-------
                                                OOOR69018
                CASE HISTORIES:

  IMPROVED ACTIVATED SLUDGE PIANT PEKFOHMAN'JE

                      BT

              OPERATIONS CONTROL
              A. W.  West - P.E.
              Sanitary Engineer
         Field Investigations Branch
        Division of Technical Support

FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
       U.S. DEPARTMENT OF THE  INTERIOR
               CINCINNATI,  OHIO
                 APRIL 1969
                        ction Agency,

-------
3&OTSCTIGU AGBiK

-------
                              CASE HISTORIES:
                IMPROVED ACTIVATED SLUDGE PLANT PERFORMANCE
                                    BY
                            OPERATIONS CONTROL
                               INTRODUCTION



       Firsthand operation experiences during Federal Water Pollution Con-

trol Administration Technical Assistance Projects at the Sioux Falls,  South

Dakota, and the St. Louis, Missouri, activated sludge treatment plants

document once again the excellent final effluent quality that can be pro-

duced "by presently available secondary treatment processes.  In these two

cases, final effluent quality was greatly improved by modifying process

control procedures, and at practically no extra cost.  In one case,  99 per-

cent BOD and suspended solids removals were obtained with readily avail-

able present day treatment processes and equipment.

       Activated sludge plants can produce final effluents containing con-

siderably less than 10 mg/1 suspended solids and 5-day biochemical oxygen

demand (BOD).  Overall reductions of 95 to 99 percent are possible.   Some

of these past experiences, especially those at Sioux Falls confirm that

there is no need to approve,  or accept, secondary treatment systems  capable

of producing only ^5 percent reductions.

       Certain essential requirements must be met,  however,  if consistent

effluent excellence is to be expected.  The treatment plant must be  proper-

ly designed with adequate built-in capacity and flexibility; plant charact-

eristics must be appropriate to the incoming load;  and the process must be

skillfully controlled by conscientious qualified operators.

-------
                                                                          2.




       Performance of the Sioux Falls and St. Louis plants was measured




"by the routine BOD and suspended solids reductions determined by the plant




chemists.  Though a detailed study of nutrient removals was not included,




a few scattered tests indicated only low level phosphorus removals ranging




from about 0 to 35 percent.  No appreciable nitrification or denitrlfication




was observed.




       Operational control adjustments were predicated upon the results of




the following tests:




            1.   Mixed liquor and return sludge specimens were




                 centrifuged to determine sludge concentration




                 and distribution.




            2.   Mixed liquor sludge settling and compaction




                 rates, observed in a laboratory cylinder,




                 revealed sludge condition.




            3-   The measured sludge blanket depth in the




                 final clarifier revealed process balance.




            h.   Air discharges were regulated according to




                 measured dissolved oxygen concentrations in



                 the aeration tanks.

-------
                                                                         3-
                 METROPOLITAN ST. LOUIS SEWER DISTRICT - MSP

                   Coldwater Creek (Activated Sludge Type)
                         Wastewater Treatment Plant
A.     PLANT DESCRIPTION

            The conventional standard rate activated sludge plant had a

       rated capacity of 21.0 MGD with 6 aerators, each of which is equip-

       ped with spiral flow pattern air diffusers and k final clarifiers,

       each equipped with plow-type sludge scrapers.

B.     PLANT PERFORMANCE

            The pollutional strength of the final effluent from this plant

       was reduced to otic-fourth of its former strength by modified opera-

       tional control.  The wholehearted support and cooperation provided

       by management, the recently appointed superintendent and the entire

       operating group contributed greatly to the success of this project.

            Previously,  the average final effluent contained ho mg/1 of BOD

       and 92 mg/1 of suspended solids.  The process responded favorably

       to modified control procedures,  and during the last week of the pro-

       ject,  the final effluent averaged 9 mg/1 of BOD and 16 mg/1 of sus-

       pended solidc.

            Other "before and after"  characteristics  are shown in the fol-

       lowing Table 1:

-------
                                 TABLE NO.  1

                      SUSPENDED SOLIDS & BOD REMOVALS

                                   at the

                           Coldwater Greek S.T.P.


                                                      Before     After

Suspended Solids
     Saw                 fao/l)                        173        198
     Primary Effluent    (mg/l)                        155        1^2
     Final Effluent      (mg/l)                         92         l6
     Activated Sludge deduction                         UO^        8956
     Total Plant Reduction                              U6>        92$

      BOD
     Raw                 ( rag/I )                         150        l62
     Primary Effluent    (rng/l)                         152        130
     Final Effluent      (mg/l)                          ho        _ g^
     Activated S.ludge Reduction                         l^k        93/J
     Total Plant Reduction                              73%        9^%

       IMPROVED OPERATIONAL CONTROL

            1.    Number of Aerators and Glarifiers in Service

                 Before changes  were made,  the activated sludge looked

                 old arid septic, smelled "bad,  and was settling too

                 rapidly.   Too many clarifiers,  and too few aerators

                 were in service.   One of the  four clarificrs was taken

                 out of service  and one additional aerator was placed

                 in service to augment the  three operating units.  The

                 computed characteristics of the 3 aerator - k clarifier

                 vs. the Ij- aerator - 3 clarifier activated sludge systems

                 were changed as shown in the  following Table 2:

-------
                    TABLE NO. 2

          COMPUTED PLANT CHARACTERISTICS

              Coldwater Creek S.T.P.



                                       Fo_rrne_r     Changed To

     Aerator-Claririer Combination      3A/'4C       ':A/3C

     Mixed Liquor Suspended Solids      7,200       3,]i-00

     Return Sludge Flow (/0 of Sew-
     age Flow)                             S3          30

     Flow Capacity (MGD)                 13.

     Aerator Detention (HRS)              3.0         5.;4

     Claririer Dcte^lioi (ESS)            2.0         2.0

     The h aerator - 3 clarifier combination provided a more

     practical theoretical mixed liquor suspended solids con-

     centration demand of approximately 3>'-i-00 rng/1 as opposed

     to the impractical 7>200 mg/1 demand of the former 3

     aerator - h clarifier combination.  Similarly, calcu-

     lations indicated that the revised plant combination could

     "be operated at 30 percent return sludge, whereas the old

     combination required in excess of 90 percent return sludge.

2.    Control Tests

     The standard 1-liter graduated cylinders were replaced by

     the larger diameter (5" dia. x 6" deep) 2- liter Mallory

     Direct-reading Settleometers for mixed liquor sludge

     settling rate determinations.  Each mixed liquor specimen

     was settled for one hour, and the volume of the cylinder

-------
                                                        6.




occupied by the settled sludge was recorded at every




5-minute interval during the first half-hour aixi at




every 10-minute interval during the second half-hour.




Mixed liquor and return sludge specimens were centri-




fuged for 15-rainute periods to determine their rela-




tive densities and the solids distribution ratios.




Sludge concentration characteristics were computed from




the settling and ccntrifuged tests.




The thickness of the settled sludge "blanket in the




fi.iul clarificra was Pleasured periodically with a




sludge blanket finder.




The dissolved oxygen concentration in the aeration tanks




was measured to indicate air discharge requirements.




Relative final effluent quality trends were determined




rapidly with a turbidimeter.




Control Ad,''ustr.ients




In this case operations and effluent quality were im-




proved "by:




         Increasing the excess sludge wasting rate to




reduce sludge age.




         Reducing the return sludge pumping rate to con-




form to the requirements of lowered mixed liquor sludge




concentrations.




         Increasing the air supply and then adjusting




it to try to maintain "between 1.0 and 3- mg/1 of dis-




solved oxygen in the aeration tanks.

-------
                                                                          7.




D.     FAVOiUBLE FEATURES AT EXISTING PLANT




            The extensive improvements would not have been possible without




       the dedicated and effective cooperation provided by the Superintendent




       and operators.




            Adequate tank capacity in multiple aerator and clarifier units




       were available to permit changing the process characteristics and to




       accommodate present dry-weather flows.




E.     PLANT DEFICIENCIES




            1.   Plow-type sludge scrapers increased the settled sludge




                 detention time in the anaerobic environment of the final




                 clarifiers.




            2.   "Spiral flow" air diffuser placement limited mixing and




                 oxygen transfer rates in the aerators.




            3.   Hydraulic short circuiting plus strong velocity currents




                 in final clarifiers were at times directly responsible




                 for carrying increased amounts of suspended solids to the




                 final effluent.




            k.   No scum removal devices were provided for the final clari-



                 fiers.




            5.   Return sludge capacity was limited.




            6.   Meter problems, and lack of remotely controlled mechani-




                 cal valve actuators or automatic sensor-controllers lim-




                 ited process controllability.




F.     FUTURE POTENTIAL




            The problems encountered at this plant indicate that the pollu-




       tional load in the effluent can be cut in half once again when the



       more significant constricting plant deficiencies are corrected.

-------
                                                                         3.
                          SIOUX FALLS, SOUTH IAKOTA
A.     PIANT DESCRIPTION
            Approximately 3-5 mgd of strong 2,500 rag/1 BOD meat-packing
       waste plus 6.0 mgd of normal domestic sewage were treated at Sioux
       Falls.  The packing plant waste was settled, pretreated in high-
       rate trickling filters, and then combined with raw domestic sev-
       age for discharge to primary clarifiers.  The activated sludge
       system treated the settled domestic sewage and polished the pre-
       treated industrial wastes.
            The aeration taaks, which operate as "complete-mix" u:iits,
       ai-v provided with effective "turbine" type aerators.  The "rim-
       flow" final clarifiers are equipped with appropriate suction type
       sludge removal mechanisms.
B.     PIAHT PERFORMANCE (Fall of 1968)
            During the October and November 1968 technical assistance
       project, when the plant is severely overloaded, the pollutlonal
       strength of the final effluent was reduced to about one-half of
       its forncr strength by modified operational control.
            During the summer months, when plant loadings are within
       design capacity, the superintendent achieves remarkable reduc-
       tions through the plant.
            During late fall and early winter,  however, industrial waste
       loads increase with the increased kill at the meat-packing plant,
       trickling filters freeze, the activated sludge unit is greatly
       overloaded, and effluent quality suffers.

-------
1.   ijiqnii'ioc. it Loading Character!sti cs

     The more significant Gctobcr-JIoveriber 1968 loading

     characteristics that influence performs.ice of this

     plant veri shown on Table 3.  Aerator loadings; \rhich

     vere high at all times, averaged 11? pou.ids of BOD per

     1,000 cubic foot of aerator.  The vacte load to acti-

     vated sludge solids ratio usually exceeded 1.0 pound

     of BOD per povid of mixed liquor solids.  (lTon,
-------
                                                             10.




2.   Control Tests




     Here again settlometers, centrifuges,  sludge blanket




     finders and turbidimeters were introduced to detect




     sludge conditions, process balance and operational




     control demands.




3.   Control Adjustments




     The effluent quality was improved by increasing the




     return sludge percentages from about 30 percent to




     as high as 200 per cent and by "tight-rope"  sludge




     wasting control to increase mixed liquor sludge con-




     centrations from about 1,000 to 3>000 mg/1 without




     upsetting the aerators and clarifiers.  The  plant




     was greatly overloaded and more aerators and clari-




     fiers, especially aerators, arc needed to handle the




     organic overload to the activated sludge system.




H.   Resultjs




     Final effluent quality produced in 1968 is compared




     with that obtained during the fall of 1967 when in-




     fluent loadings were similar (Figures 1 and  2).



     The average BOD had been reduced from 30 to  20 mg/1




     and the average suspended solids conce nitration from




     35 to Ik mg/1.   The pollutional loading to the Big




     Sioux River had been reduced almost one-half by the




     modified control procedures.

-------
                      10          SO         90
                %  OF  TIME  EQUAL TO  OR LESS  THAN

FIGURE  1  SIOUX  FALLS. S.D.   FINAL EFFLUENT  5 DAY  B.O.D.  MONTHS

             OF  OCT. a NOV.  1967 VS.  1968.
                     10         90          90
               * OF  TIME  EQUAL  TO  OR LESS THAN
99
FIGURE 2   SIOUX  FALLS, S.D.  FINAL  EFFLUENT  TOTAL  SUSPENDED

            SOLIDS   MONTHS  OF  OCT. ft  NOV.   1967  VS.  1966.

-------
100

                         10
                      %  OF
  50         90        99
EQUAL TO OR LESS  THAN
                          TIME

FIGURE  3- SIOUX FALLS. SD   5 DAY  BOD REDUCTIONS
                     PLANT  (AUG. 8 DEC.,1967).
                                                        THROUGH  ENTIRE
100
                         10          50         90
                    % OF TIME EQUAL  TO OR LESS  THAN
  FIGURE 4  SIOUX FALLS ,S.D.  SUSPENDED SOLIDS  REDUCTIONS
                 ENTIRE  PLANT (AUG. 8 DEC., 1967).
                         THROUGH

-------
   90


   8O


   70

v
e  eo
d
CD
z
Lu
   50
>-  40
Ul

t  30
LJ
   20
   10
73
                                                      15
                  I         10          5O          90        99
                      %  OF  TIME  EQUAL  TO OR LESS THAN

     FIGURE 5    SIOUX  FALLS , S.D. FINAL EFFLUENT  5 DAY  BOD  MONTHS

                            OF  AUG. 8  DEC.. 1967.
                  I         10          50          90
                      %  OF  TIME EQUAL  TO OR LESS THAN
       99
     FIGURE  6  SIOUX FALLS, S.D.  FINAL EFFLUENT  TOTAL  SUSPENDED  SOLIDS
                         MONTHS  OF AUG. 8 DEC.,1967.

-------
                                                                 11.

IAIIT I-KRFO.MMCE (Su>nraor I(}6j)

    The feature story at this plant relates to the Superintendent's

    ability to obtain 99 percent BOD and suspended solids reductions

    during summertime when the plant loadings remain witMn desired

    capacity.

    Percent .reductions during the summer (August) and the winter

    (December) are illustrated on Figures 3 and k, and the effluent

    quality (in tevtns of BOD and suspended solids concentrations) is

    shown on Figures 5 and 6.

    During August 19&7 the combined BOD of the; combined industrial

    a-id domestic wastes averaged 900 mg/1 and was reduced to an aver-

    age of 9 mg/1 iu the final effluent.  Similarly, total suspended

    solids were reduced from 6^0 to 5 rog/1.  These are remarkable

    reductions: especially in view of the high BOD loadings shown in

    Table !|.

                              TABLE NO. 4

                  SIGNIFICANT LOADING CHARACTERISTICS
          (Sioux Falls,  South Dakota, Activated Sludge Plant)
                        Summer vs.  Fall 1967

                                           SUMMER     FALL
                                        (Aug. 19C7)(Dec.  1967)
    BOD_ JLoad to Aerators
       Pounds per day                      18,000    37,tl-00
       Pounds per 1,000 cu.ft. Aerator        103       160
       Pounds per pound mixed liquor solids   1.3       1.2

   Clarifier Surface Loading Rate
       Gals./sci. ft./day                       720       6UO

   EOP Reductions
       Total - Raw to Final                    99        97
       Activated Sludge Alone                  95        90

   TSS Reductions
       Total - Raw to Final                    99        96
       Activated Sludge Alone                  96        83

-------
                                                                        12




D.     FAV03A3LE FEATURES AT THE EXISTING PIAHT




            1.   Dedicated, skilled supervision and operation, arc primarily




                 responsible for the unusually high purification efficien-




                 cies developed at this plant.




            2.   The aeration tanks were equipped with effective turbine-




                 type aerators, rather than the less efficient conventional




                 spiral flow types,  (Compressed air was discharged through




                 sparger rings located at the bottom of the aerators below




                 nlxi i ig paddle s.)




            3.   The aerators operated as "complete mix" (rather than "plug




                 flow") systems.




            h.   The final clarifiers were equipped with suction-type (rather




                 than scraper type) sludge removal mechanisms for rapid re-




                 turn of settled sludge to the aeration tanks.




            5.   Adequate return sludge pumping capacity, exceeding 150 per-




                 cent of average raw waste flows,  permitted over compensa-




                 tion when necessary.




E.     PIAIW DEFICIENCIES



            1.   Activated sludge plant was overloaded.   It needed additional



                 aerators.




            2.   Industrial waste trickling filters froze up in winter,  and




                 imposed greater loads upon the activated sludge system.




            3.   There  was insufficient air to maintain 1.0 to 2.0 mg/1 D.O.




                 in aerators at all times.




            '(-.   Scum removers had not been provided for the final clarifiers.




            5.   Lac'c of sufficient meters, remotely controlled mechanical



                 valve  actuators,  and automatic sensor-controllers limited




                 process controllability.

-------
                                 CONCLUolUNS









       Experiences at  Sioux Falls  and 3t.  Louis provide  confirmation, that




the- activated  sludge process  can be  operated  at exceptionally high  purifica-




tion efficiencies to produce  attractive  clear final effluents.




       They also highlijhted  the following design and  operation requirements:




A.     DESIGN




            1.   Frovide adequate  plant  capacity for growth and




                 for repairs  during  equipment outages.




            2.   Flexibility.  (Give*  tlie  operators a chance.)




                 Provide ability7 to  increase  or decrease  the




                 number of aerators  or clarifiers in service




                 a-it] to convert to modified activated  sludge




                 schemer, suc]^ as "step aeration" if required.




            3.   Avoid "spiral flow"  aeration.




                 Ucc suction  devices  in  final clarifiers  fox1




                 vapid removal of  fresh  sludge.  Also provide




                 surface scvin removers.




            r, .   i'lalic air supply,  sludge return and sludge




                 wc.3t.iAg equipment truly variable and  con-




                 veniently controllable.




            o.   Irovide essential meters  and sensors, remote




                 valve actuators and  automatic ratio control-




                 lers where required.

-------
                                                                          1't.




B.     OIERATION



            1.   Recruit  and retain conscientious,  intelligent,



                 trained,  and certified plant operators.



            2.   i-rovidc  practical "on-the-job"  work experience



                 type trairin~.



            3.   Provide  2'i-hour  operation.   Test,  evaluate and



                 adjust process at least once every 8-hoxor sMft.



            '-.   1'lake best use of existing facilities and advise



                 consulting  eu^ineers  of operational reqiiirc'..ients



                 for pla-it additions and modifications.

-------
Environmental! Protect ion Agency
Library, IK,-j-ion V
1 North to'acker Drive
Chicago, Illinois  60606

-------
II if 111 r II1
                        : 111

-------
   !*-.,'.  ' ;
.s,L-:m>-.';i-'-
'i''i    *:.

-------