ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
REPORT ON
EFFECTS OF WASTE DISCHARGES
WATER QUALITY OF THE SOUTH PLATTE RIVER
DENVER METROPOLITAN AREA
NATIONAL FIELD INVESTIGATIONS CENTER-DENVER
AND
REGION VIM DEN VER.COLORADO
JUNE 1972
CLEA
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ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
Report On
Effects of Waste Discharges
On
Water Quality of the South Platte River
Denver Metropolitan Area
National Field Investigations Center-Denver
and
Region VIII
Denver, Colorado
June 1972
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TABLE OF CONTENTS
Page
LIST OF APPENDICES ii
LIST OF FIGURES ill
LIST OF TABLES ill
GLOSSARY OF TERMS v
I INTRODUCTION 1
II SUMMARY AND CONCLUSIONS 3
III WASTE SOURCE EVALUATIONS 7
A. North Denver Wastewater Treatment Plant 7
General 7
Wastewater Treatment Facilities 7
Discussion of In-Plant Survey and Findings ... 8
B. Metropolitan Denver Sewage 12
Disposal Plant 12
General 12
Wastewater Treatment Facilities 17
Discussion of In-Plant Survey and Findings ... 18
IV STREAM SURVEYS 29
A. General 29
Previous Studies 29
Present Studies 31
Findings of August-September Survey 32
B. Findings of November Bacteriological Survey .... 35
C. Findings of the December Survey 38
V WATER QUALITY IMPROVEMENT MEASURES 43
REFERENCES 47
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APPENDICES
COLORADO WATER QUALITY STANDARDS
REPORT BY ENVIRONMENTAL PROTECTION AGENCY
REGION VII, KANSAS CITY, MISSOURI,
"FEDERAL ASSISTANCE PROJECT METROPOLITAN
DENVER SEWAGE DISPOSAL DISTRICT NO. 1,
OCTOBER 1969 - FEBRUARY 1970"
SAMPLING PROCEDURES
DATA ON METROPOLITAN DENVER SEWAGE
TREATMENT PLANT AND NORTH DENVER
WASTEWATER TREATMENT PLANT
ii
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LIST OF FIGURES
Figure No. Title Follows Page
Municipal Wastewater Treatment Facilities -
Metropolitan Denver Area 1
Flow Diagram North Denver Wastewater
Treatment Plant 8
Flow Diagram Metropolitan Denver
Sewage Treatment Plant 17
South Platte River from 19th Street
to 88th Avenue 31
Dissolved Oxygen Profile for the
South Platte River Downstream from
Denver Metro Effluent A3
LIST OF TABLES
Table No. Title Page
Summary of Analytical Results and
Field Measurements for the
Denver Northside Wastewater
Treatment Plant
August 1-9, 1971 10
Monthly Averages of Biochemical Oxygen
Demand and Suspended Solids Removals
at the North Denver Wastewater
Treatment Plant for 1971 11
Waste Treatment Flows and Costs
at Selected Plants 14
Other Wastewater Treatment Facilities
in the Metropolitan Denver Area 16
iii
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LIST OF TABLES (continued)
Table No. Title
5 Summary of Organic and Nutrient Data for
Metropolitan and North Denver Wastewater •
Treatment Plants
August 1-9, 1971 19
6 Summary of Heavy Metals Data for Metropolitan
and North Denver Wastewater Treatment Plants
August 1-9, 1971 20
7 Bacteriological and Chlorine Residual Data -
Metropolitan Denver Sewage Disposal Plant • 21
8 Removal Efficiencies for Denver Metro and
Denver Northside Facilities
, , August 1-9, 1971 ' .... .. 23
9 Bi-weekly Averages of Biochemical Oxygen
Demand and Suspended Solids Removals at
the Metropolitan Denver Sewage Disposal
Plant - 1971 : 25
10 Summary of Analytical Results and Field
, Measurements for the South Platte River -
19th Street to 88th Avenue
August 30-September 2, 1971 33
11 Results of Bacteriological Analyses -
South Platte River Stream Survey
November 17-21, 1971 36
12 Summary of Analytical Results and Field
Measurements for the South Platte River -
19th Street to 88th Avenue,
December 13-17, 1971 39
iv
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GLOSSARY OF TERMS
BOD - Biochemical Oxygen Demand, 5-Day
COD - Chemical Oxygen Demand
DO - Dissolved Oxygen
MPN - Most Probable Number
NH_N - Ammonia Nitrogen ;
NO -NO -N - Nitrite Nitrate Nitrogen
p - Phosphorus
PO, - Orthophosphate
TOG - Total Organic Carbon
TSS - Total Suspended Solids
VSS - Volatile Suspended Solids
cfs - flow rate given in cubic feet per second
gpm - flow rate given in gallons per minute
mgd - flow rate given in million gallons per day
mg/1 - concentration given in milligrams per liter
umhos/cm - unit of specific conductance (mho — the inverse of
the standard unit of electrical resistance, the ohm)
measured over a 1-centimeter distance, conventionally
made at 25°C
RM - river mileage
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I. INTRODUCTION
Water quality investigations were conducted in the South Platte
River Basin during August-December, 1971. Studies included an evaluation
of the waste-treatment practices at the Metropolitan Denver Sewage Dis-
posal District Plant #1 (Metro), the North Denver Wastewater Treatment
Plant (Denver Northside), and other satellite plants [Figure 1], Subse-
quently, stream surveys were conducted on the South Platte River (SPR)
to determine the impact of waste loads on water quality. The primary
objectives of the survey were to:
1. Determine if established State and Federal water quality
standards [Appendix A] were being met.
2. Ascertain if adequate treatment were provided in accordance
with established treatment requirements.
3. Determine the extent of water quality improvement in the
South Platte River Basin since the 1966 State-Federal
Enforcement Conference.—
4. Recommend water quality improvement measures.
The in-plant survey was conducted at Metro during August 1-9, 1971,
to measure the waste removal efficiency and waste loads discharged.
Effluent from the Denver Northside Plant constitutes the major portion
of flows received at Metro.
This report will discuss the results of the in-plant evaluations
and the subsequent stream surveys in relation to the aforementioned
obj ectives.
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_ JOULOEB _CO..
JEFFERSON CO
ROCKY MOUNTAIN
ARSENAL
ARAPftHOE CO
DOUGLAS* CO.
1. SOUTH ADAMS SANITATION DISTRICT
2. METROPOLITAN DENVER SEWAGE DISPOSAL PLANT
3. NORTH DENVER WASTEWATER TREATMENT PLANT
4. SOUTH LAKEWOOD SANITATION DISTRICT
5. ENGLEWOOD SANITATION DISTRICT
6. LITTLETON SANITATION DISTRICT
7. BAKER SANITATION DISTRICT
8. ARVADA
9. CLEAR CREEK VALLEY SANITATION DISTRICT
10. WHEATRIDGE
11. GOLDEN • COORS
12. AURORA SANITATION DISTRICT
13. BUCKLEY AIR FIELD
14. GLENDALE SANITATION DISTRICT
15. FITZSIMONS HOSPITAL
Figure 1. Municipal Wastewaler Treatment Facilities Metropolitan Denver Area
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II. SUMMARY AND CONCLUSIONS
1. The Denver Northside Sewage Treatment Plant had BOD removal ef-
ficiencies ranging from minus 11 percent (increase in BOD) to 58 percent
and suspended solids removal efficiencies ranging from 6 percent to 96
percent. Plant records for a 6-month period, from January to June 1971,
showed average removals between 22 and 36 percent for BOD and 39 and
60 percent for suspended solids. Bypassing from an interceptor connected
to the Denver Northside plant was evidenced by sludge banks in the South
Platte River downstream from Franklin Street. Inadequate primary treat-
ment at Denver Northside significantly affects removal efficencies at the
Metropolitan Denver Disposal District Plant #1 facility. The Colorado
Department of Health and EPA are working with the staff at the Denver
Northside waste treatment plant to improve treatment methods at this plant,
thereby reducing the wasteload contributed to the Denver Metro facility.
2. The Metro plant is overloaded hydraulically and organically. The
plant is designed for 117 mgd. Peak flows of 180 mgd were recorded during
the survey. The average BOD loading observed (182,000 Ib/day) was 110
percent of the design loading. Four of the twelve aeration basins are
being used for sludge digestion instead of for their intended use.
3. Adequate treatment was not beine provided by the Metro plant for
BOD and suspended solids removal resulting in the average discharge of
approximately 30,200 Ib/day of BOD and 119,000 Ib/day of suspended solids
to the South Platte River. Including removals at the Northside plant,
BOD removals for Denver Metro ranged from 63 percent to 96 percent on a
daily average and were below the State requirement of 80 percent BOD
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removal 20 percent of the time. Suspended solids removal ranged between
39 and 95 percent. Removals were highest during the weekend when the
overloading conditions were minimal. Moreover, adequate disinfection
was not provided, as shown by the low chlorine residuals and the high
bacteria concentrations in the effluent. Fecal coliform bacteria in the
effluent ranged from 230-430,000 organisms/100 ml. The Colorado Depart-
ment of Health recommendation for a residual chlorine value of 1 mg/1
after 15 minutes at maximum hourly flow was not maintained during the study.
4. Scouring velocities occurred in the final clarifiers at the Metro
plant during peak flows owing to the hydraulic overload and to the inade-
quate placement of the weirs. The lack of skimmers on the final clarifiers
resulted in floating solids being discharged into the receiving waters.
5. Thirteen other, small treatment plants treat less than 15 per-
cent of the liquid waste in the Metres area. Of these, nine plants
were evaluated:
South Adams Sanitation District
South Lakewood Sanitation District
Englewood Sanitation District
Littleton Sanitation District
Baker Sanitation District
Arvada
Clear Creek Valley Sanitation District
Wheatridge
Coors-Golden
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Of these, the Clear Creek Valley Sanitation District and Arvada were the
only facilities meeting the present State requirement of a minimum 80 per-
cent BOD removal.
6. Sludge-handling capacity at Metro continues to be a problem; its
inadequacy affects plant performance by causing an effluent high in sus-
pended solids.
7. Mercury discharges vary from 0.2 to 0.9 Ib/day. The majority of
the mercury comes from unknown sources discharging to the Denver Northside
wastewater treatment facility.
8. Minor changes in concentrations of ammonia and the sum of nitrate
and nitrite concentrations occur during treatment by Denver Northside and
Metro, indicating no significant reductions in total nitrogen through the
treatment process. Total phosphorus is reduced approximately 28 percent.
The total nitrogen and phosphate loads discharged to the South Platte
River, during the survey, averaged 20,000 and 7,000 Ib/day, respectively.
Removal of nitrogen and phosphorus at existing and proposed treatment faci-
lities may be necessary in the future to protect the water quality of the
South Platte River.
9. Raw sewage discharges were observed at 47th Avenue and at Franklin
Street. The Franklin Street discharge was corrected in September 1971.
The 47th Avenue sewer continues to discharge raw sewage occasionally.
Facilities to abate the 47th Avenue discharge are under construction, to
be completed by December 31, 1972.
10. However, attainment of a consistent minimum 5-day BOD removal
of 80 percent at the Metro plant will not meet official State-Federal
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water quality standards for the South Platte Rivet. To meet water quality
criteria for dissolved oxygen in the South Platte River the present efflu-
ent from the Metro facility should not exceed an average of 10,000 Ib/day
with a maximum instantaneous limit equivalent to 15*000 Ib/day of 5-day
BOD. This average limit is equivalent to an effluent concentration of
10 rag/1 of BOD and would require an estimated 95 percent BOD reduction
based on present influent values.
11. Since the studies conducted by the South Platte River Project
ia 1964-65 there has been sous improvement of water quality conditions
ir» the South Platte River. Lowering of BOD and coliform concentrations
.-jsd the increase in DO levels is due mainly to the construction and
operation of the Metropolitan Denver Disposal District Plant #1..
12. Violation of the bacterial standard occurred in the South Platte
:iiver at York Street. Salmonella were isolated in the main stem, South
rlatte River, and Burlington Ditch, indicating fecal contamination in
i'ne River.
13, The South Placte River quality, upstream of the Metro effluent,
...^.__d be improved if all necessary upstream abatement measures were ac-
..u^lishad (e.g., elimination of bypassing and upgrading of upstream
t facilities).
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III. WASTE SOURCE EVALUATIONS
A. NORTH DENVER WASTEWATER TREATMENT PLANT
General
The North Denver plant is a primary wastewater treatment facility
with a design capacity of 120 mgd. The plant was constructed in 1936,
with additional clarifiers being constructed in 1946 and 1965. Effluent
and digested sludge from this facility are piped separately to the Metro
plant for additional treatment.
This plant is staffed with a superintendent, an operations foreman,
and 30 operators. Some of these operators have Class "C" and "D"
*
Operator s Licenses. A laboratory staff of eight chemists monitors
treatment efficiency within the plant. Samples from approximately 80
industrial wastewaters discharged to the Northside plant are analyzed,
and the results are used as a basis for determining customer charges.
According to plant officials, 130 industries discharge waste to the North
Denver plant. Wastewater samples collected by the Denver County Health
Department are also analyzed in this laboratory.
Wastewater Treatment Facilities
The operation of the Northside plant has changed since it was eval-
21
uated during the South Platte River Basin Project Studies;— the effluent
now is pumped to the Metro plant for further treatment instead of being
chlorinated and discharged to the South Platte River. [The flow diagram
* The State of Colorado has a Volunteer Certification Program for
Wastewater Treatment Operators, Class "A" being the highest and
a Class "D" the lowest level of certification. There are no
operators with Class "A" or Class "B" certification at Northside.
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for this facility is shown in Figure 2.] The Northside flow constitutes
about 75 percent of the total flow to Metro. The principal components
of the system are as follows:
1. Preliminary treatment - bar screens, grit chambers (5),
'pre-aeration basins (3), grease flotation and removal.
2.' Primary clarifiers (8) - 150 feet in diameter and 14
feet deep with skimming arm to remove floating materials.
3. Digesters (heated) - 6 primary, 2 secondary; each 85
feet in diameter and 30 feet deep.
As indicated above, sludge is pumped to the Metro plant for further
treatment (i.e., secondary digestion). Denver Northside plant officials
claim that a volatile solids reduction of 65 percent is obtained in the
digestion process.
Discussion of_ In-Plant Survey and Findings
The North Denver wastewater treatment plant was evaluated during the
period from August 1 to 9, 1971. Influent samples were collected upstream
of the point of supernatant return [Figure 2-Station E], Effluent samples
from the Northside plant were collected at the point where the wastewater
enters Metro plant [Figure 2-Station G]. All samples were analyzed at
the NFIC-D laboratory for BOB, COD, TOC, and solids (total, suspended,
volatile suspended, and settleable). Nutrients were determined for the
influent samples only. Influent samples were also analyzed for selected
heavy metals in order to ascertain if concentrations were at levels which
could affect biological processes.
As previously stated, 130 industries discharge wastewater to the
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INFLUENT
• •
BAR
SCREENS
GRIT
REMOVAL
PREAERATION
GREASE
FLOTATION
AND
REMOVAL
GREASE TO
RENDERING
COMPANY
SECONDARY
DIGESTION
PRIMARY
DIGESTION
DIGESTED
SLUDGE TO
METRO
LEGEND
< G
EFFLUENT TO
METRO
STATION DESCRIPTION
E DENVER NORTHSIDE INFLUENT
G DENVER NORTHSIDE PRIMARY
(SAMPLED AT DENVER METRO PLANT]
Figure 2. Flow Diagram North Denver Wastewaler Treatment Plant.
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North Denver plant (estimated at 8-10 percent of the total flow), which
was designed for peak flows of 120 mgd; if exceeded, the excess is by-
passed to the South Platte River. Although no by-passing was observed
at the plant during the survey, an interceptor carrying wastewater to
the Denver Northside plant was observed to be overflowing to the South
Platte River at Franklin Street. Although the total flow by-passed
could not be ascertained, it was evident from the sludge bank in the
river that the interceptor had been overflowing for a prolonged period.
*
Another raw sewage discharge was observed at 47th Avenue. An official
of the City and County of Denver stated that the latter by-pass results
from overloading of the Broadway sewer. The amount of by-passed flow
was not available from the official. It was reported that a faulty
valve was causing this condition and that it was corrected during
September 1971. A contract has been let to install additional inter-
ceptor capacity by December 31, 1972. This new interceptor should
eliminate the by-passing of raw sewage to the South Platte River at
47th Avenue.
Analyses of influent and effluent data for this plant indicate
BOD and suspended solids removal ranges of -11 to 58 percent and 6 to
**
96 percent, respectively [Table 1]. A review of plant records for
the period January 1-June 30, 1971, shows that monthly removal effi-
ciencies averaged between 22 and 36 percent for BOD, and between 39 and
60 percent for suspended solids [Table 2]. Concentrations of heavy
* This discharge was observed and sampled in 1966 by the South Platte
River Basin Project. The raw sewage was being discharged to the
South Platte River.$/
** The negative BOD removal is attributed to carryover of solids from
the primary clarifiers.
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o
TABLE 1
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE
DENVER NORTHSIDE WASTEWATER TREATMENT PLANT
August 1-9, 1971
Value
Parameter
Influent
Effluent
Percent
Reduction (Range)
Flow (MGD>§/
pH
Temperature (°C).
Conductivity (umhos)
Biochemical Oxygen Demand (BOD)(mg/1)
Suspended Solids (mg/1)
Volatile Suspended Solids (mg/1)
Settleable Solids (mg/1)
Chemical Oxygen Demand (COD)(mg/1)
7.2-8.8
18-24
1000-1500
180-430
320-1240
240-1200
3.5-5.0
590-1800
76.7-92.5
105-310
30-300
30-160
0.2-0.7
160-270
(11)^-58
6-96
67-96
86-90
73-85
a/ Flow measured at Metro plant. Northside effluent samples collected at Metro (Station G-Figure 3).
Flow recording equipment at Denver Northside not considered accurate.
b/ The numbers in parentheses are negative numbers.
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11
TABLE 2
MONTHLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
SUSPENDED SOLIDS REMOVALS AT THE ,
NORTH DENVER WASTEWATER TREATMENT PLANT FOR 1971-
b/
Month"
January
February
March
April
May
June
Percent
BOD Removal
35
36
25
23
32
22
Percent Suspended
Solids Removal
60
55
44
39
53
60
a_/ Efficiencies were calculated on the basis of data provided by Northslde
officials.
b/ Supernatant was returned upstream of the pre-aeration chambers*
January-April and returned upstream of the bar screens May-June
[Figure 2].
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12
metals were low and would not affect biological treatment processes.
Plant officials do not know the source of these heavy metals.
B. METROPOLITAN DENVER SEWAGE DISPOSAL PLANT
General
The Metropolitan Denver Sewage Disposal District encompasses most
of the communities in the Denver area. The District includes:
Alameda Sanitation District
Applewood Sanitation District
City of Arvada
City of Aurora
Baker Water and Sanitation District
Bancroft Sanitation District
Berkeley Sanitation District
City and County of Denver
East Lakewood Sanitation District
Fruitdale Sanitation District
Highland Park Sanitation District
North Pecos Sanitation District
North Table Mountain Sanitation District
North Washington Street Sanitation District
Northwest Lakewood Sanitation District
Pleasant View Sanitation District
City of Thornton
Westminster Sanitation District
Westridge Sanitation District
Wheatridge Sanitation District
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13
Wastewaters from these component municipalities and sanitation
*
districts are treated by the Metro plant. The Metro plant is a secon-
dary treatment facility that began operation in May 1966. It has a pri-
mary and secondary treatment design capacity of 27 and 117 mgd, respec-
tively. The design BOD load is 166,350 Ib/day. The estimated population
served by this plant is 870,000.
The operating staff includes nine shift supervisors (9 with Class "A"
certification) and 40 operators (most have Class "C" and "D" certifications).
In addition, the laboratory has 12 employees (chemists, microbiologists,
and technicians) to collect and analyze in-plant and stream samples. (Four
of these have Class "A" certification.)
Primary treated effluent from the Denver Northside plant comprises
about 75 percent of the average daily flow received. Raw municipal wastes
are received from the Sand Creek and Clear Creek interceptors. Industrial
wastes (less than one percent of the total flow) are received directly
from the Packaging Corporation of America.
A portion of waste flows from three satellite treatment facilities
(Arvada, Wheatridge, and Baker Water and Sanitation District) is diverted
to Metro also [Figure 1]. The average waste flow treated and the average
waste flow diverted at each of these plants during the evaluation period
is shown in Table 3. Cost of treatment for these satellite plants and for
Clear Creek Valley Sanitation District is also shown. During in-plant
evaluations, Baker Sanitation District and Wheatridge were not meeting
the State requirements for 80-percent BOD removal.
* Some of the wastewaters receive primary treatment prior to being
discharged to the Metro plant.
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TABLE 3
WASTE TREATMENT FLOWS AND COSTS AT SELECTED PLANTS
Map*'
Key Name of Plant
7 Baker Water &
San. District
9 Clear Creek .
River Mile
305.5/3.0
305.5/7.0
Design
Capacity
mgd
1.0 '
2.2
Flow-
Observed
mgd
0.9
2 . 48-/
Flow
Diverted
to Denver
mgd
0.8
None-i'
Cost of ,
Treatment—
$/mil gal
63
185
Metro
Cost of ,
Treating^
$/mil gal
155^
.
123-19 2&
San. District
8 Arvada
10 Wheatridge
305.5/6.2/0.3 1.2
305.5/7.5 1.75
1.09
2.2
3.5
0.03-'
102
168
173*'
123-192J
ay See Figure 1 for location. ...
b/ Treated flow,observed during plant evaluation. -.
_c/ Receives waste from Sigman Meat Company. . • .
d/ Based on design flows and annual operation cost figures provided by plant officials.
je/ Metro officials estimate the charge to customers .for each million gallons delivered as $112/mil gal. Tne exact
charge is based on $53/mil gal flow, .$46/ton BOD, and $40/ton suspended solids. •
_f/ Based on annual cost figures of $45,000 provided by plant officials and assuming 0.8 mgd diverted to Metro.
j»/ Based on influent BOD and. suspended solids concentrations of 200-350.
h/ Based on annual cost figures of $221,000 provided by plant officials and assuming 3.5 mgd diverted to Denver.
_!/ Plant officials indicate that.flow is diverted to Metro approximately 10 minutes twice a day (between 0800-0900
and 1500-1600) to facilitate cleaning of headworks.
j/ Presently are not connected to Metro facility; plant located in close proximity to Clear Creek Interceptor.
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15
District members are charged according to the amount of BOD, suspended
solids, and flow received by the Metro plant. These charges, according
to plant officials, are $46.43 per ton BOD, $40.23 per ton suspended
solids, and $53.13 per million gallons. This combined cost amounts to
approximately $112 per million gallon delivered. The cost per family
is about $15 per year. On the basis of the cost information provided
by officials of Wheatridge and Clear Creek Valley Sanitation District
[Table 3] and influent BOD and suspended solids concentrations, treat-
ment costs for these sanitation districts are similar to the Metro treat-
ment cost rate.
The estimated operation and maintenance costs at the Arvada and the
Baker plants were provided for 1971 [Table 3]. It appears wastewater is
presently treated at these plants at much less cost than at Metro. However,
the cost of expanding these plants to take all incoming flows would in-
crease the treatment cost. For example, the cost of a trickling filter
plant (primary treatment and sludge digester included) of 1.0 mgd is
estimated at about $500,000.— At an interest rate of 7 percent and
with a 20-year life expectancy, the annual cost including amortization
of capital costs and maintenance is estimated at $47,000. If the com-
munity receives a 30 percent Federal grant, the annual cost would be
about $33,000. Therefore, at design flow, the cost to treat one mgd
varies from $90 with a grant to $130 without a grant. When labor, chem-
ical, and other costs are added, the cost per million gallons treated
is comparable to that of the Metro plant.
In addition to these four plants, nine plants operate independently
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TABLE 4
OTHER WASTEWATER TREATMENT FACILITIES IN THE METROPOLITAN DENVER AREA
Map^7
Key Name
12 Aurora Sanitation District
13 Buckley Air National Guard Field
5 Englewood Sanitation District
15 Fitzsimons General Hospital
(0. S. Army)
Flow Observed
During
Evaluation (mgd)
y
y
8.6
Receiving Stream
Sand Creek
Sand Creek
South Platte
River
Toll Gate Creek
Tributary to
Sand Creek
River Mile Remarks
306.8/5.5/1.15 Discharges sludge to
Metro.
306.8/11.9
319.7 Additional treat-
ment facilities
under, construction.
Treated wastewater
is used for irri-
gation on the hospit
14 Glendale Sanitation District
11 Coors - Golden
6 Littleton Sanitation District
1 South Adams Sanitation District
4 South Lakewood Sanitation District
3.0. Coors
2.0 Golden-
5.2
1.8
1.8
Cherry Creek.
Clear Creek
305.5/15.5
South Platte River 323.5
South Platte River 301.2
South Platte River 314.1/2.1W
grounds, excess is dis-
charged to Sand Creek.
Interceptor has been
constructed to deliver
Coors Porcelain Plant
and Golden wastes to
Metro according to
sources at Coors.
aj See Figure 1 for location.
b/ Flows were not measured.
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17
of the Metro system [Table A and Figure 1]. The South Lakewood Sanitation
District, for example, operates as a contact stabilization plant located
at 700 Depew Street, Lakewood, Colorado. Effluent from this plant is
discharged to the South Platte River. The facility is designed for
1.2 mgd, but presently receives 1.8 ragd. The plant is being expanded
to increase capacity to 1.8 mgd with the assistance of an EPA construc-
tion grant.
The total waste being treated by the aforementioned plants is less
than 15 mgd, which would represent about 12 percent of the flow now
treated by Metro. Of the five plants evaluated [Table A], none were
meeting the State requirements for 80-percent BOD removal. The planned
expansion at Metro should include provisions for the collection and
treatment of the wastewaters presently treated at the small plants and
schedules should be developed to phase out these small plants. No
further construction should be initiated at these plants unless it can
be shown that such an expansion will provide for the continued protec-
tion and enhancement of the South Platte River and tributaries.
Wastewater Treatment Facilities
The principal components for the Metropolitan Denver Sewage Disposal
District Plant #1 are as follows [the flow diagram is presented in Figure 3]
1. Preliminary treatment - bar screens, grit chambers, grease
flotation and removal.
2. Primary clarifiers (A) - each 106 feet in diameter with an
8-foot, 9-inch side water depth. Each clarifier has a
skimmer to remove floating solids.
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18
3. Activated sludge units - 12 aeration basins each consisting
of 3 tanks 210 feet long, 30 feet wide, and 15 feet deep.
4. Secondary clarifiers (12) - each 130 feet in diameter with
a side water depth of 10 feet. There are no skimmers on
these units.
5. Chlorine contact chambers (3) -> each 240 feet long, 30 feet
wide, and 15 feet deep.
6. Sludge digesters and furnaces. .
The activated sludge units and secondary clarifiers are divided into
four separate systems by piping, pumps, and control buildings. Each of
these systems, consisting of three aeration basins and three clarifiers,
functions as a separate secondary plant. In effect, there are four sec-
ondary treatment facilities at Metro which are operated separately [Fig-
ure 1 in Appendix B]. No attempt was made to determine the efficiency
of each of these "plants" during this survey. However, composite samples
were collected at the influent channel to the four plants and at the com-
bined effluent channel before and after chlorination.
Discussion jof_ In-Plant Survey and Findings
The Metro plant was evaluated August 1 through 9, 1971. All samples
were analyzed at the NFIC-P laboratory for BOD, TOC, CQD, and solids (total,
suspended, volatile suspended, and settleable). Samples for selected
stations were also analyzed for nutrients and heavy metals [Tables 5, 6,
*
B-l, B-2, and B-3 ]. Bacteriological samples were collected periodically
for the final effluent [Table 7]. Field measurements of the Metro
* Tables B-l, B-2, and B-3 are located in Appendix B.
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CLEAR
INTER
PACKAGING
0B
CORPORATION
EFFLUENT
SANO
INTEI
CREEK EFFLUENT FRO
CEPTOR NORTHSIDE PI
* -_. ^ "^ G
BAR GRIT GREASE / PRIMARY \
SCREENS REMOVAL " REMOVAL (cLARIFIERS 1
CREEK
IC6PTOR
F
M
ANT
SOUTH
PLiTTE
RIVER J !
i
PUMP
TO BURLINGTON
DITCH
CHLORINE
CONTACT
CHAMBER
/SECONDARY^
" IcLARIFIERSy
ACTIVATED
SLUDGE
1
H
LEGEND
STATION DESCRIPTION
A CLEAR CREEK RAW INFLUENT
B PACKAGING CORPORATION EFFLUENT
C SAND CREEK RAW INFLUENT
D COMBINED RAW INFLUENT TO METRO
F METRO PRIMARY EFFLUENT
<$ DENVER NORTHSIDE PRIMARY EFFLUENT
H INFLUENT TO SECONDARY UNITS
I INFLUENT TO C12 CONTACT CHAMBER
J METRO FINAL EFFLUENT
Figure 3.-Flow Diagram Metropolitan Denver Sewage Treatment Plant
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TABLE 5
SUMMARY OF ORGANIC AND NUTRIENT DATA FOR METROPOLITAN AND NORTH DENVER WASTEWATER TREATMENT PLANTS-
AUGUST 1-9, 1971
Station
A
B
C
E
G
I
J
Description
Clear Creek Raw Influent
Packaging Corporation
Effluent
Sand Creek Raw Influent
Denver Northside Influent
Denver Northside Primary
Effluent
Influent to Cl. Contact
Chamber
Final Effluent from Metro
Flow
mgd
18.9
0.4
10.3
86.7
86.7
116.3
116.3
BOD
mg/1
187
398
211
295
175
41
31
Susp.
Solids
mg/1
334
344
349
680
120
98
123
Vol.
Susp.
Solids
mg/1
283
287
305
620
80
100
117
Settl.
Solids
mg/1
5.3
6.2
5.9
1.0
0.9
1.7
COD
mg/1
475
1030
695
1250
230
213
160
NH,
mg/1
18
1.4
19
17
15
Total (KJ)-/
N
mg/1
27
5.8
30
25
20
N02+N03
mg/1
0.04
2.2
0.11
0.08
0.73
P
mg/1
10.5
0.9
13.0
9.4
7.1
a/ Values listed are averages.
b/ KJeldahl nitrogen.
-------
TABLE 6
SUMMARY OF HEAVY METALS DATA FOR METROPOLITAN AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
Station
A
B
C
E
G
I
J
Description
Clear Creek Raw
Influent
Packaging Cor-
poration Effluent
Sand Creek Raw
Influent
Denver Northside
Influent
Denver Northside
Primary Effluent
Influent to Cl_
Contact Chamber
Final Effluent
from Metro
Flow
mgd
18.9
0.4
10.3
86.7
86.7
116.3
116.3
Cadmium
mg/1
Average
< 0.03
0.02
0.02
< 0.14
< 0.02
< 0.02
Chromium
mg/1
Average
< 0.04
0.15
0.30
0.10
0.08
0.06
Copper
mg/1
Average
0.08
0.13
0.31
0.22
0.16
0.10
Lead
mg/1
Average
0.11
1.05
0.09
0.17
< 0.06
< 0.04
Zinc
mg/1
Average
0.18
3.14
0.29
1.01
0.28
0.20
Mercury
Mg/1
Average
< 0.30
< 0.57
0.55
0.58
0.53
0.50
< = Less Than
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21
TABLE 7
BACTERIOLOGICAL AND CHLORINE RESIDUAL DATA
METROPOLITAN DENVER SEWAGE DISPOSAL PLANT
Date /Time
Sampled
August 2
August 3
August 4
August 5
August 6
0400
0600
1000
1200
1400
0200
0400
0600
1000
1200
1400
0000
0200
0400
0600
1600
1800
2000
1200
1400
1700
0000
0200
0400
0600
0800
1000
1200
Chlorine
Residual
mg/1
0.01
0.01
0.40
0.06
0.04
0.04
0.01
0.06
0.06
0.08
0.08
0.08
0.08
0.64
0.32
0.28
0.03
0.03
0.03
0.01
0.02
0.16
0.21
Coliform Count/100 ml
Total
. 86,000
550,000
. 37,000
14,000,000
9,800,000
.860,000
170,000
.660,000
7,300,000
,540,000
370,000
410,000
.210,000
72,000
380,000
31,000
36,000
19,000
9,200
26,000
29,000
17,000
330,000
200,000
21,000
27,000
48,000
6,600
Fecal
1,100
13,000
390
430,000
72,000
74,000
20,000
37,000
96,000
30,000
6,600
90,000
18,000
7,800
17,000
< 2,000
< 2,000
< 4,000
230
450 .
540
1,600
16,000
3,200
2,800
270
880
720
-------
22
effluent showed: pH, 7.0-7.8; temperature, 19.0°-23.0°C; and conduc-
tivity, 875-1,200 ymhos/cm.
Daily, during the survey, large amounts of suspended solids were
observed passing over the final clarifier weirs during periods of peak
flow. This solids carry-over resulted from the scouring velocities
which prevail during peak flows.
Large accumulations of floating material were observed daily in
all treatment units. Solids were observed in the final effluent also.
The solids discharged could be reduced by the addition of skimmers on
the final clarifier.
The removal efficiency observed at the Northside and Metro facilities
[Table 8] indicated that BOD removal at the Northside plant ranged from -11
*
to 58 percent. If the Metro plant is considered alone (i.e., without
the BOD removal afforded by Denver Northside), the BOD removal efficiency
ranged from 48 to 86 and 39 to 94 percent before and after chlorination,
respectively. Under these conditions, the BOD removal efficiency at the
Denver Metro facility alone was below State standards 33 percent of the
time. If the Northside plant is considered as part of the overall Metro
system, the range of BOD efficiency increases between 66 and 91 percent
before chlorination and between 63 and 96 percent after chlorination.
The daily BOD removal efficiency including both facilities was below
State standards 20 percent of the time. Metro was designed for a BOD
load of 166,350 Ib/day. During the survey period, the influent BOD
varied from 92,000 to 279,000 Ib/day with an average of 182,000 Ib/day.
* The negative BOD removal was due to sludge blanket losses from the
clarifiers at Northside.
-------
TABLE 8
a/
REMOVAL EFFICIENCIES FOR DENVER METRO AND DENVER NORTHSIDE FACILITIES—
August 1-9, 1971
Degree of
Treatment for
Northside
Metro before C12
Metro after Cl
Metro plus Northside
BOD
Range
(11)^-58
42-86
39-94
66-91
Susp. Solids
Range
6-95
(«>V-,8
27-97
Vol. Susp. Solids
Range
66-95
(36)-/-80
(36)-/-66
32-96
Settleable Solids
Range
11-81
89-91
92-98
before Cl
Metro plus Northside
after Cl~
63-96
39-95
31-95
54-96
a/ Overall efficiencies were calculated by summing the load into and out of the plant.
b/ Numbers in parentheses are negative numbers. These negative value§ are due, to ^sludjje b,lanket
losses from clarifiers.
to
OJ
-------
24
Influent BOD loads were less than the design load during the weekend only.
Solids concentrations increase through the chlorine contact chamber.
Solids accumulate in the chamber and scour during peak flow periods. The
combined chlorine residual in the effluent varied from 0.01 to 0.64 mg/1,
significantly lower than the level (1.0 mg/1 after 15 minutes' detention)
4/
specified by the Colorado Department of Health.— Fecal coliform concen-
trations in the effluent ranged from 230 to 430,000/100 ml, indicating
inadequate disinfection [Table 7]. According to plant officials, about
one ton/day of chlorine is used (two mg/1 dosage rate at design flow).
The Colorado State Criteria recommend a minimum dosage rate of eight mg/1
for activated sludge plant effluents.
Concentrations of heavy metals discharged in the final effluent
were generally insignificant. The mercury concentrations discharged
ranged from 0.2 to 1.0 yg/1 (0.18 to 0.87 Ib/day), with an average of
0.5 pg/1 (0.48 Ib/day). The majority of the mercury received by Metro
is contained in the North Denver plant effluent. Officials of the North
Denver plant do not know the source(s) of this mercury.
The nutrient data show that only a small amount of nitrification
takes place during treatment. Total phosphorus was reduced approximately
28 percent. The total nitrogen and phosphate loads discharged to the
South Platte River averaged 34,700 and 6,900 Ib/day, respectively.
Bi-weekly operational data for the period May 30 through December 31,
1971 [Table 9] were obtained from Metro officials. The data for the
period July 25, 1971, through August 7, 1971, showed average BOD and
suspended solids removals of about 84 and 1 percent, respectively. Plant
-------
25
TABLE 9
BI-WEEKLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND SUSPENDED SOTJDS
REMOVALS AT THE METROPOLITAN DENVER SEWAGE DISPOSAL PLANT $!
1971
Bi-Weekly Period
May 30- June 12
June 13- June 26
June 27-July 10
July 11- July 24
July 25-August 7
August 8-August 21
August 22-September 4
September 5-September 18
September 19-October 2
October 3-October 16
October 17-October 30
October 31-November 13
November 14-November 27
November 28-December 11
December 12-December 25
December 26-December 31
Percent . Percent Suspended
BOD Removal Solids Removal
86.1
75.5
79.1
77.8
83.8
76.3
64.5
75.7
79.6
80.8
75.9
74.5
73.7
75.8
81.3
68.0
60.2
38.3
53.7
48.3
0.8
1.8
24.9
31.0
47.0
47.5
39.0
37.3
48.3
41.6
63.1
36.0
a/ Data were provided by Metro officials. Those data do not Include
BOD and suspended solids removed by the Denver Norths!^ Pl«nt.
-------
26
officials indicated that during this 2-week period, the sludge furnaces
were shut down and the digesters were loaded to capacity. Sludge was
being disposed of through landfill operations. Because of inadequate
trucking capacity, excess sludge was stored in the final clarifiers.
Sludge that had been stored in the final clarifiers was scoured from
these clarifiers during peak flow periods.
During 12 of the 16 bi-weekly periods [Table 9], the plant was
operating below the minimum 80-percent-BOD-removal requirement specified
in the Colorado State Water Quality Standards. These standards also
require that-adequate disinfection be provided.
Operation of the Northside plant has a marked influence on the opera-
tion and performance of the Metro plant. Since all wastes from Northside
are discharged to Metro and constitute the majority of the flow received,
failure to remove grease, for example, at the Northside plant can cause
operational difficulties at Metro. Operations of both plants need to be
under the control of a single agency in order that the combined operations
can be controlled to produce the best final effluent quality.
During the survey, Metro personnel were observed cleaning an in-
secticide tank. The wash-water containing the insecticide was flowing
to a storm drain that discharges to the South Platte River. Plant offi-
cials indicated that this practice would be discontinued. The effluent
from the storm drain appeared black and had the odor of burnt carbon.
Further investigation revealed that effluent from two ash disposal ponds
(ashes from sludge furnaces) was discharged to the drain. This practice
has been discontinued because the sludge furnaces are no longer in use.
-------
27
An in-plant study was conducted by EPA investigators during the
period October 1969 to February 1970, in order to evaluate plant opera-
tions and provide technical assistance [Appendix B]. Weirs on the final
clarifier are inadequately placed, thus allowing "scouring" velocities to
be attained. Moreover, it was determined that clarification capacity of
the final clarifier was not adequate. Also, there is no reserve capacity
of clarifiers; i.e., if a clarifier is out of service, solids are not
effectively removed and are discharged in the effluent. There is no
method of measuring the flow to each clarifier; therefore^ it is difficult
to obtain a balance. Surface skimmers were also recommended.
During the October-February study investigators found deficiencies
in the aeration basins — detention time is not sufficient, i.e.,
it is always less than four hours. Further, there is difficulty in
balancing the flow to the basin. Two of the twelve aeration basins were
being used for grease removal, an operation that should have been accom-
plished in the primary units. This practice has been discontinued and,
during the recent survey, four aeration basins (one in each area) were
being used as aerobic digesters.
-------
29
IV. STREAM SURVEYS
A. GENERAL
Previous Studies
In August 1964, December 1964 through March 1965, and September and
October 1965, surveys of the South Platte River were conducted by the
South Platte River Basin Project. During these periods stream flows at
the 19th Street station averaged 140, 50, 380, and 305 cfs, respectively.
Average dissolved oxygen values ranged from 6 to greater than 10 mg/1
at 19th Street; from 1.5 to 3.0 mg/1 at York Street; and from about 0.2
to 4.0 mg/1 in the vicinity of 88th Avenue. Bacterial densities were
high at all three stations, exceeding one million total and fecal collform
organisms/100 ml at York Street and 88th Avenue. The average BOD levels
ranged from 10 to 20 mg/1 at 19th Street; from 50 to 170 mg/1 at York
Street; and from 45 to greater than 100 mg/1 in the vicinity of 88th
Avenue.—
As a result of the above studies, it was recommended to the Second
Session of the South Platte River Basin Conference that the following
water quality objectives be established:—
1. In the main stream of the South Platte River, from the
City of Littleton to the point of discharge of the Metro
Denver sewage treatment plant, the dissolved oxygen con-
tent be maintained at not less than 5 mg/1; a five-day
biochemical oxygen demand level not be allowed to exceed
10 mg/1; and the total and fecal coliform level not be
allowed to exceed 2,400 and 500 bacteria per 100 ml,
respectively.
-------
30
2. In the main stream of the South Platte River, from just
downstream of the Metro discharge to just upstream of the
Brighton Great Western Sugar Company discharge, that the
dissolved oxygen content be maintained at not less than
4 mg/1; the five-day BOD level not be allowed to exceed
20 mg/1; and the total and fecal coliform levels not be
allowed to exceed 5,000 and 1,000 bacteria per 100 ml,
respectively.
The Colorado Water Pollution Control Commission, pursuant to the
Federal Water Pollution Control Act, as amended,— classified the South
Platte River and established water quality standards [Appendix A] for
the following reaches:
South Platte River from Exposition Avenue (RM 321.9)
to York Street (RM 313.4) -
82 - Warm Water Fishery
C - Industrial Water Supply
D! - Irrigation Water Supply
South Platte River from York Street (RM 313.4) to
Colorado-Nebraska State Line (RM 83.7)
C - Industrial Water Supply
DI - Irrigation Water Supply
Sand Creek throughout its length -
Basic Standards applicable to all waters of
the State apply.
Clear Creek from point of diversion of Farmers Highline
Canal (RM 311.1/16.8) to confluence with South Platte
River (RM 311.1) -
A - Potable Water Supply
C - Industrial Water Supply
D^ - Irrigation Water Supply
-------
31
The discharge from the Metro plant enters the South Platte River
downstream from Burlington Ditch. Facilities are available to pump
150 cfs of effluent to Burlington Ditch if, at the point of diversion,
there is not sufficient flow in the river to satisfy water rights. At
the time of the 1964-65 studies, the Metro plant was under construction.
The major source of pollution in the Denver area was the Northside plant
(RM 314.4) which discharged wastes upstream of the Burlington Ditch
diversion. Subsequently, the Northside plant discharged all wastes to
Metro (RM 312.2), thus moving the discharge downstream from the diversion.
There is presently a controversy over the ownership of the Metro effluent.
The Farmers Reservoir and Irrigation Company, e_£ al, have filed suit
against the Metropolitan Denver Sewage Disposal District Plant //I, con-
tending that it has interfered with their lawfully decreed rights as
appropriators of water from the South Platte River. The trial court entered
"final judgement" against the District on August 30, 1968, which decision
the District appealed to the Colorado Supreme Court. A decision is pending.
Present Studies
During the period August 30 to September 2, 1971, a water quality
survey was conducted on the South Platte River from Waterton to Platteville,
Colorado. A bacteriological survey was conducted,during November 17-21, 1971,
in order to determine quality of the South Platte River upstream and down-
stream from the Metro discharge (19th Street-RM 317.3, Colorado 224-RM 310.9)
and in order to evaluate Burlington Ditch. Sampling was conducted at selec-
ted stations to determine whether or not Salmonella were present. Another
stream survey was conducted in the same reach, during December 13 through
17, 1971, to determine chemical quality [Figure 4],
-------
32
During the in-plant survey and the three stream surveys the total
Metro effluent was being discharged to the South Flatte River. This
effluent comprised about 30 to 35 percent, 65 to 95 percent, and 95
percent of the flow in the South Platte River, respectively for each
survey, at the point of discharge. From August 30 to September 2 flow
conditions in the South Platte River were above normal. Survey findings
are discussed below.
Findings of August-September Survey
The August survey revealed that the South Platte River at 19th Street
(RM 317.3) was degraded [Table 10]. The benthos at this station were
dominated by pollution-tolerant forms, such as sludgeworms and midges.
Raw municipal wastes are occasionally by-passed to the South Platte
River in that reach from Denver Northside (314.4) downstream to York
Street (313.4) (see page 6). Water samples collected at York Street
were severely contaminated by fecal matter. The number of fecal colifonn
bacteria was greater than 13,000/100 ml (log mean value); numbers of
total colifonn exceeded 100,000/100 ml. The levels of organic matter
and suspended solids also were high in this reach. The DO levels at
this station ranged from 5.7 to 7.4 mg/1.
The Metro plant (RM 312.2) treats most of the domestic wastes of
the Denver area and is one of the most significant pollution sources in
the South Platte River Basin. Wastewaters discharged during the survey
period contained about 60 mg/1 BOD (62,000 Ib/day), and 85 mg/1 suspended
solids (88,000 Ib/day) [Table 10]. Total- and fecal-collfonn bacteria
-------
88th AVE
-IM-
LEGEND
1. SPR AT 19th St
2. SPR AT NORTH DENVER STP CROSSOVER
3. SPR AT YORK St
4. BURLINGTON DITCH AT YORK St
5. SAND CREEK NEAR MOUTH
6. SPR AT 1-270
7. SPR AT COLO 224
8. CLEAR CREEK AT YORK St
9. SPR AT 88th AVE
10. DENVER METRO EFFLUENT
NOT TO SCALE
Figure 4. Soulli Plalle River from 19lh Si lo 88lh Ave
-------
TABLE 10
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE SOUTH PLATTE RIVER
19th Street to 88th Avenue
August 30-September 2, 1971
Station
Date
Flow Temp. pH
cfs °C S.U.
Avg Range Range
Cond. DO
pmhos/cm mg/1
Range Range Avg
BOD5 Total Solids
mg/1 mg/1
Avg Avg
Susp. Solids
mg/1
Avg .
SPR at 19th 8/30-9/2/71 413
St. ,(RM 317.3)
a/
SPR at York 8/30-9/2/71 21CP'
St. (RM 313.2)
Denver Metro 8/30-9/2/71 192
Effluentt'
(RM 312.2)
17-24 7.2-8.3 375-600 6.0-7.6 7.0
17-22 7.4-8.1 360-580 5.7-7.4 6.9
Sand Creek
at Mouth
(RM 312.1/0.1)
8/30/9/2/71 100^ 17-21 7.5-8.0 420-600 6.4-7.3 6.8
Clear Creek 8/30-9/2/71
at York Street
(RM 311.1/0.3)
21
a/
SPR at 88th 8/30-9/2/71 700-
Avenue
(RM 308.8)
16-21 7.3-8.4 470-600 4.8-8.7 6.7
18-22 7.3-7.6 600-800 3.3-5.7 4.5
a/ Estimated flow.
b/ Data provided by Denver Metro personnel.
56
29
405
543
570
383
690
< 80
260
85
203
< 30
233
-------
34
levels, during the in-plant survey, ranged from 6,600 to 14,000,000 per
100 ml and 230 to 430,000 per 100 ml, respectively [Table 7].
During the August survey the flow in Sand Creek (RM 312.1/0.1) was
comprised primarily of overflow from the Burlington Ditch. The creek
smelled of sewage and was gray in color because Burlington Ditch carried
by-passed raw municipal sewage from the 47th Avenue sewer discharge to
the South Platte River. Log mean concentrations of total and fecal
coliform bacteria were greater than 110,000 and 8,800/100 ml, respectively.
Sand Creek transported large amounts of organic matter, and this resulted
in a BOD as high as 9 mg/1. Benthic invertebrates, dominated by pollution-
tolerant sludgeworms, inhabited the creek bottom in dense populations
(1,494/square foot). The diversity of organisms was limited to six kinds,
most of which were pollution-tolerant or facultative forms.
The South Platte River became severely polluted downstream from
these waste sources. At RM 311.5 (upstream of Clear Creek) the odor of
sewage was strong, and the water was gray, turbid, and covered with soap
suds. The river bed was covered with organic sludge. The benthic com-
munity was reduced to seven kinds and consisted mostly of pollution-
tolerant sludgeworms and snails.
Clear Creek intersects the South Platte River at RM 311.1. The
water in Clear Creek is of a better quality than that observed in the
South Platte River. The addition of Clear Creek water somewhat im-
proves the quality of the South Platte River waters.
The pollutants discharged to the South Platte River from the sewage
-------
35
treatment facilities and from polluted Sand Creek settled to the river
bottom forming sludge beds that were evident from Sand Creek downstream -
approximately 23 river miles. Throughout this river reach water
quality was degraded severely. Fecal coliforms numbered more than
7,900/100 ml and total coliforms numbered more than 320,000/100 ml.
At 88th Avenue (RM 308.8) the number of benthic invertebrates
increased to 732/square foot with a variety of only eight kinds. Ninety-
two percent of these organisms were pollution-tolerant sludgeworms.
B. FINDINGS OF NOVEMBER BACTERIOLOGICAL SURVEY
Bacteriological data [Table 11], for the November survey, showed
that the standards for a warm water fishery (B.) were being met at the
19th Street Station with a log mean coliform bacteria density of 490/100 ml
and with no more than 10 percent of the samples exceeding 2,000/100 ml.
Bacterial quality remained within the standards until York Street,
where the log mean density increased to 790/100 ml; however, more than
10 percent of the samples exceeded 2,000/100 ml. From York Street
downstream there are at present no bacterial standards for the South
*
Platte River.
Salmonella tests were conducted in the South Platte River at York
Street (RM 313.2) just downstream from the Denver Metro effluent
(RM 312.15) and in Burlington Ditch at York Street in order to determine
* The Colorado Water Pollution Control Commission adopted bacterial
water quality standards for the South Platte River, downstream from
York Street to the Colorado-Nebraska state line, in September 1971,
by classifying this reach of river suitable for a potable water
supply (Class 'A'). The State Attorney General advised the Commission
that any change in stream classification required a public hearing.
The Commission subsequently removed the "A" classification.
-------
TABLE 11
RESULTS OF BACTERIOLOGICAL ANALYSES-SOUTH PLATTE RIVER STREAM SURVEY
November 17-21, 1971
Key
Total Coliforms
Count/100 ml
Station
Fecal Coliforms % of
Count/100 ml Sample
Fecal Strep.
Count/100 ml
Range
Log Mean Range Log Mean -2000/100 ml Range Log Mean
1 South Platte River 3,800->90,000 >11,000 170-4,000 490
at 19th St. bridge
2 South Platte River 3,000-440,000 15,000 310-2,600 620
at Denver Northside
plant
3 South Platte River^ 5,000-270,000 21,000 61-10,000 790
at York St.
4 Burlington DitclA/ 3,200-210,000 16,000 410-6,500 850
at York St.
6 South Platte River 7,000-6,200,000. 340,000 70-70,000 >7,000
at 1-270 Bridge
7 South Platte River 7,100-5,400,000 200,000 160->60,000 >3,300
at Colorado 224
8 Clear Creek at York 600-190,000 7,100 <10-5,300 <190
St.
10 160-27,000 1,600
10. 330-39,000 2,100
20 360-87,000 3,800
20 570-77,000 3,500
70 150-160,000 14,000
60 980-98,000 8,200
20 220-190,000 1,800
10 Denver Metro
effluent-7
9,200-14,000,000
230-430,000
a/ See Figure 4 for location.
b_/ Isolated salmonella at this station.
c/ Data from in-plant survey August 1-9, 1971.
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37
whether or not enteric pathogenic bacteria were present. The results at
all three stations were positive. Particular serotypes isolated were
Salmonella anatum (Burlington Ditch) and 5. senftenberg (SPR stations).
The presence of these pathogenic bacteria, in attendance with fecal coli-
forms, confirms that the water is contaminated by raw or inadequately
treated sewage.
The effects of the Metro effluent, however, are very evident.
Log mean fecal-coliform bacteria densities exceeded 7,000/100 ml down-
stream from Metro at the 1-270 bridge (RM 312.0). Concentrations ex-
ceeding 3,300/100 ml (log mean) were observed at Colorado 224 (RM 310.9).
The bacterial standard for Clear Creek was violated at York Street.
Although the fecal-coliform bacteria concentration (log mean) was low
(<190/100 ml); more than 20 percent of the samples exceeded the 2.000/
100 ml limitation required for a Class A waters.
Survey results showed some improvement, since -the 1964-65 studies,
in the bacterial quality of the South Platte River downstream from 19th
Street. Total- and fecal-coliform bacterial levels were markedly lower
in November than those observed in 1964-65. Downstream from York Street,
the log mean total- and fecal-coliform bacteria numbers remained in
excess of the levels recommended by the South Platte River Basin Project
as water quality objectives (i.e., 5,000 total and 1,000 fecal/100 ml).
Adequate disinfection of the Metro discharge and elimination of raw
sewage by-passes would improve the bacterial quality of the river down-
stream from 19th Street.
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38
C. FINDINGS OF THE DECEMBER SURVEY
Flows in the South Platte River during December were about one-
fourth of those observed during August. Water samples were collected
at selected stations from 19th Street downstream to Colorado Highway
224 and analyzed for BOD, solids (total and suspended), and DO [Table 12].
The average BOD at the background station (19th Street) was 18 mg/1. The
level decreased to 14 mg/1 at Denver Northside. At York Street the BOD
averaged 9 mg/1, about 50 percent less than measured in Burlington Ditch
at York Street. One factor that could account for this difference is
the flow of the South Platte River at York Street primarily consisted of
seepage because the entire river was being diverted to Burlington Ditch.
Consequently, there was essentially a new river at York Street.
Downstream from Metro (1-270) the BOD level increased to an average
of 44 mg/1 — about five times higher than the average observed at York
Street. At this station, the river was mostly Metro effluent which
contained an average BOD of 44 mg/1.
The BOD level at the new downstream station (Colorado 224) remained
at 40 mg/1. This station is downstream from the confluence of Clear
Creek which had an average BOD of 15 mg/1 and an average flow of 54 cfs.
During the survey, the DO levels were well above the established
standard (3.0 mg/1) at all stations, with concentrations ranging from
7.8 to 9.4 mg/1 upstream of the Metro discharge and 6.0 to 6.4 down-!-
stream at 1-270 bridge.
In summary, the survey results indicated an improvement in the
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TABLE 12
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE SOUTH PLATTE RIVER
19th Street to 88th Avenue
December 13-17, 1971
Flow Temp. Cond. DO BOD5 Total Solids Susp. Solids
cfs °C pH pmhos/cm mg/1 mg/1 mg/1 mg/1
Station Date
SPR at 19th 12/13-17/71
St. (RM 317.3)
SPR at Denver 12/13-17/71
Northside plant
(RM 314.5)
SPR at York 12/13-17/71
St. (RM 313.2)
Burlington 12/13-17/71
Ditch at
York St.
Denver Metro 12/13-17/71
effluent
(RM 312.2)
SPR at 1-270 12/13-17/71
bridge
(RM 312.0)
Avg Range R^nge Range Range Avg Av£ Avg
107 3-6 7.6-7.9 775-875 8.5-10.0 9.4 18 675
135^ 3-6 7.4-7.9 825-1000 7.8-9.8 8.9 14 750
a/
2- 3-5 7.7-7.8 750-1000 7.8-9.4 8.7 9 755
142^- 3-5 7.5-7.8 850-1000 7.7-9.6 8.8 14 725
153 ' 44
160s 15-15 7.1-7.4 1000-1100 6.0-6.4 6.1 44 890
Avg
40
30
30
40
95
uo
vo
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TABLE 12 (Cont.)
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE SOUTH PLATTE RIVER
19th Street to 88th Avenue
December 13-17, 1971
Station
Date
Flow
cfs
Avg
Temp.
°C
Range
PH
Range
Cond.
ymhos/cm
Range
DO
mg/1
Range
Avg
BOD5
mg/1
Avg
Total Solids
mg/1
Avg
Susp. Solids
mg/1
Avg
Clear Creek 12/13-17/71 54 0.3-2 7.7-8.0 825-1000 9.2-10.5 9.8 15
at York St.
(RM 311.1/0.3) .
SPR at Colo. ,12/13-17/71 220^/ 8-9 7.3-7.6 950-1050 7.4-8.0 7.8 40
224 (70th Aye.) - ''
(RM 310.9)
SPR at 88th 12/13-17/71 20.0^ 3-12 7.4-7.7 775-1100 6.7-7.3 7.0
Aye. (RM 308.8)
820
a/ This is a estimated flow value.
\±l Flow w,as measured at a gage located downstream from York Street near Sand Creek.
45
70
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41
South Platte River quality downstream from Denver Northside compared
to the 1964-65 studies. Obvious improvements include reduced BOD and
higher DO values as a result of the elimination of the Northside primary
effluent. However, the BOD load discharged by the Metro plant still
results in BOD levels in the South Platte River more than twice the
limits recommended (i.e., 20 mg/1) as a water quality objective in
the South Platte River Basin Project report.
The quality of Clear Creek has also improved over that observed
in 1964-65, and during the December survey, the BOD level (11-20 mg/1)
was within the limits recommended.
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43
V. WATER QUALITY IMPROVEMENT MEASURES
Adequate design, operation, and maintenance at the Metro plant
should be an immediate priority in improving water quality in the South
Platte River. To meet projected water quality criteria a BOD removal
efficiency of greater than 90 percent will be required. Interim methods
of improving the effluent, such as chemical precipitation, should be
evaluated and initiated as soon as possible.
The dissolved oxygen concentration in the South Platte River has
been evaluated on the basis of continual discharge of Metro effluent
to the river and low-flow conditions. The 7-day, 10-year low. flow at
19th Street is 20 cfs which, assuming no diversion, would make the low
flow just upstream of the Metro effluent approximately 25 cfs. Waste
loads from Metro were predicated on 30 mg/1 BOD (August data) and 3 ng/1
DO (assumed). The BOD loading to the river winder these conditions is
29,100 Ib/day with a residual stream BOD of an additional 810 Ib/day
(includes BOD loading from Sand Creek and Clear Creek). Calculations
were made at 25°C, with the DO upstream of the Metro effluent assumed
to be at saturation. The minimum DO that would occur is approximately
0.5 mg/1 which is below the approved water quality standard of 3 mg/1
[Figure 5]. This analysis did not include possible secondary oxygen
demand from nitrification.
The same procedures were employed to determine the expected low
DO value with the Metro effluent containing 10 mg/1 BOD. All other
factors remained the same. The minimum DO which would occur is approxi-
mately 3.5 mg/1 [Figure 5],
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44
Based on the above calculations, the effluent from Metro must not
contain more than 10 mg/1 BOD to prevent violation of water quality
standards (DO of 3 mg/1). This will require the Metro wastewater treat-
ment facility to provide at least 95 percent BOD reduction.
Water quality conditions could be further improved by diverting the
Metro effluent to the Burlington Ditch and allowing normally diverted
South Platte River flows to continue downstream. The Farmers Reservoir
and Irrigation Company, which owns Burlington Ditch, has water rights of
377 cfs from the South Platte River. From May to September, the majority
of the diverted water is used directly for Irrigation, with any excess
being stored in Barr Lake, a 350,000 acre-foot reservoir, located north-
east of Denver [Figure 4]. Three other reservoirs, Horsecreek (17,000
acre-feet), Prospect (7,660 acre-feet), and Lord (1,000 acre-feet), also
receive South Platte River water from diversions into the Burlington Ditch,
generally from October to April. A flow of 130 cfs would be sufficient
to fill these reservoirs. Based on projected Metro flows, 25-100 cfs
would still have to be discharged to the river.
8/
A study done on Barr Lake in 1964-65- concluded that the lake was,
in effect, a large wastewater stabilization lagoon. The BOD and Total N
and Total PO, concentrations in the water entering Barr Lake ranged from
55 to 150; 12 to 37; and 11 to 21 mg/1, respectively. This study recom-
mended that the Metro plant provide 90 percent BOD removal, which would
be equivalent to about 20 mg/1 BOD in the plant effluent.
During the irrigation season water demands would require flows In
excess of the Metro effluent to be diverted from the South Platte River.
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Saturation at 25°c
Proposed Dissolved Oxygen Standard
Present Dissolved Oxygen Standard
Profile for present Metro effluent
BOD Concentration of 30mg/lj
Profile of Metro effluent for
BOD Concentration of 10mg/l
0.6 0.8
2.0
TIME-days
FIGURE 5 DISSOLVED OXYGEN PROFILE FOR SOUTH PLATTE RIVER DOWNSTREAM OF DENVER METRO
EFFLUENT.
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45
Adequate and reliable disinfection will be required at all times if the
*
Metro effluent is to be used directly for irrigation. A water quality
monitoring system must be established at the point of first diversion
for use.
In summary, the Metro plant must provide: (1) an effluent BOD of
not greater than 20 mg/1 when all effluent is pumped to Burlington Ditch,
(2) an effluent BOD of not greater than 10 mg/1 if all the effluent is
discharged to the South Platte River assuming a low flow in the river of
20 cfs at 19th Street, and (3) effluent BOD levels between 10 and 20 mg/1
when a portion of the effluent is being discharged to the river.
Improvements in the water quality of the South Platte River can be
achieved by the elimination of occasional raw sewage discharges.
The water quality standards of the South Platte River downstream
from York Street should be upgraded to encourage continued water quality
enhancement. As DO concentrations observed at sampling stations were
5 mg/1 or more, a warm water fishery (B_) classification is feasible
if adequate flow is maintained in the river (25 cfs).
* The State of Colorado has not developed criteria for wastewater
effluents used for irrigation of crops.
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47
REFERENCES
[1] Report to the Second Session of the Conference in the Matter of
Pollution of the South Platte River Basin, United States Department
of Health, Education, and Welfare, Federal Water Pollution Control
Administration, South Platte River Basin Project, April 27, 1966.
[2] PR-3, Municipal Waste Report, Metropolitan Denver Area, South
Platte River Basin, United States Department of Health, Education,
and Welfare, Public Health Service, Division of Water Supply and
Pollution Control, South Platte River Basin Project, Denver,
Colorado, December 1965.
[3] Appendix C - Outfall Study - Location and Sampling Results; Supple-
ment to the Basic Report A Study of Industrial Waste Pollution in
the South Platte River Basin, U. S. Department of the Interior,
Federal Water Pollution Control Administration, South Platte River
Basin Project, Denver, Colorado, December 1966.
[4] Criteria Used in the Review of Wasteaater Treatment Facilities,
Colorado Department of Health, Denver, Colorado, 1969.
[5] Modern Sewage Treatment Plants, How Much Do They Cost, United
States Department of Health, Education, and Welfare, Public Health
Service, Publication No. 1229, U. S. Government Printing Office,
Washington, D. C., 1964.
[6] Conference in the Matter of Pollution of the South Platte River
Basin in the State of Colorado, Proceedings, Second Session, Denver,
Colorado, Reconvened, November 10, 1966, U. S. Department of the
Interior, Federal Water Pollution Control Administration.
[7] Federal Water Pollution Control Act, Public Law 84-660, U. S.
Department of the Interior, Federal Water Pollution Control
Adminis tration.
[8] Barr Lake and Its Odor Relationships, R. 0. Sylvester, United
States Department of Health, Education, and Welfare, Public Health
Service, Division of Water Supply and Pollution Control, Region
VIII, Denver, Colorado, December 1965.
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APPENDIX A
COLORADO WATER QUALITY STANDARDS
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COLORADO WATER QUALITY STANDARDS
Waters of the State, the quality of which exceeds the limits set in these
standards, will be maintained at existing quality unless and until it can
be demonstrated to the State that a change in quality is justified to
provide necessary economic or social development. In that case, the best
practicable degree of waste treatment to protect the current classification
of such waters will be required. The appropriate Federal authority will be
provided with information, from time to time, required to discharge his
responsibilities under the Federal Water Pollution Control Act, as amended.
I. BASIC STANDARDS APPLICABLE TO ALL WATERS OF THE STATE;
A. All wastes capable of treatment or control prior to discharge
into any waters of the state, shall receive secondary treatment
with disinfection or its industrial waste equivalent, as deter-
mined by the State Water Pollution Control Commission. Lesser
degrees of treatment or control may be permitted only where it
can be demonstrated that the standards applicable to the classified
use of the water can be attained. Greater degrees of treatment
or control will be required where it can be demonstrated that it
is necessary to comply with the standards applicable to the
classified use of the water.
B. Free from substances attributable to municipal, domestic, or
industrial wastes, or other controllable sources that will either
settle to form unsightly, putrescent, or odorous bottom deposits,
or will interfere with the classified use of the water.
C. Free from unsightly floating debris, oil, grease, scum, and other
floating material attributable to municipal, domestic, or
industrial wastes, or other controllable source.
D. Free from materials attributable to municipal, domestic or indus-
trial wastes, or other controllable sources that will produce
objectionable odor, color, taste, or turbidity in the water, or
objectionable aquatic life which may result in eutrophication or
other conditions that interfere with the classified use of the
water.
E. Free from high temperatures, biocides, toxic, or other deleterious
substances attributable to municipal, domestic, or industrial
wastes, or other controllable sources in levels, concentrations,
or combinations sufficient to be harmful to human or animal life.
F. Radioactive materials attributable to municipal, industrial or
other controllable sources will be minimum concentrations that
are physically and economically feasible to achieve. In no case
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shall such materials in the stream exceed the limits established
in the current edition of the U. S. Public Health Service Drinking
Water Standards or the limits approved by the Federal Radiation
Council, or, in the absence of any limits specified by the U. S.
Public Health Service or the Federal Radiation Council, 1/30 of
the 168-hour-week values for other radio-active substances speci-
fied in the National Bureau of Standards Handbook 69.
II. SPECIFIC STANDARDS ESTABLISHED BY THE STATE OF COLORADO;
CLASS A - The following standards shall apply to water withdrawn
for treatment as a potable supply:
a. Bacteria; Wastes or substances from controllable sources shall
not be discharged into these waters in amounts which will cause
the number of organisms of the fecal coliform group, as deter-
mined by either multiple tube fermentation or membrane filter
techniques, to exceed a log mean of 1000 per 100 milliliters or
exceed 2000 per 100 milliliters in more than 10 percent of the
samples collected in any 30-day period.
b. Dissolved Oxygen; Dissolved oxygen shall not be less than 4
milligrams per liter.
c. pH; The pH shall be maintained between 6.0 and 9.0.
d. Taste and Odor; Free from materials attributable to municipal,
domestic, or industrial wastes, or other, controllable sources
that will produce taste or odor in the water.
e. Dissolved Solids; Total dissolved solids, annual volume weighted
average, should be less than 500 milligrams per liter.
f. Selected Chemical Constituents; The following substances shall
not be present in such amounts as to exceed the specified concen-
trations in a potable water supply according to the mandatory
requirements of the latest edition of the U. S. Public Health
Service Drinking Water Standards:
Substance Concentration - mg/1
Arsenic 0.05
Barium 1.00
Cadmium 0.01
Chromium (Hexavalent) 0.05
Cyanide 0. 20
Lead 0.05
Seleniunv 0.01
Silver 0.05
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CLASS B-2 - The following standards shall apply to waters classified
for fish and wildlife (Warm Water Fishery):
a. Bacteria: Wastes or substances from controllable sources shall
not be discharged into these waters in amounts which will cause
the number of organisms of the fecal coliform group, as deter-
mined by either multiple tube fermentation or membrane filter
techniques, to exceed a log mean of 1000 per 100 milliliters or
exceed 2000 per 100 milliliters in more than 10 percent of the
samples collected in any 30-day period.
b. Dissolved Oxygen: In warm water fisheries, dissolved oxygen
content shall in no case go below 5 milligrams per liter.
c. pH: The pH shall be maintained between 6.5 and 8.5. No control-
lable pH change will be permitted which will interfere with fish
and aquatic life.
d. Turbidity: No turbidity shall exist in concentrations that will
impair natural and developed fisheries.
e. Temperature; In warm water fisheries the temperatures shall not
exceed 90°F. No controllable temperature change will be permitted
which will interfere with spawning and other aspects of fish life.
Limits on temperature change have not been established due to
lack of historical temperature data and lack of conclusive tempera-
ture change criteria for the aquatic biota of waters of the state.
These factual data are being collected, however, to serve as a
basis for setting limits. In the meantime, an abrupt change in
temperature must be avoided and the normal pattern of diurnal and
seasonal changes must be preserved. The maximum allowable tempera-
ture increase due to waste discharges in streams will be 5°F.
f. Toxic Material; Free from biocides, toxic, or other deleterious
substances attributable to municipal, domestic, or industrial
wastes, or other controllable sources in levels, concentrations,
or combinations sufficient to be harmful to aquatic life.
g. Other Material; Free from materials attributable to municipal,
domestic, or industrial wastes, or other controllable sources
that will produce off-flavor in the flesh of fish.
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CLASS C - The following standards shall apply to waters classified
for industrial uses:
a. Dissolved Oxygen: Dissolved oxygen content shall not go below
3 milligrams per liter.
b. pH; The pH shall be maintained between 5.0 and 9.0.
c. Turbidity; No turbidity shall exist in concentrations that will
interfere with established levels of treatment.
d. Temperature: The temperature shall not exceed 90°F.
CLASS D-l - The following standards shall apply to waters classified
for irrigation:
a. Total Dissolved Solids (Salt) Concentration; A time-weighted
monthly mean at a monitoring station which exceeds the time-
weighted monthly mean for a base period established by the ,
Commission by more than two standard deviations shall be subject
to review by the Commission.
b. Sodium Adsorption Ratio; A time-weighted monthly mean at a
monitoring station which exceeds the time-weighted monthly mean
for a base period established by the Commission by more than two
standard deviations shall be subject to review by the Commission.
c. Toxic Material: Free from biocides, toxic, or other deleterious
substances attributable to municipal, domestic, industrial wastes,
or other controllable sources in concentrations or combinations
which are harmful to crop life.
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APPENDIX B
REPORT BY
ENVIRONMENTAL PROTECTION AGENCY
REGION VII, KANSAS CITY, MISSOURI
"FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE
DISPOSAL DISTRICT NO. 1
OCTOBER 1969 - FEBRUARY 1970"
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FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE
DISPOSAL DISTRICT NO. 1
OCTOBER 1969 - FEBRUARY 1970
By
Bob A. Hegg
And
John R. Burgeson
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE - REGION VII
911 WALNUT, KANSAS CITY, MO. 64106
MARCH 1971
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TABLE OF CONTENTS
PAGE NO.
I. Introduction 1
II. Purpose and Scope 2
III. Description of Plant and Area 3
IV. Summary of Assistance Project 5
A. Control Testing - Procedures and Results 5
B. Performance Evaluation - Procedures and Results 6
C. Data Analysis - Procedures and Results 9
D. Control of Areas - Procedures and Results 11
E. Control of Sludge Characteristics - Procedures and Results. ... 12
V. Data Analysis 15
A. Analysis of Sludge Production 15
B. Analysis of Secondary Clarifiers . 21
VI. Summary and Conclusions 29
VII. Recommendations 32
VIII. Appendices 33
Appendix A - A Resolution: "Concerning the Federal Government's
Responsibilities in Constructing and Operating Sewage
Disposal Facilities" . . . 34
Appendix B - References 36
Appendix C - Determination of Substrate Removal Rate (q) and
Net Growth Rate (l/ec) 38
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LIST OF TABLES
TABLE NO.
TITLE
PAGE NO.
A Summary of Various Parameters Associated with the Selected
"Steady State" Periods
Calculated Values of BC and
Operation - Areas §2 and #3
" Selected Periods of
Average Settled Sludge Volumes for "Steady State" Periods , . . .
Zone Settling Rates (V$) and Equivalent Surface Overflow
Rates (Or) for "Steady State" Periods
Waste Sludge Flow Required to Remove an Equivalent Amount of
Solids with Varying Underflow Concentrations
17
19
22
25
28
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE NO.
Plant Flow Schematic.
Influent BODs Loadings and Seven Day Moving Average, Effluent
BODs and TSS Concentrations vs Time
Weekly Average Percentage Reduction of BODs and TSS
(Secondary Only) vs Time
Waste Sludge Concentration in mg/1 vs Time
Net Growth Rate (l/6c) vs Substrate Removal Rate
Determination of Zone Settling Rate (Vs) - Height of Sludge
Interface vs Time - Area #3 Period: 2/9 - 2/16/70 Average
9:00 A.M ...........................
4
8
10
14
20
24
ii
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I. INTRODUCTION
The Metropolitan Denver Sewage Disposal District #1 (Metro Denver) plant was designed mainly as a
secondary treatment facility (activated sludge) to treat wastes from the cities and sanitary districts
in the Metropolitan Denver Area. The plant is administered by a Board of Directors who represent the
various communities and districts that are served by the facility. The largest source of flow to the
plant is the primary effluent from the City and County of Denver's North Side Sewage Treatment Plant.
The Metro Denver plant began operation in 1966 and since that time has continually experienced
difficulties. Odor problems, insufficient sludge handling facilities, air pollution from sludge
incineration; unavailability of land for sludge disposal sites, management, labor, and maintenance
problems are the more significant of the difficulties that the plant has encountered. These problems
have served to further increase the public's awareness of the Metro Denver plant.
In an effort to resolve this situation, the Board of Directors of the Metro Denver plant passed a
resolution (see Appendix A) entitled "Concerning the Federal Government's Responsibilities in Con-
structing and Operating Sewage Disposal Facilities." In the resolution, Metro Denver petitioned the
Congress of the United States and the appropriate Federal agencies to make available to the district
a special team of scientists and engineers to serve as a task force to inspect the district's acti-
vated sludge treatment plant and make appropriate recommendations. As a result of this resolution, a
three-man team from what was then the Federal Water Quality Administration was assigned to the Metro
Denver treatment facility from October 1969 through February 1970. The project officer was
Mr. Alfred West from the National Field Investigation Center (NFIC) in Cincinnati. He was assisted
by Mr. Joseph Jos 1 in and Mr. Bob Hegg of the Kansas City Regional Office.
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II. PURPOSE AND SCOPE
The most significant problem areas at the Metro Denver plant, leading to the request for assis-
tance, were the sludge handling and sludge disposal problems. The major sludge handling problem was
processing the volume and type of waste activated sludge generated by the secondary treatment process
employed at the plant. The sludge disposal problem occurred because of the plant's inability to
incinerate all of the sludge that was processed. It was decided at the on-set of the Federal Assis-
tance Project to concentrate efforts on the sludge handling problem by attempting to effect the mass
and characteristics of the sludge produced by the secondary treatment process.
Operational changes in the secondary treatment process, training in conducting various control
tests and data evaluation were the major tasks performed during the assistance project. These
functions were coupled with various operational recommendations for both short term and long term
plant operation and control.
This report documents the findings of the Federal team. Also presented are the results of
additional analyses of the data conducted after the conclusion of the project.
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III. DESCRIPTION OF PLANT AND AREA
The Metro Denver activated sludge plant is located north of Denver in Conmerce City, Colorado.
The effluent from the plant is discharged to the South Platte River, an interstate stream. The State
Water Quality Standards require a minimum of 80% removal of five-day 20°C BOD by the Metro Denver
plant before discharge to the South Platte River. Since the plant began operation in 1966, it has
generally achieved this required eighty percent reduction.
The Metro Denver plant is comprised of primary and secondary sewage treatment facilities and
includes sludge processing facilities. A flow schematic is presented in Figure 1.
The primary treatment facilities were designed to treat an average flow of 27 million gallons per
day (MGD) and a maximum flow of 50 MGD. These facilities consist of an inlet structure, bar screens,
grit and grease removal units, sedimentation basins and a grease and scum incinerator.
The secondary treatment facilities were designed to treat an average flow of 117 MGD with a
maximum flow of 234 MGD. The design (BOD5) load is 166,350 pounds per day or an average influent
concentration of 170 mg/1 BOD5. The secondary treatment facilities consist of aeration basins, the
blower building, sedimentation basins and chlorine contact chambers.
The sludge processing facilities were designed to treat 37,400 pounds per day of raw primary
sludge and 131,000 pounds per day of secondary sludge from the Metro Denver plant; and 92,700 pounds
per day of digested primary sludge from the Denver North Side plant. These facilities consist of the
waste activated sludge concentrators, sludge holding tanks and the sludge processing building which
housed the vacuum filters and incinerators.
Pertinent design information about types and sizes of equipment is discussed, as necessary, in
the following sections.
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hcrnu»T ro
10UTH H4TU
Hi PUMPING »^\ " — : *—..».-.-.
:l ! BUILDING*' V V, - v '
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1967 - FEBRUARY 1970
PLANT FLOW SCHEMATIC
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IV. SUMMARY OF ASSISTANCE PROJECT
The major emphasis during the Federal Assistance Project was aimed at the biological (secondary)
portion of the Metro Denver plant. As shown in Figure 1, the secondary portion is comprised of
twelve aeration basins each of two million gallon capacity and twelve 1.16 million gallon final
clarifiers. These twenty-four structures were equally divided into four separate areas by piping,
pumps and other control devices. Throughout the project these four areas demonstrated characteris-
tics of four different plants possibly due to undetected loading differences, flow characteristics,
etc. For this reason, operational control of each of the areas was different and was based on the
individual characteristics exhibited. Because excessive grease was contained in the influent to the
Metro Denver plant, aeration basins No. 1 and No. 2 (located in Areas #1 and #2) were used as grease
flotation units. This required that Areas #1 and #2 be operated using only two aeration basins in
combination with their respective three clarifiers. Areas #3 and #4 were operated using all three
aeration basins and three clarifiers in each area.
A. Control Testing Procedures and Results
The initial phase of the project involved instigating process control testing, as outlined by
West (1), to monitor process performance. The basic control tests are the centrifuge test, the
settleometer test, blanket depth measurements, turbidity measurements and dissolved oxygen concen-
tration determinations. The main function of each of these procedures is:
1. Centrifuge tests were conducted on the effluent from the aeration basins and on the return
sludge drawn from the final clarifiers. This test indicates the relative concentrations (by
percent volume) of solids needed for determining the solids distribution in the activated
sludge process. The results from the centrifuge test can also be used for other determina-
tions. For example, the secondary clarifiers at the Metro plant are the "vacuum" type with
twelve draw-off tubes in each clarifier. By using the centrifuge to determine the suspended
solids concentrations, the height of each draw-off tube can be adjusted so that a uniform
concentration of sludge can be drawn from the clarifier bottom.
A relationship between percent solids by centrifuge and by weight (milligrams per liter) of
total and volatile suspended solids (TSS & VSS) was obtained by comparing the results of a
centrifuge test and a suspended solids analysis made on the same grab samples. This compari-
son was made on a daily basis throughout most of the project.
2. Settleometer testing was conducted on the effluent from the aeration basins to determine the
settling rate and characteristics of the sludge. Visual observations of the sludge settling
characteristics indicated the relative removals, flocculation properties, etc. of the sludges
from the four areas. Analysis of the settleometer data coupled with centrifuge data also
-------
allowed a determination of the dewatering or concentrating ability of the various mixed
liquors. Settleometer data were normally collected four times per day at 5:00 A.M., 9:00
A.M., 1:00 P.M. and 9:00 P.M. During the last portion of the project, settleometer tests
were run every two hours. Readings of the settled sludge volume (SSV), as indicated from the
settleometer, were taken every five minutes for the first one-half hour and every ten minutes
for the second one-half hour.
3. Blanket depth determinations (depth of sludge interface from surface) were taken on each of
the final clarifiers to aid-in determining the solids distribution and solids mass in the
final clarifiers. During the last portion of the project, blanket readings were taken every
two hours, twenty-four hours per day.
4. Turbidity measurements were taken on samples of settled and skimmed effluent from the final
clarifiers and were used to indicate the relative effectiveness of the activated sludge
process in producing a clarified effluent. The samples were settled and skimmed before
turbidity measurements were made so that clarifier limitations could be eliminated from the
analysis and only the relative effectiveness of the biological system could be judged.
5. Dissolved oxygen measurements were taken to assure that an adequate oxygen supply was avail-
able to support the process.
Plant operators were trained during the project to make the above control tests and to analyze
and interpret the obtained data. Process control adjustments could then be made on a routine basis.
In addition to conducting the control tests, the operators were required to take readings of various
flow meters and to collect grab and composite samples so that the plant performance could be
moni to red.
B. Performance Evaluation-Procedures and Results
The Metro plant laboratory conducted various analyses on the collected samples to provide addi-
tional data for the project. Influent and effluent samples for the secondary treatment portion of
the plant were composited and determinations were made for BODg and TSS. In addition to overall
plant influent and effluent samples, influent and effluent samples were collected and composited on
each of the individual areas. Figure 2 illustrates the loading in pounds of BODg applied to the
secondary treatment (activated sludge) portion of the Metro Denver plant, as well as the seven day
moving average of the overall plant effluent concentrations of 6005 and TSS.
The seven day moving average BODg and TSS effluent concentrations are depicted on the lower por-
tion of Figure 2. The BOD5 in the effluent is closely, related to the TSS concentration. This
relationship emphasizes the effect of the difficulties encountered with final clarifiers at the Metro
Denver plant. Without exception, each peak on the graph can be correlated with "bulking" problems in
-------
one or more of the areas. A portion of the "bulking" problem was due to a poor-settling sludge
caused by process imbalance. However, many times an apparent good-settling sludge in settleometer
testing was hydraulically "flushed" over the effluent weirs.
It is believed that the peaks or poor effluent quality depicted in Figure 2, prior to and during
the initial phases of the Federal project, were caused by the above-average flow and BODg loadings
(See upper portion of Figure 2) that were received at the plant during the month of October. 1969.
The large peaks of effluent TSS and BOD,- experienced in the latter part of November and in December
were caused by a loss of process balance in Areas #1, #2 and #4. The exact reasons for these changes
are not known. However, it may have been the type of loading being used, temperature effects, meter
problems, etc. When Areas #2 and #4 were subsequently converted so that all the sewage was applied
at the head of each aeration basin on December 12, 1969, the trend in the effluent concentrations of
BODc and TSS decreased. Area #1 was converted to this type of loading on January 5, 1970.
The peaks depicted in the month of January were caused by loss of control of Area #3. Excessive
wasting of sludge and the breakdown of a clarifier were the main causes of this failure.
The peaks in February were caused by "bulking" problems in Areas #1 and #4. Area #1 was bulking
because an attempt was made to rapidly build up solids while Area #4 was bulking because excessive
solids had accumulated due to inaccurate flow meters on the waste sludge stream.
The effluent quality toward the end of the project (excluding the peaks in late February) was
definitely on an improving trend. The only other period of corresponding quality was experienced
during the first part of November 1969.
The effluent quality depicted in Figure 2 represents a composite of all of the areas and, there-
fore, the performance of the individual areas is not reflected directly. Areas #1 and #4 generally
had the poorest quality effluents, while areas #2 and #3 gave the most consistent high quality
effluents. The reasons for this may have been undetected differences in loading, the effects of
different operational modes or undetected difficulties with flow meters.
Also shown in Figure 2 is the loading to the secondary process in pounds of 6005 per day. The
dotted line represents the design average day loading (166,350 Ibs. BOD5 per day) which was exceeded
on various days of all weeks during the project. The average loading for the entire period of study
was 161,560 pounds BQDc, per day. However, two aeration basins were not in service as activated
sludge basins but rather as grease removal units. Thus, the aeration capacity to handle the design
load was reduced.
The BODg load was high during the month of October because of the effects of runoff from early
snows that had occurred in the Denver area. There is no apparent explanation for the higher load-
ings in the middle of January and especially the peak load on January 15, 1970.
Another trend that is not as apparent is the relationship between loading and effluent quality.
-------
FIGURE 2
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWER TREATMENT PLANT
OCTOBER-1969 to FEBRUARY-1970
INFLUENT BOD, LOADINGS AND
7 DAY MOVING AVERAGE, EFFLUENT BODS
ANDTSS CONCENTRATIONS
VS
TIME
•A 7 DAY MOVING ,AVG.TSS
AVERAGE DAY DESIGN
LM'Dm'G"l66,350 IBS. BOO,
1 DM
f'
V
TIME IN DAYS
-------
The low loading in December is reflected by a consistent high quality effluent during the first one-
half of the month. The consistent steady loading during the last half of January and the month of
February is reflected by consistently improving effluent BODc and TSS concentrations. The higher
loadings in October and in January demonstrate the adverse effect of decreasing effluent quality.
Figure 3 illustrates the percentage reduction (weekly average) of BODg and TSS achieved by the
Metro Denver plant. The percentage removal of BODc is a better indicator than effluent BODc concen-
trations of the benefits of process control. This fact is shown by the gradual increase in percen-
tage removal throughout the project. The percentage removal of TSS declined during the initial phase
of the project and then increased rapidly in December to a somewhat stable percentage reduction
during the final phases of the project.
The increasing trend in percentage BOD5 reduction in conjunction with the fluctuating effluent
BODc concentrations can be explained by the variations in the incoming BODc load. An increasing
BODc load was accompanied by increased effluent concentrations and thus a relatively constant rela-
tionship as far as percentage removal.
The average reduction of BODc, for the entire period was 85% and for TSS it was 60%. These are
reductions by the secondary treatment portion of the plant only and do not include the reductions of
BODc and TSS that were achieved by primary treatment. Therefore, the reduction of BODg for the pri-
mary and secondary processes averaged greater than for the secondary treatment process only and
adequately met the 80% minimum reduction of BODc required by Colorado's Water Quality Standards.
C. Data Analysis - Procedures and Results
Large volumes of data were obtained from the numerous control tests that were conducted and the
various monitoring or performance determinations that were made. These data were analyzed daily to
determine trends which were indicative of process performance and from these various trends process
control decisions were made. (i.e. increase or decrease return sludge flow, increase or decrease
wasting flow rate, etc.) Metro Denver plant personnel were trained in analyzing the data and
deriving the various trend relationships. Training was also provided in interpreting the various
trend curves so that control adjustments could be made.
A large number of relationships were established to determine the best parameter or combination
of parameters to use for controlling the activated sludge process. At the conclusion of the project
many of these relationships were abandoned and only those that appeared most beneficial were recom-
mended for continual use.
A summary of the more pertinent analyses performed are presented below.
The relationship between the settled sludge volume (settleometer readings) and time was plotted
to indicate the trends in settleability of the sludge. Also established was the trend outlining the
-------
100
90.
80-
70-
60-
50-
40-
30.
20-
10-
v
A/N
FIGURE 3
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER - 1969 to FEBRUARY - 1970
WEEKLY AVERAGE PERCENTAGE REDUCTION OF BOD S
AND TSS ( SECONDARY ONLY )
VS
TIME
WEEK OF 9 30 ' 10 6 I 10 13' 0 20llO 27 III 3 III 10 In 17 III 241 i 2 I I 12 8 I 12 I Si 12 2J I 12 29 • I 5 I I 12 I I 19 I I 26 I Z'Z I 2 9 1 2/16 ' 2/23 I
TIME IN WEEKS 1969 - 1970
END MARCH I. 1970
-------
ability of the sludge to concentrate or dewater. Many of the relationships were based on data from
the daily control test values. Sludge blanket depths were determined as many as twelve times per
twenty-four hour period as well as aeration tank concentrations, return sludge concentrations and
flow measurements. These values were averaged on a daily basis and such parameters as sludge age,
total sludge mass in the system, clarifier overflow rates, sludge detention time in the clarifier,
mass of sludge returned per gallon of sewage, etc. were calculated. Additional trends developed
were effluent .quality versus time as described by BODc and TSS concentrations.
All of the above-outlined analyses, as well as others, were conducted on each of the areas.
D. Control of Areas - Procedures and Results
Prior to this project, Metro Denver plant personnel were operating the secondary treatment
facilities as one large unit. All four areas were using a two aeration basin, three clarifier com-
bination and were step loading the sewage to the aeration basins. Sewage could be introduced at four
gates along the aeration basin: Gate A at the head end of the tank, Gate B approximately one-fourth
of the length from the head of the.basin, Gate C approximately one-half the length from the head of
the basin and Gate D approximately two-thirds of the length of the tank from the head of the basin.
Metro Denver personnel were loading one-half of the sewage at Gate B and one-half at Gate C. Return
sludge was introduced at Gate A.
A short summary of the major operational changes made in each area will be described below. The
majority of the operational changes were made to determine the operational mode which would allow
maximum removal of TSS and BODc and would improve the sludge characteristics to facilitate sludge
handling. • . .
1. Area #1 was operated using two aeration basins and three clarifiers throughout the project,
except for a short time (one week) when one of the final clarifiers was inoperable. Only two
aeration basins were used since the third aeration basin was required to remove the excessive
grease received at the plant. This area was operated using step loading (one.-half flow at
Gate B and one-half at Gate C) from the start of the project until January 5, 1970, when
loading was converted to introducing all the flow at the head of each aeration basin (Gate
A). This loading procedure was used until the end of the project. All the return activated
sludge was introduced at Gate A.
2. Area #2 was operated in a manner similar to Area #1. However, Area #2 was converted to
loading all sewage at Gate A on December 12, 1969. Performance in Area #2 was generally
superior to that of Area #1 throughout the project. Although the meters didn't indicate a
difference, it appeared as though Area #2 was receiving less flow than Area #1. It was
attempted to equalize the flow to all of the areas throughout the project." However, this was
11
-------
difficult to achieve because of the plant's hydraulics and, therefore, equal splitting of the
flow to each of the four areas was not successful.
3. Area #3 was converted to a three aeration basin, three clarifier basin operation within a
week after the project started. All sewage was loaded into the aeration basins at Gate A, as
well as return sludge. Area #3 provided the best overall performance during the project, as
measured by effluent BOD5 and TSS concentrations.
4. Area #4 was converted to a three aeration basin, three clarifier basin operation within a
week after the project started. However, a variety of methods of introducing loads was tried
on Area #4. Initially all return sludge was introduced at Gate A and the loading of one-half
the sewage flow to Gate 8 and Gate C was maintained. However, this was changed to loading all
the sewage at Gate D on November 12, 1969. (Contact stabilization) This loading was main-
tained until December 12, 1969 when all sewage was introduced at Gate A. Area #4, at times,
showed excellent reductions but the area was generally sporadic in its performance because of
difficulties in retaining the sludge in the final clarifiers.
The major operational changes above were affected by a variety of operational problems. Unreli-
able meter readings on the waste sludge flow, uneven flow distribution to the various areas, mechani-
cal failure of three clarifiers during the project, and a continual problem with solids "flushing" out
of the final clarifiers are but a few of the operational problems that added to the complexity of the
project.
E. Control of Sludge Characteristics - Procedures and Results
The two major problems encountered at Metro Denver were the "flushing" of solids that occurred
out of the final clarifiers and the sludge processing and handling problem. Since the initial
emphasis was to work in the secondary treatment portion of the plant, improving removal efficiencies
and effluent quality became primary considerations in operating the facility. However, a high
quality effluent representing increased removals of BODg and TSS also is associated with increased
sludge production, which served to magnify the sludge processing and handling problems. To compensate
for the increased sludge production accompanying the increased treatment efficiencies an attempt was
made to develop a sludge that would concentrate or dewater better than previous sludges. The end
result would be a lesser volume but increased mass of sludge being removed from the system.
At Metro Denver, the waste activated sludge is further concentrated by the use of chemical
coagulants in air flotation units. Therefore, it was also attempted to develop a sludge more amenable
to chemical coagulation.
Figure 4 illustrates the concentration of sludge wasted from the secondary treatment process. No
data on the waste sludge total suspended solids concentration are available for the early phases of
12
-------
the project. Consequently, no comparison is made of the overall changes in waste sludge concentra-
tions for the entire project period. The trends developed for the period of record are shown in
Figure 4. A decrease in waste sludge concentration was initially noted paralleling the operational
difficulties encountered with Areas #1, #2 and #4 in December (See IV-D above). Later in the project
(January and February) the waste sludge concentration increased steadily to a weekly average of
approximately 7,000 mg/1, representing a substantial increase over the low weekly average of 4,500
mg/1 experienced during the last week of December. Figure 4 indicates that one of the goals in con-
trolling sludge characteristics, that of increased waste sludge concentration, was achieved. However,
the benefits derived from increasing the waste sludge concentration were partially overshadowed by the
increased sludge production resulting from Increased removal efficiencies of BODg.
13
-------
Ill
1.
• DAILY CONCENTRATION
O WEEKLY AVG. CONCENTRATION
7i
«•
O
h-
z Si
m
u
z
O
u
01
O
a
3 <•
(/>
3-
2i
FIGURE 4
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER - 1969 to FEBRUARY - 1970
WASTE SLUDGE CONCENTRATION IN MG /L vs TIME
17 NOV.,'M-
1DEC.-
1FEI.
-------
V. DATA ANALYSIS
The objective of the assistance project was to operate the activated sludge process so that the
waste sludge characteristics could be controlled, thereby alleviating at least a portion of the
sludge handling problems. While trying to achieve this goal a large amount of data were collected.
At the conclusion of the project portions of these data were analyzed to further evaluate the major
problems encountered at the Metro Denver plant, namely the sludge handling problem associated with
sludge produced in the activated sludge process and the problem of solids loss from the final
clarifiers.
Certain portions of the data obtained during the project were selected so that smaller and more
workable portions could be investigated. It was decided to evaluate only Areas #2 and #3, since
these two areas covered most of the operational modes investigated and demonstrated the best
response to operational controls. Area §2 was operated with both step loading and conventional
loading and with two aeration basins in combination with the three clarifiers. Area #3 was operated
with three aeration basins in combination with the three final clarifiers. Both Areas #2 and #3
gave the most consistently good quality effluents and responded favorably to operational controls.
A. Analysis of Sludge Production
The sludge handling problems at the Metro Denver plant were affected by the amount of sludge
produced in the secondary unit. To evaluate the sludge production per pound of 6005 removed, an
application of the kinetic model which has been used and frequently outlined in the literature to
describe biological treatment systems was used. Papers by Lawrence and McCarty (2), Jenkins and
Garrison (3), Pearson (4) and McKinney (5) are a few that have discussed and presented the kinetic
model. The assumptions made in relating the data collected during the project to the analysis made
using the kinetic model are outlined in a sample calculation presented in Appendix C.
Since the kinetic model has been well documented in the literature, the following equations will
be used without a formal presentation of their theoretical basis.
Basic Kinetic Equations
q = F(S0 " $l) = Substrate removal rate Equation 1
X]V
v - Kd = FX2 * wxr Equation 2
a yjq -a
v = Yq = Specific Growth Rate Equation 3
6C = 1 = Mean cell residence time Equation 4
1/8 = Yq - Kd = FX2 * wxr = Net growtn rate Equation 5
VX1
15
-------
WHERE:
q = substrate removal rate, pounds of substrate removed per pounds of cells
in the system per day
SQ = influent substrate concentration
S-| = effluent substrate concentration
F = influent flow rate
X1 = MLSS or MLVSS concentration
V = volume of aeration plus secondary sedimentation basins
v = specific growth rate, pounds of cells produced per pounds of cells in
the system per day
Y = yield coefficient, pounds of cells produced per pounds of substrate
removed
KJ = endogenous decay coefficient, pounds of cells lost per pounds of cells
in system per day
X = effluent TSS or VSS concentration
W = waste sludge flow
X = return sludge and waste sludge TSS or VSS concentration
e = mean cell residence time (sludge age), days = pounds of cells in system
per pounds of cells lost from system per day
To derive a kinetic description of a particular waste source requires the development of a
series of'steady state conditions. In other words, the rate of change of substrate removal with
time is assumed to be zero. Although steady state is never achieved in a large dynamic activated
sludge plant such as Metro Denver's, certain periods of operation approach this condition. For
Areas #2 and #3 time periods were selected based on uniformity of aeration basin solids concentra-
tion and of sludge settling and concentration characteristics. The uniformity of these characteris-
tics best described a period of "steady state." Table 1 summarizes briefly the periods selected and
the average of selected parameters for each period.
The reciprocal of the mean cell residence time (ec) is the net growth rate. Equation 5, above,
outlines the relationship between the net growth rate 0/e ) and the substrate removal rate q.
These values are related by the yield coefficient (Y) and the endogenous respiration coefficient
(Kj). For normal domestic wastes, values for Y and K
-------
TABLE 1
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
A Summary Of Various Parameters Associated
With The Selected "Steady State" Periods
Parameter-Average For Period
Influent Flow - MGD
Return Sludge Flow - MGD
Waste Sludge Flow - MGD
Aeration Tank Concentration (ATC)
% Volume Concentration by Centrifuge
Return Sludge Concentration (RSC)
% Volume Concentration by Centrifuge
Ratio TSS/ATC *
Ratio VSS/TSS *
Influent (To Secondary) 6005
Concentration - mg/1
Effluent 6005 Concentration - mg/1
Effluent TSS Concentration - mg/1
AREA #2
1/5/70
to
1/11/70
25.62
13.85
.611
2.96
8.27
706
0.804
197
45
68
1/29/70
to
2/12/70
27.78
11.50
.262
4.46
14.89
585
0.811
197
24
36
AREA 13
12/15/69
to
1/5/70
29.64
14.41
.593
3.71
12.00
616
0.840
188
21
40
1/10/70
to
1/13/70
29.85
11.77
.490
1.36
4.61
817
0.846
194
36
44
1/20/70
to
1/25/70
26.30
23.00
.458
5.44
13.19
482
0.793
199
37
79
2/9/70
to
2/16/70
29.47
13.01
.445
3.92
14.05
684
0.782
207
13
26
The relationship between % volume concentration by centrifuge and TSS and VSS was established
by comparing results conducted on grab samples - normally daily grab samples.
17
-------
produced per milligram of waste (BOD5) removed and values of Kd = -0.048.
The value of Y (slope) and Kd (intercept) can be graphically determined by determining the value
of 6C (Equation 4) and q (Equation 1) and plotting l/ec versus q. Values of the removal rate (q)
and the mean cell residence time (e ) were calculated using the Metro Denver data for the selected
"steady state" periods. (See Appendix C for example calculations) These data are presented in
Table 2. Values derived for ec indicate a relatively low cell residence time. Normal residence
times for conventional activated sludge are five to fifteen days, with a mean of ten days [See
Jenkins (3)]. When considering ec and normal values obtained for Y and q during the period, K^
values were not within the recognized range (i.e. -.05, -.06), which could reflect a lack of aera-
tion capacity, complete mixing, etc.
The values of qBOD and l/ec determined from the project data have been plotted in Figure 5.
D
Also plotted is the line representing the relationship between l/ec and q for a typical domestic
sewage using an average of the values presented in the literature (6) (7). (Y = 0.60 K^ = -0.052)
The majority of the points determined using the Metro Denver data are located above the line drawn
for a typical domestic sewage. This indicates that the characteristics of the waste received at the
Metro Denver plant are such that they may deviate to a degree from that expected of a typical domes-
tic waste. Again, whether waste characteristic, dissolved oxygen maintenance, deviation from com-
plete mixing, etc. were responsible for the variation cannot be definitely determined. An attempt
to determine the degree of this deviation is also illustrated on Figure 5. It is recognized that
the plotted points demonstrate a considerable amount of scatter, however, a line was drawn through
the centroid of these points to estimate a yield coefficient (Y). The intercept (Kj) of the esti-
mated line was assumed to be zero to minimize any increase in slope. Since K^ must be negative, a
value of K
-------
TABLE 2
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Calculated Values of ec and qB0D
Selected Periods of Operation
Areas #2 and #3
AREA #2
Day
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Thurs
Fri
Sat
Sun
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Tues
Wed
Date
1/05/70
1/06/70
1/07/70
1/08/70
1/09/70
1/10/70
1/11/70
1/29/70
1/30/70
1/31/70
2/01/70
2/02/70
2/03/70
2/04/70
2/05/70
2/06/70
2/07/70
2/08/70
2/09/70
2/10/70
2/11/70
1BOD5
Ib/lb
0.412
0.495
0.373
0.344
0.424
0.352
0.275
0.365
0.404
0.341
0.259
0.402
0.457
0.449
0.360
0.343
0.351
0.242
0.454
0.377
0.372
9c
Days
2.533
2.160
2.510
4.263
2.736
3.128
3.947
6.514
6.250
6.714
6.750
6.706
7.586
5.409
5.261
5.311
5.273
4.818
4.952
5.561
6.053
l/ec
Days-1
0.395
0.463
0.400
0.235
0.365
0.320
0.253
0.154
0.160
0.149
0.148
0.149
0.132
0.185
0.190
0.188
0.190
0.208
0.202
0.180
0.165
AREA #3
Day
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Sat
Sun
Mon
Tues
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Date
12/15/69
12/16/69
12/17/69
12/18/69
12/19/69
12/20/69
12/21/69
12/22/69
12/23/69
12/24/69
12/25/69
12/26/69
12/27/69
12/28/69
12/29/69
12/30/69
12/31/69
1/01/70
1/02/70
1/03/70
1/04/70
1/05/70
1/10/70
1/11/70
1/12/70
1/13/70
1/20/70
1/21/70
1/22/70
1/23/70
1/24/70
1/25/70
2/09/70
2/10/70
2/11/70
2/12/70
2/13/70
2/14/70
2/15/70
2/16/70
<1BOD5
Ib/lb
0.592
0.483
0.606
0.629
0.492
0.299
0.217
0.408
0.407
0.323
0.271
0.351
0.276
0.220
0.304
0.252
0.285
0.187
0.312
0.276
0.305
0.443
0.956
0.658
0.902
0.512
0.366
0.325
0.207
0.290
0.224
0.166
0.348
0.330
0.339
0.354
0.307
0.354
0.302
0.458
ec
Days
1.72
2.03
2.29
2.59
3.38
3.78
3.50
2.94
3.53
3.84
4.75
3.88
3.44
3.51
11.42
3.17
2.59
3.66
3.40
2.31
2.84
2.27
2.02
4.94
5.62
6.22
6.66
5.09
2.98
7.55
2.97
2.36
2.70
3.68
3.75
4.38
4.75
4.29
4.24
4.88
1/9C
Days-1
0.581
0.493
0.437
0.386
0.296
0.265
0.286
0.340
0.283
0.260
0.211
0.258
0.290
0.285
0.088
0.315
0.387
0.273
0.294
0.433
0.352
0.441
0.495
0.202
0.178
0.161
0.150
0.196
0.336
0.132
0.338
0.424
0.370
0.272
0.267
0.228
0.211
0.233
0.236
0.205
19
-------
FIGURE 5
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 TO FEBRUARY 1970
NET GROWTH RATE (%c)
vs
SUBSTRATE REMOVAL RATE (flBOD5)
• AREA - 3
O AREA - 2
o.i
0.2
0.3
I I I I
0.4 0.5 0.6 0.7
i
0.8
0.9
I
1.0
1.1
1.2
I
1.3
1.4
1.5
SUBSTRATE REMOVAL RATE
Ib. BODc REMOVED PER DAY
Ib. VSS IN SYSTEM
-------
sludge produced In the secondary would have been 82,800 pounds per day. To maintain a specific cell
residence time (sludge age), this amount of sludge should have been wasted. If the estimated yield
coefficient Y » 0.72 (See Figure 5) is used, 99,300 pounds per day would have been produced and
\.
would have had to be wasted. These values are dally average values and do not represent the peaks
in loading and sludge production that occur. Both values are less than the 131,000 pounds per day
which was the design basis for the Metro Plant secondary sludge handling facilities. Although this
design loading was not exceeded on an average basis, problems did occur with the sludge handling
facilities (i.e. concentrators and incinerators).
B. Analysis of Secondary Clarifiers
Eckenfelder and O'Connor (8) have stated that the size of secondary clarlflers in biological
systems 1s related to three design factors. These factors are: (1) The permissible retention of the
settled sludge in the basin as dictated by its biological properties, (2) The area required for
clarification over the operating mixed liquor suspended solids range, and (3) The area and volume
requirements to produce by thickening an underflow of a desired concentration.
At Metro Denver sludge retention in the final clarlflers should be minimized; possibly to one
hour or less. The value of the sludge detention time, SDT, in the final clarlflers was determined
during the project on a daily average basis and normally was easily controlled by adjusting the
return sludge pumping rates. This fact implies that the volume of the clariflers and the return
sludge pumping capacity was generally satisfactory to allow rapid removal of the sludge.
The clarification and thickening capacities for a secondary clarifier can be estimated from
batch settling tests. A great number of batch settling tests were conducted during the project, and
these results were used to evaluate the clarification and thickening capacities of the Metro Denver
plant.
The limitation of this type of analysis is in the determination of a representative batch
settling test. The previously selected "steady state" periods for Areas #2 and #3 were selected for
analysis. These periods were initially selected based on uniformity of sludge settling and sludge
concentration characteristics, as well as uniformity of solids concentration. In addition, these
periods were generally the best periods of control and operation and therefore were representative
of sludge settling characteristics that were experienced during the project.
During most of the project four batch settling tests were conducted on a dally basis at 5:00 A.M.,
9:00 A.M., 1:00 P.M. and 9:00 P.M. Values for settled sludge volume for each hourly test were
averaged for the various "steady state" periods. These values are presented 1n Table 3. Table 1
gives the associated average parameters and average flow values for these same periods. The period
January 10, 1970 to January 13, 1970 for Area #3 was omitted from this analysis because of the low
mixed liquor solids concentration and resulting rapid settling.
21
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TABLE 3
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Average Settled Sludge Volumes For
"Steady State" Periods
Area and "Steady
State" Period
12
January 5, 1970
to
January 11, 1970
iZ
January 29, 1970
to
February 12, 1970
#3
December 15, 1969
to
January 5, 1970
13
January 20, 1970
to
January 25, 1970
13
February 9, 1970
to
February 16, 1970
Settling
Time (Min)
5
10
20
30
60
5
10
20
30
60
5
10
20
30
60
5
10
20
30
60
5
10
20
30
60
Average Settled Sludge Volumes for
"Steady State" Period - cc/1
5:00 A.M.
496
346
261
224
171
666
489
403
343
276
805
660
510
431
320
922
870
742
642
480
541
413
334
294
238
9:00 A.M.
523
383
279
239
184
737
545
433
376
301
855
725
585
495
360
953
914
828
717
542
604
476
382
335
264
1:00 P.M.
424
286
211
179
144
453
332
261
228
184
650
521
408
347
260
903
752
582
482
367
470
368
294
259
207
9:00 P.M.
517
332
246
213
161
617
452
362
320
249
677
523
401
348
265
936
829
598
489
381
539
421
337
308
237
22
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The clarification capacity required in a clarifier can be estimated from the Initial rate at
which the solids liquid interface subsides as outlined by Eckenfelder (8), Rich (9) and Smith and
Loveless (10). The zone settling rate (Vs) can be calculated by determining the slope of the initial
straight line portion of the sludge settling curve. This settling rate can then be expressed as the
equivalent surface overflow rate since solids will be lost 1n the plant effluent 1f the settling rate
is exceeded by the clarifier overflow rate.
0 = V x 7.5 gallons per cubic foot x 24 hours per day
Equation 6
= Vs x 180
WHERE: ' . ..
Or = Equivalent Surface Overflow Rate (gal/sq ft/day)
Vs = Zone Settling Rate (ft/hr)
Curves were drawn from each set of average settled sludge volume values for the selected periods.
The slope of the initial straight line portion of the curve was determined and thus the zone settling
rate (Vs) was estaon'shed. An example detenni.iation of V's is shown i'n Figure 6. The values of the
zone settling rates (V }, as mell as the associated equivalent overflow rates (Or), are shown in
Table 4.
The zone settling rate (Vs) varied throughout the "average" day for the selected periods. This
is to be expected since the zona settling rate is a function of the initial MLSS concentration and of
the loading rate, i.e. pounds of 30D per pounds of MLSS. [Smith and Loveless (10)]. Flow variations
throughout the day caused the MLSS and the loading rates to fluctuate, causing the observed varia-
tions in the values of Vs. No attempt was made to distinguish between the portion of the change In
Vs due to changing load and that due to change of initial MLSS concentration or 1n response to any
possible variances in growth rates. In addition, as mentioned earlier, cell residence time seldom
exceeded five to six days. Associated effects on settleability were also not separable.
It is shown In Table 4 that the maximum zone settling rate normally occurred at the 1:00 P.M.
test. However, It was observed that this was also the time of the day when most of the solids
flushing occurred. Table 4 shows the calculated overflow rates based on the daily average flow for
each area during the periods. Each area at Metro Denver had three 130, foot diameter secondary
clariflers which gave a total surface overflow area of 39,900 square feet. Generally the 1:00 P.M.
equivalent surface overflow rates exceeded the average clarifier overflow rates for the periods
investigated. However, this is based on maximum zone settling rates compared with average clarifier
overflow rates. If the maximum flow is assumed to occur at 1:00 P.M. and the design ratio of
average dav rate—= ^ ^ee Henningson, Durham and Ricnardson (11)] is applied to the clarifier
overflow rates, then in every case the equivalent surface overflow rate derived from Vs values at
23
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FIGURE 6
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER. 1969 - FEBRUARY. 1970
DETERMINATION OF ZONE SETTLING RATE ( Vc )
HEIGHT OF SLUDGE INTERFACE vi TIME
AREA #3 PERIOD: 3/9 - 2/14/70 AVG. 9:00 AM
IS It
SF/TTLING TIME
» 31
( MINUTES )
24
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TABLE 4
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Zone Settling Rates (Vs) And Equivalent Surface
Overflow Rates (Or) For "Steady State" Periods
Area and "Steady
State" Period
n
January 5, 1970
to
January 11, 1970
#2
January 29, 1970
to
February 12, 1970
#3
December 15, 1969
to
January 5, 1970
#3
January 20, 1970
to
January 25, 1970
#3
February 9, 1970
to
February 16, 1970
Zone Settling Rates (Vs)
- ft/hr and Equivalent Surface Overflow Rates (Or) -
gpsfd for "Steady State" Periods *
5:00 A.M.
3.43
620
1.72
310
1.13
204
<1
<180
3.00
544
9:00 A.M.
6.80
595
1.45
262
0.88
159
<1
<180
2.70
488
1:00 P.M.
3.30
1,225
•4.93
890
2.72
490 '
<1
<180
6.00
1,080
9:00 P.M.
3.83
690
3.03
546
2.53
456
<1
<180
3.24
585
Daily Average
Overflow Rate
For "Period"
gpsfd
644
698
744
660
740
* Vs values are given on top and Or values on bottom.
25
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1:00 P.M. is exceeded by the clarifier overflow rate and flushing of solids could be expected to
occur. Additionally, a portion of this flushing may be attributable to the normal high return sludge
pumping rates that were utilized in the operational controls.
This problem was further aggravated by locating the effluent weirs for the 130 foot diameter
clarifiers at the outer edge of the clarifiers. This allowed localized high upflow velocities to
occur in the final clarifiers. These localized high velocity currents could have been avoided if
weir placement had been such that more of the surface area in the final clarifiers was developed to
provide a more uniform upflow velocity. However, even if the additional weirs were located to
develop more of the surface area of the final clarifiers, the data shown in Table 4 indicates that
problems with flushing of solids still could occur.
Therefore, either more surface area must be provided or the settling characteristics must be
altered such that the zone settling rate is increased (i.e. a faster settling sludge). The zone
settling rate is dependent upon the initial MLSS concentration and the loading rate (which directly
affect the sludge flocculation characteristics). [See Eckenfelder (8) and Smith and Loveless (10)]
These factors are dependent upon the influent flow rate, which is highly variable and therefore makes
a positive control of the zone settling rate difficult to achieve. For ease of operation It appears
that more effective surface area, which is better developed by weir placement, is required at Metro
Denver to provide adequate clarification capacity.
The thickening capacity required in a final clarifier can also be estimated from a batch settling
test (8) (9). The average 1:00 P.M. settling test (See Table 3) was selected for analysis since this
time was assumed to coincide with normal daily peak flows which are approximated by twice the average
daily flow (11). The most rapid 1:00 P.M. zone settling rate (See Table 4) was selected to determine
a desired thickening capacity since the value determined would represent a minimum thickening area
required, (i.e. any settling rate with a lesser value would require more thickening area.) The peak
zone settling rate for Area #2 at 1:00 P.M. was 4.93 feet per hour and for Area #3 it was 6.00 feet
per hour. (See Table 4)
Rich (9) outlines an equation for determining the thickening area required:
<1Tu
A = -yr^ Equation 7
* o
WHERE:
A = cross section required to obtain a layer of a desired concentration
-- ft2
q = flow rate of the mixed liquor entering the final clarifier — ft3/sec.
26
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Z'0 = initial height of the interface in the settling column - feet (The
settleometers used at Metro Denver for the batch settling tests had a
0.5 feet depth.)
T = settling time required to attain a desired underflow concentration -
sec. [This value is obtained from a graphical analysis of a sludge
settling curve as outlined by Eckenfelder (8) and Rich (9).].
To complete the analysis of thickening capacity a desired underflow concentration must be
selected. At Metro Denver the design values for underflow concentration expected ranged between
5,000 to 15,000 mg/1. Therefore, a desired underflow concentration of 10,000 mg/1 was selected.
The settling time (Tu) required to obtain a 10,000 mg/1 underflow concentration for Area #2 for
the selected period January 29 to February 12, 1970 (Vs = 4.93) was determined by a graphical
analysis of the sludge settling curve. This value was used with the average flow for the period to
determine by Equation 7 the area required for thickening. For average flows 42,500 ft2 would be
required for thickening while for peak flows 85,450 ft2 would be required. A similar analysis con-
ducted on Area #3 for the selected period (February 9 to February 16, 1970) showed required areas of
114,000 ft2 and 57,000 ft2 at peak and average flow rates respectively.
The available surface area in Areas #2 and #3 is 39,900 ft2. This is not adequate to provide the
thickening area required to achieve a 10,000 mg/1 underflow concentration with the type of sludge
obtained during the project. The above analysis also indicates the implications of limited thicken-
ing capacity on sludge handling problems. Without sufficient thickening capacity a more dilute waste
•sludge flow concentration is realized. The effect of the dilute concentrations is shown by the
relative differences in total sludge volumes to waste 100,000 Ibs. of solids as summarized in Table
5.
The preceding materials were developed to compare actual performance results with the batch
settling data. Most importantly, Rich (9) describes the numerous departures of actual sedimentation
basin performance from that of ideal basins. "The net effect of all the factors that contribute
toward reducing the efficiency of sedimentation in an actual basin is to decrease the clarification
rate and to increase the detention time over that derived from a batch analysis. For the sedimenta-
tion of flocculent particles from dilute suspensions the overflow rate generally will be decreased by
a factor of 1.25 to 1.75 and the detention time will be increased by a factor of 1.50 to 2.00. In
scaling-up thickening operations, a factor of 1.0 to 2.0 is applied to the area required for clarifi-
cation (hindered settling) and a factor of 1.0 to 1.5 to that required for thickening."
Results of the Metro Denver settleability testing should be judged in this light and with the
reported values of loading, residence times, etc. obtained during the period.
27
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TABLE 5
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Waste Sludge Flow Required To Remove
An Equivalent Amount Of Solids With
Varying Underflow Concentrations
Underflow Concentrations -- mg/1
Waste Volume to Remove
100,000 Lbs. of Solids - Gal.
5,000
2,400,000
10,000
1,200,000
15,000
800,000
28
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VI. SUMMARY AND CONCLUSIONS
One of the objectives of the project was to instigate additional process control testing for the
secondary treatment (activated sludge) portion of the Metro Denver plant. Plant personnel were
trained to conduct process control tests on a routine basis, to evaluate and graph various selected
parameters, and to interpret these data so that adequate daily operational changes could be made.
The full beneficial effect of these process controls' was not realized because of various problems
encountered with plant operation, as outlined below:
1. Adjustment of flow to each aeration basin was difficult because each basin was fed by a gate
opening from a common channel. Balancing the hydraulic effects of ten gates to achieve equal
flow to each of the four areas required a great deal of attention. After the gates were
adjusted, determination of actual flow to each aeration basin was questionable because of
occurrences of unreliable instrument readings.
2. Two of the twelve aeration basins provided in the secondary portion of the plant were used as
grease flotation units to remove grease from the influent waste stream and were thus unavail-
able for use as a portion of the activated sludge process. This becomes important since the
average loading to the secondary during this investigation was 161,560 pounds of BOD per day,
which is approaching the design loading of 166,350 pounds of BOD per day.
3. The rate of wasting sludge was difficult to control on a continuous basis because the meters
and control instruments frequently gave erroneous readings. Several times it was discovered
that actual flow and meter readings differed by as much as.100 percent. This definitely
effected the ability to establish a process balance.
4. No reserve capacity was, available for final clarification. When a clarifier broke down
(three clarifiers broke down during the project) solids were carried over in the plant '
effluent, the effluent quality was degraded, and the process balance in the affected area was
impaired.
Other difficulties encountered were the sludge production in the secondary treatment process and
the flushing of solids from the final clarifiers into the effluent.
The initial emphasis in dealing with the problems at Metro was to control the secondary treatment
portion of the plant. Therefore, removal efficiencies and effluent quality became important consider-
ations in operating the facility. Unfortunately, a high quality effluent representing increased
removals of BODg and TSS is associated with increased sludge production, which served to antagonize
the sludge processing and handling problem. To compensate for the increased sludge production that
accompanied the slightly increased removals achieved during the project and to relieve the existing
sludge problem, an attempt was made to develop a sludge that would concentrate or dewater better than
29
-------
previously. This would have allowed a lesser volume of a more dense sludge to be wasted. Average
concentrations of 6,900 to 7,000 mg/1 were obtained in the waste sludge flow toward the end of the
project. However, the benefits derived from increasing the waste sludge concentration were not
realized because of the increased removal efficiencies and the resulting increase in the amount of
sludge produced.
Although slightly greater BOD and suspended solids removal efficiencies were realized through
operational controls, little was accomplished to alleviate the sludge handling problems at the plant.
It is hoped that the increased removal efficiencies will be maintained and the sludge handling proce-
dures modified to alleviate these difficulties. An investigation of the sludge production character-
istics at the Metro plant to compare them with presently available sludge handling facilities was
made.
A kinetic model was applied to the collected data to determine the microbiological character of
the waste stream. At Metro Denver the results of this analysis indicate that the characteristics of
the waste received at the Metro Denver plant do not deviate significantly from those expected from a
typical domestic waste. An attempt was made to determine the amount of sludge production and to com-
pare these results with the sludge handling capacities at the plant. The results indicate that the
design sludge handling capacity (131,000 pounds per day of secondary sludge) could be exceeded during
peak loading periods. It is important when sludge handling procedures or facilities are modified at
Metro Denver that the sludge production during peak loading periods be considered in the design
criteria.
The. second major operating difficulty evaluated was the flushing of solids that occurred from the
final clarifiers. Representative zone settling rates were determined for the sludge at Metro Denver
based on the numerous batch settling test data obtained. From this.analysis it was determined that
the clarification capacity of the final clarifiers at the Metro Denver plant was not adequate for
the selected periods of investigation. The type of sludge developed proved to have a zone settling
rate (V$) that was too slow to be held in the final clarifiers. A portion of the flushing problem
was also attributed to the large diameter (130 feet) final clarifiers which had effluent weirs
located at or near the outer periphery. This weir placement allowed excessive velocity currents to
develop further aggravating the solids "flushing" problem. This problem can be alleviated by a
different weir placement arrangement that allows a more uniform use of the surface area on the final
clarifiers. (i.e. another launder of weirs located nearer the center of the tank.)
It was also determined that the thickening area requirements of the final clarifiers were not
adequate to obtain a 10,000 mg/1 underflow concentration with the type of sludge developed during the
project.
Two alternatives can be used to change the effects of the slow zone settling rates of the sludge.
30
-------
The first is to increase the clarifier surface area to reduce overflow rates to less than the settling
velocity established by the zone settling rate. This would provide additional thickening area at the
same time. The second approach would be to increase the zone settling rate of the sludge at the Metro
Denver plant. The zone settling rate is a function of the MLSS concentration and the loading rate.
Because of the constantly changing load (flow) and its effect on the MLSS concentration, it is a con-
tinuous problem to maintain a proper process balance and achieve a desired zone settling rate.
31
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VII. RECOMMENDATIONS
The following recommendations are made:
1. It is recommended that control testing established during the Federal Assistance Project be
continued.
2. An effort should be made at the Metro Denver plant to assure the accuracy of all metered
values in order to adequately use control testing procedures.
3. It is recommended that Metro Denver be considered for demonstrating various comparisons.
Because of the unique arrangement of facilities at the Metro plant, four areas with an iden-
tical influent waste are available for evaluation. This arrangement is ideal for conducting
comparisons of various types of equipment (i.e. provide various types of aeration equipment,
evaluate effects of different skimmer arrangements on final clarifiers, evaluate different
weir placement patterns on final clarifiers, etc.).
4. The Metro Denver plant should be operated to achieve the maximum possible reduction of waste
pollutants. To operate and achieve these high removal efficiencies, modifications to the
sludge handling procedures or facilities must be made. Any modification of the Metro Denver
sludge handling facilities should take into account the sludge production characteristics at
the Metro Denver plant which are apparently similar to those of typical domestic sewage and
the clarification-thickening capacity requirements of the secondary clarifiers.
5. Properly located additional weirs are recommended on the secondary clarifiers to develop a
more uniform distribution of flow over the surface area provided in the relatively large
diameter final clarifiers. Surface skimmers are also recommended.
6. Additional clarifier surface area with proper weir placement is recommended or the sludge
settling characteristics must be altered by operational control in'order to assure that
solids will not be flushed into the final effluent. Additionally, increased area would
appear to improve sludge thickening, thereby reducing waste sludge volumes. More reliable
control would also be obtained by increased clarifier surface area.
32
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VIII. APPENDICES
Appendix A - A Resolution: "Concerning the Federal Government's Responsibilities in
Constructing and Operating Sewage Disposal Facilities."
Appendix B - References
Appendix C - Determination of Substrate Removal Rate (q) and Net Growth Rate (l/ec)
-------
APPENDIX A
A RESOLUTION ADOPTED BY METROPOLITAN
DENVER SEWAGE DISPOSAL DISTRICT NO. 1'S
BOARD OF DIRECTORS
ENTITLED
"Concerning the Federal Government's
Responsibilities in Constructing and
Operating Sewage Disposal Facilities"
July 11, 1969
-------
A RESOLUTION
(CONCERNING THE FEDERAL GOVERNMENT'S RESPONSIBILITIES IN
CONSTRUCTING .AND OPERATING SEWAGE DISPOSAL FACILITIES)
WHEREAS, the federal government has enacted water pollution control legislation which makes it
incumbent upon states to establish stream quality limits, or to be subjected to stream quality stan-
dards as dictated by the federal government itself, and
WHEREAS, the water pollution legislation adopted by the State of Colorado is not consistent but
rather relates to stream classification, based upon an evaluation of each stream's individual
characteristics, and
WHEREAS, the evaluation process for stream classification relates to a multitude of factors
other than the consideration of protection to health and the abatement of nuisance, and
WHEREAS, sewage treatment to the extent of providing for the development of streams and adjacent
properties into recreational areas does require an additional capital investment for treatment
facilities, as well as substantially increasing operating and maintenance expenses thereof, and
WHEREAS, the arid and semi-arid regions of the western United States have additional burdens for
capital investments and operational and maintenance expenses, due to the lack of dilution water to
the same degree as do the other regions of the United States, and
WHEREAS, the high degree of sewage treatment required to effect water pollution control does
generate additions to solid wastes to be disposed of in the form of sludge, and
WHEREAS, cities, counties and independent sanitation districts in the Metropolitan Denver area
recognized in the early 1960's their financial inability as separate political subdivisions to meet
the strict standards being forced upon them by the national Congress and the State Legislature, and
WHEREAS, these independent political subdivisions banded together and created the Metropolitan
Denver Sanitation District No. 1, prevailing upon the Colorado General Assembly to adopt Colorado
Revised Statute 89-15-5 giving them authority so to do, and
WHEREAS, property owning electorate, demonstrating their concern over the pollution threat to
the health and welfare of the total community, by a vote of 25,099 to 2,756, agreed to mortgage
their property so that bonds in the amount of $32.5 million could be issued for the construction of
a modern primary and secondary sewage treatment plant at the confluence of Clear and Sand Creeks
with the Platte River, and
WHEREAS, this plant has been constructed following review and approval of engineering and con-
struction plans by all required federal, state and regional agencies with these bond moneys, supple-
mented by some federal but no state funds, to take care of residential, commercial and industrial
34
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wastes with each participating political subdivision, by means of billings to users within their
subdivisions, paying their proportionate shares of all operating costs, and
WHEREAS, this multi-mi 11 ion-dollar plant does bring effluent dumped into the Platte River up to
water pollution control standards it does not dispose of the solid wastes resulting from such treat-
ment for a variety of reasons not the least of which is the fact that our technology has developed a
multitude of consumer goods, paper products, garbage disposal systems and detergents, handle human
waste, and . '
WHEREAS, resident property owners of Metropolitan Denver recognized their responsibilities to
take the initiative and act to abate practices which contributed to the pollution of Clear Creek,
Filial- Creek, Sand Creek and other watercourses that flowed into the Platte River as well as the
Platte River itself, and
WHEREAS, residents and taxpayers of the various political subdivisions that are now participating
in this metropolitan effort to eliminate a pollution problem are being taxed the maximum they can
afford to pay for sewage, disposal and do not have the financial capability to pay imminent additional
operating and maintenance costs or to effect the engineering, design and capital construction
necessary to increase the efficiency of this plant so as to halt continuing pollution of our
oiivi ronment;
NOW, THEREFORE, be it resolved, that the Board of Directors of the Metropolitan Denver Sanitation
District No. 1 hereby does petition the Congress of the United States and the appropriate federal
agencies to:
1. Conduct and finance extensive research to discover new techniques of handling the variety of
waste products now being dumped into the sanitary sewers of America and being carried to
traditional plants that do not have the capabilities of handling them.
2. Make available to this district a special team of scientists and engineers assembled from
appropriate federal departments to serve as a task force to inspect the District's sewage
disposal plant and make appropriate recommendations.
3. Appropriate sufficient funds so that these recommendations Ccfn be implemented, since the
Federal government has set up the standards the District is required to meet.
4. Re
-------
APPENDIX B
REFERENCES
-------
1. WEST, A. W.
Case Histories: Improved Activated Sludge Plant Performance by Operations Control -
Proceedings 8th Annual Environmental and Water Resources Engineering Conference,
Vanderbilt University. 1969.
2. LAWRENCE, A. W. and McCARTY, P. L.
"Unified Basis for Biological Treatment Design and Operation." Journal of the Sanitary
Engineering Division, ASCE, Volume 96, No. SA 3, Proc. Paper 7365, 1970, pp. 757-778.
3. JENKINS, D. and GARRISON, W. E.
"Control of Activated Sludge by Mean Cell Residence Time," Journal Water Pollution Control
Federation, Volume 40, No. 11, Part 1, 1968, pp. 1905-1919.
4. PEARSON, E. A.
Kinetics of Biological Treatment. Paper presented at: Special Lecture Series -
Advances in Water Quality Improvement, University of Texas, Austin. 1966.
5. McKINNEY, R. E.
"Mathematics of Complete-Mixing Activated Sludge." Journal of the Sanitary Engineering
Division, ASCE, Volume 88, No. SA 3, Proc. Paper 4362, 1965, pp. 45-61.
6. HEUKELEKIAN, H., OXFORD, H. E. and MANGENELLI, R.
"Factors Affecting the Quantity of Sludge Production in the Activated Sludge Process."
Sewage and Industrial Wastes, Volume 23, No. 8, 1951, pp. 945-958.
7. MIDDLEBROOKS, E. J. and GARLAND, C. F.
"Kinetics of Model and Field Extended-Aeration Wastewater Treatment Units," Journal Water
Pollution Control Federation, Volume 40, No. 4, 1968, pp. 586-612.
8. ECKENFELDER, W. W. and O'CONNOR, D. J.
Biological Waste Treatment, Pergamon Press, New York. 1961.
9. RICH, L. G.
Unit Operations of Sanitary Engineering, John Wiley and Sons, Incorporated, Publishers,
New York, London. 1961.
10. SMITH and LOVELESS
Notes on Activated Sludge, Lenexa. 1969.
11. HENNINGSON, DURHAM and RICHARDSON
Consulting Engineers Report. Metropolitan Denver Sewage Disposal District No. 1 - Metro
Plant Expansion Study, Part 1 - Immediate Requirements. 1969.
36
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12. WEST, A. W.
Listing of Abbreviations Used to Describe Activated Sludge Systems. Lecture Presentation
to Consulting Engineers and Plant Operators Concerning Control Testing for Activated
Sludge Plants Sponsored by Water Pollution Control Division, Colorado Department of
Public Health. 1970.
37
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APPENDIX C
DETERMINATION OF SUBSTRATE REMOVAL
RATE (q) AND NET GROWTH RATE (1/6C)
-------
It is the purpose of this appendix to present a sample calculation of the determinations made of
the substrate removal rate (q) and the net growth rate (l/ec). Throughout the sample calculation the
assumptions made in relating the data collected and analyzed during the assistance project to the
analysis made using the kinetic model will be stated. Data obtained for Area #3 on December 15, 1969,
will be used for the presentation of the sample calculation.
A. Determination of the Substrate Removal Rate (q)
q = p 1 [See Jenkins (3)]
1. Determination of F(S0 - S-|)
WHERE:
SQ = influent substrate concentration - For Metro Denver a BODg value based on a
composite sample was used to represent S (12/15/69 for Area #3, S = 198 mg/1).
S, = effluent substrate concentration - For Metro Denver a BODC value based on a
I b
composite sample was used to represent S1 (12/15/69 for Area #3, S.. = 16 mg/1).
F = influent flow rate (12/15/69 for Area #3, F = 34.8 MGD) - This value was obtained
from flow meters at the Metro Denver plant.
THEREFORE:
F = 34.8 MGD SQ = 198 mg/1 S] = 16 mg/1
34.8 (198-16) (8.33 Ibs/gal) = 52.760 Ibs. BOD5 removed/day
2. Determination of VX,
WHERE:
V = volume of aeration plus secondary sedimentation basins
X = MLSS or MLVSS concentration
NOTE:
VX, is a number representing the total pounds of cells in the system. Normally in
determining this value mixed liquor suspended solids concentrations by weight are used
(X,). Instead of MLSS concentrations, sludge concentrations were obtained on a percent
volume basis by using the centrifuge. During most of the project, however, daily rela-
tionships between percent concentration of sludge by volume and concentration by weight
were determined on the basis of a grab sample. These comparisons varied from 1% =
500 mg/1 TSS to 1% = 1,000 mg/1 TSS. However, during "steady state" conditions, the
relationship between spin concentrations and mg/1 remained fairly constant. Therefore,
the average of the relationship between spin concentrations and mg/1 for each "steady
state" period selected was determined and used to convert the spin concentration to
38
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mg/1 of total suspended solids. The relationship between total suspended solids (TSS)
and volatile suspended solids (VSS) was also obtained from the analysis of daily grab
samples. The average ratio of VSS/TSS for each "steady state" period was determined.
For December 15, 1969, and the associated "steady state" period the average relationship
between volume or spin concentrations and mg/1 was 1% = 616 mg/1 TSS for Area #3 and the
average VSS/TSS ratio was 0.840. Another refinement was also used in obtaining VX..,
which will be outlined below.
APPROACH: •
A value comparable to VX, called total sludge units (TSU) was determined using the Metro
Denver data. Total sludge units are equivalent to the summation of the 'aerator sludge
units (ASU) and the clarifier sludge units (CSU). A sludge unit is defined as one
gallon of sludge at 100% concentration, based on sludge concentrations obtained by cen-
trifuge testing. One of the differences between TSU and VX-, lies in the fact that a
' modification is made in determining the clarifier sludge units.
a. Determination of Clarifier Sludge Units (CSU)
Final Clarifier
CONC = RSC
WHERE: [West's Symbols (12)]
CWD = clarifier water depth (mean depth if bottom is sloped) - At Metro Denver the
'mean depth was 11.7 feet.
DOB = depth of sludge blanket - At Metro Denver blanket depth determinations were made
every two hours on each of the three clarifiers in the respective areas. These
values were averaged on a daily basis to obtain DOB (12/15/69 for Area #3, DOB =
9.7 feet).
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BIT = sludge blanket thickness - This value is equivalent to CWD - DOB (11.7 - 9.7 =
2.0 feet (BIT) for Area #3 on 12/15/69).
ATC = aeration tank concentration - This is the concentration of sludge by percent
volume in the aeration basin. This value was obtained by centrifuging samples of
the effluent from the aeration basins. A daily average of ATC values was obtained
for use in calculations. (12/15/69 for Area #3, ATC = 2.75%)
RSC = return sludge concentration - This is the concentration of sludge by percent
volume drawn off the bottom of the secondary clarifiers. This value was obtained
by centrifuging samples taken from the return sludge wet well. A daily average of
RSC values was obtained for use in calculations. (12/15/69 for Area #3, RSC =
11.25%)
CMC = clarifier mean sludge concentration - This value is obtained by the equation
ATP + !KC
tvjv/. This equation assumes a sludge concentration at the top of the blanket
equal to ATC and that at the bottom equal to RSC and a uniform distribution of
concentration. (2.75 + 11.25 = 7-0% (CMC) for Area #3 on 12/15/69)
OTHER FACTORS:
CV6 = clarifier volume in gallons per clarifier multiplied by the number of clarifiers in
operation. At Metro Denver the volume of each clarifier was 1.165 million gallons
and three clarifiers were in operation. (1.165 x 3 = 3.495 MG (CVG) for Area #3
on 12/15/69)
CSP = clarifier sludge percentage or the portion of the clarifier occupied by sludge
which is determined by the ratio of |£J. (2.0 = Q.171 (CSP) for Area #3 on
vWU I I * /
12/15/69).
From the above the clarifier sludge units can be determined by the equation: CSU =
CMC x CSP x CVG.
A modification was made in the equation for this analysis in that the CMC was multiplied
by the factor representing the conversion between percent concentration by volume and mg/1
(616 mg/1 TSS = 1% for Area #3 for 12/15/69 and the related "steady state" period).
Therefore the modified clarifier sludge mass can be determined by CSU (modified) =
CMC x 616 x CSP x CVG x 8.33 Ibs/gal.
C = 7.0 x 616 x 0.171 x 3.495 x 8.33
= 21.550 Ibs. of total suspended solids or sludge in clarifier
b. Determination of Aerator Sludge Units (ASU)
ASU = AVG x ATC
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WHERE:
AVG = aeration basin volume in gallons per aeration basin times'the number of basins
in service. At Metro Denver the volume of each aeration basin was 2.0 MG and
three basins were in operation in Area #3 (2.0 x 3.0 = 6 MG (AVG) for Area #3
on 12/15/69).
ATC = 2.75% for Area #3 on 12/15/69 (See a. above).
From the above the aeration basin sludge units can be determined. However, the per-
centage sludge concentration by volume must again be converted to mg/1 (616 mg/1 TSS =
~\% for Area #3 for 12/15/69 and the related "steady state" period).
Therefore the modified aeration basin sludge mass can be determined by:
ASU (modified) = AVG x ATC x 616 x 8.33 Ibs/gal.
= 6 x 2.75 x 616 x 8.33
= 84.670 Ibs. of total suspended solids or sludge in aeration basia
c. Determination of TSU
Using the modifications outlined above the value of TSU is assumed to oe equivalent
to the value VX^.
THEREFORE:
TSU (modified) = VX] = ASU (modified) + CSU (modified)
= 21,550 (From a. above) + 84,670 (From b. above)
= 106,220 Ibs. of total suspended solids or sludge in system
NOTE:
The value of TSU, as determined above, was obtained on a TSS basis. Normally in
determining a substrate removal rate (q) a VSS basis is used. (VSS/TSS = 0.840 for
Area #3 for 12/15/69 and the related "steady state" period)
THEREFORE:
TSU (modified) x VSS/TSS = VX] in Ibs. of VSS
= 106,220 x 0.840
= 89.220 Ibs. of_j/olatile suspended soli.d.Lj.1
3. Example Determination of q.
q = vx^
For Area #3 on 12/15/69:
F(S0 - S]) = 52,760 Ibs. BOD5 removed/day (1. above)
VX-| = 89,220 Ibs. of volatile suspended solids in system (2. above)
41
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q = 52.760
H 89,220
0.592 Ib. of BODs removed per day
1b. of VSS in system
[q for conventional activated sludge normally has a value of 0.2 to 0.5, see Jenkins (3)]
8. Determination of the Net Growth Rate l/ec
V = FX2 + UXr [See Jenkins
^ VX1
1. Determination of VX]
VX.| or its assumed equivalent was determined in Part A-2 above. This was determined for
Area #3 for the date of 12/15/69.
VX = 106.220 Ibs. of total suspended solids in system (A-2 above)
NOTE:
In the determination of l/ec it is not necessary to convert from a TSS basis to a VSS
basis since both the numerator (FX2 + WXr) and denominator (VX-|) in the calculation can be
determined on a total suspended solids basis. Therefore, VX-j on a total suspended solids
basis is given above and WXr and FXg will be calculated on a total suspended solids basis
below.
2. Determination of WXr
WX represents the mass of sludge wasted from the system per day.
WHERE:
W = waste sludge flow rate (12/15/69 for Area #3, W = 0.89 MGD) - This value was
obtained from flow meters at the Metro Denver plant.
Xr = return sludge TSS or VSS concentration - This value was not determined at Metro
Denver on mg/1 basis but rather the return sludge concentration (RSC) was deter-
mined as a percent volume using the centrifuge. This value (RSC) can be related
to Xp using the relationship established between mg/1 and percent concentration by
volume based on daily grab samples. (616 mg/1 TSS = 1% for Area #3 and the
related "steady state" period) For Area #3 the daily average RSC concentration on
12/15/69 was 11.25%.
Xr = 11.25 x 616 = 6,930 mg/1
THEREFORE:
WXr = 0.89 x 6,930 x 8.33 Ibs/gal. = 51.310 Ibs. wasted per dav
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3. Determination of FX^
F/2 represents the cells lost from the system per day in the plant effluent.
WHERE:
Xp = effluent TSS or VSS concentration - At Metro Denver the effluent TSS concentra-
tion was determined for each area based on the analysis of a composite sample
(12/15/69 for Area */3 effluent TSS = 36 mg/1). '„ . .. '" '' :
F = influent flow rate (F - 33.9 MGD for Area #3 on 12/15/69).. .
THEREFORE:
FX2 = 33.9 x 36 x 8.33 Ibs/gal.
= 10.180 Ibs. of total.suspended solids lost in the effluent per day
4. Example Determination of Net Growth Rate (l/ec)
FX? + WXr
For Area #3 on 12/15/69:
FX2 = 10,180 Ibs/day (3. above)
WXr = 51,310 Ibs/day (2. above)
VX! - 106,220 Ibs. (1. above)
THEREFORE:
, ,0 _ 10,180 + 51,310
l/ec ro67?20 --------
- 61 ,490
T06T2PO
= 0.581 jbs. TSS wasted or lost per day
The reciprocal of l/ec is equal to 0C or the mean cell residence time (sludge age). For
Area #3 on December 15, 1969, ec = 1.72 days.
Similar calculations were made for the other days included in the selected "steady state"
periods for Areas #2 and #3. The results of these analyses an; presented in Table 2 in tf>.t.
43
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APPENDIX C
SAMPLING PROCEDURES
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SAMPLING PROCEDURES
Influent samples of the Denver Northside plant and the Denver Metro
plant were collected upstream of the point of supernatant return every
half hour. Denver Northside influent samples were collected using
automatic samplers. All other samples were collected manually within
the Metro plant area. All samples were flow composited, according to
instantaneous flow readings obtained near the point of collection, and
were iced during the entire 24-hour period. Field measurements of pH,
temperature, and conductivity were made at selected stations. The
composite samples were delivered to the NFIC-D laboratory and analyzed
for BOD, total and suspended solids, volatile suspended solids, settle-
able solids, total organic carbon, chemical oxygen demand, nitrogen
series, total phosphorus, and selected heavy metals.
Samples of the final effluent from the Denver Metro facility were
analyzed for total and fecal coliforms. These bacteria samples were
iced and delivered to the NFIC-D mobile bacterial laboratory for analyses,
At the time of collection, field measurements and chlorine residual
were measured.
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APPENDIX D
DATA ON
METROPOLITAN DENVER SEWAGE DISPOSAL DISTRICT PLANT //I
AND
NORTH DENVER WASTEWATER TREATMENT PLANT
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TABLE D-l
SUMMARY OF ORGANIC DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
Station— Description
A Clear Creek Raw Influent
B Packaging Corporation
Effluent
C Sand Creek Raw Influent
D Combined Raw Influent to
Metro
E Denver Northside Influent
F Primary Effluent from
Flow
mgd
17.
0.
9.
27.
76.
27.
3-21.2
4-0.6
5-11.0
2-32.6
7-92.5
2-32.6
BOD
mg/1
140-250
280-480
140-290
190-250
180-430
120-160
Total
Solids
mg/1
930-1300
1120-2130
890-1200
1120-1640
920-1440
980-1060
Susp.
Solids
mg/1
210-480
220-480
240-440
300-620
320-1240
60-180
Vol.
Susp.
Solids
mg/1
180-440
150-400
180-420
160-540
240-1200
60-140
Settl.
Solids
mg/1
3.5-7.0
19-100
(est)
5-8
5-9
3.5-10
Trace-1
COD
mg/1
320-700
890-1200
350-1560
480-870
590-1800
250-290
TOG
mg/1
64-150
80-320
66-190
66-360
84-340
31-120
Metro
Denver Northside Primary 76.7-92.5 80-310 620-820 <20-300 <20-160 0.2-7 160-270 31-54
Effluent
Influent to Secondary 103.9-124.0 75-210 780-890 50-140 40-130 0.1-0.5 200-270 33-80
Units
Influent to C12 Contact 103.9-124.0 25-95 690-790 20-240 <20-200 Trace-5 100-410 15-69
Chamber
Final Effluent from Metro 103.9-124.0 10-100 660-830 30-240 30-240 Trace-7 80-790 18-70
a/ For location see Figures 2 and 3.
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TABLE D-2
SUMMARY OF HEAVY METAL DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
Cadmium Chromium Copper Lead Zinc Mercury
Station— Description mg/1 mg/1 mg/1 mg/1 mg/1 yig/1
A Clear Creek Raw Influent <0.02-0.05 <0.02-0.07 0.05-0.10 0.05-0.20 0.17-0.21 <0.2-0.6
B Packaging Corporation
Effluent <0.02-<0.02 0.03-0.37 0.07-0.26 0.29-2.3 0.26-6.1 <0.02-1.0
C Sand Creek Raw Influent <0.02-<0.02 0.09-0.43 0.13-0.58 0.06-0.14 0.13-0.43 0.02-1.2
E Denver Northside Influent <0.02-0.04 0.03-0.26 0.16-0.23 0.09-0.22 0.69-1.9 0.2-1.3
J Final Effluent from
Metro <0.02-<0.02 0.03-0.11 0.04-0.24 0.03-0.10 0.06-0.49 0.2-1
a/ For location see Figures 2 and 3.
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TABLE D-3
SUMMARY OF NUTRIENT DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
Station^/
A
B
C
E
J
Description
Clear Creek Raw Influent
Packaging Corporation Effluent
Sand Creek Raw Influent
Denver Northside Influent
Final Effluent from Metro
NH3 as N
mg/1
16-21
0.1-3.9
17-22
12-20
11-18
Total N as N
mg/1
23-31
4.3-8
25-37
21-29
15-34
N02 + N03 as N
mg/1
0.02-0.07
0.7-3.5
0.01-0.61
0.01-0.23
0.2-1.7
Total P
mg/1
9.6-13
0.4-2.8
11-14
7.5-12
4.8-13
a/ For location see Figures 2 and 3.
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