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WASTEWATER MASTER PLAN

TECHNICAL MEMORANDUM

Murray, Smith and Associates, Inc. Page C-1

TO: Teresa Reed-Jennings – City of Pasco DATE: December 28, 2016

FROM: Craig Anderson - MSA CC: Tracy Cork - VE

PREPARED

BY:

Dale Richwine - REI

SUBJECT: Technical Memorandum No. 8.2

Pasco WWTP CEPT Jar Testing

1 TABLE OF CONTENTS

1 TABLE OF CONTENTS ........................................................................................................1

2 EXECUTIVE SUMMARY ......................................................................................................1

3 BACKGROUND ..................................................................................................................2

4 JAR TESTING PROCEDURE .................................................................................................3

5 JAR TEST DOSAGES ...........................................................................................................5

6 JAR TEST RESULTS.............................................................................................................8

7 CHEMICAL EVALUATION ...................................................................................................8

8 RECOMMENDATION ....................................................................................................... 13

2 EXECUTIVE SUMMARY

This memorandum documents the jar testing that was performed to determine chemical

dosing and costs for implementing Chemically Enhanced Primary Treatment (CEPT) at the

Pasco WWTP during the summer of 2017. Testing was performed in the Pasco WWTP

laboratory with the assistance of city operations and laboratory staff. A review of the costs

for CEPT treatment was performed based on the dosages that produced the desired results in

the jar testing.

City of Pasco TM 8.2

Intermediate Needs Study Pasco WWTP CEPT Jar Testing

Murray, Smith and Associates, Inc. Page 2

The preferred chemical should be the chemical that produces the most benefit at the least

cost.. The cost analysis showed that the lowest cost chemical will be ferric chloride at a dose

of 20-mg/L. The annual cost to operate the process using the 20-mg/L dose is $326,000 per

year. The analysis also showed that ferric chloride had the most advantages throughout the

treatment process. These advantages should overcome the additional handling issues related

to the chemical. Based on the process advantages and cost, ferric chloride is recommended

for use in CEPT treatment. The cost to install a storage and feed system should be the same

for each chemical.

3 BACKGROUND

The degree of clarification obtained when chemicals are added to untreated wastewater

depends on the type and quantity of chemicals used, mixing times, and the care with which

the process is monitored and controlled. With chemical precipitation, it is possible to remove

80 to 90 percent of the total suspended solids (TSS) including some colloidal particles and 50

to 80 percent of the BOD5. Comparable removal values for well-designed and well operated

primary sedimentation tanks without the addition of chemicals are 50 to 70 percent of the

TSS and 25 to 40 percent of the BOD5.

Because of the variable characteristics of wastewater, the effectiveness of alternative

coagulants and the required chemical dosages need to be evaluated based on the results of jar

tests. For example, dosages of ferric chloride (FeCl3) for coagulation of raw or screened

wastewater range typically from about 15 to 40 mg/L after a short reaction time. Other

chemicals will require different dosages to obtain the same results1

Jar testing was performed on December 13, 2016 on three chemicals: ferric chloride, sodium

aluminate and ACH [aluminum chlorohydrate – Al2(OH)3Cl3]. Each chemical has specific

advantages and disadvantages. The chemical of choice will be selected on performance and

cost.

The capacity of the Pasco WWTP treatment plant is directly dependent on the character of

the influent waste stream. The unit process that limits the capacity of the treatment plant is

the activated sludge secondary treatment process. Adding chemicals to enhance the removal

of BOD5 and TSS in the primary treatment process will lower the BOD5 and TSS loadings to

the trickling filter and activated sludge processes allowing for additional treatment capacity.

The level of additional removal is dependent on the influent wastewater characteristics and

were estimated by the jar testing discussed in this technical memorandum.

1 “Wastewater Engineering Treatment and Resource Recovery”, Metcalf & Eddy-AECOM, Fifth Edition,

pp. 477-478.




4 JAR TESTING PROCEDURE

Testing was performed on 20-liters of raw influent sample that was collected as a grab from

the headworks channel directly behind the bar screens, at the location of the sampler

collection point. The sample was taken between 9:00AM and 9:30 AM.

The jar testing was done using a four-place gang stirrer as shown in Figure 1. The four 1-liter

beakers were filled from the 20-liter sample volume. The 20-liter sample bottle was mixed

with an overhead mixer while samples were drawn. The chemical dosages were added using

a micropipette, then mixed for three minutes (Figure 2), followed by a 30-minute setting

period. Supernatant was pipetted off (Figure 3) and placed in bottles (Figure 4). The

samples were refrigerated overnight for TSS, COD, and BOD5 testing the following day.

Figure 1 – Four-Place Gang Stirrer




Figure 2 – Samples Mixed for Three Minutes

Figure 3 – Removing Settled Sample by Pipette Figure 4 – Placing Settled Sample in Storage Bottles




5 JAR TEST DOSAGES

Coagulation using aluminum or iron salts provides for coagulation of colloidal solids that will

all them to settle in the primary treatment process. Jar testing was completed using ferric

chloride, sodium aluminate and aluminum chlorohydrate (ACH). Each chemical was tested at

four separate dosages to determine the additional TSS, COD and BOD5 removals that may be

possible in primary treatment. The solution strength and specific gravity of each chemical

was obtained from the Material Safety Data Sheet (MSDS) for each chemical.

5.1 FERRIC CHLORIDE

Ferric chloride, also called iron chloride, is a chemical compound with a chemical formula of

FeCl3. It is available at a solution strength of 40% FeCl3. When dissolved in water, ferric

chloride undergoes hydrolysis and gives off heat in an exothermic reaction. It is produced

industrially by the reaction of dry chlorine with scrap iron at 500 to 700 degrees Celsius.

Ferric chloride and is effective over a wider pH range of 4–11 than alum. The ferric hydroxide

floc is also heavier than alum floc, improving its settling characteristics, and reducing the size

of the clarifier

In water and wastewater treatment operations, ferric chloride is used as a coagulant or

flocculent, for odor control, phosphorus removal and hydrogen sulfide minimization.

When ferric chloride is added to wastewater the following reaction takes place:

2�� + 3�(��)� ⇄ 2�� + 3�� + 6��

The above equation shows the hydroxyl (OH-) group being provided by alkalinity available in

the wastewater. Pasco feeds lime to supplement alkalinity loss within the process. Lime will

need to be added to provide the alkalinity used in the reaction with ferric chloride. If lime is

added to supplement the natural alkalinity of the wastewater, the following reaction can be

assumed to occur:

2�� + 3�(��)� ⇄ 2��(��)� + 3��

This equates to 0.92-mg/L of alkalinity used for every mg/L of FeCl3 fed. Jar testing was

performed at four doses as shown in Table 1.




Table 1

City of Pasco WWTP

Ferric Chloride Jar Test Dosage Calculations

Ferric Chloride

Chemical Ferric Chloride Ferric Chloride Ferric Chloride Ferric Chloride

% Solution 40% 40% 40% 40%

Specific Gravity 1.42 1.42 1.42 1.42

g/l Solution 568 568 568 568

Dose (mg/L) 5 10 15 20

ml/L 0.0088 0.0176 0.0264 0.0352

5.2 SODIUM ALUMINATE

Aluminum sulfate (alum) is a chemical commonly used in coagulation in water and

wastewater treatment plants. Alum uses 0.49-mg/L of alkalinity for every mg/L of alum fed.

Another chemical, sodium aluminate was developed to provide the coagulation capability of

alum with minimal effect on alkalinity. When sodium aluminate is added to wastewater the

following reaction takes place:

�� + �(��)� + �� ⇄ ��(��)�(�) + 3��(�) + ��

Jar testing was performed at four doses as shown in Table 2.

5.3 ACH

Aluminum chlorohydrate (ACH) is another form of aluminum coagulant that is used in water

and wastewater treatment. Advantages of ACH include the following:

• low levels of residual aluminium in the treated water can be achieved, typically 0.01-

0.05 mg/L,

• PACl and ACH work extremely well at low raw water temperatures. Flocs formed

from alum at low temperatures settle very slowly, whereas flocs formed from ACH

tend to settle equally well at low and at normal water temperatures,

Table 2

City of Pasco WWTP

Sodium Aluminate Jar Test Dosage Calculations




Sodium Aluminate

Chemical Sodium Aluminate Sodium Aluminate Sodium Aluminate Sodium Aluminate

% Solution 37% 37% 37% 37%


g/l Solution 518 518 518 518

Dose (mg/L) 10 15 20 25

ml/L 0.0193 0.0290 0.0386 0.0483

• less sludge is produced compared to alum at an equivalent dose,

• lower doses are required to give equivalent results to alum.

• the increase in chloride in the treated water is much lower than the sulphate increase

from alum, resulting in lower overall increases in the TDS of the treated water.

ACH is described as a pre-hydrolyzed coagulant. When added to water, the following reaction

takes place:

��(��)�� → ��(��)��

+ �� + �� → 2��(��)� + �� + ��

Note that only one mole of hydrogen ions is produced, reflecting the hydroxylated nature of

this compound. Jar testing was performed at four doses as shown in Table 3.

Table 3

City of Pasco WWTP

ACH Jar Test Dosage Calculations

ACH

Chemical ACH ACH ACH ACH

% Solution 50% 50% 50% 50%


g/l Solution 670 670 670 670

Dose (mg/L) 5.0 10.0 15.0 20.0

ml/L 0.0075 0.0149 0.0224 0.0299




6 JAR TEST RESULTS

Samples were taken following the 30-minute settling period. The samples were stored

overnight in the lab refrigerator and TSS and COD tests were run on each sample the next

day. A BOD5 test was then run on the raw influent, settled influent and each of the jar test

samples. The BOD5/COD ratio 0f 0.368 was then calculated on the settled influent sample.

The jar test results are summarized in Table 4.

Table 4

Jar Test Results

Sample

Dosage TSS COD BOD

(mg/l) (mg/l) %

Removal (mg/l)

%

Removal (mg/l)

%

Removal

Raw Influent 0 401 - 681 - 243 -

Settled Influent

(30min) 0 176 56.1% 462 32.2% 170 30.0%

Ferric Chloride

5 49 87.8% 344 49.5% 128 47.3%

10 41 89.8% 325 52.3% 127 47.7%

15 19 95.3% 317 53.5% 120 50.6%

20 28 93.0% 299 56.1% 114 53.1%

Sodium Aluminate

10 88 78.1% 389 42.9% 154 36.6%

15 78 80.5% 373 45.2% 135 44.4%

20 77 80.8% 371 45.5% 141 42.0%

25 80 80.0% 366 46.3% 137 43.6%

ACH

5 82 79.6% 384 43.6% 134 44.9%

10 66 83.5% 367 46.1% 131 46.1%

15 54 86.5% 338 50.4% 136 44.0%

20 24 94.0% 274 59.8% 112 53.9%

7 CHEMICAL EVALUATION

There are a number of factors that must be considered when selecting a chemical for CEPT.

This include:




• Cost and reliability of supply.

• Sludge considerations, both volume and characteristics.

• Compatibility with other upstream or downstream treatment processes.

• Environmental effects.

• Labor and equipment requirements for storage, feeding and handling.

Each of these variables are discussed in the following sections.

7.1 ESTIMATED CHEMICAL COSTS

Chemical costs were obtained from Northstar Chemical. Northstar Chemical currently

provides chemical to the City of Pasco and is willing to provide a storage tank for the

chemical with a contract. The chemical pump feed skid and associated piping will need to be

provided by the city. The chemicals and their costs provided by Northstar Chemical are

summarized in Table 5.

Table 5

Northstar Chemical Pricing

Solution

Strength

Minimum Order

(Pounds) Cost/Pound Cost/Gallon

Aluminum Chlorohydrate 50% 48,000 $0.3275 $3.66

Ferric Chloride 40% 48,000 $0.2375 $2.87

Sodium Aluminate 39% 48,000 $0.2775 $3.24

7.2 SLUDGE PRODUCTION

One of the issues with chemical precipitation is that the volume of sludge is increased and the

resulting sludge will change the dewatering characteristics. First, the increased removal in

the primaries will increase the primary sludge production, but there will be a corresponding

decrease in secondary sludge production. This will benefit the digestion process as primary

solids are easier to digest. Second, each of the chemicals produce a metal hydroxide that adds

to the sludge volume. The aluminum hydroxides will not produce any benefit in the

anaerobic digestion process and has proven to affect the dewatering process with lowering

the cake solids that can be produced. The ferrous hydroxides will react with sulfur

compounds resulting in less H2S in the waste stream and will lower the H2S in the biogas




produced in the digester, lowering the corrosive nature of the biogas. In addition, ferrous

hydroxides have proved to improve solids dewatering. The quantity of chemical sludge is

dependent on the dose that is fed. The unity quantity of chemical sludge produced for each

chemical is summarized in Table 6.

Table 6

Chemical Sludge Production

Chemical mg/L Sludge per

mg/L Dose

Aluminum Chlorohydrate 1.226

Ferric Chloride 0.659

Sodium Aluminate 1.310

7.3 COMPATIBILITY WITH OTHER PROCESSES

The options that were tested with an aluminum based and iron based chemicals. The

advantages and disadvantages of each are summarized in Table 7.

7.4 ENVIRONMENTAL EFFECTS

Both chemicals will reduce the concentration of phosphorus in the process. This will lower

the concentration of phosphorus in the plant effluent, minimizing the potential for algae

growth downstream in the Columbia River.

The ferric chloride may show an improvement in the air quality as it will tie up the H2S in the

wastewater lowering the odor potential of the primary clarifiers. In addition, the H2S in the

anaerobic digestion process will be die up chemically, improving the biogas quality.

Table 7

Chemical Compatibility with Other Processes

Aluminum Salts Iron Salts

Advantages Advantages

1. Lowers BOD5 and TSS lowering loading on

downstream processes.

2. Removes phosphorus

3. Easier to handle than iron salts

1. Lowers BOD5 and TSS lowering loading on

downstream processes.

2. Removes phosphorus

3. Reacts with H2S lowering odor potential in

primary clarifiers




4. Improves digester gas quality.

5. Improves solids dewatering

Disadvantages Disadvantages

1. Produces chemical sludge

2. Hinders biosolids dewatering

1. Difficult to handle

7.5 LABOR AND EQUIPMENT REQUIREMENTS

Each of the chemical will require a bulk chemical tank and chemical feed pumps and

associated piping. The ferric chloride is a highly corrosive chemical and must be handled

with care. It will stain any concrete black that it comes in contact with. ACH and sodium

aluminate are not as corrosive and will be easier to handle by the operations staff.

7.6 DOSAGES AND OPERATING COST

The jar tests have demonstrated the removals that can be obtained at various dosages for

each chemical. Note that this testing was done on a single sample and a low volume. Full

scale results will most likely be different, but the jar testing provides a place to start and to

compare the chemicals.

The goal of CEPT will be to get a minimum of 50% BOD5 removal so loadings to the

downstream activated sludge process can be reduced resulting in increased capacity for the

treatment plant. TSS removal will also improve downstream process performance and will

lower the volume of waste activated sludge produced.

7.6.1 Chemical Costs

The jar testing showed that ferric chloride can obtain the desired 50% BOD5 removal at a

dose of 15-mg/L. Sodium aluminate was not able to get 50% removal at doses up to 25-

mg/L, so a dose of 40-mg/L will be assumed for this analysis. ACH got better than 50% BOD5

removal at 20-mg/L. The estimated chemical costs are summarized in Table 8.

Table 8

Estimated Chemical Requirements and Operating Cost

Chemical Dose Solution

Strength

Specific

Gravity

lbs/day

Required Cost/lbs Cost/day

Ferric Chloride 15 40% 1.42 1877 0.2375 $445.67

Ferric Chloride 20 40% 1.42 2502 0.2375 $594.23

ACH 20 50% 1.34 2002 0.3275 $655.52

Sodium Aluminate 25 39% 1.40 3208 0.2775 $890.13




7.6.2 Alkalinity Replacement Cost

The treatment plant uses hydrated lime to supplement the loss alkalinity in the wastewater

to maintain effluent pH. Hydrated lime is supplied as calcium hydroxide which comes in a

white power that does not require slaking. When hydrated, lime is added to water, the

following reaction occurs producing alkalinity:

�(��)� + �� → �� + ��

For every pound of hydrated lime that is added, an estimated 0.9-pounds of alkalinity is

produced depending on the quality of the hydrated lime. The estimated cost for lime are

summarized in Table 9. The cost of hydrated lime, including delivery, was assumed to be

$300/ton. It was also assumed that the lime produced 0.9-pounds of alkalinity per pound of

lime fed.

Table 9

Estimated Alkalinity Replacement Cost

Chemical Dose

(mg/L

Alkalinity

Used

(mg/mg)

Lime to

Alkalinity

Ratio

Alkalinity

Produced

(lbs./day)

Lime

Cost

($/ton)

Lime

Cost

($/day)

Ferric Chloride 15 0.92 90% 767 $300 $115.09

Ferric Chloride 20 0.92 90% 1023 $300 $153.46

ACH 20 0.30 90% 334 $300 $50.04

Sodium Aluminate 25 0.00 90% 0 $300 $0.00

7.6.3 Solids Handling Cost

The addition of the chemical produces additional chemical sludges. This will result in

additional solids handling costs to process and dispose of the additional solids. For this

analysis, it was assumed that the solids handling cost is $200/dry ton. The estimated cost for

the additional solids handling are summarized in Table 10.

Table 10

Estimated Chemical Sludge Handling Cost




Chemical Dose

Unit

Sludge

Production

Lbs

Sludge

Produced

Solids

Handling

Cost

Cost/day Cost/year

Ferric Chloride 15 0.659 495 $200 $49.46 $18,055

Ferric Chloride 20 0.659 660 $200 $65.95 $24,073

ACH 20 1.226 1227 $200 $122.70 $44,785

Sodium Aluminate 25 1.31 1639 $200 $163.88 $59,817

7.6.4 Estimated O&M Cost

The addition of the CEPT process will require additional operations and maintenance by the

plant staff to handle, feed and monitor the process. In addition, the feed equipment will

require additional maintenance. O&M costs were assumed equal for each of the chemicals.

Table 11

Estimated O&M Cost

O&M Group Units Estimate

Operations (hours/week) 5.0

Maintenance (hours/week) 1.0

Laboratory (hours/week) 2.5

Loaded $/hour $60.00

Supplies $/year $2,500

Daily Cost $/day $79.71

Annual Cost $/year $29,093

8 RECOMMENDATION

The preferred chemical should be the chemical that produces the most benefit at the least

cost. The costs have been estimated and are summarized in Table 12. This shows that the

lowest cost chemical will be ferric chloride at a dose of 20-mg/L. An analysis of the

advantages and disadvantage for each chemical was summarized in Table 7. This also

showed that ferric chloride had the most advantages throughout the treatment process.

These advantages should overcome the additional handling issues related to the chemical.




Based on the process advantages and cost, ferric chloride is recommended for use in CEPT

treatment.

Table 12

Estimated Total CEPT Treatment Cost

Chemical Dose Chemical

Cost

Lime

Cost

Solids

Handling

Cost

Labor

Cost

Total

Daily

Cost

Annual

Cost

Ferric Chloride 15 $445.67 $115.09 $49.46 $79.71 $689.93 $251,825

Ferric Chloride 20 $594.23 $153.46 $65.95 $79.71 $893.34 $326,069

ACH 20 $655.52 $50.04 $122.70 $79.71 $907.97 $331,409

Sodium Aluminate 25 $890.13 $- $163.88 $79.71 $1,133.72 $413,809

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