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
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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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