THE EFFECT OF A BAN ON PHOSPHATES INHOUSEHOLD DETERGENTS ON THE TREATMENT OF

MUNICIPAL WASTEWATER

A report prepared for

THE SOAP AND DETERGENT ASSOCIATION

by

GANNETT FLEMING ENVIRONMENTAL ENGINEERS, INC.

in Asaociation with

John B. Nesbitt

Professor Emeritus of Civil Engineering

The Pennsylvania State University

CONTENTS

Page

Tables iii

Figures v

1. Introduction 1

2. Concentration of Phosphates in Wastewaters 1

3. Effect of Phosphate Reduction on Phosphate Removal Processes 23.1 Land Treatment 23.2 Biological Phosphorus Removal 33.3 Chemical Precipitation with Lime 33.4 Chemical Precipitation with Aluminum and Iron 3

4. Effect of Phosphate Reduction of Sludge Production and Handling 134.1 Sludge Production 134.2 Sludge Handling 14

5. Summary 15

References 16

Appendix A—i

A—i. Summary A—2A—i.i Back River, Baltimore — Case Study No. 1 A—2A—1.2 Lower Potomac, Fairfax County — Case Study No. 2 A—3A—1.3 Arlington — Case Study No. 3 A—S

A—2. Case Study No. 1: Back River Waste Water Treatment Plant A—6A—2.1 Description of Treatment Processes A—6A-2.2 Results of Back River Data Analysis A—8

A—3. Case Study No. 2: Lower Potomac Water Polluction Control Plant A—17A—3.1 Description of Treatment Processes A—17A—3.2 Results of Lower Potomac Data Analysis A—19

A—4. Case Study No. 3: Water Pollution Control Plant, Arlington,Virginia A30

A—4.1 Description of Treatment Processes A—30A—4.2 Results of Arlington Data Analysis A—31

11

TABLES

Page

Table 1. Filter Alum Doses Required to Achieve Indicated Soluble 5Phosphate Residual. Initial pH 7.0.

Table 2. Filter Alum Doses Required to Achieve Indicated Soluble 5Phosphate Residual. Initial pH 7.5.

Table 3. Ferric Chloride Doses Required to Achieve Indicated 6Soluble Phosphate Residual. Initial p14 70.

Table 4. Ferric Chloride Doses Required to Achieve Indicated 6Soluble Phosphate Residuals. Initial pH 7.5.

Table S. Reduction in Chemical Doses Required to Achieve 7Indicated Soluble Phosphate Residual. Initial p11 7.0.Initial Soluble Phosphorus Reduced from 5 to 3 mg I’lL bya Phosphate Detergent Ban.

Table 6. Reduction in Chemical Doses Required to Achieve mdi— 7cated Soluble Phosphate Residual. Initial pH 7.5. Initial Soluble Phosphorus Reduced from S to 3 mg P/L by aPhosphate Detergent Ban.

Table 7. Reduction in Chemical Doses Required to Achieve mdi— 8cated Soluble Phosphate Residual. Initial p14 7.0. Initial Soluble Phosphorus Reduced from 4 to 3 mg P/L by aPhosphate Detergent Ban.

Table 8. Reduction in Chemical Doses Required to Achieve Indi— 8cated Soluble Phosphate Residual. Initial pH 7.5. Initial Soluble Phosphate Reduced from 4 to 3 mg PIL by aPhosphate Detergent Ban.

Table 9. Percentage Reduction in Chemical Doses Required to 10Achieve Indicated Soluble Phosphate Residual. InitialpH 7.0. Initial Soluble Phosphorus Reduced from 5 to 3mg PIL by a Phosphate Detergent Ban.

Table 10. Percentage Reduction in Chemical Doses Required to 10Achieve Indicated Soluble Phosphate Residual. Initialp14 7.5. Initial Soluble Phosphate Reduced from 5 to 3mg I’lL by a Phosphate Detergent Ban.

Table 11. Percentage Reduction in Chemical Doses Required to 11Achieve Indicated Soluble Phosphate Residual. InitialpH 7.0. Initial Soluble Phosphorus Reduced from 4 to .3mg P/L by a Phosphate Detergent Ban.

Table 12. Reduction in Chemical Doses Required to Achieve Indi— 11cated Soluble Phosphate Residual. Initial pH 7.5. Ini—

iii

tial Soluble Phosphate Reduced from 4 to 3 mg P/L by aPhosphate Detergent Ban.

Table 13. Typical Wastewater Characteristics at Bay Area Treatment 12Plants.

Table 14. Ferric Chloride Savings for Indicated Phosphorus Resi— 12dual. Alkalinity 150 mg CaCO3/L, pH 7.

Table A—i. Sludge Densities Before and After WPL Addition, Back A—9R. WWTP

Table A—2. Comparison of Elutriation Performance Before and After A—8Polymer Dose Reduction, Back R. WWTP.

Table A—3. Sludge Production Before and After WPL Addition, Back A—liR. WWTP.

Table A—4. Gravity Thickener and Elutriation Performance Before A—13and After WPL Addition, Back R. WWTP.

Table A-5. EIMCO Vacuum Filter Performance Before and After WPL A—i4Addition, Back R. WWTP.

Table A—6. Comparison of Dewatering Performance Before and After A—15Elutriation Polymer Dose Reduction, Back R. WWTP.

Table A—7 Primary Sludge Density and Gravity Thickener Perform— A—20ance Before and After Ferric Chloride PrecipitantAddition, Lower Potomac WPCP

Table A—S. Flotation Thickener Performance at Lower Potomac Under A—2lFour Operating Conditions.

Table A—S. Sludge Production and Vacuum Filter Operation at Lower A—22Potomac Under Four Operating Conditions.

Table A—10. Comparison of Vacuum Filter Performance for Combined A—32and Separate Sludges, Arlington WPCP.

iv

A

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~b~d

THE EFFECT OF A BAN ON PHOSPHATES INHOUSEHOLD DETERGENTS ON THE TREATMENT OF

MUNICIPAL WASTEWATER

1. Introduction

Banning of phosphates in household detergents has beensuggested as a means of reducing wastewater treatment costs int.hree ways:

1. Chemical requirements to precipitatephosphorus would be reduced,

2. Sludge quantities would be decreased, and3. Sludge handling costs would be reduced.

These points appear to be very straightforward; decreasinginfluent phosphorus by some proportion might be expected todecrease treatment costs by that same proportion. Carefulanalysis reveals that this simple viewpoint probably overstatespotential savings accruing from a ban of phosphates in householddetergents by a substantial amount. The simple analysis breaksdown for several reasons:

1. Phosphorus precipitation chemical dosagesdepend on wastewater characteristicsother than phosphorus concentration, aswell as on effluent limitations.

2. Chemical sludge avoided by removing asmall amount of phosphorus from treatmentplant influent may be less thanprecipitating chemical savings.

3. Phosphorus removal sludges are generallynot difficult to dewater.

This report explores several aspects of wastewater phosphorusremoval as they relate to a hypothetical reduction of influentphosphorus concentration achieved through a household detergentphosphate ban.

2. c2flcentration of Phosphates in Wastewaters

Laundry products became significant contributors of phosphates to municipal wastewaters following World War II as synthetic detergents were introduced to the American market. In 1966Nesbitt (1) surveyed the literature and concluded that the concentration of phosphates in municipal wastewater effluentsaveraged about 8 mg P/L. This amount included phosphates fromsynthetic detergents as well as those from human sources. Studies reported by Metcalf and Eddy (2) and Tofflemire and Hetling(3) showed that phosphorus concentration continued at this leveluntil the mid—1970s, when reformulation of synthetic detergentsdecreased the concentration of phosphates in municipal waste—

1

waters. Berthouex (4) presented data showinq that in Wisconsinprior to the introduction of a hart on phosphates in householddet.erqents, phosphate concentration in municipal wastewatera haddecreased from 7 mq P/L in 1976 to 5 mq P/L in 1978. From asurvey of phosphorus 1o~ds to the Chesapeake Bay, Lunq (5) concluded that in 1984 the averaqe pho.~phorus concentration ~twastewater treatment pla:its in the Bay area was:

Averaqe ConcentrationWastewater (mgp/L) ____

Raw 6.5Settled 5.9 to 6.2Effluent 5.0

Recent data presented by Berthouex (4) showed that similarbans on phosphates in household laundry deterqents imposed byWisconsin and Michiqan resulted in influent phosphorus loadreduction of 0.3 kq per capita per year. Such a reduction wouldconstitute about 23~ of an influent concentration of 6.5 mq P/L.The reduction reported by Berthouex was determined from a sophis—t.icat.ed statistical analysis of data from operatiniq treatmentplants. Althouqh the analysis showed the overall effect of theban was a reduction of phosphorus concentration at some plants,t.here was no chanqe or phosphorus concentration actually ii—creased at other plant-s. These incongruous results indicate therelatively small impact a ban on phosphates in household deterqents exerts on municipal wastewater. In many cases in banareas, the effect of the ban was lost amonq the other factorsinfluencing the concentration of phosphorus in the wasbewater.

3. Effect of_Phosphate Reduc t ion on the Pho.sph ate moval Processes

Discussion of the effect of a ban on phosphates in householddetergents on treatment processes must consider the particulart.reatment process used. Althouqh there are many processes thatwill remove phosphorus from wast.ewater, presently any one offour processes have generally been adopted as effective for suchservice:

1. Land treatment2. Biological treatment3. Chemical precipitation with lime4. Chemical precipitatioi: with salts of aluminum

or iron.

3.1 Land Treatment

Land treatment by any of the several application methodseffectively prevents all phosphorus in the wastewater from ewt.erinig surface waters. A reduction in wastewater phosphoru~

concentration would have absolutely no effect on the constructionor operating costs of a land treatment system, nor on its perfor—mance.

32 Biological Phosphorus Removal

Biological phosphorus (BPR) removal began to receive consideration in the U.S. during the early 1970’s. Process development has progressed to the point where plants can be designed andoperated to achieve effluent phosphorus levels as low as 1 mg P/Lwith little or no chemical use. Lamb (7) has expressed optimismfor the eventual widespread use of the process. Other commentsmade at the September 1984 Workshop on Phosphorus Removal sponsored by the Soap and Detergent Association indicated a steadyimprovement in basic understanding of the mechanisms and requirements of the process. BPR is currently employed ata number of plants throughtout the United States. Again, thereduction in wastewater phosphorus concentration resulting from aban on phosphates in household detergents would have no effect atall on the construction or operating cost of a BPR facility, norwould it affect performance.

3..3 Chemical Precipitation with Lime

Phosphorus can be precipitated with lime either within theprimary treatment units at a wastewater treatment plant or intertiary units constructed for that purpose. Construction costswould be the same with or without a ban in phosphorus in household detergents, since the quantity of chemical required toprecipitate phosphorus is dependent on the alkalinity of thewastewater and is entirely independent of the water’s phosphorusconcentration. Jenkins and James (9) presented data showing thatwastewaters from areas using all non—phosphate detergents wouldhave the same alkalinity as the wastewaters from areas usingphosphate—based detergents. Therefore, a ban on phosphates inhousehold detergents also would have no effect on the operatingcosts for plants using lime precipitation for phosphorus removal.Although lime precipitation is a proven process, it is not popular currently, probably because of calcium carbonate scalingproblems.

3.4 Chemical Precipitation with Aluminum and Iron

Nesbitt (1) concluded in 1966 that chemical precipitationwith salts of the metals aluminum and iron would initially be themost cost-effective method for precipitating phosphorus frommunicipal wastewaters. 5everal salts of these two metals can beused. Iron sulfate available in waste pickle liquor from themetal processing industry is used at many large treatment plants.?4et~l salts may be added at several points in the treatmentprocess: before the primary clarifier, in the aeration tanks of

3

4

an activated sludge punt, before the secondary clarifier, in atertiary treatment facility • or at two or more of these points.The most frequently used points of addition are in the activatedsludge aeration tank or oust before the final clarifier. Thesepoints require capital expenditures only for cbemicaZ feed equipment as long as the sludge handling and treatment facilities areadequate.

With salts of either metal, the metal dose r.qu4$~4’)~j?. afunction of the quantity of phosphorus present at the: j,0ii~~ ofaddition. Current wastewater treatment process design utilizesmetal to phosphorus ratios suggested by EPA (6) to size chemicalfeed equipment and estimate sludge production. However, metalsalt requirements depend on more than the quantity of phosphOfltsto be removed. Additional determinants of dosage are alkalinity,which competes with phosphorus for reaction with the metal, andpH, which determines the solubility of various precipitation products. Jenkins and James (9) have developed a computer—basedmodel to predict precipitant dosages. based on chemical equilibria among chemical compounds. The model has been tested onchemical dose data from treatment plants in various parts of theU.S. and found to be reasonably accurate • The model was used tocalculate the chemical doses required to precipitate phosphorusfrom wastewaters having initial soluble phosphorus concentrations.of 5. 4 and 3 mg P/I. (Tables 2.2.3 and 4). Chemical savings thatwould be realized by reduction in phosphorus concentration at thepoint of chemical addition from 5 to 3 mg P/L. and 4 to3mg P/I..are illustrated on Tables 5, 6. 7 and 8. Chemical- doses andreductions have been calculated for two pH and three ..~lkalinityvalues and for various effluent phosphorus concentrations using~both aluminum sulfate (most commonly applied as °filter aJuC)and ferric chloride as precipitating chemicals. The value of 5mg P/I. was chosen as a typical concentration in treated effluents(and therefore in the effluent end of the activated sludge tanks.the most popular point for chemical additions). The pH alues of7.0 and 7.5 and the 100. 200, and 300 mg/I. alkalinities cover therange of these parameters usually found in the aeration basins ofactivated sludge planti. The 2 mg P/I.. reduction in phosphorusconcentration (5 to 3 mg P/I.) represents the largest reductionthat might be expected to result from a ban on phoiphates inhousehold detergents. The I mg P/I. reduction (4 to 3 mg P/I.)represents a possible minimum reduction in phosphorus concentrations resulting from such a ban.

From the data presented on Tables 5 through 8 it isapparent that:

1. When the concentration of soluole phosphorus at thepoint of chemical addition is reduced from 5 to 3 mgP/t. savings in precipitating chemical (either filterslum or ferric bhloride) vary from about 14 pounds ofchemical per pound of phosphorus down to a negligibleamount. For a reduction from 4 to 3 mg P/I. thechemical savings are in generml slightly lower. This

4

Table 1. Filter Alum Doses Required to Achieve Indicated SolublePhosphate Residual. Initial pH 70.

mg Filter Alum/L Required

Initial Soluble P= Initial Soluble P Initial Soluble PSoluble 5 mg P/L 4 mg P/L 3 mg P/LPhosphate Initial Alkalinity Initial.Alkaliriity Initial AlkalinityResidual (sng CaC0~/L) (mq CaC0~/L) (mq CaC0~/L)

mq PIL* 100 200 300 100 200 300 100 200 300

1.5 50 56 65 35 37 55 23 28 471.1 58 67 92 42 57 82 33 51 770.5 81 135 180 75 127 180 65 122 1700.1 150 280 —— 150 285 —— 155 285 ——

Table 2. Filter Alum Doses Required to Achieve Indicated SolublePhosphate Residual. Initial pH 7.5.

rag Filter AlurnJL Required

Initial Soluble P= Initial Soluble P= Initial Soluble PSoluble 5 rag P/L 4 rag P/L 3 rag P/LPhosphate Initial Alkalinity Initial Alkalinity Initial AlkalinityResidual (rag CaCO~/L) (rag CaC0~/L) (rag CaC0~/L)

rag P/L* 100 200 300 100 200 300 100 200 300

1.5 64 100 132 51 78 110 35 75 1061.1 76 120 157 64 103 140 54 96 1400.5 107 175 225 90 160 235 90 160 2350.1 180 300 —— 175 300 —— 170 300 ——

* 1.5, 0.5 and 0.1 rag P/I.. soluble phosphate residuals are required to achieve2.O~ 1.0 and 0.2 rag P/L total phosphate residuals respectively.

Table 3. Ferric Chloride Doses Required to Achieve Indicated SolublePhosphate Residual. Initial pH 7.0.

mg Ferric Chloride/L Required

Initial Soluble P Initial Soluble P Initial Soluble PSoluble 5 mg P/L 4 mg P/L 3 ~g P/LPhosphate Initial Alkalinity Initial Alkalinity Initial AlkalinityResidual (sq CaC0~/L) (sq CaC0~/L) (sq CaC0~/L)!2~L~ 100 200 300 100 200 300 100 200 300

1.5 22 30 36 17 25 30 12 19 281.1 28 38 49 25 38 49 20 29 480.5 46 58 102 44 73 107 41 73 9901 93 160 —— 87 151 —— 87 154 ——

Table 4. Ferric Chloride Doses Required to Achieve Indicated SolublePhosphate Residuals. Initial pH 7.5.

~q Ferric Chloride/L Required

Initial Soluble P= Initial Soluble P= Initial 5oluble Psoluble 5 sq P/L 4 sg P/L 3 sq P/LPhosphate Initial Alkalinity Initial Alkalinity Initial AlkalinityResidual (sq CaC0~/L) (sq CaC0,~/L) (sq CaC0~/L)sq P/L* 100 200 300 100 200 .300 100 200 300

1.5 37 54 74 29 46 70 23 44 601.1 44 65 190 38 61 90 28 57 810.5 59 93 136 58 102 136 52 94 1320.1 84 151 —— 93 174 —— 90 174 ——

* 1.5, 0.5 and 0.1 sg P/L soluble phosphate residuals are required to achieve2.0, 1.0 and 0.2 mg P/L total phosphate residuals respectively.

Table 5. Reduction in Chemical Doses Required to Achieve Indicated SolublePhosphate Residual. Initial pH 7.0. Initial Soluble PhosphorusReduced from 5 to 3 mg P/L.

Reduction in Chemical mg/mç~ P or #/# P

Soluble Precipitant: Filter Alum Precipitant Ferric CloridePhosphate Initial Alkalinity Initial AlkalinityResidual ~CaCO~/L) ____~~_c~cP:iLj~ ——

100 200 300 100 200 300

1.5 14 14 9 10 11 81.1 13 8 8 8 9 10.5 8 7 5 5 0 30.1 0 0 6 (6)

Table 6. Reduction in Chemical Doses Rec~uired to Achieve Indicated SolublePhosphate Residual. Initial pH 7.5. Initial Soluble PhosphorusReduced from 5 to 3 mg P/L.

Reduction in Chemical mg/w*q P or #/# P

Soluble Precipitant: Filter Alum Precipitant: Ferric CioridePhosphate Iritial Alkalinity Initial AlkalinityResidual ~~C0~/L)_!s1_fLi~L~ 122. ~22. ~22.

1.5 15 13 13 14 10 141.1 11 12 8.5 16 8 90.5 9 8 0 7 0 00.1 5 0 0 0

~ 1.5, 0.5, and 0.1 ~q P/I. soluble phosphate residuals are required toachieve 2.0, 1.0. and 0.2 m~ P/L total phosphate residuals respectively

Table 7. Reduction in Chemical Doses Required to Achieve IndicatedSoluble Phosphate Residual. Initial pH 7.0. InitialSoluble Phosphorus Reduced froM 4 to 3 r~ P/L.

Reduction in Che,~ical iiiq/?~g P or #/# P

Table 8. Reduction in CheMical Doses Required to Achieve IndicatedSoluble Phosphate Residual. Initial p11 7.5. InitialSoluble Phosphate Reduced froM 4 to .3 ~g P/L.

5

Reduction. in CheMical Mq/~ P or #/# P

2

3 0

* 1.5, 0.5 and 0.1 ~q Soluble P/L resIduals are required to achieve 2.0,1.0 and 0.2 ~g total P/L residuals respectively.

Soluble Precipitant: Filter AluM Precipitant: Ferric CloridePhosphate Initial Alkalinity Initial AlkalinityResidual (~g~aCO~L)

~q ELi~L

1.5 12 9 8 5 6 21.1 9 6 5 5 9 10.5 10 5 10 3 0 80.1 0 0 —- 0 0 —

5oluble Precipitant: Filter AluM Precipitant: Ferric CloridePhosphate Initial Alkalinity . Initial AlkalinityResidual (Mg_CaCO~. —~ (~_CaCO~~jL)

Mg P)L* 100 200 300 10’ 200 300

1.51.10.50.1

1610

7

37

100

400

610

648

1094

4

range of results can be expected to define the possible impact of a ban on phosphates in householddetergents.

2. Chemical savings are affected dramatically by therequired effluent phosphorus concentration for allconditions of initial pH and al’calinity.

3. An increase in alkalinity at the point of chemicaladdition from 100 to 300 mg Pit reduces the chemicalsavings. The reduction is most noticeable at requiredeffluent phosphorus concentrations of 0.5 and 0.1.ag Pit.

4. An increase in pH at the point of chemical additionfrom 7.0 to 7.5 increases the chemical savings, butthen changes are minor compared to those realizedfrom changes in effluent phosphorus concentration andinitial alkalinity.

Data from Tables I through 8 have been used to calculate thepercentage of savings of precipitating chemical (filter alum andferric chloride) that the ban on phosphates in household detergents would generate. The percentages are based on the doserequired to reduce soluble phosphate from either 5 or 4 mg Pit tothe residual specified. The results shown in Tables 9 and 10represent a 2 mg Pit reduction in initial phosphorus concentration (5 to 3 mg Pit) but are exprôssed as percentage reductionper mg Pit reduced at the point of chemical addition. The results shown in Tables 11. and 1.2 represent a 1. mg ~it reduction ininitial phosphorus concentration (4 to 3 mg Pit) again expressedas percentage reduction per mg Pit reduced at the point of chemical addition. Again, results for initial pH and alkalinityvalues of 7.0. 7.5 and 100. 200. 300 mg CaCO3it respectively arelisted. The percentage reductions are similar for both sets oftables. These reductions are greatest (9 to 27k for the 5 to 3mg Pit change .in influent concentration and 4 to 34k for the 4 to3. mg Pit change) when the required effluent soluble phosphorusconcentration is 1.5 mg Pit and become very small or negligible(for both S to 3 and 4 to 3 mg Pit changes in influent solublephosphorus concentrations) at effluent soluble phosphorus concentrations of 0.1 mg Pit.

A typical Chesapeake Bay area wastewater is postulated tohave the following characteristics:

Total influent P: S mg PitSoluble P availablefor precipitation 4.2 mg PitAlkalinity: 150 mg CaCO3itpH: 7

.9

Table 9~ Percentaqe Reduction in Chemical Doses Required to AchieveIndicated Soluble PhosDhate Residual. Initial pH 7.0. InitialSoluble Phosphorus Reduced from 5 to 3 mg P/L.

Reduction in Chemical Dose*(Perceiit of Dose f~>r Initial Concentration 5 ~g P/L)

Soluble Precipitant: Filter Alum Precipitant: Ferric CloridePhosphate Initial Alkalinity Initial AlkalinityResidual (m~a_2~cQ3LL) ____ ç~co~/L)

~QP. 300

1.5 27 25 14 23 19 121.1 22 12 8 22 12 20.5 10 5 3 7 0 00.1 0 0 —— 3 (2) —~

Table 10. Percentaqe Reduction in Chemical Doses Required to AchieveIndicated Soluble Phosphate Residual. Initial pH 7.5. InitialSoluble Phosphate Reduced from 5 to ~ mg P/L.

Reduction in Chemical Dose*<Percent of Dose for Initial Concentration = 5 mg PIL)

Soluble Precipitant: Filter Alum Precipitant: Ferric CioridePhosphate Initial Alkalinity Thitial AlkalinityResidual ~CacQ3/L) _~caco~L) —~

~22 300 300

1.5 23 13 10 18 9 91.1 14 10 5 18 7 50.5 8 4 0 6 0 00.1 3 0 0 0

* Results are percentaqe reduction in chemical dose per / mg P/L reduced atthe point of chemical addition.

Table 11. Percentage Reduction in Chemical Doses Required to P~chieveIndicated Soluble Phosphate Residual. Initial pH 7.0. InitialSoluble Phosphorus Reduced from 4 to 3 mg P/L.

Reduction in Chemical Dose*(Percent of Dose for Initial Concentration - 4 mq P/L)

Soluble Precipitant: Filter Alum Precipitant: Ferric CioridePhosphate Initial Alkalinity Initial AlkalinityResidual (~.accQ3Lj~.)~______ _______ç~q_ç~ç~i~~_—~

1.5 34 24 15 29 24 71.1 21 11 6 20 24 20.5 13 4 6 7 0 70.1 0 0 0 0

Table 12. Reduction in Chemical Doses Required to Achieve IndicatedSoluble Phosphate Residual. Initial pH 7.5. InitialSoluble Phosphate Reduced from 4 to 3 mg P/L.

Reduction in Chemical Dose*(Percent of Dose for Initial Concentration = 4 mq P/L)

Soluble Precipitant: Filter Alum Precipitant: Ferric CloridePhosphate Initial Alkalinity Initial AlkalinityResidual ______ maC~C03/L) _____ (m~C~COa/L)_____~?±L_ ~ 1 200 300

1.5 31 4 4 21 4 141.1 16 7 0 26 7 100.5 7 6 0 10 8 30.1 3 0 3 0

* Results are percentaqe reduction i.n chemical dose per mq P/L reduced atthe point of chemical addition.

Table 13. Typical Wastewater Characteristics at Bay AreaTreatment Plants.

Alkalinity pHLocation (mq CaCO~/L) (5tandard Units)

Baltimore 120 6.8Howard County 160 6.8Lower Potomac 170 7.0Arlington 170 7.1Piscataway 150 6.7

Table 14. Ferric Chloride 5avings for Indicated PhosphorusResidual. Alkalinity 150 mg CaCO3/L, pH 7.

Phosphorus Residual Ferric chloride savings(mq total P/L) (Percent)

2.0 131.0 50.2 2

4

Alkalinity and pH values were derived from observationa of Bayarea discharges (Table 13). Soluble phosphorus available forprecipitation was projected based on typical removals from primary and secondary wastewater treatment. This typical Bay areawastewater was evaluated by the Jenkins and James model to pre—diet precipitating chemical savings that would result if a ban onphosphates in household detergents reduced influent phosphorusconcentration by 1 mg P/I.. Model predictions for effluent tar-gets of 2, 1, and 0.2 mg total P/I.. are presented on Table 14.

4 • Effect of Phosphate Reductions on Sludge Pr~djjçJjon ajijjlwiflina

Since a ban on phosphates in household detergents would notreduce wastewater concentrations enough to eliminate the need forphosporus removal, treatment plants will continue to removephosphates to meet effluent phosphorus limitations. Such a banwould potentially affect sludge production and handlingcharacteristics only at plants using iron or aluminum salts toprecipitate phosphorus. as discussed in Section 3.4. The impacton sludge production and handling at these plants would vary inrelation to the reduction in chemical precipitant dose achievedand the resulting reduction in precipitate formation.

4.1 Sludge Production

Precipitant dose reductions can vary from 0 to 34 percentdepending on the precipitant used. wastewater characteristics.and the desired effluent phosphorus concentration. Since thesludge created by chemical precipitation is 20 to 30 percent oftotal sludge prodcution using ferric chloride (11. case study N 1appended). and 40 to 50 percent using alum (11, 12. 13). totalsludge production could be reduced at most by 7 to 9 percentusing ferric chloride and 14 to 20 percent using alum.

Data regarding the sludge production that would be avoidedby imposing a ban on phosphate in household detergents are briefand inconclusive. Berthouex (4) has presented observations ofsludge quantities at Milwaukee’s wastewater treatment pLantswhich indicate an increase in total sludge production at onetreatment plant. and a decrease at another, coinciding withimposition of the ban in Wisconsin. These results should not beviewed as illustrating that a ban will increase sludge production——obviously. reducing influent phosphorus will reduce phosphate precipitate solids, all other variables being constant.The Milwaukee .,bservations provide empt-asis to a very importantconsideration in deliberations of broad wastewat.er managementstrategies: water pollution control entails innumerable variables. many of them outside the control of “regulatory officials.or even local ~urisdictzons. The impacts, of broad strdteg*es.although seemingly important “on paper”, can be easily lost amongthe impacts of all the ‘other variabLes.

13

4

4.2 Sludge Handling

The effects of phosphorus reductions on sludge handlingactivities Must be judged indirectly, from pilot studies andobservations at wastewater treatment plants engaged in phosphorusremoval by chemical precipitation. Pilot study reports artdtreatment records from periods before and after initiation ofphosphorus removal can be analyzed to define changes in sludgehandl.ing operations. If all variables other than phosphorusprecipitation are constant, then impacts on plant operation dueto phosphorus removal can be defined. This definition providesat least an indirect measure of the effectiveness of a ban onphosphates in household detergents as a measure to relieve costsand operational problems associated with handling precipitatedsolids.

In general, sludges from treatment plants using ferricchloride or alum to remove phosphorus are not difficult to dc-water. In some cases, dewatering is improved by the chemicaladdition. Campbell and L.eClair (11) studied the impacts offerric chloride and alum addition for phosphorus removal on thethickening characteristics of waste activated sludges from anextended aeration activated sludge system. Compared to non-chemical sludge, the alum sludge improved setteability and do—waterability by basket and scroll—type centrifuges. Baillod ardCressey (12) also reported improved dewatetability of aerobicallydigested waste sludge from a contact stabilization activatedsludge system after the addition of alum for phosphorus removal.Ferric chloride inhibits thickening somewhat, but satisfactoryresults can be obtained by adjusting dewatering system variablesto optimize performance (11) • This pattern was also observed atBaltimore and at Arlington and Fairfax County. Virginia (see casestudies, appended): plant personnel were able to cope with thechanges in sludge characteristics and achieve performance as goodor better than pre—chemical—sddition performance. At Baltimoreand Ki lwaukee . (14) substantial decreases tn ~apses of ferricchloride used to• cbndit•iqñ sludgà âiPdiw~eiinê”were achievedafter the plant began using fèiric chloride to remove phosphorus.Analysis of Baltimore data showed that the incremental unit costof dewatering the additional sludge creited by ferric chlorideaddition was less than the unit cost of dewatering sludge beforeferric addition. A savings estimate based on unit costs for.sludge processing for the sludge avoided by a phosphate ban inhousehold detergents would probably be overstated because theunit cost for sludge processing would rise as the proportion cfferric—related sludge decreased. Thul while a bàn on phosphatesin household deteigents might reduce sludge production by as muchas 9 percent for plants using ferric chloride and as much as 20kfor plantq using alum, the impacts on sludge handling performanceand cost would be less than proportional to the impact on sludgeproduction.

14 -

4

5. ~j~pmarv

1.. A ban on phosphates in household detergents would reducethe phosphate concentrstion in municipal wastewaters byabout I to 2 mg P/L.

2. Predicted reduction of influent phosphorus will havea fairly minor effect on precipitating chemical requirements where effluent phosphorus limitations are 2 ag P/I.(total) or less (corresponding soluble P requirementis 1. mg P/I..

3. Phosphorus precipitation sludge that would be avoided bybanning phosphates in household detergents cannot bedetermined from existing data. The impact qf a ban maybe so small as to be undetectable among other wastewatertreatment variables that affect sludge production. Forthe plants studied, phosphorus removal sludge has notbeen observed to be difficult to dewater. Overalldewstering performance improved at Baltimore afterphosphorus removal sludge entered the sludge processingsystem. and overall dewatering performance waS notadversely affected at Arlington and Lower Potomac.There is even some indication, that the precipitation ofphosphorus with ferric chloride at some treatment plantscould cause a reduction Li quantity of sludgeconditioning chemicals required from the quantityrequired before phosphorus precipitation. In such acase it would be safe to say that a ban on phosphates inhousehold detergents might cause an increase in the costof sludge conditioning chemical. The incremental costof handling and dewatering phosphorus removal sludgeappears to be less than such costs for other sludges.Thus. projecting sludge processing cost savings based ontotal sludge unit costs probably overstates thepotential savings.

15

REFERENCES

1. Nesbitt, J.B., Removal of Phosphates from Municipal SewagePlant Effluents, Engr. Res. Bull. B—93, The PennsylvaniaState University, University Park, PA, 1966.

2. Metcalf and Eddy, Inc., Wastewater Engineering, McGrawHill, New York, NY, PP 64—65, (1979).

3. Tofflemire, T.J.., Hettling, L.J., A Guide to Chemical andClarifier Selection for Wastewater Treatment, New YorkState Department of Environmental Conservation, TechnicalPaper No. 29, pp 7—13 (1973).

4. Berthouex, P.M., Current Contribution of Detergents toSewage Phosphates in Pre—Ban, Post—Ban Situations,Paper presented at the Phosphorus Removal Workshop,Baltimore, ND, Sept. 28, 1984.

5. Lung, Wu—Seng, Phosphorus Loads to the Chesapeake Bay fromPOTWa, Paper presented at the Phosphorus Removal Workshop,Baltimore, MD, September 28, 1984.

6. EPA, Process Design Manual for Phosphorus Removal, EPA,625/1-76—OOla, 1976.

7. Lamb, J.C. III, Biological Phosphorus Removal: CurrentStatus arid Future Prospects, Paper presented at the Phosphorus Removal Workshop, Baltimore MD, Sept. 28 1984.

8. Rummel, Kiepper and Kahl, Evaluation of Costs for ReducingMaryland POTU Phosphorus Discharges to Chesapeake Bay. Areport prepared for the Soap and Detergent Association,January 25, 1984.

9. Jenkins, D.I., James B., Results of Chemical EquilibriumCalculation, Paper presented at the Phosphorus RemovalWorkshop, Baltimore, MD, Sept. 28, 1984.

10. Jones, E.R., Presentation to the Subcommittee on Phosphates,Senate of Maryland Finance Committee in Support of a Phosphate Detergent Ban, Sept. 18, 1984.

11. Campbell, H.W., LeClair, B.P., Sludge Dewatering Alternatives for Waste Activated Sludges from Phosphorus Removal Facilities, Journal WPCF, Nay, 1979.

12. Baillod, CR., Cressey, G.M., Beaupre, R.T., Influence ofPhosphorus Removal on Solids Budget, Journal WPCF, January,1977.

13. EPA, Enhancing Trickling Filter Plant Performance By Chemical Precipitation, EPA—670/2--73-060, August, 1973.

16

LI

etst‘.xaqwe;de~‘O9O—CL—~/OL9—Vd3‘.xonbç~eTMDTdAqsn.xoqd~oq~~a~owaej;uetcje6pnigpa’e~nzvCOWOO~‘Vd31’t

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A—i. Summary

Sludge handling issues were investigated by carrying outcase studies at three treatment plants discharging to the Chesapeake Bay or its tributaries:

1. Back River Wastewater Treatment Plant, Baltimore,Maryland;

2. Lower Potomac Water Pollution Control Plant, FairfaxCounty, Virginia;

3. Arlington Water Pollution Control Plant, Arlington,Virginia.

Each of these plants met two conditions for case study:

1. A period of record preceding and following initiation ofphosphorus precipitation, with no major changes in plantunits or operating procedures during the period.

2. A detailed, credible body of data involving parametersof interest.

Sludge handling and dewatering system performance was judgedby five criteria:

1. Propensity of sludge to thicken,2. Dewatering equipment solids loadings,3. Solids capture,4. Dewatered cake dryness, and5. Chemical conditioning requirements.

Sludges were characterized according to these criteria by compiling and evaluating monthly plant operating reports, and bydiscussions with operations personnel. Additional insights wereprovided by a phosphorus removal demonstration project at BackRiver, using waste pickle liquor.

A-i.1 Back River, Baltimore — Case Study No. 1

Sludge production at Back River increased by about 29 percent on a dry solids basis and 17 percent on a wet solids basisfollowing initiation of phosphorus precipitation with wastepickle liquor. The lesser increase in wet weight is important.It illustrates the greater success of dewatering following initiation of phosphorus removal, compared to the pre—removalp€~riod.

Propensity of raw primary and waste activated sludges tot.hicken showed decreases following initiation of phosphorus re—woval. Parts of these decreases have been attributed to otheroperational changes; the extent attributable to any one change isnot known Gravity thickened sludqe (mi~’ed primary, tricklingfilter, and waste activated sludge) and digested mixed sludge

illustrated no change with waste pickle liquor addition. Afairly dramatic increase in density of elutriated sludge coincided with phosphorus removal and has been sustained since thatt.ime. Polymer (a coagulating chemical) dosages had been marii—pulated and optimized during that time, and the contribution ofany one change to elutriated sludge density is unknown. It canbe observed, however, that phosphorus removal sludge did notupset the thickening and elutriation processes, and may havecontributed to more efficient operation of the latter system.

Solids capture in the thickening and elutriation processesimproved in the general time period of waste pickle liquor addition. These improvements were most likely caused by operational changes. Again, phosphorus removal sludge appeared tohave no negative impact on solids capture.

Dryness of the dewatered vacuum filter cake increasedsignificantly following initiation of waste pickle liquoraddition. Conditioning chemical dose required to achievedewatering decreased significantly. Host of this improvement insludge dewaterability can be assigned to the presence ofphosphorus removal solids in the sludge mixture. Improved de—watering accounts for the lesser increase in weight of wet sludgecompared to dry solids cited earlier. Thus, at Back River, theeffort and cost required to dewater an increment of phosphorusremoval sludge is less than that required to dewater the sameincrement of primary, waste activated and trickling filter sludgemixture (Figure A—i). The cost savings to be experienced by notdewatering and disposing of the phosphorus removal sludge thatwould be avoided by a ban on phosphate in household detergents inthe Back River service area should be determined using the unitcost difference shown in Figure A—i ($157/dry ton). Estimatesprepared by Jones (10) for Blue Plains considered unit costssimilar to the after phosphorus removal cost in Figure A—i. Thepossiblity of overstating the cost impact of avoiding phosphorusremoval sludge is apparent.

A—1.2 Lower Potomac, Fairfax County - Case Study No. 2

Phosphorus removal at Lower Potomac had mixed impacts on thepropensity of sludges to thicken. Primary sludge showed nosignificant change in density after chemical addition. Wasteactivated sludge density was substantially greater after chemicaladdition, but thickened to the same levels as before chemicaladdition. Gravity thickening of primary sludge was adverselyaffected by chemical addition, but thickener performance wasrestored to pre—chemical addition levels with the addition ofpolymer. A significant improvement in solids capture in thegravity thickening and dissolved air flotation processes (DAF)was observed to coincide with phosphorus removal. This improvement may be attributable in the case of the DAF unit to thecoaqulating effect of the iron in the pnospnorus removal s±uoqeand in the case of the gravity thickener to the addition of

BEFORE PHOSPHOROUS REMOVAL

Ho dry toa~ ~ter~ ~auiem34.75~

6800 lb polyner~ Total Coat $13,930~~0.0685 = $4~)

$199/dry ton

AFTER PHOSPHORUS REMOVAL

670 wet tons128 dry tons Dewatering hauled ~ E34.75

$23,280

7720 lb poly~er~ Total Cost $24,330$O.0685 = S52~J

$190/dry ton

Coat attributable to phosphorus ren oval sludge:

( $24,330 — $19,930 ) / 28 $1S7 I dry ton

Fiure A-i. Co~pariaon of Sludge Ouantities, ConditioningChe~icai Coat, and Hauling Cost. Back River WWTP.Note: 100 dry tons is unit of convenience.

polymer. The presence of such sludges certainly had no lastingdeleterious effects on thickening.

Sludge dewatering presented a similar picture. The threechemical regimes investigated affected dewatering differently:two regimes resulted in dewatered sludge dryness reductions of1.3 and 2.0 percent, while the third had no significant impact ondewatered sludge dryness. Substantial conditioning chemical dosereductions were observed under all of the chemical additionregimes, but quantification of these reductions are difficult dueto anomolies in the sludge production data.

Lower Potomac data do not provide the lengthy periods ofunvaried operation offered by Back River records. Possiblepositive effects of phosphorus removal sludge cannot be separatedfrom benefits derived by optimizing the sludge handling system.Thus, generating unit costs for phosphorus removal sludgehandling would be risky. The case study certainly does notpresent a picture of a plant troubled by phosphorus precipitationsolids. On the contrary, such solids are nearly certain to becontributing to sludge handling improvements at Lower Potomac.

A—i.3 Arlington — Case Study No. 3

This plant has a brief period of record which allowscomparison of vacuum filter dewatering of mixed primary and wasteactivated sludge and the same mixture with phosonorusprecipitation solids added. A decrease in cake dryness wasobserved when phosphorus solids were added. Conditioningchemical dose required for dewatering remained essentially con—stant, on a dry solids basis, when the phosphorus solids wereadded.

A—2. Case Study No.. 1: Back River Waste Water Treatment Plant

A—2.1 Description of Treatment Processes

The Back River Waste Water Treatment Plant (WWTP) providespreliminary, primary and secondary treatment for about 190nillion gallons per day of domestic, commercial, and industrialwastewater collected from Baltimore City and Baltimore County,Nary land.

Preliminary treatment removes large solids and grit from thewastewater. Primary treatment is accomplished in largesedimentation basins in which about 30 to 50 percent of thesuspended materials settle by gravity and are removed as primarysludge.

In secondary treatment, most of the remaining suspended anddissolved contaminants are removed by one of two biologicaltreatment systems, trickling filters or activated sludge.Trickling filters receive about two-thirds of the primarytreatment effluent. Primary treatment effluent is sprayed onto arock filter media where a layer of bacteria and otheri~iicroorganisms attached to the rock surface feed on the finelysuspended and dissolved organic material remaining after primarytreatment. The water then goes through a final settling processfrom which it is conveyed to either the chlorination facilitiesfor disinfection and discharge to Back River, or the BethlehemSteel corporation at Sparrows Point for use as industrial water.

The remaining third of the primary effluent is treated inthe activated sludge process where it is mixed with a biologicalsludge and aerated. The organisms in the sludge feed on thesuspended arid dissolved materials in the primary effluent.Following mixing and aeration, the organisms and other settleablematerials are separated from the treated wastewater insedii~ientation basins. Effluent from the sedimentation basins iseither disinfected and discharged to Back River, or conveyed toBethlehem Steel for use as industrial water.

Nost of the sludge from the activated sludge sedimentationbasins is retained in the system and mixed with more primaryeffluent. Due to the growth of organisms in the sludge and theaccumulation of other primary effluent solids, a portion of thesludge is removed from the secondary treatment system; thisportion of sludge is called waste activated sludge.

The primary and waste activated sludges are thickened,stabilized, conditioned, and dewatered prior to dist~osal Bothsludges are pumped to gravity thickeners in which sludge solids

are concentrated by allowing them to settle by gravity beforefurther processing. The thickener supernatarit is returned to theliquid treatment units. Thickened sludge is stabilized byanaerobic digestion that reduces the sludge’s organic content.The digested sludge contains a high concentration of alkalinitythat is “washed~ out by an elutriation process before dewatering.Alkalinity is removed in this way because it exerts a significantand costly chemical demand when the sludge is chemicallyconditioned for dewatering. The elutriated sludge is chemicallyconditioned with polymer and processed by large filters thatcreate a vacuum which draws water from the sludge through afilter cloth, leaving a sludge ~cake” that is collected fordisposal.

Phosphorus Removal at the Back River WWTP

Phosphorus is removed from wastewater at Back River by acombination of physical, biological, and chemical processes.Some phosphorus is contained in solids in the wastewater thatsettle by gravity in primary treatment. Phosphorus is anessential nutrient for the biological treatment systems(trickling filter and activated sludge) and is removed by beingincorporated into the biological sludges. Zlost of the remainingphosphorus is dissolved in the wastewater as phosphates that canbe chemically precipitated and removed as chemical sludge. AtBack River the precipitating chemical is the iron contained inwaste pickle liquor obtained from the Bethlehem 5teelCorporation. Waste pickle liquor is added to the activatedsludge system aeration tanks in which both the chemical andbiological solids are formed. The chemically precipitated andbiologically incorporated phosphorus is removed from the systemas waste activated sludge.

Phosphorus removal using waste pickle liquor wassuccessfully demonstrated at Back River in 1978 through anagreement between the Bethlehem Steel Corporation and the Mayorand City Council of Baltimore. Full—time addition of wastepickle liquor began in June, 1981.

/

A—2..2 Results of Back River Data Analysis

Propensity to Thicken: Table A—i

The propensity of sludge to thicken was evaluated bycomparing the density of sludge before and after waste pickleliquor (WPL) addition at six points in the sludge handlingsystem. This evaluation is summarized below:

Density (~ Solids) Percent StatisticallySludge Type Before WPL After WPL Change ~g~~,ificant*

Primary 2.85 1.87 —34 YesWaste Activated 0.68 0.58 —15 YesTrickling Filter 0.85 0.93 — 9 NoGravity Thickened 4.23 4.26 — 0.7 NoDigested 2.71 2.73 — 0.7 NoElutriated 4.42 5.97 +35 Yes

* Statistical significance at the 90~ confidence level.

Note: Waste activated, thickened, and elutriated sludgedensities were influenced by other aspects of systemoperations.

Table A—2 shows the performance of the elutriation systems beforeand after the polymer dose was reduced by 50 percent. Asignificant reduction in overflow suspended solids (and increasein solids capture) was achieved.

Sludge Product ion: Table A—3

Sludge production before and after WPL addition is presentedin Table A—3. Dry tons production increased 29 percent and wettons increased 17 percent WPL addition. The percent increase inwet. tons was less than the percent increase in dry tons due toimproved vacuum filter performance. The vacuum filteroperational strategy was the same during the period covered bythe data in Table A—3. Solids loadings to the plant (raw wastewater) showed a slight decrease (1 to 5~) during this period;this decrease is not considered to be significant.

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TABLE A—2. Comparison of Elutriation Performance Beforeand After Polymer Dose Reduction, Back R. WWTP

Before Dose Reduction

Elutriation #1 Elutriation #2 Elutriation ElutriatedOverflow Percent Overflow Percent Polymer Dose Sludge Density

Month (mg/L) Capture (mg/L) Capture (#IDry Ton) (‘~ Solids)

Jun—81 291 93 219 96 2.4 5.4Jul—81 339 91 374 92 2.3 5.2Aug—81 515 91 289 95 3.2 4.9Sep—81 800 88 837 88 2.7 5.4Oct—81 359 92 714 88 2.1 6.4Nov—81 357 92 195 95 1.5 7.1Dec—81 366 90 211 94 2.1 6.0Jan—82 414 86 185 94 2.4 6.8Feb—82 384 88 203 93 2.3 6.6

Average 425 90 359 93 2.3 6.0Std. Dev. 145 2 232 3 0.4 0.7Minimum 291 86 185 88 1.5 4.9Maximum 800 93 837 96 3.2 7.1

After Dose Reduction

Mar—82 381 91 180 92 1.3 5.5Apr—82 351 93 313 94 1.0 5.6May—82 400 91 320 95 1.3 5.1Jun—82 328 92 218 94 1.1 5.7Jul—82 311 94 208 95 1.5 5.4Aug—82 296 92 213 94 1.6 5.3Sep—82 280 93 321 92 1.6 5.4Oct—82 307 92 206 95 1.7 6.2Nov—82 350 95 2.1 6.0Dec—82 340 95 2.6 6.6Jan—83 285 95 2.7 6.3Feb—83 301 93 254 95 2.1 6.2Mar—83 326 92 239 94 6.4Apr—83 285 94 202 95 7.2May—83 310 95 194 96 1.6 6.1Jun—83 335 94 244 96 1.8 6.4

Average 324 93 255 94 1.7 6.0Std. Dcv. 34 1 56 1 0.5 0.5Minimum 280 91 180 92 1.0 5.1Maximum 400 95 350 96 2.7 7.2

Student’s t-Test for the difference between means:2.06 —3.17 1.31 —1.79 3.17 0.05

Critical t values at the 90’~ confidence level:1.72 1.72 1.71 1.71 1.72 1.71

TABLE A—3. Sludge Production Before and After WPL Addition, Back R. WWTP

Before WPL Addition After WPL AdditionMonthly Production Monthly Production

Month Dry Tons Wet Tons Month Dry Tons Wet Tons

Jul—79 1939 11224 Jun—81 2483 13793Aug—79 2761 14918 Jul—81 2670 13561Sep—79 2067 10645 Aug—81 2553 13370Oct—79 2545 13317 Sep—81 2751 13874Nov—79 2463 13908 Oct—81 3116 16575Dec—79 1824 10314 Nov—81 3287 16777Jan—80 2142 11775 Dec—81 3124 17028Feb—80 1992 11151 Jan—82 2360 13004Mar—80 2399 13337 Feb—82 2199 12206Apr—80 2302 12569 Mar—82 2703 15115May—80 2579 14468 Apr—82 3144 16284Jun—80 2469 14302 May—82 3373 17264Jul—80 1933 11873 Jun—82 3105 15571Aug—80 1572 9232 Jul—82 3028 15282Sep—80 1386 8029 Aug—82 2725 13897Oct—80 1686 9663 Sep—82 2420 11942Nov—80 1664 9636 Oct—82 2528 12468Dec—80 1375 7946 Nov—82 2606 13104Jan—81 1706 9930 Dec-82 2339 11776Feb—81 1930 11267 Jan—83 2233 11433Mar—81 2766 16246 Feb—83 2269 11525Apr—81 2652 15506 Mar—83 3008 14843May—81 2904 17049 Apr—83 2814 13902

May—83 3222 15957Jun—83 2704 13671

Average 2133 12100 2747 14129Std. Dev. 449 2609 349 1729Minimuia 1375 7946 2199 11433Naximun 2904 17049 3373 17264

Solids Capture: Table A—4

Solids capture for the gravity thickener and elutriationsystems before and after WPL addition are shown in Table A—4.Operational changes had more impact on performance than did thepresence or absence of WPL. Note improvements (higher capture)in thickener performance four months after WPL addition, andimprovements in elutriation performance two months before WPLaddition. (See also Table A—2 and its discussion above).

Cake Dryness: Table A—S

Vacuum filter cake dryness before and after WPL addition isshown in Table A—S. The cake solids content increased from ~to l9.1~ and the increase was statistically significant at the90~ confidence level. Vacuum filter operational strategy wasconsistent during this period.

Table A—6 shows a comparison of dewatering performancebefore and after a 50 percent reduction in the polymer dose usedin the elutriation system. Polymer dose reduction wasaccomplished by reducing the polymer solution strength to optimumlevels. The data show an increase in cake dryness in the periodafter WPL addition but before elutriation polymer dose reductionfrom 17.6 ~ solids to 18.5 ~‘ solids (Table A—5). A furtherincrease in cake dryness to 19.4 ~ solids occured after theelutriation polymer dose reduction

Vacuum F i iter Condition ipg_ n i cal Use:

Conditioning chemical (polymer) use before and after WPLaddition are shown in Table A—S. Polymer dose measured inlbs./Dry Ton showed a significant decrease of 11~~ after WPLaddition; the polymer dose decreased from 68.0 lbs./Dry Ton to60.3 lbs./Dry Ton.

Table A—S shows a comparison of dewatering performancebefore and after a 50 percent reduction in the polymer dose usedin the elutriation system. The data show an decrease inconditioning chemical (polymer) dose from the period before WF’Laddition (68.0 lbs./Dry Ton) but before elutriation polymer dosereduction (66.5 lbs./Dry Ton). A further decrease in vacuumfilter polymer dose to 55..1 lbs./Dry Tori occured after theelutriation polymer dose reduction.

The 1978 WPL addition demonstration at Back River resultedin observations by plant operations of the impact of WPL onvacuum filter polymer needs:

Comment 1. . .a definite secondary benefit from the use ofwaste pickle liquor, in the large reduction of

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TABLE A—S. EIMCO Vacuum Filter Performance Before andAfter WPL Addition, Back R. WWTP

Before WPL Addition After WPL Addition

Cake Polymer Cake PolymerDryness Dose Dryness Dose

Month (‘~ Solids) (#/Dry Ton) Month (~ Solids) (#/Dry Ton)

Jun—81Jul—81Aug—81Sep—81Oct—81Nov—81Dec—81Jan—82Feb—82Mar—82Apr—82May—82Jun—82Jul—82Aug—82Sep—82Oct-82Nov—82Dec—82Jan—83Feb—83Mar—83Apr—83May-83Jun—83

Jul—79 17.9 78.3 18.0 68.8Aug—79 18.5 61.9 19.0 62.5Sep—79 19.5 62.6 18.2 90.9Oct—79 19.1 62.8 17.7 88.7Nov—79 17.7 64.2 19.5 70.5Dec—79 17.7 77.2 19.6 52.1Jan—80 18.1 71.7 18.3 S1.8Feb-80 17.9 73.7 18.0 59.3Mar—80 18.0 70.0 17.8 53.7Apr—80 18.3 74.2 17.S S6..8May—80 17.8 69.1 18.3 61.1Jun—80 17.3 62.3 18.9 61.7Jul—80 16.3 64.0 19.4 67.2Aug—80 17.1 S8..6 19.4 62.6Sep—80 17.2 61.5 19.2 46.3Oct—80 17.4 63.1 19.8 65.0Nov—80 17.3 68.2 20.1 55.4Dec—80 17.3 69.1 19.8 59.7Jan—81 17.2 70.5 19.7 55.7Feb—81 17.1 73.7 19.3 60.7Mar—81 17.0 66.9 19.5 51.0Apr—81 17.1 70.2 19.9May—81 17.0 70.4 19.9

19.8 55.819.9 60.4

Average 17.6 68.0 19.1 60.3Std. Dev. 0.7 5.3 0.8 10.6Minimum 16.3 58.6 17.5 46.3Maximum 19.5 78.3 20.1 90.9

Student’s t—Test for difference between means —6.47 3.11

Critical t values at the 90’s confidence level: 1.68 1.68

TABLE A—6. Comparison of Dewatering Performance Before and AfterElutriation Polymer Dose Reduction, Back R. WWTP

Student’8 t—Test for the difference between means:—3.36 2.34 —1.29

Critical t values for the 90~ confidence level:

Before Dose Reduction~TMCO Filter K/S Fi1t~r

Cake Polymer Cake PolymerDryness Dose Dryness Dose

Month (‘~ Solids) (#/Dry Ton) (‘~ Solids) (#/Dry Ton)

Jun—81Jul—81Aug—81Sep—81Oct—SiNov—81Dec—81Jan—82Feb—82

18.019.018.217.719.519.618.318.017.8

18.50.7

17.719.6

68.862.590.988.770.552.151.859.353.7

66.614.051.890.9

AverageStd. DevMinimumMaximum

20.420.820.619.718.918.818.5

19.70.9

18.520.8

38.757.170.381.694.5

68.419.338.794.5

After Dose ReductionEIMCO Filter K/S Filter

Cake Polymer Cake PolymerDryness Dose Dryness Dose

Month (~ Solids) (#/Dry Ton) (~ Solids) (#/Dry Ton)

Mar—82 17.5 56.8 18.5 79.2Apr—82 18.3 61.1 19.3 64.7May—82 18.9 61.7 20.3 54.3Jun—82 19.4 57.2 20.5 72.6Jul—82 19.4 52.6 20.5 69.5Aug—82 19.2 46.3 20.2 68.5Sep-82 19.8 65.0 20.7 63.8Oct—82 20.1 55.4 21.1 64.6Nov—82 19.8 69.7 20.5 74.1Dec—82 19.7 55.7 20.2 67.9Jan—83 19.3 60.7 19.8 75.4Feb—83 19.5 51.0 19.9 65.4Mar—83 19.9 43.5 20.5 55.9Apr—83 19.9 48.8 20.4 48.8May—83 19.8 55.8 20.5 57.2Jun—83 19.9 60.4 19.4 62.0

Average 19.4 55.1 20.1 65.2Std. Dev 0.7 5.3 0.6 8.0Minimum 17.5 43.5 18.5 48.8Maximum 20.1 61.7 21.1 79.2

0.36

1.71 1.71 1.72 1.73

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A—3. Case Study No.. 2: Lower Potomac Water Pollution Control Plant

A—3.1 Description of Treatment Processes

The Lower Potomac Water Pollution Control Plant (WCPC)provides preliminary, primary, secondary, and advanced treatmentfor about 33 million gallons per day of domestic, commercial, andindustrial wastewater collected from Fairfax County, Virginia.

Preliminary treatment removes large solids from thewastewater by passing the flow through coarse screens..Settleable solids are removed by gravity in primary sedimentationbasins and collected as primary sludge.

Secondary treatment at Lower Potomac is accomplished by theactivated sludge process which mixes primary treatment effluentwith a biological sludge that removes most of the suspended anddissolved contaminants. The mixture is aerated for several hoursand ‘then conveyed to settling tanks where the sludge is separatedfrom the treated water..

The secondary effluent is conveyed through flow equalizationponds to the advanced wastewater treatment (AWT) units. The AWTunits were originally designed for phosphorus removal by two—stage lime precipitation. These units are currently used forphosphate precipitation with ferric chloride

Description of ~~ge Processing

Sludges generated in primary and secondary treatment arethickened, conditioned and dewatered prior to disposal. Cyclonesare used to remove grit from primary sludge before thickening ingravity thickeners.. Liquid separated from the sludges in thethickeners is returned to the liquid treatment systems. Wasteactivated sludge is conditioned with polymer and thickened inflotation thickeners. The thickened primary and waste activatedsludges are then blended and conditioned with lime and ferricchloride before dewatering by vacuum filtration.

The chemical sludge produced by the AWT system is processedseparately from the primary and secondary sludge. Chemicalsludge is gravity thickened, conditioned with polymer, anddewatered with centrifuges..

Fhg~phorus Removal at the Lower Potomac WPCP

Phosphorus removal at Lower Potomac began in 1979 with two—stage lime precipitation in the AWT system.. Problems wereencountered in the operation of the precipitation and sludgerecycling systems, and in 1980 ferric chloride replaced lime as

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A—3.2 Results of Lower Potomac Data Analysis

Propensity to Thicken: Table A—7 and Table A—8

The propensity of sludge to thicken was evaluated bycomparing the density of primary and gravity thickened sludgebefore and after ferric chloride addition to the primaryclarifiera (Table A—7), and waste activated and OAF (dissolvedair flotation) thickened sludge under four operating conditions(Table A—8):

(A) no chemical addition (except to the AWT system),(B) addition of ferric chloride to the activated

sludge aeration basin,(C) addition of ferric chloride to the activated

sludge aeration basin and the primary clarifier,and

(D) addition of ferric chloride to the primaryclarifier and ferrous sulfate to the activatedsludge aeration basin.

Primary sludge density increased 3 percent after ferricchloride addition, but the change was not statisticallysignificant. Gravity thickened sludge density dropped from 6.0~to 5.6k total solids in the first month after ferric chlorideaddition (December 1982). In January 1983 operations baganadding polymer to the gravity thickener to improve performance.The polymer addition restored thickening performance to levelsachieved before ferric addition and improved solids recovery (seebelow).

A comparison of waste activated and OAF thickened sludgedensity under the no—addition regime to sludge production undereach of the chemical addition regimes is presented below:

Waste Sludge_Solids OAF Thickened SludgeRegime (mg/L) (~‘ Change) (Percent)

(A) 3110 4.9(B) 4640 +49 4.9(C) 6820 +119 4.6(0) 5580 +79 4.9

In all chemical addition regimes waste sludge density wassubstantially higher than under the no—chemical regime (A). TheOAF thickened sludge was the same in all regimes; the averagedensity in regime (C) was 6~ lower, but this decrease was notstatistically significant at the 90~ confidence level.

TABLE A—7. Primary Sludge Density and Gravity Thickener PerformanceBefore and After Ferric Chloride Precipitant Addition,Lower Potomac WPCP

Before Ferric Addition After Ferric Addition

Primary Thickened Thickener Primary Thickened ThickenerSludge Sludge Overflow Sludge Sludge Overflow

Month (mg/L) (~ Solids) (mg/L) Month (mq/L) (% Solids) (mg/L)

Jan—80 4631 270 Dec—82 5833 5.6 282Feb—80 4103 241 Jan-83 4344 6.1 136Mar—80 3781 234 Feb—83 6551 6.7 190Apr—80 5490 337 Mar—83 8002 7.0 169May—80 6427 7.5 437 Apr—83 8141 5.6 364Jun—80 5763 6.2 370 May—83 7357 6.8 165Jul—80 6806 6.8 412 Jun-83 7080 7.4 176Aug—80 7465 6.1 319 Jul—83 7405 6.1 166Sep—80 9604 6.8 313 Aug—83 7476 6.4 202Oct—80 7465 6.8 340 Sep—83 7264 6.3 173Nov—80 6442 6.7 284Dec—80 6705 6.4 270 Nov—83 5860 6.4 208Jan—81 6755 7.3 306 Dec—83 5987 6.6 186Feb—81 7276 7.1 345 Jan—84 6554 6.1 193Mar—81 5799 7.1 383 Feb-84 6344 6.5 154Apr—81 6475 7.0 298 Mar—84 5713 6.1 193May—81 6156 7.4 344Jun—81 6521 6.8 279Jul-81 7235 7.5 382Aug—81 6553 6.4 325Sep-81 8157 6.3 468Oct—81 7211 6.1 345Nov—81 6435 6.2 363Dec—81 7157 6.1 494Jan-82 6362 6.0 303Feb-82 6600 6.1 419Mar—82 7674 6.6 355Apr—82 6419 6.5 409May-82 6226 6.3 457Jun—82 6378 6.5 325Jul-82 5930 6.4 306Aug—82 6176 6.5 231Sep—82. 6250 6.5 255Oct—82 5759 6.0 224Nov—82 6234 6.0 285

Average 6469 6.6 335 6661 6.4 197Std. Dcv. 1041 0.5 68 980 0.5 55Ninimun 3781 6 224 4344 5.6 136Maximum 9604 7.5 494 8141 7.4 364

Student’s t—Test for the difference between means: —0.62 1.38 7.56Critical t values at the 90~ confidence level: 1.68 1.68 1..68

Note: Statistics for the after-ferric-addition period do not include theDecember 1982 data.

TABLE A—8. Flotation Thickener Performance at Lower Potomac Under FourOperating Conditions.

(A> Before FeC13 Precipitant Addition

Waste Sludge Thickened Sludge Effluent SolidsSuspended Solids Suspended Solids Suspended Solids Recovery

Month (mg/L) (~ Solids> (~g/L) (~)

Jan—80 3000 4.9 152 94.9Feb—80 2950 4.3 175 94.1Mar—80 2900 4.1 150 94.8Apr—80 3400 5.1 210 93.8May—80 3510 4.8 395 88.7Jun—80 5.1Jul—80 3128 5.2Aug—80 2680 5.1Sep—80 3317 5.1

Count 8 9 5 5Std. Dev. 263 0.4 92 2.3CV* 0.08 0.08 0.42 0.02Average 3111 4.9 216 93.3

(B> FeC13 Precipitant Addition to Aeration Basins

Oct—80 3643 4.7Nov—80 3883 4.8Dec-80 5084 4.6Jan-81 4833 5.2Feb—81 4111 4.7Mar—81 3792 5.7Apr—81 6970 5.8May—81 4340 5.6Jun—81 4513 5.6Jul—81 3590 5.8Aug—81 3681 4.7Sep—81 4690 4.1Oct—81 4828 4.1Nov-81 5512 4.1Dec—81 4196 4.8Jan—82 3669 4.6Feb—82 4712 4.6Mar—82 4472 5.0 85 98.1Apr—82 4480 5.1 70 98.4May—82 4219 4.7 69 98.6Jun—82 4378 4.8 60 98.6Jul—82 4425 4.8 54 98.8Aug-82 5140 5.0 34 99.3Sep-82 5086 5.2 29 99.4Oct—82 5881 5.2 31 99.5Nov—82 6529 4.8 34 99.5

Count 26 26 9 9St~. 0ev. 837 0.5 19 0.5

0.18 0.10 0.37 .00Average 4641 4.9 51 98.9

(TABLE A—8. CONT’D)

(C) FeCl3 Precipitant Addition to Primary and Aeration Basins

Waste Sludge Thickened Sludge Effluent SolidsSuspended Solids Suspended Solids Suspended Solids Recovery

Month (mg/L) ~ Solids) (mg/L) (~)

Dec—82 6908 4.8 37 99.5Jan-83 6860 4.5 54 99.2Feb—83 7602 4.4 47 99.4Mar—83 7989 4.3 47 99.4

Sep—83 4181 5.4 47 98.9

Nov—83 7652 4.8 55 99.3Dec—83 8218 4.9 32 99.6Jan—84 7377 4.7 30 99.6Feb—84 7465 4.5 34 99.5Mar—84 6850 4.0 47 99.3

May—84 5349 4.2 22 99.6Jun—84 5332 5.0 20 99.6

Count 12 12 12 12Std. Dev. 1180 0.4 11 0.2CV* 017 008 029 00Average 6815 4.6 39 99.4

(D) FeCI3 Precipitant Addition to Primary andFe504 Precipitant Addition to Aeration Basins

May—83 6447 6.2 44 99.3Jun—83 5650 4.6 48 99.2Jul—83 4628 4.8 67 98.8

Count 3 3 3 3Std. 0ev. 744 0.2 6 0.2CV* 0.13 0.05 0.11 .00Average 5576 4.9 50 99.1

(TABLE A—8. CONT’D)

Student’s t—Test tables for the difference between means:

Thickened Sludge Solids (~ Solids)(B) (C) (D)

(A) —0.45 1.41 —0.06(B) ******* —29.15 0.34(C) *************** —1.35

Effluent Suspended Solids (mg/L)(B) (C) (D)

(A) 3.99 4.30 4.05(B) ******* 1.61 0.14(C) *************** —2.28

Solids Recovery (%)(B) (C)

(A) —5.40 —5.93(B) ******* —2.81(C) ***************

Critical t Values(B) (C)

(A) 1.69 1.73(B) ******* 1.69(C) ****************

Critical t Values(B) (C)

(A) 1.78 1.75(B) ******* 1.73(C) ****************

Critical t Values(B) (C)

(A) 1.78 1.75(B) ******* 1.73(C) ****************

1.831 • 701.77

1.811.701.77

1.941.81177

1.941.811.77

Variation (Std. Dev. / Average)

Waste Sludge Solids (mg/L) Critical t Values(B) (C) (D) (B) (C)

(A) —8.11 —10.49 —5.60 (A) 1.69 1.73(B) ******* —5.75 —2.03 (B) ******* 1.69(C) *************** 2.26 (C) ****************

(D)

(D)

(D)

(D)(D)—5.58—0.762.26

* CV = Coefficient of

Note: All critical t values are at the 90’~ confidence level.

Sludge Production: Table A—9

Table A—9 presents cbmparisons of sludge production (wet anddry tons) under the four operating conditions listed above.. Acomparison of sludge production under the no—addition regime tosludge production under each of the chemical addition regimes ispresented below:

Sludge Production(Dry Tons Per

?IGD of Plant Flow) Percent ~

(A) 1.70(B) 1.58 —7(C) 1.06 —38(D) 1.12 —34

The data indicate that the same amount or less sludge perNGD of plant flow was produced after chemical precipitation.Normalization by solids and BOO removal and solids removal alonegive similar results. These data conflict with chemicalprecipitation theory which says that more sludge should beproduced. Possible explanations (sources of error) are:

— sampling and analytical error (sludge density data)— instrumentation error (flow measurements)— variations in wastewater characteristics (e.g.,

biodegradability)— variations in treatment systems operations

Solids Capture: Table A—7 and Table A—8

Solids capture impact was evaluated by comparing the gravitythickener overflow solids concentrations before and after ferricchloride addition to the primary clarifiers (Table A—7), and OAFthickener performance under the four operation conditions listedabove (Table A—8).

In the first month of ferric chloride addition (December1982), overflow solids showed no significant change from theprevious month, and a drop of less than one standard deviationfrom the average of the previous 35 months. After polymeraddition began in January 1983, solids recovery improvedrnarkedly: overflow solids (averages) decreased ~ giving asolids recovery increase from 95~~ to ~

A comparison of OAF effluent suspended solids and percentsolids recovery under the no—addition regime to sludge productionunder each of the chemical addition regimes is presented below:

— 4

TABLE A—9. Sludge Production and Vacuum Filter Operation at Lower PotomacUnder Four Operating Conditions

(A) Before FeC13 Precipitant Addition

Sludge Production Per:Plant Solids BOD&SS Cond. Chem. Dose Cake ProductionFlow Remov’d Remov’d Lime FeC13 Dryness Wet Dry

Month (DT/MGD) (DT/DT) (DT/DT) (#/DT) (#/DT) (% Solids) Tons Tons

Mar-80 1.21 1.66 1.25 731 161 16.4 6293 963Apr—80 1.39 2.06 1.50 539 159 18.0 6442 1091May—80 1.58 2.15 1.65 637 134 18.6 7248 1258Jun—SOJul—80 1.89 226 1.70 621 129 19.7 7167 1315Aug—80 2.00 2.50 1.87 454 18.1 7247 1260Sep-80 2.12 2.16 1.63 601 18.6 8259 1455

Std.Dev. 0.33 0.25 0.19 86 12 1.0 642 158CV* 0.19 0.12 0.12 0.14 0.08 0.05 0.09 0.13Average 1.70 2.13 1.60 597 143 18.2 7110 1224

(B) FeC13 Precipitant Addition to Aeration Basins

Oct—80 2.08 2.43 1.72 596 118 17.7 9295 1547Nov—80 1.88 2.25 1.65 534 154 16.4 8816 1369Dec—80 2.39 2.71 2.00 516 160 15.8 11439 1716Jan—81 2.31 2.84 2.13 488 115 16.5 10516 1653Feb-81 1.83 2.06 1.57 543 127 16.0 9134 1387Mar—81 1.49 1.85 1.38 630 126 16.6 8455 1321Apr—81 1.52 1.74 1.31 535 140 17.7 8088 1351May—81 1.53 1.97 1.40 407 140 18.0 8090 1384Jun-81 1.54 1.89 1.33 374 135 17.5 8410 1409Jul—81 1.45 1.78 1.32 352 138 18.0 7791 1343Aug-81 1.49 1.84 1.38 371 120 17.4 8015 1338Sep—81 1.78 2.13 1.58 466 131 17.6 10072 1684Oct—81 1.81 2.31 1.69 445 83 16.4 10115 1590Nov—81 1.69 2.16 1.51 518 88 16.9 9573 1535Dec—81 1.78 2.54 1.77 522 104 17.3 10109 1654Jan—82 1.38 1.93 1.39 472 108 16.3 8704 1351Feb-82 1.19 1.96 1.45 546 118 16.1 9354 1430Mar—82 1.51 2.65 1.89 453 101 16.6 10751 1701Apr—82 1.23 1.89 1.36 432 103 16.0 9172 1407May—82 1.23 1.79 1.31 385 113 16.4 8752 1375Jun—82 1.08 1.61 1.19 333 111 16.8 7868 1271Jul—82 1.28 1.76 1.27 332 83 17.8 7307 1251Aug—82 1.24 1.92 1.37 326 86 16.8 7620 1237Nov—82 1.21 1.72 1.24 277 80 16.4 7546 1199

Std. Dev. 0.34 0.34 0.24 92 22 0.7 1091 154CV* 0.22 0.16 0.16 0.20 0.19 0.04 0.12 0.11Average 1.58 2.07 1.51 452 116 16.9 8968 1438

(TABLE A—9. CONT’D)

(C) FeC13 Precipitant Addition to Primary and Aeration Basins

CD) FeC13 Precipitant Addition toFeSO4 Precipitant Addition to

Primary andAeration Basins

Student’s t—Test tables for the difference between means:

(A) 3.65 2.85(B) ******** —0.83

3.180.05

Critical t Values(B) (C)

1.70 1.761.69

Sludge Production Per:Plant Solids BOD&SS Cond. CheM. Dose Cake ProductionFlow Reaov’d Remov’d Line FeC13 Dryness Wet Dry

Month (DT/MGD) (DT/DT) (DT/DT) (#/DT) (#/DT) (~ Solids) Tons Tons

17.4 6612 1100

7990816081419405

1184124112651468

Dec—82 1.07 1.47 1.07 453 138 15.5Jan—83 1.08 1.64 1.17 573 119 16.1Feb—83 1.07 1.66 1.20 438 91 16.2Mar—83 1.24 1.90 1.41 382 94 16.1

Sep—83 1.05 1.24 0.93 404 120

Nov—83 1.09 1.40 1.10 415 128Dec—83 1.03 1.71 1.26 428 145Jan—84 1.18 2.03 1.46 523 126Feb—84 1.04 1.79 1.30 575 119Mar—84 0.79 1.37 1.04 582 89

Std. Dev. 0.11 0.24 0.16 74 19CV* 0.10 0.15 0.13 0.15 0.16Average 1.06 1.62 1.20 477 117

17.1 7720 126217.1 8540 138815.9 9778 147415.5 9718 142515.7 7969 1189

0.7 938 1230.04 0.11 0.0916.2 8403 1299

1.23 1.66 1.26 393 67 17.7 8596 14581.05 1.38 1.07 438 79 18.2 7102 12351.09 1.25 0.96 519 100 17.8 7415 1251

0.08 0.17 0.12 52 14 0.2 643 1020.07 0.12 0.11 0.12 0.17 0.01 0.08 0.081.12 1.43 1.10 450 82 17.9 7704 1314

May—83Jun—83Jul—83

Std. Dcv.CV*Average

Lime Dose (#/Dry Ton)(B) (C) CD)

(A)(B) ***********

(D)1.901.71

(C) ***************** 0.71 (C) ******************* 1.80

(TABLE A—9 CONT’D)

FeC13 Dose (#/Dry Ton)(B) (C) (0)

(A) 3.62 3.13 6.17(B) ******** —0.12 3.74(C) ***************** 3.55

Cake Dryness (~ Solids)(B) (C) (0)

(A) 3.23 4.38 0.82(B) ******** 2.45 —5.35(C) ***************** —6.59

Cake Production (Dry Tons)(B> (C) (0)

(A) —0.11 —1.00 —1.04(B) ******** 2.78 1.85(C) ***************** —0.23

Cake Production (Wet Tons)(B) (C) (0)

(A) —5.37 —3.27 —1.31(B) ******** 1.50 2.90(C) ***************** 1.47

Total Dry Tons Per MGD(B) (C)

(A) 0.77 4.54(B) ******** 6.59(C) *****************

Plant Flow(0)4.055.53

—1.03

Critical t Values(B) (C)

(A) 1.71 1.78(B) *********** 1.69(C) *******************

Critical t Values(B) (C)

(A) 1.70 1.76(B) *********** 1.69(C) *******************

Critical t Values(B) (C)

(A) 1.70 1.76(B) *********** 1.69(C) *******************

Critical t Values(B) (C)

(A) 1.70 1.76(B) *********** 1.69(C) *******************

CD)1.901.711.80

Total Dry Tons Per Ton(B) (C)

(A) 0.49 4.02(B) ******** 0.60(C) *****************

of Solids RemovedCD)4.895.311.52

Critical t Values(B) CC)

(A) 1.70 1.76(B) *********** 1.69(C) *******************

CD)1 .901.711.80

Total Dry Tons Per Ton of(Solids + 0.4*800) Removed

(B) (C) CD)(A) 0.96 4.35 4.78(B> ******** 4.44 4.80(C) ***************** 1.15

Critical t Values(B) (C)

(A) 1.70 1.75(B) *********** 1.69(C) *******************

* CV = Coefficient of Variation (Std. 0ev. I Average)

(0)2.021.711.80

CD)1.901.711.80

CD)1.901.711.80

(0)1.901.711.80

Critical t Values(B) (C)

(A) 1.70 1.76(B) *********** 1.69(C) *******************

CD)1.901.711.80

Note: All critical t values are at the 9O~ confidence level.

Effluent Suspended Solids Solids Recovery~gime (mglL) Percent Change (Percent)

(A) 216 93.3(B) 51 —76 98.9(C) 39 —82 99.4(0) 50 —77 99.1

Cake Dryness: Table A—9

Table A—9 presents comparisons of sludge cake dryness underthe four operating conditions listed above. A comparison of cakedryness under the no—addition regime to sludge production undereach of the chemical addition regimes is presented below:

Cake Change inDryness Cake Dryness

Regime (~ Solids) ~ Solids)

(A) 18.2(B) 16.9 —1.3(C) 16.2 —2.0(0) 17.8 —0.4

The change in cake dryness under regimes (B) and (C) werestatistically significant at the 90 percent confidence level; thechange in cake dryness under regime (0) was not statisticallysignificant. There were no significant differences in vacuumfilter operation among the four regimes.

Vacuum Filter Conditioning Chemical Use: Table A—9

Table A—S presents comparisons of conditioning chemical useunder the four operating conditions listed above. A comparisonof conditioning chemical use (ferric chloride and lime) under theno—addition regime to sludge production under each of thechemical addition regimes is presented below:

Ferric Chloride Dose Lime Dose~~gime (lbs/Dry Ton) 0’ Change) (lbs/Dry Ton) 0~ Chanq~

(A) 143 —— 597 ——

(B) 116 —19 452 — 24(C) 117 —18 477 — 20(D) 82 —43 450 — 25

All decreases in conditioning chemical doses werestatistically significant at the 90 percent confidence level.There were no significant differences in vacuum filter operationz~.rnonq the four reqisnes.

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A-4. Case Study No. 3: Water Pollution Control Plant, Arlington,Virginia

A—4..1 Description of Treatment Processes

The Arlington Water Pollution Control Plant (WPCP) providespreliminary, primary, secondary, and advanced wastewatertreatment for about 26 million gallons per day of domestic,commercial, and industrial wastewater collected from ArlingtonCounty and part of Fairfax County, Virginia.

Coarse solids and grit are removed from the wastewater inpreliminary treatment. Settleable solids are removed by gravityin primary clarifiers and collected as primary sludge.

Secondary treatment at the Arlington WPCP is accomplished bythe activated sludge process. The secondary teatment effluent isconveyed to the advanced wastewater treatment (AWT) systemoriginally designed for phosphorus removal by lime precipitation.

Description oi_ .luc1~e Processing

Primary sludge is thickened in gravity thickeners. Wasteactivated sludge is conditioned with polymer and thickened bydissolved air flotation Liquid separated from the sludges int.he thickeners is returned to the liquid treatment systems. Thethickened primary and secondary sludges are blended andconditioned with lime and ferric chloride before being processedby plate filter presses that “squeeze~ water out of the sludge.Prior to the installation of the plate filter presses, vacuumfilters were used to dewater primary and secondary sludge.

AWT sludge is conditioned with polymer and dewatered bycentrifuges prior to disposal.

Pho.~.phorus_Removal at the Ar1ij~~p_WPCP

As mentioned previously, the AWT system was designed forphosphorus removal by lime precipitation. Operational problemsled to the use of ferric chloride for phosphate precipitation inplace of lime in 1981. The ferric sludge from AWT was initiallyhsndled separately from primary and secondary sludge anddewatered with centrifuges. Beginning in October, 1982 theferric sludge was conveyed to the activated sludge system whereit. was eventually removed with the waste activated sludge. Thispractice was discontinued in 198~, and current operation is toprocess the ferric sludge separately.

A—4..2 Results of Arlington Data Analysis

Propensity to ThickenSludge Production/Solids LoadingSolids Capture

No operational data were available to characterizeperformance before precipitant addition.

Cake Dryness: Table A—bVacuum Filter Conditioning Chemical Use: Table A—b

Table A—b shows vacuum filter cake dryness and chemicaldose data for non—chemical sludge (primary and secondary sludgesonly; chemical sludge dewatered by centrifuge) and combinedprimary, secondary, and chemical sludges. Cake dryness for theseparate, non—chemical sludge was higher (17.3k) than the cakedryness for the combined sludge (16.2k); the difference wasstatistically significant. Conditioning chemical dose (lbs/dryton) was 2.2k higher for the combined sludge, but this differencewas not statistically significant.

TABLE A—b. Comparison of Vacuum Filter Performance forCombined and Separate Sludges, Arlington WPCP

Non—Chemical Sludge Combined Sludge

Cake Chemical Cake ChemicalDryness Dose Dryness Dose

Month (~ Solids) (#/Dry Ton) Month (% Solids) (#JDry Ton)

Jul—81 18.0 210 Sep—82 15.8 198Aug—81 18.7 191 Oct—82 15.4 203Sep—81 17.3 194 Nov—82 17.0 218Oct—81 17.2 187 Dec-82 17.7 210Nov—81 18.3 194 Jan—83 15.7 232Dec—81 16.5 223 Feb-83 15.7 203Jan—82 16.4 198 Mar—83 15.9 180Feb—82 163 204 Apr-83 16.4 189Mar—82 17.6 202 May—83 17.2 201Apr—82 17.5 186 Jun—83 15.5 198May—82 17.3 181Jun—82 17.3 229Jul—82 18.4 180Aug—82 15.9 204

Average 17.3 199 16.2 203Std. 0ev. 0.8 14 0.8 14Minimum 15.9 180 15.4 180Maximum 18.7 229 17.7 232

Student’s t-Test for difference between means: 3.41 —0.74

Critical values at the 90’s confidence level: 1.72 1.72