charles county...the solids mass balance developed as part of the 2013/2014 mattawoman wwtp...

Charles County Mattawoman WRF Dewatering Study

Dewatering Alternatives Analysis

June 2015

This report has been prepared by GHD for Charles County and may only be used and relied on by Charles County for the purpose agreed between GHD and Charles County as set out in Section 1.3 of this report.

GHD otherwise disclaims responsibility to any person other than Charles County arising in connection with this report. GHD also excludes implied warranties and conditions, to the extent legally permissible.

The services undertaken by GHD in connection with preparing this report were limited to those specifically detailed in the report and are subject to the scope limitations set out in the report.

The opinions, conclusions and any recommendations in this report are based on conditions encountered and information reviewed at the date of preparation of the report. GHD has no responsibility or obligation to update this report to account for events or changes occurring subsequent to the date that the report was prepared.

GHD | Report for Charles County - Mattawoman WRF Dewatering Study, 86/15181/ | i

Table of contents 1. Introduction.......................................................................................................................................... 1

1.1 Background ............................................................................................................................... 1 1.2 Objective and Goals .................................................................................................................. 1

1.3 Scope ........................................................................................................................................ 1

2. Basis of Design ................................................................................................................................... 4

2.1 Existing Facilities, Practices, and Performance ........................................................................ 4

2.2 Flows, Loads, and Solids Characteristics ................................................................................. 6 2.3 Design Criteria .......................................................................................................................... 8

3. Overview of Alternatives ................................................................................................................... 11

3.1 High-Solids Centrifuge ............................................................................................................ 11

3.2 Belt Filter Press ....................................................................................................................... 15

3.3 Rotary Fan Press .................................................................................................................... 18

4. Evaluation of Alternatives .................................................................................................................. 21

4.1 Summary of Capital Costs ...................................................................................................... 21

4.2 Summary of O&M Costs ......................................................................................................... 22

4.3 Summary of Lifecycle Costs ................................................................................................... 26

4.4 Sensitivity Analysis ................................................................................................................. 28 4.5 Non-Cost Considerations ........................................................................................................ 31

5. Discussion and Recommendations ................................................................................................... 33

Table index Table 1 Summary of Historical Plant Data .................................................................................................... 4

Table 2 Basis of Design Thickened Sludge Flows and Loads ...................................................................... 7

Table 3 Solids Composition ........................................................................................................................... 7

Table 4 Equipment Design Criteria ............................................................................................................... 9

Table 5 High-Solids Centrifuge Design Criteria .......................................................................................... 12

Table 6 Belt Filter Press Design Criteria ..................................................................................................... 16

Table 7 Rotary Fan Press Design Criteria .................................................................................................. 19

Table 8 Summary of Capital Costs.............................................................................................................. 21

Table 9 General Inputs for O&M Costs ....................................................................................................... 23

Table 10 Alternative-Specific Parameters for O&M Costs .......................................................................... 24

Table 11 Summary of Dewatering O&M Costs at Current Conditions ........................................................ 24

ii | GHD | Report for Charles County - Mattawoman WRF Dewatering Study, 86/15181/

Table 12 Summary of Dewatering O&M Costs at Current Conditions ........................................................ 25

Table 13 General Inputs for Lifecycle Costs ............................................................................................... 26

Table 14 Summary of Lifecycle Costs ......................................................................................................... 26

Table 15 Ranking of Non-Cost Considerations ........................................................................................... 32

Figure index Figure 1 Historical Cake Solids Probability Plot ............................................................................................ 5

Figure 2 Historical Polymer Dose Probability Plot ......................................................................................... 6

Figure 3 Design Flows and Loads ................................................................................................................. 7

Figure 4 Historical Thickened Sludge Solids Concentration Probability Plot ................................................ 8

Figure 5 Illustration of Unit Sizing for Firm Capacity ................................................................................... 10

Figure 6 Proposed Location for Temporary Dewatering Staging Area ................................................. 14

Figure 7 Proposed Location for Equipment Installation (Front of Building) .......................................... 14

Figure 8 Proposed Location for Phase 1 of BFP Equipment Installation .............................................. 17

Figure 9 Summary of Capital Costs ............................................................................................................ 22

Figure 10 Summary of Dewatering O&M Costs .......................................................................................... 25

Figure 11 Summary of Lifecycle Costs ....................................................................................................... 27

Figure 12 Relative Magnitude of Total Lifecycle Costs ............................................................................... 27

Figure 13 Lifecycle Cost Sensitivity Analysis for Varying Land Application Costs ..................................... 29

Figure 14 Lifecycle Cost Sensitivity Analysis for Varying Cake Solids Concentration ................................ 30

Figure 15 Lifecycle Cost Sensitivity Analysis for Varying Polymer Dose .................................................... 31

Appendices Appendix A - Summary of Capital Costs

Appendix B - Conceptual Layout Figures

GHD | Report for Charles County – Mattawoman WRF Dewatering Study, 86/15181 | 1

1. Introduction 1.1 Background

Charles County owns and operates the 20 million gallons per day (mgd) Mattawoman Water Reclamation Facility (WRF). The current annual average daily flow is approximately 11 mgd and the average solids production is approximately 11 dry tons per day (DT/d).

The solids dewatering equipment consists of three 2-meter Belt Filter Presses (BFPs) installed in 1987. Since 2005, the County has contracted a private biosolids management company to dewater, lime-stabilize, haul, and land-apply the Class B biosolids generated at the WRF. The County has used the same contractor for approximately ten years.

In response to rising contract costs, the County solicited proposals for biosolids services in October 2014. The solicitation stipulated that in addition to providing biosolids management services, bidders would be required to replace the existing dewatering equipment. The County provided bidders with the flexibility to size, design, and select the new dewatering equipment., and the type of technology to be used was not specified in the solicitation documents. In February 2015, the County cancelled the solicitation with the intent of re-issuing a separate solicitation for new dewatering equipment once the type of technology was established.

Soon after the bid cancellation, the County commissioned GHD to conduct an alternatives analysis to develop concept-level design and budgetary costs of the following three dewatering technologies: High-Solids Centrifuge (HSC), BFP, and Rotary Fan Press (RFP). The results of the analysis would then be used by the County to select the type of dewatering technology that will replace the existing BFPs.

1.2 Objective and Goals

The objective of the Mattawoman WRF Dewatering Study is to evaluate alternatives for dewatering equipment and provide recommendations on the type of technology to be used. During the project chartering meeting, the following critical success factors were established:

Recommended alternative has clear justification,

Reliable planning-level opinions of cost are provided,

County input is obtained and addressed throughout the project,

County has strong comfort level with the selected alternative for dewatering,

Non-cost factors and O&M costs are accounted for in the alternatives analysis, and

Schedule is maintained.

1.3 Scope

The scope of the Mattawoman WRF Dewatering Study is outlined herein.

Part 1: Basis of Design Confirmation

Conduct site visit to evaluate the footprint and layout of the existing Dewatering Building and observe the condition of the existing BFPs, as well as related equipment such as the polymer feed systems, sludge feed pumps, cake conveyors, and lime stabilization.

2 | GHD | Report for Charles County - Mattawoman WRF Dewatering Study, 86/15181/

Organize and attend Teleconference to accomplish the following:

– Review the three dewatering alternatives that shall be evaluated: Belt filter press, rotary press, and High-Solids Centrifuge.

– Select two manufacturers that will be evaluated for each dewatering alternative.

– Discuss and establish critical success factors and design criteria, including sludge quantities and characteristics, assumed unit costs, anticipated hours of operation, and redundancy requirements for each alternative.

Part 2: Develop Concept-Level Design and Budgetary Cost

Develop capital and 30-Year operation and maintenance (O&M) costs for each of the three selected alternatives.

– For each alternative, two manufacturers (selected at Teleconference) will be selected to provide proposals and equipment information.

– Opinions of capital costs will include supply and installation of dewatering equipment, as well as required additional components such as plant water booster pumps, conveyor modifications, and electrical and controls.

– Opinions of O&M costs will include labor, equipment maintenance and parts replacement, electricity and polymer usage, and cake hauling and land application costs.

– Capital and O&M costs will be used to develop 25-year Net Present Value (NPV) evaluations.

Provide a sensitivity analysis to illustrate the impact of varying factors and unit costs on the NPW comparison.

Non-cost factors will also be presented, including: compatibility with existing and future solids processes, odor/splash concerns, space constraints, mechanical reliability, consistency of solids characteristics, filtrate composition, ease of operation and maintenance, options for equipment phasing, availability of service/support/parts, and impact on downstream operations (lime stabilization, truck loading, hauling, and land application).

Provide figures illustrating conceptual layout plans for each alternative.

Summarize results in a draft report.

Organize and attend Workshop with Charles County to review the draft report.

Edit draft report as necessary to address County's review comments.

Submit final report to Charles County.

1.3.1 Assumptions

The scope was based upon the following assumptions:

The solids mass balance developed as part of the 2013/2014 Mattawoman WWTP Biosolids Study, which was based on 2010-2012 operating data, will be used to establish the current solids quantities and characteristics. Analysis of more recent plant data (2013-2015) was not included in this scope.

Design solids loads will be projected using the County planning growth rate of 1.6% per year to establish 25-year basis of design quantities. The design solids flows to the dewatering process will be based upon current characteristics (e.g., 2% solids concentration).


In order to provide a fair and thorough comparison, O&M costs for each alternative will be calculated based on the number of operator hours, chemical and electricity usage, and cake output, as opposed to a fixed unit price per ton that the biosolids contractor typically charges.

1.3.2 Exclusions

The following items were excluded from the scope of work:

Compilation and analysis of historical plant data beyond that obtained as part of the Mattawoman WWTP Biosolids Study.

Site visits to other dewatering installations.

Evaluation (pricing, analysis, code requirements, etc.) of Dewatering Building systems, including HVAC, electrical, and lighting.

Evaluation of replacement of ancillary equipment systems such as polymer, sludge feed pumps, and lime stabilization

Pilot studies or detailed design.


2. Basis of Design 2.1 Existing Facilities, Practices, and Performance

The dewatering processes at the Mattawoman WRF are located on the southern half of the upper floor of the Dewatering Building (refer to Figure 01 in the Appendix). The existing solids dewatering equipment consists of three 2-meter BFPs manufactured by Ashbrook-Simon Hartley and installed in 1987. The upper half of the upper floor of the Dewatering Building is occupied by three gravity belt thickeners (GBTs), which have not been used in over ten years. The lower floor of the Dewatering Building contains the dry polymer feed system and polymer feed pumps for the dewatering process. The remainder of the lower floor is primarily used for storage.

The sludge generated at the WRF consists of primary sludge, waste activated sludge, waste chemical sludge1, and septage. The waste streams are blended and sent to gravity thickeners. The annual average quantity of gravity-thickened sludge is 128,000 gallons per day at 2% solids. Historical sludge production is shown in Table 1.

Table 1 Summary of Historical Plant Data

Process Flow Flow, gpd % Solids TSS, lb/d Primary Sludge (PS) 91,750 (1) 1.2% (4) 9,560 Waste Activated Sludge (WAS) 128,250 (2) 0.6% (2) 6,850 Waste Chemical Sludge (WCS) 545,000 (3) 0.07% (5) 3,130 Septage (SPT) 60,000 (3) 0.6% (6) 2,950 Total Unthickened Sludge 825,000 (3) 0.3% (6) 22,490 Total Thickened Sludge 128,000 (7) 2.0% (3) 21,370

Notes: Unless otherwise noted, all values are annual averages of 2010-2012 plant data. WAS flow and load are calculated only for days that WAS is in operation (not annual average). Estimated typical values, based on discussions with plant operators. Values determined by conducting mass balance using known data. Based on 2001 BNR Sludge Study and calculations of chemical sludge due to TP precipitation. Value determined by conducting mass balance using known data. Thickened Sludge: 2% solids based on historical data. 95% TSS capture of unthickened sludge assumed.

The thickened sludge is pumped to Aerobic Digesters No. 6 through 11 for weekly storage. When the dewatering process is in operation, thickened sludge from the digesters is macerated by a grinder and is pumped to the BFPs using two Vogelsang rotary-lobe pumps.

GHD conducted an evaluation of the gravity thickeners in 2014 and found them to be over-loaded. It is anticipated that their performance could be improved, resulting in a greater thickened sludge percent solids, which in turn could lead to reductions in capital and O&M costs for dewatering processes. Potential solutions for improving thickening performance include diverting the waste chemical sludge to the head of the plant and using a separate mechanical thickening process for the waste activated sludge.

1 Waste chemical sludge consists primarily of aluminum-phosphate precipitate formed in the tertiary clarifiers. Although the waste chemical sludge accounts for two-thirds of the total sludge volume, it accounts for approximately one-eighth of the total solids load due to its low solids concentration.


Scum from the primary, secondary, and tertiary clarifiers and gravity thickeners is also processed by the dewatering equipment. Scum is pumped to and stored in Aerobic Digesters No. 1 through 5. A progressive cavity pump conveys scum from the digesters to the BFPs.

Since 2005, the County has contracted a private biosolids management company to dewater, lime-stabilize, haul, and land-apply the Class B biosolids generated at the WRF. The County has used the same contractor for approximately ten years. The contractor is typically on-site for eight to ten hours a day, three to five days per week. Based on an analysis of the historical plant data, the dewatering performance of the existing belt filter presses appear to be generally good; the average solids concentration of the dewatered cake is 21.5%, and the average polymer dose is 8 pounds of active polymer per dry ton of solids feed. The hydraulic and solids feed rates to the existing presses generally range from 80 to 100 gpm per meter and 750 to 1,120 pounds per hour per meter.

Charts of the historical dewatering performance from 2010 through 2012 are presented in Figure 1 and Figure 2.

Figure 1 Historical Cake Solids Probability Plot

Notes: 1. Based on 2010-2012 operating data provided by Charles County.

The chart is read as follows: Dewatered cake solids concentration is < 19.2% 5% of the time < 20.7% 25% of the time < 21.6% 50% of the time < 22.8% 75% of the time < 25.0% 95% of the time Another interpretation of the data in the chart is that the historical cake solids concentration ranged between 20.7-22.8% solids 50% of the time, and between 19.2-25.0% solids 90% of the time.


Figure 2 Historical Polymer Dose Probability Plot

Note: 1. Based on 2010-2012 operating data provided by Charles County.

Summary of Existing Electrical Systems

The existing Dewatering Building (DWB) is fed from two 750 KVA transformers located just outside the north wall of the structure. The transformers are powered from redundant Medium Voltage Switchgear located in the Electrical Building. Likewise, the Dewatering Building MCC is a dual fed line up such that each side of the MCC is fed from a separate electrical distribution system back to, and including, the Plant’s incoming service.

The existing, dual fed MCC has been sized to support the entire connected load from either of the 750 KVA transformers. The addition of about 25% more load can be placed on the existing MCC while maintaining the ability to supply the entire connected load in the event of a failure in one of the power distribution networks.

This expansion capacity is sufficient to support modest load changes and additions. It is likely that electrical load changes resulting from the replacement of the Belt Filter Presses with similarly sized units would not trigger major electrical upgrades to the power distribution system. Under the proposed HSC alternative, however, more significant power upgrades will be required; these are discussed in more detail in Section 3.1.3.

2.2 Flows, Loads, and Solids Characteristics

The total thickened sludge flows and loads presented in Table 1 were used as the basis of design for this study. Based on information from the County, a 25-year planning period and annual growth


rate of 1.6% were used to establish the sludge production in the design year (2040). Based on historical plant data, a factor of 1.5 was applied to the annual average solids production to estimate the maximum month loading rate. The design flows were calculated based on the assumption that the solids concentration of the thickened sludge would remain at 2%. The design flows and loads are presented in Table 2 and Figure 3.

Table 2 Basis of Design Thickened Sludge Flows and Loads

Process Flow Current Conditions Basis of Design Average Maximum Month Average Maximum Month Flow, gpd 128,000 192,000 190,000 286,000 TSS, lb/d 21,000 32,000 32,000 48,000

Note: 1. Solids are assumed to be blended sludge (per Table 1), gravity-thickened to a solids concentration of 2%.

Figure 3 Design Flows and Loads

The characteristics and composition of the solids feed can greatly impact dewatering performance. Typically, dewatering performance is better for primary sludge, anaerobically-digested sludge, and well-thickened sludge. As shown in Table 3 and Figure 4, the solids characteristics of the BFP feed sludge at the Mattawoman WRF are not ideal for dewatering: primary sludge accounts for less than half of the total solids, the sludge is not anaerobically digested, and the sludge is heavily diluted by the high volume of waste chemical sludge.

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Table 3 Solids Composition

Parameter Primary Sludge Waste

Activated Sludge

Waste Chemical Sludge

Septage

Percent of total blended sludge by volume, % 11% 16% 66% 7% Percent of total blended sludge by weight, % 43% 30% 14% 13% Solids concentration prior to thickening, % solids 1.2% 0.6% 0.1% 0.6%

Figure 4 Historical Thickened Sludge Solids Concentration Probability Plot

2.3 Design Criteria

The dewatering equipment considered in this study was sized to fully process the maximum month design flows and loads on a 12-hour shift, 5 days per week schedule. The net hours of operation for each type of technology were adjusted to account for differences in the ease of and time required for startup, shutdown and operational adjustments. Because the equipment will likely be operated by a private contractor specifically hired to manage the biosolids process, it was assumed that the equipment would not run unattended for any period of time.

The design criteria provided to the selected manufacturers are presented in Table 4.


Table 4 Equipment Design Criteria

Parameter High-Solids Centrifuge Belt Filter Press Rotary Fan Press

Number of Shifts 1 1 1 Length of Shift, hr 12 12 12 Operation Schedule

Startup Time, hr 1 1 0.5 Mid-day downtime, hr 1 1 1 Shutdown time, hr 1 1.5 0.5 Total downtime, hr 3 3.5 2 Net Operation Time1, hr 9 8.5 10

Net Operation hrs/wk 45 42.5 50 Loading Rates

Hydraulic Loading Rate2, gpm Current Average 350 300 330 Current Maximum Month 530 450 500 Design Average 520 440 490 Design Maximum Month 780 670 740 Solids Loading Rate2, lb/hr Current Average 3,520 3,000 3,330 Current Maximum Month 5,280 4,490 4,990 Design Average 5,240 4,450 4,950 Design Maximum Month 7,850 6,680 7,420

Notes: 1. Net Operation Time = Shift Length – Total downtime.

Loading Rates represent the required firm capacity (total capacity with one unit out of service) for each alternative.

In this study, equipment was sized for 100% redundancy at maximum month design conditions at the County’s request. These criteria result in a total capacity approximately equal to 200% of average design conditions, as illustrated in Figure 5. It is not common to have this level of redundancy for dewatering equipment; instead, many facilities opt to eliminate the need for redundancy by planning for longer operation hours during high loading conditions or when a unit is out of service. A reduction in capital costs may be possible if the sizing requirements were lessened during the design phase. Alternatively, the equipment installation can be phased such N-1 units are initially installed, and the final unit is installed at a later date, when flows and loads increase.


Figure 5 Illustration of Unit Sizing for Firm Capacity


3. Overview of Alternatives The primary aim of this study is to compare the following three dewatering technologies for the Mattawoman WRF: High-Solids Centrifuge (HSC), Belt Filter Press (BFP), and Rotary Fan Press (RFP). For each type of technology, two manufacturers were contacted for budgetary pricing and design criteria. The two manufacturers were selected by the County during the study kick-off meeting. Once a technology type is selected, the design criteria may be refined and proposals from additional manufacturers may be sought.

3.1 High-Solids Centrifuge

3.1.1 General Description

Adapt the following text to provide a general description of HSC:

High-Solids Centrifuges (HSCs) dewater sludge by applying centrifugal forces that cause the suspended solids to migrate away from the liquid. Major components of a HSC are the bowl, scroll, frame, and drive. The centrifugal force is applied by rotating the bowl at high speeds.

HSCs can generally achieve solid concentrations comparable to or higher than BFPs but have much higher energy and polymer requirements. The high rotational speeds present structural, safety and controls considerations that must be addressed during design.

HSC dewatering is a closed process, which facilitates the containment of odors. Dewatered HSC cake is generally more odorous than that of BFPs, however, because odor control can be provided at point sources, foul air volumes are minimized.

There are several centrifuge manufacturers that provide units for wastewater applications, including Alfa Laval, Centrisys, GEA Westfalia, Andritz, Flottweg.

3.1.2 Manufacturer Design Criteria

The design criteria provided by the HSC manufacturers are presented in Table 5.


Table 5 High-Solids Centrifuge Design Criteria

Parameter Manufacturer A Manufacturer B Manufacturer Alfa Laval Westfalia Model ALDEX G3 115 CF 8000 Number of Units Recommended 3 (2+1 standby) 3 (2+1 standby) Rated Capacity per Unit

Hydraulic Loading Rate, gpm Solids Loading Rate, lb/hr

Limiting factor

450

4,500 SLR

525

5,000 SLR

Nominal Bowl Diameter, inches 26 inch 30 inch Main Motor Size 100 HP 100 HP Back Drive Motor Size 40 HP 40 HP Anticipated total grid load at maximum month design conditions1, kW

80 90

Specific power consumption1, Watt-hours per gallon feed

3.5 4.1

Anticipated Solids Capture Efficiency1 95% 95% Anticipated Cake % Solids1 23-27% 24-30% Anticipated Polymer Dose1, active lb/DTfeed 10-24 12-20 Plant Water (PLW) Requirements 60 gpm @ 45 psi,

intermittent 65 gpm @ 45 psi,

intermittent Anticipated Average PLW Use2, galPLW/galfeed 0.03 0.03 Anticipated Centrate Production2, galcentrate/galfeed 1.03 1.03 Empty Equipment Weight, each3 14,300 lb 22,150 lb

Notes: 1. The anticipated values presented herein are manufacturer estimates based on the solids characteristics

and design criteria described in Section 2.2. These values are not guaranteed. 2. Plant water and centrate values were calculated using a mass balance based on manufacturer’s

anticipated performance. 3. The differences in equipment weight between manufacturers A and B are primarily due to differences in

the methods of construction and minor differences in the equipment sizing. The proposed equipment for Manufacturer B is more conservatively sized and has more structural steel than Manufacturer A. These differences do not affect the conclusions of this study and can be addressed during the detailed design phase.

3.1.3 Considerations for Mattawoman WRF

As shown in Table 5, three High-Solids Centrifuges (2+1 standby) are anticipated to be able to process the entire flows and loads at design maximum month conditions. As shown in Figures 02 and 03 of the Appendix, the HSCs occupy the smallest footprint.

Typically, HSCs are able to dewater more effectively than BFPs and often achieve a higher cake solids concentration, thereby minimizing total volume for hauling and land application. Based on the preliminary cost analysis performed in this study, land application costs are the greatest single line item in the overall lifecycle costs.

The high rotational speeds require structural analyses to ensure that existing structures are capable of handling the dynamic loading of the centrifuges, particularly for upper floors. Based on a preliminary structural analysis using 1987 record drawings, it appears that the existing structure can support the static and dynamic loads associated with the centrifuges without major structural


improvements. Concrete pedestals would be required under each HSC support leg to raise the elevation of equipment so that the conveyor can be installed underneath. An overhead travelling bridge crane is recommended in order to lift out heavy components, such as the rotating bowl assembly and motors. It is anticipated that the runway beams for the bridge crane would be supported by concrete haunches constructed on the side of the existing vertical columns. A short access platform along one side of the units would be provided to facilitate operator access for inspection and maintenance. While the major maintenance items can be easily removed using the bridge crane, major repairs must be performed by or in consultation with the manufacturer. Overall, the required structural and architectural modifications are anticipated to represent an insignificant portion of the lifecycle costs and can be further developed during detailed design.

HSCs are known for their high installed horsepower requirements and electrical consumption. It is anticipated that electrical upgrades would be required in order to accommodate HSCs. The demolition of the existing three BFP units will remove approximately 65 HP of power demands, but nearly 400 HP of new loads are associated with the HSC alternative. Each of the three new HSC units will add a 100 HP main drive motor and a 20 to 40 HP back drive motor. This will increase the Dewatering Process loads above the rated capacity of the existing Dewatering Building electrical system. To maintain the level of redundancy of the present system, the electrical system from the medium-voltage (MV) transformers (750KVA transformers) through the Dewatering Building MCC will require replacement. According to the 1987 record drawings, the MV feeders between the Electrical Building and the Dewatering Building Transformers are sufficiently sized to support an expansion of the Dewatering Building loads.

Although the HSCs are associated with a greater electrical consumption, electricity constitutes a small portion of the overall lifecycle costs, as noted in Section 4.2. HSCs also tend to require more polymer than BFPs, which is a greater fraction of the lifecycle costs.

This study assumes that the HSCs would be installed in the location of the existing BFPs to minimize the distance to convey dewatered cake to the existing lime stabilization system. This layout would likely require a temporary dewatering system during installation, in the back of the building. If the cake produced during the temporary dewatering system is to be lime-stabilized, a temporary conveyor belt could be used to lift the product to the second floor of the Dewatering Building, above the lime stabilization facility (see Figure 6). It is anticipated that the centrifuges would be lifted into the building through one or more openings cut into the south wall of the upper level, as shown in Figure 7. The openings could then be covered with removable translucent panels.


Figure 6 Proposed Location for Temporary Dewatering Staging Area

Figure 7 Proposed Location for Equipment Installation (Front of Building)


Advantages • Dewatering performance anticipated

to exceed current system, resulting in lower hauling and land application costs.

• Compact footprint facilitates access to and maintenance of equipment.

• Fully-enclosed to mitigate odors and splashing.

• Number of units match number of existing sludge feed pipes and polymer pumps.

• No water booster pumps required.

Disadvantages • Higher equipment cost (up to 20%

greater than BFPs).

• Major electrical improvements required.

• Temporary dewatering system may be required during installation.

• Higher electricity and polymer consumption.

• Noisy operation.

• Major repairs must be made by manufacturer.

3.2 Belt Filter Press


Belt filter presses (BFPs) dewater sludge in multiple zones. The first zone is the gravity belt section in which the sludge is plowed by chicanes and free water drains through a moving, porous fabric belt. Solids are then pressed between two belts that move in a serpentine pattern over a series of rollers. Each pass imparts additional force, removing additional water. Solids are contained within the belts and free water is removed. The primary components of a BFP consist of the frame, belt, rollers, tensioning system, and belt wash system. The speed and tension of the belts are key control parameters.

BFP dewatering is an open process, which can result in splashback and mist from spray water and odors from the solids. Odor control of BFPs can be costly because the air from the surrounding area must also be treated.

The BFPs at the Mattawoman WRF have been in operation since 1987 and have performed generally well, typically achieving between 20 and 22 percent cake solids. Advancements in BFP technology since then, such as three-belt configurations and low-profile designs, have resulted in improved reliability, reduced misting and odors, and improved cake solids concentrations.

There are many BFP manufacturers, including Ashbrook Simon-Hartley, Andritz, Charter Machine Company, Komline-Sanderson, and BDP Industries.


The design criteria provided by the BFP manufacturers are presented in Table 6.


Table 6 Belt Filter Press Design Criteria

Parameter Manufacturer A Manufacturer B Manufacturer Andritz Ashbrook Model Quantum S8

Low-Profile G3-200

Winklepress Number of Units Recommended 4 (3+1 standby) 4 (3+1 standby) Belt Width 3 m 3 m Rated Capacity per Unit


Limiting factor

Not provided Not provided

n/a

Not provided Not provided

n/a Belt Motor Size (2) 3 HP (2) 3 HP Hydraulic Pump Motor Size 1 HP 1 HP Water Booster Pump Motor Size 15 HP 15 HP Anticipated total grid load at maximum month design conditions1, kW

16 16


1.0 1.0

Anticipated Solids Capture Efficiency1 96% 95% Anticipated Cake % Solids1 20-24% 22% (3) Anticipated Polymer Dose1, active lb/DT 7-10 8 (3) Plant Water (PLW) Requirements 90 gpm @ 120

psi, continuous 90 gpm @ 120 psi, intermittent

Anticipated Average PLW Use2, galPLW/galfeed 0.40 0.40 Anticipated Filtrate Production2, galfiltrate/galfeed 1.35 1.35 Total Equipment Weight, each 25,000 lb 30,500 lb


and design criteria described in Section 2.2. These values are not guaranteed. 2. Plant water and filtrate values were calculated using a mass balance based on manufacturer’s anticipated

performance. 3. Anticipated values for Manufacturer B based on historical performance of the units at the Mattawoman

WRF.


As shown in Table 6, four 3-meter Belt Filter Presses (3+1 standby) are anticipated to be able to process the entire flows and loads at design maximum month conditions. As shown in Figure 04 and 05 of the Appendix, the BFPs occupy the greatest amount of footprint. Due to their larger width (the existing BFPs are 2-meter units), the proposed BFPs would have to be configured in a 2 x 2 arrangement in order to fit in the dewatering equipment room. This would require demolition of the abandoned Gravity Belt Thickeners and would preclude the use of half of the Dewatering Building upper floor for future uses, such as for mechanical sludge thickening. The 2 x 2 arrangement would also increase the cost and complexity of the dewatered cake conveyors.

It may be possible to install the four BFPs without major disruptions to the dewatering operation. The two BFP units in the north half of the room (Units No. 3 and 4) could be installed without having to take the existing BFPs out of service by conveying the new units through an opening in the west wall of the Dewatering Building, as shown in Figure 8. Once installed and commissioned, the two


units could be placed into service and operated. At that time, the existing units could be taken out of service and the two remaining units could be installed through the south wall of the Dewatering Building.

Figure 8 Proposed Location for Phase 1 of BFP Equipment Installation

As shown in Figure 04, the height of manufacturer B’s equipment requires an elevated platform to access the top of the units. In contrast, there are multiple manufacturers that offer low-profile BFP designs that require lower access platforms (such as manufacturer A) or none at all, thereby facilitating operation and maintenance.

Both BFP manufacturers noted that if the solids concentration of the feed sludge could be increased to 5% or greater, three units (2+1) may be able to process the design flows and loads.

The capital costs include replacement of the existing trolley and hoist, water booster pumps to provide adequate pressure for spray water, and an additional polymer solution pump.


Advantages • Lowest capital costs.

• Installation may be possible without the need for temporary dewatering.

Disadvantages • Large footprint; occupies most of the

Dewatering Building upper floor.

• Additional related equipment (hydraulic pump, water booster pumps, two conveyors, and a new polymer pump).

• Open units exposes operators and staff to splashes, mist, and odors.

3.3 Rotary Fan Press


Rotary fan presses (RFPs) dewater sludge by pushing the solids through a channel bound by wedge wire or perforated plate screens on each side. Sludge feed pumps and a pressure-controlled outlet of the channel develop pressure within the channel that extracts free water through the screen. There are two manufacturers of RFPs: Prime Solutions and Fournier.


The design criteria provided by the RFP manufacturers are presented in Table 7. Despite repeated requests for information, Manufacturer B, Fournier, was non-responsive, and as such was excluded from the study.


Table 7 Rotary Fan Press Design Criteria

Parameter Manufacturer A Manufacturer B Manufacturer Prime Solutions Fournier Model FRP48Q Non-responsive Number of Units Recommended 4 (3+1 standby) Number of Channels per Unit, Channel Size 4, 48” Rated Capacity per Unit


Limiting factor

260

3,900 HLR

Main Motor Size 8.5 HP Anticipated total grid load at maximum month design conditions1, kW

6.3


0.05

Anticipated Solids Capture Efficiency1 95% Anticipated Cake % Solids1 20-25% Anticipated Polymer Dose1, active lb/DT 5-20 Plant Water (PLW) Requirements 80 gpm @ 45 psi,

intermittent

Anticipated Average PLW Use2, galPLW/galfeed 0.02 Anticipated Filtrate Production, galfiltrate/galfeed 0.98 Total Equipment Weight, each 17,000 lb


and design criteria described in Section 2.2. These values are not guaranteed.

2. Filtrate values were calculated using a mass balance based on manufacturer’s anticipated performance.


Four Rotary Fan Presses (3+1 standby) are anticipated to be able to process the entire flows and loads at design maximum month conditions. As shown in Figure 06 of the Appendix, the RFPs occupy a moderate amount of footprint. As with the HSCs, the proposed location of the RFPs would require temporary dewatering while the existing BFPs are replaced.

Dewatering performance of RFPs can vary greatly depending on the feed solids characteristics; they tend to be better-suited to applications with fibrous material and primary solids. The solids concentration of the dewatered cake product can range to less than that achieved by a BFPs and greater than a HSC in some cases; some installations have only been able to achieve 10% solids2, while others have been able to achieve up to 30%. Due to this uncertainty, a "best case" and a "worst case" scenario have been provided for Manufacturer A, based on the manufacturer’s anticipated range of 20-25% cake solids concentration.

Similar to the dewatered cake percent solids, the polymer requirements also vary greatly depending on the installation.

2 Crosswell, S., Young, T., & Benner, K. (2004). Performance Testing Of Rotary Press Dewatering Unit under Varying Sludge Feed Characteristics. Proceedings of the Water Environment Federation, 2004(14), 309-323.


Although not considered in this study, the RFP is commonly operated unattended, with minimal operator attention. Some facilities operate the dewatering system on a 24-hour basis. This method of operation can greatly reduce the sizing of rotary press equipment required to complete plant dewatering operations. However, this mode of operation would require either continuous operation of the lime stabilization system or overnight storage of the dewatered cake.

It should also be noted that the RFPs are modular, allowing their capacity to be expanded over time. The model proposed for this study has four channels to provide sufficient capacity for design flows and loads; however, the units could be instead be provided with only two or three channels for current conditions and later expanded as the system approaches capacity.

The RFP manufacturer noted that if the solids concentration of the feed sludge could be increased to 5% or greater, three units (2+1) may be able to process the design flows and loads.

A hoist and trolley is recommended in order to lift out the channels for maintenance. The capital costs include a monorail crane centered above the units and extending over the existing floor hatch.

Advantages • Dewatering performance may

exceed current system, resulting in lower hauling and land application costs.

• Compact footprint facilitates access to and maintenance of equipment.

• Fully-enclosed to mitigate odors and splashing.

• Quick startup and shutdown.

• Ability to phase-in channels to reduce upfront costs.

• No water booster pumps required.

• Common to have equipment operate unattended (not accounted for in study).

Disadvantages • Highest capital cost of equipment

(up to 50% greater than BFPs).

• Uncertainty of dewatering performance.

• Only two manufacturers available.

• Four units will require modifications to piping and additional polymer pump.

•


4. Evaluation of Alternatives 4.1 Summary of Capital Costs

Opinion of probable construction cost estimates were prepared based on supplier quotes, similar project bid tabulations, and discussions with equipment manufacturers. Where this information was not available, estimates were made based on costs from previous similar projects, RS Means Facilities Cost Data, and previous vendor quotations adjusted for inflation.

For preparation of the capital costs, the following criteria were used:

All costs are presented in 2015 US dollars, rounded to the nearest $10,000.

Contractor general conditions were assumed to be 10-percent of the construction subtotal.

Contractor overhead and profit were assumed to be 20-percent of the construction subtotal.

A 30-percent contingency was included with all construction costs.

Replacement of the MCC was included for all alternatives due to its age.

The following items were not included in the capital costs:

– Project costs associated with administration, legal, engineering, construction management services, or pilot testing.

– Dewatering Building systems, including odor control, HVAC, electrical, and lighting.

– Replacement of ancillary equipment systems such as dry polymer feed system3, sludge feed pumps, and lime stabilization.

A summary of opinions of capital costs is presented in Table 8 and illustrated in Figure 9.

Table 8 Summary of Capital Costs

Cost Item High-Solids Centrifuge Belt Filter Press Rotary Fan

Press Mfr. A Mfr. B Mfr. A Mfr. B

Equipment $ 1,760,000 $ 1,830,000 $ 1,510,000 $ 1,830,000 $ 2,280,000 Installation/Sequencing $ 400,000 $ 400,000 $ 290,000 $ 290,000 $ 250,000 Electrical/Controls $ 960,000 $ 970,000 $ 810,000 $ 910,000 $ 1,010,000 Piping/Structural Modifications $ 910,000 $ 910,000 $ 780,000 $ 780,000 $ 780,000 General Conditions $ 400,000 $ 410,000 $ 340,000 $ 380,000 $ 430,000 Contractor Overhead and Profit $ 890,000 $ 900,000 $ 750,000 $ 840,000 $ 950,000 Contingency $ 1,600,000 $ 1,630,000 $ 1,340,000 $ 1,510,000 $ 1,710,000 Total $ 6,920,000 $ 7,050,000 $ 5,820,000 $ 6,550,000 $ 7,410,000

Note: 1. Refer to Appendix A for an itemized list of capital costs for each alternative.

3 However, the cost of an additional polymer solution feed pump was included for alternatives with more than three dewatering units.


Figure 9 Summary of Capital Costs

4.2 Summary of O&M Costs

In order to provide a fair and thorough comparison, O&M costs for each alternative were calculated based on indicators such as the number of operator hours, chemical and electricity usage, and cake output, as opposed to a fixed unit price per ton that the biosolids contractor typically charges.

The O&M costs presented herein include the following items:

Electricity consumption of the dewatering units and related equipment (notably plant water booster pumps);

Polymer consumption;

Land Application, including related costs, such as hauling, testing, permitting, site selection, and storage (assuming a Class B product);

Plant Water consumption;

Filtrate, quantified by the cost of pumping filtrate at the influent pump station;

Labor for a contract operator to be on-site during dewatering operations; and

Maintenance, estimated as a percentage of equipment cost per year.

The O&M costs do not account for factors that do not vary significantly between alternatives or factors that do not affect the results. These include the following:

Costs associated with grinder or sludge feed pumps;

Costs associated with lime stabilization, including cost of labor and lime;

$0

$1

$2

$3

$4

$5

$6

$7

$8

HSC Mfr. A HSC Mfr. B BFP Mfr. A BFP Mfr. B RFP

Cap

ital C

ost,

Milli

on U

SD

Contingency

Overhead & Profit

General Conditions

Electrical/Controls

Installation/Sequencing

Related Equipment

Dewatering Equipment


The cost of treating filtrate solids that are returned to the plant;

The value of plant water as a marketable reclaimed water product;

Contract operator overhead and profit; and

Differences in labor costs between alternatives (all alternatives are assumed to have the same labor cost).

Table 9 General Inputs for O&M Costs

Parameter Value Notes Cost of Electricity, $/kWh $ 0.13 Selected during Kick-Off Meeting Cost of Polymer, $/active lb $ 2.00 Typical value Cost of Land Application, $/WT $ 70 See note 1 Cost of Plant Water, $/kgal $ 0.08 See note 2 Cost of Filtrate, $/kgal $ 0.05 See note 2 Cost of Contractor Labor, $/hr $ 100 Selected during Kick-Off Meeting Maintenance Costs 3% 3% of equipment cost per year Contractor Labor, hr/year 1,400 See note 3

Notes: 1. Land Application cost includes hauling, permitting, site selection, and storage. A sensitivity analysis to

evaluate the impact of the land application cost is presented in Section 4.4. The baseline value of $70 per wet ton was determined during the 2013/2014 Mattawoman WRF Biosolids Study.

2. The costs of plant water and filtrate were calculated based on the electricity use of the Plant Water Pumps and Influent Pumps, respectively, using the following formula: $/gal = $/kWh * (0.749 kW/HP) * (HP/gpm) ÷ (60 min/hr), where HP/gpm = TDH ÷ 3960 ÷ pump efficiency

3. Contractor labor = 3,120 hour/year at design conditions * (current load ÷ design load), where 3,120 hours per year = 12 hour shift per day * 5 shifts per week * 52 weeks per year

The O&M costs are dependent on the performance of the dewatering equipment, such as cake solids concentration, specific energy use, and polymer consumption.

The values for BFPs are primarily based on historical data collected at the Mattawoman WRF (discussed in Section 2.1). Values for HSCs and RFPs are assumed based on the manufacturer proposals, existing installations, and previous project experience. Because the values are uncertain, a sensitivity analysis was performed to estimate the lifecycle costs if the equipment performs better or worse than assumed (discussed in Section 4.4).

Furthermore, due to the wide variation in performance of RFPs depending on the feed solids characteristics, a "best case" and a "worst case" scenario have been provided to evaluate the anticipated range in RFP O&M costs based on the potential performance of the equipment. Values were selected based on discussions with the manufacturer and results of published pilot study results in which RFP performance was compared to that of BFPs and HSCs.

The baseline equipment performance values used in this study are presented in Table 10.


Table 10 Alternative-Specific Parameters for O&M Costs

Cost Item High-Solids Centrifuge Belt Filter Press Rotary Fan Press

Mfr. A Mfr. B Mfr. A Mfr. B Best Case Worst Case Cake % solids 25% (1) 25% (1) 22% (2) 22% (2) 25% (3) 20% (3) Capture Efficiency, % 95% 95% 95% 95% 95% 95% Electrical Consumption, kWh/kgalfeed 3.5 4.1 1.0 1.0 0.5 0.5 Polymer Consumption, active lb/DT 15 (4) 15 (4) 8 (2) 8 (2) 7.5 (5) 18.75 (5) Plant Water Demand, gal/DT 360 380 4,800 4,800 290 290 Filtrate, galfiltrate/galfeed 1.03 1.03 1.35 1.35 0.98 1.02

Notes: 1. HSC cake % solids assumed to be 3% points greater than BFP. 2. BFP cake % solids and polymer demand based on historical data. 3. RFP cake % solids could be as high as centrifuge (best case) or lower than BFP (worst case) 4. HSC Polymer consumption is assumed based on discussions with manufacturers, references, and

previous project experience. A sensitivity analysis to evaluate the impact of lower or greater values is presented in Section 4.4.

5. RFP Polymer consumption assumed to range between 50% (best case) and 125% (worst case) of HSC polymer demand.

The inputs from Table 9 were applied to the alternative-specific parameters in Table 10 to determine the O&M Costs at current conditions, which are presented in Table 11 and Figure 10.

Table 11 Summary of Dewatering O&M Costs at Current Conditions


Mfr. A Mfr. B Mfr. A Mfr. B Best Case Worst Case Electricity $ 21,100 $ 24,900 $ 6,400 $ 6,400 $ 2,900 $ 2,900 Polymer $ 117,000 $ 117,000 $ 62,400 $ 62,400 $ 58,500 $ 146,200 Land Application $ 1,058,400 $ 1,058,400 $ 1,206,000 $ 1,206,000 $ 1,058,400 $ 1,296,500 Plant Water $ 100 $ 100 $ 1,500 $ 1,500 $ 100 $ 100 Filtrate $ 2,300 $ 2,300 $ 3,000 $ 3,000 $ 2,200 $ 2,300 Operator Labor $ 279,700 $ 279,700 $ 279,700 $ 279,700 $ 279,700 $ 279,700 Maintenance $ 76,300 $ 78,400 $ 63,000 $ 74,200 $ 88,200 $ 88,200 Total $ 1,554,900 $ 1,560,700 $ 1,622,000 $ 1,633,200 $ 1,489,900 $ 1,815,900 $ per Dry Ton $ 400 $ 400 $ 415 $ 420 $ 380 $ 465

Notes: 1. These are the anticipated annual O&M costs in the first year of operation. 2. Annual Cost of Electricity = current average gal/year * kWh/gal * $/kWh 3. Annual Cost of Polymer = current average DT/year * lb/DT * $/lb 4. Annual Cost of Land Application = current average DT/year * capture efficiency ÷ % solids * $/WT 5. Annual Cost of Plant Water = current average DT/year * galPLW/DT * $/kgal ÷ 1,000 6. Annual Cost of Filtrate = current average DT/year * galfiltrate/DT * $/kgal ÷ 1,000 7. Annual Cost of Operator Labor = hrs/year (current) * $/hr 8. Annual Cost of Maintenance = % of equipment cost


Figure 10 Summary of Dewatering O&M Costs

In order to provide a comparison to the current O&M costs incurred by the County, the estimated costs associated with lime stabilization and contract operator overhead and profit were added to the dewatering O&M costs. These costs are summarized in Table 12.

Table 12 Summary of Dewatering O&M Costs at Current Conditions


Mfr. A Mfr. B Mfr. A Mfr. B Best Case Worst Case Total Dewatering O&M Cost (1) $1,554,900 $1,560,700 $1,622,000 $1,633,200 $1,489,900 $1,815,900

$ per Dry Ton $ 400 $ 400 $ 415 $ 420 $ 380 $ 465

Lime Stabilization

Lime (2) $105,300 $105,300 $105,300 $105,300 $105,300 $105,300

Labor (3) $279,700 $279,700 $279,700 $279,700 $279,700 $279,700

Total Stabilization O&M Cost $385,000 $385,000 $385,000 $385,000 $385,000 $385,000

Stabilization $ per Dry Ton $100 $100 $100 $100 $100 $100

Total Dewatering & Stabilization O&M Cost $1,940,000 $1,946,000 $2,007,000 $2,018,000 $1,875,000 $2,201,000

Dew. + Stab. $ per Dry Ton $500 $ 500 $515 $520 $480 $565

Total Dewatering & Stabilization O&M Cost, with Contract Operator Overhead & Profit (4)

$2,231,000 $2,238,000 $2,263,000 $2,275,000 $2,117,000 $2,476,000

Dew. + Stab. $ per Dry Ton, with Contract Operator

Overhead & Profit (5) $575 $575 $590 $600 $550 $650

Notes: 1. Total Dewatering O&M Cost obtained from Table 11.

$0.0

$0.2

$0.4

$0.6

$0.8

$1.0

$1.2

$1.4

$1.6

$1.8

$2.0

HSC Mfr. AHSC Mfr. B BFP Mfr. A BFP Mfr. B RFP(BestCase)

RFP(WorstCase)

Annu

al C

ost a

t Cur

rent

Con

ditio

ns, M

illion

USD

Maintenance

Operator Labor

Filtrate

Plant Water

Land Application

Polymer

Electricity


2. Annual Cost of Lime based on historical data provided by Charles County; = current average DT/year * 0.15 ton lime per DT * $180 per ton of lime.

3. Annual Cost of Labor for stabilization assumed to be equal to dewatering. 4. Contract Operator Overhead and Profit assumed to be 15%, applied to both the Dewatering and

Stabilization O&M Costs. 5. The Dewatering and Stabilization O&M Cost per Dry Ton with Contract Operator Overhead & Profit is

presented as a comparison to the 2014 rate of $570 per dry ton.

4.3 Summary of Lifecycle Costs

Table 13 presents the assumptions used to translate the capital and O&M costs into a net present value (NPV) of total lifecycle costs over a 25-year period. The potential salvage value of the equipment was excluded from the lifecycle cost calculation.

Table 13 General Inputs for Lifecycle Costs

Parameter Value Notes Period of Study (No of years) 25 Selected at Kick-Off Meeting Growth Rate (1) 1.6% Selected at Kick-Off Meeting Inflation Rate 3% Selected at Kick-Off Meeting Discount Rate 1.8% Selected at Kick-Off Meeting Net Rate 2.8% See note 2

Notes: 1. Maintenance costs are not scaled by the growth rate. 2. Net rate = (1+growth rate) * (1+inflation rate) ÷ (1+discount rate) – 1

Table 14 and Figure 11 provide a summary of the 25-year NPVs of capital, O&M, and lifecycle costs for the different dewatering alternatives.

Table 14 Summary of Lifecycle Costs


Mfr. A Mfr. B Mfr. A Mfr. B Best Case Worst Case Capital Costs $6.9 $7.1 $5.8 $6.6 $7.4 $7.4 NPV of O&M Costs $54.7 $54.9 $57.2 $57.5 $52.3 $63.9 Lifecycle Costs $61.6 $62.0 $63.0 $64.1 $59.7 $71.3

Note: 1. Values are presented in units of million 2015 US dollars. 2. O&M costs do not include stabilization or contract operator overhead and profit.


Figure 11 Summary of Lifecycle Costs

The relative magnitudes of the components on the total lifecycle cost are presented in Figure 12.

Figure 12 Relative Magnitude of Total Lifecycle Costs

Note: 1. Values shown are based on the average values across all alternatives.

$0

$10

$20

$30

$40

$50

$60

$70

$80

HSC Mfr. A HSC Mfr. B BFP Mfr. A BFP Mfr. B RFP(Best Case)

RFP(Worst Case)

Annu

al C

ost a

t Cur

rent

Con

ditio

ns, M

illion

USD

Capital Costs NPV of O&M Costs Lifecycle Costs

Operator Labor, 16%

Capital, 10%

Polymer, 5%

Other, 4%

Land Application, 64%

Operator Labor

Capital

Polymer

Other

Land Application


4.4 Sensitivity Analysis

Due to the uncertainty surrounding some of the values assumed in this study, sensitivity analyses were performed to evaluate the impact of adjusting the parameters which are believed to have the greatest impact on the overall lifecycle costs, as shown in Figure 11.

Land application is the greatest component of the lifecycle costs, accounting for approximately two-thirds of the total. It is directly affected by the unit cost of land application and the solids concentration of the dewatered cake. The values for both parameters are not precisely known, and therefore a sensitivity analysis has been performed for each.

The second-greatest component of the lifecycle costs is contractor labor, which for the purposes of this study, is assumed to be equal for all alternatives and is approximately 16% of the total lifecycle costs. Capital costs and polymer consumption account for approximately 10% and 5% of the total lifecycle costs, respectively. A sensitivity analysis was also performed on the HSC and RFP polymer consumption.

The costs of electricity, plant water, and filtrate constitute less than 5% of the total, suggesting that differences in those parameters across alternatives will not significantly affect the results of this study, and therefore sensitivity analyses were not performed for those parameters.

The lifecycle costs presented herein for BFPs and HSCs are based on the averaged lifecycle cost of both manufacturers. The RFP lifecycle costs are based only on the “best case” scenario; a sensitivity was not performed for the “worst case” RFP scenario because it had the greatest lifecycle cost under all conditions.

4.4.1 Unit Cost of Land Application

The unit cost of land application (which for the purposes of this study includes related activities such as hauling, testing, storage, permitting, and site identification) does not vary based for each alternative. It is affected by regulations and market factors which are difficult to predict and impossible to control. It can be reasonably assumed however, that the cost would increase over time due to proposed regulations in the Chesapeake Bay region that could potentially limit the availability of land application sites, thereby raising costs. An increase in the unit cost of land application would favor dewatering technologies that are able to achieve higher percent solids concentration of dewatered cake.

Figure 13 illustrates the total lifecycle cost for the three dewatering technologies as a function of the Class B land application unit cost. The baseline unit cost of $70 per wet ton is indicated on the chart. The “break-even” point between HSCs and BFPs occurs at approximately $45. This value is not likely based on discussions with facilities that use contract operators for land application only (as opposed to dewatering, stabilization, and land application as is done at the Mattawoman WRF). Furthermore, the unit cost of land application is anticipated to continue to rise as regulations and market forces limit the availability of land application sites. For that reason, it is believed that the likelihood of encountering this “break-even” condition is low.


Figure 13 Lifecycle Cost Sensitivity Analysis for Varying Land Application Costs

4.4.2 Improvements in Cake Solids Concentration

Land application costs are inversely related to solids concentration. In other words, if the solids concentration could be doubled, then the annual cost of land application would be halved. A single point increase in the cake percent solids could yield an annual savings of tens of thousands of dollars, which over the 25-year planning period would be equivalent to more than a million dollars.

Baseline values for the percent solids for each alternative have been assumed in this study based on a literature review published studies, discussions with manufacturers, interviews of operators at other installations, historical data (where available), and previous project experience.

While the anticipated performance of the Belt Filter Presses can be reliably estimated based on historical plant data, the performance for the other alternatives cannot be reliably estimated without further investigation. While it is highly likely that the HSC can achieve higher cake solids concentration than the BFP, the HSC manufacturers cannot provide a guarantee without either an analysis of a feed solids sample or a pilot study.

The baseline solids concentration for the HSC and RFP (best case) alternatives was assumed to be 3 percentage points greater than the historical value achieved by the existing BFPs. As shown in Figure 14, the break-even point for the difference in percent solids is less than 2%, which is very unlikely.

$40

$45

$50

$55

$60

$65

$70

$75

$80

$40/WT $50/WT $60/WT $70/WT $80/WT $90/WT

25-Y

ear L

ifecy

cle

Cos

t, M

illion

USD

Hauling & Land Application Cost, $ per wet ton

Belt Filter Press High-Solids Centrifuge Rotary Fan Press (Best Case)

Break-Even Point: ~$45/WT

Baseline value: $70/WT


Figure 14 Lifecycle Cost Sensitivity Analysis for Varying Cake Solids Concentration

4.4.3 Polymer Consumption for HSC and RFP

Polymer consumption is the third-greatest item for lifecycle cost. As discussed previously, the required polymer dose to achieve good dewatering performance can vary widely based on sludge characteristics and equipment design.

The baseline values for HSC and RFP (best case) were 15 and 7.5 pounds of active polymer per dry ton of solids, respectively. As shown in Figure 12, the “break-even” point between HSC and BFP occurs at 22 lb/DT for the HSC, respectively. This “break-even” value is at the upper end of the manufacturers' anticipated range of values.

The polymer consumption for the RFP “best case” scenario is anticipated to be half that of the HSC, and therefore, the RFP polymer dose in Figure 15 to shown as half of the value shown on the x-axis.

There is a moderate possibility that the polymer consumption for the HSC and RFP are greater than anticipated, and as such, the likelihood of encountering the “break-even” point is moderate.

$40

$45

$50

$55

$60

$65

$70

0% (22%) 1% (23%) 2% (24%) 3% (25%) 4% (26%) 5% (27%)

25-Y

ear L

ifecy

cle

Cos

t, M

illion

USD

Improvement in Cake Solids of HSC and RFP over BFP, Percentage Points (HSC and RFP Solids Concentration shown in parentheses)


Break-Even Point: 1.8% point difference in cake solids content

Baseline value: 3.0% point difference in cake solids content


Figure 15 Lifecycle Cost Sensitivity Analysis for Varying Polymer Dose

4.5 Non-Cost Considerations

Non-economic evaluation criteria were developed jointly with the County during the Kick-Off Meeting to address considerations that will be important in this decision-making process.

The following criteria were proposed during the Kick-Off Meeting, but were not evaluated due to marginal differences between alternatives, or because they have been accounted for as capital or O&M costs:

Compatibility with existing and future upstream biosolids processes;

Solids capture efficiency;

Filtrate composition;

Ability to handle fluctuating solids feed;

Impact on downstream operations (e.g., lime);

Mechanical reliability;

Ease of adjustments during operation;

Ease of installation;

Ease of maintenance; and

Availability of service/support/parts.

The remaining non-economic evaluation criteria were assigned a score for each alternative, using a ranking system of 1 to 3, with 3 representing the most favorable score. The scores are presented and totaled in Table 15. The HSC and RFP outrank the BFP due to the more compact and accessible layout, ease of startup and shutdown, and enclosed units. The HSC alternative is more

$40

$45

$50

$55

$60

$65

$70

9 lb/DT 12 lb/DT 15 lb/DT 18 lb/DT 21 lb/DT 24 lb/DT

25-Y

ear L

ifecy

cle

Cos

ts, M

illion

USD

High-Solids Centrifuge Polymer Use, Active Pounds per Dry Ton Historical BFP polymer use = 8 lb/DT; RFP polymer use = 50% centrifuge


Break-Even Point: 22 pounds active polymer per dry ton feed for HSC (11 lb/DT for RFP)

Baseline value: 15 pounds active polymer per dry ton feed for HSC (7.5 lb/DT for RFP)


highly ranked than the other two for “Compatibility with future Class A processes” because it is anticipated to result in the highest cake solids concentration, which in turn, would result in the lowest O&M costs for a thermal dryer, which the County may consider in the future to achieve Class A biosolids and minimize the total volume hauled off-site. The RFP is lowest ranked for “Consistency of cake characteristics” due to the relatively wider range in performance, depending on the feed sludge characteristics.

Table 15 Ranking of Non-Cost Considerations

Criteria High-Solids Centrifuge Belt Filter Press Rotary Fan Press Odor/splash concerns 3 1 3 Ease of startup/shutdown 2 1 3 Noise level 1 3 2 Space constraints and access for maintenance 3 1 2

Opportunities for equipment phasing 1 2 3

Compatibility with future Class A processes, such as thermal drying

3 1 1

Consistency of cake characteristics 3 3 1

Total 16 12 15


5. Discussion and Recommendations As shown in Table 14, the High-Solids Centrifuge (HSC) alternative is anticipated to have lower lifecycle costs than Belt Filter Presses (BFP). This is primarily due to the anticipated higher solids concentration of the dewatered cake from HSC compared to BFP, which reduces land application costs. HSCs also have higher scores for non-cost criteria than BFPs, as shown in Table 15. For those two reasons, HSCs are recommended over BFPs. Although the Rotary Fan Press (RFP) alternative is shown as potentially having the lowest lifecycle costs, RFPs are not recommended for further consideration due to the limited number of installations at similar facilities and their typically wider variability in performance, both of which reduce the certainty of the RFP lifecycle costs.

The County may wish to consider reducing capital costs by phasing-in equipment installation. Installation of two of the three HSC units would save approximately $1M USD, or 15-20% of the capital costs. As discussed in Section 2.3 and illustrated in Figure 5, only one unit is required to process current average loads. During current maximum month loading conditions, either a single unit can be operated for longer hours, or two units can be operated without the need for overtime. The third unit could then be installed when loads increase or a higher degree of redundancy is desired.

It is recommended that the County pursue on-site pilot testing of HSCs to validate the assumptions used in this study, to establish performance criteria for the design and bid of dewatering improvements, and possibly to either shortlist or pre-select the equipment. Pilot testing protocols should be carefully developed and applied equally to all manufacturers to ensure that a fair comparison is made among the various HSC manufacturers.

GHD | Report for Charles County - Mattawoman WRF Dewatering Study, 86/15181/

Appendices

Appendix A - Summary of Capital Costs

ENGINEER'S ESTIMATE OF PROBABLE CONSTRUCTION COSTProject: Mattawoman WWTP Dewatering Study Computed By: SESLocation: La Plata, MD Checked By: VMMOwner: Charles County Design Status of Est.: ConceptDescription: Capital Costs of Alternatives Project No: 8615181

Alternative Centrifuge Belt Filter Press Rotary FanMfr. A Mfr. B Mfr. A Mfr. B Press

Number of Dewatering Units 3 3 4 4 3Dewatering EquipmentDewatering Units 1,173,000$ 1,825,000$ 1,480,000$ 1,801,000$ 2,280,000$ Hydraulic Pump n/a n/a incl incl n/aWater Booster Pumps n/a n/a 30,000$ 30,000$ n/a

Related EquipmentConveyor 100,000$ 100,000$ 250,000$ 250,000$ 100,000$ Additional Polymer Pump n/a n/a 25,000$ 25,000$ 25,000$ Lifting Equipment - - - - - └ Bridge Crane 300,000$ 300,000$ - - - └ Monorail Crane - - - - 125,000$ └ Trolley/Hoist (replace in-kind) - - 15,000$ 15,000$ -

Installation/SequencingTemp. Dewatering Operations 320,000$ 320,000$ 160,000$ 160,000$ 320,000$ Exist. BFP Demolition 18,000$ 18,000$ 18,000$ 18,000$ 18,000$ Exist. GBT Demolition 18,000$ 18,000$ 18,000$ 18,000$ 18,000$ Bldg. Demo. for Equip. Installation 6,000$ 6,000$ 12,000$ 12,000$ 6,000$ Crane Rental for Equip. Installation 44,000$ 44,000$ 55,000$ 55,000$ 44,000$ Equipment Installation 315,000$ 445,000$ 360,000$ 424,000$ 506,000$ Equip. Startup/Performance Testing 14,000$ 14,000$ 18,000$ 18,000$ 14,000$ Restore Bldg after Equip Install 60,000$ 60,000$ 120,000$ 120,000$ 60,000$ Mods to Sludge Feed Pipe 5,000$ 5,000$ 15,000$ 15,000$ 10,000$ Mods to Filtrate Drain Pipe 5,000$ 5,000$ 5,000$ 5,000$ 5,000$ Mods to Equipment Curb 10,000$ 9,000$ 9,000$ 9,000$ 9,000$ Access Platforms 25,000$ 25,000$ 20,000$ 60,000$ -

Electrical/ControlsElectrical Demolition 9,000$ 9,000$ 9,000$ 9,000$ 9,000$ New MCC 125,000$ 125,000$ 125,000$ 125,000$ 125,000$ Transformer Replacement 135,000$ 135,000$ - - - Electrical Installation 45,000$ 45,000$ 45,000$ 45,000$ 45,000$ General E,I,&C 600,000$ 600,000$ 600,000$ 600,000$ 600,000$

Subtotal 3,328,000$ 4,109,000$ 3,390,000$ 3,815,000$ 4,320,000$ General Conditions (10%) 333,000$ 411,000$ 339,000$ 382,000$ 432,000$

Subtotal 3,660,000$ 4,520,000$ 3,729,000$ 4,197,000$ 4,752,000$ Overhead (10%) 366,000$ 452,000$ 373,000$ 420,000$ 475,000$

Profit (10%) 366,000$ 452,000$ 373,000$ 420,000$ 475,000$ Subtotal 4,393,000$ 5,424,000$ 4,475,000$ 5,036,000$ 5,703,000$

Contingency (30%) 1,318,000$ 1,627,000$ 1,342,000$ 1,511,000$ 1,711,000$ TOTAL 5,710,000$ 7,050,000$ 5,820,000$ 6,550,000$ 7,410,000$

\\ghdnet\ghd\US\Bowie\Projects\86\15181\TECH\01 Dewatering Evaluation\Cost Estimates\Capital Cost Estimate.xlsxDeliverable 6/12/2015

Appendix B - Conceptual Layout Figures Figure 01: Existing Dewatering Layout

Figure 02: Centrifuge Manufacturer A Layout

Figure 03: Centrifuge Manufacturer B Layout

Figure 04: Belt Filter Press Manufacturer A Layout

Figure 05: Belt Filter Press Manufacturer B Layout

Figure 06: Rotary Fan Press Layout

Plot Date: Cad File No:5 June 2015 - 1:38 PM G:\86\15181\CADD\Drawings\Figures\Sludge Dewatering Bldg Figures\86-15181 - Grit & Rotary Figures.dwg

FigureDate

RevisionJob Number

16701 Melford Boulevard, Suite 330, Bowie MD 20715 USA T 1 301 805 5629 F 1 301 805 4665 E [email protected] W www.ghd.com

01

CHARLES COUNTY, MARYLANDMATTAWOMAN WWTPBIOSOLIDS STUDYSLUDGE DEWATERING BUILDINGEXISTING PLAN AND SECTION

86-15181A05/2015

SCALE: 1/8"=1'-0"

SECTIONAFIG 01 3/32" = 1'-0"SCALE :

0 12'-0"4'-0" 8'-0"

SCALE 1/8"=1'-0" AT ORIGINAL SIZE

0


16'-0"12'-0"8'-0"4'-0"

NOT TO SCALE

GRAVITY BELT THICKENER (ABANDONED)

POSITIVE DISPLACEMENT PUMP (ABANDONED)


FigureDate

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02

CHARLES COUNTY, MARYLANDMATTAWOMAN WWTPBIOSOLIDS STUDYSLUDGE DEWATERING BLDG PLAN& SECTION - CENTRIFUGE MFR. A

86-15181A05/2015

0 12'-0"4'-0" 8'-0"



0


16'-0"12'-0"8'-0"4'-0"

SCALE: 1/8"=1'-0"


FigureDate

RevisionJob Number


03

CHARLES COUNTY, MARYLANDMATTAWOMAN WWTPBIOSOLIDS STUDYSLUDGE DEWATERING BLDG PLAN& SECTION - CENTRIFUGE MFR. B

86-15181A05/2015

0 12'-0"4'-0" 8'-0"


0


16'-0"12'-0"8'-0"4'-0"


SCALE: 1/8"=1'-0"


FigureDate

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CHARLES COUNTY, MARYLANDMATTAWOMAN WWTPBIOSOLIDS STUDYSLUDGE DEWATERING BLDG PLAN& SECTION - BELT PRESS MFR. A

86-15181A05/2015

0 12'-0"4'-0" 8'-0"


0


16'-0"12'-0"8'-0"4'-0"


NOT TO SCALE

SCALE: 1/8"=1'-0"


FigureDate

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05

CHARLES COUNTY, MARYLANDMATTAWOMAN WWTPBIOSOLIDS STUDYSLUDGE DEWATERING BLDG PLAN& SECTION - BELT PRESS MFR. B

86-15181A04/2015

0 12'-0"4'-0" 8'-0"


0


16'-0"12'-0"8'-0"4'-0"


NOT TO SCALE

SCALE: 1/8"=1'-0"

LANDING STAIR

UP


FigureDate

RevisionJob Number


06

CHARLES COUNTY, MARYLANDMATTAWOMAN WWTPBIOSOLIDS STUDYSLUDGE DEWATERING BLDG PLAN& SECTION- ROTARY PRESS MFR. A

86-15181A05/2015

SCALE: 1/8"=1'-0"

0 12'-0"4'-0" 8'-0"


0


16'-0"12'-0"8'-0"4'-0"


GHD Inc.

16701 Melford Boulevard Suite 330 Bowie MD 20715

T: 1 240 206 6810 F: 1 240 206 6811 E: [email protected]

© GHD Inc. 2015

The document may only be used for the purpose of assessing our offer of services and for inclusion in documentation for the engagement of GHD. Unauthorized use of this document in any form whatsoever is prohibited. \\ghdnet\ghd\US\Bowie\Projects\86\15181\WP\Reports\Dewatering Study\Technology Analysis Report FINAL.docx

Document Status

Rev No.

Author Reviewer Approved for Issue Name Signature Name Signature Date

A SES V. Maillard On File T. Young 6/12/2015

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