EPA-R2-73-264

 August 1973
Environmental Protection  Technology Series
 PHYSICAL  - CHEMICAL  TREATMENT

OF A  MUNICIPAL  WASTEWATER

USING  POWDERED  CARBON

                                      Ui
                                      0
                                      Office of Research and Development

                                      U.S. Environmental Protection Agency

                                      Washington, D.C. 20460

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             EPA Review Notice
This report has been reviewed by the Environ-
mental Protection Agency and approved for
publication.  Approval does not signify that
the contents necessarily reflect the views
and policies of the Environmental Protection
Agency, nor does mention of trade names or
commercial products constitute endorsement
or recommendation for use.
                    11

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                          ABSTRACT
A municipal wastewater was treated in a nominal  100 gpm pilot plant
by chemical coagulation-precipitation, powdered  activated carbon
adsorption and granular media filtration.   Spent carbon was  gravity
thickened, vacuum filter dewatered and thermally regenerated in a
fluidized bed furnace.  Solids-contact units were used for chemical
treatment and carbon contacting.

Ferric chloride, alum or lime were all found to  effectively  produce
coagulation and phosphorus insolubilization.  Based on total  treat-
ment costs, including sludge disposal, alum treatment was estimated
to be the economic choice for Salt Lake City municipal wastewater.

Organic removal in the powdered carbon contactors was substantially
enhanced by anaerobic biological activity.   The  use of solids-
contact treatment units for carbon contacting resulted in effecting
gravity clarification without the use of chemicals.

The powdered carbon physical-chemical treatment  system produced a
treated effluent similar to that expected  for biological  treatment
followed by tertiary treatment for phosphorus removal.

Carbon losses of 17 to 60 percent were experienced across the
fluidized bed furnace regeneration system.   The  cause of high carbon
losses was identified as ignition of carbon instead of gas which was
injected into the fluidized bed to scavenge excess oxygen.

This report was submitted by Eimco Processing Machinery Division of
Envirotech Corporation in fulfillment of Project #17020 EFB,
Contract #14-12-585 under the sponsorship  of the Office of Research
and Monitoring, Environmental  Protection Agency.
                                iii

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                      CONTENTS



Section                                                Page
  I     Conclusions                                      1



  II    Recommendations                                  3



  III   Introduction                                     5



  IV    Laboratory Study                                17



  V     Pilot Plant Description                         35



  VI    Approach to Pilot Plant Operation               49



  VII   Pilot Plant Results                             55



  VIII  Economic Analysis                              181



  IX    Additional Studies                             193



  X     Acknowledgements                               195



  XI    References                                     197



  XII   Publications and Patents                       201



  XIII  Abbreviations and Symbols                      203
                         v

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                       FIGUP.ES
                                                    PAGE
 1  PROCESS FLOWSHEET  OF  POWDERED CARBON
    PILOT PLANT

 2  OVEPALL PHOTO  OF PAC-PCT PILOT PLANT

 3  ALUM TREATMENT OF  RAW WASTEWATER

 4  FeCl3 TREATMENT OF RAW WASTEWATER

 5  LIME TREATMENT OF  RAW WASTEWATER

 6  LIME TREATMENT:  EFFECT OF INITIAL
    ALKALINITY

 7  LIME TREATMENT:  EFFECT ON HARDNESS

 8  LIME TREATMENT:  SOLIDS PRODUCTION

 9  LIME TREATMENT:  EFFECT OF POLYELECTROLYTE

10  FeCl3 TREATMENT:   EFFECT OF POLYELECTROLYTE

11  POWDERED CARBON TREATMENT:  ADSORPTION
    EQUILIBRIUM  ISOTHERM  TESTS

12  POWDERED CARBON TREATMENT:  EFFECT OF
    PRETREATMENT

13  POWDERED CARBON TREATMENT:  EFFECT OF
    PRETREATMENT

14  POWDERED CARBON TREATMENT:  CONCENTRATION
    EFFECT ON CLARIFICATION

15  EIMCO REACTOR-CLARIFIER SOLIDS-CONTACT
    CHEMICAL TREATMENT UNIT

16  VACUUM FILTRATION  OF  SPENT POWDERED CARBON

17  FLUIDIZED BED  REGENERATION FURNACE

18  PAC FLUIDIZED  BED  REGENERATION FURNACE

19  GRANULAR MEDIA FILTRATION STATION
 9

18

19

20

22


23

24

26

27

29


31


32


33


36


40

42

43

45
                          VI

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                   FIGURES (cont.)
20  COMPOSITE  SAMPLING AND PROCESS
    TURBIDITY  MONITORING DEVICE

21  FeCl3 TREATMENT:   FEED AND EFFLUENT
    SUSPENDED  SOLIDS  AND PHOSPHORUS

22  FeCl., TREATMENT:   POST-PRECIPITATION
    OF IRON

23  FeCl3 TREATMENT:   SLUDGE THICKENING

24  FeCl3 TREATMENT:   SLUDGE THICKENING

25  ALUM TREATMENT:   DOSAGE, FEED AND
    EFFLUENT SUSPENDED SOLIDS AND PHOSPHORUS

26  ALUM TREATMENT:   SLUDGE THICKENING

27  LIME TREATMENT:   FEED AND EFFLUENT
    SUSPENDED  SOLIDS

28  LIME TREATMENT:   FEED AND EFFLUENT
    PHOSPHORUS

29  LIME TREATMENT:   FEED AMD EFFLUENT
    SUSPENDED  SOLIDS

30  LIME TREATMENT:   FEED AND EFFLUENT
    PHOSPHORUS

31  LIME TREATMENT:   EFFECT OF SLUDGE
    AGE

32  LIME TREATMENT:   SLUDGE PRODUCTION

33  LIME TREATMENT:   SLUDGE THICKENING

34  LIME TREATMENT:   SLUDGE THICKENING

35  LIME TREATMENT:   SLUDGE THICKENING

36  LIME TREATMENT:   SLUDGE THICKEING

37  LIME TREATMENT:   SLUDGE DEWATERING

38  LIME TREATMENT:   SLUDGE DEWATERING
PAGE

 47


 59


 60


 64

 65

 69
 83
 85


 86


 90

 93

 94

 95

 97

 98

101
                          VII

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                 FIGURES  (cont.)

                                                   PAGE

39  CARBON TREATMENT:  INDIRECT EFFLUENT          116
    SUSPENDED SOLID MEASUREMENTS

40  CARBON TREATMENT:  EFFLUENT SUSPENDED         118
    SOLIDS

41  CARBON TREATMENT:  EFFLUENT SUSPENDED         119
    SOLIDS

42  CARBON TREATMENT;  EFFLUENT SUSPENDED         120
    SOLIDS

43  CARBON TREATMENT:  TRANSIENT  TURBIDITY        122
    EFFECT ON CLARIFICATION

44  CARBON TREATMENT:  FEED VERSUS  EFFLUENT       123
    SUSPENDED SOLIDS

45  GRANULAR MEDIA FILTRATION:  CYCLE TIME        128
    VERSUS FILTRATION RATE

46  GRANULAR MEDIA FILTRATION:  HEADLOSS          130
    DISTRIBUTION

47  CARBON TREATMENT:  SCOD REMOVAL FOR           138
    TWO-STAGE COUNTER-CURRENT TREATMENT

48  CARBON TREATMENT:  SCOD REMOVAL FOR SINGLE    140
    AND TWO-STAGE COUNTER-CURRENT TREATMENT

49  CARBON TREATMENT:  ORGANIC REMOVAL MODEL      144
    (SCOD)

50  CARBON TREATMENT:  RELATIONSHIP BETWEEN       146
    FEED AND EFFLUENT SCOD AND CARBON DOSAGE

51  CARBON TREATMENT:  TYPICAL EFFLUENT SCOD      148
    VARIATIONS

52  CARBON TREATMENT:  TYPICAL EFFLUENT SCOD      149
    VARIATIONS

53  CARBON TREATMENT:  EFFECT OF  MASSIVE          150
    CARBON DOSAGE
                          vi 11

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                 FIGURES  (cont.)

                                                   PAGE

54  PILOT PLANT EFFLUENT  QUALITY  FOR              170
    RUNS F-3 AND C--14

55  PILOT PLANT EFFLUENT  QUALITY  FOR              171
    RUNS A-2 AND C-7

56  PILOT PLANT EFFLUENT  QUALITY  FOR              172
    RUNS L-9 AND C-8

57  PILOT PLANT EFFLUENT  QUALITY  FOR              173
    RUNS L-ll AND C-9

58  PILOT PLANT EFFLUENT  QUALITY  FOR              174
    RUNS L-4 AND C-ll

59  POWDERED ACTIVATED  CARBON PCT                 182
    TREATMENT SYSTEM
                          IX

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 No.
                      TABLES

                                                  Paqe
 1      Scheduled Analytical Tests for                53
       Composite Samples

 2      Fed- Treatment:  Summary of Results          57

 3      FeCl3 Treatment:  Summary of Sludge           62
       Production Data

 4      FeCl3 Treatment:  Vacuum Filtration           66
       Leaf Test Results

 5      Alum Treatment:  Summary of Results           63

 6      Alum Treatment:  Cost Trade-Off of            71
       Polyelectrolyte and Clarification
       Area for 10 NHD Flow

 7      Alum Treatment:  Summary of Sludge            73
       Production Data

 8      Alum Treatment:  Vacuum Filtration Leaf       76
       Test Data

 9      Lime Treatment:  Summary of Results           77

 10     Lime Treatment:  Sludge Production            89

 11     Suggested Design Parameters for Lime-       100
       Sewage Sludge Thickening and Dewatering

 12     Summary of Suggested Chemical Treatment     103
      Process Design Parameters

 13    Summary of Two-Stage Counter-Current Carbon 105
      Treatment Results

14    Summary of Single-stage Carbon Treatment    108
      Results

15    Determination of Solids Inventory Within a  113
      Carbon Contactor
                         x

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                  TABLES (cont.)

No.                                               Page

16    Sulfide Profile Through the PAC-PCT Pilot   115
      Plant

17    Cost Trade-Off of Polyelectrolyte and       125
      Clarification Area for Carbon Treatment
      (10 MGD Flow)

18    Granular Media Filtration:   Clarification   127
      Effectiveness at High Feed Solids

19    Carbon Treatment:  Summary of SCOD Removal  132
      Data

20    Carbon Treatment:  Summary of STOC Removal  134
      Data

21    Correlation of Soluble TOC with Soluble COD 135

22    Carbon Treatment:  Adsorption Models of     137
      SCOD Removal Data

23    Carbon Treatment:  Model of SCOD Removal    143
      Data

24    Summary of Spent Carbon Gravity Thickenincr  154
      Results

25    Summary of Spent Carbon Vacuum Filtration   156
      Results

26    Summary of Spent Carbon Dewatering Data     160

27    Carbon Regeneration:  Furnace Operating     162
      Conditions

28    Comparison of Regenerated and Virgin Carbon 168
      Treatment Effectiveness

29    Ammonia Nitrogen Profile                    175

30    Assumed Unit Costs for Economic Analysis    183

31    Major Equipment Sizes                       184

32    Estimated Chemical Treatment Costs          185
                         XI

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                  TABLES  (cont.)

No.                                                Page
33    Estimated Powdered Carbon Treatment          187
      Costs

34    Estimated Pov/dered Carbon Treatment          190
      Costs for Various Regeneration Losses

35    Estimated Pov/dered Carbon Regeneration       191
      Costs
                        Xll

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                     SECTION I

                    CONCLUSIONS


1.  The powdered activated carbon - physical-chemical
    treatment process evaluated produced a highly
    clarified effluent with COD values of 8 to 36 mg/&
    for carbon dosages of 350 to 75 mg/Jl.

2.  Alum, ferric chloride and lime were equally effective
    in achieving coagulation and phosphorus insolubiliza-
    tion.

3.  Alum treatment of 10 mgd of Salt Lake City waste-
    water for phosphorus removal and clarification was
    estimated to be less expensive than Fed, or lime
    treatment.

4.  The removal of soluble COD by powdered activated
    carbon was not significantly influenced by the
    type of chemical used .in the chemical treatment
    step.

5.  Gravity clarification in the carbon contactors was
    accomplished at overflow rates up to 0.8 gpm/sq ft
    without the addition of chemical flocculating agents.

6.  Two-stage counter-current carbon contacting was
    found to require less carbon than single-stage
    carbon contacting to produce a given effluent
    soluble COD; however/ the pilot plant results were
    not precise enough to define the difference with
    a significant level of statistical confidence.

7.  Anaerobic biological activity in the carbon contactors
    resulted in removal of significant amounts of soluble
    organic material.

8.  Laboratory equilibrium adsorption isotherm test re-
    sults could n6t predict pilot plant soluble organic
    removal.

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9.   Alum - powdered carbon  treatment  of  10  mgd  of  Salt
    Lake City wastewater, with  thermal regeneration and
    reuse of  carbon,  to  produce an effluent containing
    0.5 mg/£  phosphorus,  5  mg/£ suspended solids and
    24  mg/£ COD  was estimated to cost 18.3£/1000 gallons,
    If  powdered  carbon were not regenerated, but used
    only once, the  total  treatment cost was estimated
    to  be 21.5C/1000  gallons.

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                    SECTION II

                  RECOMMENDATIONS
1.   Conduct a long term study using powdered carbon
    physical-chemical treatment process under con-
    ditions of diurnal flow to develop design,
    operating and efficiency data.

2.   Evaluate the use of automatic process monitoring
    and control systems, for example:

    a.  automatic organic carbon monitoring around the
        carbon treatment process.

    b.  automatic phosphate monitoring after the chemical
        treatment stage.

    c.  automatic density control of chemical and carbon
        slurry and blowdown solids.

    d.  automatic coagulation control.

3.   Conduct pilot plant scale gravity thickening and
    dewatering tests of chemical-sewage sludge to de-
    velop design data.

4.   Conduct a comparative study of granular activated
    carbon and powdered activated carbon systems at
    pilot plant scale following chemical treatment of
    raw wastewater.

5.   Conduct a thorough economic analysis of the powdered
    carbon process to determine the effect of plant size
    and effluent requirements, identifying areas of
    applicability.  Carbon on a throw-away basis should be
    included.

6.   Additional studies should be made to refine the powdered
    carbon regeneration process and obtain long-term regener-
    ation and reuse data.

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                    SECTION III

                   INTRODUCTION
Physical-Chemical Treatment (PCT) of wastewater, as
discussed herein, consists of chemical coagulation-
precipitation followed by activated carbon contacting.
Raw wastewater is treated with chemicals and gravity
settled to remove suspended solids and phosphorus.
The clarified wastewater is then contacted with powdered
activated carbon to remove soluble organic material.  If
a highly clarified effluent is desired, granular media
filtration is employed.

Physical-Chemical Treatment was originally developed as
a tertiary method for reclamation of secondary biological
effluents.  In recent years, PCT has been evaluated as a
method for treatment of raw wastewaters.  Because of well
developed regeneration technology, major emphasis has been
placed on studying granular activated carbon.  The use of
powdered activated carbon  (PAC) has, however, several poten-
tial advantages when compared to granular carbon; namely:

1.  The cost of powdered carbon per pound is 1/4 to 1/3.

2.  Powdered carbon will equilibrate with soluble wastewater
    organics in a fraction of the time.

3.  Powdered carbon is easily slurried and transported, and
    can be supplied on demand by metering pumps.

4.  Powdered carbon might be supplied on demand to meet
    varying feed organic strength.

5.  A powdered carbon system requires a fraction of the
    carbon inventory.

6.  A powdered carbon adsorption system has considerably
    less headloss.

A recent study has indicated that thermal regeneration of
powdered carbon is technically feasible and may be economical.1
This fact coupled with the above potential advantages prompted
the present study.

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 The specific objectives of this study were as follows:

 1.  Establish operating parameters of a PAC-PCT treatment
     system.

 2.  Determine the effect of PAC dosage and methods of plant
     operation (i.e., single-stage versus two-stage counter-
     current) on removal of soluble organics.

 3.  Accumulate operating and process efficiency data to
     establish process design criteria for the production
     of high and moderate quality effluents.

 4.  Demonstrate fluidized bed thermal regeneration and reuse
     of powdered carbon.

 5.  Make an economic analysis comparing different chemical
     and PAC treatment approaches, establishing total and
     incremental treatment costs.

 6.  Determine if a correlation exists between accepted
     laboratory simulation methods and pilot plant scale
     data.
 APPROACH

 During the last six months of 1969,  a nominal 100 gpm con-
 stant flow pilot plant was constructed.   The powdered carbon
 regeneration facility was not constructed at this time.

 During this same period,  laboratory  tests were conducted
 for the purpose of determining PAC and chemical requirements
 for producing desired effluents and  for  predicting plant
 operating conditions.

 The first six month period was designated as Phase I of
 the study.

 Phase  II  comprised calendar year 1970 and the first six
 months  of 1971.   Three chemicals (lime,  ferric chloride,
 and  alum)  and the effect  of polyelectrolytes were studied.
 Single-stage  and two-stage counter-current adsorption
 systems were  evaluated at six and four powdered carbon
 dosage  levels respectively.   The multiplicity of variables
 evaluated necessitated short plant test  runs of two  to six
 weeks.

 During Phase  II,  design of the fluidized  bed  furnace  for
 carbon regeneration was finalized and construction funds
were obtained.   Installation of  the regeneration system
was completed  in March, 1971.

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The last three months of the contract period involved a
concentrated evaluation of the carbon regeneration sub-
system.
PROCESS DESCRIPTION

A process flow diagram of the powdered carbon physical-
chemical treatment process studied is shown in Figure 1.
Both chemical and PAC adsorption treatment were accomplished
in solids-contact treatment units similar to those which
have been successfully applied for years in potable water
treatment.  The granular media filter was also similar
to that used in water treatment applications.

The spent carbon regeneration system consists of:

1.  Gravity thickening,

2.  Vacuum filtration dewatering,

3.  Thermal regeneration in a fluidized bed furnace,

4.  Collection of regenerated PAC by venturi water scrubbers.

All these unit operations are well established in the art,
but have never been used at this scale to regenerate spent
carbon.

With exception that no means were provided for thickening,
dewatering and ultimate disposal of the chemical-sewage sludge
or effluent disinfection, the process described and tested
was a complete wastewater treatment system.  A photograph of
the pilot plant is shown in Figure 2.


PCT PROCESS BACKGROUND

Chemical Treatment

The first major unit process in PCT is chemical treatment
of raw wastewater.  Normally, coarse screening, comminution,
and possibly degritting would be provided prior to chemical
treatment.  Chemical treatment comprises the addition of
chemicals to wastexvater to achieve coagulation of suspended
solids and insolubilization of phosphorus compounds, followed
by liquid-solids separation by gravity sedimentation.  Unit
operations historically employed are rapid mixing for chemical
dispersion and reaction  (coagulation, precipitation), gentle
mixing for flocculation  (floe growth) and quiescent detention

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   RAW SEWAGE—
   CoanM-Screened
   and Comminuted
HOLDING TANK
                                                                                          Plant Effluent
                                                                                         Plant Pressurized
                                                                                          Water System
                                                                             PAC = POWDERED ACTIVATED CARBON
                               PAC- REGENERATION
         FIGURE I:   PROCESS  FLOWSHEET OF  POWDERED CARBON  PILOT PLANT

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FIGURE 2:  OVERALL PHOTO OF PAC-PCT PILOT PLANT

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for sedimentation.  Considerable art on the subject of
chemical treatment of wastewaters has been reviewed else-
where2 .

A recent development for effecting chemical treatment of
raw wastewater has been the use of solids-contact treatment.
The interest in this approach is indicated by several pilot
plant studies, for example, at Washington, D. C.; Cleveland,
Ohio and Clay County, New York3'1*'5.

The key feature of solids-contact treatment units is the^
ability to maintain high concentrations of suspended solids
in contact with the raw wastewater.  Precipitated solids
are accumulated within the unit to a desired quantity and
kept in suspension by a submerged pumping turbine.  Solids
are wasted at an  average rate equal to the rate of solids
accumulated resulting from removal of raw wastewater sus-
pended solids and chemical precipitates.

Coagulation of suspended solids and phosphorus precipitation
by alum or ferric salt treatment are very rapid reactions,
usually being completed in a matter of seconds6'7.  Conse-
quently, efficient rapid dispersion of alum or  ferric salt
throughout the raw wastewater must be accomplished prior
to solids-contacting.  Presumably, the benefit of solids-
contacting results from improved flocculation efficiency.
It has been shown that flocculation efficiency is directly
proportional to mixing energy, mixing time and the
number  (or concentration) of particles present8.  Solids-
contact treatment provides relatively high particulate con-
centrations and relatively long floe detention times.  For
example, for chemical treatment of raw wastewater, 10-30
times as many suspended solids are maintained in contact with
the wastewater in a solids-contact unit than would exist
in a once through flocculation system (e.g., 0.3 - 0.9 per-
cent suspended solids versus about 0.03 percent).

The hydraulic retention time for solids-contacting will
normally be 15-30 minutes, however, the floe mean resi-
dence time will be at least several hours.

Coagulation and phosphorus insolubilization by lime treat-
ment involves complex chemical and physical interactions.
The addition of lime to wastewater simply adjusts the solu-
tion pH to a level which results in precipitation of various
chemical compounds.   For example, above certain pH values,
phosphorus is insolubilized (e.g., hydroxylapatite), and
CaC03  and  Mg(OH)   precipitated.  It has been reported that
certain  condensed phosphates are removed from solution by
adsorption on chemical precipitates9.   The coagulation-
                         10

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flocculation effectiveness of lime treatment presumably
results from destabilization and/or agglomeration of waste-
water colloids with precipitated Mg(OH)2 floe.  It would
seem logical to expect solids-contact treatment to enhance
lime treatment precipitation, adsorption and flocculation
reactions.

It has been reported that lime treated wastewater is
supersaturated with CaCO3 and other precipitating sub-
stances; hence, there is a tendency for scale to form on
equipment and pipe surfaces10.  Application of solids-contact
treatment to lime softening of water has shown that a stable
water can be produced.  The presence of condensed phosphates
and soluble organics in raw wastewaters inhibit the growth
of CaCC>3 precipitates.  However, solids-contacting should
provide more efficient reaction of lime and more complete
precipitation of CaCC>3, compared to a once through rapid-
mix, flocculation and sedimentation approach.

The presence of a large inventory of chemical-sewage solids
in a solids-contact unit presents a possible problem.  A
sudden flow increase  (greater than designed for) or chemical
upset  (interrupted chemical feed) could result in gross
carryover of suspended solids.  Proper operation will mini-
mize this danger which also exists to a lesser degree,
in a once through rapid mix flocculation and sedimentation
system with or without sludge recycle.
Powdered Carbon Treatment

Appendix A presents  a discussion of some academic aspects
of soluble organic adsorption on activated carbon.  The
often used Freundlich model and the effect of counter-current
contacting are discussed.

In the practical  application of activated carbon to waste-
water, soluble organics are removed from solution by more
than just physical adsorption.  The concentration of soluble
biodegradable organics on the carbon surface by physical
adsorption should provide a very favorable environment for
biological activity.  The relatively long carbon  (and bio-
mass) retention time in granular carbon columns should en-
hance anaerobic biological activity.  In at least two studies
anaerobic biological activity was considered to significantly
increase organic  removal compared to physical adsorption
only11'12.   Such  an  observation has not been reported for
powdered carbon systems.  The reason for this may be due to
considerably shorter carbon retention times which would mini-
mize anaerobic activity.
                          11

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 Conventional application of powdered carbon involves three
 steps:  1) rapid mixing for carbon dispersion,  2)  gentle mix-
 ing for a desired contact time, and 3)  liquid-solids separa-
 tion by gravity sedimentation and granular media filtration.

 Effective gravity sedimentation of powdered carbon suspen-
 sion has required considerable chemical additions  to achieve
 particle growth and settleabilityl3'l  'l  '  -   Alum and/or
 polyelectrolytes have been used for achieving coagulation
 and/or aiding flocculation.

 Multiple stages of counter-current carbon contacting can
 result in significantly reduced carbon  dosage requirements
 to obtain a given system effluent organic concentration (see
 example in Appendix A).  One economic analysis  has indicated
 that two-stage counter-current contacting of powdered carbon
 was the economic choice for treating secondary  biological
 effluents15.   The use of a single solids-contact treatment
 unit for powdered carbon treatment of secondary biological
 effluent has  been shown to result in about one  and a half
 stage efficiency13.   In other words, 33 percent less carbon
 would have been required for solids-contact treatment compared
 to a conventional once  through carbon contacting system.  These
 results were  later confirmed for the treatment  of  primary
 effluent17.   In both of the above studies, it was  implied
 that solids-contact  treatment provided  enhanced physical
 adsorption.   It is,  however, more reasonable to assume that
 biological oxidation of soluble organics  caused the improved
 treatment  results.   This conjecture is  based on the fact
 that carbon and biomass residence time  in a solids-contact
 unit is  considerably greater than in a  conventional once
 through system.

 The  use  of solids-contact units for powdered carbon contact-
 ing  should provide an additional benefit  due to "adsorptive
 buffering  capacity".  This is,  the maintenance  of  a large
 inventory  (mass)  of  carbon in contact with a time  varying
 concentration of  soluble organics results in only  slight
 changes  in system effluent.   This effect  can best  be illus-
 trated by  an example of soluble COD (SCOD)  removal on powdered
 carbon.  Consider a  constant flow,  single-stage adsorption
 system  (see Figure A-2 ,  Appendix A), whose adsorptive relation-
 ship is described by the Freundlich model (see  Curve A,  Figure
A-l, Appendix A) :

     C —C
     -~-^ =  (3.7 x  10-5)ce2-5                          (1)
                          12

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where:  C  = feed SCOD, mg/£
        Ce = effluent SCOD, mg/£
         M = PAC dosage, mg/S,

The following conditions are assumed:

   Flow = 100 5,/min
   Reaction zone hydraulic retention time =  30 min
   Reaction zone SS concentration = 11.5 g/5, of PAC
   C0 = 50 mg/£ SCOD
   Ce = 20 mg/£ SCOD

From Equation  (1):

   Organic Loading = 3.7 x 10~5  (20 mg/£)2'5
                   = 0.067 g SCOD/g PAC

   Reaction Zone PAC =  100 £/min  (30 min) 11.5 g PAC/£
                     =  34,500 g PAC

   SCOD Adsorbed = 34,500 g PAC  (0.067 g SCOD/g PAC)
                 = 2310 g SCOD

If the feed SCOD  (Co) abruptly increases from 50 to  60 mg/£
and the PAC dosage  (M)  remains constant, the maximum incre-
mental increase, after  two hours  (120 min) operation, in
SCOD adsorbed on the PAC inventory would be  as follows:

   A SCOD adsorbed - 120 min  (60-50 mg/& SCOD)(100  £/min)
                   - 120,000 mg SCOD
                   = 120 g SCOD

   New organic Loading  = "10 |4*g° +g j|° " SCOD
                        = 0.070 g  SCOD/g PAC

Substitution of the new organic loading into Equation (1):

   New effluent SCOD =  20.5 mg/£

Thus, for the example given, a 2.5 percent increase  in
effluent SCOD would result two hours after a 20 percent
increase  in feed SCOD.  Had no PAC inventory been  present
 (e.g., once through contacting versus solids-contacting),
then the effluent SCOD  would have increased  8.5 percent.

The solids-contact approach may provide another substantial
benefit when applied to the powdered carbon  process.   It
                          13

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has been reported in the literature that suspensions of
powdered carbon exhibit a self-flocculating character-
istic15'18.  In one study, concentrated suspensions were
found to settle much more rapidly than dilute suspensions.
This observation prompted a recommendation of sludge-blanket
clarification for achieving effective liquid-solids separa-
tions of carbon slurries15.

In another laboratory study, it was observed that following
gravity sedimentation supernatant carbon concentration
decreased significantly as the initial carbon concentration
increased above 150 mg/£18.

As indicated earlier in this section, solids-contacting
should provide improved flocculation efficiency by virtue
of the high particulate concentrations and relatively lona
particle residence time.


Powdered Carbon Regeneration

The  most promising approach to regenerating powdered carbon
appears to be by thermal methods.  The spent carbon is sub-
jected to a temperature of 1200-1600 °F for a period of
several seconds in an atmosphere containing less than about
1 percent oxygen by volume.  Water associated with the spent
carbon is vaporized and adsorbed organics are volatilized
and  oxidized.  Proposed thermal regeneration systems require
a very efficient powdered carbon off-gas separation step.
Since wetting and degassing are necessary prior to reuse, wet
scrubbing methods are applied to capture the regenerated
carbon.

There have been at least four approaches evaluated for thermal
regeneration of powdered carbon:

1.  Indirect heated transport reactors

2.  Partial wet air oxidation

3.  Direct heated transport reactor

4.  Fluidized bed furnace

No public disclosures of indirect heated transport reactors
are available.   In private communications, representatives
of one firm indicate carbon losses across their entire full
scale regeneration system of less than 5 percent19.  The
regenerated product is used in a chemical processing system.
                          14

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The wet air oxidation system involves subjecting a thickened
powdered carbon slurry  (about 6-8 percent solids by weight_
to detention in a pressurized, steam heated reactor20.  The
reactor product  (carbon slurry) is passed through a decant
tank prior to reuse.  Results of a laboratory evaluation
indicated effective recovery of carbon adsorption properties.

The direct heated transport reactor -approach involves feed-
ing thickened spent PAC  (about 10 percent solids by weight)
into a direct flame reactor in which the temperature is
maintained at about 1400-1600°F2l.  The carbon detention
time in the reactor is approximately one second.  The carbon
is captured in water and air cooled jet condensers.  Evalua-
tion of a 4 Ib/hr  (dry carbon feed unit indicated recoveries
of 90 percent and near complete recovery of adsorption character-
istics l.  Another evaluation of the same direct heated trans-
port reactor indicated average PAC recoveries of 84 percent1.
In this latter study, considerable difficulty was encountered
in maintaining a "choke" ring in the gas burning chamber.

The fluidized bed furnace approach was developed by Battelle
Memorial Institute22.  It involves injection of dewatered,,
spent powdered carbon  (about 25 percent solids by weight)
directly into a fluidized bed of inert material (sand).  The
fluidized bed is maintained at 1200-1500°F by combustion gas
flow.  Excess oxygen in the exhaust gases is held at less
than 1 percent by volume.  The carbon detention time is about
4-8 seconds.  Evaluation of a 4 Ib/hr  (dry carbon feed) unit
indicated recoveries of 86 percent1.  Operation of the fluidized
bed furnace system was considered successful with no major
difficulties.  A comparative evaluation of the above direct
heated transport reactor and fluidized bed furnace resulted
in the latter being chosen for development at a larger scale1.
                          15

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                    SECTION IV

                  LABORATORY STUDY
Laboratory studies were conducted during Phase I to
develop background data on the response of Salt Lake
City raw wastewater to the physical-chemical unit processes
embodied in the pilot plant.

Analytical and testing procedures used are presented in
Appendix B.  Of basic importance is the definition of
soluble pollutants as those that pass through a 0.45 micron
membrane filter.
CHEMICAL TREATMENT

Three chemical treatments which are generally considered
to provide both coagulation and phosphorus precipitation,
were evaluated by jar tests of several raw wastewater samples.
The chemicals used were alum, FeCl3 and hydrated lime.  Figures
3, 4 and 5 show typical data from these tests.  Note that
soluble COD  (SCOD) and phosphorus, are shown.

Alum treatment data in Figure 3 indicates a drop in pH
for increasing alum dosage, as expected.  An optimum alum
dosage based on phosphorus precipitation and turbidity re-
duction, occurs at 20 mg/Jl Al  .  Above this dosage, re-
sidual turbidity increases, indicating a redispersion of
colloidal aluminum precipitate (presumably a hydroxide).
Soluble phosphorus remains very low, indicating that the
phosphorus precipitate is not solubilized.

Of interest is the removal of some 10-20 percent of the
SCOD.  The significance of this observation is that a re-
duced amount of SCOD would report to the subsequent carbon
adsorption step.  Consequently, a proportionate reduction
in carbon requirements would be expected.

The ferric chloride treatment results, shown in Figure 4
follow the same general trends as for alum, except that
redispersion was not observed for FeCl3 dosages up to 135
mg/a of Fe+3.  The optimum Fe+3 dosage appears to be about
65 mg/£.
                          17

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FIGURE  3: ALUM TREATMENT OF  RAW WASTEWATER
          Soluble Total Phosphorus
                                                             in
                                                             ro
                                                             O)




                                                             of
                                                             3
                                                             a
                                                             in
                                                             o
                                                             r
                                                             a.

                                                             15
                                                             O
                                                            w
   20
                40           60


            Alum Dosage, mg/l as AI+3
80
                18

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                  FIGURE 4:  FeCI3 TREATMENT OF  RAW WASTEWATER
80
70
                                                                          6__3
                                       Soluble Total Phosphorus
                                                                                 in
                                                                                 n
                                                                                 o>



                                                                                 in



                                                                              2  1
                                                                                 0.
                                                                                 OT
                                                                                 o

                                                                                 Q.
                                                                                 _

                                                                                 £1
                                                                                 3

                                                                                 O

                                                                                 V)
                             50           75           100


                        Ferric Chloride Dosage, mg/l as Fe4*
125

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            FIGURE 5:  LIME TREATMENT OF RAW WASTEWATER
16 i.
14 X
12..
•2*  10j_
H5
!5
|    84-


o>
Q.
 6-L
 44-
                                                 Raw Wastewater

                                               Turbidity = 26 JTU
                                                                           11.2
                                                                        I  1.0
                                                                          0.8
                Soluble Total

                 Phosphorus
                                                                        I  0.6
                                                                               in
                                                                               (B
                                                                               O)
                                                                               O

                                                                               a
                                                                               V)
                                                                               o
                                                                                  a>
                                                                                  3

                                                                                  o
                                                                        I  0.4
                                                                       _L 0.2
                                                                        I o.o
  9.0
                       9.5              10.0


                             Lime Treatment pH, Units
                                                     10.5
11.0

-------
It appears that Al   is more effective than Fe   based, on
the optimum dosages noted above  (e.g., 0.74 millimoles Al+J
versus 1.2 millimoles Fe  ) .  Assuming filter alum )9.1
percent Al+3 by weight) costs 3.5*/lb"and Fed-, costs
5C/lb, the above optimum dosages result in FeCl3 chemical
costs being 22 percent more than for alum.

The response of raw wastewater to hydrated lime, Ca(OH)2f
treatment is indicated in Figures 5 through 8.  As lime'
is added to and reacts with the wastewater, the solution
pH increases as indicated in Figure 6.  One reaction
occurring is the conversion of biocarbonate to carbonate
alkalinity.  This reaction is essentially complete at a
pH of about 9.  The amount of bicarbonate alkalinity initially
present affected the lime dosage required to obtain a given
treatment pH  (see Figure 6).

Figure 7 indicates that as the pH is raised above 9.5,
calcium is precipitated  (as CaCOO and non-calcium hard-
ness cations begin to precipitate  (e.g., MgfOHjj)*  For
the wastewater samples tested, minimum CaCO, solubility
appears to be at a pH of 10.4.  Magnesium hydroxide is
generally considered to be the chemical species effecting
coagulation for lime treatment.  An operating pH in excess
of about 10.5 is required to provide precipitation of sig-
nificant quantities of magnesium hydroxide.  From data
presented in Figure 5, a turbidity reduction of 90 percent
is not achieved until a treatment pH in excess of about
10.7 is reached.  The soluble total phosphorus is reduced
to about 0.3 mg/£ at pH 10.7.

An example of solids production resulting from lime treat-
ment is shown in Figure 8.  Solids production in the pH
range of 9.5 to 10.5 is mainly due to precipitation of
CaC03.  In the pH range 10.5 to  11.5 few additional solids
are produced, presumably only small quantities of MgCOH)^.
Solids production in this pH range is about 7000 Ib/MG
 (840 mg/A).  Above a pH of 11.5  solids production can
only be explained as being due to unreacted CafOH^-
As the pH increases from 10.4 to 12.5, the ratio of pounds
of solids produced per pound of  lime added is seen to de-
crease from 1.7 to 0.7.

Based on typical jar test results presented, the following
approximate dosages of chemicals tested would be required
to provide effective clarification  (<10 JTU turbidity)
and soluble total phosphorus removal  (<0.3 mg/£):
                          21

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        FIGURE 6:  LIME TREATMENT: EFFECT OF INITIAL ALKALINITY
900- -
800 - -
                              Raw Wastewafer
                                 Alkalinity
                              mg/l as CaCO3  300
                            9            10

                           Lime Treatment pH, Units
                            7 7

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FIGURE 7:  LIME TREATMENT: EFFECT ON HARDNESS
   Raw Wastewater
   Alk = 240 mg/l
      (as CaCO3)
      pH = 7.75
             9           10

        Lime Treatment pH, Units
              23

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                    FIGURE 8:  LIME TREATMENT :  SOLIDS  PRODUCTION
   1600..
                    --1.6
    1400--
    1200..
    1000- -
CO
0)

I
CO
    800- -
    600--
    400- -
    200- -
                                                                              0.0
                                9           10

                               Lime Treatment pH, Units
11
            12

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          Chemical _ Dosage _

          Alum                    150 mg/A
          FeCl3                   150 mg/Jl
          Ca(OH)2                 450-600 mg/£

These approximate dosages were used in subsequent pilot
plant tests.

Since a solids-contact unit was to be used in pilot plant
tests, an attempt was made to simulate this process by
modified jar tests  (see Appendix B for the procedure) .
Tests were conducted with 200 mg/£ of FeCl3, 220 mg/Jl filter
alum and lime treatment at a pH of 11.  Several tests were
conducted with 4 to 6 contacts and one lime treatment test
was carried through 20 contacts.  The contacts indicate the
number of times the settled sludge is accumulated from a
single jar test.  No significant change in supernatant
turibidity, total phosphorus or floe settling rates were
observed in any of the jar tests.  It was, therefore, con-
cluded that any benefit of solids-contact treatment would
have to be demonstrated by pilot plant tests.

Anticipating that polyelectrolyte flocculation aids
would improve chemical treatment floe settling rates ,
jar tests were conducted to quantify relative effects.
Preliminary screening tests indicated that moderately
anionic polyelectrolytes were effective flocculation
aids for the three chemicals studied  (alum, FeCl^ and
lime).  Atlasep 2A2 , a product of Atlas Chemical
Industries, was used in subsequent jar test studies.

Figure 9 shows that lime treatment floe settling rates
were increased three fold with a dosage of 0.75 mg/Jl
polyelectrolyte.  It is also apparent that this poly-
electrolyte dosage affected removal of substantial
turbidity causing material not removed without poly-
electrolyte.
Figure 10 shows the effect of polyelectrolyte on
treatment floe settling rates and supernatant turbidity.
An optimum dosage of polyelectrolyte exists between 0.25
and 0.50 mg/£.  The significant increase in floe settling
rates would superficially appear to warrant the use of
polyelectrolyte with FeCl3 treatment.
                          25

-------
FIGURE 9: LIME TREATMENT: EFFECT OF POLYELECTROLYTE
          Anionic Polyelectrolyte Dosage, mg/l

-------
            FIGURE  10: FeCI3 TREATMENT:  EFFECT OF POLYELECTROLYTE
E
~^
in
o
01
c
0)
CO

u
_o

u.

•o
0)


ai
0.2           0.4           0.6



   Anionic Polyelecrolyte Dosage, mg/l
                                                            0.8
1.0

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POWDERED CARBON TREATMENT

Equilibrium adsorption isotherm tests were used to
simulate removal of soluble organics by physical ad-
sorption on powdered carbon.  The TOC analyzer was not
available when the laboratory adsorption tests were
conducted so soluble COD was used as a measure of
organic concentration.  Total COD measurements of
powdered carbon suspensions in tap water indicated
that 1 mg/£ of powdered carbon (Aqua Nuchar A, a pro-
duct of Westvaco Corporation) exerted a COD of about
1 mg/£.  Therefore, all samples, including blanks,
were filtered through 0.45 micron membrane filters
prior to COD determinations and the results reported
as soluble COD  (SCOD).

Brief screening tests failed to show any superior ad-
sorption characteristics for four different commercial
powdered activated carbons.  The decision was made to use
Aqua Nuchar A based on its relatively low cost and the
fact that it had been used in several other relevant
studies14'15-16'17'23.

Figure 11 shows results of several  equilibrium tests
on raw wastewater.  It is readily apparent that most
of the equilibrium results cannot be modeled  by the
often used Freundlich equation.  The  trend of several
curves toward a vertical asymptote  at  low values of
equilibrium SCOD might be due to the  existance of an
unadsorbable SCOD fraction.

Equilibrium tests were conducted to determine if different
chemical pretreatments affected the adsorption of SCOD on
powdered carbon.  Raw wastewater samples were coagulated-
flocculated and settled using:
     1.  150 mg/£ of  FeCl3
     2.  No chemical
     3.  Lime  (Ca(OH)2) to pH 12.0  ±  0.2

Supernatants from the settled samples were filtered through
0.45 micron membrane  filters and equilibrium  adsorption
isotherm tests conducted using Aqua Nuchar A.
                         28

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    0.8


    0.6



    0.4
                   FIGURE 11:  POWDERED  CARBON TREATMENT:
                   ADSORPTION EQUILIBRIUM ISOTHERM TESTS
    0.2
ra
o>
     0.1
    0.08
     0.06
     0.04
    0.03
    0.02
    0.01

    0.008


    0.006  _
I
I     I
 Symbol

   O
   A
   D
  I      l^
   Initial
SCOD, mg/l
    51
    57
    46
    41
    52
           , 0.45 Micron Membrane Filtered Raw Wastewater
                        Aqua NucharA
                                          I
                                                 JL
                                      JL
                                     I
                       8   10      15    20      30    40
                               Equilibrium SCOD (Ce) mg/l
                                          50  60
                                              80
                               29

-------
Results of these tests are presented in Figures 12  andn^-
The pretreatment did not significantly affect the equilibrium
test results.   It was, therefore,  assumed that results ot
the pilot plant adsorption system would not .be, si^if icantiy
influenced by the chemical used in the chemical treatment step.

Jar tests were conducted to determine the effect of carbon
concentration and polyelectrolyte flocculation aids on
gravity sedimentation.  Jar test data in Figure 14 show
that increasing carbon dosages improved supernatant clarity.
For a dosage of 10,000 mg/Jl, or 1 percent suspension.
essentially all PAC was settled.  This observation tends
to substantiate the self-flocculating character^of PAC
suspensions indicated by other investigators   '

Jar test screening of several types of polyelectrolytes
indicated that anionic polyelectrolytes were most effective
in increasing powdered carbon suspension settling rates.
About 1 mg/£ of these flocculation aids resulted in about
a threefold increase in floe settling rates to 1.5
inch/minute.
                          30

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                                  FIGURE 12: POWDERED CARBON TREATMENT:
                                          EFFECT OF PRETREATMENT
    0.4  . .
    0.2
    0.1
  |i0.08
_,   0.06 ..
    0.04 . .
    0.02 ..
   0.01  . .
   0.008 .
   0.006

Curve
o
A
X

Pretreatment
150 mg/l, Fed,
Lime to pH 12.0
None
Initial
SCOD, mg/l
51
44
57
                                                              Ambient Temperature, pH = 7.5,
                                                                     Aqua Nuchar A
                          O
I	1	1	1	
 30      40     50   60
   Equilibrium SCOD (Ce) mg/l
        10
                           A
                           20
                                         31

-------
 0.6
               FIGURE 13: POWDERED CARBON TREATMENT:
                       EFFECT OF PRETREATMENT
                                  Ambient Temperature, pH = 7.5
                                        Aqua Nuchar A
0.01
                      20         30      40     50
                        Equilibrium SCOD (Ce) mg/l

-------
                                                FIGURE 14: POWDERED CARBON TREATMENT: CONCENTRATION
                                                                 EFFECT ON CLARIFICATION
                100
to
                                                                                                      Lime Pretreatment
                                                                                                          pH = 7.7
                                                                                                          °C = 18
                                                                 Supernatant
                                                                Concentration
                                  100
200
         300             400

Initial Powdered Carbon Concentration, mg/l
500
                                                                                                                600
                                                                                                                                10,000

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                     SECTION V

              PILOT PLANT DESCRIPTION
RAW WASTEWATER FLOW

The pilot plant influent was coarse screened and comminuted
Salt Lake City raw wastewater.  About 350 gpm was diverted
from the main Salt Lake City pump station discharge header
to the pilot plant raw wastewater sump.   Flow not used was
returned to the pump station wet well by gravity.  Some
accumulation of very coarse grit occurred in the sump.
The pilot plant raw wastewater pump was sized for a
maximum flow of 150 gpm.  The pump discharged to the
chemical treatment unit via a magnetic flow meter-con-
troller.  Plant flow was automatically controlled at any
constant flow rate equal to or less than 150 gpm.  This
flow was continuously recorded and totalized.
CHEMICAL TREATMENT UNIT

Chemical treatment and clarification of raw wastewater was
accomplished in a 12 ft diameter Eimco Reactor-Clarifier
solids-contact treatment unit, manufactured by Eimco
Processing Machinery Division, Envirotech Corporation,
Salt Lake City, Utah.

Figure 15 shows a schematic of this unit.  Raw wastewater
entered the unit via the influent pipe A to a draft tube E.
Inorganic coagulants were added to the raw wastewater at B.
Lime was added at point C.  A slow speed turbine F pumped
raw wastewater, chemicals, previously formed chemical
precipitates and wastewater solids up the draft tube and
into the reaction zone.  The pumping turbine capacity was
estimated to be about 5-8 times the average hydraulic
throughput.  Polyelectrolyte flocculation aids were
introduced into the reaction zone at point D.  Reaction
zone slurry flowed under the reaction zone cone Q, into
an increasing area upflow clarification zone.  Settled
solids were moved to the center of the unit by sludge rake,
H, and either drawn up the draft tube or removed through
the thickening cone I.
                          35

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FIGURE 15: EIMCO REACTOR-CLARIFIER,  SOLIDS-CONTACT
               CHEMICAL  TREATMENT UNIT
                   C    D
                                                                                   W,V
Symbols:
A.  Influent Pipe                        M.
B.  Inorganic Coagulant Feed             N.
C.  Lime Feed  '                        0.
D.  Polymer Feed                        P.
E.  Draft Tube                          Q.
F.  Pumping Turbine                     R.
G.  Sample Point, Reaction Zone           S.
H.  Sludge Rake                        T.
I.   Sludge Thickening Cone              U.
J.   Expanding Area Clarification Zone      V.
K.  Liquid Surface Skimmer               W.
L.   Float Baffle
Peripheral V-Notched Launder
Acid Feed Point
Effluent to First Carbon Contactor
Effluent to Second Carbon Contactor or Drain
Reaction Zone Cone
Sludge Slowdown Line
Timer Controlled Sludge Valve
Process Water Blowback Valve
Vacuum Breaker
Effluent Sample Point
Flow Splitter Box
                                  36

-------
Partially thickened sludge was automatically removed from
the treatment unit by gravity flow through line R and a
timer controlled sludge valve S.  An automatic water back-
flush of line R was provided at valve T.  Chemical sludge
blowdown was routed  to a 2000 gallon (8 ft. diameter)
holding tank which was equipped with a turbine mixer.

Since the chemical treatment unit received raw wastewater,
provision was made for clarification zone surface skimming
by mechanism K.  Floatable materials were kept from passing
over the peripherial effluent launder M  (a V-notched weir)
by baffle L.  Effluent neutralization was accomplished by
addition of concentrated sulfuric acid to the effluent
launder at point N.  Clarified effluent exited the
unit at splitter box W which divided flow to one or two
carbon contactors, or to waste.  A sample of clarifier
effluent was continuously withdrawn at point V and
conveyed to a composite sampling and process turbidity
monitoring system.  The approach to operation of the
solids-contact unit used is presented in Appendix C.
CHEMICAL STORAGE AND HANDLING FACILITIES

Liquid alum or ferric chloride solutions were obtained in
bulk quantities and stored in one of two 560 gallon
 (4 1/4 ft diameter) rubber lined tanks.  Solution was
removed from either tank at a point about 4 inches above
the center of the bottom and fed by a positive displace-
ment metering pump through PVC piping to point B in the
chemical treatment unit influent line.

Concentrated sulfuric acid was obtained in bulk quantities
and stored in a 1000 gallon covered mild steel tank.
The acid was fed by a positive displacement metering
pump through black iron piping to point N in the chemical
treatment unit.  An automatic acid neutralization system
consisted qf a process pH meter, recorder and controller.
The pH probe was located in the chemical treatment unit
effluent splitter box.  The recorder had a low pH set
point at which the acid feed pump was turned off.  As the
pH increases above the set point, the acid feed pump was
turned on.  Manual trim of the acid pump rate allowed
minimizing frequent OFF-ON pump action.
                          37

-------
High purity hydrated lime (Ca(OH)2)  was obtained in 50
pound bags.  Dry lime was continuously slurried witn
tap water and pumped through plastic tubing by a positive
displacement pump to point C (Figure 15) in the chemical
treatment unit draft tube.  The lime slurry pump was
operated at a constant rate sufficient to prevent deposi-
tion in the feed lines.  Lime dosage was varied by manually
adjusting the dry lime feeder rate.

Two 560 gallon  (4 1/4 ft diameter) polymer make-up tanks
were provided for dissolving dry polymer into pilot plant
effluent or tap water and storing polymer solution during
use.  High speed mixers  (1750 rpm) were used to_aid the
solution of polymers and provide intermittent mixing of
tank contents.  The polymer solution was fed by positive
displacement metering pumps through indicating  flow meters
to any of four treatment units  (three  solids-contact units
and the granular media filter).
PAC CONTACTORS

PAC treatment of chemically clarified raw wastewater was
accomplished in one or two 10  ft diameter solids-contact
treatment units.  These units  were  identical  in detail to
the chemical treatment unit  (Figure 15) with  the  exception
that they did not have surface skimmers and that  submerged
orifice launders were used.  The units were piped  to be
operated either in parallel, as single-stage  carbon contactors,
or in series, as a two-stage counter-current  carbon
contacting system.

Partially thickened spent PAC  slurry was automatically
removed from each contactor by gravity flow.

Virgin PAC was made up in a 840 gallon  (5 ft  diameter)
rubber lined tank containing a mixer.  When available,
pilot plant effluent was used,  otherwise tap  water was
used to wet and slurry the PAC.  PAC was obtained  in 35
pound bags and manually poured, very slowly,  into  the
make-up tank half filled with  water.  The make-up  tank
had a hinged plywood cover to  prevent gross dusting
problems during initial mixing  of the PAC.  Normally,
12 to 24 hours mixing was allowed for thorough wetting
before transferring the PAC slurry  to a second 840 gallon
rubber lined feed tank.
                         38

-------
Virgin PAC slurry was fed to the influent line of the
carbon contactors by a positive displacement  (ball
check) pump.  When the two carbon-contactors were operated
in series, virgin PAC slurry was fed only to the second-
stage unit.  Underflow from this unit was intermittently
pumped by a peristaltic pump to the influent line of the
first-stage unit.  Spent PAC exited the first-stage unit
via blowdown to a thickener.  No attempt was made to
identically match the PAC mass transfer rate between
units with the virgin PAC mass feed rate.  Rather, a
PAC transfer rate was maintained at that required to
enable stable operation of the second-stage solids-
contact carbon contactor.  For this reason, it may have
taken 2-4 days of plant operation to reach steady-state
PAC mass  flow.  The approach to operation of the solids
contact treatment units used is presented in Appendix C.
POWDERED CARBON REGENERATION SYSTEM

The regeneration system consisted of four major unit
operations:  carbon sludge concentration by gravity
thickening, vacuum dewatering, regeneration in a fluidized
bed furnace and off-gas carbon capture by wet venturi
scrubbing.  This system is shown as part of Figure 1.

Spent carbon was removed from the carbon contactors by
gravity flow to a five  (5) ft diameter gravity thickener.
Thickener underflow was transferred to a carbon inventory
and sampling tank  (about 500 gallons).  A small peristaltic
type pump was used for this transfer operation.  The
slurry volume of thickened carbon was measured.  Then,
after thorough mixing, a representative sample was obtained
for laboratory tests.  The inventoried, thickened carbon
was then transferred to a 1700 gallon conical storage
tank.  To prevent bridging in the .conical storage tank,
carbon was recirculated, externally, at a rate of about
5 gpm from the bottom outlet to the top of the tank.

Vacuum filter dewatering was accomplished with a three
(3) ft diameter by three  (3) ft face EimcoMet Eimco-
Belt filter manufactured by Eimco Processing Machinery
Division, Envirotech Corporation, Salt Lake City, Utah.
The vacuum filter station consisted of the filter,
flocculation tank, vacuum pump, filtrate pump and receiver
all mounted on a platform.  Figure 16 shows the vacuum
filter in operation.  All components of the filter which
                          39

-------
 FIGURE 16:  VACUUM FILTRATION OF SPENT POWDER CARBON

•

-------
contacted carbon slurry were made of corrosion resistant
thermoplastic.  A rubber lined chemical flocculation
tank had two mixing compartments to achieve chemical
dispersion and floe growth.  A 55 gallon drum, high
speed mixer and variable speed positive displacement
diaphragm chemical feed pump comprised the conditioning
chemical make-up and feeding facility.

The filter cake discharged into a hopper which had a
capacity of about 300 Ib of wet filter cake.  A ribbon
screw advanced the cake along the bottom of the hopper
to the throat of the feed pump.  The ribbon screw reconstitu-
ted the filter cake for form a paste which the pump readily
transported to the fluidized bed furnace.

A schematic of the furnace is shown in Figure 17 and a
photograph of the unit in Figure 18.  The outer dimensions
were 5 1/4 ft diameter by 14 ft high.  The outer steel
shell was lined with suitable fire and insulating brick
and castable refractory to provide and following approximate
internal dimensions:

     1.  3 ft diameter by 3 ft high fire box
     2.  3 ft diameter by 3 ft high sand bed chamber
     3.  3 1/4 ft diameter by 6 ft high freeboard chamber

Thermocouples and pressure taps  (P/I) were located as
shown in Figure 17.  Stainless steel tuyeres  (nozzles)
were provided to retain the sand and provide distribution
of fire box gases into the sand bed.

The fuel used was natural gas.  Combustion air was
provided by a 200 SCFM capacity blower.  Injection of
natural gas directly into the fluidized bed was provided
by six nozzles/ equally spaced around the circumference.
These nozzles entered the bed just above the tuyeres.

Natural gas was fired in the burner chamber with about
150 percent  (by volume) excess air to keep the fire box
temperature below about 2000 °F.  This limited temperature
was required to protect the refractory and stainless steel
tuyeres.  Hot gas flow from the fire box at a superficial
velocity of about one  (1) ft per second was required to
maintain the 15 x 30 U.S. Mesh sand bed in a fluidized
state.  Prior to feeding carbon, the oxygen content of
the furnace off-gas was trimmed with bed injection gas
feed.  Dewatered carbon was automatically fed at a rate
which maintained the bed temperature at a preset value.
                          41

-------
                FIGURE  17:  FLUIDIZED BED REGENERATION FURNACE
         Thermocouple
                                                                      Quench Water
          Access
          Opening
                                                         P/l ' (Pressure/Indicator)
                                 15 x 30 U.S. Mesh
       Thermocouples
                                                       Dewatered Carbon Cake
                                                       Injection
                                                                One of Six Natural Gas
                                                                Injection Nozzles
Stainless
Steel
                                                     Burner Chamber
                                                                                    To Venturi
                                                                                    Wet Scrubbers
       Tuyeres

Clean Out Opening


        Thermocouple
                                                                               Natural
                                                                               Gas
                                        42

-------
         FIGURE 18:  PAC FLUIDIZED BED REGENERATION FURNACE
r
                                     43

-------
 The hot furnace  off-gasses, containing the regenerated
 carbon, were  quenched  to about  200°F by the addition of
 about 15 gpm  of  recycled scrubber water to the furnace
 outlet duct.   The cooled gases  were then passed through
 a 6 inch and  then a  4  inch diameter wet venturi scrubbers,
 in series to  capture essentially all of the regenerated
 carbon.   Scrubber water flow was about 30 and 15 gpm to
 the 6 and 4 inch venturies respectively.  Scrubber water
 underflow was discharged to a 1700 gallon conical decant
 tank which provided  some separation of carbon.
 Decant tank overflow was pumped through a heat exchanger,
 prior to reuse as quenching and scrubber water.  Pilot
 plant effluent was used for heat exchanger water.  The
 fluidized bed furnace  and venturi scrubbing system were
 highly instrumented  for safety  and ease of operation.

 Carbon regeneration  runs were conducted on a batch basis.
 All the stored,  thickened  spent carbon was run through
 the vacuum filter and  regeneration furnace system at one
 time.   Spent  carbon  ret reaching the furnace was accounted
 for by collecting all  vacuum filter filtrate, spillage and
 all washings  containing spent carbon.  An isolated regen-
 eration room  floor drain system with an intercepting sump
 facilitated this operation.
GRANULAR MEDIA FILTRATION  STATION

Effluent from one of the carbon  contactors  was  applied
to the granular media  filter.  The  filter was a 3.5  ft
diameter by 6 ft high  clear plastic unit of conventional
downflow gravity design with a coal-sand filter bed.  Back-
washing of the filter  bed  was accomplished  by an automated
air-scour hydraulic method.

The sand layer of the  dual media filter bed was 12 inches
of 20 x 30 U.S. Mesh filter sand.   The coal layer was
about 12 inches of specially sized  anthracite coal.  The
coal effective size was 1.1 mm and  the uniformity coeffi-
cient was less than 1.4, after installation and removal
of two inches of fines from the  top of the  backwashed
and settled filter bed.

Figure 19 is a schematic of the  granular media  filtration
station.  In the filtering mode, influent flowed through
a U-tube to the filter inlet.   The dual-media filter bed
rested directly on a false bottom.   Flow was collected in
the filter outlet plenum and routed to an effluent weir
                         44

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                                  FIGURE 19: GRANULAR  MEDIA  FILTRATION STATION
Influent
                                                                                         To Backwash
                                                                                   _^~ Equalization Tank
                                                      . Polymer
                                                   31/2  foot diameter
                                                       plexiglass
                                                         filter
                                                                                                    Weir Box
                                         QAP Cell
                                        (Converter)


                                        AP Recorder
                                      Clearwell
Symbols
A.  Influent Valve
B.  Effluent Valve
C.  Backwash Outlet Valve
D.  Backwash Inlet Check Valve
E.  Underdrain Nozzle
                                                  45

-------
 box located at an  elevation which  insured that  liquid  in
 the filter  bed was never  at less than  atmospheric pressure.
 Filter flow rate was  indicated by  an orifice-plate  bypass
 flow meter.   A sample of  filter effluent was  continuously
 pumped from the effluent  weir box  to a composite sampler and
 process turbidimeter.   Clarifier wastewater flowed  from the
 effluent weir box  to  a 5000 gallon (12 ft diameter)  clear-
 well which  provided treated water  storage for plant use and
 filter backwash.

 Two columns of pressure taps  (90°  apart) were located  at
 6 inch intervals up the side of the filter housing.  Pressure
 differentials (AP) between the outlet  plenum  and each  pressure
 tap were automatically measured and recorded  once  each hour
 for a duration of  8-10 minutes.  The filter was automatically
 backwashed  when the total filter bed headloss (including
 underdrain)  reached a preset value which was  routinely set
 at 7 ft of  water.   The operational sequence during back-
 washing is  presented  in Appendix D.

 Backwash water was collected in a  3600 gallon (10  ft dia-
 meter)  equilization tank  which was equipped with  a low speed
 mixing turbine.  Equilization tank contents were  pumped to
 the reaction zone  of  the  first-stage carbon-contactor  at a
 rate of about 5 gpm.


 COMPOSITE SAMPLER  AND PROCESS TURBIDIMETER

 An automatic sample compositor  and turbidity  measuring and
 recording system was  developed  for this project (see Figure
 20).   All process  stream  samples   (five) were  piped to  a
 central location.   Each stream  passed  upward  into  a hopper
 shaped  container,  sized to maintain solids  in suspension.
 Sample  continuously overflowed,  the hopper via  a  1 inch
 diameter horizontal pipe  to a common waste drain.   Normally-
 closed  solenoid valves were located  in a vertical  line just
 below the horizontal  pipes.  Outlets from all five solenoids
 emptied into a common trough which drained into a  flow-through
 process turbidimeter.   A  multiple  cam  timer programmed each
 solenoid to  be opened for 12-15 minute intervals once  each
 hour.   The raw wastewater sample was not monitored  for tur-
 bidity,  since  continual plugging of the solenoid valve was
 experienced.

Twenty-four  hour,  time composite samples were obtained  from
the flow  through the hopper container  mentioned previously
Approximately  30 ml of  samples were collected in plastic cur>«?
                         46

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                     FIGURE 20: COMPOSITE  SAMPLING AND PROCESS
                              TURBIDITY MONITORING  DEVICE
        Drain
       Trough
    Drain
  Process
Turbidimeter
             Sample Cups with
             rubber stoppers
       Turbidity
       Recorder
                                                                                      Sample to
                                                                                      Refrigerator
                                                                                      (by gravity)
Sample
 Inlet
                                           47

-------
 each  30 minutes.  The plastic cup bottoms had rubber stoppers
 to facilitate cleaning.  Samples were transferred from the
 sample collection trough to refrigerated storage vessels.
 Composited samples were refrigerated at about 34°F until re-
 moved for analysis.


 LABORATORY FACILITIES

 Analytical laboratory facilities were located at the pilot
 plant site.  The laboratory was equipped to conduct all
 analyses reported except ammonia nitrogen, BOD5 and sul-
 fides.  These analyses were made at the Eimco Corporation's
 Sanitary Engineering Research and Development laboratory.
 Sludge thickening and vacuum dewatering tests were also
conducted at the Eimco laboratory.
                        48

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                    SECTION VI

         APPROACH TO PILOT PLANT OPERATION


Initially, the approach to the pilot plant test program
consisted of choosing desired effluent water quality
criteria for each unit operation.  The plant was then
operated to determine optimum conditions (e.g., minimum
chemicals, maximum flows, etc.) which would result in the
desired effluent quality.  Emphasis was placed on predicting
desirable plant operating conditions based on laboratory
test results.  For example, chemical coagulant dosage and
polymer type and dosage were obtained from standard jar
tests.

The above approach was followed during the first 3 months
of plant operation with less than satisfactory success.
In general, the plant was "over operated" by frequent chang-
ing of operation variables such as FeCl3 and polyelectrolyte
feed rates.  Because of the hourly and daily variability of
the raw wastewater, minimal available operator time and a
six day per week plant operating schedule, meaningful process
results were extremely difficult to obtain.  Consequently, the
following approach was adopted and adhered to for the
remainder of the test program:

1.  Based on previous operating experience and/or laboratory
    jar test results, operating conditions were established
    (chemical type and dosage, PAC dosage and operating
    mode).

2.  The plant was brought on a stream at a nominal hydraulic
    loading for two to three days to establish near steady
    state conditions.  The flow was then increased by 10-20
    percent increments each day, until the effluent
    clarity consistantly exceeded about 25 JTU.  This
    observation indicated that the maximum hydraulic
    loading had been reached.  The flow was then reduced
    to 75-85 percent of the maximum established.

3.  The plant was operated under the established operating
    criteria for one to three weeks during which time twenty-
    four hour composite samples were collected and analyzed
    and treatment efficiency established.
                          49

-------
 CHEMICAL MONITORING

 Alum and Fed,,:  Each new batch of these chemical solutions
 were immediately sampled and the Al+3 or Fe+J weight con-
 centration and  solution density determined.  Typical solution
 strengths Vere  42 percent by weight FeCl3 and 15 percent by
 weight A1203.   The actual solution volumetric feed rates
 were measured four to ten times daily.  In addition, daily
 volume inventory data were collected on each chemical  feed
 tank, along  with the total flow through the chemical treat-
 ment unit.   The average dosage rate was established from
 these average daily values.

 Lime:  A lirae availability was run on every seconder  third
 shipment of  100 fifty pound bags of high quality lime,
 Ca(OH)9.  Availabilities of about 90 percent were observed.
 The  rate of  lime feed was based on observed pH  values  of
 samples from the reaction zone of the chemical  treatment unit.
 If the observed pH was more than 0.2 units above or below
 the  specified operating level, the rate of dry  lime feed was
 appropriately adjusted.  This- manual control of treatment
 pH was generally acceptable for the constant-flow plant
 operation conditions.  However, on several occasions,
 bridging in  the lime feed hopper and changes in the raw
 wastewater alkalinity and/or pH caused  significant departures
 from desirable  operating pH with noticeable treatment  upset
 resulting.   The actual dry lime weight  feed rate was measured
 four to ten  times per day and averaged.   In addition,  the
 total number of bags of lime used was recorded  and an  average
 lime feed rate  computed using the total flow  through the
 chemical treatment unit.

 Acid:  Concentrated acid  (94 percent  H2S04 by weight)  feed
 rate was determined by a daily  inventory  of the acid storage
 tank and the chemical treatment unit  total daily flow.

 Polymer:  Polymer solutions of  0.025  percent to 0.050  per-
 cent were made  up according to  supplier recommendations.
 Monitoring of polymer feed rates were identical to the  pro-
 cedure used  for alum and
Powdered Activated Carbon:  PAC  feed  slurry  concentrations
of 2.5 and 5.0 percent by weight were used.   The  2.5  percent
concentration was used for low plant  flow  and/or  low  PAC
dosage conditions.  The volumetric feed rate  of PAC slurry
was measured four to ten times per day.  A daily  inventory
of the PAC feed tank contents was made along with a measure-
ment of total flow passing through the carbon contactors.
The average daily dosage was determined from these observations.
                          50

-------
PILOT PLANT START-UP

Numerous start-up problems were encountered.  Typical problems
involved inadequate plumbing and electrical circuitry, under-
designed mixing equipment, and PAC slurry corrosion.  The
more important equipment operation problems will be discussed
later.

With the many mechanical start-up problems, two months were
required to achieve a acceptable level of operator training
and plant operation.  During this period, the plant was on-
stream no more than six days per week  (it was shut down on
Sundays).  Operators were on duty only during about two-thirds
of the time.  This situation proved untenable in as much as
frequent mechanical or process failures occurred during times
that operators were not present, resulting in unsatisfactory
plant performance.  Also, after a day of plant down time, at
least a day was required to re-establish steady state treat-
ment conditions.  Therefore, after the third month of opera-
tion, it was decided to increase the operating staff and keep
the pilot plant on-stream continuously except during holidays.
SCHEDULE OF PLANT TEST

Because laboratory results indicated that chemical pretreat-
ment did not significantly effect the adsorption of SCOD on
PAC, and because of multiplicity of treatment variables were
to be studied, the chemical treatment and PAC adsorption
tests were independently scheduled.  The following is a list-
ing of the major variables studied.

A.  Chemical treatment:

    1.  Ferric chloride

        a.  Overflow rate
        b.  Fed3 dosage
        c.  Need for polyelectrolyte

    2.  Lime [Ca(OH)2]

        a.  Overflow rate
        b.  Treatment pH

    3.  Alum

        a.  Overflow rate
        b.  Need for polyelectrolyte
                          51

-------
B.  PAC contacting

    1.  Two-stage counter-current contacting

        a.  PAC dosage
        b.  Need for polyelectrolyte
        c.  Overflow rate

    2.  Single-stage contacting

        a.  PAC dosage
        b.  Overflow rate

C.  Granular Media Filtration

    1.  Filtration rate

    2.  Need for polyelectrolyte


SCHEDULE OF ANALYTICAL TESTS

The basic philosophy during this  pilot  plant study
was that the following priority of  functions be followed:

No. 1:  Steady state plant operating conditions were well
        established.

No. 2:  Representative samples of all process streams were
        collected.

No. 3:  A spectrum of analytical  tests  on the composite
        samples of the various process  streams were  made.

If priority items 1 or 2 were  not satisfied then item 3
was not undertaken.

The spectrum of analytical tests  run on composite samples
is presented in Table 1.  In addition,  suspended solids
analysis were run on samples of the reaction zone slurry
and sludge blowdownfrom each chemical and PAC solids-
contact treatment units.  These samples were 24-hour composites
of grab samples taken at two hour intervals.

At weekly to bi-weekly intervals, a  sample of 24-hour com-
posited chemical-sewage sludge was collected and laboratory
thickening and vacuum filter leaf tests conducted.
                         52

-------
                      TABLE 1:   SCHEDULED ANALYTICAL TESTS  OF COMPOSITE SAMPLES
                                                            PAC CONTACTOR
u>
          Water Quality Parameter
                              Raw
                             Waste-
                             water
Chemical
Treatment
First
Stage
Second
 Stage
GM Filter
Turbidity                      a
Suspended Solids               a

Total Phosphorus               a
Soluble Total Phosphorus       a

Total Organic Carbon           a
Soluble Total Organic Carbon   a
Chemical Oxygen Demand         a
Soluble Chemical Oxygen
  Demand                       a
Biochemical Oxygen Demand      b

pH                             a
Total Alkalinity               a
Total Hardness                 a
Calcium Hardness               a

Sulfides                       b
Ammonia - Nitrogen             b
Total Soluble Iron             c
    a
    a

    a
    a

    a
    a
    a

    a
    b

    a
    a
    a
    a

    b
    b
    c
                                                             a
                                                             a
           a
           a
            a
            a
                                                             a
                                                             a
                                                             a
                                                             b
           a
           a
           a
           b
                                                             b
                                                             b
                                                             c
           b
           b
           c
            a
            a
            a

            a
            b

            a
            a
            a
            a

            b
            b
            c
          a - Routine analysis on each 24-hour composite
          b - No more frequently than once per week
          c - Intermittent during FeCl3 campaign

-------
PLANT OPERATING DATA

Plant operators routinely monitored and recorded equipment
and process data, 5 to 10 times per day, to assure that the
plant was operating under specified conditions.   All chemical
and process flows were observed or measured for all tne
solids-contact units, as were pumping turbine speed, rake
speed and torque, and blowdown conditions (time interval
and duration).

Two liter samples of each solids-contact unit reaction zone
slurry were collected every two to four hours and :> minute
settling tests conducted.  The location of the slurry pool
in the clarification zone of each un.it was also observed
every two to four hours by drawing samples from the three
sample taps.  The highest sample tap at which copious
amounts of sludge appeared was recorded.

Turbidity, pH and temperature measurements were made of
grab samples of all process streams taken at 2  to  6
hour intervals.

The comprehensive plant  operating  data  collection  was con-
sidered desirable to eliminate potential treatment upsets
due to malfunctioning of equipment and  variable raw waste-
water characteristics.   Had  longer plant test  compaigns been
possible, less surveillance would  have  sufficed.
                         54

-------
                   SECTION VII

                PILOT PLANT RESULTS
Pilot plant results will be presented and discussed in
the following separate sections.

1.  Chemical treatment step:

    The purpose of this treatment step was to provide the
    majority of phosphorus and suspended solids removal.
    Other physical-chemical treatment schemes and some
    chemical-biological treatment schemes could include
    this chemical treatment step.  Thus, chemical treat-
    ment results are presented separately.

2.  Powdered activated carbon treatment step;

    The purpose of PAC contacting was for removal of soluble
    organics only.  The granular media filter was considered
    part of this treatment step since it removed final traces
    of the PAC after contacting and gravity sedimentation.

3.  Spent powdered activated carbon regeneration system;

    A major objective of this study was to determine the
    effectiveness of powdered carbon regeneration and re-
    use.  Thus, the preliminary results obtained are present-
    ed and discussed separately.

4.  Typical overall treatment;

    To allow comparison of PAC-PCT effectiveness with other
    treatment approaches and provide an indication of efflu-
    ent quality variations, these results are presented
    separately.

5.  Plant operating and equipment problems;

    Problems encountered, which were considered to have had
    an effect on treatment results or recommended prototype
    design, are presented and discussed.
                          55

-------
Pilot plant operating and treatment  results_will  be
presented as average values with the exception  of the
following data which will be presented  as  median  values
(that value for which fifty percent  of  the observed
values were less than or equal to):

1.  Total and soluble TOC, COD and P
2.  Suspended solids                       ,,   ,
3.  Solids-contact units reaction zone  and blowdown
    solids concentration                          ,      .
4.  Solids-contact units sludge blowdown volumes   (percent
    of flow)
5.  Alum and polymer dosages

The chemical and powdered carbon operating and treatment
results will be presented in tabular form for different
test runs.  The runs will be broken down into chemical
type and dosages, carbon dosage and number of contacting
stages.  Since more than 6000 pieces of data were compiled,
only selected data are presented in total.  These selected
data will be SS and P for  some chemical treatment runs, SS
and SCOD for some carbon treatment  runs and SS,  TOC, COD
and P for typical plant effluent results.


CHEMICAL TREATMENT STEP

Ferric Chloride Treatment  Results

After pilot plant start-up and  shake down, evaluation of
ferric chloride in the chemical  treatment step began.
About 3 1/2 months of operation  followed.  The operating
and process treatment results for the  four Runs  conducted
are presented in Table  2.

Run F-l was the first plant test conducted and minimal
data was compiled, compared to other Runs.  Run  F-2 was
conducted using operating  conditions similar to  Run F-l
except that a different polyelectrolyte and a high
FeCl3 dosage was used.  During Run  F-3 higher dosages of
FeCl-j and polyelectrolyte were used at a  reduced overflow
rate for the purpose of establishing the  best quality effluent
obtainable by chemical treatment with FeCl^.  Excellent COD,
SS and total phosphorus removals were achieved.  However, chem-
ical costs alone (FeCl3 and polyelectrolyte) amounted to about
7C/1000 gallons.  Run F-4, only four days long, was  conducted at
a reduced overflow rate to obtain an indication of whether or not
                         56

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                      TABLE 2:
                      FeCl3 TREATMENT:
SUMMARY OF RESULTS
Ul
OPERATING RESULTS:

Run Number
Length of run, days
Overflow rate, gpm/sq ft
FeCl3, mg/i
Polymer, type
Polymer, mg/£
Reaction zone solids, g /H
Slowdown Volume, % of flow
Slowdown Cone. , g /%
Slowdown solids , Ib
          PROCESS TREATMENT RESULTS
F-l
52
0.75
99
Dow A23a
1.0
—
--
—
—
P-2
37
0.75
119
Atlasep
1.0
2.9
0.9
17
1280
F-3
13
0.50
145
2A2b Atlasep 2A2
1.5
3.3
1.3
13
1410
F-4
4
0.25
116
--
0
1.2
2.0
10
1670
INF.  EFF.

36    24/9
96    30
5.0   0.7
62    32
                                                   INF,
                                               EFF.
              INF.   EFF.
INF
EFF.
          Turbidity, JTUC
          Suspended solids, mg/J,
          Total phosphorus, mg/£
          TOC, mg/i
          COD, mg/£
          pH, units
          Total iron, mg/£ as Fe
          Temperature, °C

          a = A product of Dow Chemical Company, Midland, Michigan
          b = A product of Atlas Chemical Company, Willmington, Delaware
          c = Effluent Turbidity - 24 Hr. composite/average of 8-10 grabs samples per day
33
75
6.0
60
121
—
—
18
16/10
12
0.9
30
38
__
—
--
52
94
7.8
77
255
7.6
1.2
21
26/5
14
0.2
21
54
6.9
6.2
—
59
138
7.3
64
271
7.5
1.9
21
42/5
33
0.5
22
65
6.9
8.5
—

-------
polyelectrolyte flocculation aid  could  be  eliminated without
loss of clarification effectiveness.  Effective  cian
and phosphorus removal was accomplished without
addition of polyelectrolyte.

The variability of feed and effluent suspended solids  and
phosphorus during Run F-2 is shown in Figure 21.  *eea
and effluent suspended solids varied by an order or
magnitude  (i.e., a factor of 10).  The  effluent phosphorus
concentration also varied over an order of magnitude,
whereas, the feed concentration was more uniform, varying
only by a factor of about 2 from low to high values
measured.

The test results for FeCl3  treatment in Table 2 do not
show any quantitative correlations between clarification
effectiveness and overflow  rate or chemical dosage.  As
would be expected, however, the data does generally
indicate that the phosphorus residual  is  inversely
proportional to FeClo dosage and directly related to
chemical treatment clarifier effluent  grab  samples
turbidity  (i.e., clarification effectiveness).

Some 10-15 percent of the  iron fed  to  the raw waste-
water appeared  in the chemical treatment  clarifier effluent
during Runs F-3 and F-4.   Figure  22  shows that  at higher
overflow rates, or, conversely,  shorter liquid  detention
times, the ratio of effluent composite sample turbidity
to instantaneous, or grab-sample, turbidity decreased
substantially.Either the nature of the  suspended
solids, as measured by turbidity, changed during
sample storage  or post precipitation of some  compound
was occurring.  The solids  present  in  stored  samples had
a reddish-brown color and  resembled  ferric  floe.

It has been indicated by others  that the  iron phosphorus
material, precipitated by  addition of  ferric  iron to
an aerobic phosphorus bearing wastewater, will  release
phosphorus when subjected  to an anaerobic environment21*'25.
These investigators conjectured that the  ferric iron
was reduced to ferrous iron in the anaerobic  environ-
ment.
                         58

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FIGURE 21: Fed, TREATMENT: FEED AND EFFLUENT
     SUSPENDED SOLIDS AND PHOSPHORUS
        20   30  40  50  60   70   80
         % Of Occurances < Value Shown
90
     95
           98

-------
                    FIGURE 22: FeCI3 TREATMENT:POST-PRECIPITATION OF  IRON
                                      (340)
I'
o
O
16

 0)
 0)
 TO
       74-
       64-
                                                            Approximate Liquid Detention
                                                                (170) Time In Minutes
  F   54-
  iw
       44-
       34-
                                                                                  (110)0
                                 0-25                        0.50



                                     Overflow Rate, GPM/ft3
                                                                                    0.75

-------
It is probable that addition of ferric iron to the raw
wastewater, which was devoid of dissolved oxygen,
resulted in some ferric iron being reduced to
ferrous iron.  If, at some later time, this wastewater
adsorbed oxygen, the ferrous iron could have been oxidized
to ferric iron and precipitated as hydrated ferric oxide
(iron flow).

The data in Figure 22 show that long liquid detention
times result in high levels of turbidity increases in
stored  (composite) samples.  Operation of the solids-
contact unit entailed maintenance of an approximately
constant inventory of sludge within the unit to accomplish
solids-contacting and some sludge thickening.  Thus, the
longer the liquid detention time  (i.e., low overflow rate)
or the lower the solids production rate, the greater will
be the average sludge age.  During Run F-4 at about
5 1/2 hour liquid detention time, the sludge blowdown
was considerably more odorous and darker in color
than previously experienced, indicating septic conditions.
It is probable that the greater the anaerobic activity
of the sludge the more pronounced is the problem of
turbidity increases in stored chemical clarifier effluent
samples.
Sludge Production

Sludge production can be determined from the data in Table
2.  The blowdown solids represent the median amount of
sludge removed from the wastewater via the chemical clari-
fier underflow, including both raw wastewater solids and
chemical solids  (i.e., ferric floe).

Table 3 is a summary of sludge production data for ferric
chloride treatment Runs F-2, 3 and 4.  It is seen that
between 0.6 and 0.8 pounds of chemical solids (ferric floe)
was produced for each pound of FeCl3 fed to the wastewater.
A value of 0.87 pounds chemical sludge produced per pound
FeCl3 used has been reported elsewhere  .


Sludge Thickening and Dewatering

The chemical treatment unit underflow concentration ranged
from 10 to 17 g/£, or about 1.0 to 1.7 percent dry solids
by weight  (Table 2).  This concentration range was somewhat
                          61

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to
               TABLE 3:  FeCl3 TREATMENT:  SUMMARY OF SLUDGE PRODUCTION DATA
           Run f                                    F-2        F-3        F-4
Slowdown SS, Ib/MG*
Slowdown SS , mg/ia
Clarifier Effluent SS, mg/£
Total Chemical and Sewage SS, mg/i
Raw Wastewater SS, mg/£
Chemical SS, mg/j,
FeCl3 Dosage, mg/Jl
lb Chemical Solids/lb Fed, Fed
1280
154
	 12_
166
	 75
91
119
0.77
1410
169
	 1£
183
	 9£
89
145
0.61
1670
200
	 32
233
138
95
116
0.82
           % Chemical Solids in Slowdown Sludgeb      55         49
40
          a = Based on total plant flow
          b = Assuming clarifier effluent suspended solids are one-half  chemical
              and one-half raw wastewater solids.

-------
less than anticipated for the approximately 1:1 ferric-
primary sludges.  The total-solids circulation feature of
the solids-contact treatment unit employed may have pre-
cluded effective sludge thickening within the chemical
treatment unit.

No attempt was made to maximize underflow concentration by
varying sludge blowdown duration and/or frequency.  The
actual duration and frequency of blowdown used was determined
by the plant operators on the basis of controlling the
sludge pool depth at about two feet above the sludge rakes
which insured solids contacting.  At low hydraulic load-
ings, less concentrated blowdown solids were produced
and therefore, larger blowdown volumes were required
to remove the sludge produced.  Recall that low hydraulic
loadings are correlated with long sludge age for the
solids-contact units used.  It is possible that the
older the sludge  (longer sludge age), the poorer it would
thicken in the solids-contact unit.

Laboratory sludge thickening tests were conducted on three
24-hour composite samples of chemical-sewage sludge collected
during Runs F-3 and 4.  Results of these tests indicated that
this sludge would gravity thicken to a maximum concentration
of 3 to 4 percent solids by weight.  Again, this concen-
tration was less than was anticipated for the 1:1 ferric-
primary sludge mixture experienced.  Figure 23 presents
thickener solids loading and underflow solids concentration
predicted from laboratory test results for different sludge
samples.  Based on judgment and experience, an operating
line was drawn which would result in a high degree of
sludge thickening.  A plot of thickener loading and under-
flow concentration at the intersection of each curve in
Figure 23 with the operating line is plotted in Figure 24.
These plots represent suggested design data.

A weighted average of chemical clarifier underflow data
in Table 2 indicates that about 1.5 percent solids were
produced.  A conservative extrapolation of the data in
Figure 24 would result in prediction of a thickener
loading and underflow concentration of about 12 Ib/day-
sq ft and 4.5 percent solids.

Vacuum filtration leaf tests were conducted on three
partially thickened 24-hour composite sludge samples
of chemical clarifier underflow.  The results of these
tests, summaried in Table 4, indicate that sludges
of from 1.6 to 3.3 percent concentration were dewatered
                          63

-------
                                  FIGURE 23: FeCI3 TREATMENT:

                            LABORATORY SLUDGE THICKENING RESULTS
      20
                                                        Solids Specific Gravity

                                                              1.1   g/ml
                                                     0.98% — Feed Solids
      15-
 ra
•o
 O>



I!

1 I
V> 
 c a
o  «
f  8
«  w
ra  oo
W  S
•o
      10-
                                         Operating
                                           Line
                                                                    Maximum
                                                                  Concentration •
                                              2                   3


                               Thickener Underflow Solids, % by Wgt.
                                   64

-------
                                                FIGURE 24:  FeCI3 TREATMENT: SLUDGE THICKENING
ui
            10
            •o
           "O
            IB
            O
           en
            at
           _0

           £
        B
        m
        •o

        "o
        v>


        &

        •c
        9
        •e

        3
        &E
        9?
        e
                                            0.4                       0.8


                                                      Thickener Feed Solids,' % by Wgt.
1.6

-------
en
en
               TABLE  4;  FeCl-j  TREATMENT:   VACUUM FILTRATION LEAF TEST RESULTS


                                                       Full Scale
                   Feed Solids     Cycle  Time     Filtration Yield      Cake Moisture
Test
1
2
3

4,5
6
% by Weight
2.5
3.3
1.6
b
1.6
1.6°
Minutes
16
20
25

5
5.3
lb/hr-sq ft
0.37
0.32
0.27

1.0
1.0
% by Weight
85
83
80
*
82
83
           a = Maximum possible yield of dry solids  (based on feed and chemical
               solids)  filter cake, at 33% submergence and a 0.8 scale-up factor.
           b = 24%  Ca(OH)2 by weight added for conditioning.
           c = 47%  Ca(OH)2 by weight added for conditioning.

-------
to 80-85 percent moisture at predicted full scale filter
yields of about 0.3 pounds of dry solids per hour per
square foot of filter area.  These filter yields were
predicted for a 3/16 inch filter cake thickness which
was only marginally dischargable.  Conditioning of the
dilute ferric-sewage sludge with 24 percent lime on a
dry solids basis resulted in a dischargable 3/16 inch
filter cake and a filter yield of 1 Ib/hr-sq ft.

The thickening and vacuum dewatering test results reported
are considered to be conservative.  Additional studies
of ferric-sewage sludge handling and chemical conditioning
are necessary to achieve reliable design data.


Alum Treatment Results

Two brief comprehensive Runs were conducted using liquid
alum to effect coagulation of suspended solids and phosphorus
precipitation.  A summary of operating and process treatment
results is presented in Table 5.  Runs A-l and A-2 were con-
ducted using identical alum dosages.  During Run A-l no
polyelectrolyte was added while during Run A-2, 0.25 mg/£
of anionic polyelectrolyte was added.  The purpose of these
comparative Runs was to determine the increased hydraulic
loading possible when using polyelectrolyte flocculation
aid.  The dosage and type of polyelectrolyte were chosen
on the basis of jar test results.  The type used was the
most effective of four anionic polyelectrolytes evaluated
and the dosage near optimum based on floe settling rates.
It was assumed that a raw wastewater phosphorus concen-
tration of 6-7 mg/£ would be experienced and could be
reduced to less than 1.0 mg/£ at an aluminum to phosphorus
molar ratio of 2:1.  Therefore, an alum dosage of about
140 mg/£ was used.

The operating results in Table 5 show that use of 0.25 mg/£
polyelectrolyte allowed an increase in overflow rate from
0.35 gpm/sq ft without polyelectrolyte, to 0.60 gpm/sq ft.
Both of these overflow rates were about 80 percent of the
maximum rates possible to maintain reasonably stable operating
and effluent quality conditions.

Process treatment results in Table 5 show that near identical
effluent quality was produced during the two runs.  A
similar variation of raw wastewater and chemical treatment
unit effluent suspended solids and phosphorus values is
shown in Figure 25.
                          67

-------
                           TABLE  5:   ALUM TREATMENT:  SUMMARY OF RESULTS
         OPERATING RESULTS:
gpm/sq ft
"
-------
           FIGURE 25: ALUM TREATMENT: DOSAGE, FEED AND EFFLUENT

                     SUSPENDED SOLIDS AND PHOSPHORUS
      6- -
      4- -
  -   2
  Dl
  O
  o
  £
  Q.

  1 - -








 0.6- -






 0.4- -





 0.3- -






200



160
Z „-  140- -
I
    120


    100
            --300






             -200




             -150






            --100



            --80
                                                                            o>
                          Feed SS
                                                                            o
                                                                            CO
                                                                        10
                          20   30  40  50  00  70   80


                          % o» Occurrences < Value Shown
90
     95
            98
                             69

-------
One aspect of the cost effectiveness of using P
lyte can be determined by comparing the operating cost
using polyelectrolyte versus the capital cost of kuvin9    .
increased clarification area.  Table 6 shows such a compari-
son for alum treatment.  The estimated installed cost: or
solids-contact treatment equipment to treat 10 mgd flow
without polyelectrolyte is 0.47C/1000 gallon.  If poly-
electrolyte is used, the tabulated values show the overflow
rate required to justify use of polyelectrolyte on the
basis of holding total treatment cost constant.  It is
indicated that to justify use of 0.15 mg/£ of polyelectro-
lyte, the overflow rate would have to be increased more
than five fold (i.e., from 0.27 to 1.46 gpm/sq_ft).
For alum treatment it would appear more economical to
design on the basis of operating without polyelectrolyte.
However, since use of polyelectrolyte does substantially
increase floe settling rate, it would be recommended that
polymer make-up and feed facilities be provided to in-
crease treatment flexibility and reliability.

Based on effluent turbidity values of 10 and 11 JTU shown
in Table 5, good clarification was experienced.  No
difference was observed between the turbidities of 24-
hour composite samples and the average turbidity of 8 to
10 grab samples per day.  The effluent suspended solids
values of 24 and 30 mg/£ were higher than the desired
10 to 20 mg/£.  Presumably effluent turbidities of 4 to
6 JTU should have been strived for rather than the
1-15 JTU level set as an operating criteria.

Comparison of effluent total and soluble phosphorus values
indicates that 60 to 67 percent of the chemical clarifier
effluent total phosphorus was particulate  (i.e., the dif-
ference between total phosphorus and soluble phosphorus).
After subsequent treatment in the powdered carbon contactors
and the granular media filter, the total phosphorus in
the plant effluent was identical to the soluble phosphorus
in the chemical clarifier effluent.  Thus, complete removal
of particulate phosphorus was obtained for the PCT plant.
The low phosphorus value of 0.4 mg/Jl was achieved at
aluminum to total phosphorus molar ratios of 2.6:1 and 3.4:1.

Of significance was the removal of 20 and 24 percent soluble
TOG and 25 and 60 percent SCOD across the chemical treatment
step.   Obviously, alum treatment coagulated some organic
material (soluble or colloidal)  which would pass a 0.45
micron membrane filter.  This observation verifies the
laboratory jar test data using alum where some 10 to
20 percent removal of SCOD was observed.
                         70

-------
          TABLE 6:  ALUM TREATMENT:  COST TRADE-OFF OF POLYELECTROLYTE
                    AND CLARIFICATION AREA FOR 10 MGD FLOW
SOLIDS-CONTACT UNIT
Overflow
Rate
(gpm/sq ft)
0.27
0.48
0.97
1.46
Amortized Capital
Costa
(C/1000 gal.)
0.47
0.39
0.33
0.28
POLYELECTROLYTE
Dose
(mg/£)
0
0.06
0.11
0.15
Chemical
Cost*3
(C/1000 gal.)
0
0.08
0.14
0.19
Total
Cost
(C/1000 gal.)
0.47
0.47
0.47
0.47
a - 7 1/2% interest, 20 year for estimated erected equipment

b - @$1.50/lb of polymer

-------
It should be noted that during the alum treatment Runs,
the raw wastewater strength was weaker than usual.  This
condition does not negate the effectiveness of alum treat-
ment for clarification of raw wastewater.  Overall chemical
treatment process results for Runs A-l and A-2 indicate
removals of 82 percent particulate TOC, 75 percent
particulate COD and 72 percent suspended solids.
Sludge Production

A summary of alum treatment sludge production data is
presented in Table 7.  Between 0.4 and 0.5 pounds of
chemical sludge was produced for each pound of alum
fed to the raw wastewater.  This range is somewhat
higher than 0.25 to 0.40 Ib/lb reported by others2 .
Sludge Thickening and Dewatering

Alum-sewage sludge thickening and dewatering properties
were not at all impressive.  To begin with, a concentrated
reaction-zone suspension was never established in the
solids-contact unit.  Solids concentrations of 0.8 and 0.6
g/SL were not considered to constitute solids-contact
treatment.  A concentration of about 2 g/£ would have
been considered acceptable.

The alum-sewage sludge was not effectively thickened within
the chemical contactor.  During Run A-l the blowdown
solids were just about double the concentration of the
reaction-zone solids concentration.  During Run A-2,
when polyelectrolyte was used, a seven fold increase
in blowdown solids concentration was achieved.  Evidently,
the total-solids circulation feature of the solids-contact
unit used was ineffective for alum-sewage sludge thickening.
Because of very high blowdov.'n volumes employed  (3.5 to
6.2 percent of total flow), solids were withdrawn not
only from the sludge thickening cone but also from the
reaction-zone.  Use of shorter blowdown durations would
have eliminated solids removal from the reaction-zone,
resulting in a more concentrated underflow.  From the
blowdown volume and concentration data in Table 5, it is
apparent that use of polyelectrolyte results in a more
concentrated underflow.  The economic impact of more
concentrated underflow on sludge thickening and dewatering
was not evaluated.
                        72

-------
        TABLE 7:  ALUM TREATMENT:  SUMMARY
             OF SLUDGE PRODUCTION DATA
Run #                                    A-l       A-2

Blowdown SS, lb/MGa                      930       1280

Blowdown SS, mg/£a                       112       154

Clarifier Effluent SS, mg/£              24        30
Total Chemical and Sewage SS, mg/Jl       136       184


Raw Wastewater SS, mg/Jl                  £2_        110

Chemical SS, mg/i                        54        74


Ib Chemical SS/lb Alum Fed               0.38      0.52

% Chemical Solids in Blowdown Sludge     40        40
a - Based on total plant flow

b - Assuming clarifier effluent suspended solids are one-half
    chemical and one-half raw wastewater solids
                         73

-------
During Run A-l, two laboratory thickening tests were con
ducted on 24-hour composite samples of alum-sewage sludge.
The test results are shown in Figure 26.   The maximum
solids concentration obtained was 2 to 3  percent dry
solids by weight.  To produce a thickened sludge of 1.5
percent from a 0.36 percent feed, a predicted thickener
solids loading of less than 6 Ib/day-sq ft is indicated.
Of significance is that an increase in thickener feed
solids of 40 percent  (from 0.26 to 0.36 percent) would
allow a three fold increase in thickener  solids loading.
Though none were evaluated, the use of a  polymer sludge
conditioning chemical should improve the  alum-sewage
thickening properties.

Vacuum filtration leaf test data indicated that dilute
alum-sewage sludges, of from 0.5 to 1.0 percent dry solids
by weight, would not effectively dewater or produce a
dischargable cake without chemical conditioning.

Leaf test data presented in Table 8 indicates that the
alum-sewage sludge can be dewatered to 77 to 85 percent
moisture, albeit at very low filter yields and high
conditioning chemical costs  (approximately 1/3 to 1/2
-------
                   FIGURE 26:  ALUM TREATMENT:

             LABORATORY  SLUDGE THICKENING RESULTS
    15
                    I
 0)
 
=>
 u
 re
 Q.
=>

.2
 (0

OT  10
00
o
re
•o
en
re
o

(A
C/}
^
0)

0)
•o
£
o
                I             I


           Feed Solids Cone. 0.36%


                Solids Specific Gravity

                      1.1 g/ml
Feed Solids
Cone. 0.26%
                             Maximum    —
                             Concentration
                             @ 3.3%
                    I
                                              Maximum
                                              Concentration
                                              @ 1.8%
                   0.5           1.0           1.5

                Thickener Underflow Solids, % by Wgt.
                                         2.0
                          75

-------
   TABLE 8?  ALUM TREATMENT:  VACUUM FILTRATION
                  LEAF TEST DATA
Test #                                  II

Peed Solids, % by wgt                  0.70      0.36

Cycle Time, Minutes                       8        23

Yielda, Ib /hr-sg ft                   0.38      0.14

Cake Moisture, % by wgt                  85        77

Polymer Type                           anionic   cationic

Polymer Dosage, Ib /ton of Dry Solids   8.6        14
a - Maximum possible rate for producing a dischargeable
    3/16 inch thick cake, @33% submergence and 0.8 scale -
    up factor
                        76

-------
TABLE 9:  LIME TREATMENT:  SUMMARY OP RESULTS
                    L-l
                    9
                    0.2-0.5
                    270
                    9.8
                    2000
                    0.73
L-2
10
0.51
470
10.6
1800
0.71
L-3
16
0.50
425
10.8

8.6
190
0.49
9170
OPERATING CONDITIONS:

Run #
Length of Run (days)
Overflow Rate, gpm/sq ft
Lime Dosage, mg/fc  [Ca(OH)2l
Reaction Zone pH, units
H2S04 Dosage, lb/MG
Reaction Zone Solids, g /I
Blowdown Concentration, g /£,
Slowdown Volume, % of flow
Blowdown Solids, lb/MG a

PROCESS TREATMENT RESULTS

Turbidity, JTU
Suspended Solids, mg/£
Total Phosphorus, mg/fc
Soluble Total Phosphorus, mg/J,
TOG, mg/jl
STOC, mg/i
COD, mg/fc
SCOD, mg/fc
BOD5, mg/fcb
pH, Units
Temperature, °C
Alkalinity, mg/Jl as CaCO-j
Total Hardness, mg/Jl as CaC03
Ca++ Hardness, mg/fc Its CaCO3

a - Blowdown solids are the median of observed values and are not based on median
    values of blowdown concentration and volume
b - BODg values are  for less than 25 percent of the observations for
    other parameters
INF.
4T~
78
4.3
3.2
60
25
146
55
—
7.6
18
270
365
212
EFF.
13-
17
2.4
1.7
49
32
128
73
—
6.1
—
69
446
278
INF.
65
140
7.2
4.2
—
—
190
33 /
—
7.3
—
309
420
251
EFF.
5
10
1.5
0.98
—
	 :
42
33
—
8.3
—
119
369
318
INF.
4T~
100
7.2
2.6
66
22
200
—
144
7.5
23
275
383
230
EFF.
ICT
16
1.1
0.50
30
18
62
39
47
8.0
—
110
335
265

-------
                         TABLE  9  (cont.):   LIME TREATMENT:   SUMMARY  OF RESULTS
-j
CO
OPERATING CONDITIONS:

Run #                              L-4
Length of Run (days)               20
Overflow Rate, gpm/sg ft           0.96
Lime Dosage, mg/i [Ca(OH)2l        365
Reaction Zone pH, units            10.8
H2SO4 Dosage, Ib/MG                1970
Reaction Zone Solids, g /i
Slowdown Concentration, g /i       100
Slowdown Volume, % of flow         0.88
Slowdown Solids, lb/MO             7010

PROCESS TREATMENT RESULTS
                                INF.    EFF.
Turbidity, JTU                  52      5
Suspended Solids, mg/i          170     8.0
Total Phosphorus, mg/i          6.7     1.3
Soluble Total Phosphorus, mg/i  3.8     0.9
TOC, mg/i
STOC, mg/i
COD, mg/i                       240     50
SCOD, mg/i                      37      41
BOD5, mg/£                      68      16
pH, Units                       7.6     7.6
Temperature, °C
Alkalinity, mg/i as CaCO3       306     62
Total Hardness, mg/i as CaC03   404     327
Ca++ Hardness, mg/i as CaCO3    251     265
                                                               L-5
                                                               16
                                                               1.3
                                                               420
                                                               10.8
                                                               1710
                                                               2.1
                                                               64
                                                               0.75
                                                               5250
                                                            INF.
                                                            26
                                                            92
                                                            3.8
                                                            2.2
                                                            47
                                                            23
                                                            86
                                                            38

                                                            7.6
                                                            15
                                                            336
                                                            465
                                                            280
EFF.
4~
13
0.3
0.2
28
25
52
45

7.9

123
410
263
L-6
16
0.4-1
390
10.9
3000
1.9
113
0.45
5840
INF.
28
56
49
22
130
55
7.5
18
312
433
270


.0







EFF.
7
12
30
26
88
50
7.8
—
89
406
309

-------
                       TABLE  9  (cent):   LIME  TREATMENT:   SUMMARY OF RESULTS
vo
OPERATING CONDITIONS:

Run #
Length of Run  (days)
Overflow Rate, gpm/sq ft
Lime Dosage, mg/j,  [Ca(OH)2l
Reaction Zone pH, units
H2SO^ Dosage, lb/MG
Reaction Zone Solids, g /&
Blowdown Concentration, g /
Slowdown Volume, % of flow
Blowdown Solids, lb/MG

PROCESS TREATMENT RESULTS

Turbidity, JTU
Suspended Solids, mg/£
Total Phosphorus, mg/Ji
Soluble Total Phosphorus
TOC, mg/£
STOC, mg/Ji
COD, Tfig/Si
SCOD, mg/£
BOD5, mg/5,
pH, Units
Temperature,  °C
Alkalinity, mg/£ as
Total Hardness, mg/£ as
Ca++ Hardness, mg/£ as CaC03
L-7
23
0.7
526
10.9
2550
3.8
81
1.4
8340
INF.
50
120
8.0
4.8
75
24
260
35
7.5
15
341
444
255










EFF.
4
7.0
1.6
0.96
30
24
54
43
7.7
—
63
367
297
L-8
24
0.7-
490
11.0
2500
12
185
0.40
7340
INF.
24
58
5.3
1.6
90
40
57
7.8
22
313
383
229


1.0







EFF
7
17
1.0
0.5
65
44
46
7.3
—
54
320
265
L-9
8
1.1
586
11.0
3690
2.2
54
1.5
7260
INF.
46
92
4.9
3.0
76
19
155
41
154
7.5
15
364
503
283










EFF.
5
1.7
0.98
0.7
25
20
53
44
27
7.6
—
62
469
409

-------
                       TABLE 9  (cont.):  LIME  TREATMENT:   SUMMARY OF RESULTS
oo
o
OPERATING CONDITIONS:

Run f
Length of Run  (days)
Overflow Rate, gpm/sq  ft
Lime Dosage, mg/Ji  [Ca(OH)2l
Reaction Zone  pH,  units
H2S04 Dosage,  lb/MG
Reaction Zone  Solids,  g  /£
Slowdown Concentration,  g /
Slowdown Volume, % of  flow
Slowdown Solids, lb/MG

PROCESS TREATMENT  RESULTS

Turbidity, JTU
Suspended Solids,  mg/J,
Total Phosphorus,  mg/jl
Soluble Total  Phosphorus
TOC, mg/A
STOC, mg/£
COD, rag/Jl
SCOD, mg/£
BOD5, mg/Jl
pH, Units
Temperature, °C
Alkalinity, mg/S, as
Total Hardness, mg/Jl as
Ca++ Hardness, mg/Jl as CaCO3
                                                     L-10
                                                     20
                                                     0.5-0.7
                                                     800-1000
                                                     11.3-11.6
                                                     4200-6600
                                                     5.8
                                                     54
                                                     1.4
                                                     6300
                                                  INF
                                                  72
                                                  3.8
                                                  2.5
                                                  120
                                                  44
                                                  65
                                                  7.6
                                                  21
                                                  316
                                                  392
                                                  216
EFF.
7
6.0
0.5
0.4
79
62
47
6.8

67
543
512
             L-ll
             25
             0.4
             1530
             11.6
             14,300
             4.4
             42
             2.8
             12,100
INF.
55~
170
7.8
4.5
220
40

7,5
15
330
464
280
EFF.
4
6.5
1.0
0.5
40
35

7.6

80
1550
1500

-------
Hydraulic loading and treatment pH were the primary opera-
tional parameters evaluated.

Run L-l was conducted at a pH of 9.8.  Effluent suspended
solids and turbidity were 17 mg/£ and 15 JTU.  During
Run L-l, a reduction of overflow rate from 0.5 to 0.2
gpm/sq ft did not significantly reduce effluent suspended
solids.  An effluent phosphorus concentration of 2.4 mg/Jl
was observed.  The low phosphorus removal at pH 9.8 was not
unexpected.  Laboratory jar test results had indicated
that a higher treatment pH was required to reduce phosphorus
to lower levels.

Runs L-2 through L-9 were conducted at moderate treatment
pH's ranging from 10.6 to 11.1 and overflow rates ranging
from about 0.5 to 1.3 gpm/sq ft.  Clarification effectiveness
ranged from marginal  (10 JTU, 17 mg/& SS and 1.6 mg/£ P)
to excellent (4 JTU, 2 mg/£ SS and 0.3 mg/£ P).  Runs
L-10 and L-ll were conducted at relatively high treatment
pH's, above 11.3.  Excellent clarification was achieved.
Typical feed and effluent suspended solids and phosphorus
data for moderate and high treatment pH  (10.9 and 11.6)
Runs are presented in Figures 27 through 30.

An attempt was made to correlate percent suspended solids
removal or concentration of effluent suspended solids with
treatment pH or overflow rate.  No precise correlation was
found with either of these treatment parameters.  Recognizing
that the coagulation effectiveness of lime treatment is
generally attributed to the precipitation of MgfOH)?*
effluent suspended solids were compared with non-calcium
hardness  (*Mg++) removals.  This correlation was also
imprecise.

Figure 31 presents the only precise correlation found
between operational parameters and clarification effective-
ness.  It is seen that poorer effluent quality is associated
with increasing sludge age within the chemical treatment
unit.  The relative sludge age shown is directly related
to the reaction-zone suspended solids concentration and
inversely related to the hydraulic loading and solids
production rate.  The actual sludge age was estimated to
never have exceeded more than one day.
                          81

-------
    400
   200
o>
E
100


 80



 60




 40
                  FIGURE 27: LIME TREATMENT: FEED AND  EFFLUENT

                                SUSPENDED  SOLIDS
                                             Feed SS
8-  20-
3
U)
   10


    8



    6--




    4--
                                            Effluent SS
                     10      20    30   40  50  60  70   80

                           % Of Occurrences < Value Shown
                                                          90
                                                                95
98

-------
          FIGURE 28: LIME TREATMENT: FEED  AND EFFLUENT PHOSPHORUS
  10.0




   8.0





   6.0








   4.0
f  3.0




3


O


Q-  20
w

O
o

o
  1.0




   0.8





   0.6








   0.4. _





   0.3
  I      I

Run L-7
               I
I
                                      Effluent P (Soluble)
I    I     I
I
                 10     20    30   40 50   60  70   80


                          % Of Occurances < Value Shown
                                                 90
                                  95
                                 98

-------
FIGURE 29: LIME TREATMENT: FEED AND EFFLUENT

             SUSPENDED SOLIDS
        20    30  40  50  60  70   80

       % Of Occurrences < Value Shown
 t-
90
      95
98

-------
    5.0-


    4.0-



    3.0--





    2.0--
(A
as
O)


in
o.
a>
O

CL

*

O
 1.0
 0.9.

 0.8.

 0.7.

 0.6.


 0.5 --


 0.4--




0.3--
    0.2 --
                   FIGURE 30: LIME TREATMENT: FEED  AND  EFFLUENT

                                       PHOSPHORUS
                     FeedP
                 Run L-11
                                                             O
                                              Effluent P
                                               Effluent P (Soluble)
    0.1
               H	H	1	1	I—I	1	1	1	H
               10      20    30   40  50  60   70    80     90    95


                        % Of Occurrences < Value Shown
                                                                          98

-------
                 FIGURE 31:  LIME TREATMENT: EFFECT OF SLUDGE AGE


                H	1	1	1	1
                               Treatment pH = 10.6 to 11.0
   15- -
01
E

«T
TJ


W  10-
TJ

0)
Q.

-------
Based on the data in Figure 31 and considering the
operation conditions existing during pilot plant
operation, it appears that reaction-zone suspended
solids should be kept below about 4 to 6 g/H.  Effluent
suspended solids would then be expected to average less
than about 10 mg/fc.

The highest overflow rate evaluated over a sustained
period of time was 1.3 gpm/sq ft, during Run L-5 at a pH
of about 11.0.  Just prior to Run L-5 overflow rates
as high as 1.5 gpm/sq ft were tried, but control of the
sludge level in the solids-contract unit proved difficult.
Thus, for moderate treatment pH, a maximum sustained
overflow rate of about 1.3 gpm/sq ft is suggested.  The
hydraulic capacity of the pilot plant was limited to an
overflow rate of 1.5 gpm/sq ft.  Consequently, an evaluation
of the effect of polyelectrolyte flocculation aid on
clarifier overflow rate was impossible.

Because of limited lime feeding facilities, the maximum
hydraulic loading for high treatment pH (11.5) Runs could
not be determined.  During Runs L-10 and L-ll excellent
clarification was obtained at overflow rates from 0.4
to 0.7 gpm/sq ft.  As" will be developed later, chemical
sludge production and sludge properties were somewhat
similar for moderate and high treatment pH values.  It
is, therefore, conjectured that the maximum overflow
rate for high treatment pH would be similar to that
experienced for moderate treatment pH's.

Data in Table 9 indicates a range of SCOD removals from
13 percent to -41 percent (i.e., an increase) across the
chemical contactor.  These data were quite variable and
did not precisely correlate with operational parameters
such as relative sludge age, treatment pH or hydraulic
retention time at treatment pH.  Since any increase in
SCOD across the chemical treatment step will result in
an increased demand for powdered carbon in the subsequent
treatment step, future lime treatment studies should be
designed to more precisely evaluate SCOD removal.
                       87

-------
The hardness data in Table 9 indicate that some soften-
ing was accomplished at treatment pH's between 10.6 to
11.1.  Above and below this pH range hardness was added
to the wastewater.  At all pH's tested calcium hardness
was found to increase.  Some 80 to 85 percent of the
biocarbonate alkalinity was removed at moderate treatment
pH values.  When lime at dosages above 600 mg/£ was added
to reach high treatment pH levels, considerable calcium
increases occurred because CO| was not available to
precipitate the additional Ca*+ as CaC03.  If high dissolved
solids are objectionable, then recarbonation of high
treatment pH effluent to pH 9.5 to 10.5 with C02 would
be required to reduce the high calcium concentration.
A batch test during Run L-ll indicated that recarbonation
with CC>2, to a pH of 10.4, reduced soluble calcium from
1500 mg/£ to about 160 mg/£ Ca++ (as CaC03).  This
recarbonation resulted in some 11,000 Ib of CaCO3 sludge
per MG of wastewater flow (i.e. , 1320 mg/& of solids
precipitated).
Sludge Production

Table 10 presents a summary of observed chemical and
sewage sludge production data.  Chemical sludge production
is seen to range from 551 to 1016 mg/£ at moderate treat-
ment pH values and from 690 to 1289 mg/£ for high treatment
pH values.  The variability in the data prompted an
attempt to correlate chemical sludge production with
treatment parameters such as pH, lime dosage and alkalinity.
The best correlation found is shown in Figure 32 which
indicates that the pounds of chemical sludge produced
per pound of lime fed decreased in the pH range 10.7 to
11.1.  Jar test results presented in Figure 8, did not
show the leveling off at high treatment pH's.

Because of the variability of raw wastewater alkalinity
and actual treatment pH between Runs, no precise correla-
tion between lime dosage required to attain a given pH and
alkalinity was found.

The following assumptions were made in an effort to relate
chemical sludge production to changes in water quality
parameters caused by lime treatment.
                         88

-------
                            TABLE 10:   LIME TREATMENT:   SLUDGE PRODUCTION
        Run
                                                                              10
                                                                                11
oo
        Treatment pH
        Slowdown SS,  lb/toGa
        Slowdown SS,  mg/J,a
        Clarifier Effluent SS,
          mg/fc

        Total Chemical  and
          Sewage SS ,  mg/fc
Raw Wastewater SS,
  mg/Jl
Chemical SS Produced,
  mg/jl
Lime Dosage, mg/Z
  Ca(OH)2
Ibs Chemical Solids/
  Ib Ca(OH)2 Fed
% Chemical Solids
10.7
9170
1100
16
1116
100
1016
425
2.39
92
10.8
7010
842
8
850
170
680
365
1.86
80
10.8
5250
630
13
643
92
551
420
1.31
86
10.9
5840
700
12
712
^56
656
390
1.68
93
10.9
8340
1000
7
1007
120
887
525
1.68
88
11.0
7340
880
17
897
58
839
490
1.70
94
11.0
7260
872
2
874
92
782
585
1.33
90
11.3-11.6
6300
756
6
762
72
690
800-1100
0.73
91
11.6
12,100
1450
7
1457
170
1287
1530
0.48
89
         a -  Based on Total Flow

-------
                     FIGURE  32:  LIME TREATMENT: SLUDGE PRODUCTION
     3.0 L.
•o
0)
u
3
TJ
O
a
0)
     2.0
                      O
  . ro
  O,
0)
O
O
"o
•a
o
o>
•u
55
     1.0 i
                        O
                                                                               O
     o.o
      10.6
                                                  1
                    10.8
11.0           11.2
 Lime Treatment pH, Units
                                                              11.4
11.6

-------
1.   The reduction of bicarbonate alkalinity results from
    precipitation of CaCO-,

2.   The reduction in non-calcium hardness results from
    precipitation of Mg(OH)2

3.   The reduction in phosphorus results from precipitation
    of Ca5OH(P04)3

Based on these assumptions, computations indicated that
about 470 mg/£ of CaCO-j was produced at moderate treatment
pH values (10.6 to 11.1).  The computed chemical sludge
distribution was found to be 85 percent CaCO-,, 10 percent
Mg(OH)2 and 5 percent Ca50H(PO.)3.  A mass balance of
calcium indicated that some 14 percent of the calcium in
the sludge was present in a form other than CarOH(P04)3 or
CaCO-j.  This amount of calcium was equivalent to about 60
mg/£ of Ca(OH)?.  Computed chemical sludge values were
20 to 30 percent less than the observed chemical sludge
production values in Table 10.

From Table 10 it is seen that 80 to 94 percent of the
lime-sewage sludge produced was chemical sludge.  From
the above discussion, it would appear that moderate
treatment pH, lime-sewage sludge consisted of the following
approximate consitutents:

1.  10% sewage solids

2.  60% CaC03

3.  10% Mg(OH)2 and Ca5OH(P04)4

4.   8% some other calcium precipitate

5.  12% unaccounted for chemical solids

From this estimate of the distribution of sludge con-
stitutents, it is predictable that the large fraction of
CaC03 should result in an easily thickened and dewatered
lime-sewage sludge.
                          91

-------
Sludge Thickening and Dewatering

Numerous laboratory gravity thickening and vacuum filter
leaf tests were conducted on moderate and high treatment
pH lime-sewage sludges.   The effect of polyelectrolyte
flocculation aid was also established.

Figure 33 shows the results of laboratory thickening
tests.  Each curve represents one sludge sample and
shows the thickener loading (i.e., no scale-up factor)   (
related to various thickened sludge concentrations.  The
data are somewhat erratic, reflecting variable sludge
characteristics experienced over the eight month
period during which the  tests were conducted.  It is
apparent from the feed solids data in Figure 33 that
the moderate treatment pH sludges tested were generally
more concentrated than the high treatment pH sludges.
This observation reflects the results shown in Table 9.

The lower-right extremity of the curves in Figure 33
represents the sludge thickness attained after 24-
hours of gravity thickening and is defined as the maximum
possible or ultimate concentration.  A plot of maximum
thickened concentration  versus initial or feed solids
concentration is presented in Figure 34.  It  appears
that the more concentrated the chemical clarifier under-
flow (initial solids) the more concentrated are the settled
solids after 24-hours of settling.

One approach to using the thickening data entails drawing
an operating line through each set of curves.  For the
data presented, high and moderate treatment pH sludges
are separately considered.  Generally, higher vacuum
filter yields and drier  filter cakes are obtained with
higher feed solids concentration  (i.e., thickener underflow
solids concentration).  Since vacuum dewatering costs
are considerably higher  than gravity thickening costs,
the operating lines in Figure 33 are drawn at reasonably
high underflow solids concentration values.  If the
thickener solids loading and underflow concentration at
the intersection of each thickening curve with the operating
line is plotted versus thickener feed solids, a suggested
design  curve can be drawn.

Figure 35 presents such  a plot of suggested design and
thickening data for the  high and moderate treatment
pH sludges.  A scale-up  factor of 0.80 was applied to
the observed thickener solids loading values taken from
                          92

-------
  250
                           FIGURE 33:  LIME TREATMENT: SLUDGE THICKENING
                                                   15.7 — Feed Solids Cone., % by Wgt.
  200
o
OT
  150
 : 100
   50
        Operating Line
                                                                              .  pH < 11.0


                                                                             0 pH  >11.5
                                                                        Solids Specific Gravity
                                                                               1.76 g/ml
                                                                             Operating Line
                                                                              18.0
                                                                         15.7
                               10                        20

                                Thickener Underflow Solids, % by Wgt.
                                                                                    30
                                         93

-------
FIGURE 34: LIME TREATMENT: SLUDGE THICKENING
    6            8           10           12



        Initial Solids Concentration, % by Wgt.
14
             16
18

-------
            FIGURE 35: LIME TREATMENT: SLUDGE THICKENING


  70H	1	1	1	1	1	1	
   60--
               Scale-up factor of
                   0.80 used
   50--
ra
•o
   40--
o>
in
T5
o
W
30--
I  20-
u
V)
   10--
    0--
                                                                 --30
                                                                 --20
                                                                          01

                                                                          >,
                                                                          ffl
                                                      CO

                                                      _o
                                                      t:
                                                      a>
                                                      •o
                                                                    --10
                                           H  (g) — pH > 11.5

                                           El  0 — pH < 11.0
        8           12


Thickener Feed Solids, % By Wgt.
                                                        16
                                                                 20
                               95

-------
Figure 33.  The linear regression lines shown in Figure 35
are for the two separate treatment pH ranges.  A linear
regression of all treatment pH values of thickened
solids loading and underflow solids data on feed solids
would result in correlation coefficients of 0.90 and
0.98 respectively.  This observation would imply that the
moderate and high treatment pH sludges had similar
thickening properties.  This implication is possibly
dependent, however, on the choice of the location of the
operating lines drawn in Figure 33 and, hence, is not a
valid general conclusion.

The effect of polyelectrolyte flocculation aid on thicken-
ing results is indicated in Figure 36 for a sample of high
treatment pH sludge.   The data shows that the lower the
feed solids concentration, the greater the effect on
thickener solids loading.  The cost of polyelectrolyte
probably cannot be justified on the basis of reduced
thickener size.  Polyelectrolyte use on a part-time
basis may be justified.   For example, consider an
installation designed for thickening 6 percent feed solids
to 12 percent, at 21  Ib/day-sq ft, without polyelectrolyte.
If for some operational  reason, the feed solids dropped
to 3 percent the thickener would still produce 12 percent
underflow if about 0.04  Ib polyelectrolyte per Ib dry
sludge solids were added.

Numerous vacuum filter leaf tests were conducted on
both high and moderate treatment pH sludges.  A synthetic
filter media, Polypropylene-852F, was found to result in
good filtrate clarity of less than 200-300 mg/£ suspended
solids and would discharge the cake easily.  The filter
leaf tests results are presented in Figure 37.  Maximum
predicted vacuum filter  yields for the operating conditions
indicated are shown.   The 33 percent drum submergence and
20 inches of Hg vacuum level are acceptable design values.
The results in Figure 37 indicate that treatment pH and
feed solids significantly affect the vacuum filter yield.
The linear regression lines shown have correlation coefficients
of 0.90 and 0.96 for  high and moderate treatment pH values
respectively.

Several tests were conducted with anionic polyelectrolyte
flocculation aid (Dow Chemical Co., AP-30) at dosages
ranging from 0.2 to 0.6  Ib/ton dry solids.  Vacuum filter
yields were found to  increase from 30 to 70 percent above
those shown in Figure 37 for several feed solids concentration.
                         96

-------
               FIGURE 36: LIME TREATMENT: SLUDGE THICKENING
   30
   25
m
•o
c  20
'o
re
o
"5
V)
   15
re
w  10
                          ^  No Additive
                          O  0.03 - 0.05 % by Wgt. Separan AP-30 Added
                           Treatment pH -11.5
                           Thickener Underflow Solids — 12% by Wgt.
                                                                       10
                        Thickener Feed Solids, %by Wgt.

-------
                              FIGURE 37: LIME TREATMENT SLUDGE  DEWATERING
   100.0

    90.0

    80.0

    70.0

    60.0


    50.0


    40.0



    30.0





    20.0
.Q
01
"ra
cc

§   10.0

2   9.0

^   8.0
    4.0
    3.0-
    2.0-
    1.0
Operating Conditions:
  3/16 inch cake
  33% Drum Submergence
  20 inches of Hg Vacuum
  0.8 Scale-Up Factor
  No Conditioning Chemicals
        Filter Cake
      Moisture Content
      68-72% by wgt.
                                                                Filter Cake
                                                               Moisture Content
                                                              65-68% by wgt.
                                               O = Data at pH > 11.5
                                               A = Data at pH<  11.0
                                  8     10     12    14      16     18

                                     Feed Suspended Solids, % by Wgt.
                                                   20
                                                         22
-H-
 24
                                                                       26
                                            98

-------
The utility of the lime-sewage sludge thickening and  de-
watering data presented can best be illustrated by  the
following example which indicates suggested design  cri-
teria and results for lime-sewage sluge produced in this
study.  Table 11 is a summary of the following example:

Chemical clarifier underflow is taken as  the weighted
average of all such data presented in Table 9.  From
Figure 35, thickener solids loading and underflow con-
centration is determined.  For the observed thickener
underflow concentration  (vacuum filter feed solids) a
filter yield is determined from Figure 37.  For the
vacuum filter operating conditions specified in Figure
37, the following relationships would exist:
          CT =
       FT
      0.33
                                              (2)
          QD = 0.50 CT

                        /-im
           W = Yield x  £±.
                        oU
                                              (3)

                                              (4)
Where:    CT = drum cycle  time,  min

          FT = cake form time, min

          QQ = cake dry time, min

           W = cake weight,  Ib/sq ft

       Yield = full scale  filtration  rate,  Ib/hr-sq  ft

Figure 39 presents the observed  relationship  between
filter cake moisture  content and a modified correlating
factor  (0D/W) for the treatment  pH and filter feed solids
conditions indicated.  Determination  of filter cake  moisture
content presented in  Table 11 was as  follows  (example is
for moderate treatment pH):
     1.

     2.
      3.
CT =
     U t
          =1.8 min
9D = (0.5) (1.8) = 0.9 min
            =  (12.8)
                    60
                        Ib/sq ft
(0.8)  |D . (0.9)10^-8) . 1-9 min.sq ft/lb
                           99

-------
 TABLE 11:  SUGGESTED DESIGN PARAMETERS FOR LIME-
            SEWAGE SLUDGE THICKENING AND DEWATERING
                                           Treatment pH
Item
                                      Moderate
          High
Chemical Clarifier
underflow concentration
(weighted avg.,  of all data)
% by wgt

Predicted thickener underflow
solids3 - % by wgt

Predicted thickener solids
loading3 - Ib/day-sq ft

Predicted vacuum filter
yieldb - Ib/hr-sq ft

Required filter cake form time -
min (from leaf test results)

Modified correlating factor-
min-sq ft/lb  (includes 0.8
scale-up factor)

Filter Cake moisturec -
%  by wgt
11.5


17.9


47


12.8


 0.6



 1.9


67
 4.8


 9.4


18


 4.5


 1.37



 5.4


72
a = from Figure 35
b = from Figure 37
c = from Figure 38
                         100

-------
                                 FIGURE 38: LIME TREATMENT: SLUDGE DEWATERING
   80
                                                                  o
en
   70
o
O

I
*•«
in
'5
5
                                                                               O
   60
                                                      pH < 11.0
                                                      17 - 20% Feed Solids Cone.
                                                                                             O
                                    pH> 11.5
                                    8-12% Feed
                                    Solids Cone.
                                4            6

                              Modified Correlating Factor,
 8
?D.
 W
         10
12
min.-ft.2
   IBsT
14
16

-------
From Figure 39 a moisture content of 67 percent is indicated
at 0D/W = 1.9.


Summary of Chemical Treatment Results

As predicted by laboratory jar tests, all three chemicals
tests were effective in precipitating phosphorus and
coagulating suspended solids.  The results indicate that
Salt Lake City raw municipal wastewater could be chemically
treatment to produce an effluent of about 10 JTU Turbidity,
10-25 mg/Z suspended solids and 1 mg/£ phosphorus.  The
raw wastewater characteristics encountered varied widely;
however, it could be generally classified as a moderately
weak municipal wastewater.  It is conjectured that
similar treatment effectiveness, could be obtained when
treated a normal to moderately strong municipal wastewater.

To facilitate comparison of the three treatment chemicals
studied, a summary is presented in Table 12.  The chemical
dosages and chemical contactor operating conditions presented
should result in production of the above mentioned effluent
quality.  Though use of polyelectrolyte flocculation
aid is not indicated, it is strongly recommended that
facilities be provided for feeding polyelectrolyte to all
three unit operations of clarification, thickening and
vacuum dewatering.  Doing so will provide reserve treatment
capacity, thus enhancing performance reliability.

Because of the limited number of FeCl3 and alum sludge
thickening and filtration tests conducted, the data
presented for these sludges should be considered pre-
liminary.  Additional tests are recommended.

It can be noted that high pH lime treatment results are
not presented in Table 12.  Any benefits achieved by high
treatment pH, compared to moderate treatment pH, were off-
set by significantly increased lime requirements, increased
sludge production and poorer sludge thickening characteristics.
Actually, the high pH lime-sewage sludge thickening properties
were significantly poorer than for moderate pH sludges.

The ultimate choice of which type of chemical should be
used must be based on an economic analysis of total
treatment costs.  The design conditions presented in
Table 12 will be used later in this report as the basis
for such an economic analysis for treating Salt Lake City
wastewater.
                         102

-------
TABLE 12:  SUMMARY OF SUGGESTED CHEMICAL TREATMENT
           PROCESS DESIGN PARAMETERS FOR SALT LAKE
           MUNICIPAL WASTEWATER
                                                    Hydrated
Treatment Chemical:                FeClo  Alum      Lime
Chemical Dosage, mg/i              120    140       400-500
Acid (H2SO4) Dosage, mg/&            0      0       330

Chemical-Contactor;

Peak Overflow Rate, gpm/sq ft      0.5    0.4       1.3
Reaction Zone Solids, % by wgt     0.2    0.1       0.5
Underflow Solids, % by wgt         1.3    0.5-1.0   11.5

Sludge Production;

Chemical-Sewage Sludge, mg/£a      180    145       850
% Chemical Sludge                   52     40        90
Ib Chem. Sludge/lb Chem. Fed       0.78   0.41      1.7

Gravity Thickening;

Solids Loading,  Ib/day-sq ft        10    5-8        47
Underflow Concentration, % by wgt   4.0   2.5        18

Vacuum Filtration;

Yield,  Ib/hr-sq  ft                 1.0b   0.6-1.Ob  12.5
Filter Cake Moisture, % by wgt      82    82        67
a = based on total plant flow
b = with conditioning chemicals:  20-25%  Ca(OH)2 or  0.5%
    polymer.
                         103

-------
The problem of "post precipitation" of iron compounds
remains imprecisely defined and without a proven solution.
If the problem is ultimately defined as being the reduction
and subsequent oxidation of soluble iron, then a possible
solution can be suggested.  In the PAC-PCT process evaluated,
an oxidation operation could be accomplished after
carbon contacting and prior to granular media filtration.
Aeration at this point should effectively convert
Fe+2 to Fe+3, with precipitation of the latter as a
filterable hydrated ferric oxide.  Oxygen requirements
and aeration contact time and method requirements will
have to be determined before this approach can be
accepted.
POWDERED CARBON TREATMENT STEP

The major purpose of the carbon treatment tests was to
determine the effect of carbon dosage and number of contact
stages (1 or 2) on carbon contactor operation and removal
of soluble organics from chemically treated and gravity
clarified raw wastewater.  Results of spent carbon handling,
concentration and regeneration are presented and discussed
later in this report (see page 152).

Based on laboratory equilibrium adsorption isotherm test
results,  it was concluded that the type of chemical used
for pretreatment did not significantly affect the
adsorption of SCOD by carbon.   Thus,  the pilot plant
carbon treatment Runs were scheduled independently of
the chemical treatment Runs.

A summary of operating conditions and treatment results is
presented in Tables 13 and 14.  Chronologically, Runs C-14
and C-13  were conducted first, followed by Runs C-2, C-l
and then C-3 through C-12.  Certain single-stage contact-
ing Runs  were conducted simultaneously by operation of
the two carbon contactors in parallel (for example, Runs
C-9 and C-10; C-ll and C-12).   The chemical pretreatment
Run numbers shown refer to Tables 2,  5 and 9.  It should be
noted that the carbon and chemical treatment Run periods
generally do not precisely coincide,  thus chemical stage
effluent results differ slightly between Tables 13 and 14
and Tables 2, 5 and 9.

The approximate solids retention time (SRT) of the carbon
in the contactors was computed as follows:

    SRT = (Reaction Zone Solids)(Volume of Carbon Slurry)
                 (Flow Rate)(Carbon Dosage)
                         104

-------
                           TABLE 13:   SUMMARY OF TWO-STAGE COUNTER-CURRENT
                                            CARBON TREATMENT RESULTS
o
tn
Run I
Length of Run, Days

OPERATING CONDITIONS:

Chemical Pretreatment, (Run #)
Hydraulic Loading, gpm/sq ft
  (1st stage/2nd stage/GMF)

Carbon Dosage, mg/£
Polyelectrolyte Dosage, mg/j?,
  (1st stage/2nd stage/GMF)

Reaction Zone SS, g /£
  (1st stage/2nd stage)
Blowdown Volume, % of Flow
Approximate SRT, days
  (1st stage/2nd stage)
                                             C-l
                                             12
       L-3

       0.76/0.73/4.2

       325

       0/0/0

       17/19

       0.9

       2.0/2.2
          PROCESS TREATMENT RESULTS:

          Effluent From

          Suspended Solids, mg/£
          Turbidity, JTU
          % Transmittance

          SCOD ,  mg/£
          STOC,
          8005,
Chem.  1st    2nd
Stage  Stage  Stage  GMF
                                   C-2
                                   34
L-8

0.69/0.69/3.1

150

0.3/0.3/0.3

9/8



2.4/2.2
                                                        Chem.  1st    2nd
                                                        Stage  Stage  Stage  GMF
          pH,  units
          Temperature
14
6
45
	
""• —
7.1
22
12
6
12
—
_ —
— —
--
7
2
11
—
— —
__
—
3
1
12
--
— —
7.5
—
32
10
42
22
47
8.3
22
38
6
23
15
31
— _
__
17
4
18
12
16
Mm ^ _
_ —
12
4
19
12
13
8.0
__

-------
                TABLE  13  (cont.):   SUMMARY OF TWO-STAGE COUNTER-CURRENT
                                         CARBON TREATMENT RESULTS
Run  #
Length of  Run, Days

OPERATING  CONDITIONS;

Chemical Pretreatment,  (Run  #)
Hydraulic  Loading, gpm/sq  ft
   (1st stage/2nd stage/GMF)

Carbon Dosage, mg/i
Polyelectrolyte Dosage, mg/i
   (1st stage/2nd stage/GMF)

Reaction Zone SS, g ./I
   (1st stage/2nd stage)
Slowdown Volume, % of Flow
Approximate SRT, Days
   (1st stage/2nd stage)
PROCESS TREATMENT RESULTS;

Effluent From

Suspended Solids, mg/i
Turbidity, JTU
% Transmittance

SCOD, mg/i
STOC, mg/i
     , mg/i
C-3
23
L-10

0.56/0.52/1.4

110

0/0/0

6/10



2.7/4.5
C-4
8
L-10

0.79/0.79/4.7

75

0/0/0

2/2



1.0/1.0
pH , Units
Temperature
Chem.
Stage
8
7
63
49
6.0
21
1st
Stage
12
3
30
18
—
2nd
Stage
6
2
22
12
—
GMF
2
3
22
13
6.3
Chem.
Stage
7
6
66
--
8.2
19
1st
Stage
16
4
39
—
—
2nd
Stage
12
3
32
--
—
GMJ
3
1
36
—
8.

-------
            TABLE 13  (cent.):  SUMMARY OF TWO-STAGE COUNTER-CURRENT
                                     CARBON TREATMENT  RESULTS
Run #
Length of Run, Days

OPERATING CONDITIONS:

Chemical Pretreatment,  (Run #)
Hydraulic Loading, gpm/sq ft
  (1st stage/2nd stage/GMF)

Carbon Dosage, mg/Jl
Polyelectrolyte Dosage, mg/jl
  (1st stage/2nd stage/GMF)

Reaction Zone SS, g: ./£
  (1st stage/2nd stage)

Approximate SRT, Days
  (1st stage/2nd stage)
PROCESS TREATMENT RESULTS:

Effluent From

Suspended Solids, mg/i,
Turb i di ty , JTU
% Transmit tance
SCOD,
STOC, mg/Jta
     , mg/Jl
       C-8
       29
       L-7,L-9

       0.45/0.40/1.6

       150

       0/0/0

       14/17


       6.1/7.4
Chem.  1st    2nd
Stage  Stage  Stage  GMF
       C-14
       16
       F-2

       0.75/0.73/1-2

       600

       0.7/0.8/0

       -15/-21


       0.9/1.3
Chem.  1st    2nd
Stage  Stage  Stage  GMF
pH, Units
Temperature
6
4
98
45
24
7.7
15-18
16
7
82
18
11
7.4
—
3
5
93
11
9
7.4
—
1.3
1
—
4.7
6
7.5
—
13
16
—
37
28
6.9
—
28
13
--
15
15

—
7.5
11
—
15
12

__
2.7
5
--
10
13

__
a - For Run C-14 only Total COD and TOC shown

-------
                                 TABLE 14:   SUMMARY OF SINGLE-STAGE
                                            CARBON TREATMENT RESULTS
o
00
Run t
Length of Run, Days
OPERATING CONDITIONS:
Chemical Pre-ferteatment, (Run #)
Hydraulic Loading, gpm/sg ft
(Carbon Contactor/GMF)
Carbon Dosage, mg/J,
Reaction Zone SS, g /£
Slowdown Volume, % of flow
Approximate SRT, Days
C-5
21

L-6, L-l
0.53/0
95
8.3
0.23
4.6
C-6
14

L-6, A-l
0.53/3.7
300
3.4
0.65
0.6
C-7
16



A-l, A-2
0.68/2.6
105
3.2
0.59
1.2


         PROCESS TREATMENT  RESULTS:
                                     Chem.   Carbon   Chem.  Carbon        Chem.  Carbon
         Effluent From               Stage   Cont.     Stage  Cont.    GMF   Stage  Cont.   GMF

         Suspended  Sqli,ds,  mg/£
         Turbidity, JTU
         % Transmittance

         SCOD, mg/i
         STOC, mg/i
         BOD5, mg/a

         pH, Unit
         Temperature,  °C
14
9
58
28
58
7.2
18
24
7
24
10
21
7.4
—
21
15
36
25
35
7.6
.,--
14
7
10
13
23
— —
— ;
3
2
18
12
16
.5
-
27
11
28
16
39
7.0
17
10
6
16
13
8
«»M
—
2
2
16
11
10
6.8
__

-------
                      TABLE 14 (cont.j:  SUMMARY OF SINGLE-STAGE
                                         CARBON TREATMENT RESULTS
Run * C-9
Length of Run, Days 24
OPERATING CONDITIONS:
Chemical Pretreatment, (Run #) L-ll
Hydraulic Loading, gpm/sq ft
(Carbon Contactor/GMF) 0.30/1.2
Carbon Dosage, mg/£
Reaction Zone SS, g /A
Slowdown Volume, % of flow
Approximate SRT, Days
PROCESS TREATMENT RESULTS:
Effluent From
Suspended Solids , mg/S,
Turbidity, JTU
% Transmittance
SCOD , mg/A
STOC, mg/i
BODs , mg/£
pH, Unit
Temperature, *C
Copper, mg/£
146
9
5

Chem.
Stage
6
4
98
35
34
7.6
15
--
.5
.9

Carbon
Cont . GMF
30 2
6 2
91 99
24 23a
13 13
2-11 8.0
-- — -
C-10
24
L-ll
0.30/~
146
11.
7.2

Chem.
Stage
6
4
98
35
34
7.6
15
--

5

Carbon
Cont.
30
9
81
25
17
2-11
2.4
C-ll
20
L-4
0.75/2-5
345
2.2

Chem. Carbon
Stage Cont.
7.7 53
5 8
97 76
41 6.4
22
-- --



GMF
1.8
2
99
3.6
__
__
a - Total COD

-------
                      TABLE 14  (cont.):   SUMMARY OF SINGLE-STAGE
                                         CARBON TREATMENT RESULTS
 Run  #
 Length  of  Run,  Days

 OPERATING  CONDITIONS:

 Chemical Pretreatment,  (Run  #)
 Hydraulic  Loading, gpm/sq ft
   (Carbon  Contactor/GMF)

 Carbon  Dosage,  mg/£

 Reaction Zone SS, g  /£
 Slowdown Volume,  % of  f lov/
 Approximate SRT,  Days
PROCESS TREATMENT RESULTS:

Effluent From

Suspended Solids, mg/J,
Turbidity, JTU
% Transmittance
SCOD,
TOC, mg/4

pH, Unit
Temperature, °C
C-12
20
L-4
0.75/—
317
1.6
Chem. Carbon
Stage Cont.
7.7 20
5 5
97 90
41 13.2
7.6 7.8
22
C-13
13
P-3
0.75/~
0
6
0
00
Chem. Carbon
Stage^ Cont.
18 18
31 32
55 38
21 15
__
b - For Run C-13, Total COD and TOC  shown

-------
The numerator is an approximation of the inventory of
carbon (pounds)  within the solids-contact units and the
denominator is the carbon fed  (Ib/day).  The carbon
inventory, so calculated, was  found to be within ±25
percent of that determined by  a more comprehensive
procedure to be presented later.

STOC data is presented for only a few Runs.  Considerable
difficulty was experienced maintaining the TOC analyzer
in an operable condition.  The need for frequent repairs
and delayed delivery of parts  were common experiences.
The BOD5 data presented in Tables 13 and 14 are for only
5 to 20 percent of the number  of samples for SCOD data.
Operation of Carbon Contactors

As indicated in Appendix C  (Operation of Solids-Contact
Units), the principal operational feature of the carbon
contactors was maintenance  and control of copious amounts
of powdered carbon within the treatment units.  The
5-minute slurry settling test was routinely used to
monitor reaction zone carbon concentration  (see Anpendix
C).

The volume of carbon slurry within the carbon contactors
was estimated by observation of slurry pool depth.  The
approximate location of slurry pool depth was determined
by withdrawing samples from clarification zone sample
taps, which were located at depths of 13, 30 and 58
inches from the bottom of the 126 inch high clarifier
tank wall.  The lower extremity of the reaction zone
skirt was located at a depth of 22 inches.  Normal
operation entailed maintaining the carbon slurry pool
just above the middle sample tap.  If the 5-minute settling
test of a sample taken from the top sample tap was more
than 5-10 percent, the carbon blowdown rate was increased.
This caused the slurry pool to fall below the middle sample
tap within one-half to two  hours.  This operational pro-
cedure resulted in a 0 to 2 1/2 foot deep carbon slurry
pool  (i.e., sludge blanket) existing in the variable
area clarification zone.

Carbon inventory within the contactors was determined
on three occasions.  Samples from three taps in the
clarification zone and a single tap in the reaction
                          111

-------
zone were analyzed for carbon slurry concentration.  Base
on the geometry of the units, volumes were associated wit
each sample tap and a total weight of carbon computed.  A
example is shown in Table 15.  The results of all carbon
inventories indicated that multiplication of reaction zon
suspended solids by total volume of concentrated carbon
slurry within the units would estimate carbon inventory
within ±25 percent.  This fact is understandable since
the reaction zone volume constitutes about 2/3 of the
total slurry volume and the variation of suspended solids
between sample taps was usually less than ±20 percent.

The uniform distribution of carbon and the "total solids
circulation" feature of the solids-contact units provided
the basis for a good biological reactor.  During pilot
plant start-up and shakedown, before solids inventory
control was attempted, significant odors were noted at
the surface of the carbon contactors (especially above thi
reaction zone).   The odors were typical of anaerobic
decomposition with occasional sulfide odor occurring.
Addition of 1-2 SCFM of air per 10 gpm of flow into the
reaction zone significantly reduced the anaerobic odors
but did not eliminate them.

During Run C-14, a minimal odor level existed.  The
high carbon dosage (600 mg/Jl) prompted an evaluation of
carbon residence time (SRT).  The rationale applied was
that adsorption of biodegradable organics at the
carbon surface could enhance bioactivity and that a
biomass could be located at the external surface of the
carbon particles.  Thus, carbon SRT may approximate
biomass SRT.  Anaerobic biological kinetic studies
have indicated that methane fermentation systems cannot
be maintained at SRT's less than about 5-7 days and
sulphate reduction systems at SRT's less than about
2-4 days27'28.

Based on the above rationale, and the fact that during
Run C-14 carbon SRT was less than about 1.5 to 2.5
days, it was considered desirable to attempt to main-
tain carbon SRT to less than about 2-3 days in each
carbon contactor for odor control.

Data in Tables 13 and 14 show that attempts to control
SRT were not always successful.  Indeed, during Run C-8
SRT's of approximately 6-7 days actually occurred.
                          112

-------
 TABLE 15:  DETERMINATION OF SOLIDS INVENTORY WITHIN
            A CARBON CONTACTOR *
                    Solids
 Sample Tap         Concentration      Volume            Solids
 Location           g ./&	      1000 liters       Kg

 Reaction Zone         18.1               7.0            127

 Bottom Tapa           17.1               2.5              44

 Middle Tapa           14.0               1.8              25

 Top Tapa              nil
    TOTALS                                11.3             196
* Run C-14, first-stage contactor

 Estimated Solids = Reaction  zone  solids  x  slurry volume
                  = 1 ai g /H (11,300  *>)  10~J Kg /g
                  = 205 Kg - 196  Kg
 a = sample taps at 13,  30  and  58  inches  from the  tank
     bottom and located  at  the  wall
                          113

-------
However, no significant odor problems were experienced.
Possibly the low temperature of 15-18°C and variation
in SRT due to operation (e.g., variations in carbon sludge
blowdown rate to control carbon slurry pool height)
minimized the chance of maintaining a prolific anaerobic
system.  It will be indicated later in this section that
substantial biological removal of soluble organics (SCOD)
probably occurred within the carbon contactors.  Thus,
elimination of anaerobic biological activity would not
be considered desirable.  Obviously, future studies
should be designed to quantify odor problems (e.g.,
carbon contactor off-gas analysis)  and evaluate the
effect of plant operation (e.g., SRT) on anaerobic activity.

An attempt to quantify sulfide production was made during
several Runs.  Table 16 shows grab sample sulfide profiles
through the pilot plant.  It is apparent that excessive
net increase of sulfide was not found across any of the
PCT unit operations.
Clarification Effectiveness of Carbon Contactors

During pilot plant operation, evaluation of carbon contactor
effluent clarity was made by three methods.  First, the
plant process turbidity system continuously monitored and
recorded turbidity.   The turbidity sensor used operated
on a combination light scattering and transmitting
principal.   This device provided a useful instantaneous
indication of clarity to operation personnel.  Secondly,
composite sample turbidity was determined with a 90°
light scattering laboratory turbidimeter.  A good corre-
lation was found between 90° turbidity and suspended solids
for virgin carbon suspensions in distilled water at
concentrations below 30-40 mg/& (see Figure B-l in
Appendix B).  However, composite sample turbidity and
suspended solids did not correlate, as typical data
presented in Figure 39 show.  The third method used,
during the last few Runs (C-8 to C-12), was the measure-
ment of transmittance of 772 my wave length light.
Both laboratory calibration  (see Figure B-l in Appendix
b) and plant data (see Figure 39)  correlated well over
the range of carbon contactor effluents encountered,
It is, therefore, recommended that in future studies,
carbon contactor effluent clarity be monitored by a
light transmittance device.
                         114

-------
          TABLE 16:   SULFIDE PROFILE THROUGH THE  PAC-PCT  PILOT PLANT

          Approximate                                            _
          SRT,  Days      	Sulfide  Concentration?  mg/& as

Run
Number
C-2
C-3
C-5
C-6
C-7


First
Stage
2.4
2.7
4.6
0.6
1.2


Second
Stage
2.2
4.5
—
—
—

Raw
Sewage
0.76
0.10
0.11
5.56
0.68

Chemical
Effluent
0.35
0.02
<0.1
0.03
0.14
First
Stage
Effluent
0.46
0.02
<0.1
0.04
0.16
Second
Stage
Effluent
0.96
<0.01
—
—
—
Plant
(Filter)
Effluent
0.36
<0.01
<0.1
0.05
0.15
Based on grab samples

-------
                                     FIGURE 39: CARBON TREATMENT:
                           INDIRECT EFFLUENT SUSPENDED SOLID MEASUREMENTS
   15
       100
     --90
                                                                        Run C-11
                                                         o
   10
       30
0!
O
CO
•p
3
=  5
      ©

      2:
  70  J1

      •o
      CD


      1
      c
      03
--60
                                                                                          o    --
      E
      eg
                      o
                         O
                                                          % Transmittance
O
                                ' Turbidity
       50
                 20
                         40           60           80          100

                         Carbon Contactor Effluent Suspended Solids, mg/l
                                                        120
                                                                                            140

-------
Evaluation of carbon contactor effluent suspended solids
data in Tables 13 and 14 indicates that they varied widely
from Run to Run, with median values ranging from 3 to
53 mg/&.  Figures 40 and 41 show effluent suspended solids
variation during two Runs.

It should be recalled that no arbitrary effluent quality
parameters (e.g., suspended solids) were sought after
during pilot plant operation.  Rather operating conditions
were specified and effluent quality determined for these
conditions.

Carbon solids removal was accomplished by gravity sedi-
mentation followed by granular media filtration.  As
will be shown in the next section of this report, the
granular media filter effectively removed carbon solids,
even at feed solids of 160 mg/Jl.  However, filter station
efficiency, expressed as backwash water recycle require-
ments, suffered greatly at these high feed solids levels.
Recognizing that granular media filtration efficiency
is related to carbon contactor effluent suspended solids
an attempt was made to quantify the effect of carbon
contactor operating parameters on effluent solids.

Evaluation of hydraulic loading data indicated that the
carbon contactors were operated at less than some critical-
ly high hydraulic loading which would have precluded
good clarification.  In general, the plant data was not
precise enough to show a useful correlation between hydraulic
loading and effluent suspended solids.

As discussed in Section IV, concentrated powdered carbon
suspensions exhibit a "self flocculation" property.
Since reaction-zone suspended solids concentration was
representative of the total carbon contactor slurry
concentration, and varied over a range of 2-21 q/H,
an attempt was made to correlate same with effluent solids
A correlation was found for the single-stage carbon
contacting Runs  (Table 14), and is shown in Figure 42
 (Reaction-Zone Solids for Runs C-ll and C-12 were estimated
from 5-minute slurry settling test data).  The data
show that effluent suspended solids increased as reaction-
zone solids concentration increased over the range of
data shown.  This observation does not necessarily refute
the "self flocculation" property noted above in as much
as some minimum concentration required may have been
exceeded during all operating periods.  The data in Figure
                          117

-------
         FIGURE  40: CARBON TREATMENT: EFFLUENT SUSPENDED SOLIDS

                             -\	1—I—I—I
                                                     2nd Stage
                                                      Carbon
                                                     Contactor
               1st Stage
                Carbon
               Contactor
UJ
                        20   30   40  50  60   70    80


                       % Of Occurrences < Value Shown
90
95
                                lie

-------
        FIGURE  41: CARBON TREATMENT: EFFLUENT SUSPENDED SOLIDS
  200
   60--
   40--
   30--
                                               Carbon
                                              Contactor
D)

E

0)
2  20-

o
C0
0>
•o

0)
a
v>

«  10--

c:
Q)


I   8~l~
E
    6--
    4--
    3--
    o	
                 o
                 10
                       20   30  40   50  60   70    80

                        % Of Occurrences < Value Shown
                                                              95
98

-------
            FIGURE 42: CARBON TREATMENT: EFFLUENT SUSPENDED SOLIDS


           	1	1	1	h
    50
                      Single-Stage
                   Carbon Contacting
-   40
O)
E
CO
 (V
T3
 C
 0)
 D.
 at

co   30--


 0)
 3
UJ
O
JS

o
O


5  20
k.
CO
O
   10
                                   O
                                                 O
                    H	1	1_
                     5               10              15

                      Reaction Zone Suspended Solids, gm/l
                                                                   20
                                  120

-------
42 indicates that the solids^contact unit achieved a
constant 99.7 percent removal of reaction zone suspended
solids.   Based on the relationship shown in Figure 42,
one could conclude that operation at low reaction zone
solids concentration is required if low effluent solids
concentration is desirable.  It will be shown later in this
report that the levels of effluent solids shown in Figure
42 were readily removed by the granular media filter.
Thus, a low concentration of carbon contactor effluent
solids is not necessary to maintain low solids levels in
the plant effluent.

Figure 43 is a typical plot of turbidity for all process
streams through the pilot plant over a 24-hour period.
The turbidity data is from the plant process turbidimeter
print out.  It is apparent that the chemical and carbon
treatment clarifier effluent turbidities vary as their
feed turbidities vary.  Peak and minimum turbidities for
the various streams are displaced by about the hydraulic
retention time of the units.  Positive liquid-solids
separation was provided by the granular media filter
resulting in production of a consistent plant effluent
clarity.  The similar trends in clarifier effluent
turbidity prompted an analysis of the effect of feed
solids on effluent solids.  For two-stage counter-current
contacting data in Table 13, there is a general trend of
higher carbon contactor effluent suspended solids for
higher feed suspended solids.  However, a precise correla-
tion does not exist.  For the single-stage contacting data
in Table 14, a fairly precise negative correlation was
found between effluent and feed suspended solids.  Figure
44 shows this correlation.  It is significant to note
that lower carbon contactor effluent solids values occurred
with alum or iron chemical pretreatment  (see Table 14).
It is probable that the small amounts of alum and iron
floe present in the carbon contactor feed aided floccula-
tion of fine carbon particles.

A direct comparison of the effect of carbon contactor feed
solids on effluent solids shown in Figures 43 and 44 indi-
cates a contradiction.  Though the data in Figure 43, is
for only one days operation, it represents a generally
observed system response.  It is very probable that the
response shown in Figure 44 is more a function of the type
of suspended solids than the concentration of solids in
the feed.

Others have reported the necessity of substantial amounts
(1/2 - 1 mg/&) of floccuation aids to effect good gravity
                         121

-------
                            FIGURE 43:  CARBON TREATMENT:
                     TRANSIENT TURBIDITY EFFECT ON CLARIFICATION
    80
    70
                    Chemical Treatment Run A-2

                    Carbon Treatment Run C-7
    60
   50--
.•=  40
jo
!5
D
   30--
   20--
   10-
                             Carbon Contactor
                                 Effluent
                                                      Chemical Treatment O
                                                           Effluent
     12
                      A.M".
    12


Clock Time
                                                                                  12
                                                              P.M.
                                  122

-------
          FIGURE 44: CARBON TREATMENT : FEED VERSUS  EFFLUENT SUSPENDED SOLIDS

    35-,	1	1	1	1	1	
     30--
     25--
O)
o
V)

•Q
0)



|

3
CO

c
0)


w
     20--
     15--
     10--
      5--
                         L-11
                          QL-4
                                                     Single Stage
                                                     Carbon Contactor
                                            L-1,6
                                                      F-3  (Chemical Treatment
                                                    L-6, A-1
10          15           20

 Feed Suspended Solids , mg/l
                                                                            A-1,2 ..
                                                                    25
                                                                                 30
                                    123

-------
clarification of carbon suspensions13'11*'15'16.  During
the first few months of plant operation, anionic polyelectro-
lyte was fed to the reaction zone of the carbon contactors
at dosages ranging from 0.3 to 1.5 mg/fc.  Clarification
effectiveness was satisfactory as indicated by the data
for Runs C-14 and C-2 in Table 13.  During Run C-l, use of
polyelectrolyte was discontinued and yet good clarification
was experienced at a 0.76 gpm/sq ft hydraulic loading.
An evaluation was made of the economic trade-off between
polyelectrolyte cost and installed solids-contact treatment
unit amortized cost.  Table 17 shows this analysis.  If
acceptable clarification was obtained at a designed
hydraulic loading of 0.48 gpm/sq ft without polyelectrolyte,
then similar clarification would have to be achieved at
a three-fold increase in hydraulic loading to justify
use of only 0.14 mg/£ polyelectrolyte.

After Run C-2, no polyelectrolyte was used for aiding
carbon flocculation.  During Run C-ll, excessive carbon
carryover from the clarifier was experienced (as high
as 180 mg/£).  Perhaps polyelectrolyte should have been
used, however, the granular media filter effectively
removed this excessive carbon carryover as the data in
Figure 41 shows.

Polyelectrolyte feeding capabilities are recommended for
the carbon clarification system used in this study, but
polyelectrolyte should only be fed if plant effluent
suspended solids are excessive or if inefficient filter
operation is experienced.  Filter operation is discussed
in the next section.

In summary, it can be concluded that the 78 to 99 percent
removal of powdered carbon plus feed suspended solids was
an acceptable clarification effectiveness by the carbon
contactors.
Granular Media Filtration

Mechanical operation of the 3.5 ft diameter plexiglass,
automated filter was satisfactory.  However, on two
occasions, excessive pressure was applied to the filter
housing resulting in failure of plexiglass-solvent bonds.
Not withstanding the several weeks downtime and loss
of data due to structural failures, the ability to visually
observe filtering and backwashing action was very valuable.
Visual observations were used to verify conclusions made
from analysis of headloss data; for example, the existance
of a schmutzdecke,  or failure to remove same during back-
washing, or penetration of carbon through the coal layer
to the sand layer,  or the existance of mudballs.
                         124

-------
                            TABLE 17:  COST TRADE-OFF OF POLYELECTROLYTE
                                       AND CLARIFICATION AREA FOR CARBON
                                       TREATMENT  (10 MGD FLOW)
SOLIDS-CONTACT UNIT
Overflow
Rate
gpm/sq ft
0.48
0.97
1.46
Amortized Capital
Costa
(C/1000 gal.)
0.39
0.33
0.28
POLYELECTROLYTE
Dose
(rag A)
0
0.08
0.14
Chemical
Cost0
(C/1000 gal.)
0
0.06
0.11
Total
Cost
(C/1000 gal.)
0.39
0.39
0.39
ro
en
           a -  7 1/2% interest, 20 year for
               estimated erected equipment
           b  -  @$1.50/lb of anionic polymer

-------
The effectiveness of granular media filtration for
clarifying carbon contactor effluent is evidenced by
the consistantly low concentrations of suspended solids
shown in Tables 13 and 14.   With the exception of Run
C-2 filter effluent suspended solids ranged from 1.3
to 3 mg/£ at hydraulic loadings of from 1.2 to 4.7 gpm/
sq ft.  The ability of the  filter to remove high levels
of feed suspended solids is indicated by data compiled
during Run C-ll and shown in Table 18.  It is apparent,
however, that very short filter cycles were experienced
for the high carbon concentration applied, resulting in
high volumes of backwash recycle.

Figure 45 shows the effect  of filtration rate on cycle
time when low filter feed suspended solids were encountered.
The dashed curve was constructed to show the filtration
rate - cycle time relationship that results in a five
percent backwash recycle.  The region above and to the
right of the dashed curve represents less than 5 percent
backwash recycle.  Water backwashing consisted of 26
gpm/sq ft for 6 minutes after air-scour at 4.5 to 5.5
SCFM/sq ft for 1.5 minutes  (see Appendix D).

The backwash rate, or upflow velocity required to expand
the filter bed and allow flushing out of solids is
governed by the media size  and density, and the water
temperature.  An acceptable bed expansion of about 25
percent was attained at 26  gpm/sq ft.  The duration of
backwash is governed by the geometry of the filter housing.
The pilot plant filter had  a freeboard of 1 1/2 times the
bed depth.  Most commercial designs have a freeboard
of only 1/2 to 3/4 times the filter bed depth.  Thus, the
volume of water to be displaced from the pilot plant filter
chamber was 65 to 110 percent more than for most commercial
designs.  The backwash conditions used during this study
(26 gpm/sq ft @ 6 minutes)  amounted to displacement of
five  (5) volumes of filter  chamber liquid.  Several commercial
filters are designed to accomplish satisfactory flushing of
dislodged solids with displacement of approximately three
(3) volumes of filter chamber liquid.  Needless to say,
extrapolation of backwash water recycle requirements to
full scale operation must take into consideration the
characteristics of the specific filtration equipment con-
sidered.  Based on the above factors of filter chamber
volume and number of displacements, it is probable that
about 30 to 40 percent less backwash recycle than experienced
in this study would be required for full scale filtration
systems.
                          126

-------
                           TABLE 18:  GRANULAR MEDIA FILTRATION:
                                      CLARIFICATION EFFECTIVENESS
                                      AT HIGH FEED SOLIDS

                        (Averages of data obtained during Run C-ll)
# of
Filter
Cycles
5
14
7
Suspended Solids , mg/£
Feed
31
76
160
Effluent
0.8
5.0
2.0
Filtration
Rate
gpm/sq ft
5.0
1.9
2.1
Cycle
Timea
hr
5.7
7.0
5.3
Backwash
Recycle b
%
9
20
23
KJ
-a
          a - To a terminal headloss of 7 ft of water

          b - H20 backwash @ 26 gpm/sq ft for six minutes

-------
                 FIGURE 45: GRANULAR  MEDIA FILTRATION:

                     CYCLE TIME vs. FILTRATION RATE

                -H	1	1	1
    60--
O
   50--
    40--
o
u
>i
O
    30--
   20--
   10--
                  Runs C-3, 4

                  Avg. Feed SS = 6.2 mg/l

                  Avg. Effluent SS = 3.6 mg/l

                    Terminal Headloss
                      7 feet of  H,O
                                               O
                                                        -t-
                                                        4
                            Filtration Rate, GPM/ft2
                               128

-------
Evaluation of incremental headloss data measured at six
(6)  inch height increments throughout the filter bed
depth indicated a deficiency in the filter bed design
used.  Figure 46 shows headloss profiles at the start
and end of two filter cycles during Runs C-l and C-2.
The headloss profile at the end of filter Run 923 is
representative of about 90 percent of all filter  Runs
analyzed.  Essentially all the headloss occurred over
the top few inches of the coal layer indicating that the
size of coal  (1.0 mm) was too small to allow penetration
of carbon particles, even at filtration rates of 4-5
gpm/sq ft.  The headloss distribution at the end of
Run 819  (Figure 46) was an exception and shows a much
more desirable headloss pattern.  The headloss is uniformly
distributed throughout most of the filter bed depth.  No
apparent reason was found for the desirable headloss
pattern found in Figure Run 819.  The significance of
obtaining a more desirable headloss distribution is
indicated by comparing the volume of water filtered and
backwash water recycle requirements.  Some 64 percent
more water was filtered during Run 819 compared to Run
923 and, hence, 40 percent less backwash recycle water
was required.

Because the carbon particles were removed at the top
surface of the coal layer, use of 0.1 to 0.3 mg/£ of
anionic polyelectrolyte floe strengthener during a few
filter Runs produced no discernable benefit of improved
headloss distribution or filtrate clarity.  For the
same reason,  filtration of feed suspended solids as
high as 160 mg/£ resulted in no deterioration in filtrate
clarity.  Obviously, once a schmetzdecke of carbon particles
is formed, the existance of "tough" floe or high feed solids
concentrations will not affect effluent clarity or headloss
distribution.

Six  (6) times during the course of this study, about 1 to
1 1/2 inches  of coal media was removed from the filter bed
surface and replaced with new coal media.  It was hoped that
removal of coal fines would allow penetration of carbon par-
ticles.  No significant improvement in headloss distribution
was observed.

During Runs C-3 and C-4, the filter was operated for several
filter cycles at a filtration rate of about 1.3 then 3.2
and finally at 4.2 gpm/sq ft.  At 1.3 gpm/sq ft, cycle times
were about 50 hours as seen in Figure 45.  Under these
operating conditions, numerous "mud balls" were observed,
ranging in size from.1/2 to as large as 1 1/2 inches in
                          129

-------
           FIGURE 46:  GRANULAR  MEDIA FILTRATION:  HEADLOSS DISTRIBUTION
 90
               Sand
             (0.6 mm)
             12" Sand
                                                       Coal
                                                     (1.0 mm)
                                                    153/4" Coal
 80
 70
                                 Feed SS = 5 - 20 mg/l

                                 Effluent SS = 2 - 5 mg/l

                                 Effluent Turbidity = 0.5 JTU
 60
q
i
"o
c

0)
in
O

as
d>
I
15
"5
 50
                                                                          End of
                                                                        Run #923
                                                                         (13 hrs.)
40
30-
20-
10-
                                                           End of
                                                         Run #819
                                                          (19 hrs.)
                                                                      4.2 GPM/ftJ
                                                                             Start
                                                                           Run #819
                                                                              Start
                                                                            Run #923
                                 12              18

                        Distance from Bottom of Filter Bed, inches
                                                                    24
                                                                                    30

-------
major dimension.  The normal air-scour, water backwashing
procedure did not eliminate the "mud balls".  However, when
the filtration rate was increased to 3.2 gpm/sq ft, the cycle
time was reduced to about 22 hours and the mud balls were
completely eliminated by the normal backwash procedure.
Evidently, detention of carbon material on the filter
bed surface for 50 hours results in "cementation" of the
solids whereas detention for 22 hours did not.  It is
possible that biological slimes were produced at 50 hours
carbon detention time, but not at 22 hours carbon detention
time.  Regardless of the cause, it is suggested that
the granular media filter be programmed to backv/ash at
least once per day to minimize the problem of mud balls.

The results presented and discussed show that carbon
contactor effluent was effectively clarified by granular
media filtration.  Additional studies are needed to
develop improved efficiency of filter operation.  It
is recommended that coarser coal media be evaluated to
determine a size which will allow significant penetration
of carbon particles to the underlying sand layer.  The
effect of polyelectrolyte can then be determined and
optimum filtration rates established.  It is also recom-
mended that future studies be designed to verify or define
near optimum backwashing procedures.
Removal of Soluble Organics

The singular purpose of powdered carbon treatment was
removal of soluble organics from the wastewater.  Thus,
SCOD, STOC and carbon dosage data from Tables 13 and 14
were analyzed in an attempt to determine the relationship
between carbon system feed and effluent soluble organics
and carbon dosage.  For obvious reasons, the applicability
of an adsorption model was evaluated.

Tables 19 and 20 present observed median SCOD and STOC data
and reduced data which indicate incremental organic reduc-
tions, organic removals and feed organic loadings.  During
pilot plant operation, granular media filtration of all carbon
contactor effluent was impossible  (e.g. , when carbon contactors
were run in parallel).  Thus, the effluent SCOD and STOC con-
centration shown•are for the carbon contactors and not the
granular media filter.

All STOC and SCOD data were analyzed to ascertain whether
or not a consistant and precise correlation existed
between the two.  Table 21 shows the results of linear
                          131

-------
                     TABLE 19:  CARBON  TREATMENT:   SUMMARY OF SCOD REMOVAL  DATA
                                      (Two-Stage Counter-Current)
OBSERVED DATA
Run
#
Carbon
Dosage
(H)
mg/£
C-l | 325
C-2 150
C-3 150
C-3 110
C-4 75
SCOD, mg/H
Feed
(Cn)
50
43
45
6-8
70
Inter-
mediate
Stage
(C±)
12
21.5
18
28
38
Effl.
(O
12
18
11
22
30
REDUCED DATA
SCOD Removed ,
mg/£
1st
Stacre
(X"f
38
21.5
27
40
3.2
2nd
Stage
(X1)
0
3.5
7
G
8
All
Stages
(X)
38
25
34
46
40
Organic
Remova 1
q/g
All
Stages
X
M
0.12
0.17
0.23
0.42
0.53
2nd
Staae
X'
M
0.000
0.023
0.047
0.055
0.107
1st
Stage
X"
M
0.12
0.14
0.10
0.36
0.43
Organic
Loading/ C0\
\to)'
mg/£/mg/5,
1st
and
All
Stages
0.15
0.29
0.30
0.63
0.91
2nd
Stage
0.04
0.14
0.12
0.26
0.50
OJ
tsj

-------
TABLE 19  (cont.):   CARBON TREATMENT:   SUMMARY OF SCOD RFMOVAL DATA
                       (Sinale-Stage)
OBSERVED DATA

Run
#
C-ll
C-12
C- 6
C- 9
C-10
C- 7
C- 5
Carbon
Dosage
(M)
mg/£
345
317
300
146
146
105
95
SCOD, mg/£

Feed

41
41
40
35
35
30
58

F,ffl.

6.4
13
"12
25
23.5
17
22
REDUCED DATA
1
SCOD Removed
mg/£

All
Stages
(X )
34.6
28
28
12
10
13
36
Organic
Remova 1
g/g
All
Stages
x
M
Organic
Loading /C0\
I M;
mg/£/mg/£

All
Stages
0.099 0.12
0.086
0.093
0.076
0.068
0.124
0.380
0.13
0.13
0.24
0.23
0.29
0.61

-------
TABLE 20:  CARBON TREATMENT:
           SUMMARY OF STOC
           REMOVAL DATA
OBSERVED DATA
Run
#
C-2
C-8
C-6
C-7
C-5
Carbon
Dosage
(M)
mg/£
150
150
300
150
95
STOC, nig/ 1
Feed

22
24
25
16
28
Inter-
mediate
Stage
(Ci)
r
15
11
_
—
—
Effl.

-------
                                   TABLE 21:  CORRELATION OP SOLUBLE TOC
                                              WITH  SOLUBLE COD
Ul
Carbon
Treatment
Run #
C-2



C-7


Effluent
From
Chemical Contactor
First Stage
Carbon Contactor
Second Stage
Carbon Contactor
GM Filter
Chemical Contactor
Carbon Contactor
Linear
Regression
Equation
STOC = 13 + 0.19 SCOD
STOC = 12 + 0.16 SCOD
STOC = 11 + 0.10 SCOD
STOC = 12 - 0.018 SCOD
STOC = 2.7 + 0.49 SCOD
STOC = 2.0 + 0.56 SCOD

Correlation
Coefficient
0.61
0.47
0.31
0.09
0.98
0.98

-------
regression analysis of STOC and SCOD.  Data from Run C-7
are precisely correlated and indicate that from 2.0 to
2.7 mg/£ STOC would exist if the SCOD were zero.  The
slope, or ratio of STOC/SCOD of about 0.5 is within the
range of data by others29'30.   The data from Run C-2
did not correlate precisely, but do seem to indicate
that about 12 rag/£ of STOC would exist if the SCOD were
zero.  Data from Run C-6 correlates similarly to Run
C-2, whereas data from Runs C-5 and C-7 did not correlate.
It has been reported that silicates will interfere with the
TOC analysis31.  Silicate concentrations of 10 to 50
mg/£  (as SiO?) were reported to register as 3 to 4 mg/£
TOC.  Analysis of Salt Lake City tap water showed the
presence of 10-15 mg/£ of Si02.  Thus, STOC data presented
in this report are probably high by about 3 mg/Jl of STOC.
Application of Adsorption Model

Correlation of SCOD removal data with the Freundlich math
model (see Appendix A)  was not very precise as indicated
by regression analysis  results in Table 22.  As shown,
however, a more precise correlation exists when organic
removal (X/M, g of SCOD removed per g of carbon fed) was
regressed on effluent SCOD (Ce)  rather than the log of
organic removal on the  log of effluent SCOD as for the
Freundlich math model.

Figure 47 is a plot of  organic removal data for two-stage
counter-current contact Runs, with regression curves.
Approximately, 80 to 88 percent of the SCOD was removed in
the first-stage, with the exception of Run C-l, where all
measured SCOD removal occurred in the first-stage.  This
level of removal in the first-stage of contacting is con-
siderably higher than would be predicted by the Freundlich
model.  As discussed in Appendix A, adsorption theory
indicates that the first-stage and second-stage curves
should be identical if  the physical and chemical pro-
perties of adsorbed organics in both stages are identical.
Considering the heterogeneous nature of soluble wastewater
organics, it is probable that certain species are preferen-
tially adsorbed in the  first-stage of contacting.  Thus,
                         136

-------
TABLE 22:
CARBON TREATMENT:
ADSORPTION MODELS
OF SCOD REMOVAL
DATA

Contact
Stage
Single-stage
Two-Stage
Counter-Current
(2SCC)
First Stage
of 2SCC
Second Stage
of 2SCC
Single-stage
plus 2SCC
J£
Log ^ vs Log Ce
(Freundlich Model)
Regression
Equation
x - n ni7r °-90
H - 0.013Ce
X 12
JJ = 0.0087Ce
| = 0.0043Ci1'3
^'= S.SxlO^Ce3'1
X IT
M = 0.0087Ce •*•
Correlation
Coefficient
0.68
0.80
0.93
0.71
0.71
I™6-
Linear
Regression
Equation
| = -0. 085+0. 017Ce
ff = -0. 079+0. 020Ce
§ = -0.10+0.017CL
-'= -0. 033+0. 0043C0
M **
§ = -0.11+0.020Ce
Correlation
Coefficient
0.80
0.89
0.95
0.79
0.87

-------
  FIGURE 47:  CARBON TREATMENT:  SCOD REMOVAL FOR TWO-STAGE
                   COUNTER-CURRENT TREATMENT

              	1	1	1	1	
o

o>
£C

Q
O
O
CO

D)
•o
£
o
O)
  o
  E
  0)
  oc
  ra
  o>
         0.5 --
         0.4--
         0.3--
         0.2
     0.1

    0.09

    0.08

    0.07


    0.06


    0.05
        0.04 --
        0.03--;
       0.02-^
                       Both Stages
                                                  Stage
                                           Second Stage
                                     Range of
                                     Laboratory
                                     Adsorption
                                     Test Results
                       15       20         30      40

               Carbon Contactor Effluent SCOD (Ce), mg/l
                                                    50
                           138

-------
it would be unrealistic to expect the observed first and
second-stage results to be described by a precisely
similar model.  It would be just as unrealistic,  however,
to assume that the dramatic difference between the
organic removal for the two stages could be explained
away as being due to "preferential adsorption" in the
first stage.  A much more plausible explanation for the
disporportionally high organic removal in the first-
stage would be that biological oxidation of soluble
organics was occurring.  Qualitative indications of the
presence of anaerobic biological activity were alluded
to earlier in this section.

The cross-hatched area in Figure 47 represents the range
of laboratory adsorption equilibrium isotherm test results
Organic removal during these tests was by adsorption only.
The similar results for organic removal in the second-
stage contactor and for the laboratory adsorption tests
would seem to indicate that the major removal mechanism
in the former was also adsorption.  Organic removal
in the first-stage contactor is seen to be considerably
higher than predicted for adsorption by the laboratory
adsorption test results.  This fact reinforces the thesis
that an organic removal mechanism in addition to ad-
sorption existed in the first-stage carbon contactor.

Figure 48 shows SCOD removal results for both single-
stage and two-stage counter-current contacting.  It
appears that organic removals, X/M, for two-stage
treatment are generally higher than for single-stage
treatment.

Evaluation of carbon SRT and type or level of chemical
pretreatment conditions failed to reveal any consistant
or definable effects on organic removal or effluent SCOD
concentrations.  Either no effects existed or the data,
as modeled by the Freundlich equation, is not precise
enough to define the effects.

The SCOD removal data from Runs C-9 and C-10 were not
included in the above comparison of single-stage and
two-stage treatment results.  These two Runs were spe-
cifically conducted in an effort to quantify the effect
of biological activity on SCOD removal.  The two carbon
contactors were operated in parallel at similar carbon
dosages, overflow rates and carbon SRT's  (see Table 14).
                          139

-------
             FIGURE 48: CARBON TREATMENT: SCOD REMOVAL FOR
            SINGLE AND TWO-STAGE  COUNTER-CURRENT TREATMENT
      0.60-
      0.50 - -
      0.40--
      0.30--
x 5
      0.20--
      0.15--
      0.10--O
      0.08--
      0.06-
                     Two-Stags Counter-Current
                             o
                                                    Single-stage

                                                    Runs C-9,10
!     10        15      20         30

 Carbon Contactor Effluent SCOD (Ce), mg/l
H-
 40
                                                                50
                            140

-------
A copper sulfate solution was fed to one contactor  (Run
C-10)  at a dosage of 2.4 mg/& of Cu++.  A laboratory
equilibrium adsorption test was conducted to determine whether
or not the addition of 20 mg/£ of Cu++ would affect the
adsorption of SCOD from neutralized chemical contact effluent.
The presence of Cu++ did not affect organic removal, X/M,
in the equilibrium SCOD range tested  (15-50 mg/Jl) .  The
presence of 2.4 mg/£ Cu++ in the feed to the carbon
contactor was considered to eliminate biological  activity.

During Run C-9  (concurrent with C-10), no Cu++ was fed,
and a relatively long carbon SRT of 5.9 days was establish-
ed in an effort to promote biological activity.   However,
no quanitative or qualitative indications of the  presence
of biological activity were experienced.  Inspection of
plant records indicated that during Runs C-9 and  C-10
 (chemical pretreatment Run L-ll) the carbon contacting
system feed pH was extremely erratip.  The pH varied
from 2 to 11 at frequencies of 1/2 to 3 hours.  For two
days the pH was about 10.7 due to a breakdown of  the acid
feeding system.  Because of the widely varying pH during
Run C-9, it is extremely doubtful that any significant
level of biological activity was ever established.  Thus,
organic removal results from both Runs C-9 and C-10
were considered to be representative of non-biologically
enhanced systems.  The significance of allowing natural
anaerobic process to occur is indicated by the fact that
organic removals experienced in Runs C-9 and C-10 are
only 1/3 of that predicted by the single-stage regression
curve in Figure 48.  Unfortunately, this observation is
not absolutely conclusive in as much as the widely varying
pH experienced during Runs C-9 and C-10 may have  affected
organic removal by adsorption.  The effect of pH  on organic
removals for PCT carbon adsorption systems has not been
established, or reported in the literature.

The existance of a biological organic removal mechanism
is indicated by data from Run C-13.  During this  Run
no virgin carbon was fed to the contactor.  Effluent
carbon was captured by the granular media filter  and recycled
                          141

-------
to the carbon contactor.  During this 13 day Run about
30 percent removal of COD and TOG was observed.  At an
overflow rate of 0.75 gpm/sq ft, the wastewater - powdered
carbon slurry contact time was less than 30 minutes,
while the carbon SRT was indefinitely long.

The STOC organic removal data in Table 20 are contrary
to what adsorption theory would predict.  For both
single-stage and two-stage contacting, higher organic
removals, X/M, are associated v/ith lower equilibrium
STOC concentrations,, Ce.
Alternate Organic Removal Model

Recognizing the inappropriateness of describing the pilot
plant results by an "adsorption" model several attempts
were made to more precisely relate organic removal and carbon
dosage.  The following emperical relationship, which was
suggested by the project officer, was found to precisely
describe the results:

     X/M = Kj_ + K2 2a                              (6)

Where:   X/M = mg/Jl SCOD removed in any given stage
              per mg/£ of carbon.

         CQ = mg/£ feed SCOD to any given, stage per
         M    mg/£ of  carbon.

      K,, &2 ~ constants

Table 23 presents linear regression equations and cor-
relation coefficients  for SCOD removal results.  Corre-
lation coefficients of 0.97 to 0.99 indicate a presice
fit of the data.  A linear plot of X/M vs CQ/M for all
stages of treatment is shown in Figure 49.
A statistical analysis of significance using the student's
"t" distribution (see Reference 32) resulted in accepting
the hypothesis that the slopes, K2, of the single-stage,
two-stage counter-current and combined data were not
significantly different.  Student  "t" values of 0.4 and
0.9 were computed for 3 and 8 degrees of freedom respec-
tively.  To determine if the height of the single-stage
curve in Figure 49 was significantly different than for
the two-stage counter-current curve, an estimate of X/M
                          142

-------
                    TABLE  23:   CARBON TREATMENT:  MODEL OF  SCOD REMOVAL DATA
OJ
Contact
Stage
Single-stage
Two-Stage
Counter-Current
(2SCC)
First Stage
of 2SCC
Second Stage
of 2SCC

Single-stage
plus 2SCC

Linear
Regression
Equation
X
H ~
x
*\
M
X"
M =
X|
_
M
Y
4\
M =

0.0116 + 0.557 2°
M
Cn
0.0397 + 0.558 -P.
M

0.0413 + 0.445 co
M
f^ •
0.00070 + 0.216 Ii
M

W.W-L,^ ^ W.^,^ 0
M
Correlation
Coefficient
0.97

0.99


0.99

0.97


0.99


-------
          FIGURE 49: CARBON TREATMENT: ORGANIC  REMOVAL MODEL (SCOD)
                                            Two-Stage Counter-Current
0.1
             0.2
0.3           0.4

  Organic Loading
0.5           0.6
    g Feed SCOD
     g PAC Fed
                                                                              0.7
0.8
                                                                                                        0.9

-------
at the combined average CQ/M of 0.36 was determined from
the regression equations.  This average value of C0/M
was chosen because the variance of the estimated X/M's
would be a minimum at this point.  The hypothesis that
the estimated X/M's  (0.21 and 0.24) were not significantly
different resulted in a student's "t" of about 1.7 at
3 degrees of freedom.  The hypothesis was marginally
accepted.  Had the variance of the estimated X/M's been
slightly less, the hypothesis would have been rejected
and the height of the regression curves considered
significantly different.  Combination of single-stage
and two-stage counter-current data reduced the variance
of estimated X/M's by approximately 60 percent.

Based on the above statistical analysis, it was concluded
that the variability of pilot plant results precluded
quantifying the difference between X/M values for single-
stage and two-stage counter-current contacting, with a
significant degree of statistical confidence.  Additional
pilot plant studies should provide more precise estimates
of results and allow definitive determination of any
economic benefit of multiple stage contacting.  The
importance of making such a determination can be appre-
ciated by recognizing that carbon dosage requirements,
predicted by the regression equations in Table 23, indicate
that about 3 1/2 times more carbon is required for single-
stage than for two-stage counter-current contacting.  It
is interesting to note that an example in Appendix A,
for SCOD removal by physical adsorption, shows 3.3 times
more carbon is required for single-stage than for two-
stage counter-current contacting.

The cost of providing a second-stage carbon contactor would
amount to about 0.39C/1000 gal.  This cost is for installed
solids-contacting equipment designed at an overflow rate
of 0.48 gpm/sq ft  (see Table 17).  The concentration of
virgin powdered carbon, at 10C/lb, which must be saved
to justify a second-stage contactor, at a cost trade-off
of 0.39C/1000 gal.,  is 4.7 mg/£.  The concentration of
regenerated carbon,  estimated to cost 3C/lb, which must
be saved is 16 mg/£.

Figure 50 shows predicted effluent SCOD versus carbon dosage
for different feed SCOD concentrations as per the combined
single-stage and two-stage counter-current regression
equipment in Table 23.  The insensitivity of effluent SCOD
                          145

-------
                      FIGURE 50:    CARBON TREATMENT: RELATIONSHIP BETWEEN
                      FEED AND EFFLUENT SCOD AND CARBON DOSAGE

                  -I	1	1	1	
                                                                 -t-
    30--
    25- -
en
    20
Q
O
U
c
0)
(A
C
O
•e
(0
U
    15- -
   10--
    5--
                           Carbon System Organic Removal Model:


                               Co—Ce                Co
                               —	= 0.0179 + 0.579 -gj-
                                 M                   M
                                                             . w.  80mg/l —Feed SCOD (Co)
100
                                                                 60
                                                            ^^  40
                 100
                             200
       300         400         500

          Carbon Dosage (M), mg/l
                                                                             600
                                                                                         700
                                                                                                      800

-------
to carbon dosage is indicated by the slope of the lines
which show that a 100 mg/£ incremental increase in carbon
dosage results in removing only 1.8 mg/£ of additional
SCOD.  Comparison of carbon dosage required for different
feed SCOD's at a given effluent SCOD value, indicate
that an increase of about 24 mg/£ of carbon is required
per mg/£ increase in feed SCOD.

As noted previously, the STOC removal data was not
realistically described by an adsorption model.  Com-
bined single-stage and two-stage counter-current results
did correlate fairly well when plotted as X/M vs CO/M.
A linear regression equation of X/M = 0.045 + 0.78 CO/M,
with a correlation coefficient of 0.91 resulted.  This
observation lends credence to the applicability of this
emperical relationship to the carbon contacting system studied,


Other Observations

As noted previously the variability of SCOD removal
results precluded precise definition of the difference
between single-stage and two-stage counter-current
contacting effects.  Variability during any given Run
can be attributed to varying wastewater quality and
plant operation.  For example, carbon contactor feed
and effluent SCOD concentrations varied from day to
day as indicated by typical data in Figures 51 and
52.  Some of the variation in effluent SCOD can be
attributed to varying average daily carbon dosages.
Comparison of carbon contactor effluent and feed SCOD
concentrations at relatively constant carbon dosages
indicated a general trend toward higher effluent con-
centrations at higher feed concentrations.  However,
no precise correlation was found.

Another possible source of variability might have been
the presence of an unadsorbable fraction of SCOD.  During
Runs C-9 and C-ll an attempt was made to quantify any
"unadsorbable" fraction by the following procedure.
Aliquots of plant effluent composite samples were
contacted with massive dosages  (30-60 g/£) of degassed
virgin powdered carbon.  Duplicate SCOD analysis were
conducted on 0.45 micron membrane filtrate after one
hour of contacting.  Figure 53 shows results obtained
during Run C-ll.  These results were not precisely modeled
by either the Freundlich adsorption model or the
                          147

-------
      FIGURE 51: CARBON TREATMENT:
     TYPICAL EFFLUENT SCOD VARIATIONS
                             Granular Media Filter
10     20    30   40   50
   Percent of Occurrences
 60   70   80
; Observed Value
90
95
98
                .148

-------
   60--
   40--
   30--
=;  20
D)
E

Q"
o
o
E:
ffi
=  10-

uj
    8--



    6--





    4 --



    3
                        FIGURE  52: CARBON  TREATMENT:

                      TYPICAL EFFLUENT SCOD VARIATIONS
             Run C-12
Chemical Contactor

        O
                                              Carbon Dose
            --400
                                                  — 300
                                                  -- 200
                                   A
                              Carbon Contactor
                                                                              o>
                                                                              E
                    o
                    Q

                    O
                   •o
                   0)

                   0)
                   sn
                  10     20    30   40  50

                    Percent of Occurrences :
                     60   70    80

                     - Observed Value
90
95
98
                                    149

-------
    FIGURE 53: CARBON TREATMENT:  EFFECT OF MASSIVE CARBON DOSAGE

       	1	1	1	1	
   14--
  12--
   10--
O>
i
O
O
£
0)
J3


iS  8-

o


2
"S
o
O

e
©
£  6-
(9
O
                    Run C-11

            Carbon Dosage 30—60 9/I
                  0
          0
                              0
                               0
                                                                G
                 2468

                 SCOD After Massive Carbon Dosage, mg/l
                                                                 10
                             150

-------
X/M versus CO/M model.  The trend toward lower SCOD
concentrations, after massive carbon treatment, at
lower carbon contactor effluent SCOD would seem to
indicate little if any SCOD was "unadsorbable".


Summary of Powdered Carbon Treatment Results

Solids-contact units were found to be very effective
for use as powdered carbon contactor-clarifiers.
The total solids recycle and variable area clarification
zone features of the units used were considered to be
key factors in providing a significant level of biological
activity without odor problems and in accomplishing
effective removal of carbon solids.  Effective gravity
clarification of carbon suspensions was achieved at overflow
rates up to 0.8 gpm/sq ft without the use of flocculation
aids.

Granular media filtration effectively removed carbon
particles from carbon contactor effluent.  However,
the coal media size was too small to allow penetration
and removal of suspended solids "in depth".  Conse-
quently, backwash recycle was excessive.  Filtration
cycles in excess of 24 hours should be avoided to
minimize "mud ball" formation.

Soluble organics removal results were not precisely
described by the Freundlich adsorption model.
However, use of this model did indicate the presence
of a soluble organic removal mechanism in addition
to physical adsorption.  Biological oxidation was the
most probable mechanism.  The more generally applicable
emperical relationship, X/M = KI+ K2  (CQ/M), was found
to precisely describe the pilot plant organic removal
results  (both SCOD and STOC).  A statistical analysis of
these results indicated that two-stage counter-current
contacting was probably more efficient  (i.e. , required
less carbon) than single-stage contacting.  However, the
data were too variable to precisely quantify the difference
in carbon requirements.  Additional pilot plant studies are
strongly, recommended to more precisely define this difference,
If ^differences of at least 20 to 30 mg/Jl carbon dosages are
found, then two-stage counter-current contacting would be
an economic choice over single-stage contacting.
                          151

-------
Both the Freundlich and the X/M versus CO/M models
indicate that the carbon dosage required to produce a
constant system effluent SCOD,  is linearly related
to the carbon system feed SCOD.  Therefore, if a
reliable automatic feed SCOD analyzer (direct or
indirect)  were available, the carbon feed rate could
presumably be automatically controlled to match the
feed SCOD and thus, result in production of a uniform
effluent SCOD.  Such a device must measure soluble
organics concentration very precisely since a small
change in feed organics indicates a substantial change
in carbon feed required to maintain a constant system
effluent organics concentration.   One possible approach
entails use of ultra violet light absorption measurements
to indirectly indicate soluble organic concentration.
CARBON REGENERATION SUBSYSTEM

Regeneration and reuse of spent carbon was to be evaluated
during a six (6) month extension to the original 18
month research contract.   Due to uncontrollable delays in
funding and installation of carbon dewatering and regen-
eration equipment,  only about two months of operating
data was obtained.   The carbon regeneration results should
be considered very  preliminary, but do provide a good
basis for additional studies.

Due to the limited  available time, the following approach
was used to evaluate spent carbon regeneration and reuse.
During carbon treatment Run C-ll, spent carbon was allowed
to build-up in the  thickener, carbon contactor, inventory
tank and holding tank.  A total of about 4,500 pounds of
virgin carbon was fed with some 1,200 pounds being
advanced to the holding tank for vacuum filtration and
thermal regeneration.  After the first regeneration Run
no virgin carbon was used, only regenerated carbon.
The existing carbon inventory was regenerated and reused
for the remainder of the study.  This approach resulted
in passing all carbon through the regeneration system
at least once.

The following is a  presentation and discussion of the
carbon regeneration system consisting of graivty thickening,
vacuum filtration,  thermal regeneration and reuse.
                         152

-------
Gravity Thickening

Normal operation of the thickener entailed intermittant
feed and underflow withdrawal.  Approximately 30-70
gallons of carbon contactor blowdown was fed to the
thickener every 1/2 to 1 1/2 hours at a rate of 50
to 70 gpm.  Thickener overflow was collected in a 55
gallon drum and pumped to the granular media filter
backwash collection tank and subsequently recycled
back to the carbon contactor.  Thickener underflow
was pumped to the spent carbon inventory tank, at
about 5 gpm for 1/2 to 4 minutes durations each 10
minutes.

During operation of the regeneration furnace, thickener
underflow had to be shut off because the single carbon
inventory tank was used to inventory and sample regen-
erated carbon.  Thus, just prior'to a regeneration run,
carbon concentration in the contactor and thickener
was reduced by advancing carbon to the holding tank.
During each regeneration Run, lasting about 20 hours,
carbon was allowed to build up in the contactor and
thickener.  Thus, immediately after a regeneration
Run, the flux of carbon  (Ib/day) through the thickener
was considerably higher than normal.

The above operational procedures resulted in considerable
variation of thickener solids loading and underflow concen-
trations.  Table 24 shows the range of results.  The
average thickener loading for the 28 days of data presented
in Table 24, was 7.8 Ib/day-sq ft, and the weighted
average of underflow solids 124 g/£.  Generally speaking,
as thickener solids loading increases, the underflow  solids
concentration should decrease.  Such a trend is not
apparent from the results in Table 24.  It is quite
probable that the thickener was conservatively loaded.

Thickener feed and overflow solids were not routinely
monitored.  Therefore, the effect of thickener feed
solids on thickener underflow solids concentration
could not be determined.  Carbon dosage and carbon
contactor blowdown volume data in Tables 13 and 14
indicate that carbon blowdown solids were  30 to 50
                          153

-------
                       TABLE  24 :  SUMMARY  OF  SPENT  CARBON
                            GRAVITY THICKENING RESULTS
                       Spent
                       Carbon
                    Inventoried
Period
  Thickener
Solids Loading0
 (Ib/day-sq ft)
Thickener Solids
   Underflow
 Concentration
Prior to Run #la
Average
Between Runs
#1 and #2
Average
Between Runs
#2 and #3
Average
Between Runs
#3 and #4
Average
209
599
438
1246

381
383
249
1013
687
615
1302
134
469
133
736

7.6
26.0
5.3

5.2
9.8
7.1
18
14
8.1
7.7
9.8

56
151
122
125b

121
86
52
91b
180
134
158b
46
121
106
105b

a - Regeneration Runs -
b - Weighted Average Based on Spent  Carbon
    Advanced
                 c - Based on Underflow  Solids

-------
Summarizing the gravity thickening results, it appears
that spent carbon solids of 30 to 50 g/£ can be thickened
to 100 to 120 g/£ at a thickener solids loadings of 10
Ib/day-sq ft or greater.  It is recommended that future
pilot plant tests be designed to evaluate the effect of
loadings of at least 20 to 30 Ib/day-sq ft and the effect
of feed solids concentration on underflow concentration
and to quantify the capture of carbon solids by the
thickener.
Vacuum Filtration Dewatering

The vacuum filter was operated during each regeneration
Run primarily to provide dewatered spent carbon for
feeding to the fluidized bed furnace.  No attempts were
made to "optimize" filter operation.

Vacuum filter yields  (capacity) were about three times
greater than designed for.  Thus, the filter was run
for only one hour out of each 3 to 4 hours of furnace
operating time.  During each regeneration Run, the filter
was operated for three to five  one hour periods.  Single
grab samples were taken during each filter Run for
determining filter feed solids concentration, filtrate
solids concentration, filter cake solids concentration
and filter cake thickness.  The volume of carbon sludge
dewatered and the polymer feed solution used during each
Run was determined by inventory measurements  (i.e., depth
measurements  in the carbon sludge holding tank and polymer
feed tank).  Because complete mixing conditions did not
exist in the carbon holding tank, filter feed solids varied
from Run to Run.  Polymer dosages in the range of 0.1 to
0.7 Ib polymer per 100 Ib dry carbon solids were attemnted
by setting the polymer feed rate based on the known overall
average holding tank solids concentration.  The polymer
used was Dow Chemical Company's C-31, a cationic polyelectrolyte
with amine functional groups.  Spent carbon sludge was
stored in the holding tank for from 1 to 14 day periods
prior to dewatering.

Table 25 presents grab sample results for each filter
Run.  Filter operating conditions were generally fixed
by the type of machine used  (i.e., a continuous belt
vacuum filter).  Actual drum submergence was  less
than the 33 percent design.  The drum cycle times were
                          155

-------
                                TABLE 25:   SUMMARY OF  SPENT CARBON VACUUM
                                                 FILTRATION RESULTS
cr\
Regeneration Run #
Vacuum Filtration Run .#
OPERATING CONDITIONS
Cycle Time, min/rev
Submergence, %
Polymer Feed, % by wgt
Feed Solids, c, /£
Filtrate Solids, g /£
Solids Capture, %
FILTER CAKE
Thickness, inbhes
Moisture, % by wgt
Solids, Ib /sq ft
Filter Yield,
11111
12345
8.8 8.8 8.8 8.8 8.8
22 27 30
0.3 0.4 0.4 0.2 0.2
132 115 111 105 105
8.4 6.3 19 18
93 94 82 83
3/4 3/4 3/4 3/4 3/4
62 79 77 78 75
1.8 1.0 1.1 0.9 1.1
12 6.8 7.5 6.1 7.5
222
123
8.8 8.8 8.8
28
0.8 0.8
148 97 71
7.9 6.1 6.8
95 94 90
3/4 7/8 3/4
80 78 58
1.1 1.1 1.8
7.5 7.5 12.2
2 2
4 5
8.8 8.8
28 28
2.5 0.2
26 262
15 19
42 93
5/8 7/4
77 78
0.6 2.2
4.1 15.0
            Ib /hr-sq ft

-------
                           TABLE  25 (cont.):  SUMMARY OF  SPENT CARBON VACUUM
                                                    FILTRATION RESULTS
01
Regeneration Run 1
Vacuum Filtration Run #
OPERATING CONDITIONS
Cycle Time, min/rev
Submergence, %
Polymer Feed, % by wgt
Feed Solids, g /%
Filtrate Solids, g /a
Solids Capture, %
FILTER CAKE
Thickness, inches
Moisture, % by wgt
Solids, Ib /sq ft
Filter Yield,
T l_ /!. .- i
3
1

9.7
28
0.5
162
7.5
95

1
78
1.5
9.2
3
2

9.7
29
0.4
109
21
80

5/4
78
1.7
10.5
3
3

9.7
28
0.9
91
36
60

1
79
1.4
8.9
3
4

9.7
28
2.4
29
—
--

1
79
1.1
6.8
4
1

9.7
27
0.1
90
45
50

1
79
1.4
8.9
4
2

7.0
24
<0.1
70
17
76

1/2
78
0.63
6.1
4
3

9.7
27
<0.1
106
--
—

3/4
78
1.0
9.8

-------
arbitrarily chosen at about the maximum possible.  Cake
form times were about 6 and 12 percent of the cycle  time.
A dry time of about 44 percent of the cycle time was used.

Several preliminary, yet pertinent observations can  be
made concerning the data in Table 25 and other operational
observations.  First it war., qualitatively established, vcrv
early in the test work, that polymer conditioning of carbon
sludge was necessary to achieve a readily clischargable filter
cake.  A 3/4 to 1 inch thick filter cake could be formed  and
dried without polymer, but it did not discharge easily.

The level of polymer dosage appears to have effected
carbon solids capture by the filter.  At dosages of
less than 0.2 Ib C-31/100 Ib dry carbon solids or at
dosages greater than 0.9 Ib C-31/100 Ib carbon, solids
capture was poor  (generally less than 75 percent).   Polymer
dosages of 0.4 to 0.8 Ib C-31/100 Ib carbon results
in from poor to fair captures of 80 to 95 percent.

The nature of the carbon solids results in filter cake
shrinkage and formation of large ''cracks" during cake
drying.  These cracks formed at about 1/4 to 1/3 of  the
dry cycle time and caused very low operating vacuums
of less than about one and one-half inches of mercury
during the dry cycle.  Since the filter was equipped
with a single vacuum pump and filtrate receiver, the
form vacuum was also quite low, being in the range of
one to five inches of mercury.

Because of varying operating parameters of cycle time,
submergence and polymer dosage and varying filter cake
thicknesses, the data in Table 25 does not show a precise
correlation between filter yield and feed solids concentra-
tion.  There is a general trend toward higher yields at
higher feed solids concentration.

During all filter Runs, a total of 4300 Ib of carbon
sludge  (dry weight basis) was fed to the vacuum filter
during 16.2 hours of filter operating time.  For the
28.3 sq ft filter, the overall average yield, assuming
90 percent capture, was 8.4 Ib/hr-sq ft  (e.g., 4300
x 0.90/16.2 x 28.3).  The weighted average of filter
feed solids was 12 percent solids, by weight.
                          15!

-------
Based on results of this study, a summary of suggested
vacuum filter operation conditions and performance is
presented in Table 26.  An average filter cake density of
16 Ib/cu ft was observed, excluding the obviously low"mois-
ture content samples of 62 and 58 percent in Table 25.  Eased
on a 3/4 inch thick cake and a cycle time of 9 minutes, a
filter yield of 6.7 lb/hr-sa ft was computed.

Future studies in at least three areas should result in
demonstrating significantly improved filter performance.
First, a tighter filter media should be evaluated for
the purpose of improving solids capture.  The media used
was Polypropolene-907, which has an air flow rate classifi-
cation of 300 CFM/sq ft, a 2/2 twill weave of 12 millimeter
mono-filament and a thread count of 68 x 29.  It is
recommended that a similar type of media be used which
has a lower air flow rate classification; for example,
Polypropolene-873 which is rated at 30 CFM/sq ft.  Use of
the tighter media would probably re-suit in reduced filter
yields.  Laboratory filter leaf test results indicated that
solids captures in excess of 95 percent could be obtained
with Polypropolene-873.

The second area of improving filter operation results
involves more efficient use of the filter cycle time.
From Table 26 it is seen that cake form time was only about
12 percent  (1.1 min/9 min) of the cycle time.  Had the
full design submergence of 33 percent been used for cake
form time, the cycle time could have been reduced to
3.3 minutes  (9 x 12/33).  The filter yield would have been
expected to increase to over 18 Ib/hr-sq ft  (recall Equation
 (4) where yield a 1/CT).  Adequate dry time could be main-
tained at the reduced cycle time of 3.3 minutes.

The third area of improving vacuum filter performance would
be the use of two vacuum receivers wherein form and dry vacuum
could be at different levels.  All other factors being equal
an increase in form vacuum from 5 to 15 inches of Hg  should
result in 40 to 50 percent increase in yields.


'Thermal Regeneration

The primary objectives  of the fluidized bed carbon regen-
eration furnace tests were to determine the carbon losses
across the system and demonstrate the operability of  the
system at pilot plant scale.  The quality of regenerated
carbon was evaluated by reuse in the carbon contactor
treatment step.
                          159

-------
                     TABLE 26:
              SUMMARY OF SPENT CARBON
                  DEVIATE RING DATA
    Item


Filter Cake Density

Filter Cake Thickness

Dry Cake Weight (W)

Filter Drum Cycle Time (CT)

Filter Cake Form Time (FT)

Filter Cake Dry Time (D)

Filter Yield

Filter Cake Moisture Content(MC)

Drum Submergence

Solids Capture

Polymer Dosage (Dow C-31)

Form and Dry Vacuum
  Value


16 Ib/cu ft

3/4 inch

1.0 lb/sq ft

9 minutes

1.1 minutes

4.0 minutes

6.7 Ib/hr-sq ft

78 percent

30 percent

90 percent

0.4-0.6 lb/100 Ib carbon

5 inches of Eg
                        160

-------
Because of limited time, evaluation of the effect of
various furnace system operating variables was not
attempted.  The approach used was to operate the system
as per the manufacturers and process consultants recom-
mendations.  Valuable input on furnace operation was
received from Mr. Ed Berg of the Environmental Protection
Agency and Mr. Bob Thompson of Stamford, Connecticut
(a private consultant).

Four batch regeneration Runs were completed.  A fifth was
started but equipment failures caused termination of that
Run.  The following is a discussion of each separate Run
in the order that they were conducted.
Regeneration Run #1

The purpose of the first Run was to check out operating
and testing techniques and procedures, and obtain
preliminary carbon loss data.  Furnace system operating
conditions are presented in Table  27, which summarizes
operating data for all four regeneration Runs.

During Run #1, the oxygen analyzer was not functioning
properly and control of furnace exit oxygen content
was impossible.  Normal operation would have entailed
adjusting bed injection gas flow rate to provide
about 1 1/2 percent excess oxygen prior to carbon
feed and about 1/2 percent after carbon feed.  Because
of the inoperative oxygen meter, the air to fuel volume
ratio was maintained well below the theoretical stoichio-
metric ratio of 10:1.  Since the actual ratio was 6.7:1
 (air:gas), it was presumed that no oxygen existed in
the furnace off-gases.

From Table 27 it is seen that the  temperature at the top
of the furnace freeboard was 70°F higher than the sand
bed temperature.  This observation indicates that heat
was being generated between the top of the sand bed
and the freeboard thermocouple.  Burning of either gas,
carbon or both in this region obviously occurred.  Carbon
loss results indicate that considerable carbon was burned.
During Run #1, 1250 pounds of total solids was
advanced from the spent carbon holding tank to the vacuum
filter station.  An estimated 950  pounds was fed to the
furnace.  The estimated difference, or 300 pounds of
solids, left the vacuum filter station via filtrate
 (120 Ib), belt washing and spillage  (80 Ib) and final
                          161

-------
                         TABLE 27:  CARBON REGENERATION:
                                    FURNACE OPERATING CONDITIONS
OPERATING_CONpITIONS:

Burner Air Flow, SCFM
Burner Gas Flow, SCFM
Bed Injection Gas Flow, SCFM
Off-Gas Oxygen Concentration,
  % by Volume
Temperature Profile  (°F)
  Freeboard
  Sand Bed
  Fire Box
Pressure Profile (inches of H20)
  Freeboard
  Bottom of Sand Bed
  Across 24 inches of Sand Bed
  Fire Box
Scrubber and Quench Water:
  FlOW, gpm
  Temperature, °F
        2a
 2b
126
6.7
12,0
__
1600
1530
1920
_4
28
28
42
62
61
65
2.8
8,3
-<2.0
1740
1740
1920
-6
22
25
26
60
51
125
5.1
11.4
<0.8
1650
1650
1890
_4
23
26
40
60
61
126
6.2
9.8
0.0
1650-1750
1650-1750
1900
-4
49
40
67
66
62
119
5.1
9.2
0.0
1510
1540
1940
-4
46
33
63
57
56
Furnace Operating Time, Hours
18
21
22
12

-------
cleaning of piping, flocculation tank, vacuum filter
vat and furnace feed hopper  (100 Ib).  of the estimated
950 pounds of solids fed to the furnace only 350 pounds
were recovered in the scrubber system decant tank.
Thus, 63 percent of the total solids fed were lost.
The recovered carbon was inventoried and advanced to
the carbon contactor feed system.

The furnace temperature and pressure profiles were very
stable during the course of the Run.  No evidence of
carbon was observed in the furnace  stack gas.  The automated
carbon feed system worked well, with an average of about
53 pounds of dry solids being fed per hour to the furnace
(950 Ib /18 hr ).  No obvious explanation was apparent
for the very high carbon losses.
Regeneration Run #2

Run #2 was started because of a need for regenerated
carbon in the pilot plant.  As the furnace was brought
up to operating temperature, considerable difficulty
was experienced in trimming the stack-gas oxygen level
to less than 2 percent by volume.  As indicated in
Table 27, the air flow rate was considerably reduced
during Run #2a.  During furnace start-up it was observed
that as bed injection gas flow was reduced, the free-
board temperature was also reduced, compared to the sand
bed temperature.  Unfortunately as bed  injection gas
flow was reduced, the stack-gas oxygen  concentration
increased above 2 percent by volume.

Run #2a was commenced even though the air and gas flow
rate was slightly less than the design  fluidization rates.
Within a four hour period, bed fluidization was lost twice.
Pressure readings became very erratic and the upper and
lower sand bed temperature differed significantly.  It was
decided to terminate the Run, leaving the regenerated_carbon
and spent carbon inventories in place.  A representative of
the furnace manufacturer and the process consultant
 (Mr. B. Thompson) were summoned to assist in operation
and evaluation of the furnace system.   Under their super-
vision, Run 2b  (continuation of 2a) was completed at the
operating conditions indicated in Table 27.
                         163

-------
Of 1010 pounds of carbon solids fed to the vacuum filter
station,, some 760 pounds were estimated to have reached
the furnace.   Only 400 pounds of solids were recovered,
as determined from inventory measurements.  Thus, carbon
losses were at least 47 percent.  The furnace feed solids
were 4., 7 percent ash and. the furnace product 23 percent
ash.  Visual inspection of the regenerated carbon indicated
the presence of fine sand particles.  As with Run #1,
no obvious explanation for gross carbon losses was
apparent for Runs 2a and 2b.  The process and equipment
consultants did offer several suggestions for improving
equipment performance.  For example, the furnace shell
was pressure tested and several major air leaks found.
It, was conjectuered that leaks around the top of the
furnace  (at a. flange) might have allowed air to be drawn
into the unit due to the slight vacuum conditions at this
location.  Thus, all leaks were sealed by welding prior
to Run #3.

It was also recommended that an additional two feet of
sand be placed in the furnace to provide a greater
detention time of carbon within the bed.  This was also
done prior to regeneration Run #3.
Regeneration Run #3

At this point in the test work most minor equipment and
operating technique problems had been repaired or sat-
isfactorily worked out.  Some new plumbing and procedures
were also implemented to more precisely monitor the amount
of carbon reaching the furnace.  In essence, all carbon
bearing flows from the vacuum filter station, except
the cake discharge; were collected and inventoried for
volume and concentration of total suspended solids.
This included any spillage and hosing down of the
filter station after use.

During Run #3 the furnace operating conditions were similar
to previous Runs as indicated in Table 27.  The increased
sand bed depth did result in higher pressure readings.
The freeboard temperature was, once again, equal to the
sand bed temperature.  During the Run, the sand bed temp-
erature set point  (automatic carbon feed controller) was
increased by 25°F increments at about one-hour intervals.
The air and gas flow rates ware not changed.  To achieve
the higher bed temperature the carbon feed rate was
automatically reduced.  Immediately after each adjustment
of bed temperature set point, the freeboard temperature
dropped about 30 to 5Q°F,  However, within one-half hour,
                         164

-------
the freeboard and sand bed temperatures would merge to the
same values.

Carbon losses were excessive once again.  Only 520 pounds
of total solids were recovered from 1100 pounds fed to
the furnace, for a loss of 53 percent solids.  The furnace
feed  (spent carbon) ash content was 4.7 percent by weight
and furnace product ash content 30 percent by weight.
As in Run #2 considerable sand was present in the furnace
product.  About 65 percent of the non-ash material was
lost across the furnace.  The average furnace feed rate
during Run #3 was 50 pounds of total dry solids per hour
(1100 lb/22 hr).
Regeneration Run #4

Run #4 was started without a clear cut direction in mind
to reduce carbon losses.  The only change in furnace oper-
ating conditions was to set the automatic carbon feed con-
troller to maintain a sand bed temperature of 1540°F which
was 100 to 200°F less than for the two previous Runs.
The stack off-gas oxygen level was again mantained at
zero.  During Run #4, the furnace system operated beautifully.
No adjustments of any operating variables were made during
the Run.  The furnace temperature profile remained absolutely
constant during the   12 hour Run.  For 'the first time,
the freeboard temperature remained slightly below  (30°F)
the sand bed temperature..

Some 740 pounds of total solids were fed to the vacuum
filter, of which 360 pounds did not reach the furnace.
This high percentage loss of carbon solids across the
vacuum filter station was presumably partly due to the
very poor captures experienced  (see Table 24).  In addi-
tion, the 750 pounds started with was considerably less
than the 1010 to 1300 pounds in previous Runs.  Con-
sequently, spillage and clean up losses were propor-
tionally higher.

Of the 380 pounds of total solids  (740 minus 360) fed to
the furnace 320 pounds were recovered.  This resulted
in total solids losses of 16 percent.  The ash content
of the furnace feed was 11 percent and of the furnace
product 28 percent.  Apparently some previously
regenerated product had been cycled through
                         165

-------
the carbon contacting step and advanced to the spent
carbon holding tank.   The increase in spent carbon ash
content from 4.7 percent in Runs #2 and #3 (basically
once used carbon)  to  11 percent in Run $4 indicates
recycling of regenerated carbon.  Small gold-colored
flecks routinely seen in the furnace product were
visually observed in  small quantities in Run #4 furnace
feed material.
Regeneration Run #5

With only enough time left for one additional furnace
Run, a special test was designed to demonstrate that
low carbon losses could be obtained with the fluidized
bed furnace system. It was decided to operate the
furnace without bed injection gas.  The oxygen level
was controlled by adjustment of burner air and gas flows.
Thus, no excess oxygen would enter the sand bed region.
It was recognized that this mode of operation would result
in excessive temperature (about 3000°F) in the fire chamber
of the furnace.  The furnace manufacturer was consulted
about probable damage to the furnace.  It was indicated
that the stainless steel tyeres would probably be deformed
at 3000°F but that they could be replaced if damaged.

Run #5 was started with a burner air flow of 118 SCFM
and a burner gas flow of 4 SCFM.  The stack off-gas oxygen
content was under 1/2 percent by volumes.  The carbon feed
temperature set point was at 1400°F.  After two hours of
furnace operating time, the fire box refactory failed
(melted), and Run #5 had to be aborted.  No data could
be collected to determine carbon losses.  A re-evaluation
of furnace refactory material characteristics indicated that
the fire box refactory was not designed for temperature in
excess of about 2250°F.  Three of the seven tyeres sustained
severe damage also, with one being completely melted.
Discussion:

The preliminary carbon regeneration test results indicated
gross burning of powdered carbon.  The 83 percent recovery
obtained in Run #4 was encouraging but still not as high
as the 90 percent plus anticipated by the developers
of the process.  Obviously, there was a major shortcoming
in the furnace design, or possibly, operation.  Review of
the furnace design revealed a weakness.  The carbon
feed point was located about 6 inches above and
                         166

-------
16 degrees horizontally from one of the sand bed
gas injection nozzles.  Thus, spent carbon entered
the fluidized bed at a point only 8 inches from a gas
injection nozzle.  Apparently, excess oxygen was not
being consumed by preferential burning of"bed injection
gas.  It superficially seemed desirable to feed carbon
at a higher elevation in the sand bed, further removed
from the gas injection points.  Actually, two new carbon
feed points were installed 18 and 36 inches above one
of the six  (6) gas injection nozzles.  Lack of available
time precluded determing the effect of these new carbon
feed points.

A similar.study of regeneration of powdered carbon by a
fluidized bed furnace was conducted by others shortly
after the end of this study.  In this other study, a
similar sized furnace was used without bed injection gas.
Cooled off-gas  (void of oxygen) was recycled to control
furnace operating temperature.  Preliminary results from
operation of this furnace indicated carbon recoveries
well in excess of 90 percent of the carbon33.  This
fact coupled with acceptable results from a study using
a 4 Ib/hr pilot plant1 indicate that the fluidized bed
furnace approach to powdered carbon regeneration is
feasible.   It is, however, quite obvious that additional
development studies of the furnace used in the present
study are required before it can be considered a potential
alternate to other powdered carbon regeneration systems.
 Reuse of Regenerated Carbon

 Over a two week period  about  1600  pounds  of  once  regenerated
 carbon was used in  the  pilot  plant.   Chemical  pretreatment
 was with lime  at  a  treatment  pH  of 10.9.  Approximately
 0.77 MG of chemically treated wastewater  was processed
 by single-stage carbon  contacting.   Table 28 presents the
 pertinent results for this carbon  treatment  Run  (C-15)
 and, for comparison, the  data from the  previous carbon  Run
 (C-ll) using virgin carbon.   The overall  average  carbon
 dosage shown is about 250 mg/£,  (i.e.,  1600  lb/0.77
 MG equals 250  mg/i) . However, the  actual  average  daily
 carbon feed rate  varied over  a range of 150  to 300 mg/fc.

 The organic  loadings  (CO/M)  for Runs C-ll and C-15  were
 0.12 and 0.13  mg/A  feed SCOD  per mg/£ carbon.   The organic
 removals  (X/M) were 0.10  and  0.098 mg/Jl SCOD removed per
 mg/£ carbon, respectively.  Considering the  similar  effluent
                          167

-------
                            TABLE 28 :   COMPARISON OF REGENERATED AND
                                       VIRGIN CARBON TREATMENT EFFECTIVENESS
         Run Number
         Length of Run, Days
Virgin Carbon

    C-ll
     20
           Regenerated
             Carbon

              C-15
               14
CO
         OPERATING CONDITIONS:

         Hydraulic Loading,  gpm/sq  ft
           (Carbon Contactor/GMF)

         Carbon Dosage,  mg/£
         PROCESS TREATMENT RESULTS;

         Effluent From


         Suspended Solids, mg/£

         SCOD,  mg/£

         Temperature,  °C
 0.75/2-5


    345
Chem.
Stage

 7.7

 41

 22
Carbon
 53

 6.4
             0.76/1.3


              -250
Chem.  Carbon
Stage  Cont.
 14

 33

 20
35

8.4

-------
SCOD's of 6.4 and 8.4 mg/A, it is apparent that no gross
difference existed between virgin and once regenerated
carbon, based on treatment effectiveness.  These results
are obviously of limited scope and future studies are
required to more precisely define the properties and
treatment effectiveness of regenerated carbon.
TYPICAL PILOT PLANT EFFLUENT QUALITY

Figures 54 through 58 present average pilot plant effluent
quality for five different combinations of chemical and
carbon treatment conditions.  Average raw wastewater
quality values are also noted.  It should be noted that
average results are presented and not median values
shown in previous tabulations.  Removal of COD ranged
from 87 to 97 percent.  Suspended solids and total
phosphorus removals range from 94 to 98 percent and 91
to 97 percent respectively.  Overall performance of the
PAC-PCT system was considered quite good and variations
in effluent quality during any given Run not unreasonable.
Recall that the pilot plant was operated under relatively
constant chemical and carbon dosage conditions.  Varying
raw wastewater quality  (especially SCOD and phosphorus)
account for some of the variations in plant effluent
quality.  If continuous on-line evaluation of SCOD and
phosphorus were accomplished, then chemical and carbon
feed rates could probable be adjusted to maintain a more
uniform plant effluent quality.  Future studies should be
designed to evaluate such an operating approach.

The PAC-PCT process studied did not incorporate a nitrogen
removal scheme.  Since the entire plant flow was void of
oxygen, little or no nitrite or nitrate nitrogen should have
been present.  Any nitrogen material would have been present
principally as ammonia or organic nitrogen.  After carbon
treatment and removal of suspended solids the major form
of nitrogen was probably ammonia.  Table 29 shows several
single composite ammonia nitrogen profiles through the
pilot plant.  The data indicates that a slight increase
in ammonia nitrogen occurred through the pilot plant,
presumably due to the breakdown of organic nitrogen.
                          169

-------
 COD, mg/l
   BOD5,
   mg/l
 Suspended
  Solids,
   mg/l
   Total
Phosphorus,
   mg/l
                 FIGURE 54: PILOT PLANT  EFFLUENT QUALITY
                            FOR RUNS F-3 AND C-14
 TOC, mg/l   1Q_.
             25 -
             20--
             15--
             10--
              5--
                  Average FEED 134 mg/l
                  12 mg/l—Average
             10--
 5--
               Average FEED 95 mg/l
                   3.6 mg/—Average
0.6
0.4
0.2
0.0
                   Average FEED 6.8 mg/l
0.21 mg/l—Average
  au./;i mg/i—Mveragi
"TTfh
                11   13   15   17   19   21    23   25   27
                                June 1970

-------
 TOC, mg/l
   BODg,
    mg/l
 Suspended
   Solids,
    mg/l
                       FIGURE 55: GRANULAR MEDIA FILTRATION:
                                FOR RUNS A-2 AND C-7
             40
              30--
              20--
              10--






Average FEED— 68 mg/
15 mg/l — Average I
Lf^J-



1
—
H


              40--
              30--
 COD, mg/l    20--
              10--
                             Average FEED—176 mg/l

                                 22 mg/l—Average
15-T
10
 5
 0
Average FEED — 93.5


mg/l





              10 -
 5--
           Average FEED—172.1 mg/l

     3.6 mg/l—Average
             0.8 -  Average FEED—5.7 mg/l
   Total      0.6
Phosphorus,
   mg/l

                    2    4    68    10   12   14   16   18   20
                                   December 1970

-------
TOC, mg/I
 COD, mg/I
            FIGURE 56: PILOT PLANT EFFLUENT QUALITY
                       FOR RUNS L-9 AND C-8
            15-F
             5 --
                         Average FEED 87 mg/
                         8.8 mg/l—Average
            10
                        Average FEED 176 mg/I
                                6.4 mg/I—Average
 Suspended
   Solids,
    mg/l
A
verage FEED 123 mg/l -
	
1.7 mg/l — Average
L_J

   Total
Phosphorus,
   mg/l
                               Average FEED 6.4 mg/l
                     20  22   24   26   28
                           March 1971
30

-------
       FIGURE 57: PILOT PLANT EFFLUENT  QUALITY FOR RUNS L-11 AND C-9
 COD, mg/l   20
BOD  , mg/l
             0

            20
Suspended
  Solids,
   mg/l     10--




12 mg/l Average
Average
FEE[
) 154 mg/I
^HB















mrnaa

Average FEED 225 mg/l
5.5 mg/l Average
L-^_r-L_-,
           1.2

           1.0
                 I	1	1	1	1	1—4	1	1   I  I   I—H
 Average FEED 7.8 mg/l




0.43 mg/l Average
               25    27    29

                 April 1971
                11    13   15
      May 1971

-------
BODs, mg/l
Suspended
  Solids,
  mg/l
    Total
 Phosphorus,
    mg/l
                 FIGURE 58: PILOT PLANT EFFLUENT QUALITY

                          FOR RUNS  L-4 AND C-11
             20
             15
COD, mg/l    1Q..
              5-
                                       Average FEED—268 mg/l
                                                 7.3 mg/l—Average
8--
6--
4 -
2--
0--
                     Average FEED—68 mg/l
                                              n
8
6t
4
2
0
                                  Average FEED—281 mg/l
2.6 mg/l—Average
             0.0
Average FEED — 6.8


mg/l



•mBb
n i h
0.63 mg/l — Average
L_J



MiH



                23   25   27   29   31

                        May 1971
                                          8    10    12
                                   June 1971

-------
     TABLE 29:  AMMONIA NITROGEN PROFILE, mg/fc AS N
Run t
C-l
C-2
C-3
C-5
C-7
Raw
Sewage
8.8
7.2
10.6
8.5
9.5
Chemical
Effluent
7.4
10.1
11.0
9.0
10.9
1st PAC
Stage
Effluent
8.6
9.9
11.3
9.6
— —
2nd PAC
Stage
Effluent
9.0
10.1
12.0
—
10.9
Plant
(Filter)
Effluent
9.4
10.7
11.1
10.2
11.0
AVERAGE
8.9
9.7
10.5
                            175

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COMPARISON OF LABORATORY AMD PILOT PLANT RESULTS

A direct comparison of laboratory and pilot plant treatment
results is impossible since the laboratory study was conducted
prior to pilot plant operation.  However, certain pilot plant
results were qualitatively predicted by laboratory tests.

The removal of SCOD by alum treatment was predicted by jar
tests.   The insolubilization of phosphorus by alum, ferric
chloride and lime treatment was also fairly well predicted.
The relative effect of lime dosage, or more specifically
treatment pH, on hardness distribution and sludge production
was also indicated by jar tests.

Chemical-sewage floe settling rates were not precisely
predicted by jar tests.   For example, jar test data in
Figure  9 show that, without polyeLectrolyte, lime-sewage floe
settling rate of 1.4 inches per minute, which is equivalent
to 0.8  gpm/sq ft was observed.   Pilot plant results in Table
9 show  thn': a well clarified effluent was produced at
a hydraulic loading of 1.3 gpm/sq ft, for similar treatment
pT's.  The relative effect of polyelectrolyte on chemical-
scwage  floe settling rates  was predicted.  That is, the
use of  polyelectrolyte did result in providing effective
clarification at increased hydraulic loadings.

Effective clarification of carbon slurry at a carbon contactor
hydraulic loading of 0.8 gpm/sq ft was not predicted by
laboratory jar test results.  However, the laboratory tests
did indicate a "self flocculating" property of concentrated
carbon  slurry.  Being able to maintain a concentrated carbon
slurry  in the carbon contactors could explain the effective
clarification obtained.

Laboratory equilibrium adsorption isotherm tests were not
indicative of the organic removals obtained by the pilot
plant.   The obvious shortcoming of these laboratory tests
was the inability to account for organic removal by any
mechanism other than physical adsorption.  The usefulness
of t.ie  laboratory equilibrium isotherm test for predicting
organic removals is seriously questioned.

In summary, certain laboratory tests did provide a
11 first  approximation" of pilot plant treatment results.
It is quite safe to note, however, that reliable design
and efficiency data can only be obtained by pilot or
full scale plant operation over an extended period of
time.
                          176

-------
OPERATIONAL AND EQUIPMENT PROBLEMS

Chemical Treatment System:  Difficulty was experienced
with the dry lime  [Ca(OH)2] feeder system during humid
and rainy periods.  The lime adsorbed moisture, balled
up and bridged in the feeder.  Though several treatment
upsets were experienced, due to reductions of treatment
pH, major problems were averted by operator attention.
Basically, the operators would have to remove or crush
balled up lime which blocked the two lime feeder discharge
ports.  These lime feedings problems could have been averted
had lime been stored in a dry place.


Difficulty was experienced in maintaining a uniform
effluent pH with the automated acid neutralization system
due to the following reasons:

1.  Insensitive acid feed pumping equipment.

2.  Inadequate acid mixing and pH sensing, resulting in
    erratic signals to the automated acid control system.

3.  Frequent interruption of flow due to timer controlled
    chemical sludge blowdown.

Two features of the existing acid neutralization system
were considered poor design:  a) feeding acid in the
effluent launder, and b) off-on acid feed pump operation.
It is recommended that acid be fed to a tank with 1 to
2 minute detention time which is completely mixed.  In
addition, off-on acid feed pump should be eliminated and
an automatically controlled variable feed pump used.  On
two occasions, the acid feed line  (1/2 inch diameter
black iron pipe) was completely plugged with a fairly
hard chemical deposit.  It was cleared by rodding and
flushing.

The solids-contact chemical treatment unit performed very
well considering that it was basically designed as a
potable or industrial water treatment unit.

Twice during this  study, after about three months of
operation with lime treatment, the sludge circulation
pumping turbine clogged with a mixture of rags and
deposits.  The deposits were easily removed by hand
scraping.
                          177

-------
This problem, a loss of mixing turbine pumping capacity,
should be overcome by redesign of the turbine blades to
prevent rag build-up.

No significant CaCCK deposits, other than those noted
above, were observed in"the chemical treatment unit during
more than six months of lime treatment operation.  Less
than about 3/16 inch deposition of CaCO3 was observed on
the interior walls of the reaction zone and no significant
deposition was ever found on the walls of the clarification
zone.

After ten months of operation, the rubber lining in an
eccentric sludge blowdown valve wore out and the valve
internals had to be replaced.  This failure was pre-
sumably due to the presence cf grit in the raw waste-
water which caused1 erosion of the rubber lining.

PAC Treatment System:  No problems were encountered with
the solids-contact units.  Powdered carbon dusting
problems originally encountered during carbon make-up
were solved with the assistance of a carbon manu-
facturer.  Covered make-up and feed tanks, a vacuum
collection and a water scrubbing recirculation system,
and careful handling and mixing (wetting) minimized
carbon dusting.

Several  corrosion and/or erosion problems were en-
countered in the concentrated PAC slurry handling
system.  Cast iron and steel components of pumps and
pipe fittings corroded badly.  In one instance, a
stainless steel high speed (1750 rpm) mixina impeller
shaft corroded at the water line in the virgin PAC make-
up tank resulting in a shear failure at that point.
A diaphragm pump with stainless steel ball checks
was found suitable for pumping virgin PAC.  For trans-
ferring solids-contact unit or thickener underflow,
peristalic pumns with rubber tubing were found adequate.

Granular Media Filtration System:  Several structural and
hydraulic problems were experienced with the 3.5 ft dia-
meter plexiglass filter and appurtenances.  A significant
process problem was associated with obtaining effective
backwashing of the filter bed.  Some of the causes were:
                          178

-------
(1)  unsatisfactory backwash water distribution,  (2)
insufficient bed expansion during water backwash  (less
than 20 percent expansion at about 20 gpm/sq ft) and
(3)  "mud ball" formation during long filter Runs  (50
hours).  The first problem was effectively reduced by
installation of a stainless steel underdrain septum over
the entire filter bed area.  The second problem was
eliminated by installation of a larger backwash pump
and larger piping.  This allowed attainment of 25
percent filter bed expansion at a 26 gpm/sq ft backwash
rate.  The third problem was eliminated by backwashing
the filter at least once each day.

Process Stream Sampling:  Considerable difficulty was
experienced throughout this study in obtaining a com-
posite sample of raw wastewater.  Daily cleaning and
frequent operator surveillance of the sampler shown
in Figure 24 was necessary in order to collect a
representative 24-hour composite sample.  A check
of the sampler performance was made by comparing the
suspended solids content in an automatically collected
composite sample and a 24-hour composite of hourly
grab samples taken from the raw wastewater sump.
Less than 5 percent difference was found.

The possibility was considered that carbon present
in the carbon contactor effluent 24-hour composite
samples adsorbed additional SCOD due to .the extended
contact period.  This possibility was evaluated by
collection of two identical 24-hour composites of
hourly grab samples.  One grab sample was immediately
filtered through a 0.45 micron membrane whereas the
other was stored as collected.  Soluble COD analysis
of the two composite samples indicated that the
presence of 30 mg/£ of spent carbon caused no discernable
reduction in SCOD.

Instrumentation:  Problems were encountered with nearly
all plant instruments.  Most notable were the electronic
devices  (recorders and controllers) which exhibited
considerable corrosion of electrical contacts.  The
relatively humid plant atmosphere, the presence of
ferric chloride fumes and lime dust x^ere the obvious
cause of corrosion.  Obviously, delicate mechanical
and electrical control devices and instruments  should
not be subjected to such an atmosphere for extended
periods of time.
                         179

-------
Considerable difficulty was experienced in maintaining the
laboratory TOG analyzer in operable condition.  Nearly 20
percent of the original instrument cost was spent in
the first year for instrument calibration and repairs.

Carbon Regeneration System:  The only significant problem
encountered with the vacuum filtration operation was the
variable feed solids concentration.  The cause was the
lack of well mixed sludge in the spent carbon holding
tank.  This problem of nonuniform solids concentration
made it impossible to achieve the desired polymer con-
ditioning chemical dosage.  Provisions for better mixing
of vacuum filter feed sludge would eliminate this problem.

Numerous problems were experienced with the fluidized
bed furnace during  start-up and during the first two
regeneration Runs.  The problem of gas leaks in the
steel furnace shell has already been alluded to.  The
control valves on the two gas and single air flow lines
were very insensitive and made precise adjustment
of flow difficult.  An exposed hot (1500°F)  off-gas
duct created a fire hazard and had to be insulated.

On several occasions, the dewatered carbon feed line
plugged at the furnace inlet, presumably due to drying
of carbon sludge at this point.  Had the carbon feed
inlet been water-jacketed, it is probable that this
clogging problem would have been minimized.   There
was no isolation valve on the carbon feed inlet pipe.
Thus, when plugging occurred, the furnace air and gas
flow had to be reduced to less than that required for
bed fluidization.  Otherwise, hot sand would fall out
of the carbon feed line when unplugged.  A suitable
isolation valve and quick-couple connection was provided
by the furnace manufacturer upon request.

In general, the furnace and off-gas scrubbing system
performed with a minimum of operational problems.
                         180

-------
                   SECTION VIII

                 ECONOMIC ANALYSIS
The following economic analysis of the PAC-PCT process
evaluated during this study is presented for the purpose
of showing the relative economic impact of different
types of chemical treatments and powdered carbon dosages.
The economi-c analysis is presented in three parts:  chemical
treatment costs, carbon treatment costs and total treatment
costs.  The analysis is based on the treatment of Salt
Lake City raw municipal wastewater.  The average design
flow used for analysis was 10 mgd and peak design flow
was 15 mgd.  All unit operations employed are presented
in figure 59, which shows the overall PAC-PCT system.
Assumed unit costs are presented in Table 30.  Major
equipment sizes are presented in Table 31.
CHEMICAL TREATMENT COSTS

Estimated chemical treatment costs are shown in Table 32.
The process design parameters used to size equipment and
determine chemical costs are those presented in Table 12
(page 103).  Predicted effluent quality for all three
chemical treatments is 5-10 JTU turbidity, 10-25 mg/2, SS,
0.5 to 1.0 mg/£ total phosphorus and 55-60 mg/£ COD.

Preliminary treatment includes bar screening and comminution.
Incineration operation and maintenance  (O&M) costs include
operators, utilities  (power, water and fuel), maintenance
and haulage of ash to land fill disposal.  The power and
maintenance and the supervision and labor costs shown
are for one-half of the estimated total PAC-PCT treatment
plant costs, excluding incineration O&M costs.  The con-
tingency costs (50 percent of total capital costs) include
engineering, administration and legal costs in addition to
interconnecting piping, valves, instruments, buildings, etc.

The absolute costs shown in Table 32 are considered reasonable
and the relative costs for different chemical treatments
valid.  It is seen that alum treatment is the least expen-
sive chemical treatment approach.  Capital costs for the
three types of chemical treatments are approximately
the same.  The major cost differences arc operational
costs for chemical and, in the case of lino treat-
ment, incineration operation ami inaintena iee  (O&V,^
eosts.  The incineration O&M cost difference  is  due  i^
                          181

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                                  FIGURE 59:

            POWDERED ACTIVATED CARBON PCT TREATMENT SYSTEM
                                      Raw
                                     Waste
                                   Preliminary
                                   Treatment
FeCI3 or Alum
   or Lime
                                                                            Lime Conditioning
                                                r
                                                t
                                   Chemical
                                   Treatment
      Acid
  Neutralization
                     (Lime Treatment)
        Virgin
PAC     +
     Regenerated
               Gravity
             Thickening
                                   PAC
                                 Treatment
_ „ —..JJ
    ^^1
  Gravity
Thickening
                                 Granular Media
                                    Filtration
CL, ,'Chlorine Gas)
                                  Chlorination
                                    Treated
                                     Waste
                                                                  Vacuum
                                                                 Filtration
                                                              PAC (FBF)
                                                             Regeneration
                                                                                   (FeCU or Alum
                                                                                     Treatment)
                                                                                           Vacuum
                                                                                           Filtration
                                                                                         Incineration
                                                                                           (MHF)
                                                                                          Disposal
                                                                                           Polymer
                                                                                         Conditioning

-------
TABLE 30:  ASSUMED UNIT COSTS FOR ECONOMIC ANALYSIS
Chemicals;

Alum
Ferric Chloride
Lime  (Ca[OH]2)
Acid  (H2S04)
Polymer
Powdered Carbon
Chlorine
 3.5 «/lb
 5.0 0/lb
 1.0 C/lb
 1.0 <=/lb
40.0 C/lb
10.0 C/lb
 6.0 <=/lb
Capital Costs;

All equipment costs were estimated as installed equipment
by the authors firm and amortized at 7 percent interest
for 20 years.
Operating Costs:

Power
Sludge Incineration
(16 hr /day):
   Alum & FeCl3
   Lime
Carbon Regeneration
(16 hr /day)
Ash Haulage
Maintenance
Supervision  and Operators'
(seven men for the total
PAC-PCT Plant)
 3.0 $/MG
 3.4 $/ton of wet sludge
 4.1 $/ton of wet sludge
 3.4 $/ton of wet sludge

 1.5 $/ton
 1% of capital costs/year
 87,600 $/year
a does not  include  incineration  or  regeneration operation
  costs
                          183

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         TABLE 31:  MAJOR EQUIPMENT SIZES
CHEMICAL TREATMENT
Solids-Contact Units:
   Number
   Diameter, ft

Gravity Sludge Thickener
  Diameter, ft

Vacuum Filter :
   Number
   Drum Size
   (diameter x face) , ft

Sludge Incinerator  (MHF)
   Diameter, ft
   No of Hearths
                                Alum
56
          FeCl.
44
         Lime
2
130
j
2
116
2
72
44
3
8 x 16
16'9"
6
2
8 x 16
16 '9"
6
2
8x8
22' 3"
8
CARBON TREATMENT

Carbon Dosage, mg/£

Solids-Contact Units:
   Number
   Diameter, ft

Gravity Thickener
   Diameter, ft

Vacuum Filter:
   Number
   Drum Size
   (diameter x face) ft

Regeneration Furnace
   Diameter, ft

Granular Media Filters
   Number
   Diameter, ft
      75
       4
      90
      20


       1

     4x4


     10.75
       6
      22
    300
      4
     90
     40


      1

    8 x 10


      18
      6
     22
                         184

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TABLE 32:  ESTIMATED CHEMICAL TREATMENT COSTS
           (10 MGD PLANT)
Capital Costs:  (1000 of $)

Preliminary treatment
Chemical treatment
Gravity thickening
Vacuum dewatering
Sludge incineration

Total
Contingency  (50%)

Total capital cost

Amortized cost, 0/1000 gal.


Operating Costs;  (0/1000 gal.)

Treatment chemical
Neutralization  acid
Sludge conditioning chemical
Incineration O&Ma
Power and maintenance
Supervision and labor

Total operating cost, 0/1000 gal.

Total Treatment Cost, 0/1000 gal.
                                   Alum
FeC I-
Lime
50
475
55
360
320
1260
630
1890
4.9
4.1
0.0
0.2
0.3
0.7
1.2
6.5
11.4
50
381
69
263
438
1201
600
1801
4.7
5.0
0.0
0.3
0.3
0.7
1.2
7.5
12.2
50
320
55
170
600
1195
598
1793
4.6
3.8
2.8
0.0
1.7
0.7
1.2
10.2
14.8
a - O&M, operation  and maintenance
                          185

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about six times more dry sludge solids and about 3 times
more water being fed to the incinerator for lime treatment
than for alum or ferric chloride treatment.

It would be possible to reduce lime treatment neutrali-
zation costs by 1.5 to 2.0C/1000 gal if the CO2 content
of incineration off-gas were used.   Since incineration
operation was scheduled for only 16 hr/day, stand-by
acid or carbon dioxide feed facilities would be required.
It is doubtful that lime-wastewater sludge recalcination
could be justified for single-stage lime treatment of
Salt Lake City wastewater.   Limited CaCO^ content of
the sludge (about 60 percent of the dry solids) and
increased furnace O&M costs would probably prevent
economical recalcination and reuse of lime.

In summary, alum treatment  of Salt Lake City raw municipal
wastewater is the economic  choice for chemical treatment.
It should be noted that as  wastewater feed phosphorus
concentration increases and  alkalinity decreases, the cost
difference between alum and lime treatment would decrease.
POWDERED CARBON TREATMENT COSTS

Estimated powdered carbon treatment costs are preliminary
due to the lack of definitive data on the PAC  regeneration
system performance.   Table 33 shows preliminary estimated
PAC costs.  The regeneration O&M costs include operating
labor and furnace utilities requirements.  Power and main-
tenance and labor and supervision costs are estimated
as one-half of that estimated for the complete PAC-PCT
plant, excluding regeneration O&M costs.   Pertinent process
design parameters, based on results presented and discussed
in Section VII, are as follows:

1.  Mode of carbon contacting - two-stage counter-current

2.  Carbon contactor average design overflow rate - 0.5 gpm/
    sq ft

3.  Thickener solids loading - 20 Ib/day-sq ft

4.  Vacuum filter yield - 6.7 Ib/sq ft-hr
                          186

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                                TABLE 3 3: ESTIMATED POWDERED CARBON
                                               TREATMENT COSTS
                                                (10MGD PLANT)

        Carbon Dosage,  rag/A                            ^5               3QQ

        CAPITAL COSTS:   (1000 of $)

        Carbon Treatment	568               580
        GM Filtration	228               228
        Gravity Thickening 	   36                50
        Vacuum Dewatering	   25                72
        Thermal Regeneration 	  225               450

        Total	1082             1380
        Contingency (50%)	541               690
i_,
GO
-J       Total Capital Cost	1623             2070
        Amortized Cost, C/1000 gal	4.2              5.4


        OPERATING COSTS;   (C/IOOO gal.)

        Carbon Make-up (15% losses)	0.9              3.8
        Dewatering chemical	0.1              0.5
        Regeneration O-fM	0.1              0.4
        Power and Maintenance	0.7              0,7
        Supervision and Labor	1.2              1.2

        Total Operating Cost, C/1000 gal	3.0              6.6


        TOTAL TREATMENT COST, C/1000 gal	7.2             12.0

-------
5.,  Filter cake moisture content - 78 percent

6.  Carbon sludge conditioning polymer - 0.5 percent by
    wgt

7.  Granular media filter average design rate - 3.0  gpm/sa ft

Tr-ble 33 shows costs for two dosages of PAC.  These
dosages were chosen to indicate the effect of dosage
on total costs.

Organic removal is predicted using the two-stage counter-
current model in Table 23.  The carbon system feed SCOD
is assumed to be 50 mg/£  (recall that the chemical treatment
step produced an effluent with 55-60 mg/£ of total COD).
For the 75 mg/£ carbon dosage, CO/M equals 50/75, or
0.67 mg/£  SCOD fed/mg/£ PAC and an X/M of 0.41 mg/£
SCOD removed/mg/£ PAC was computed.  This results in
a value of X equal to 0.41 x 75 or 31 mg/£ of SCOD
removed and an effluent SCOD of 50-31, or 19 mg/£.
For the 300 mg/£ carbon dosage, C /M equals 50/300 or
0,167 mg/£ SCOD fed/ing/£  PAC and an X/M of 0.133 mg/£
SCOD removed/mg/£ PAC was computed.  This results in
a value of X equal to 0.133 x 300, or 40 mg/£ SCOD
removed, and an effluent SCOD of 50-40, or 10 mg/£.
It. is assumed that the granular media filter does not
remove 5 mg/£ of particulate COD.

Predicted PAC-PCT plant effluent quality is less than
5 JTU turibidity, less than 5 mg/£ SS and 0.4 to 0.8
mg/£ phosphorus, for both carbon dosages.  The plant
effluent COD would be 24 and 15 mg/£ for 75 and 300 mg/£
carbon dosages respectively.  Based on the BOD  data
presented in Section VII, it was assumed that effluent
BODS would be about 12 and 8 mg/£ for 75 and 300 mg/£
carbon dosages  respectively
.y.
From the total treatment costs in Table 33  it is seen
that a substantial increase in cost, 4.8
-------
The total treatment costs in Table 33 are based on
assumed regeneration loss of 15 percent.  Table
34 shows the economic impact of regeneration losses
on total powdered carbon treatment"costs.  It is
quite apparent that the higher the carbon dosage
the greater the increase in total treatment costs as
regeneration losses increase.

Table 35 shows the relative effect of assumed regen-
eration losses and carbon dosage on estimated powdered
carbon regeneration costs.  It is germain to note
that even with up to 40 percent losses,  it would be
cheaper to regenerate and make-up losses with virgin
carbon than to use virgin carbon only.

Using the capital and operating costs in Table 33, the
total cost of powdered carbon treatment without regen-
eration was computed.  For the 75 mg/£ carbon dosage,
a total PAC treatment cost of 10.4 £/1000 gal. was determined,
At 300 mg/£ carbon dosage, a total PAC treatment cost of
30.2 C/1000 gal. was determined.  As plant size  (mgd)
decreases below 5 mgd, the unit capital  and operating
costs increase substantially while virgin carbon costs
remain essentially constant.  A rigorus  economic analysis
would identify a given plant size below which powdered
carbon regeneration would not be economically feasible,
especially at a nominal carbon dosage of about 100 mg/£.
A rough estimate of this plant size would be in the 1 to
2 mgd range.
TOTAL PAC-PCT TREATMENT  COSTS

An indication of  total PAC-PCT  process  treatment costs
for  Salt Lake City municipal wastewater is obtained
from data presented  in Tables 32  and  33.  An  additional
cost of 0.4  £/1000 gal.  was estimated for chlorination
of the plant effluent with 5 mg/& of  chlorine.

Alum treatment  followed  by two-stage  counter-current
carbon contacting with 75 mg/Jl  dosage would cost 18.3
C/1000 gal.  The  predicted plant  effluent quality
would be considerably better than a secondary
biological  treatment effluent for all parameters,  but
                           189

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  TABLE  34   ESTIMATED POWDERED CARBON TREATMENT
             COSTS FOR VARIOUS REGENERATION LOSSES
Carbon Dosage, mg/£              75            300

      Assumed
   Regeneration                Total Treatment Costs,
     Losses ,  %                 	C/1000 gal.	
        0                       6.3            8.2

        5                       6.6            9.5

       10                       6.9           10.8

       20                       7.5           13.4

       30                       8.1           16.0

       40                       8.7           18.6

       50                       9.3           21.2
                         190

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        TABLE 3 5 :  ESTIMATED POWDERED CARBON
                      REGENERATION COSTS
Carbon Dosage, mg/ A             ^5                300

      Assumed
   Regeneration                Total Regeneration Costs
     Losses, %                    C/lb of PAC used
        0                      2.1                1.2

        5                      2.6                1.8

       10                      3.0                2.3

       20                      4.0                3.3

       30                      5.0                4.4

       40                      5.9                5.4
                          191

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especially with respect to phosphorus and suspended
solids.   It is doubtful whether secondary biological
treatment followed by tertiary treatment for phosphorus
removal  could be accomplished for less than 18.3 C/1000
gal.
                         19 2

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                    SECTION IX

                 ADDITIONAL STUDIES
The results of the present study have demonstrated
the operability and treatment effectiveness of the
PAC-PCT process.  Estimated economics indicate that
the process may be an economic alternative to presently
available treatment approaches for certain wastewaters.
However, several areas need further study to develop
new and/or more reliable design data.  Because of the
above factors, a follow-on contract was granted for
one additional year of studies.

The major objectives of these studies are as follows:

1.  Determine the effect of diurnal flow variations
    on plant performance, especially the solids-contact
    treatment units.

2.  Attempt to quantify the effect of biological activity
    in the carbon contactors on organic removal.

3.  Continue development of the fluidized bed furnace
    to minimize carbon losses.

4.  Determine the properties of regenerated carbon,
    especially its effectiveness in the carbon
    treatment system.

5.  Obtain pilot plant scale results for gravity
    thickening and vacuum filter dewatering of chemical-
    sewage sludges and compare same with laboratory
    test results.

6.  Evaluate different granular media filter bed designs
    to improve the efficiency of filter operation; also
    evaluate the effect of various backwash parameters.

7.  Evaluate the use of continuous on-line ultra violet
    adsorption analysis of carbon system feed and effluent
    to determine if carbon can be fed at a minimum rate
    necessary to produce a uniform quality feed effluent.
                          193

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8.   Obtain long term plant performance and operating
    data.
                         194

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                     SECTION X

                 ACKNOWLEDGEMENTS
The support and indulgence of the Salt Lake City Com-
missioner of Water and Sewers, city engineers and
municipal sewage pumping plant personnel is acknowledged.

Special acknowledgement is due Messrs. Jim Snarr,
Darrell Cook and Richard Wallace who nursed the pilot
plant through start-up and kept it operating under
adverse conditions.

The support, counsel and patience of the project
officer, Mr. James Westrick and Mr. Jesse M. Cohen
of the Advanced Waste Treatment Research Laboratory,
National Environmental Research Center Cincinnati,
Ohio, Environmental Protection Agency is acknowledged
with sincere thanks.
                           195

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                    SECTION XI

                    REFERENCES


1.  Berg, E. L. , Villiers, R. V., Masse, A. N., and
    Winslow, L. A. , "Thermal Regeneration of Spent
    Powdered Carbon Using Fluidized-Bed and Transport
    Reactors", Chemical Engineering Progress, Vol. 67,
    No. 107, pp. 154-164.

2.  Gulp, G. L. , "Chemical Treatment of Raw Sewage, Part
    1 and 2", Water and Waste Engineering, p. 61  (July,
    1967) and p. 55 (October, 1967).

3.  Bishop, D. F. , O'Farrell, T. P. and Stamberg, J. B.,
    "Physical-Chemical Treatment of Municipal Wastewater",
    Journal WPCF, Vol. 44,. No. 3, pp. 361-371 (March, 1972).

4.  Shuckrow, A. J., Bonner, W. F., Presecan, W. L., and
    Kazmierczak, E. J., "A Pilot Study of Physical-Chemical
    Treatment of the Raw Wastewater at the Westerly Plant
    in Cleveland, Ohio", presented at the International
    Association on Water Pollution Research Workshop,
    Vienna, Austria (September, 1971).

5.  O'Brien and Gere Engineers, Inc., "Town of Clay Chemical-
    Physical Process Investigators", private communication,
    Syracuse, New York  (January, 1971).

6.  Moffett, J. W., "The Chemistry of High-Rate Water Treat-
    ment" ,_jJpjirjial_AWWA_, Vol. 60, p. 1205  (1968).

7.  Recht, H. L. and Ghassemi, M., "Kinetics and Mechanism
    of Precipitation and Nature of the Precipitate Obtained
    in Phosphate Removal from Wastewater Using Aluminum  (III)
    and Iron  (III) Salts", FWQA Water Pollution Control
    Research Series 17010EKI04/70  (April, 1970).

8.  Harris, H. S., and Kaufman, W. J., "Orthokinetic
    Flocculation of Polydispersed  Systems", Sanitary
    Engineering Research Laboratory University of Cal-
    ifornia, SERL Report No. 66-2  (July, 1966).
                         197

-------
 9.   Schmid,  L.  A.,  "Optimization of Phosphorus Removal
     with Lime Treatment",  unpublished Ph.D.  Thesis,
     University of Kansas Library (1968).

10.   Black &  Veatch  Consulting Engineers,  "Process Design
     Manual for Phosphorus  Removal" , EPA Contract ITo.
     14-12-936 (1971).

11.   Parkhurst,  J. D.,  Dryden, F. D.,  McDermott, G. N.,
     and English,  J. ,  "Pomona Activated Carbon Pilot
     Plant" ',  Journal VJPCF,  Vol.  39,  p. R69 (1967).

12.   Weber, W. J., Jr., Hopkins,  C.  B., and Bloom, R. Jr.,
     "Physicochemical  Treatment of Wastewater", Journal
     WPCF, Vol.  42,  No. 1,  pp. 83-99  (January, 1970).

13.   Beebe, R. L., and  Stevens,  J. I., "Activated Carbon
     System for Wastewater  Renovation", Water and Waste
     Engineering,  pp.  43-45 (January,  1967).

14.   Garland, C.  F.,  and Beebe,  R. L., "Advanced Waste-
     water Treatment Using  Powdered  Activated Carbon in
     Recirculating Slurry Contactor-Clarifiers",Water
     Pollution Control  Research Series, 17020FKB07/70
     (July, 1970).

15.   Davies,  D.  S.,  and Kaplan,  R. A., "Removal of Refrac-
     tory Organics from Wastewater with Powdered Activated
     Carbon", Journal  VJPCF, Vol.  35, No. 3, p. 442  (1966).

16.   Anon., "Advanced  Waste Treatment Seminar", FWOA Portland,
     Oregon  (February,  1969).

17.   Campman, K.  I.,  "The Effect of  Solids-Contact Treatment
     on PAC Adsorption", unpublished project reports, Sanitary
     Engineering Research and Development Project No. DP
     6066, Eimco Corporation (June,  1969).

18.   Letterman,  R. D.,  Ouon, J.  E.,  and Cemmel, R. S.,
     "Coagulation of Activated Carbon Suspensions",
     Journal  AWWA, Vol. 62, No.  10,  pp. 652-658  (October, 1970)

19.   Corn Products Company, private communication, Argo,
     Illinois (September, 1970).

20.   Knopp, P. V., and  Gitchel,  W. R., "Wastewater Treatment
     with Powdered Activated Carbon Regeneration by Wet Air
     Oxidation", presented  at the 25th Purdue Industrial
     Waste Conference  (May, 1970).

-------
21.   Bloom, R. Jr., Joseph, R. T., Friedman, L. D., and
     Hopkins, C. B. , "New Technique Cuts Carbon Regener-
     ation Costs", Environmental Science and Technology,
     Vol. 3, No.. 3 (March, 1969).

22.   Battelle Memorial Institute, "The Development of a
     Fluidized-Bed Technique for the Regeneration of
     Powdered Activated Carbon", FWQA Water Pollution
     Control Research Series 17020FBD03/70  (March, 1970).

23.   West Virginia Pulp and Paper Company,  "Study of
     Powdered Carbons for Wastewater Treatment and
     Methods for Their Application", FWPCA Water
     Pollution Control Research Series 17020DNQ09/69
     (September, 1969).

24.   Malhotra, S. K. , Parrillo, T. P., and Hartenstein,
     A. G., "Anaerobic Digestion of Sludges Containing
     Iron Phosphates" , Journal of the Sanitary Engineering
     Division, Vol. 97, No. SA5, p. 629  (1971).

25.   Jebens, H. J., and Boyle, W. C., "Enhanced Phosphorus
     Removal in Trickling Filters", a paper presented at
     the 26th Annual Purdue Industrial Waste Treatment
     Conference, Purdue University, Lafayette, Indiana
     (1971).

26.   Ockershausen, R. W. , "Phosphorus Removal-Chemical
     Requirements and Sludge Production", Wastewater
     News, Industrial Chemicals Division, Allied Chemical
     Mooristown, New Jersey (1971).

27.   Lawrence, A. W., and McCarty, P. L., "Unified Basis
     for Biological Treatment Design and Operation",
     Journal of the Sanitary Engineering Division, American
     Society of Civil Engineers, Vol. 96, No. SA3, p. 757
     (1970).

28.   McCarty, P. L., "Energetics and Bacterial Growth",
     presented at the 5th Research Conference, Rutgers,
     The State University, New Brunswick, New Jersey
     (July, 1969).

29.   Schaffer, R. B., Van Hall, C. E., McDermott, G. N.,
     Earth, D., Stenger, V. A., Sebesta, S. J., Griggs,
     S. H./'Application of a Carbon Analyzer in Waste
     Treatment", Journal WPCF, Vol. 37,  No. 11, pp. 1545-
     1566  (1965).
                          199

-------
30.   Rickert,  David,  A.,  Hunter,  Joseph V-,  "Effects
     of Aeration Time on  Soluble  Organics During Activated
     Sludge Treatment", Journal WPCF,  Vol.  43, No. 1, pp.
     134-138 (1971).

31.   Johnson,  R. L.,  and  Baumann, E. R.,  "Advanced Organics
     Removal by Pulsed Adsorption Beds",  Journal WPCF
     Vol.  43,  No.  8,  pp.  1640-1657  (August,  1971).

32.   Snedecor,  George W.,  Statistical  Methods, 5th edition,
     The Iowa  State  University Press,  Ames,  Iowa  (1962).

33.   Bonner, W.  F.,  private communication,  Battelle North-
     west,  Richland,  Washington (1971).

34.   Joyce, R.  S., and Sukenik, V. A., "Feasibility of
     Granular  Activated-Carbon Adsorption for Wastewater
     Renovation",  PHS, AWTR-10 (May, 1964).

35.   Joyce, R.  S. , and Sukenik, V. A., "Feasibility of
     Granular  Activated-Carbon Adsorption for Wastewater
     Renovation:  2", PHS, AWTR-15  (October,  1965).

36.   Ryan,  L.  S.,  "Countercurrent Adsorption for Optimum
     Efficiency",  presented at the 38th Annual WPCF Confer-
     ence,  Atlantic  City  (October, 1965).

37.   Standard  Methods, 12th edition, American Public Health
     Association,  Inc. (1965).
                         200

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                    SECTION XII

             PUBLICATIONS AND PATENTS
Shell, G. L., and Burns, D. E., "PAC-PCT Process for Waste-
   water Treatment", Public Works  (February, 1972).

Burns, D. E., and Shell, G. L. , "Physical-Chemical Treatment
   of a Municipal Wastewater Using Powdered Activated Carbon",
   presented at the 44th Annual WPCF Conference, San Francisco,
   California (October, 1971).  Submitted for publication in
   the WPCF Journal.

Shell, G. L., and Burns, D. E., "Powdered Activated Carbon
   Application, Regeneration and Reuse in Wastewater Treatment
   Systems" , presented at the  6th  Internationa,! Conference
   on Water Pollution Research, Jerusalem  (June, 1972).  Will
   be published in proceedings.

Shell, G. L. , Lombana, L., Burns,  D. E., and Stensel, H, D.,
   "Regeneration of Activated  Carbon", presented at the
   Application of New Concepts of  Physical-Chemical
   Wastewater Treatment Program, Nashville, Tennessee,
   September, 1972.
                          201

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                   SECTION XIII

             ABBREVIATIONS AND SYMBOLS


Abbreviations;

BOD5                     five-day, 20°C-Biochemical Oxygen
                         Demand

COD                      Chemical Oxygen Demand

CT                       Vacuum filter drum cycle time

FT                       Vacuum filter cake form time

ft                       feet

gal                      gallon

g                        gram

GMF                      granular media filter

gpd                      gallons per day

gpm                      gallons per minute

hr                       hour

JTU                      Jackson turbidity units

Kg                       kilogram

S,                        liter

lb                       pound

Log                      logarithm

mgd                      million gallons per  day

mg                       milligram

MG                       million gallons
                          203

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MHF                      multiple hearth furnace

min                      minutes

ml                       milliliter

mm                       millimeter

GSM                      operation and maintenance

AP                       incremental pressure

PAC                      powdered activated carbon

PCT                      Physical-Chemical Treatment

P/I                      pressure indicator

rpm                      revoluations per minute

SCOD                     soluble chemical oxygen demand

SCFM                     standard cubic feet per minute
                         (@ 20°C, sea level)

sec                      second

SG                       specific gravity

sq                       square

SRT                      solids retention time

SS                       suspended solids

STOC                     soluble total organic carbon

TOG                      total organic carbon

Temp                     temperature

W                        vacuum filter dry cake weight

wgt                      weight

2SCC                     two-stage counter-current

Kj_, K2                   constants in Equation  (6)

A, n                     constants in Equation  (7)
                          204

-------
Symbols;

@                        at

°C                       degrees  Centigrade


CQ                       feed organic concentration

C^                       intermediate stage organic concen-
                         tration

Ce                       effluent organic concentration

°F                       degrees  Fahrenheit

M                        powered carbon concentration

X                        organics removed  (CQ-Ce)

GD                       vacuum filter cake dry time

C                        cents

$                        dollars

»                        infinite

<*                        proportional to
                          205

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                    SECTION XIV
                    APPENDICES
                    APPENDIX A

               ADSORPTION OF SOLUBLE
              WASTEWATER ORGANICS ON
                 ACTIVATED CARBON
Adsorption is defined as the concentration of material at
an interface between two phases, one of which has the capa-
bility of dispersing the material.  Applied to soluble waste-
water organic material and activated carbon, adsorption is
the concentration of soluble organics at the water-carbon
interface or the activated carbon surface.  Based on the
chemical and physical properties of the organics, water, and
carbon surface, there is a unique distribution of organics
between the bulk of the water and the water-carbon interface.

There are several theoretical models which have been used to
describe the adsorption phenonmenon.  None have been shown
universally applicable to wastewater-activated carbon systems.
This is not surprising, considering the extremely hetero-
genous nature of soluble organics in wastewaters  (molecular
size, concentration, functionality, etc.) and of activated
carbon  (pore size and distribution, surface functionality).

The emperical Freundlich model has been widely used for waste-
water-activated carbon adsorption systems11*'  ' 2 3' 3 **'3 5.
However, its complete adequacy has not been fully established.
Two major shortcomings are that a maximum adsorption capa-
city  (loading) or any unadsorbable soluble organic fraction
are not accounted for.

When evaluating relative effects of carbon type, pretreatment
and method of contacting, the above shortcomings do not
limit utility of the Freundlich model.

In as much as a laboratory and pilot plant soluble organic
removal data were evaluated by the Freundlich model and that
multi-stage counter-current carbon contacting was evaluated,
the following is a presentation of the model and  the impact
of counter-current contacting.

Figure A-l is a log-log plot of SCOD adsorbed from Salt Lake
City raw wastewater  (after 0.45 micron membrane filtration)
onto Aqua Nuchar A carbon versus equilibrium SCOD concentration.
These data were developed from a laboratory equilibrium isothern
test.
                          207

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                 FIGURE A-1 : ADSORPTION  OF SOLUBLE  COD ON  CARBON

      0.50 T—        I	1	1	1	1	1	r-
      0.40-
      0.30-•
                                    Curve C
                                 infinite Stages
      0.20-•
•a
o>
•S
o
Q
O
O
w
Ul
  o
  <
  Q.
  en
              Curve B
             Two-Stage
          Counter-Current
0.10-



0.08-
                                      Curve A
                                    Single-Stage
X 5  0.06- •
63
O

0)
cc
o
'E

E>
o
      0.04 - •
      0.03-
      0.02-•
                                                   C0 = 41 mg/I
                                        M
                                             =  (3.7 x10'5) Ce2'5
                                               Ambient Temperature
                                               Aqua Nuchar A
                                               pH =  7.6
      0.01'
          10
                      15       20    25    30      40
                             Equilibrium SCOD (Ce), mg/I
                                                       -h—h
                                                       50   60
                                                                80
                                   20!

-------
The data can be described by the Freundlich model,  (Curve A):

         X/M = A Cg                               (7)

Where:   X = Weight of organics adsorbed
         M = Weight of carbon
        Ce = Equilibrium organic concentration in the
             bulk solution
      A, n = Are empirical constants

For the data shown in Figure 60, the constants A and n are
0.000037 and 2.5 respectively, for Ce in mg/J, of SCOD and
X and M in similar weight units.  If it is assumed that there
is no "unadsorbable fraction" of SCOD and that the maximum
possible adsorption capacity of the carbon used is greater
than 0.40 Ibs SCOD/lb PAC  (i.e., X/M at C  for Curve A),
then the equation,                       °

         X/M - 0.000037  (Ce)2*5                   (8)

will describe a single-stage adsorption system as depicted
 in Figure A-2.

From Equation  (8) the concentration of PAC required to produce
any desired system effluent Ce can be computed.  For example,
if a 15 mg/£ SCOD effluent  (Ce) is required and Co is 41 mg/£
SCOD, then from Equation  (8) X = 41-15 = 26 mg/fc SCOD and M
is found to be 26/0.031 = 850 mg/£ PAC.  This high carbon
dosage requirement is due to the low loading, X/M, at a Ce
of 15 mg/fc .  A significantly reduced carbon dosage could be
used if a treatment scheme were used where the carbon was
equilibrated at a higher Ce value.

The two-stage counter-current treatment scheme depicted in
Figure A-3will reduce the concentration of carbon required
to produce a given effluent Ce, compared with the single-
stage system.  This results from the carbon leaving the ad-
sorption system being equilibrated at Ci which is greater
than Ce.

If it is assumed that the chemical and physical characteristics
of the organics  (SCOD) are identical throughout the adsorption
system, the following development will lead to a model of
the two-stage counter-current system:

Given:   X/M = A  (Cj.)n                            (9)
         X'/M = A  (Ce)n                           d°)
         X1 = Ci - Ce                             (ID
         X = C0 - Ce                              (12)
                           209

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          FIGURE A-2 :  SINGLE-STAGE CARBON  ADSORPTION SYSTEM
                                    1
                        Virgin PAC
                        M
              Influent
              SCOD
                                  Single-
                                   stage
                            T
                 Spent PAC
                 M (Loaded @ -£•)
                                      Ce
                                    Effluent
                                     SCOD
                           Where:   1) X  = Co — Ce
                                   2) all units, mg/l
                  FIGURE A-3 : TWO-STAGE COUNTER-CURRENT
                         CARBON ADSORPTION SYSTEM
                  I
     Spent PAC
     M (Loaded at
X/M)
I
Virgin PAC
M
  Cp

Influent
 SCOD
1st Stage
                     Ci
                 Intermediate
                    SCOD
                   2nd Stage
                                      Ce
                                    Effluent
                                     SCOD
                            M (Loaded @  X'/M )
                                            Where:  1) X'  = Cj — Ce
                                                   2) X  = C0 — Ce
                                                   3) all  units, mg/l
                                      2 in

-------
Solving Equation  (10) for A and substitution of its value
in Equation  (9) will result in:
                                                        (13,
Substitution of the values for X and X' from Equations  (11)
and (12) into Equation  (13) will give:
rearranging,  (Ci)n+1 -  (Ce)(Ci)n =  (CQ)(Ce)n -  (Ce)n+1  (14)

For a given wastewater - carbon system  (i.e., C0, A and n),
it is seen that Cj_ is a non-linear  function of Ce.  Therefore,
the two-stage counter-current system cannot be modeled by
a Freundlich equation.  In other words, a log-log plot of
X/M versus Ce for the two-stage response will not be a
straight line in Figure A-l.

Using Equations (9) through  (12) and A, n and C  from Figure
A-l, a trial and error, solution to  Equation 14 was used to
determine the X/M versus Ce relationship for a two-stage
counter-current system.  This relationship is shown as Curve
B in Figure A-l.  The same assumptions made for Equation  (8)
hold for this relationship.

Using a two-stage counter-current adsorption system to produce
an effluent of 15 mg/JJ, SCOD  (for C  = 41 mg/H SCOD) would
require 260 mg/£  of PAC as opposed to 850 mg/S, when using a
single-stage adsorption system.

For an infinite number of counter-current contact stages,
the carbon loading would be constant for any value of C
(Curve C shown in Figure A-l).  The PAC would be equilibrated
with the highest possible C  value  (i.e., C ).   It is theoreti-
cally possible to approach infinite stage efficiency by
employing packed-bed adsorption columns  .  For  such a system
the adsorption relationship shown in Figure A-l would indicate
a carbon loading of 0.40 Ib SCOD/lb PAC.  In summary, the
following carbon dosages would be required for producing a
15 mg/£ SCOD effluent.

# of Counter-Current Contacting Stages     PAC Dosage, mg/£

                  1                              850

                  2                              260

               Infinite                           66
                          211

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Some investigators have used laboratory equilibrium
adsorption isotherms to predict organic removals for
granular carbon column applications.  The normal pro-
cedure used is to extrapolate the equilibrium test results
to the feed organic strength (Co) and observe the organic
removal (X/.M)  at that point.  That this procedure results
in imprecise conclusions, even when precise equilibrium
adsorption isotherm data is used, can be shown by the
following example.  The equilibrium data for Curve A
in Figure A-l were statistically analyzed.   A linear
regression of log X/M on log C& resulted in a 0.99 correla-
tion coefficient,  indicating a very precise fit of the
data.  Extrapolation of the regression curve 13 SCOD units,
to a C0 of 41 mg/£, indicated a X/M loading of 0.40 g
SCOD/g PAC.   However, the 95 percent confidence interval
for this "estimated" value of X/M at Co is  from 0.28
to 0.55 g SCOD/g PAC, indicating that extrapolation of
very precise equilibrium data can result in imprecise
estimates of organic loading.
                         212

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                    APPENDIX B

             WATER QUALITY PARAMETERS
                AND TEST PROCEDURES
TURBIDITY
Turbidity of grab and composite samples were determined with
a Hach Chemical Company, Model 2100 laboratory turbidimeter.
This device is a nephelometer  (light scattering) which was
standardized with a plastic rod.  Turbidity is reported as
Jackson Turbidity Units  (JTU).

Caution must be exercised when interpreting turbidity of
samples containing powdered carbon.  Since powdered carbon
absorbs white light, the normal relationship between
turbidity and suspended solids does not exist.  Figure
B-l shows that powdered carbon concentration is directly
related to the amount of transmitted light but not to
turbidity.

The plant process turbidimeter used as a Keene Instruments
Company flow-through device which measured both scattered
and transmitted light.  The process turbidimeter was routinely
calibrated against the laboratory unit to facilitate comparison
of results.
SUSPENDED SOLIDS

Suspended solids were defined as material retained by a 0.45
micron membrane filter.  The Standard Methods37 procedure for
Nonfilterable Residue was used.  It should be noted that
for the sample sizes used, samples with less than 10 mg/£
SS had weighing errors greater than about 10 percent.

Concentrated samples of chemical-sewage sludge and PAC
slurries were filtered through glass mat filter pads  (Type
GFB) .
PHOSPHORUS

Total Phosphorus was determined by the persulfate method37.
Soluble total phosphorus was defined as  that phosphorus pass-
ing through  a 0.45 micron membrane filter.


                          213

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                               FIGURE B-1  • POWDERED  CARBON:
                      TURBIDITY AND LIGHT TRANSMITTANCE OF SUSPENSIONS
100  _
                                                         Aqua Nucnar A
                                                         in distilled water
                       100
                                      200
                                                     300
                                                                     400
                                           PAC, mg/l

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TOTAL ORGANIC CARBON

Total and soluble organic  carbon  (TOC,  STOC) was  determined
with a Beckman Instruments Company  Total Organic  Carbonaceous
Analyzer.  Prior to analysis,  inorganic carbonates were  re-
moved from the samples by  acidification and  stripping with
inert gas.


CHEMICAL AND BIOCHEMICAL OXYGEN DEMAND

Total and soluble chemical oxygen demand  (COD,  SCOD) and
5-day, 20°C BOD5 were determined  according to  Standard
Methods  .  Total COD was  not  determined on  carbon con-
tactor effluent  samples  since  one mg/£  of  powdered carbon
was found to exert about 1 mg/£ COD.
pH

The pH data  reported  were obtained with a digital read-
out laboratory  pH  meter.   The process  pH meter and re-
corder were  used only to  automatically control acid neu-
tralization  of  lime  treatment effluent.  The plant instru-
ment was  calibrated  against the laboratory unit which was
calibrated with standard  buffered solution.
HARDNESS,  ALKALINITY,  SULFIDES,  IRON,  ALUMINUM,  AND AMMONIA
  NITROGEN

These parameters  were  determined according to Standard
Methods 3 7.
AVAILABLE  LIME INDEX

"The  available lime index" of hydrated lime was determined
using the  procedure presented in "Standard Analysis of
Limestone,  Quicklime,  and Hydrated Lime", ASTM, Part, 9,
1964  C24-58,  p.22.
 OXYGEN

 Oxygen content of furnace off-gases was analyzed by means
 of  a Model 715 Process Oxygen Monitor manufactured by Beck-
 ™ —v^ Tn C't-T-mTi^n-t- ea  TTI/-I   T?n ^ 1 fit-j-n-n  fa 4 1 •Fi-ivn 1 a
man
Instruments, Inc., Fullerton, California
                          215

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TOTAL SUSPENDED SOLIDS,  ASH,  AND VOLATILE SOLIDS

Total suspended solids of carbon slurry samples was de-
termined according to Standard Methods"37.  Ash content
of carbon solids was determined according to the procedure
presented in ASTM, Part 28 (1964),  D1506-59, p. 750.
Volatile solids of carbon samples was determined according
the the procedure presented   in ASTM, Part 28 (1964) ,
D1620-60, p. 811.  Numerous volatile solids determinations
of spent and regenerated carbon samples were, invalid due
to burning of some fixed carbon.  The problem appeared to
be caused by several factors.   The depth of carbon cake
placed in the oven, of up to 1 inch, didn't allow good
heat distribution.  Also, the time the sample was left in
the furnace was critical.  Too long a time resulted in
burning of carbon.  These problems were recognized late
in the study.
JAR TEST PROCEDURE

A six place Turbitrol Jar Test Apparatus, made by the Taulman
Company was employed.  Sample volumes of 1.0 or 1.5 liters
were used.   The following procedure was established as a
"standard":

1.   Measure the wastevater sample volume in a 2-liter graduate
    cylinder and pour into the jar test beaker.

2.   Start rapid mixing of samples at 100 rpm and add desired
    chemical (aluminum, ferric salt or lime) and continue
    mixing  for one (1) minute.  [Note!  If a polymeric floc-
    culation aid was  used, it was added just prior to the
    end of  the 100 rpm mixina period.]

3.   Reduce  mixing speed to 30-50 rpm, making sure that the
    majority of floe  particles are maintained in suspension,
    and slow mix for  10 minutes.

4.   After slow mixing, the samples were allowed to quiescently
    settle  for 10 minutes.  If floe settling rate was to
    be determined, the height of the solids (solids-lima id
    interface)  was noted at appropriate time intervals, or
    the time at which the majority of floe had settled to
    the bottom of the beaker was noted.  In the former case,
    a plot  of height  versus time was made and floe settling
    rate, in inches/minutes, obtained from the. linear portion
    of the  curve after the influence of initial mixing dis-
    turbance was  eliminated.
                          216

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5«  After the 10 minutes of quiescent settling period, a
    supernatant sample was withdrawn one  (1) inch below
    the liquid surface for desired analytical testing
    (e.g., turbidity, pH, total and/or soluble phosphorus,
    total and/or soluble COD, hardness, etc.).

6.  When floe settling rates were to be determined, the
    settled floe were resuspended, after Step 5, by slow
    mixing at 30-50 rpm for 2-3 minutes and the settling
    rate of floe noted again.  The average settling rates
    of the first (Step 4) and second (Step 6) test was reported.

In an attempt to simulate solids-contact treatment, an
alteration of the above procedure was used:

7.  After Step 5  or 6, decant as much clear liquor as
    possible, leaving the concentrated settled solids in
    the beaker.

8.  With the sludge in Step 7, repeat Steps 1 through 7.
    In addition to any or all of the data previously noted,
    measure the depth of sludge present after each contact.

9.  Repeat Step 8 for 4 to 8 times.

A graphical plot of floe settling rate, supernatant turbidity
or other parameters are plotted versus number of contacts
(e.g., number of times Step 8 is repeated plus one) to indi-
cate any effect of simulated solids-contact treatment.

During Phase I of this study, laboratory reagent grade
chemicals were used.  After pilot plant start-up, jar
tests "ere usually conducted using plant chemical supplies.


EQUILIBRIUM ADSORPTION ISOTHERMS

Suitably sized raw wastewater samples were chemically pre-
treated as desired and the following procedure used,  em-
ploying the six place Turbitrol Jar Test Apparatus:

1.  Acid rinse all glassware.

2.  Prepare powdered carbon samples as follows:

    a.  tare five 100 ml beakers.
    b.  add a desired weight of oven dryed  (110°C) carbon
        to each of the beakers and add 26-30 ml of dis-
        tilled water.
    c.  place beakers, covered with watch glasses, on a
        hot plate and bring contents to a boil, then re-
        move from hot plate and cool to   near ambient temperature,
                        217

-------
3.   Add 1.0 to 1.5 liter  samples of chemically pretreated
    and 0.45 micron membrane filtered wastewater to each
    of six beakers and mix at 100 rpm.

4.   Measure the initial temperature and pH of each sample,
    adjusting the pH with concentrated HoSO^ or NaOK if
    desired (normal test  pH was 7.0-7.5).

5.   To the mixing samples, effect a quantitative transfer
    of degassed powdered  carbon (from Step 2), recording
    the amount of distilled water used.  A blank wastcwater
    sample was always run without any carbon.

6.   nix samples for one (1)  hour at 100 rpm  (preliminary
    tests had indicated that at least 95 percent SCOD
    removals was obtained at 15-20 minutes contact time).

7.   At the end of one (1)  hour determine pH and temperature
    of each sample.

8.   Filter a suitable sized sample from each beaker
    through a 0.45 micron membrane filter and determine
    the organic concentration (as measured by COD or TOG
    analysis) .

Standard procedure involved running triplicate organic on-
ccntration tests on the blank and duplicate tests on each
carbon contact sample.  The difference between the blank
and carbon contact organic concentration was considered
adsorbed organics.  The organic removal (mg/£ adsorbed
organics/mg/£ carbon) was plotted versus the equilibrium
organic concentration (mg/£) on log-log graph paper.
GRAVITY THICKENING TESTS

The gravity thickening characteristics of sludge samples
were determined by the following test procedure using the
laboratory test device shown in Figure B-2:

1.   A 24-hour composite of sludge blowdown was obtained.
    If tests were to be run at different initial solids
    concentrations, then a sample of clarifier overflow
    was also obtained for dilution of the sludge.

2.   Pour two liters of representative sludge into the 2-liter
    graduated cylinder for which the volume versus depth
    relationship is known.
                        218

-------
FIGURE B-2 : SLUDGE THICKENING TEST APPARATUS
 Ring Stand-
                                              Picket Thickener
                                                Mechanism
Two-Liter
Graduated
 Cylinder
                        219

-------
3.   Gently mix the contents to insure uniform suspension
    (a rubber stopper on the end of a rod works well).
    If a conditioning chemical was used,  it was added during
    this  gentle mixing.

4.   Immediately insert the picket thickener mechanism into
    the sludge and start it rotating at 6 revolutions per
    hour.   Also,  immediately start a clock timer.

5.   Observe and record sludge interface height (milliliters)
    at appropriate time intervals such that a smooth curve
    is identified.  The test is normally run until no fur-
    ther thickening is observed (8-24 hours).

6.   Remove the picket mechanism and decant as much clear
    supernatant as possible recording the volume of
    thickened sludge.

7,   Filter all of the thickened sludge through a Whatman
    #1 filter paper, using a Buchner funnel,  saving the
    filtrate for a determination of supernatant specific
    gravity.

8.   Dry the filtered sludge at 110°C to constant weight
    to determine  the mass of sludge solids (supernatant
    from Step 6 is assumed to contain no SS) .

9.   Determine thickener loading by the following method:

    a.  Plot sludge interface height versus time as in
        Figure B. 3.
    b.  Draw tangents AB and CD and bisect their obtuse
        angle as  per line EF.
    c.  Construct line GH perpendicular to line EF and
        tangent to the thickening curve.  Curve AH is
        the " working   line" which is used to compute
        predicted solids loading at a given underflow
        concentration.
    d.  Compute predicted full scale thickener loading
        (U) :

        U  - C-*^                        ,15,
              tx
        where:   Co = initial suspended solids con-
                     centration,  Ib  (dry solids)/ cu  ft

                HQ = initial sample depth, ft

                tx = from Figure B. 3, days

                 K = desired scale up factor,  normally about 0.8

                 U = is reported in Ib  (dry solids) per
                     day per square foot of thickener area.

                         220

-------
               FIGURE B-3: TYPICAL  SLUDGE THICKENING CURVE
                        I
I
T
         H
en
'55
o>
o

•S

£
"c


"5
o
0.

0)
O)
•o
3

55
                    E    \

          Desired Full      B
        Scale Underflow
                     24-Hour

                 Settled Volume
                        I
                                    Time
                                  221

-------
The laboratory thickening data was reduced in the follow
ing manner:

1.  A desired underflow concentration in percent solids
    by weight was assumed.

2.  Knowing the specific gravity of the solids  (SGS)
    and supernatant (SG^)  and the weight of solids  (Ws) ,
    the volume of slurry  (Vsjj,) associated with the
    assumed underflow concentration (%S) was computed
    as follows.
    v .  =  a  +  i_                                     (16)
     s£   SGS   SG£

Where:  W  = weight of liquid in underflow
                         g


3.  The sludge pool interface height associated with
    the computed volume of slurry was determined.

4.  The value of tx associated with volume of slurry
    via the working line (AH) in Figure B-3 was
    observed and the predicted full scale thickener
    solids loading (U)  computed using Equation  (15) .

5.  Repeat Steps 1 through 4 for several values of
    assumed underflow concentrations, thus generating
    data to provide a smooth curve of thickener solids
    loading vs underflow solids concentration for a
    given sample of sludge (i.e. , initial solids
    concentration) .

Laboratory thickening test results shown in Figures
23, 26 and 33 were developed in the above manner.
                         222

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VACUUM FILTER LEAF TESTS

Leaf tests were conducted on thickened 24-hour composite
sludge samples.  The filter leaf used had an area of 0.10
sq ft.  The following types of filter media were used
for the various sludges tested:

           Sludge                 Media

        Lime-Sewage           NY-527-F, POPR-853, POPR-852-F,
                              POPR-353-F

        FeCl3-Sewage          PO-801-KF, PO-802-HF

        Alum-Sewage           NY-527-F

        Spent Carbon          MY-432-F, NY-527-F, POPR-P73

The general arrangement of laboratory equipment for con-
ducting the leaf test is shown in Figure B-4. The proce-
dure f olloxved was:

1.  Place about 1.5 liters of a representative sample of
    sludge in a 2 liter beaker.

2.  If conditioning chemicals are used, they are gently
    mixed into the sludge with a large spatula.

3.  Apply a vacuum to the filter leaf, normally 15-20
    inches of Pig.

4.  Immerse the properly sealed and conditioned filter
    leaf into the mixed sludge for a desired cake form
    time (FT) normally 1/2 to 4 minutes.

5.  Remove the leaf from the sludge and maintain the
    vacuum for a desired cake dry time  (0D) normally
    4 to 1/2 minutes.   (Mote!  Dry time used is inversely
    proportional to form time).

    a.  If cake cracks, note the time.
    b.  Note any reduction in vacuum level during dry time.
                          223

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                                           FIGURE B-4 : SLUDGE  DEWATERING  TEST APPARATUS
NJ
 To Vacuum
(15-20" Hg)
                                                                         Flexible
                                                                      Vacuum Hose
                                                                                  2-Liter
                                                                                  Sludge
                                                                                  Sample
 Filter
 Leaf
(0.10 ft2)
                      /" /  Tr  1  ff  / /  /  / /  / /  / /  /  7  7  7  r/7 7  7  /

-------
 6-   Turn off vacuum at end of dry time.

 7.   Mote any difficulty in physically removing cake from
     leaf.

 8.   Place all of cake on a tared evaporation dish and weigh
     immediately.  This will give wet filter cake weight.

 9.   Measure filter cake thickness.

10.   Dry the filter cake to constant weight at 110°C -
     this will give the dry filter cake weight (W).

11.   Determine filtrate volume  (contents of vacuum flask)
     and filtrate suspended solids.

12.   Repeat Steps 3 through 11 for various  (usually 4 or 5)
     combinations of form and dry times.

 From the above data the maximum full scale filter yield
 (Ib dry solids/sq ft-hr) was determined for producing a
 dischargable cake thickness, assuming a desired drum
 submergence and scale up factor  (normally  33 percent
 submergence and 0.8 scale up factor).
                              225

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                    APPENDIX C

         OPERATION OF SOLIDS-CONTACT UNITS


Operation of solids-contact treatment units used in this
stuQv involved monitoring and controlling the inventory of
soiids within the unit.   There  were four zones within the
unit where control was desirable (letters refer to Figure
15) :

I..  Initial mixing zone or draft tube (E) .
2.  Secondary mixing zone or reaction zone (Q).
3,  Clarification zone (J).
4.  Sludge removal zone (I).

Solids monitoring was routinely conducted at all zones ex-
cept the initial mixing zone.  Since the contents of the
initial mizing zone flows into  the secondary mixing zone,
the solids content of the two zones were considered to be
equivalent.  Solids concentrations were determined periodical-
ly by conducting suspended solids tests on samples from the
reaction zone, the three clarification zone sample taps and
sluge blowdown.  Because of the time and expense required
to make suspended solids determinations, an indirect measure
of solids concentration was employed as a routine operational
tool.  This method, referred to as a 5-minute settling test,
consisted of obtaining a two(2) liter sample in a 2-liter
graduated cylinder.  The sample was allowed to settle
quiescently for exactly five (5) minutes and the height of
settled sludge observed.  The percent volume of sludge
settled in five minutes was found to be precisely related
to the slurry concentration.

Two aspects of solids inventory were considered important.
First, the concentration of solids in the different zones
was important.  Generally speaking, a relatively high solids
concentration was desired, in all zones but the clarification
zone   Second, the total solids mass within the unit was impor-
tant.  For a given solids inventory  (mass), the solids flux
through the treatment unit established the mean solids resi-
dence time  (SRT).  The solids flux depended upon flow, feed
solids removed and chemical precipitates removed.  In waste-
water treatment applications, retention  of biodegradable material
for excessively long times may result in anaerobic biological
-,-tivity -iith possible odor and gassification.  Therefore,
                         226

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control of SRT by monitoring and adjustment of solids in-
ventory was desirable.  The concentration of solids and
the volume of slurry establish the solids inventory
within a treatment unit.  For a given volume of slurry,
the higher the solids concentration, the larger the
sludge inventory.  The volume of sludge in the solids-
contact units was approximated by withdrawina samples from
the clarification zone sample taps and noting the highest
tap at which sludge was present.

Operation of the solids-contact unit to control solids
concentration and inventory involved manipulation of the
pumping turbine and sludge rake rotational speeds, and
the sludge blowdown frequency and duration.  Increasing
pumping turbine speed increased the sludge pumpage, or
circulation rate and usually resulted in a more concentrated
suspension being circulated.  Normally, a given pumpage
rate exists above which no increase in solids concentration
or benefit of additional contacting is obtained.  In addi-
tion, there is a maximum turbine tip speed desirable de-
pending on the type of floe solids being handled.  High tip
speeds may shear previously formed floe particles.

The desired sludge rake rotational speed depends upon the
rate of solids circulation and blowdown.  Generally speak-
ing, the higher the pumping turbine speed, the higher the
rake speed required.  In addition, the higher the solids
flux through the treatment unit, the higher the required
rake speed to move settled solids to the sludge outlet.
An interacting factor is the extent to which settled sludge
thickens.  Obviously, the more concentrated the sludge, the
lower the rake speed required to transfer a given quantity
of sludge from the clarification zone to the draft tube in-
let and sludge outlet.  It should also be noted that an
excessive rake speed will hinder sludge concentrating.

Sludge blowdown was accomplished automatically by an adjust-
able timer controlled blowdown valve.  An available static
head of about 16 feet of water provided the driving force
and the automatic control simply activated the sludge valve
air operator.  In order to maximize sludge blowdown solids
concentration, short blowdown durations, or more precisely
small blowdown volumes were used.  Practically speaking,
each blowdown volume should be no larger than the volume of
the sludge thickening cone of the solids-contact unit.  Given
the desirable blowdown duration, the frequency of blowdown
was dictated by the flux of solids through the unit.  For
high flow rates and sludge production, as with lime treatment
or high  carbon dosages, relatively frequent blowdowns were
required.
                          227

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Once a suitable blowdown duration and frequency was
established by operating experience, adjustment of
solids inventory was accomplished by increasing or de-
creasing the blowdown frequency.   The proper solids in-
ventory was obtained when the sludge and 5-minute sludge
volume were at the levels desired.  The blowdown frequency
was then returned to approximately the previously
established  evel.

During start-up of the chemical treatment unit, when solids
are being accumulated, blowdown frequency was neven allowed
to exceed more than two hours.   This prevented accumulation
of raw wastewater grit and probable plugging of "the blowdown
line.

Blowdown from the carbon contactors was commenced almost
immediately after start-up.   The reason for this operatina
procedure was that the desired carbon inventory was added
to the unit prior to start-up.

Solids-contact treatment was defined as operation with
the sludge level approximately 1/2 to 1 foot above the bottom
of the reaction zone cone.  This operation assured sub-
mergence of the draft tube inlet.  When the sludge level
was allowed to assume a depth greater than two to three f  t
above the bottom of the reaction zone cone, operation was de-
fined as being solids-contact treatment with sludge-
blanket clarification.  With the type of solids-contact
unit used in this study, the advantages of sludge-blanket
clarification could be realized.   This was because of the
increasing area clarification zone which provided a more
stable sludge level.  Also of importance was the fact
that all slurry to be clarified passed through the sludge
blanket which existed above the bottom of the reaction
zone skirt.

A summary of typical solids-contact unit operating
conditions used in this study are presented in Table
C-l.
                         228

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            TABLE C-l:   SOLIDS-CONTACT UNITS OPERATING CONDITIONS
Chemical Contactor
TREATMENT:
HYDRAULIC LOADING:
gpm/sq ft
PUMPING TURBINE:
rpm
Tip Speed, ft/sec
SLUDGE RAKE:
rpm
Tip Speed, ft/sec
SLOWDOWN :
Frequency, min
Duration, sec
Solids, g /£
% Vol. of Total Flow
REACTION ZONE:
Solids, g /£
5-min Settled Vol., %
Sludge Pool Depth3, ft
Approximate Sludge Flux,
Lime
pH 10.8

1.0

45
5.3

0.56
0.32

120
10
190
0.5

16
30
0
7000
Lime
pH 10.9

0.9

37
4.4

0.80
0.45

45
20
105
1.0

—
29
0
7900
Lime
pH 11.6

0.4

23
2.7

0.56
0.32

30
15
53
3.5

4
60
0
12000
- FeCl3
120 rng/A

0.7

29
3.4

—
—

60
25
17
0.9

3
45
0
1300
Alum
143 mg/£

0.6

12
1.4

0.26
0.15

40
30
4
3.5

0.6
85
—
1300
Carbon
Contactor
300
mg/fc

5-15

30
3.6

0.30
0.16

60
21
--
—

5-15
50
1-2
3^2500
150
mg/fc

10-20

30
3.6

0.30
0.16

90
10
—
—

10-20
40
1/2-1
«1250
  Ib /MG
a - Depth above bottom of Reaction Zone Cone

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                    APPENDIX D

               GRANULAR M^DIA FILTER
               BACKWASHING OPERATION


The letters in the following procedure refer to Figure 19.

During the filtration mode of operation, the filter influent
(A) and effluent (B)  valves were open and the backwash outlet
(C),  air  (AIR) and check valve  (D) closed.

Backwashing the filter involved an automated sequence of
valve munipulations and time delays.  Backwash was manually
or automatically initiated.  Automatic backwashing was initiated
when the filter bed headloss reached a preset  (adjustable)
value.  The sequence of backwashing events were:

1.  When the pre-set terminal headloss was reached  (normally
    7 ft of H00) ,  the effluent sample pump, AP pressure
    tap solenoids  and polymer feed pump were shut off, the
    influent valve (A) closed and backwash valve  (C) opened.

2.  An adjustable  time delay  (normally 25-30 minutes) allowed
    the liquid level in the filter to lower to within 2-4
    inches of the  filter bed surface.

3.  The effluent valve  (B) was then closed and the air valve
    opened.

4.  Air scour for  0-10 minutes  (adjustable, normally 1 minute)
    at 4-5 CFM/sq  ft.

5.  Air at 4-5 CFM/sq ft and water at 25 gpm/sq ft flowed  sim-
    ultaneously through the filter bed for about  1/2 minute
    until the liquid level in the filter neared the outlet at
    which time the air flow was shut off.

6.  Hydraulic backwashing continued for 5-10 minutes  (adjust-
    able) after which the backwash pump shut off, backwash
    outlet valve  (C) closed and influent valve  (A) opened.

7.  A 1/4 minute time delay was provided to insure that  the
    rubber lined butterfly valve  (D) had firmly seated,  then
    effluent valve  (B) opened allowing the water  level in  the
    influent stand pipe to assume an operating level of  from
    1/2 to 1 feet above the surface of the filter bed.   At this
    time the effluent sample pump, AP sensor system and  polymer
    feed pump were turned on.
                         230
                                         . GOVERNMENT PRINTING OFFICE.197 3 546-509/18

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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
          PHYSICAL-CHEMICAL TREATMENT OF A MUNICIPAL
          WASTEWATER USING POWDERED CARBON
           Burns, D. E.,  and Shell, G. L.
 9. Organization:
    Eimco Processing Machinery Division
    Envirotech Corporation
    Salt Lake City,  Utah
    Environmental Protection Agency report number,
    EPA-R2-73-264, August 1973.
                                                                           17020 EFB
14-12-585
          A municipal wastewater was treated in a nominal 100  gpm pilot plant by chemi-
cal coagulation-precipitation, powdered activated carbon adsorption  and granular media
filtration.  Spent carbon was gravity thickened,  vacuum filter dewatered and thermally
regenerated in a fluidized bed furnace.  Solids-contact units  were used for chemical
treatment and carbon contacting.

Ferric chloride, alum or lime were all found to effectively produce  coagulation and
phosphorus insolubilization. Based on total treatment costs, including sludge disposal,
alum treatment was estimated to be the economic choice for Salt Lake City municipal
wastewater.  Organic removal in the powdered carbon contactors was substantially
enhanced by anaerobic biological activity.   The use of solids-contact treatment units
for carbon contacting resulted in effecting gravity clarification without the use of
chemicals.
The powdered carbon physical-chemical treatment system produced a treated effluent
similar to that expected for biological treatment followed by  tertiary treatment for
phosphorus removal.  Carbon losses of 17 to 60 percent were experienced across the
fluidized bed furnace regeneration system.   The cause of high  carbon losses was
identified as ignition of carbon instead of gas which was injected into the fluidized
bed to scavenge excess oxygen.
 * Waste treatment,  *Adsorption,  *Coagulation,  Activated carbon,  Filtration,
   Solids contact process, sludge treatment
   *Physical-Chemical treatment,  *Powdered carbon,  *Carbon regeneration, Lime, Alum
 Ferric chloride, Sludge thickening,  Sludge dewatering,. Costs
                              05 D

J. F. Kreissl

[ 	 !
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D.C. 20240
Environmental Protection Agency, National
Environmental Research Center-Cincinnati

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