $8,790,000 $2,860,00022 $5,990,000 $0 $510,000 $420,000 $2,500,000 $9,420,000 $2,900,00023 $6,370,000 $0 $540,000 $440,000 $2,740,000 $10,100,000 $2,950,00024 $6,770,000 $0 $580,000 $450,000 $3,010,000 $10,810,000 $2,990,00025 $7,190,000 $0 $620,000 $460,000 $3,300,000 $11,570,000 $3,030,00026 $7,630,000 $0 $660,000 $480,000 $3,610,000 $12,360,000 $3,070,00027 $8,080,000 $0 $700,000 $490,000 $3,940,000 $13,210,000 $3,110,00028 $8,560,000 $0 $740,000 $510,000 $4,300,000 $14,110,000 $3,150,00029 $9,060,000 $0 $780,000 $520,000 $4,700,000 $15,060,000 $3,190,00030 $9,580,000 $0 $830,000 $540,000 $5,120,000 $16,070,000 $3,220,000

TOTAL $131,500,000 $0 $11,100,000 $9,800,000 $53,300,000 $205,700,000 $73,500,000

Assumes $0.07/kWhr initial electrical cost.

Page 73: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 73/77

Sludge Dryer and Dewatering Evaluation TM

TABLE D.6 - KOMLINE-SANDERSON PADDLE WWRWRF DESIGN ESCALATED DOLLARS

YEAR POWER SLUDGE DISP. CHEMICAL MAINT. GAS TOTAL TOTAL (PV)

1 $970,000 $0 $70,000 $90,000 $190,000 $1,320,000 $1,250,0002 $1,110,000 $0 $80,000 $90,000 $230,000 $1,500,000 $1,350,0003 $1,250,000 $0 $90,000 $90,000 $270,000 $1,700,000 $1,450,0004 $1,400,000 $0 $110,000 $90,000 $320,000 $1,920,000 $1,550,0005 $1,560,000 $0 $120,000 $100,000 $370,000 $2,140,000 $1,640,0006 $1,720,000 $0 $140,000 $100,000 $420,000 $2,380,000 $1,730,0007 $1,890,000 $0 $150,000 $100,000 $490,000 $2,640,000 $1,810,0008 $2,080,000 $0 $170,000 $110,000 $560,000 $2,910,000 $1,890,0009 $2,270,000 $0 $190,000 $220,000 $630,000 $3,300,000 $2,040,00010 $2,470,000 $0 $210,000 $220,000 $710,000 $3,610,000 $2,110,00011 $2,680,000 $0 $220,000 $230,000 $800,000 $3,940,000 $2,180,00012 $2,900,000 $0 $240,000 $240,000 $900,000 $4,280,000 $2,250,00013 $3,130,000 $0 $270,000 $240,000 $1,010,000 $4,650,000 $2,320,00014 $3,380,000 $0 $290,000 $250,000 $1,120,000 $5,040,000 $2,380,00015 $3,630,000 $0 $310,000 $260,000 $1,250,000 $5,450,000 $2,440,00016 $3,900,000 $0 $340,000 $270,000 $1,390,000 $5,890,000 $2,500,00017 $4,180,000 $0 $360,000 $270,000 $1,540,000 $6,360,000 $2,560,00018 $4,480,000 $0 $390,000 $280,000 $1,700,000 $6,850,000 $2,610,00019 $4,780,000 $0 $420,000 $290,000 $1,880,000 $7,370,000 $2,660,00020 $5,110,000 $0 $450,000 $300,000 $2,070,000 $7,920,000 $2,710,00021 $5,440,000 $0 $480,000 $310,000 $2,280,000 $8,510,000 $2,760,00022 $5,800,000 $0 $510,000 $320,000 $2,500,000 $9,130,000 $2,810,00023 $6,170,000 $0 $540,000 $330,000 $2,740,000 $9,780,000 $2,860,00024 $6,550,000 $0 $580,000 $340,000 $3,010,000 $10,480,000 $2,900,00025 $6,960,000 $0 $620,000 $350,000 $3,300,000 $11,220,000 $2,940,00026 $7,380,000 $0 $660,000 $360,000 $3,610,000 $12,000,000 $2,980,00027 $7,820,000 $0 $700,000 $370,000 $3,940,000 $12,830,000 $3,020,00028 $8,280,000 $0 $740,000 $380,000 $4,300,000 $13,710,000 $3,060,00029 $8,760,000 $0 $780,000 $390,000 $4,700,000 $14,630,000 $3,100,00030 $9,270,000 $0 $830,000 $400,000 $5,120,000 $15,620,000 $3,130,000

TOTAL $127,300,000 $0 $11,100,000 $7,400,000 $53,300,000 $199,100,000 $71,000,000

Assumes $0.07/kWhr initial electrical cost.

Page 74: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 74/77

Sludge Dryer and Dewatering Evaluation TM

TABLE D.6 – KRUGER WITH ERS WWRWRF DESIGN ESCALATED DOLLARS

YR POWER SLUDGE DISP. CHEMICAL MAINT. GAS TOTAL TOTAL (PV)

1 $990,000 $20,000 $70,000 $150,000 $30,000 $1,250,000 $1,190,0002 $1,130,000 $20,000 $80,000 $150,000 $30,000 $1,420,000 $1,270,0003 $1,270,000 $30,000 $90,000 $160,000 $40,000 $1,590,000 $1,350,0004 $1,430,000 $30,000 $110,000 $160,000 $50,000 $1,770,000 $1,430,0005 $1,590,000 $30,000 $120,000 $170,000 $50,000 $1,960,000 $1,500,0006 $1,760,000 $40,000 $140,000 $170,000 $60,000 $2,160,000 $1,570,0007 $1,930,000 $40,000 $150,000 $180,000 $70,000 $2,370,000 $1,630,0008 $2,120,000 $50,000 $170,000 $180,000 $80,000 $2,600,000 $1,690,0009 $2,310,000 $50,000 $190,000 $370,000 $90,000 $3,020,000 $1,860,00010 $2,520,000 $60,000 $210,000 $380,000 $100,000 $3,270,000 $1,910,00011 $2,740,000 $60,000 $220,000 $390,000 $120,000 $3,530,000 $1,960,00012 $2,960,000 $70,000 $240,000 $410,000 $130,000 $3,810,000 $2,010,00013 $3,200,000 $70,000 $270,000 $420,000 $150,000 $4,110,000 $2,050,00014 $3,450,000 $80,000 $290,000 $430,000 $160,000 $4,410,000 $2,090,00015 $3,710,000 $90,000 $310,000 $440,000 $180,000 $4,730,000 $2,120,00016 $3,990,000 $90,000 $340,000 $460,000 $200,000 $5,070,000 $2,150,00017 $4,270,000 $100,000 $360,000 $470,000 $220,000 $5,430,000 $2,180,00018 $4,570,000 $110,000 $390,000 $490,000 $250,000 $5,800,000 $2,210,00019 $4,890,000 $120,000 $420,000 $500,000 $270,000 $6,190,000 $2,240,00020 $5,220,000 $120,000 $450,000 $520,000 $300,000 $6,600,000 $2,260,00021 $5,560,000 $130,000 $480,000 $530,000 $330,000 $7,030,000 $2,280,00022 $5,920,000 $140,000 $510,000 $550,000 $360,000 $7,480,000 $2,300,00023 $6,300,000 $150,000 $540,000 $560,000 $400,000 $7,960,000 $2,320,00024 $6,700,000 $160,000 $580,000 $580,000 $440,000 $8,450,000 $2,340,00025 $7,110,000 $170,000 $620,000 $600,000 $480,000 $8,970,000 $2,350,00026 $7,540,000 $180,000 $660,000 $620,000 $520,000 $9,520,000 $2,370,00027 $7,990,000 $190,000 $700,000 $630,000 $570,000 $10,090,000 $2,380,00028 $8,460,000 $200,000 $740,000 $650,000 $620,000 $10,690,000 $2,390,00029 $8,960,000 $220,000 $780,000 $670,000 $680,000 $11,310,000 $2,390,00030 $9,470,000 $230,000 $830,000 $690,000 $740,000 $11,970,000 $2,400,000

TOTAL $130,100,000 $3,000,000 $11,100,000 $12,700,000 $7,700,000 $164,600,000 $60,200,000

Assumes $0.07/kWhr initial electrical cost.

Page 75: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 75/77

Sludge Dryer and Dewatering Evaluation TM

Appendix E – Natural Gas Usage

Year

Average Daily Flow

(mgd)

Max Month Flow (mgd)

DT/year

Natural Gas use (million cf/yr)

Total dryer hours required

5 days, 24 hrs, 52 weeks

7 days, 24 hrs, 52 weeks

2011 8.3 9.9 2020 27.1 2290 6240 8736 2012 8.9 10.6 2210 29.0 2450 6240 8736 2013 9.5 11.3 2390 30.9 2610 6240 8736 2014 10.1 12.0 2580 32.8 2780 6240 8736 2015 10.6 12.7 2760 34.7 2930 6240 8736 2016 11.2 13.4 2950 36.7 3100 6240 8736 2017 11.9 14.2 3130 38.7 3270 6240 8736 2018 12.6 15.0 3320 41.0 3460 6240 8736 2019 13.5 16.1 3500 44.0 3720 6240 8736 2020 15.2 18.2 3690 49.5 4190 6240 8736 2021 16.1 19.2 3930 52.7 4460 6240 8736 2022 17.0 20.2 4170 55.9 4730 6240 8736 2023 17.9 21.2 4400 59.1 5000 6240 8736 2024 18.8 22.3 4640 62.3 5270 6240 8736 2025 19.7 23.3 4880 65.5 5540 6240 8736 2026 20.6 24.3 5120 68.6 5810 6240 8736 2027 21.5 25.4 5360 71.8 6080 6240 8736 2028 22.4 26.4 5600 75.0 6350 6240 8736 2029 23.3 27.4 5830 78.2 6620 6240 8736 2030 24.2 28.5 6070 81.4 6890 6240 8736

From the above chart, the capacity of the Phase I dryer (5500 dt/year) is exceeded in 2027, on an average flow basis. On a maximum month flow basis, the capacity is exceeded in 2023. In both cases that assumes running the dryer 5 days, 24 hours a day. The capacity can be extended by running the dryer for longer each week.

Page 76: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 76/77

Sludge Dryer and Dewatering Evaluation TM

APPENDIX F Sludge Quantities and Dryer Operations

WESTERN WAKE INFLUENT FLOWS, SLUDGE QUANTITIES AND VOLUMES, DRYING TIMES AND ESTIMATED ENERGY USE FOR THERMAL BIOSOLIDS DRYING EVALUATION

KRUGER DRYER

Influent Flows Cake Dry Tons 18% Solids Kruger Dryer Operating Times Kruger Natural Gas Cost, Based on MMbtu/Hour Volume Natural Gas 18% Solids

Year

Average Daily Flow (mgd)

Max Month Flow (mgd)

Average lb dewaterd cake/MG

Influent flow (lb/MG)

Average dewatered

cake (lbs/day)

Average Solids Conc., WAS

(mg/L)

Average dewatered cake (gpd)

Dry Tons of Sludge per

Year in (TONS / YEAR)

Dewatered Sludge

Volume in Gallons at 18% solids

(GALLONS)

Weeks per Year (WEEKS)

Lbs. of Sludge to

Process Per Week (LBS SLUDGE @

18% SOLIDS)

Kruger dryer cake Loading

Capacity, lbs/hour, 1

train

Kruger Dryer

Operating Hours Per Week with

1-train

Annual Operating Hours Per

Year with 1-Train

Annual Operating Hours Per Year with 2-Trains

Kruger Dryer,

# of 24-hour

operating shifts per

week, 1- train

Kruger Dryer, # of

24-hour operating shifts per week, 2-

trains

Kruger Dryer Fuel Consumpti

on of Natural

Gas Conversion Factor, Kruger

Literature,in

(MMbtu/hr, 1-Train)

Kruger Dryer

Natural Gas Use,

(MMbtu per Week)

Kruger Dryer Fuel

Consumption in Therms

Per Week

Natural Gas Cost,

with 3% Escalation,

($ Dollars / MMbtu)

Natural Gas Estimated Cost Per Week in

(DOLLARS)

Natural Gas Cost Per Month

in (DOLLAR

S)

Natural Gas Cost Per Dry

Ton

Volume of Natural Gas

Used Per Week in

Cubic Feet

Cost of Natural

Gas, $ per Cubic

Feet of Natural

Gas

Volume of Natural

Gas Used Per Dry Ton of

Biosolids Processed in (Cubic

Feet)

Annual Volume of Dewatered Sludge in Gallons at

18% solids, (GALLONS)

2011 8.3 9.9 1,350 11,210 3,000 447,800 2,040 2,724,000 52 436,900 4,900 89 4,640 2,320 3.7 1.9 6 540 5,350 $9.00 $4,820 $20,900 $122 535,000 $0.01 13,610 2,724,000

2012 8.9 10.6 1,350 11,970 3,100 463,200 2,190 2,911,000 52 467,000 4,900 95 4,960 2,480 4.0 2.0 6 570 5,720 $9.27 $5,300 $23,000 $126 571,800 $0.01 13,610 2,911,000

2013 9.5 11.3 1,350 12,760 3,200 478,000 2,330 3,102,000 52 497,500 4,900 102 5,280 2,640 4.2 2.1 6 610 6,090 $9.55 $5,820 $25,200 $130 609,200 $0.01 13,610 3,102,000

2014 10.1 12.0 1,350 13,580 3,300 493,500 2,480 3,302,000 52 529,600 4,900 108 5,620 2,810 4.5 2.3 6 650 6,480 $9.83 $6,380 $27,600 $134 648,500 $0.01 13,610 3,302,000

2015 10.6 12.7 1,350 14,350 3,400 506,100 2,620 3,489,000 52 559,600 4,900 114 5,940 2,970 4.8 2.4 6 690 6,850 $10.13 $6,940 $30,100 $138 685,200 $0.01 13,610 3,489,000

2016 11.2 13.4 1,350 15,160 3,500 519,400 2,770 3,686,000 52 591,200 4,900 121 6,270 3,140 5.0 2.5 6 720 7,240 $10.43 $7,550 $32,700 $142 723,900 $0.01 13,610 3,686,000

2017 11.9 14.2 1,350 16,010 3,600 533,300 2,920 3,893,000 52 624,400 4,900 127 6,630 3,310 5.3 2.7 6 760 7,650 $10.75 $8,220 $35,600 $146 764,500 $0.01 13,610 3,893,000

2018 12.6 15.0 1,350 16,940 3,700 549,000 3,090 4,119,000 52 660,700 4,900 135 7,010 3,510 5.6 2.8 6 810 8,090 $11.07 $8,950 $38,800 $151 809,000 $0.01 13,610 4,119,000

2019 13.5 16.1 1,350 18,210 3,850 567,200 3,320 4,428,000 52 710,200 4,900 145 7,540 3,770 6.0 3.0 6 870 8,700 $11.40 $9,910 $43,000 $155 869,600 $0.01 13,610 4,428,000

2020 15.2 18.2 1,350 20,570 4,000 616,700 3,750 5,002,000 52 802,300 4,900 164 8,510 4,260 6.8 3.4 6 980 9,820 $11.74 $11,540 $50,000 $160 982,400 $0.01 13,610 5,002,000

2021 16.1 19.2 1,350 21,780 4,000 652,700 3,970 5,294,000 52 849,200 4,900 173 9,010 4,510 7.2 3.6 6 1040 10,400 $12.10 $12,580 $54,500 $165 1,039,800 $0.01 13,610 5,294,000

2022 17.0 20.2 1,350 22,980 4,000 688,800 4,190 5,587,000 52 896,000 4,900 183 9,510 4,750 7.6 3.8 6 1100 10,970 $12.46 $13,670 $59,200 $169 1,097,100 $0.01 13,610 5,587,000

2023 17.9 21.2 1,350 24,180 4,000 724,800 4,410 5,879,000 52 942,900 4,900 192 10,010 5,000 8.0 4.0 6 1150 11,550 $12.83 $14,810 $64,200 $175 1,154,500 $0.01 13,610 5,879,000

2024 18.8 22.3 1,350 25,390 4,000 761,200 4,630 6,174,000 52 990,200 4,900 202 10,510 5,250 8.4 4.2 6 1210 12,130 $13.22 $16,030 $69,400 $180 1,212,500 $0.01 13,610 6,174,000

2025 19.7 23.3 1,350 26,600 4,000 797,200 4,850 6,466,000 52 1,037,100 4,900 212 11,010 5,500 8.8 4.4 6 1270 12,700 $13.61 $17,290 $74,900 $185 1,269,900 $0.01 13,610 6,466,000

2026 20.6 24.3 1,350 27,810 4,000 833,600 5,080 6,762,000 52 1,084,500 4,900 221 11,510 5,750 9.2 4.6 6 1330 13,280 $14.02 $18,620 $80,700 $191 1,327,900 $0.01 13,610 6,762,000

2027 21.5 25.4 1,350 29,010 4,000 869,600 5,290 7,054,000 52 1,131,300 4,900 231 12,010 6,000 9.6 4.8 6 1390 13,850 $14.44 $20,010 $86,700 $196 1,385,300 $0.01 13,610 7,054,000

2028 22.4 26.4 1,350 30,210 4,000 905,700 5,510 7,346,000 52 1,178,200 4,900 240 12,500 6,250 10.0 5.0 6 1440 14,430 $14.88 $21,460 $93,000 $202 1,442,700 $0.01 13,610 7,346,000

2029 23.3 27.4 1,350 31,410 4,000 941,700 5,730 7,638,000 52 1,225,000 4,900 250 13,000 6,500 10.4 5.2 6 1500 15,000 $15.32 $22,980 $99,600 $208 1,500,000 $0.02 13,610 7,638,000

2030 24.2 28.5 1,350 32,630 4,000 978,100 5,950 7,933,000 52 1,272,400 4,900 260 13,500 6,750 10.8 5.4 6 1560 15,580 $15.78 $24,590 $106,600 $215 1,558,100 $0.02 13,610 7,933,000

Page 77: App H--Evaluation of Sludge Dryer and Dewatering Facilities

Technical Memorandum - Addendum to the Evaluation of Primary Clarifiers and Anaerobic Digestion at the Western Wake Regional Water

Reclamation Facility

Western Wake RWRF 77/77

Sludge Dryer and Dewatering Evaluation TM

Influent Flows Wet Volumes & Btu's Req. for Evaporation Dry Sludge Volume from Kruger Drying Process Ash Volume, for 75% Volatile Content Based on Bulk Density Volume Reduction

Year

Average Daily Flow (mgd)

Max Month Flow (mgd)

Annual Volume of

Water to Evaporate From

Dewatered Sludge to

Obtain 90% Dry Biosolids,

(GALLONS)

Annual Volume of

Biosolids in Dewatered

Cake at 18% Solids (GALLONS)

Annual MMBtu's

Required for Drying Based

on Energy Required to Evaporate

Water (MMBtu's)

Weekly MMBtu's Required Based on Energy

Required to Evaporate Water from Dewatered

Cake, (MMBtu's)

Annual Tons of Sludge at

90% Dry Basis in (TONS / YEAR)

Annual Volume of

Dried Biosolids at

90% Dry Basis in (CUBIC YARDS)

Weekly Volume of

Dried Biosolids

at 90% Dry Basis in (CUBIC YARDS)

Weekly Weight of

Dried Biosolids at 90%

Dry Basis in (TONS)

Number of Weeks

Storage with 250 Tons of Silo Storage

Capacity Assuming NO ERS

USE (WEEKS of STORAGE)

Annual Weight of

Dried Biosolids, 90% Dry Basis, in

(LBS)

Assumed Volatile

Content of Dried

Biosolids that would

be Consumed

During Incineratio

n (PERCEN

TAGE)

Annual Estimated Weight of

Incinerated Ash

Assuming a Volatile

Content of 75% in (LBS.)

Bulk Density of Incinerated Ash from Biosolids,

(LBS/CUBIC FEET)

Annual Volume of Incinerated

Ash Assuming

75% Volatile Content in

Dried Biosolids (CUBIC FEET)

Annual Volume of Incinerated

Ash Assuming

75% Volatile Content in

Dried Biosolids (CUBIC YARDS)

Annual Bags of

Ash Produced Assuming

Bag Loading

System at 2.5 Cubic Yards Per

Bag (NUMBER OF BAGS)

Weekly Number of

Bags of Ash

Produced Assuming 2.5 Cubic Yards Per

Bag (NUMBER OF BAGS)

Annual Dewatered

Cake, Sludge Volume @ 18% solids, (GALLONS)

Annual Dewatered

Cake, Sludge

Volume, @ 18% solids,

(CUBIC FEET)

Annual Volume of Water from Dewatered

Cake at 18% solids

to Evaporate

during Drying

(Gallons)

Annual Volume of Water from Dewatered

Cake at 18% solids

to Evaporate

during Drying in (CUBIC FEET)

Annual Volume of Dry Sludge at 90%

Dry Basis in (CUBIC FEET)

Annual Volume of Ash,

Assuming 75% Volatile Content,

& 50 lbs/ft^3

Bulk Density

of Ash, in (CUBIC FEET)

Percent Volume of Dried Biosolids at 90%

Dry Basis

Compared Against Dewater

ed Sludge Volume at 18% Solids

Percent Volume of Ash when

Compared

Against Original Dewater

ed Sludge Volume at 18% Solids

2011 8.3 9.9 2,179,000 544,900 27,270 520 2,270 6,010 116 44 5.7 4,544,300 75 1,136,100 50 22,700 840 337 6 2,724,400 364,200 2,179,500 291,400 162,300 22,700 45 6

2012 8.9 10.6 2,329,000 582,300 29,140 560 2,430 6,420 124 47 5.4 4,856,300 75 1,214,100 50 24,300 900 360 7 2,911,500 389,200 2,329,200 311,400 173,400 24,300 45 6

2013 9.5 11.3 2,481,000 620,400 31,040 600 2,590 6,840 132 50 5.0 5,173,900 75 1,293,500 50 25,900 960 383 7 3,101,800 414,700 2,481,500 331,700 184,800 25,900 45 6

2014 10.1 12.0 2,642,000 660,400 33,050 640 2,750 7,290 140 53 4.7 5,507,900 75 1,377,000 50 27,500 1,020 408 8 3,302,100 441,500 2,641,700 353,200 196,700 27,500 45 6

2015 10.6 12.7 2,791,000 697,800 34,920 670 2,910 7,700 148 56 4.5 5,819,900 75 1,455,000 50 29,100 1,080 431 8 3,489,200 466,500 2,791,300 373,200 207,900 29,100 45 6

2016 11.2 13.4 2,949,000 737,200 36,890 710 3,070 8,130 156 59 4.2 6,148,400 75 1,537,100 50 30,700 1,140 455 9 3,686,100 492,800 2,948,900 394,200 219,600 30,700 45 6

2017 11.9 14.2 3,114,000 778,600 38,960 750 3,250 8,590 165 62 4.0 6,493,400 75 1,623,300 50 32,500 1,200 481 9 3,892,900 520,400 3,114,300 416,400 231,900 32,500 45 6

2018 12.6 15.0 3,296,000 823,900 41,230 790 3,440 9,090 175 66 3.8 6,871,100 75 1,717,800 50 34,400 1,270 509 10 4,119,400 550,700 3,295,500 440,600 245,400 34,400 45 6

2019 13.5 16.1 3,542,000 885,600 44,310 850 3,690 9,770 188 71 3.5 7,385,800 75 1,846,400 50 36,900 1,370 547 11 4,427,900 592,000 3,542,300 473,600 263,800 36,900 45 6

2020 15.2 18.2 4,002,000 1,000,500 50,060 960 4,170 11,040 212 80 3.1 8,343,900 75 2,086,000 50 41,700 1,550 618 12 5,002,300 668,800 4,001,900 535,000 298,000 41,700 45 6

2021 16.1 19.2 4,236,000 1,058,900 52,990 1,020 4,420 11,680 225 85 2.9 8,831,200 75 2,207,800 50 44,200 1,640 654 13 5,294,500 707,800 4,235,600 566,300 315,400 44,200 45 6

2022 17.0 20.2 4,469,000 1,117,300 55,910 1,080 4,660 12,330 237 90 2.8 9,318,500 75 2,329,600 50 46,600 1,730 690 13 5,586,600 746,900 4,469,300 597,500 332,800 46,600 45 6

2023 17.9 21.2 4,703,000 1,175,700 58,830 1,130 4,900 12,970 249 94 2.7 9,805,700 75 2,451,400 50 49,000 1,820 726 14 5,878,700 785,900 4,703,000 628,700 350,200 49,000 45 6

2024 18.8 22.3 4,939,000 1,234,800 61,790 1,190 5,150 13,620 262 99 2.5 10,298,500 75 2,574,600 50 51,500 1,910 763 15 6,174,100 825,400 4,939,300 660,300 367,800 51,500 45 6

2025 19.7 23.3 5,173,000 1,293,300 64,710 1,240 5,390 14,270 274 104 2.4 10,785,800 75 2,696,400 50 53,900 2,000 799 15 6,466,300 864,500 5,173,000 691,600 385,200 53,900 45 6

2026 20.6 24.3 5,409,000 1,352,300 67,670 1,300 5,640 14,920 287 108 2.3 11,278,500 75 2,819,600 50 56,400 2,090 835 16 6,761,700 904,000 5,409,400 723,200 402,800 56,400 45 6

2027 21.5 25.4 5,643,000 1,410,800 70,590 1,360 5,880 15,560 299 113 2.2 11,765,800 75 2,941,400 50 58,800 2,180 872 17 7,053,800 943,000 5,643,100 754,400 420,200 58,800 45 6

2028 22.4 26.4 5,877,000 1,469,200 73,520 1,410 6,130 16,210 312 118 2.1 12,253,100 75 3,063,300 50 61,300 2,270 908 17 7,346,000 982,100 5,876,800 785,700 437,600 61,300 45 6

2029 23.3 27.4 6,110,000 1,527,600 76,440 1,470 6,370 16,850 324 123 2.0 12,740,300 75 3,185,100 50 63,700 2,360 944 18 7,638,100 1,021,100 6,110,500 816,900 455,000 63,700 45 6

2030 24.2 28.5 6,347,000 1,586,700 79,400 1,530 6,620 17,500 337 127 2.0 13,233,100 75 3,308,300 50 66,200 2,450 980 19 7,933,500 1,060,600 6,346,800 848,500 472,600 66,200 45 6