S&A-TSB-21
    TECHNICAL  ASSISTANCE  PROJECT
VAIL  WASTEWATER  TREATMENT   FACILITY
           VAIL,  COLORADO
        MARCH  -  APRIL,  1973
       .ECHNICAL SUPPORT  BRANCH
   SURVEILLANCE AND  ANALYSIS  DIVISION
U.  S. ENVIRONMENTAL  PROTECTION  AGENCY
               REGION  VIII

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                             TABLE OF CONTENTS










      SECTION                                                  PAGE NUMBER








  I.   INTRODUCTION	     1





 II.   DESCRIPTION OF PLANT	     1





      A.  BACKGROUND	     1





      B.  PLANT FACILITIES	     2





III.   SUMMARY OF LABORATORY ASSISTANCE	     4





 IV.   SUMMARY OF OPERATIONAL ASSISTANCE	••     6





      A.  CONTROL TESTING	     6





      B.  PROCESS MODIFICATIONS	     7





      C.  PERFORMANCE RESULTS	    18





  V.   SUMMARY AND CONCLUSIONS	    22





 VI.   RECOMMENDATIONS	    25

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                               LIST OF FIGURES








       FIGURES                                                   PAGE NUMBER











1.   PLANT FLOW SCHEMATIC	      3





2.   TURBIDITY VS TIME	     19





3.   EFFLUENT BOD5 VS TIME	     21





4.   PERCENT REDUCTION OF BOD5 VS TIME	     23

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 I.  INTRODUCTION







      On September 14,  1972 Region VIII  of the Environmental  Protection Agency




 (EPA),  received a letter from the Colorado Department of Health requesting




 assistance concerning  the operation of  the Vail Wastewater Treatment Facility.




 An initial evaluation  of the Vail plant was made on October  26 and 27, 1972.




 Various plant deficiencies were observed during the initial  evaluation and




 recommendations were made to correct the observed problems.   After the plant




 had been modified a formal technical assistance project was  initiated on




 March 19, 1973.




      The first objective of the assistance project was to improve effluent




 quality from the Vail  facility by initiating a series of operational control




 tests and analyses.  In addition, those portions of the facility which hindered




 or limited successful  operation were to be identified.  This report summarizes




 the results and findings of the technical assistance project and proposes




 several recommendations for future consideration at the Vail plant.







II.  DESCRIPTION OF PLANT






     A.   BACKGROUND.







     Vail .and the surrounding area is provided wastewater treatment by two




 separate Sanitation Districts.  The Vail Sanitation District (VSD) serves




 primarly the Town of Vail and discharges its effluent into Gore Creek.  The




 Upper Eagle Valley Sanitation District  (UEVSD)  serves localities upstream




 (The Big Horn Area) and downstream of the Town of Vail.  The UEVSD discharges




 its effluent to the Eagle River downstream of the confluence of the River




 with Gore Creek.

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     Since a portion of the area served by the UEVSD is located upstream of




the Vail facility, an agreement between the two districts was reached pro-




viding for a portion of Vail's collection lines to be used by the UEVSD to




transport sewage to the Upper Eagle treatment plant.




     Flow from the Big Horn area is measured prior to entering the Vail




interceptors.  This flow is transmitted to the Vail plant along with sewage




from Vail.  At the Vail facility the flow is split and an amount approxi-




mately equal to that flow measured from the Big Horn area is directed to the




UEVSD plant.  Vail is required to pay the UEVSD for all wastewater sent to




the UEVSD plant in excess of that measured at the Big Horn metering station.




It is noted that the interrelationship that exists between the plants pro-




vides a means to adjust flows to a desired quantity between the two facilities




and therefore must be considered an important operational tool.







     B.  PLANT FACILITIES
     Figure 1 shows the plant flow schematic for the Vail Wastewater Treat-




ment facility.  A brief discussion of each unit and its interrelationship




with other units is described below.




     Flow enters the plant and is directed through a parshall flume, bar




screen, and grit channel before entering the aeration basins.  Flow may enter




the aeration basins at the head end, near aerator #3, half way down, near




aerator #2, or at the far end of the basin, near aerator #1.  A concrete wall




is located near the end of the aeration basins, and physically separates




aeration basin #1 from basins #2 and #3.  During the initial EPA evaluation




made at the Vail plant it was recommended that an opening be provided in the




wall between basin #1 and basins #2 and #3 to allow for series operation.

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grit channel and
 grease removal
             FIGURE 1

   TECHNICAL ASSISTANCE PROJECT

VAIL WASTEWATER TREATMENT FACILITY

          VAIL, COLORADO

         MARCH-APRIL, 1973

       PLANT FLOW SCHEMATIC
                                                      parshall  flume
                                                                                                               waste sludge pump
                                                                                      polymer  feed  tank
                                 sludqe to incinerator
                                     T or landfill
               grease separation      I
                   screen          ^ I
                          return  sludge
                          pumps
                                                                ickened   i  I i
                                                                udge        |_J  floatation
                                                                ±	1   1  unit
                                                                                                                     :al
                                                                                                                   clarifiers
                                                                                                                   (scum
                                                                                                                    separation
                                                                                                                   zone)

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       Dissolved oxygen is introduced and mixing is provided in the aeration




  basins by three fixed surface mechanical aerators.   After flow passes through




  the aeration basin it is directed to two rectangular final clarifiers.   Flow




  to the clarifiers may be varied by manually adjusting the inlet gates.   The




  clarifier effluent is chlorinated and discharged to Gore Creek.




       Both final clarifiers are separated into two zones, a scum separation




  zone and overflow zone.   Once each day, the scum is drawn off the front




  portion of the final clarifier, screened and incinerated.  Settled sludge




  in the clarifiers is pulled by scrapers back to the head end of each clar-




  ifier.  Sludge is removed from the clarifiers through four telescoping valves




  and is collected in a return sludge wet well.  Return sludge flow rates are




  varied by adjusting the  height of the telescoping valves.  Sludge may be




  returned directly to aeration basin #3 or can be returned to the influent




  sewage channel.




       Excess activated sludge is removed from the process (wasted) to a




  flotation type thickening unit.  Polymer addition is used to affect the




  separation and flotation of the waste activated sludge.   Thickened sludge




  is held in a storage tank and then dewatered on a vacuum filter.  The filter




  cake can be either incinerated or buried.  Supernatant from the sludge




  thickener and vacuum filter is recycled to the aeration basins.







III.  SUMMARY OF LABORATORY ASSISTANCE







      The major emphasis of the assistance project was to improve plant




  operational control and  effluent quality.  In addition,  plant personnel




  were taught the procedures used in collecting, storing,  and analyzing




  samples for the biochemical oxygen demand (BOD^) and suspended solids tests.

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     Prior to the assistance project, plant personnel at Vail had infrequently




collected grab samples of plant influent and effluent (prior to chlorination)




and had performed a BOD^ analysis on these samples using a proprietary method.




Attempts were also made to conduct suspended solids analysis on these samples;




however, adequate laboratory equipment was not available at the Vail plant.




During assistance all plant personnel were taught the proper techniques used




to collect, composite and store treatment plant influent and effluent (prior




to chlorination)  wastewater samples.  Both influent and effluent samples were




collected every two hours through the operational day (i.e. 8:00 am to 10:00




pm).   No attempt was made to composite the samples proportional to flow.




Samples were stored in a refrigerator until the following day.




     Suspended solids and BODg analyses were performed on the composited




influent and effluent samples.  Due to the nature of these analyses, the




emphasis on plant operational controls, and the limited number of plant oper-




ators at the facility only two plant operators were given insturctions in




the procedures used to run the 8005 and suspended solids analyses.  Both




operators were taught the proper techniques required to analyze wastewater




samples for BOD5 using the cylinder dilution technique as outlined in




Standard Methods for the Examination of Water and Wastewater  (1).  Instruction




was also given in determining the dissolved oxygen concentrations in the BOD^




analysis using the azide-modification to the dissolved oxygen method again




as listed in Standard Methods.  The techniques used in conducting the




suspended solids analysis using the gooch crucible and glan fiber filter method




as listed in the manual entitled Operation of Wastewater Treatment Plants (2)




was also explained to the operators.

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      As a result of the laboratory assistance  all  personnel  at  the Vail plant




 are capable of properly collecting,  compositing  and  storing  wastewater samples




 for the BOD5 and total suspended solids  analyses.  Two  operators  are  capable




 of properly performing the BODg and total  suspended  solids analyses.




      Conducting the laboratory tests;  however, placed an additional respon-




 sibility on the Vail plant operators.  In  order  to release the  plant  operators




 to do their other tasks and to provide for consistent laboratory  data it  is




 suggested that additional personnel be hired to  perform primarily the laboratory




 functions.   Consideration should also  be given to  sharing such  a  laboratory




 technican with the Upper Eagle Wastewater  Treatment  Facility.







IV.  SUMMARY OF OPERATIONAL ASSISTANCE







     A.   CONTROL TESTING






     In addition to instruction in conducting various laboratory tests, plant




 personnel were given instruction in conducting and interpreting various  "control"




 tests.   Centrifuge tests, turbidity, settleability tests, and sludge  blanket




 depth were the control tests that were initiated.  All  except the settleability




 tests were conducted seven times per day seven days  a week during the project.




 The settleability tests were conducted twice a day seven days a week.




     Centrifuge tests were used to determine variations  in solids  concentrations




 from day to day.  Tests were conducted on  samples  of mixed liquors  taken  at the




 discharge end of the aeration basin and  on samples of return sludge.  The centri-




 fuge test values are expressed in percent  solids by  volume.  Although it  is not




 necessary for control, a correlation between percent solids  by  volume and solids




 by weight was made.  The results of this correlation indicated  that during the

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project one percent by volume was approximately equal to 690 mg/1 by weight.




This correlation will vary as the characteristics of the sludge vary.  For this




report all solids concentrations by weight were determined by using the corre-




lation of one percent by volume equal to 690 mg/1 by weight.




    Turbidity tests were performed on samples of the effluent from the final




clarifier.  In all cases attempts were made to exclude any solids in the samples




since test results were used to monitor the performance of the actived sludge




process (i.e. the ability of the activated sludge to convert colloidal and




dissolved BOD^ to sludge solids).




     Settleability tests were conducted on samples of the mixed liquor collect-




ed at the discharge end of the aeration basins.  Settleability tests were used




to monitor and observe sludge settling characteristics.




     Sludge blanket depth determinations were made on the final clarifiers.




Results were used to monitor changes in the depth of the blanket and to deter-




mine the amount of sludge that was accumulating in the final clarifier.




     Data obtained from the various control tests were used to perform cal-




culations and develop various graphs.  The calculations and graphs were used




to interpret plant performance and control plant operations.  Since the termi-




nation of the Federal assistance project, Vail has purchased the equipment




necessary to run the control tests and are using these tests to control plant




operations.







     B.  PROCESS MODIFICATIONS
     Many process modifications were made at the Vail Wastewater Treatment




Facility as a result of the technical assistance effort.  These modifications




are outlined below:

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     A major deficiency which limited plant flexibility  was  noted  during  the




October 26 and 27, 1972 on-site evaluation survey.   The  plant  could  not be




operated in a "contact stabilization" mode nor could effective use of  all the




aeration basins be provided if the plant was operated in a "conventional" mode.




The location of the opening in the concret wall which separates aeration  basin




#1 from aeration basins #2 and #3 allowed flow from these basins to  be directed




only to the final clarifiers.  In order for the plant to be  operated in the




"contact stabilization" mode the effluent from basins #2 and #3 should have been




directed to basin #1, the contact zone.  For the plant to be operated  in  the




"conventional" mode all the sewage had to be entered into basin #3.  However, if




all the sewage were entered into aeration basin #3, basin #1 could not be used,




thereby eliminating one third of the aeration capacity.




     To eliminate the inadequacies posed by the concrete wall  it was recommended




that a second opening be placed in the concrete wall to  enable flow  from  basins




#2 and #3 to pass directly to basin #1.  Plant personnel acted on  this recommen-




dation and a second opening in the wall was made prior to the  beginning of  the




formal technical assistance project.




     In order to discuss process modifications made during the formal  technical




assistance project it will be necessary to briefly outline operation of the




plant prior to assistance.  It is noted that approximately one week  before




assistance began significant process control changes were made. These changes




are also outlined.




     Using the new opening in the concrete wall, the Vail facility was operating




in the "contact stabilization" mode.  The major empahsis of plant  operation was




to control bulking and thereby eliminate the numerous citizen  complaints  that

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were received when bulking did occur.   As a result of this operational emphasis




little sludge bulking occurred; however, plant effluent quality was not




completely satisfactory.  The method used by plant operators to stop the




bulking sludge was to decrease the return sludge flow rate (i.e. raise the four




telescoping valves).   Since the mode of plant operation at that time was contact




stabilization the decreased return sludge flow rate served to decrease the quan-




tity of sludge entering the re-aeration zone (basins #2 and #3)  and thereby




decrease the suspended solids being "displaced" to the contact zone.  This




decrease in "displacement" of solids resulted in a. decrease in the mixed liquor




suspended solids concentration (MLSS).   The decreased MLSS concentrationrin the




contact zone resulted in a lower solids loading to the final clarifiers and had




the short term effect of stopping the sludge bulking.  Plant effluent quality




continued to be unsatisfactory; however, due to the larger quanities of




colloidal and dissolved BODs in the effluent caused by the inability of the




lower concentrations of sludge in the contact zone to effectively convert BODg




to sludge solids.  The practice of decreasing the return sludge flow rate at




Vail in order to eliminate sludge bulking without considering other factors in




plant operations such as sludge wasting, long term effects, aerator operation,




etc., was unsatisfactory.




     During the week before the assistance project a second factor, the volume




of sludge wasted, was used as a means of controlling plant operation and speci-




fically the sludge bulking problem.  During this week the volume of sludge to be




wasted was determined as a percentage of the volume of sewage flow received at




the plant and was wasted irrespective of the waste sludge solids concentration.




Using this approach,  large quantities of sludge were wasted during this week,




March 12-17, 1973.  As the wasting was substantially increased, the return

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sludge flow rate was for the most part set at a low flow rate and  maintained.




This combination of large quantities of sludge wasted and low return sludge




flow rates greatly reduced the MLSS concentration in the contact zone of  the




contact stabilization process.  At the beginning of the assistance project the




MLSS concentration in the contact zone had decreased to about 1000 mg/1.   This




low MLSS concentration in the contact basin greatly reduced the solids loading




to the clarifier and no problems with sludge bulking occurred;  however, plant




effluent quality was unsatisfactory.  Colloidal and dissolved BODs remained  in




the effluent because the low concentration of sludge in the contact zone  was




inadequate to convert this BOD to removable sludge solids.   The practice  of




controlling the quantity of sludge wasted and not adjusting the rate of return




sludge flow also proved to be an unsatisfactory mode of operation.




     At the beginning of the assistance project plant effluent quality was




unsatisfactory.  No problems with sludge bulking occurred,  but large quantities




of colloidal and dissolved 6005 were present in the plant effluent (effluent




turbidity was about 20 JTU).  The major emphasis at this point of  the assistance




project was to increase the MLSS concentration in contact with the sewage.




Operational flexibility at Vail enabled the plant to be operated in either of




three different modes of operation; contact stabilization,  step loading,  or




conventional.  Prior to formal assistance and after the opening between aeration




basins #2 and #3 and basin #1 has been provided, the plant has been operated in




the contact stabilization mode.  The advantages of this mode of operation are




claimed to be decreased plant upsets due to wide variations in hydraulic  load




and decreased operational controls required because of the relative insensitivity




to changing hydarulic loads.




     At the beginning of the assistance project the plant mode of  operation
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was changed from contact stabilization to conventional.  The change was made




primarily to take immediate advantage of the sludge solids that were "stored"




in the re-aeration zone (basins #2 and #3).   For example the suspended solids




concentration in the contact zone was about 1000 mg/1 and the suspended solids




concentration in the re-aeration zone was about 5000 mg/1.  By distributing




these solids throughout the system a desirable MLSS concentration of about




2700 mg/1 throughout all the basins was achieved.  In addition to the MLSS




increase, the sewage detention time in the aerators also increased from about




7.3 hours to 21.9 hours (average flow of 1,703 cu m/day(450,000 gal/day).




     Immediately after the change in the mode of operation sludge bulking




occurred for approximately four days.  Reasons for the bulking were high solids




loading to the clarifiers and a relatively young and undeveloped sludge that




exhibited poor settling characteristics.  During this bulking period, every




attempt was made to minimize solids lost and allow time for the settling




characteristics of the sludge to improve.  Close control over the return sludge




flow rate was provided and the volume of sewage received at the plant was




reduced by diverting flow to the Upper Eagle facility.  After four days of




maintaining the relatively high MLSS concentration coupled with a longer sewage




detention time in the aerator, the settling characteristics as well as the




removal characteristics of the sludge began to improve; (i.e. turbidity decrease




from 20 JTU to 5 JTU).




     The volume of sewage received at Vail prior to the assistance project was




approximately 2,650 cu m/day(700,000 gal/day).  During the four day period when




problems with sludge bulking occurred the volume of flow received at Vail was




reduced to about 1,628 cu m/day(430,000 gal/day).  When the sludge began to




settle better the flow rate to Vail was increased by 379 cu m/day(100,000 gal/day)
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Additional flow was not accepted at Vail because of problems encountered with




the operation of the final clarifier and continued sludge bulking.   It should




be pointed out that the ability to decrease the sewage flow to the  Vail




facility during the troublesome period greatly reduced the total pollutional




load to the receiving stream and was a significant factor in maintaining a




required high MLSS concentration.  This interrelationship between the Vail plant




and the Upper Eagle plant must continue to be used as an operational tool in




future difficulties with either plant.




     Numerous problems were encountered with the final clarifiers and attempts




to improve their performance were attempted.  The effect of poor clarifier




performance was to allow solids to be lost in the plant effluent and although




effluent quality was significantly improved it never reached an optimum because




of the clarifier performance.




     The major problem with the final clarifiers at Vail was inadequate control




over flow splitting to the two clarifiers.  Flow to the clarifiers  was adjusted




by opening or closing rectangular inlet gates.  These adjustments;  however,




were not precise enough to attain equal flows to each clarifier.  Also, rags




and other debris would routinely clog the gate openings.  High flow would be




directed to one clarifier causing sludge bulking in that clarifier while the




other clarifier would maintain a deep sludge blanket.  Many different methods of




splitting the flow equally to each clarifier to include using a butterfly split-




ter, 2x6 boards, etc., were tried to eliminate the splitting problem.  However,




all the methods tried required that the plant operators adjust and control the




flow to each clarifier and balance the sludge blanket depth.  Problems occurred




during the night when plant operators were not on duty.  Unequal flow to the




clarifier continued unchecked and solids bulked over one or the other clarifier.
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Major modifications to the Vail plant must be made in order to control




adequately flow splitting to the two clarifiers.   These modifications should




provide for positive direct control over the flow to each clarifier.   An




intermediate solution would be to provide 24-hour operation so that the plant




operators can make the necessary adjustments to prevent solids losses during




the night.




     The other major problems with the final clarifiers at Vail resulted from




inadequate design features.  The clarifiers are rectangular in shape and are




separated into two zones.  The first zone is a scum flotation zone where grease




and other floating material is removed.  The second zone is a weir overflow




zone where the effluent weirs are located.  Flow in the final clarifiers is




directed through the scum removal zone to the overflow weir zone and discharges




to the chlorine contact basin.  The settled sludge in the clarifier is pulled




countercurrent to the flow back to the head end of the clarifier and returned




to the aeration basins.   These countercurrent flow patterns have a tendency to




create shear stresses in the sludge blanket and cause lower return sludge




concentrations than would normally be expected, especially because of the




shallow depth of the clarifier (approximately 9 feet).  A through investi-




gation of the proposed shear stresses in the final clarifier was not made,




however, the effects of the stresses were observed in the results of the control




tests.  A method to correct the inadequate design features of the final clarif-




iers would be to complete major modifications (i.e. deeper clarifiers, co-




current sludge removal,  etc.).  A second and more immediate method would be to




reduce the flow to the clarifiers.  Reduced flow would reduce the effects of the




shallow depth and countercurrent flows.  It is recommended that the second




approach to reduce the flow to the final clarifiers, be considered.  The maximum






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volume of flow these clarifiers are capable of accepting should be determined




by a trial and error procedure.




     Another problem encountered with the clarifiers at Vail was caused by a




series of baffles that had been installed in the clarifiers.  Four baffles had




been placed in each clarifier with the intent of keeping the majority of the




settled sludge in the head end of the clarifier.  In actuality the baffles




increased the flow velocity past each baffle (the cross-sectional area of the




clarifier was decreased at that point) and hindered the settling of the




activated sludge flow.  Also/ each baffle acted like a hydraulic "barrier" to




inhibit pulling the sludge back to the head end of the clarifiers.  The result




of these "barriers" was to force sludge to accumulate in the weir overflow




section of the clarifiers and aggravate the sludge bulking problems.  The




baffles were removed and the sludge bulking problem was reduced substantially.




     During the assistance project, various other modifications to plant operation




were made and recommendations for future modifications were given.  Modifications




to control the return sludge flow rate, control of the waste sludge operation,




measurement of the return sludge flow rate, measurement of the waste sludge




flow rate, control of the aerator operation, and control of the waste sludge




thickening unit were made during the assistance project.  Suggestions for future




modifications to control the vacuum filter operation were also made.  Each of




these modifications are briefly discussed in this report.




     The modification to controlling the return sludge flow rate involved drastic




changes in the operators approach.  Prior to the assistance project, the rate of




return sludge flow was varied to control sludge bulking.  This approach was in-




adequate.  During assistance, the return sludge flow rate varied throughout the




day as the incoming flow rate varied and was varied from day to day based on
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results of the control tests.   Direct control over the rate of return sludge




flow was maintained and positive control over plant operation from this stand-




point was achieved.




     Modifications to procedures for wasting excess activated sludge were




made.  A method of determining the quantity of sludge to be wasted and a change




in the location of the sludge wasting draw off point were initiated.  Prior to




the assistance project the quantity of sludge to be wasted was not used as




a tool for plant operation.  A specific volume of sludge was wasted each day




based on the influent flow rate.  Since this volume was wasted irrespective of




its solids concentration the quantity of sludge wasted could vary significantly




and drastically change the quantity of sludge in the activated sludge system.




During assistance the quantity of sludge wasted was determined based on the




results of the control tests.   Both the volume and concentration of sludge wasted




was included in the calculations.  Using this method, complete control over the




quantity of sludge in the activated sludge system was achieved disregarding the




uncontrolled sludge bulking problems that existed.  The location of the sludge




wasting draw off point had to be changed after the plant mode of operation was




switched from contact stabilization to conventional.  Prior to assistance, sludge




was wasted from aeration basins #2 and #3, the re-aeration zones of the contact




stabilization mode of operation.  After the mode of plant operation was changed




to conventional the mixed liquor from aeration basins #2 and #3 was too thin




for wasting.  Initially attempts were made to waste return sludge using the




return sludge pumps.  This method resulted in decreasing the rate of return




sludge flow to the head end of the aeration basins and an alternative method of




sludge wasting had to be provided.  An alternative method was provided by




modifying the separate waste sludge pump piping arrangement so that return






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sludge could be directed to the separate waste sludge pump and wasted without




disrupting the return flow to the head of the aeration basins.




     Measurement of the return sludge flow rate was initiated by developing a




flow chart for the four telescoping return sludge valves.   Prior to assistance




the four telescoping valves had been adjusted to control the rate of return




sludge flow; however, the volume of sludge returned was not determined.   No




return sludge flow meters are provided at the Vail facility.  During assistance




an indication of the rate of flow of return sludge was made by determining the




time required to fill a specific volume in the return sludge wet well and




calculating the corresponding flow rate.  Flow rates were determined for various




settings of the telescoping valves and a graph showing the telescoping valve




setting versus the flow rate was developed.  This method of determining the




rate of return sludge flow is satisfactory as an interim measure.  It is




recommended that future plant modifications include a return sludge flow meter




in order to attain more precise return sludge flow measurements.




     A method of measuring the waste sludge flow rate was also initiated.  A




waste sludge flow meter is provided at Vail, but was not calibrated properly




at the time of assistance.  During assistance the waste sludge flow rate was




determined by measuring the time required to fill a specific volume in the




sludge thickening unit.  It is recommended that this method of determining the




waste sludge flow rate be used until the available flow meter is properly




calibrated.




     Aerator operation was modified at the same time the plant mode of operation




was switched from contact stabilization to conventional.  The modifications




involved changing the operation of the three surface mechanical aerators from




an on-off time clock operation to a continuous operation.  Prior to assistance







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various on-off time cycles for all three aerators were tried in order to




improve plant effluent quality.  During assistance all three aerators were




operated continuously.  It was felt that continuous operation would provide for




better mixing conditions and better mixing would yield a higher quality plant




effluent.  It is recommended that all three surface mechanical aerators




continue to be operated on a continuous basis.




     The modification made concerning control of the sludge thickening operation




involved adjusting the quantity of polymer added to the selected quantity of




sludge entering the flotation unit.  At Vail sludge is wasted to a flotation




unit and a polymer is mixed with the wasted sludge causing the sludge to float




and thicken.  The supernatant  (clear liquid) from the flotation is recycled to




the aeration basins.  An adequate quantity of polymer must be mixed with the




sludge or a clear supernatant cannot be attained.  When attempts were first




made to waste sludge to the flotator, a clear supernatant could not be




attained.  The polymer feed rate was checked and was found to be inadequate




due to a clogged line.  After the line was flushed, adjustments were made in




the quantity of polymer added to the flotator per quantity of sludge added to




the flotator by adjusting the polymer concentration, polymer pump rate, poly-




mer pump stroke, and sludge feed rate to the flotator.  Prior to assistance,




these adjustments were not varied and a consistently clear supernatant from




the flotator could not be maintained.  During assistance all adjustments were




varied and a consistently clear supernatant was obtained.  Time during the




assistance project; however, did not permit an extensive analysis of the




flotator portion of the sludge handling system.  Additionally an extensive




analysis was not made of the vacuum filter portion of the sludge handling system.




In both cases suggestions regarding possible alternative investigations to op-






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timize the sludge handling operation were given.   It is recommended that inves-




tigations be continued to determine the most efficient operational method for




both the sludge flotator unit and vacuum filter.   The results of these investi-




gations should give the methods of operation necessary to achieve the desired




thickener and vacuum filter operation at the most economical cost.







     C.  PERFORMANCE RESULTS






     Prior to the technical assistance project effluent water quality data was




incomplete and questionable.  During assistance,  BOD^ and suspended solids




analyses were conducted on composited samples of plant influent and clarifier




effluent each day.  In addition turbidity tests were conducted on the clarified




effluent seven times per day.  After assistance BOD^ analyses were conducted on




composited samples of plant influent and clarifier effluent periodically, tur-




bidity tests were conducted on the clarified effluent seven times per day, and




the suspended solids analyses were conducted infrequently.  For this report only




the 6005 and turbidity data are discussed quantitatively.




     Figure 2 shows the daily average turbidity values of the clarified effluent




during and after the assistance project.  It should be noted that in all cases




attempts were made to exclude suspended solids in the turbidity sample.  The




purpose of the turbidity test was to indicate the ability of the mixed liquor




suspended solids in the aeration basin to convert colloidal and dissolved BODs




in the waste stream to sludge solids.  A high turbidity normally indicates a




larger quantity of colloidal and dissolved BODs present in the clarifier




effluent and low turbidity normally indicates smaller quantities of colloidal




and dissolved BODs in the clarifier effluent.  It is noted that a low turbidity




value reported as outlined above does not necessarily mean low effluent total





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                                                                                                    TECHNICAL ASSISTANCE  PROJECT
                                                                                                 VAIL WASTEWATER TREATMENT FACILITY
10
         3/20
                                                                                                                  23
                                                                                                                         25
                                                                                                                               27
                                                                                                                               29  5/1
                                                       TIME

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     values because of the possible presence of suspended solids in the




clarifier effluent.




     Figure 2 shows a dramatic decrease in the turbidity within one week after




the beginning of the assistance project and a continued decrease in turbidity




until formal assistance was completed.   The dramatic decrease in turbidity was




the result of the changes in plant operation as discussed earlier in the report,




(e.g. changed plant mode of operation,  changed return sludge flow operation,




changed aerator operator operation, etc.).  The continued slower decrease in




turbidity after the initial drop indicates the length of time required for the




activated sludge biological system to change and develop.  After the formal




technical assistance project was completed the turbidity increased, then decreased,




and then increased again.  These changes in turbidity indicate the continued




problems encountered with the final clarifiers and the resultant solids loss due




to uncontrollable "sludge bulking".  Sludge bulking occurred primarily because of




inadequate flow distribution to the two final clarifiers.  The uncontrolled




solids loss caused lower MLSS concentrations resulting in additional colloidal




and dissolved BODs in the plant effluent.




     Figure 3 shows the daily composited secondary clarifier effluent BODg test




results.  At the beginning of the assistance project most of the BOD^ in the




effluent was due to the colloidal and dissolved organic matter, (refer to




Figure 2 for an indication of amount of colloidal and dissolved organic matter




in the effluent as measured by turbidity).  During assistance less of the BODg




was due to colloidal and dissolved organic matter and more of the 6005 was due




to suspended solids "lost" in the effluent.  As can be seen from Figure 3, a




drastic reduction in the BOD^ occurred during the assistance project  (i.e.




approximately 110 mg/1 to 45 mg/1) and an even further reduction occurred after






                                     20

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     140
     120
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                                                                                                          FIGURE  3





                                                                                                TECHNICAL ASSISTANCE  PROJECT





                                                                                             VAIL WASTEWATER TREATMENT. FACILITY





                                                                                                       VAIL, COLORADO





                                                                                                      MARCH-APRIL, 1973





                                                                                                    EFFLUENT BOD5 VS  TIME
                                                                                        Periodic BOD,- Test Results
                Daily BOD5  Tests Results
                                                                               11    13    15     17     19    21    23    25    27     29   5/1
          3/20    22
                 24     26


                  MARCH

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formal assistance was completed (i.e. approximately 45 mg/1 to 30 mg/1).   However,




the present Colorado Water Quality BOD^ Standard (30 mg/1)  was not consistently




being met.  The primary reason this standard was not met was the continued




problems associated with the final clarifier.  If the problems with the final




clarifiers are eliminated, it is felt that the Vail treatment facility will be




capable of consistently discharging BOD^ and suspended solids concentrations




less than 30 mg/1.




     The reduction in clarifier effluent BOD^ due to technical assistance re-




presents nearly a 73% reduction in BOD5 or a reduction of about 136.2 Kg




(300 Ibs.) of BOD^ per day in the effluent (assume average plant flow of 1,703




cu m/day  (450,000 gal/day) during assistance).   Figure 4 shows that the present




reduction in BOD^ through the Vail facility increased from about 45% to about




75% due to assistance.




     Greater reductions can be expected with appropriate modifications to the




secondary clarifiers.






V.  SUMMARY AND CONCLUSIONS
     Region VIII of the Environmental Protection Agency (EPA)  received a letter




from the Colorado Department of Health requesting assistance concerning the




operation of the Vail Wastewater Treatment Facility.  An initial evaluation of




the Vail plant was made on October 26 and 27, 1972.  Various plant deficiencies




were observed during the initial evaluation and recommendations were made to




correct the observed problems.  After the plant had been modified, a formal




technical assistance project was initiated on March 19, 1973.




     During assistance, plant personnel.were taught the proper techniques used




in collecting, compositing, and storing wastewater samples for the BOD5 and total






                                    22

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      100
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                          Daily BOD  Test  Results
                                                                                           Periodic  BOD  Test Results
                                                                                                                FIGURE 4




                                                                                                      TECHNICAL ASSISTANCE PROJECT




                                                                                                   VAIL WASTEWATER TREATMENT FACILITY




                                                                                                             VAIL, COLORADO




                                                                                                            MARCH-APRIL, 1973
                                                                                                     PERCENT REDUCTION BOD5 vs TIME
           3/20
                                                                                                                                       29  5/1
                                                          TIME

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suspended solids analyses and were given instructions in the procedures used to




run the 6005 and total suspended solids tests.   However, limited manpower in-




hibited obtaining consistent analytical test results.  Future plant considerations




should include a position for a laboratory technician to insure consistent moni-




toring of plant performance by analytical tests.




     Plant personnel were also given instructions in conducting and interpreting




various "control" tests.  Initiation of the control tests and data interpretation




methods aided in solving problems encountered when controlling plant operation.




The operators should be able to use these methods to solve future operational




problems.




     Prior to technical assistance, the Vail facility had been operated with the




major emphasis on eliminating sludge bulking.  As a result of this emphasis,




little sludge bulking or loss of solids occurred, but effluent quality was not




satisfactory.  The procedures that had been used to control bulking resulted in




low concentrations of sludge solids in contact with the sewage and ineffective




conversion of colloidal and dissolved BOD^ to "activated" sludge solids.




     Numerous process modifications were made at the Vail plant in conjunction




with the results of the control tests and data interpretation.  The most sig-




nificant modifications were the conversion from the contact stabilization mode




to the conventional mode of activated sludge operation and the initiation of




continuous aerator operation.  As a result of these modifications, as well as




others, effluent quality was substantially improved; however, optimum performance




was not achieved due to various design deficiencies that existed.




     Several plant deficiencies were corrected during the project including; the




removal of baffles from the final clarifiers, the changing of the location for




withdrawing waste or excess activated sludge, and the adjustment and cleaning of





                                     24

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 the polymer feed equipment.  Other deficiencies which were noted were not




 modified during the project.  These included the shallow rectangular final




 clarifiers which were designed to remove sludge by returning it to the head of




 the clarifiers (countercurrent to the sewage flow)  and the inadequate method of




 splitting flow to the final clarifiers.




      All modifications to the Vail facility combined to drastically reduce the




 clarifier effluent 6005 from about 110 mg/1 to about 45 mg/1 during assistance




 and to about 30 mg/1 after formal assistance was completed.   The percent reduc-




 tion in BODg through the plant increased from about 45% to about 75%.  Even




 though the BOD^ was reduced significantly,  the Vail facility was not consistently




 meeting the Colorado Water Quality BOD5 Standard of 30 mg/1.  The primary reason




 why the BOD^ standard was not met consistently was the continued problems




 associated with the secondary clarifiers.  If these problems are eliminated, it




 is felt that the Vail facility will be capable of consistently discharging BOD,.




 and suspended solids concentrations of less than 30 mg/1.




VI.  RECOMMENDATIONS







      Based on the results of the assistance project, the following recommendations




 are made:




      1.  Methods of operational control and control testing outlined during the




          assistance project should be continued.




      2.  The relationship between the Vail  treatment facility and the Upper Eagle




          treatment facility should continue to include flow splitting capability




          so that the Upper Eagle facility can accept additional flow while the




          Vail facility is experiencing operational problems or the Vail facility




          can accept additional flow while the upper Eagle facility is experi-




 '-.        encing operational problems.







                                      25

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 3.   All three surface mechanical  aerators  should be  operated  continuously.




 4.   Plant modifications should be made  to  provide  for positive  flow  split-




     ting capability to e'ach final clarifier.




 5.   Lower flows should be accepted  at 'the  Vail  facility  to  reduce  the




     problems associated with the  existing  clarifiers.  The  maximum volume




     of flow that clarifiers are capable of accepting and adequately




     treating, should be determined  by a trial and  error  procedure.




 6.   The clarifier capacity as established  by a  trial and error  procedure




     should be considered in future  designs if increased  plant capacity




     is desired.




 7.   Plant modifications should be made  to  provide  for more  precise return




     sludge flow measurements.




 8.   The method of determining the waste sludge  flow  rate as established




     during assistance should be used until the  waste sludge flow meter




     is properly calibrated.




 9.   Investigations should be continued  to  determine  the  optimum flotation




     unit and vacuum filter operation.




10.   A separate laboratory technician should be  considered to perform all




     analytical work.  If one technician at Vail is not  feasible, consid-




     eration should be given to sharing  a technician  with the Upper Eagle




     treatment facility.




11.   The plant should be operated  on a  twenty-four  hour  basis to allow




     manual adjustments to the present  flow splitting devices on the  final




     clarifiers.  This interim activity should  continue  until an adequate




     automatic flow splitting device can be installed.





                                 26

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                       REFERENCES
1.   Standard Methods for the Examination of Water and
    Wastewater,  13th Edition,  American Health Associ-
    ation,  1015  Eighteenth Street,  N.W.  Washington,
    D.C.,  20036
2.  Operation of Wastewater Treatment Plants,  A Field
    Study Training Program, prepared by Sacramentao
    State College for the Environmental Protection
    Agency, Office of Water Programs, Division of
    Manpower and Training.
                           27

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