SUMMARY OF PLANT EVALUATION
CITY AND COUNTY OF DENVER'S NORTHSIDE
    WASTEWATER TREATMEMT FACILITY

       AUGUST - SEPTEMBER 1972
                  Thornton
        Arvada
                       COMMERCE
                        CITY
        Lakewood
                            i Aurora
                   Englewoo
                Littleton



       TECHNICAL  SUPPORT BRANCH

  SURVEILLANCE AND ANALYSIS  DIVISION
U. S. ENVIRONMENTAL PROTECTION AGENCY

                REGION  VIII

              DECEMBER 1972

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                                             S&A/TSB-7
      SUMMARY OF PLANT EVALUATION
      CITY AND COUNTY OF DENVER'S
NORTHSIDE WASTEWATER TREATMENT FACILITY
       AUGUST - SEPTEMBER, 1972
       TECHNICAL SUPPORT BRANCH
  SURVEILLANCE AND ANALYSIS DIVISION
 U. S. ENVIRONMENTAL PROTECTION AGENCY
              REGION VI-II
             December 1972

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                          TABLE OF CONTENTS
  I.   Introduction 	      1
 II.   Scope	      1
III.   Description of Plant Facilities  and  Operation   	      1
           A.   Wastewater	      2
           B.   Sludge	      4
           C.   Supernatant 	      5
           0.   Grease	      5
           E.   Grit	      6
           F.   Screenings	      6
           G.   Digester Gas	      6
 IV.   Summary  of Evaluation  	      6
           A.   Plant Operations   	      6
           B.   Other Areas of Evaluation  	      9
  V.   Conclusions	    10
 VI.   Recommendations	    12

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                     LIST OF FIGURES AND TABLES

                                                                Page
Figure 1 - Plant Flow Schematic 	      3

Table 1 - Evaluation of Digester Capacity	     11
                                   ii

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  I.   INTRODUCTION

           The Denver Northside Wastewater  Treatment facility  is  a  large
      primary plant which serves the City and  County of Denver as well  as
      numerous industries and  sanitary districts.   The  effluent from  the
      Denver Northside plant is discharged  to  a  large secondary facility
      (Metropolitan Denver Sewage Disposal  District #1  - MDSDD #1).

           As a portion of the Accomplishment  Plan  developed for  the  Metro
      Denver - South Platte River Basin by  Region VIII  of the  U.S.  Environmental
      Protection Agency (EPA), an evaluation was made of the Denver Northside
      Wastewater Treatment Plant.  The purpose of this  evaluation had many
      facets as would be expected with a plant of this  size and complexity.
      Basically, however, the  purpose of the evaluation was to determine
      through discussions with personnel involved with  the plant, whether
      or not the facility was  being operated and maintained satisfactorily
      to achieve the best protection for the waters of  the South  Platte River.
      This technical review was to then serve  as a  basis to determine what
      Regional resources, if any, could best be  used to help Denver Northside
      with the various problems that they might  be  facing.  The evaluation  of
      the Northside plant led  into areas including:  industrial wastes, plant
      operations, administrative controls,  sewer ordinances, relationship with
      MDSDD #1, and numerous others.  These aspects of  the evaluation are
      summarized in this report.

 II.   SCOPE

           The evaluation of the Northside  Wastewater Treatment Plant was
      achieved by interviews with staff personnel concerned with  the  operation
      of the Northside facility.  Three or  four  visits  were made  to the plant
      by various EPA employees to discuss facets of the plant's operations,
      as well as collect pertinent data. A short meeting was  held  with
      MDSDD #1 personnel in conjunction with the Northside evaluation.

           On site sampling by EPA personnel was not conducted during the
      evaluation of the Denver Northside Plant.  All data collected and
      presented in this report were taken from plant records.

           This report will outline in general the  findings of the  EPA
      evaluation of the Northside Plant. An attempt is made to discuss
      those areas where improvements or modifications could most  benefically
      affect the water quality of the South Platte  River.

III.   DESCRIPTION OF PLANT FACILITIES AND OPERATION

           Figure 1 shows a schematic flow  diagram  of the Denver  Northside
      Wastewater Treatment Facility.  The major  plant units consist of  flow
      measuring devices (two large venturi  meters), mechanically  cleaned
      bar screens (5 units), grit removal facilities (5 channels),  pre-
      aeration and grease flotation tanks (2 units), primary clarifiers

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(8 units), and anaerobic digesters (8 units).

     The various flow patterns within the plant for sewage,  sludge,
supernatant, grease, grit, screenings, and digester gas will  be outlined.

A.  Wastewater

    Flow enters the plant through four main interceptor lines; the
Delegany and Franklin Sanitary Sewer, the South and West Sanitary
Sewer, the Broadway Relief Sanitary Sewer, and the Globeville Sanitary
Sewer.  Several problems exist with the Northside plant's collection
system, such as existing combined sewers in the downtown area, limited
capacity of the collection lines, and old age.  The result of some of
these problems is that frequently (two to three times a week) raw
sewage (quantities are not known) is by-passed from the system directly
to the South Platte River.  Efforts are currently underway to alleviate
the by-passing.  Several new left stations are being built,  separation
of storm and sanitary sewers is being practiced, etc.

    Flow from three of the four main interceptors enters the plant by
gravity.  Flow from the Globeville interceptor is pumped from a wet
well located on the plant site to raise it to the level of the inlet
structure.  A new lift station is being constructed on the plant site
to pick up the flow from the recently constructed South Platte Inter-
ceptor No. 2.  A portion of the flow in this new interceptor will be
that raw sewage which is presently being by-passed from the automatic
overflow on the South and West sanitary sewer.

    Flow entering the plant is metered by two large venturi  meters.
Difficulties have been encountered with the venturi meters in keeping
them cleaned and properly calibrated.  This effort appears to require
almost constant attention.  Average daily flow entering the Northside
plant for 1971 was 80.3 million gallons per day.

    Two channels direct the influent to the screen-house where the
flow is passed through mechanically cleaned bar screens with one inch
openings.  The two influent channels present a problem in sampling
the combined flow entering the plant from the major interceptors.
Presently a uniformly sized sample is collected from each channel
hourly and composited.  Samples are not composited proportional to
flow.

    After the sewage passes through the bar screens, it is directed
to the grit chambers.  The amount of flow dictates how many of the
five grit removal channels are in operation at any one time, i.e.
velocity in the grit removal channels is controlled by increasing or
decreasing the number of channels in service as the flow increases
or decreases.

    The flow leaving the grit chambers is directed to two pre-aeration
basins each followed by grease floatation and removal units.  The
effluent from the grease floatation units is split and directed to two
sets of four primary clarifiers.  The effluent from the eight primary
clarifiers is recombined and transported through a 90 inch line to the
MDSDD #1 plant to receive secondary treatment.

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    PRIMARY TREATMENT OF
          SEWAGE

  CITY & COl'NTY OF DENVER

       Flow Diagram
Grit to
Landfill
                 Bar      Grit
               Screens  Channels
                Sewage Flow

                Sludqe Flow

                Grease

                Supernatant
              Figure 1
     Treatment Plant Evaluation
Denver Northside Wastewater Treatment
              Facility
            August 1972

        Plant Flow Schematic
Grease to Rendering
    Plant
                                                                                                                        Dinested Sludge
                                                                                                                         To  MOSDD
                                                         Sludge Distribution Well

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    Denver Northside is charged a service rate by MDSDD #1  which is
determined from a formula which includes flow (45.51% of rate),
8005, (30.88% of rate), and suspended solids (23.61% of rate).   The
total amount Northside pays is adjusted annually according  to the
MDSDD #1 budget.

    Another operational consideration that should be discussed  is
the present by-passing policy followed at the Northside plant.   After
heavy rains, peak flows will occur at the Northside plant.   When these
flows are at or near 130 million gallons per day, the quantity in
excess of 130 MGD is by-passed manually to the river.  The  reasons given
for by-passing at 130 MGD include the fact that the flights on the
grease removal units become submerged and removal of grease is no longer
effective, the primary clarifier weirs become submerged, the grease
traps on the primary clarifiers become flooded and this flow is recir-
culated eventually back through the Globeville lift station to the
influent compounding the flow problem, grit removal is less effective,
the bar screens become clogged, etc.  Although operationally the plant
is by-passed at 130 MGD, the exact capacity of the facility is not known.
Using an accepted overflow rate of 800 gpdsf on the clarifiers, the
mean capacity is calculated to be 106 MGD.  A recent study  by a consulting
engineering firm working on expansion of the MDSDD #1 facilities concluded
that hydraulically 160 MGD of flow could pass through the Denver Northside
plant.  MDSDD #1 flow records indicate that flows of this quantity have
been received from the Northside plant.

B.  Sludge

    Sludge is settled in the eight primary clarifiers at the Denver
Northside plant.  This sludge is removed from the clarifiers by piston
pumps in the two pumphouses which are centrally located between each
set of four clarifiers.  The sludge pumping cycles are controlled to
attempt to draw a sludge with a high solids concentration.   A low solids
concentration in the primary sludge would increase the heating require-
ments in the anaerobic digesters as well as reduce the effective solids
handling capacity.  The solids concentration from the primary clarifiers
is monitored by the use of a centrifuge and also by the operator's
experience in recognizing a "thick" or "thin" sludge.  Solids concentra-
tion from the primary clarifiers averaged 5.6 percent by weight in 1971.
This is less than the 7 to 10 percent concentration of solids that MDSDD
#1 removes in their primary sludge.  It is possible that different influent
characteristics or better clarifiers at MDSDD #1 could account for this
difference.  However, a significant increase in digester capacity can
be realized from pumping a "thicker" sludge and any increase in the solids
concentration from the primary clarifiers should be strived for.

    Sludge removed from the primaries is pumped to a sludge distribution
well located centrally between the eight anaerobic digesters.  From this
distribution well, the operator "feeds" the sludge to those  digesters that
are being used as primary digesters.  Presently four of the eight digesters
are being used as primary digesters, three are being used for secondary
digesters, and one is out of service for modifications and  repair.

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    Digested sludge from the secondary digesters is pumped twice a
week (Tuesday and Thursday) by MDSDD #1 personnel  to holding tanks
on the MDSDD #1 plant site.  The digested sludge is required to have
a concentration of 5 percent solids by weight.  The Northside plant
is not charged directly for the removal of the digested sludge by
MDSDD #1.  The digested sludge from Northside is mixed in the MDSDD
#1 holding tanks with raw sludge from Metro's primary clarifiers and
with aerobically digested waste activated sludge from the MDSDD #1
secondary process.

C.  Supernatant

    Supernatant liquor is drawn off the secondary digesters at the
Denver Northside facility and is presently being returned to the inlet
structure ahead of the bar screens.  (See Figure 1)  It is noted that
the supernatant liquor could be returned to the plant flow following
the grit removal facilities.  Several difficulties are encountered by
returning the supernatant to the head of the plant.  The major problem
is that the supernatant is included in the influent sample, thus dis-
torting the determination of the actual influent load from the collection
system.  Another major problem is the fact that the flow pattern of the
supernatant through the plant is such that it only affects one half of the
facility, thus theoretically overloading that portion of the plant.  Some
Denver Northside personnel feel that the supernatant should be returned
to the head of the plant because it represents a load to the facility
and therefore should be included in the determination of plant efficiency
and also because they feel some removal benefit is gained by passing the
supernatant through the grit removal facilities.

    Supernatant removal from the secondary digesters is not a continuous
process, but rather a draw and fill type process.  Normally supernatant
is drawn approximately four times a shift (12 times a day) from the
secondary digesters.  The obvious effect of this type of operation is
the slug loading situation that it places on the other plant fcilities.

    Efforts to improve the quality of the digester sludge supernatant
have been tried at the Denver Northside facility.  The most recent
investigation involved pumping the supernatant to an asphalted area
which serves as a large shallow settling basin.  The liquor from this
basin is decanted from the top and the excess solids are left on the
asphalt surface.  At the time of the EPA evaluation, the asphalted area
was full of solids and this practice of treating supernatant had been
discontinued until the solids could be removed from the area.

D.  Grease

    Grease removed at Denver Northside is critical because no facilities
are supplied at MDSDD #1 for removal of grease.  Air flotation and
skimming provide the first step in removing the grease at the Denver
Northside plant.  Skimmers are also provided on each of the eight primary
clarifiers to aid in the removal of grease.  Removal of grease was reported
for 1971 as 5 tons per day for the air flotation units and 16 tons per
day for the clarifiers.  All grease that is removed is picked up by a
local rendering plant for processing.  Although grease removal appears

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     to be accomplished  in  a  satisfactory manner  at  Denver  Northside
     problems concerning grease  have  still  been encountered at  the  MDSDD
     #1 facility.   It may be  that increased pre-treatment at the  local
     packinghouses will  be  necessary  to  decrease  any adverse effects  pre-
     sently being  encountered with grease.

         Settled solids  are removed from the grease  flotation and pre-aeration
     tanks by scrapers and  returned mechanically  by  augers  to the main  dis-
     tribution channel for  the eight  clarifiers.

     E.  Grit

         Grit is mechanically removed from  the grit  channels, taken by  an
     auger to a truck, and  hauled daily  to  a landfill  site  operated on
     Lowery Air Base. The  average quantity of grit  for 1971 was  22 tons
     per day.

     F.  Screenings

         Screenings larger  than  one inch in diameter are removed  by the
     mechanically  cleaned bar screens, and  deposited on a pan where they
     are left to drain.   They are then taken by a conveyor  belt to a  gas
     fired (digester gas) incinerator.  The ash from the incinerator  is
     removed and hauled  with  the grit to be buried daily.  In 1971  an
     average of ten tons per  day of screenings was fed to the incinerator.

     G.  Digester  Gas

         Gas produced by the  primary  and secondary digesters is used  to
     mix the primary digesters by gas recirculation.  It is also  used as
     a fuel for heating  the plant, the screenings incinerator,  sludge heat
     exchangers, and other  gas-fired  equipment.

         It is noted that Denver Northside  presently has an EPA construction
     grant to provide modifications to its  present anaerobic digesters.  Each
     of the digesters will  be provided with fixed covers and gas  recirculation
     equipment as  well as other  modifications.

IV.   SUMMARY OF EVALUATION

     A.  Plant Operations

         The evaluation  of  the Northside plant  indicated that the plant
     follows basically a sound operational  program that should  routinely
     provide adequate treatment.  This mode of operation was arrived  at,  for
     the most part, by selecting the  best methods based on  operational  ex-
     periences. Although operation was  sound,  it may be that detailed
     special  studies into various aspects of the  plant's operations will
     yield a more  optimum performance from  the facility. Suggestions for
     areas of study are  outlined as follows:

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1.  Supernatant Liquor

    The supernatant liquor represents that portion of the plant's
operations that visually has the most significant effect on effluent
quality.  For this reason, improving the quality of supernatant liquor
would be a good starting point in improving the plant's performance.

    The most obvious method to decrease the effect of the supernatant
liquor is to improve or optimize digester operations to produce the
best quality supernatant.  Although digester modifications are not
yet completed, it may be possible to improve present operations by
changing the ratio of primary digesters to secondary digesters, i.e.,
change from 4 primaries and 3 secondaries to 5 and 2, or 6 and 1, etc.
Improved digestion may also be accomplished by increasing the concentration
of solids removed from the primary clarifiers.  An increase of one percent
or even one-half of one percent in solids concentration can affect digester
performance.  Loading or "feeding" the digesters is another area that
should be evaluated to determine the optimum loading rate.  For example,
it may prove more advantageous to load the primary digesters in smaller
quantities at more frequent intervals.

    Transfer of sludge to the secondaries should be evaluated to assure
minimum disturbance of the contents within the secondary digester.  It
may also be beneficial to study ways of making drawoff from the secondary
digesters a continuous or displacement type operation rather than the
present draw and fill operation.

    Each of the above outlined procedures will take time and laboratory
support to investigate, but will insure that optimum operation has been
achieved.  When digester modifications are completed, further studies
will have to be made to again determine the best mode of operation for
the digesters.

    When optimum digester operation has been established through controlled
operational modifications, the best quality supernatant that can be
achieved at the plant should be available for return to the plant flow
scheme.  It may, however, still be necessary to provide additional
treatment for the supernatant to insure that its return to the flow
scheme has a minimum effect on the plant's performance.  Additional
supernatant treatment could consist of the asphalted settling beds
presently being used, chemical precipitation or polymer addition for
better removal of suspended matter, or other methods of separate super-
natant treatment.

    A controlled program to minimize the effect of supernatant liquor
on Northside's performance will provide not only an optimum level of
treatment, but will also provide factual information to designers,
planners, MDSDD #1, etc., as to the full capabilities of the Denver
Northside plant.

2.  Plant Sampling

    Sampling is another area in which suggestions can be made to modify
plant procedures.  Although a change in sampling procedures will not
modify plant performance, it is felt that the benefits derived from

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 obtaining  factual  information can  be  used  in future design modifications
 to the Denver  Northside  plant,  as  well as  in design considerations for
 the entire Metropolitan  Denver  wastewater  treatment system.

     Present sampling  of  plant influent is  inadequate  to describe  the
 incoming waste load  to the  Northside  plant.  Sampling is  not done
 proportional  to incoming flow and  supernatant  liquor  is included  in
 the influent sample.

     Proportional  sampling throughout  the plant would  provide a much
 better insight into  the  actual  loading to  the  facility.   Proportional
 sampling should be tried and results  compared  with the normal way of
 sampling,  i.e., compositing uniformly-sized grab  samples.

     Two approaches can be taken to eliminate the  effect of the supernatant
 liquor on  the  influent samples.   If the grit removal  facilities aid in
 the treatment  of the  supernatant liquor as is  claimed by  plant personnel,
 then it is necessary  that piping modifications be made so that a  repre-
,sentative  sample of  plant influent can be  collected.   The other alter-
 native is  to return  supernatant through present facilities to the point
 following  the  grit channels.

     If the effect of  supernatant on plant  efficiency  must be determined,
 then the supernatant  waste  stream  must be  sampled (composite proportional
 samples) and its waste characteristics analyized. This determination of
 "in-plant load" could  then be added with the incoming  waste load to determine
 a total load to the  plant.  Using  this approach,  the  overall reduction of
 incoming load  plus in-plant load could oe  determined.

     Whatever is done  with the supernatant  at Denver Northside, it is
 mandatory  that the quality  and  quantity of the incoming wastewater be
 known.  In fact, future  modifications to wastewater treatment systems
 in the Metropolitan  Denver  area may require an even more  completecharacter-
 ization of the incoming  waste to Northside in  order to adequately design
 treatment  facilities. For  example, if water reuse becomes a reality  then
 tertiary or advanced  waste  treatment  methods will become  necessary.
 Parameters such as nitrogen, phosphorus, heavy metals, etc., will become
 important.  Background information or rather baseline data in these areas
 should be  gathered now,  prior to the  design of such facilities.   The  size
 and importance of the Northside plant in the overall  treatment of wastes
 in the Metro area make it mandatory for this facility to  collect  repre-
 sentative  samples to  provide data  for future designs  and  modifications.

 3.  Miscellaneous Operations

    .Many areas at the Denver Northside plant appeared to  be adequate.
 The laboratory appears to be well  equipped and capable of producing
 reliable data.  Although the laboratory personnel estimated that  seventy
 percent of its work was  done for the  treatment plant  (the other work  is
 done in the Industrial Waste program), there seemed to be little  flexi-
 bility or  time to do  specialized testing to improve plant operations.
 The importance of flexible  laboratory support  to  aid  in optimization  of
 plant performance cannot be overstated.

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    The maintenance program and preventative maintenance program at
the Denver Northside facility is very good.  Records and schedules
are kept on all pieces of equipment and back up supplies are provided
wherever it is economically feasible.  An alternate power source is
being developed.

    The Industrial Waste program has done a commendable job in reducing
the strength of waste discharges from the various "customers" to the
Northside system.  This has alleviated much of the load on the Denver
Northside facility as well as the MDSDD #1 plant.  The only comment
necessary concerning this program is that there must be an awareness
of the types and strength of waste that affect not only a primary
facility, but a secondary facility as well.  Efforts should be made
to eliminate all quantities or sources of wastes that could affect a
secondary plant despite the fact that they may have little effect on a
primary facility.

    The efforts of the City and County of Denver to improve their col-
lection system must also be mentioned.  The separation of combined
sewers, the use of T.V. cameras and sealing equipment, mechanical
tapping, reduction of flow from industries, etc., have all aided in
improving flow control in the Northside system.

    Flow measurement at the Northside plant has continually provided
problems.  It appears that continuous cleaning, maintenance, and
adjustment will be necessary to maintain reliable flow readings.

B.  Other Areas of Evaluation

    One of the most difficult problems that Denver Northside faces
as well as people or organizations dealing with Northside is trying
to establish the facilities capacity.  Since the capacity of Northside
directly affects expansions at MDSDD #1, it is imperative that Northside
capacity be established.  Northside admittedly by-passes manually to the
river at approximately 130 MGD.  This is far below the 160 MGD capacity
that was reported in a recent predesign study done for MDSDD #1.

    The lack of information on Denver Northside's capacity points to
another difficult problem which is one of separate planning, design,
and expansion activities of the Northside and MDSDD #1 facilities.
This is apparently true not only for Northside and MDSDD #1, but also
for the other facilities in the Metropolitan Denver area.  Despite
the available mechanisms for area wide planning, the job of coordinating
wastewater treatment plant development to affect an interrelated system
capable of economically accomplishing the water quality goals is not
being done.

    This is evidenced by the lack of coordination between expansion
efforts between the two largest facilities in the area, Denver Northside
and MDSDD #1.   Apparently the recent predesign study done on the MDSDD
#1 did not consider the possible use of the expanded digester capacity
that may be available at the Northside plant when digester modifications
are completed.   An analysis was made of the potential  capacity of the
Denver Northside digesters using current design parameters available

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    in the literature.   A portion of this analysis  is  shown  in  Table  1.
    Although different  assumptions (i.e., more secondary digesters  and
    less primary digesters or use of all  eight digesters, etc.) would
    yield different results, the table shows that at design  flow of 106
    MGD at Northside, the digesters could still  take a minimum  of 26,000
    Ibs. of solids per  day to a possible  maximum of 113,200  Ibs.  of solids
    per day from the MDSDD #1 plant.  This analysis assumes  that the  digester
    modifications underway at Denver Northside are  complete  (i.e. gas recir-
    culation, cleaning, etc.).

        Many other facets of the two plants should  be  studied jointly in
    a system approach,  rather than an individual plant approach.  This
    situation must be resolved and future efforts must include  an evaluation
    of the two plants as a system if the  best possible treatment is to  be
    economically achieved.

V.  CONCLUSIONS

        The Denver Northside plant follows a basically sound operational
    program that should routinely provide adequate  treatment.  However,  many
    areas of the plant  have not been studied in sufficient detail to  assure
    that the optimum performance is being obtained. Specific areas which
    need special studies to achieve optimum treatment  are digester  operations
    and handling of supernatant liquor.    Other areas  that might also benefit
    from special studies are plant sampling procedures, sludge  drawoff  from
    primary clarifiers, chemical or polymer precipitation studies,  etc.
    Emphasis on these types of special studies as well as laboratory  support
    for these studies was not available at the Northside plant.

        Many areas at the Denver Northside plant and in the  Northside system
    were adequate.  The laboratory was generally well  equipped  and  was  apparently
    providing reliable  data.  The preventative maintenance program  was  good      <
    and appeared to be  adequate to handle most situations that  may  occur or
    indeed prevent many breakdowns from occurring.   The Industrial  Waste pro-
    gram has aided in reducing the quantity of waste discharged by  the  various
    industrial contributors to the Northside system.  The City  and  County of
    Denver has initiated effective programs to control the flow discharged
    to the collection system.

        Because Northside is a prominent  portion of the wastewater  treatment
    system in the Metropolitan Denver area, it must assume responsibility
    for completely characterizing its wastewater to aid in future design and
    modifications to the Metropolitan Denver wastewater treatment system.

        The capacity of the Denver Northside plant  is  not exactly known.
    This makes future predications concerning use of the plant  difficult
    to determine.  Presently by-passing is done by  Northside personnel  when
    the flow is approximately 130 MGD. The flow in excess of 130 MGD must
    be adequately treated in the future.

        Present planning for expansions or modifications to  the Denver
    Northside and MDSDD #1 do not appear  to be coordinated to obtain  the
    most satisfactory and economical treatment of wastewater.  This situation
    must be altered so  that future modifications can be determined  on a
                                    10

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                                          TABLE 1
                                 TREATMENT PLANT EVALUATION
                       DENVER NORTHSIDE WASTEWATER TREATMENT FACILITY
                                        AUGUST 1972
                    "EVALUATION OF DENVER NORTHSIDE DIGESTER CAPACITY"
 Daily
   DNS
Suspended
Proposed
                                                               Assume MDSDD #1 Possib
Suspended
r/eraqe
'lant
,:low 1
MGD
80.3
80.3
80.3
80.3
80.3
80.3
106.0
106.0
106.0
106.0
106.0
106.0
^^^^^^^•M
Solids
Concentration
To Digesters 2
MG/L
56,000
56,000
56,000
80,000
80,000
80,000
56.000
56,000
56,000
80,000
80,000
80,000
^^^^^^^^^^^^^^^^^^^^^^H
Total Flow
To
Digesters 1
MGD
0.390
0.390
0.390
0.390
0.390
0.390
0.390
0.390
0.390
0.390
0.390
0.390
Flow
To
Digesters 4_
MGD
0.22
0.22
0.22
0.154
0.154
0.154
0.312
0.312
0.312
0.22
0.22
0.22
MDSDD #1
Flow
To Digesters
MGD
0.170
0.170
0.170
0.236
0.236
0.236
0.078
0.078
0.078
0.170
0.170
0.170
Solids
Concentration
To Digesters
MG/L
40 ,000
60,000
80,000
40,000
60,000
80,000
40,000
60,000
80,000
40,000
60,000
80.000
load
To
Digesters
Lb/Day
56,600
85,000
113,200
78,600
118,000
157,200
26,000
39,000
52,000
56,600
85,000
113,200
1_.   80.3 MGD = 1971 Average Daily
    106.0 MGD = Assumed Maximum Average Daily Flow at DNS

2_.  56,000 MG/L = 1971 Average Suspended Solids Concentration Pumped to Digesters
                  (Denver Northside Data)
    80,000 MG/L = Assumed Concentration Pumped to Digesters - Maybe Possible With
                  Improved Operation

3.  Total Flow Based on 5 Primary Digesters (781,000 Ft.3 Capacity) and 15 Days
    Detention Time in Primary Digesters (D.T. In Secondary Digesters = 6 Days).

4_.  0.22  MGD = 1971 Average Flow to Digesters (Denver Northside Data)
    0.154 MGD = 0.22 MGD X 56.000 MG/L (i.e., Same Number of Pounds of Sludge Pumped
                           80,000 MG/L  To Digester as in 1971, But At a Thicker
                                        Concentration)
    0.312 MGD = Flow to Digesters With 106.0 MGD Influent Flow; 254 mg/1 Influent
                Suspended Solids Concentration; 65% S.S. Removal; and 56,000 mg/1
                S.S. Sludge Concentration
    0.22  MGD = Same as 0.312 MGD Except With 80,000 MG/L S.S. Sludge Concentration

NOTE:  The following assumptions were made:
       1.  5 Digesters Used as Primaries and 2 Digesters Used as Secondaries
       2.  Detention Time in Primary Digesters = 15 Days
       3.  1 of the 8 DNS Digesters Will Always Be Down For Repair
       4.  Primary Digesters Will Be Continuously Fed, Completely Mixed With
           Gas Recirculation
       5.  DNS Average Influent Suspended Solids Concentration Will Be The Same
           At 106.0 MGD As At 80.3 MGD (i.e., 254 MG/L)
       6.  At 106.0 MGD, DNS will remove 65« Of The Suspended Solids Load
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     complete system approach rather than a separate plant approach.

VI.  RECOMMENDATIONS

         The results of the evaluation of the Denver Northside Wastewater
     treatment plant led to the following recommendations:

         1.  An intergrated approach to the design and development of the
             entire Northside - MDSDD #1 system must be taken to assure the
             most satisfactory and economical treatment of wastewater.   This
             should include modifications presently underway.

         2.  Areas of the plant's operations must be studied in detail  to
             ascertain that the optimum performance is being obtained from
             each portion of the facility.  A few areas suggested for this
             type of study include:  digester operation, primary clarifier
             sludge drawoff, handling of supernatant liquor, plant sampling,
             influent waste characterization, flow measurement, and by-passing
             practices.

         3.  The exact capacity of the Denver Northside facility for all por-
             tions of the plant (i.e., digesters, clarifiers, grease removal
             units, etc.) must be determined.

         4.  Sampling at the Denver Northside facility must be modified to
             assure that baseline data on influent and effluent flow is
             obtained for future design requirements.  This must include
             parameters that may be needed to adequately design advanced
             waste treatment systems necessary for water reuse.

         5.  Coordination between the separate management groups of the
             Denver Northside and MDSDD #1 must continue to improve.

         6.  Efforts to eliminate all by-passing from the Denver Northside
             collection system must continue.
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