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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.
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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.
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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
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Figure 2 – Samples Mixed for Three Minutes
Figure 3 – Removing Settled Sample by Pipette Figure 4 – Placing Settled Sample in Storage Bottles
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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.
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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
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Sodium Aluminate
Chemical Sodium Aluminate Sodium Aluminate Sodium Aluminate Sodium Aluminate
% Solution 37% 37% 37% 37%
Specific Gravity 1.40 1.40 1.40 1.40
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%
Specific Gravity 1.34 1.34 1.34 1.34
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
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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:
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• 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
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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
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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
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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
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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.
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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