PHOSPHATE REMOVAL BY ACTIVATED SLUDGE

                  -  Amenability Studies at
                       Mansfield, Ohio
                             by

          M. R. Scalf, B. L. DePrater, F. M. Pfeffer,
       L. D. Lively, J. L. Witherow, and C. P. Priesing*
*The authors are respectively, Research Sanitary Engineer, Research
Chemist, Research Chemist, Research Chemist, Research Sanitary
Engineer, and Acting Chief, Treatment and Control Research Program,
Robert S. Kerr Water Research Center, Federal Water Pollution Control
Administration, U. S. Department of the Interior, Ada, Oklahoma.

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                        TABLE OF CONTENTS


     Item                                             Page

ABSTRACT	   ii

INTRODUCTION  	    1

     Experimental Procedures 	    3

RESULTS AND DISCUSSIONS   	    6

     Plant Characteristics  	    6
     Detention Studies 	    8
     Plant Performance	   10
     Aeration Jug Studies	   11
     Plant Manipulation	   27
     Sewage Characterization 	   29
     Microbiological Studies 	   30

SUMMARY	   32

CONCLUSIONS    	   34

RECOMMENDATIONS	   36

APPENDIXES	   37

     Appendix I - Analytical Procedure 	   37
     Appendix II - Plant Operational Data	   42

ACKNOWLEDGMENT	   43

TABLES

  1    Plant Monitoring Data 	   12
  2    Jug Components — Suspended Solids Variation. .   14
  3    Analytical Results — Suspended Solids Variation  14
  4    Jug Components--BOD Variation 	   16
  5    Analytical Results—BOD Variation	   16
  6    Jug Components—Orthophosphate Variation  . .   19
  7    Analytical Results—Orthophosphate Variation    19
  8    Jug Components —Chemical Addition   	   23
  9    Analytical Results—Chemical Addition ....   23

FIGURES

  1    Sewage Treatment Plant,  Mansfield, Ohio ...    7
  2    Dye Detention in Aeration Tanks         ...    9
  3    Effect of BOD on Phosphate Removal      ...   18
  4    Effect of Phosphate Concentration on Removal-   21

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                             ABSTRACT






    Biological phosphate removal was investigated in pilot and plant




scale at Mansfield, Ohio, to determine waste and sludge amenability




and the suitability of the activated sludge plant for a full-scale




research or demonstration project.  Pilot studies on the effect of




MLSS, BOD, phosphate, and hardness concentrations showed only BOD




exerted a significant change in phosphate removal.  The addition of




iron or aluminum salts effectively precipitated the phosphate.




Amenability was established following sludge acclimatization when




high levels of phosphate were removed from the primary effluent




supplemented with a BOD material.  Plant studies prior to and




following manipulation of the operating conditions did not reveal




phosphate removal.  The plant is not suitable for full-scale research




or demonstration studies without design modifications.
                                 11

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                           INTRODUCTION







    This report describes investigations  at  the Mansfield, Ohio,




Sewage Treatment Plant concerned with the removal of phosphate




from municipal sewage by the activated sludge process.  Field




research conducted at San Antonio, Texas, established that high




removals of orthophosphate from the liquid to the suspended solids




were accomplished in the aeration tank.  The efficiency of the




process was found at San Antonio to be controlled by operational




and design parameters including aeration detention times, mixed




liquor suspended solids (MLSS) and dissolved oxygen (DO) concen-




trations, biochemical oxygen demand (BOD) and phosphate loads,




rapid solid-liquid separation, minimum solids detention time in




the final clarifiers, and separate disposal  of the phosphate




concentrates.




    The purposes of the amenability studies  conducted were:




    1.  To determine if biological phosphate removal is feasible




in municipalities of various geographical locations, populations




served, and sewage characteristics by pilot  and plant investi-




gations .




    2.  To locate activated sludge plants in various geographical




regions to be used for demonstration of biological phosphate removal




by operation in accordance with parameters identified at San Antonio.

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     3.  To locate one activated sludge plant of suitable design and




operational flexibility for use as a full-scale research plant to




further specify, define, and optimize the biological phosphate




removal process.




     4.  To verify on pilot scale that biological phosphate removal




can be controlled by the parameters identified at San Antonio




and/or isolate and identify additional controlling parameters.




     Aerated jugs of mixed liquor have been previously shown to




simulate an aeration tank.  Aerated jugs circumvent many of the




limitations exerted by normal operational characteristics in




activated sludge plants, such as control of aeration rate, sewage




flow, suspended solids concentration, and phosphate and BOD load-




ings.  Sludge solids and waste from various points in the secondary




system may be conveniently studied.  Detention time of the mixed




liquor in the aerated jug system is rigidly controlled.  For these




reasons, the method  is  selected  for testing the amenability of the




waste and activated sludge to phosphate removal.




     By deliberate variation of the operational parameters, the




conditions for sludge response and maximum phosphate removal can




be established.  These amenability studies indicate those waste




and activated sludges most readily adaptable and, in conjunction




with plant investigations, aid in specifying operational levels,




design changes, or time for sludge adaptability necessary to attain




phosphate removal in the full-scale plant.

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Experimental Procedures




                          Plant Analysis




     The plant was surveyed to determine pertinent design and




operational characteristics.  Programs of plant sampling and




tracer studies were carried out in addition to jug studies to




determine plant performance.




     Plant records were examined for sewage flow, concentrations




of BOD, suspended solids, and orthophosphate,  other chemical and




physical parameters, and performance characteristics.  Typical




data are presented in Appendix II.  Plant personnel provided




information on sampling practices, analytical procedures,




anomalies of wastes being treated, and peculiarities of oper-




ational control.  The schedule for wasting raw and activated




sludges was determined.  Disposal methods of waste activated




sludge, primary sludge, digester supernatant,  sludge thickener




supernatant, drying bed underflow, and other waste streams were




studied in anticipation of auxiliary, inhibitory, or latent




effects on the phosphate removal process.




     Tracer studies were conducted using Rhodamine WT dye on




aeration tanks and final clarifiers to determine hydraulic




characteristics such as detention, short circuiting, and degree




of longitudinal mixing.




     Grab samples were collected to determine  the phosphate




levels and degree of removal.   These samples were analyzed for

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concentration of orthophosphate and, occasionally, total phosphates,




suspended solids, total oxygen demand (TOD),  nonvolatile organic




carbon (NVOC), and soluble nonvolatile organic carbon (SNVOC).




Chemically fixed samples were shipped to the Robert S. Kerr Water




Research Center at Ada, Oklahoma for total phosphate analyses.




The sample sources were raw sewage, primary effluent, return sludge,




aeration tank influent, aeration tank effluent, and final effluent.




Occasionally, supernatant samples were taken from digestion tanks




and sludge thickeners.  Dissolved oxygen was measured in con-




junction with the sampling program.  If phosphate was being removed,




more detailed sampling on a slug-flow basis was undertaken to




specify the magnitude of removal.







                       Aeration Jug Studies




    Return sludge or mixed liquor from various points in the




secondary system was mixed with primary effluent or raw sewage to




obtain the desired test conditions.  The mixtures were prepared




in five-gallon polyethylene jugs for subsequent aeration.




    A portable air compressor produced the air supply.  Air was




delivered through a manifold containing individual needle valves




and rotometers for each jug.  Polyethylene tee fittings were used




as diffusers.  The air flow was maintained constant throughout




the experiment, except where noted.




    The dissolved oxygen content and the temperature of the mixed




liquor were monitored several times during each run.

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     Samples were withdrawn from the jugs usually at half-hour or




hourly intervals.  Preceding sample collection, approximately




200 ml of mixed liquor was siphoned through a plastic withdrawal




tube for purging and returned to the original jug.  A volume of




100 ml was sufficient for orthophosphate analysis, and 250 ml was




taken when additional analyses were planned.

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                     RESULTS AND DISCUSSIONS







Plant Characteristics




      The Mansfield, Ohio, Sewage Treatment Plant shown in Figure 1




is an activated sludge system which treats an average of 8-9




million gallons per day (mgd).  The system has three tanks for




preaeration, grit, and grease removal; two primary clarifiers;




six aeration tanks; and two final clarifiers.  Approximately 90




and 95 percent of the BOD and suspended solids, respectively, are




removed by these processes.




      Four of the six aeration tanks were in operation during these




studies.  Compressed air at a rate of about 6.0 million cubic feet




per day (mcfd) was supplied to these tanks by one of four blowers.




(Another 0.5 mcfd of air was delivered to the preaeration tanks.)




The aeration tanks were operated as a conventional activated sludge




system; however, design of the tanks also permits operation of a




step aeration process, reaeration, or combinations of these.  Return




sludge rates varied from about 20 to 50 percent of the sewage flow




during these studies.




      The primary sludge and excess activated sludge are pumped to




one of two 0.15 million gallon sludge thickeners.  Thickened




sludge is pumped to three primary digesters and thence to a single




secondary digester.  Sludge from the secondary digester is




dewatered by vacuum filtration for land disposal.  The gas produced

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in the digesters is used as fuel for the boilers and gas engines




that drive the blowers.  Filtrate from vacuum filters and super-




natant from thickeners and digesters are returned to the primary




system.







Detention Studies




    Tracer studies were conducted on two of the aeration tanks on




May 16, 1967.  Aeration Tanks No. 5 and 6 use longitudinally placed




air diffusion tubes while Aeration Tanks No. 3 and 4 use transverse




tubes.  To determine the difference in the hydraulic efficiencies




of the two systems, Tanks No. 4 and 5 were selected for dye




tracing.




    Two liters of 20 percent Rhodamine WT solution were introduced




to the influent end of both aeration tanks, and dye concentrations




were monitored at the effluent ends.  Dye dispersion curves are




presented in Figure 2.




    Both tanks exhibited appreciable short circuiting with 90




percent of the tracer reaching the effluent within the theoretical




displacement time.  Tank No. 4, which has transverse diffusion




tubes, demonstrated a peak tracer concentration at 30 percent of




the theoretical detention time.  Tank No. 5 with longitudinal




diffusion tubes showed a peak concentration at 60 percent of the




theoretical detention time.  The tanks with longitudinal diffusion




tubes were hydraulically nearer plug flow than the tanks with

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                                                                      GO

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10




transverse tubes, but the dye studies indicate that much of the




waste to both tanks receives less than three hours' detention




time.  These conditions are not considered conducive to good




phosphate removal.




Plant Performance




     Examination of plant records indicated that raw waste to the




plant had an average BOD of about 190 mg/1.  Approximately five




hours' displacement time in the preaeration tanks and primary




clarifiers reduces the BOD to less than 100 mg/1 in the primary




effluent.  Further reduction in the aeration tanks and final




clarifiers produces a final effluent with 15 to 20 mg/1 BOD and




suspended solids.




     Dissolved oxygen concentrations were, unusually high in the




raw sewage and in the primary clarifiers, often 1 to 2 and 3 to




4 mg/1, respectively; however, about 6 mcfd of compressed air or




0.7 cubic feet per gallon of waste was insufficient to maintain




dissolved oxygen concentrations above 1.0 mg/1 in the aeration tank




effluent.  As a result of the high primary effluent concentrations,




dissolved oxygen was often significantly higher in aeration tank




influents than effluents.




     The plant was usually operated with mixed liquor suspended




solids between 3,500 and 4,500 mg/1.  The return sludge contained




0.5 percent total phosphate as P on a dry weight basis.  Soluble

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                                                             11


phosphate and BOD loadings were about 0.3 Ib. P/day/100 Ibs. MLSS

and 9 Ibs. BOD/day/100 Ibs. MLSS, respectively.

     Mansfield has a significant amount of industry including some

metal plating.  The waste to the sewage treatment plant formerly was

subject to heavy concentrations of chromium and, on some occasions,

still exhibits appreciable concentrations.  On May 20, 1967, the

raw waste was green, and a grab sample of the primary effluent

contained 50 mg/1 total chromium.  Although the toxicity of this

concentration of hexavalent chromium on activated sludge organisms

has not been found significant,1  other metals associated with the

metal plating industry such as copper, cadmium, and zinc could be

present in concentrations detrimental to biological activity.

     Samples collected and analyzed during approximately 10 days

of studies at the Mansfield Sewage Treatment Plant indicated that

the plant did not remove significant amounts of phosphate either

in the aeration tanks or through the plant as a whole.  Soluble

phosphate concentrations in the raw waste ranged from 2.7 to 4.3

mg/l-P and in the final effluent from 2.1 to 5.8 mg/l-P.  Results

of plant sampling are presented in Table 1.


Aeration Jug Studies

     A series of experiments was devised to test the amenability

of sewage and sludge to orthophosphate removal.  Factors tested

for their effect on the rate and magnitude of orthophosphate
1 U. S. Department of Health, Education, and Welfare, Public Health
Service, "Interaction of Heavy Metals and Biological Sewage Treatment
Processes," Public Health Service Publication No. 999-WP-22.  May
1965.

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                                                                13




removal were:  suspended solids, BOD, and orthophosphate concen-




trations; metal precipitants; and sludge condition.   Results from




these experiments served as a guide to the utilization of plants




for process demonstration.




                    Suspended Solids Variation




     Studies at other activated sludge plants have shown that high




orthophosphate removal occurs within a limited range of mixed liquor




suspended solids concentrations; outside this range percent removal




decreases.




     To determine the optimum suspended solids concentration, a




series of jug experiments was performed on May 17, 1967.  Seven




jugs were prepared for aeration with MLSS concentrations ranging




from 450 to 4,300 mg/1.  Jug components are recorded in Table 2




and results in Table 3.




     The results were reasonably consistent with respect to initial




and final orthophosphate concentration.  There was a tendency for




percent removal to increase (28 to 42 percent) with increasing




suspended solids concentration; however, significant levels of




removal were not obtained, and an optimum MLSS concentration was




not determined.  The remaining jug studies were run at a concen-




tration range considered practical for the Mansfield Plant, i.e.,




3,000 to 3,500 mg/1.

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 14
       TABLE 2.   Jug Components—Suspended Solids  Variation
Jug No.-/
   1
   2
   3
   4
   5
   6
   7
Primary
Effluent
  Final
Effluent
Return
Sludge
     (Liters of Component Added)

  10              4.6            0.4
  10              4.2            0.8
  10              3.8            1.2
  10              3.4            1.6
  10              3.4            2.0

  10              1.3            3.7
= ,Aeration rate for all jugs - 15 liters per minute.
-Mixed liquor from aeration tank influent.
Mixed „ ,
Liquor-
                                15
      TABLE 3.  Analytical Results—Suspended Solids Variation
Jug No.
Aeration 1
Time-Hrs
0 (11:15 am) 2.5
1 1.8
2 2.0
3 1.8
4 1.8
5 1.8
6 1.8
ML Settled
(30 min) 1.8
% Removal 26.5
MLSS (mg/1) 454.0
Note: During the
2
2.5
1.8
2.0
1.8
1.8
1.8
1.8

1.8
26.5
937.0
aeration
3456
Orthophosphate (mg/1 P)
2.8
2.0
2.0
1.8
2.0
1.8
1.8

2.0
35.2
1369.0
period,
2.6
2.0
2.0
1.8
1.8
1.8
1.8

2.0
31-. 1
1794.0
mixed
2.8
2.0
1.8
1.8
1.8
1.6
1.8

1.8
35.2
2251.0
2.6
1.8
1.6
1.6
1.8
1,6
1.6

1.8
37.5
4300.0
7
3.1
2.0
1.6
1.6
1.6
1.8
1.8

1.8
42.1
3154.0
liquor temperature
       increased from 14 to 18°C.  Similarly, dissolved oxygen
       concentration fluctuated randomly between 8.5 and 10 mg/1.

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                                                          15




     Jug No. 6, composed of mixed liquor from the influent end of




an aeration tank, served as a control for comparing removal




efficiency between mixed liquor prepared in the plant and in the




jugs.  The removal efficiency of this jug was most comparable to




that of Jug No. 7, which also had a comparable suspended solids




concentration.




                           BOD Variation




     Studies at other activated sludge plants have indicated




that orthophosphate removal is also affected by primary effluent




BOD concentration.  On May 18, 1967, a set of jugs was prepared to




determine the magnitude of this effect.




     The components of the aeration jugs are shown in Table 4 and




analytical results in Table 5.  The BOD's of the jug components




were not measured directly but were roughly estimated by adding to




each jug a known quantity of Metrecal, which had a BOD of 290 mg/ml.




Generally, the jug studies were based on a substrate or primary




effluent volume of 10 liters with the remaining 5 liters a mixture




of concentrated return sludge and final effluent to provide the




desired solids concentration.  In this experiment, Jug No. 1 was




considered the base with 10 liters of primary effluent estimated to




have a BOD equivalent to the "normal" or annual average, i.e.,




95 mg/1.  Metrecal was then added to the primary effluent for Jugs




No. 2 through 5 to increase the BOD concentrations by a factor of




1.8, 2.3, 3.1, and 4.7, respectively.

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16
              TABLE 4.   Jug Components—BOD Variation
       I/
           Substrate
Jug No.-7 (Est. BOD)
             mg/1
  I
  2
  3
  4
  5
  6
  7
              95
             173
             220
             295
             440
              95
             190
                          ml
 2.7
 4.3
 6.9
12.0
Primary
Effluent
Liters
10
10
10
10
10
~"~" 1 /
4 /
10-'
Return
Sludge
Final
Effluent
Mixed
Liquor
of Component Added
2.7
2.7
2.7
2.7
2.7
—

2.7
2.3
2.3
2.3
2.3
2.3
__

2.3
__
—
—
—
—
15

—
•= -Aeration rates for all jugs - 15 liters per minute.
^Metrecal contains 1.1 rag/ml 0-PO, and BOD of 290 mg/ml.
- Raw sewage used in lieu of primary effluent.
            TABLE 5.   Analytical Results—BOD Variation
                                     Jug No.
Aeration
  Time
  Hrs.

0 (10:00 am)
1
2
3
4
5
ML Settled
 (1 Hour)

% 0-PO,
 Removed      17.9    38.3    50.0    59.0    66.7    16.1    32.4
MLSS  (mg/1) 3440.0  3214.0  3356.0  3434.0  3244.0  4374.0  3346.0

Note:  During the aeration period, mixed liquor temperature increased
       from 14 to 17°C.  Similarly, dissolved oxygen concentration
       increased from 4 to 8 mg/1.
1
2.8
2.5
2.3
2.3
2.3
2.3
2.5
2
3.4
2.5
2.1
2.0
2.0
2.1
2.1
345
Orthophosphate (mg/1 P)
3.6
2.5
2.0
2.0
1.8
1.8
2.0
3.9
2.5
1.8
1.8
1.6
1.6
1.6
3.9
2.5
1.5
1.5
1.3
1.3
1.3
6
3.1
2.8
2.5
2.5
2.5
2.6
2.6
7
3.4
2.5
2.1
2.3
2.1
2.3
— —

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                                                            17







     Jug No. 6 was composed of mixed liquor from the effluent end of




the aeration tanks.  It served as a control for comparison  of plant




and synthetic jug mixed liquor.  The removal efficiency of  this  jug




was comparable to Jug No. 1 which contained no supplemental BOD.




     The raw sewage, with an annual average BOD of 190 mg/1, was




used in Jug No. 7 in lieu of primary effluent to increase the esti-




mated BOD concentration of the substrate to twice that of the




primary effluent.  The orthophosphate removal efficiency in this




jug was most comparable with Jug No. 2 which was supplemented with




Metrecal to produce an estimated BOD 1.8 times that of a "normal"




primary effluent.




     Figure 3 presents percent orthophosphate removal versus esti-




mated BOD concentration for the jugs in this experiment plus three




other jugs aerated during a later study on orthophosphate variation.




Orthophosphate removal generally increased with increased BOD with




the greatest effect at estimated BOD concentrations less than about




300 mg/1.  Thus, benefit from supplemental BOD would be limited




at concentrations above 300 mg/1.  Subsequent jug studies were run




with supplemented BOD loading to obtain maximum phosphate removal.




                     Orthophosphate Variation




     A set of six jugs was prepared on May 19, 1967, to determine




the effect of orthophosphate concentration on its removal at the




Mansfield Plant.  Jug components are given in Table 6 and analytical




results in Table 7.

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                                                                19
        TABLE 6.  Jug Components—Orthophosphate Variation
Ju&
No.

Substrate
(Est. BOD)
mg/1
Metrecal
ml
Primary
Effluent
Return
Sludge
                             Final
                           Effluent
                                                               Mixed
                                                               Liquor
                            mg-P
           Liters of Components Added
 1      95
 2     790          24               10       2.7
 3     480          15       —       5       2.7
 4     440          12       50      10       2.7
 5     440          12      450      10       2.7
 6     440          12       —      10       2.7

-^Aeration rate for all jugs - 15 liters per minute.
•=.City water in lieu of final effluent.
-0.4 liters each of thickener and digester supernatant added.
                             2.3
                             7.3-
                             2.3
                                       15
      TABLE 7.  Analytical Results—Orthophosphate Variation
                                      Jug No.
Aeration
Time-Hrs
0 (11:00 am)
1
2
3
4
5
6
ML Settled
(30 Min.)
3.8
3.4
3.4
2.6
2.5
2.8
3.0

3.0
0-PO  Removed
 (mg/1)
234
  Orthophosphate (mg/1 P)
3.8
3.4
3.4
2.6
2.5
2.8
3.0
3.0
0.8
4.6
2.8
2.1
1.1
0.8
—
0.7
0.7
3.9
2.3
1.0
0.6
0.3
0.3
—
0.5
0.5
1.5
6.6
5.4
5.2
3.1
3.4
—
3.1
3.4
3.2
37
34
31
26
24
—
23
22
5.0
3.8
2.6
2.1
—
1.3
—
—
1.3
2.5
 Removed      21.0      84.8      78.3      53.0      38.8      65.8

MLSS (mg/1) 4494.0    3595.0    3208.0    3464.0    3532.0    3366.0

Note:  During the aeration period, mixed liquor temperature increased
       from 15 to 23°C.  Similarly, dissolved oxygen concentration
       increased from 3 to 8 mg/1.

-------
20




    Jug No. 1 contained plant mixed liquor for removal efficiency




comparison with phosphate and BOD supplemented and synthesized mixed




liquor.  Tap water was used in Jug No. 3 to reduce the orthophosphate




concentration to approximately 50 percent of that in the control




jug, and additional Metrecal was added to compensate for BOD reduction.




Potassium dihydrogenphosphate was added to Jugs No. 4 and 5 to produce




initial soluble phosphate concentrations of about 7 and 35 mg/1  as  P,




respectively.  In addition, 0.4 liter each of thickener and digester




supernatant was added to Jug No. 5.  The high orthophosphate load




was added to simulate potential levels should thickener and digester




supernatant streams be returned to the activated sludge system.




Jug No. 6 served as a control for the study.  Metrecal addition to




Jugs No. 3 through 6 increased BOD loading to the level which gave




highest phosphate removal in the BOD variation study.  Jug No. 2




had twice the quantity of Metrecal used in the control jug to




obtain supplemental data on BOD addition.  Mixed liquor suspended




solids concentrations ranged from about 3,200 to 4,500 mg/1.




    Figure 4 indicates that supplemental orthophosphate (Jugs No,




4 and 5) increased the magnitude of removal but decreased the




percent removal.  Jug No. 3 with decreased phosphate showed decreased




magnitude but increased percent removal, and a better quality effluent




was obtained.  Thus, supplemental phosphate was detrimental to the




phosphate removal process in terms of both percent removal and




effluent quality.

-------
o>
E
    40
    35
    30
    25
UJ

<   20
Q.
V)
o
I
Q.
O
DC
O
                                                            21
                                  -JUG NO. 5
                        234

                       AERATION  TIME  (MRS.)
6
               FIGURE  4 — EFFECT  OF PHOSPHATE  CONCENTRATION

                          ON  REMOVAL

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22
     Jug No. 2 with an estimated substrate BOD of 790 mg/1 removed




about 20 percent more orthophosphate than the control (Jug No. 6)




which contained an estimated 440 mg/1 substrate BOD.  These results




agree with those discussed in the previous experiment and are shown




in Figure 3.






                         Chemical Addition
     Three jugs were set up May 21, 1967, to determine the effect




of iron and aluminum salts on orthophosphate removal.  The mixed




liquor was prepared using primary effluent, concentrated return




sludge, and final effluent.  Jug components are recorded in Table 8




and results in Table 9.




     Jug No. 1 served as a control while Jugs No. 2 and 3 were dosed




with 25 mg/1 of ferric and aluminum ion, respectively.  Aluminum




sulfate and ferric chloride were the chemicals used; pH was not




controlled.  Orthophosphate concentrations of the primary effluent




plus final effluent components before chemical and return sludge




additions ranged from 4.0 to 4.2 mg/1 as P.  After chemical




addition and thorough mixing, orthophosphate concentration was




determined on the contents of Jugs No. 2 and 3 and before the




return sludge was added and on all the jugs just after the addition




of return sludge.

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                                                                23
            TABLE 8.  Jug.Components—Chemical Addition
Jug No. -
Primary
Effluent
Return
Sludge
  Final
Effluent
                Liters of Components Added
                                                     Fe
                                                       4-3
         Al
           +3
                                          mg/1 Added
   1
   2
   3
   4
   5
  10
  10
  10
  103
  10-'
  2.7
  2.7
  2.7
  2.7
  2.7
   2.3
   2.3
   2.3
   2.3
   2.3
25
          25
-Aeration rate for all jugs - 15 liters per minute.  12 milliliters
  of Metrecal was added to all jugs to increase the estimated substrate
  ,BOD to 440 mg/1.
0/8.6 liters of deionized PE plus 1.4 liters straight PE.
-4.2 liters of deionized PE plus 5.8 liters straight PE.
          TABLE 9.  Analytical Results—Chemical Addition
Aeration
Time-Hrs


1
i /
0 (12:30 pm)i/ —
0—'
1
2.5
3.5
4
ML Settled
(30 Min.)
% 0-PO.
4
Removed
4.5
4.7
3.9
3.9
3.8

4.4


15.5

Jug No.

234
Orthophosphate (mg/1 P)

0.7
1.2
0.3
0>24/
0-2-'
—

0.2


95.6

0.4
0.1,.
0.2-3/
—
—
—

0.2


95.6

—
4.5
5.1
4.8
4.8
4.8

5.7


—

5

—
4.2
5.5
4.6
4.4
4.5

5.1


—
MLSS (mg/1)  2628.0     2836.0     2686.0     2740.0

w,Primary effluent plus chemical additive
•5,After return sludge addition.
T/Aeration stopped at 1 hour and ML settled.
- Aeration stopped at 3.5 hours and ML settled.
                                            2694.0
Note;  Temperature of the jug mixed liquor ranged from 14-18 C.
       Initial and final dissolved oxygen concentrations of the
       jug mixed liquor were about 4 and 8.5 mg/1.

-------
24




     Two additional jugs were prepared to determine the effect of




hardness on orthophosphate removal.  Primary effluent was passed




through a cation exchange resin to reduce the hardness.  The mixed




liquor was prepared using concentrated return sludge, final effluent,




and appropriate quantities of unaltered and deionized primary




effluent.  Jugs No. 4 and 5 were prepared with hardness concentrations




of 75 and 250 mg/1, respectively.




     Mixed liquor suspended solids in the five jugs ranged from about




2,500 to 3,000 mg/1.  Metrecal was added to increase the BOD concen-




tration to an estimated 300 mg/1.




     Addition of iron and aluminum resulted in immediate orthophosphate




removal.  Aluminum produced the most dramatic effect in that greater




than 90 percent of the orthophosphate was immediately precipitated.




The jug containing iron removed 83 percent by precipitation and




greater than 95 percent overall after two and one-half hours of




aeration time.  Only 16 percent orthophosphate removal occurred in




the control jug compared to about 60 percent in previous jugs with




similar contents.




     Phosphate removal was not accomplished in Jugs No. 4 and 5.




Both jugs indicated a greater quantity of orthophosphate at the end




of the experiment than at the beginning.  Decreasing the hardness




was not beneficial to phosphate removal.  However, the previous

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                                                             25




high phosphate removals under conditions similar to the control jug




suggest that the slug of metal waste in the sewage on May 20 may




have altered the phosphate removal characteristics of the sludge.




                        Sludge Adaptation




     On June 19, a study was begun to acclimate sludge microorganisms




to environmental conditions suitable for phosphate removal.  The




activated sludge biota was maintained at a concentration of 2,000-




4,000 mg/1 suspended solids in the presence of sufficient supply




of oxygen and food for several days.




     Jug No. 6, which was used as a control during the phosphate




concentration experiment on June 19, was used for the acclimatization




procedure.  Following the initial six hours of aeration when 65




percent of the soluble phosphate was removed, 400 milliliters of




a Metrecal-phosphate-distilled water solution (174 mg/ml BOD;




0.3 mg/ml P) was fed continuously at a rate of 0.5 ml/min, during




overnight aeration.  Decanting the supernatant from the settled




mixed liquor in the jug and the addition of fresh primary effluent




to the sludge were planned for the following day; however, because




the primary effluent contained a high chromium concentration, no




fresh primary was added.  Instead, 600 milliliters of Metrecal-




phosphate-distilled water solution was added during aeration




throughout the next day and again overnight.

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26




    On May 21, the contents in the jug were allowed to settle, the




supernatant was decanted and replaced with 10 liters of primary




effluent and 12 milliliters of Metrecal.  Five hours of aeration at




15 liters of air per minute reduced the soluble phosphate 58 percent




from 5.9 to 2.5 mg/1 as P.  A control jug, with identical primary




effluent but containing fresh sludge, was aerated simultaneously




and removed less than 20 percent of the soluble phosphate.  The




contents of the test jug were again settled, decanted, and charged




with 10 liters of fresh primary effluent.  About 400 milliliters of




the Metrecal feed solution was again added during overnight aeration.




    On May 22, the jug was again decanted and fresh primary effluent




with a 24 milliliter slug of Metrecal was added.  During the sub-




sequent 8 hours of aeration at 15 liters of air per minute, soluble




phosphate was reduced 86 percent from 9.6 to 1.3 mg/1 as P.




    This acclimation test established that the activated sludge




at Mansfield, Ohio, could be highly amenable to phosphate removal




under optimum conditions of operation.  Although increased removals




resulted from operation at increased concentrations of suspended




solids, dissolved oxygen, and BOD in addition to an adapted sludge,




none of these parameters have been sufficiently specified for trans-




lation into plant operating criteria at Mansfield.

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                                                            27




Plant Manipulation




     Following the amenability studies at Mansfield, Ohio, minimal




operational changes were made to induce phosphate removal in the




plant.  Although phosphate removal had not been obtained in the




plant during these studies, high removals were accomplished in




the jugs at high dissolved oxygen concentrations by increasing




the BOD concentration.  Therefore, operational modifications were




designed to increase the BOD load to the plant and increase dissolved




oxygen in the aeration tank effluents.  The changes agreed upon by




the city and plant officials were:




     1.  Increase rate of return sludge and wasting of sludge to




         reduce and maintain mixed liquor suspended solids concen-




         trations at 2,000 to 3,000 mg/1.




     2.  Place all six aeration tanks in service and operate one




         blower at full capacity.  If DO concentrations in aeration




         tank effluents remain below 1.0 mg/1, utilize two blowers




         at full capacity.




     3.  Discharge all digester supernatant and sludge filtrate to




         lagoons to prevent recirculation of phosphate.




     These conditions were to be maintained for about two weeks




before monitoring the plant again for phosphate removal.  If no




removal was occurring, it was agreed that one of the primary

-------
28




clarifiers would be removed from operation to increase the BOD load




to the secondary system.  Following another stabilization period, the




plant was to be monitored again for phosphate removal.




     Grab samples collected on June 21, 1967, two weeks after initial




changes were made, indicated that DO concentrations in the aeration




tank effluents were consistently less than 1.0 mg/1.  Analyses of




samples collected also indicated that no significant phosphate




removal was occurring in the plant.




     Following failure of initial modifications to induce phosphate




removal at Mansfield, two blowers were operated to increase the DO




concentration.  In addition, one of the primary clarifiers was




taken out of service to increase the BOD load to the aeration tanks.




After operation for one month under these conditions, the plant was




again monitored on July 19, 1967.  The DO levels had increased but




were not consistently above 1.0 mg/1 in the aeration tank effluent.




Grab samples indicated that there was still no phosphate removal




through the aeration tanks.




     Following the July 19 visit, both blowers were increased to




their full capacity for a two-week stabilization period.  The last




visit on July 30 and 31 showed dissolved oxygen concentrations at




the effluent ends of the aeration tanks from 0.3 to 5.1 mg/1; how-




ever, grab samples collected continued to indicate no phosphate

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                                                                 29






 removal as noted  in Table  1.  During  this  last monitoring,  two




 previous  days  of  rain had  diluted  the BOD  concentration,  and  the




 raw  and primary effluent exhibited a  yellowish-green  color  of




 chromium  waste.




     Although  dissolved oxygen  concentrations in  all  the  aeration




 tank effluents were not maintained at satisfactory levels for an




 extended  period of study,  it was concluded  that modifications other




 than the  increased air and BOD  would  be necessary for phosphate




 removal.  The  aeration tanks would require  physical modification




 to reduce short circuiting and  increase plug-flow conditions and




 mixed  liquor detention time.




 Sewage Characterization




     A related purpose of  the amenability analytical program was to




 characterize samples from  the various unit processes of activated




 sludge plants with regard  to selected chemical parameters.




Additional samples from an aeration jug study were included in the




 characterization scheme.    These samples were taken from a jug




 study whose operations and constituents were those which resulted




 in maximum phosphate removal.  Primarily, the intention was to




 search for trends or correlatable  functions within or between




various chemical parameters which would be useful in defining




 the phosphate removal process.  Frequently, phosphate removal




realized from jug aeration was higher than that occurring in the

-------
30

aeration tanks.  During such instances, the probability of identify-

ing gross differences of possible significance was greatly enhanced.

     The samples were analyzed with and without solids to differen-

tiate between the quantity of each respective chemical parameter

associated with the solids and that associated with the liquid.

Solids separation was accomplished by first decanting, then sub-

jecting the resulting supernatant to further solids removal using

a Sharpies Super-Centrifuge.  Samples resulting from such treatment

are referred to as centrates of the original sample.

     The samples characterized and the results therefrom will not

be discussed in this report since the basic purpose was for com-

parison with similar data from other studies.  Data and comparisons

are made and reported under separate cover.2


Microbiological Studies

     The microbiological studies conducted at the plants tested for

amenability to phosphate removal were divided into two phases.

Phase I consisted of selection of predominant colonial types, trans-

fer of such to agar slants, and shipment to the Ada laboratory for

identification.  The final portion of this phase is under way.  The

results from Mansfield and the other amenability studies are a separate
2Lively, L. D., et al., "Phosphate Removal by Activated Sludge,
Waste Characterization," Internal Report, USDI, FWPCA, Robert S.
Kerr Water Research Center, Ada, Oklahoma.  1968.

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                                                                31

report.3  Phase II consisted of determining bacterial number by

the total plate count method from various plant and aeration jug

samples.  A correlation was sought relating bacterial population

with phosphate removal and suspended solids concentration.

     There is no apparent relationship between suspended solids

content and bacterial contents.  The bacterial counts remain

essentially constant through the aeration tanks and during the

course of the jug runs.  Bacterial counts and phosphate removal,

if related, were not detectable by the methods employed.
3Moyer, J. E., et al., "Survey of Activated Sludge Treatment Plants
for Predominant Bacterial Types," Internal Report, USDI,  FWPCA,
Robert S. Kerr Water Research Center, Ada, Oklahoma.   1968.

-------
  32
                             SUMMARY







     Studies conducted at the activated sludge plant of Mansfield




Ohio, from May 16 to May 26, and follow-up investigations on three




other occasions after plant manipulation during June and July 1967,




revealed no phosphate removal by the plant.




     Dye tracer studies conducted on the aeration tanks showed




appreciable short-circuiting, especially those tanks containing




transverse air diffusers.  Air supplied to these tanks during the




experimental periods was insufficient to maintain dissolved oxygen




concentrations consistently above 1.0 mg/1.




     The industry in Mansfield,  including metal plating, subjected




the waste influent to occasional high concentrations of metals.




One grab sample had a chromium concentration of 50 mg/1 indicating




the presence of associated metals of the metal plating industry




such as copper, cadmium, and zinc which could be detrimental to




biological activity.




     The plant usually operated within a mixed liquor suspended




solids concentration range of 3,500 to 4,500 mg/1, and the return




sludge rate varied from about 20 to 50 percent of the sewage flow.




Air supplied averaged approximately 0.7 cubic foot of air per gallon




of waste treated.

-------
Min.
:.7
1.1
1.9
Max.
4.3
3.8
5.3
Min.
4.4
3.7
4.5
Max.
9.9
13.4
7.3
(.Urtho/Total)
0.5
0.5
0.7
                                                              33

     Phosphate concentrations in the waste streams during the study

were:


Source       Ortho (mg/l-P)     Total (mg/l-P)   Average Ratio
             Mil

Raw Sewage  2.7

Pri. Effl.  2.1

Final Effl. 3.9

     The return sludge contained 0.5 percent total phosphate as P

on a dry weight basis.  Soluble phosphate and BOD loadings were

0.3 Ib. P/day/100 Ibs. MLSS and 9 Ibs. BOD/day/100 Ibs. MLSS,

respectively.

     Pilot studies were conducted in aerated jugs to determine the

effects of varying concentrations of MLSS, BOD, phosphate, hardness,

and iron and aluminum salts.  With the exception of iron and

aluminum salts which precipitated the phosphate on contact, only

BOD concentration exerted a significant effect on phosphate removal

within the ranges studied.

     Phosphate removal was increased in the aeration jugs from less

than 20 percent where no supplemental BOD was added, to almost 85

percent when about 700 mg/1 of supplemental BOD in the form of

Metrecal was added to the substrate at the start of the aeration

period,

     An "acclimation" process produced a sludge which, with the

addition of BOD,  removed 86 percent of the soluble phosphate during

an 8-hour aeration period.

-------
34






                            CONCLUSIONS







1.  The Mansfield, Ohio, activated sludge plant, at the time of




    these investigations, was not removing phosphate.




2.  The aeration  tanks exhibit a high degree of short-circuiting




    which is not  conducive to good phosphate removal.




3.  The aeration  tanks with transverse diffuser systems exhibit




    greater short-circuiting than those tanks with longitudinal




    diffusers.




4.  The air supplied and the hydraulic conditions in the aeration




    tanks are insufficient to maintain dissolved oxygen concentrations




    necessary for phosphorus removal.




5.  The detention time in the preaeration and grit tanks and primary




    clarifiers is long, and the primary effluent BOD may contain




    insufficient  substrate for the development and maintenance of




    a phosphate removing sludge.




6.  The phosphate removal in jug studies is greatly increased by




    the addition  of substrate in the form of Metrecal.




7.  Varying mixed liquor suspended solids between about 1,300 and




    4,300 mg/1 has little effect on phosphate removal.




8,  Within the ranges studied, increased hardness concentrations




    did not significantly increase phosphate removal.




9.  Iron and aluminum salts were very effective in precipitating




    phosphate with aluminum having the most immediate effect.

-------
                                                             35





10.    The failure to induce phosphate removal in the plant by limited




      operational modifications was attributed to  (a) the poor




      hydraulic conditions in the aeration tanks,  (b) failure to




      maintain sufficient DO in the aeration tank  effluent,  (c)




      insufficient BOD load to the aeration tanks, and  (d) the




      possibility that slugs of metal wastes were  detrimental to




      biological activity.

-------
36




                         RECOMMENDATIONS






     The Mansfield,  Ohio Sewage Treatment Plant is not recommended




for demonstration of phosphorus removal without design modifications




and operational changes.  The changes necessary prior to such utili-




zation are:




     1.  Convert the six single-pass aeration tanks into two




         three-pass  tanks,  all with longitudinal diffusers,  to




         improve hydraulic  efficiency.




     2.  Increase the air supplied to the aeration tanks,  if




         necessary after tank modification,  to maintain aeration




         tank effluent dissolved oxygen concentrations at  2  to 4




         mg/1.




     3.  Prevent return of  sludge thickener  supernatant and




         digester supernatant to the system  unless phosphate




         is chemically precipitated beforehand.




     Another amenability study would be desirable before undertaking




a full-scale program.

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                                                                 37

                            APPENDIXES

                            Appendix I

                      Analytical Procedures

                                by

                          B.  L.  DePrater

Sample Preparation

     Samples collected for analyses in  the field were processed as

outlined in the respective analytical test procedures.

     Samples returned to the Robert S.  Kerr Water Research Center

are referred to as whole,  centrate, whole fixed, and centrate fixed.

     The following table lists the treatment each type received prior

to shipment to Ada.

                                         Treatment
Sample

1.  Whole

2.  Whole Fixed


3.  Centrate
     4.  Centrate Fixed
Shipped as is with no treatment.

Shipped as is plus 1 ml cone, sulfuric
acid per liter of sample.

The sample was passed through a Sharpies
motor driven laboratory model continuous
centrifuge, equipped with a clarifier
bowl driven at 23,000 rpm.  The sample
was delivered to the centrifuge by a
peristaltic pump at a feed rate of 150
ml/min.  The bowl was cleaned and rinsed
with distilled water after each sample.

The centrate sample plus 1 ml/1 cone.
sulfuric acid.
     All samples were shipped in either 250 ml polyethylene bottles

or 1,000 ml cubetainers.*
*Hedwin Corporation, 1600 Roland Heights Avenue,  Baltimore,  Maryland
21211.

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38

Chemical Tests

     1.  Orthophosphate

         In the field, initial samples for orthophosphate were

filtered immediately using Schleicher and Schuell No. 588 paper.

Subsequent analysis by the stannous chloride procedure in Standard

Methods5 included the use of a B&L Spectronic 20 at  690my.

         A continuous automatic sampling device, built specifically

to support jug-study phosphate analyses, supplied whole samples to a

Technicon  AutoAnalyzer platformed according to the method by Gales and

Julian.  The Manifold and reagents were modified, however, to more

closely approximate Standard Methods.5  The arrangement, in order of

sequence, was as follows:

         a.  A six-port peristaltic pump circulating jug mixed liquor

continuously.

         b.  An open-shut solenoid valve system selectively sampling

the flow from a T-connection in each circulating jug line.

         GO  A stepping relay alternately activating one of six jug

sample solenoids or the solenoid to a distilled wash water supply.
5Standard Methods for the Examination of Water and Wastewater, 12th
Edition, p. 234-236.  1965.

6M. E. Gales, Jr., and E. C. Julian, "Determination of Inorganic
Phosphate or Total Phosphate in Water by Automatic Analysis."
Presented at the 1966 Technicon Symposium on Automation in
Analytical Chemistry.

-------
                                                                39




         d.  A master timer regulating the stepping relay at




two-minute intervals.




         e.  A Technicon proportioning pump providing the flow




of samples and distilled water to a Technicon continuous filter.




This pump also diluted filtered samples with distilled water in




the ratio of 1:40, respectively.




         Whole plant samples were run on the Technicon AutoAnalyzer




using a Technicon Sampler II and a continuous filter with samples




reaching the filter within thirty minutes.  No significant ortho-




phosphate bleedback occurred in unfiltered samples during this




period.




     2.  Total Phosphate




         Analyses were conducted on fixed whole samples at the




Ada laboratory within 15 days of sample collection.  Initially




whole samples were blended for three to five minutes in a Waring




Blendor and then analyzed by the persulfate procedure of Gales




and Julian.6  The procedure was modified to more closely approxi-




mate the Standard Methods5 procedure for orthophosphate in that




the samples were neutralized after digestion.  Also the manifold




design and reagents for the AutoAnalyzer were adjusted to deliver




approximately the amount of reagents per sample outlined by




Standard Methods.5

-------
40

     3.  Total Carbon and Total Nonvolatile Organic Carbon

         Whole samples were run in the field using the methods of

Van Hall, Safranko, and Stenger7 and Van Hall,  Earth,  and Stenger.?

A Beckman Carbonaceous Analyzer was used.  Preliminary homogeni-

zation with a Waring Blendor provided representative syringe

sampling of whole samples.  As the whole acidified sample was

further purged with nitrogen gas for five minutes, results were

reported as total nonvolatile organic carbon.  Acetic  acid stan-

dards were used for instrument calibration.

     4.  Total Oxygen Demand

         Whole samples were run by the method of Stenger and Van

Hall^ using the instrument and techniques described therein.  Pre-

liminary homogenization with a Waring Blendor was practiced.

Sodium acetate standards were used.

     5.  Total Hardness

         In the field, hardness was determined by EDTA titrimetry

according to Standard Methods, Method B, p. 147-152.5
7C. E. Van Hall, J. Safranko, and V. A. Stenger, "Rapid Combustion
Method for the Determination of Organic Substances in Aqueous
Solutions," Anal. Chem. 35:3, p. 315-319.  1963.

8C. E. Van Hall, D. Barth, and V. A. Stenger, "Elimination of
Carbonates from Aqueous Solutions Prior to Organic Carbon
Determination," Anal. Chem. 37:6, 769.  1965.

9V. A. Stenger and C. E. Van Hall, "Rapid Method for Determination
of Chemical Oxygen Demand," Anal. Chem. 39:2, 207.  1967.

-------
                                                             41


    6.   Total Chromium

         Chromium was determined in the field using the procedure

of Standard Methods5  (Total Chromium Method B, p. 474-479).

         Color was measured photometrically on a Beckman Model B

Spectrophotometer.

Physical Tests

    1.   Solids

         Tests for total suspended and total volatile suspended solids

were conducted according to Standard Methods  (Methods C & D, p. 424-

425).  Reeve Angel 2.4 cm glass fiber filters grade 934AH were used

in lieu of asbestos mats.  Gooch crucibles were fired at 600°C, cooled,

and the mats placed in the crucibles and dried at 103 C for at least

1 hour before initial weighing.  At intervals crucibles with filters

were subjected to 600°C furnace temperatures to check for weight loss

due to the filter.  Total and total volatile solids were determined

according to Standard Methods5 (Methods A & B, p. 423-424).

    2.   Dissolved Oxygen

         Measurements were made in situ with a YSI Model 51 Oxygen

Meter equipped with a Model 5103 oxygen/temperature probe.  The meter

was calibrated against the Azide Modification of the Winkler Method

described in Standard Methods5(Method A, p. 406-410).  The meter was

also calibrated against saturated air at the temperature at the test

medium.
NOTE;  Mention of products and manufacturers is for identification
only and does not imply endorsement by the Federal Water Pollution
Control Administration or the U. S. Department of the Interior.

-------
42
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                                           oo *"H  oo in
                                           oo CM  r-» <•  i   i
                                             «  .,   *  «  i   i
                                           o^ ro  ro co
                             **-!

                             C
                                           vO
               I
               a
                             3
                             00

                             c

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-------
43
                         ACKNOWLEDGMENT




     Grateful acknowledgment is given to many individuals who




significantly contributed to this study.  The major portion of




this work was made possible through the cooperation of the City




of Mansfield, Ohio.  Particular recognition is given to Mr. David




Conant, Jr., Manager, Sewage Treatment Plant, for invaluable




assistance during the field phase of these studies.  Appreciation




is also expressed for the cooperation of Mr. George R. Cunitz,




Engineer-Manager of the City of Mansfield, and Mr. Merle Lutz,




Assistant Manager of the Sewage Treatment Plant.  Members of the




Robert S. Kerr Water Research Center staff who participated




extensively were Mr. J. F. McNabb, Microbiologist; Mr. B. D. Newport




and Mr. M. L. Cook during field investigations; and Mr. K. F. Jackson




and Mr. B. Bledsoe during laboratory phases.

-------