ENVIRONMEN'TMsJ'ROTECTION A
                  OFFICE OF  i;\HMI< KMKNT
                        REPORT ON
               EFFECTS OF WASTE DISCHARGES
         WATER QUALITY OF THE  SOUTH PLATTE RIVER
                DENVER METROPOLITAN  AREA



NATIONAL FIELD INVESTIGATIONS CENTER-DENVER


                          AND
                      REGION VIII
                 DENVER, COLORADO

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      ENVIRONMENTAL PROJECTION AGENCY

           OFFICE OF ENFORCEMENT
                 Report On

        Effects of Waste Discharges
                    On
  Water Quality of the South Platte River
         Denver Metropolitan Area
           DRAFT FOR REVIEW ONLY
National Field Investigations Center-Denver
                    and
                Region VIII
             Denver, Colorado
               February 1972

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                         TABLE OF CONTENTS


                                                          Page

LIST OF TABLES	    ii

LIST OF FIGURES	   ill

INTRODUCTION 	     1

WASTE SOURCE EVALUATIONS 	     3
  Denver Northside Wastewater Treatment Plant	     3
    General	     3
    Wastewater Treatment Facilities	     3
    Discussion of In-Plant Survey and Findings 	     5

  Metropolitan Denver Sewage Disposal Plant	     9
    General	    13
    Wastewater Treatment Facilities	    13
    Discussion of In-Plant Survey and Findings 	    15

STREAM SURVEYS	    25
  General	    29
  Findings of November Bacteriological Survey	    32
  Findings of the December Survey	    34

WATER QUALITY IMPROVEMENT MEASURES	    39

CONCLUSIONS	    43

RECOMMENDATIONS	    46

REFERENCES	    48

APPENDICES
  A  SAMPLING PROCEDURES 	   A-l

  B  DATA ON METROPOLITAN DENVER SEWAGE TREATMENT PLANT
     AND NORTH DENVER WASTEWATER TREATMENT PLANT ....   B-l

  C  REPORT BY ENVIRONMENTAL PROTECTION AGENCY, REGION
     VII, KANSAS CITY, MISSOURI, "FEDERAL ASSISTANCE
     PROJECT METROPOLITAN DENVER SEWAGE DISPOSAL DISTRICT
     NO. 1, OCTOBER 1969 - FEBRUARY 1970"	   C-l

  D  COLORADO WATER QUALITY STANDARDS	   D-l

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                         LIST OF TABLES

Table
Number                    Description                      Page
  1    SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASURE-
       MENTS FOR THE DENVER NORTHSIDE WASTEWATER TREATMENT
       PLANT	   7

  2    MONTHLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
       SUSPENDED SOLIDS REMOVALS AT THE NORTH DENVER
       WASTEWATER TREATMENT PLANT FOR DENVER 	   8

  3    WASTE TREATMENT FLOWS AND COSTS AT SELECTED SATELLITE
       PLANTS	  11

  A    OTHER WASTEWATER TREATMENT FACILITIES IN THE
       METROPOLITAN DENVER AREA	  12

  5    SUMMARY OF ORGANIC AND NUTRIENT DATA FOR NORTHSIDE
       AND METRO PLANTS, August 1-9, 1971	  16

  6    SUMMARY OF HEAVY METALS DATA FOR METRO AND NORTHSIDE
       PLANTS, August 1-9, 1971	  17

  7    BACTERIOLOGICAL AND CHLORINE RESIDUAL DATA,
       METROPOLITAN DENVER SEWAGE DISPOSAL PLANT	  18

  8    REMOVAL EFFICIENCIES FOR DENVER METRO AND DENVER
       NORTHSIDE FACILITIES	  20

  9    BI-WEEKLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
       SUSPENDED SOLIDS REMOVALS AT THE METROPOLITAN DENVER
       SEWAGE DISPOSAL PLANT 	  22

 10    SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS
       FOR THE SOUTH PLATTE RIVER, 19th Street to 88th Avenue,
       August 30-September 2, 1971	  30

 11    RESULTS OF BACTERIAL ANALYSES-SOUTH PLATTE RIVER
       STREAM SURVEY, November 17-21, 1971	  33

 12    SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS
       FOR THE SOUTH PLATTE RIVER, 19th Street to 88th
       Avenue, December 13-17, 1971	  36-37

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                          LIST OF FIGURES

Figure
Number                      Description                      Page

  1      MUNICIPAL WASTEWATER TREATMENT FACILITIES -
         METROPOLITAN DENVER AREA	  2

  2      FLOW DIAGRAM - NORTH DENVER WASTEWATER TREATMENT
         PLANT	  4

  3      FLOW DIAGRAM - METROPOLITAN DENVER SEWAGE
         TREATMENT PLANT	 14

  4      SOUTH PLATTE RIVER FROM 19TH STREET TO 88TH
         AVENUE	 28

  5      DISSOLVED OXYGEN PROFILE FOR THE SOUTH PLATTE
         RIVER DOWNSTREAM FROM DENVER METRO EFFLUENT	 41
                                iii

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                           INTRODUCTION






     Water quality investigations were conducted in the South Flatte




River Basin during August-December, 1971.  Studies included an evaluation




of the waste treatment practices at the Metropolitan Denver Sewage Disposal




Plant (Metro), the North Denver Wastewater Treatment Plant (Denver North-




side), and other satellite plants [Figure 1].  Subsequently, stream




surveys were conducted on the South Platte River 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 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 Enforcement




         Conference .




     4.  Recommend water quality improvement measures.




     The in-plant survey was conducted at Metro during August 1-9, 1971,




to measure the operation 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




objectives.

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KULGCR
                                                                                    —ccu53i"Z5	
                                                        I. SOUTH  ADAMS SANITATION  OISTIICT
                                                         . KETIOPOLITAN DENVER SEWAfiE DISPOSAL PLANT
                                                         . NORTH  DENVER WASTCWATER  TREATMENT PLANT
                                                         . SOUTH  LAKEWOOD SANITATION DISTRICT
                                                         . EN6LEWOOD SANITATION DISTRICT
                                                          UTTLfTON SANITATION DISTRICT
                                                         . IAKER  SANITATION DISTRICT
                                                         . AIVADA
                                                         . CLEAR  CREEK VALLEY  SANITATION DISTRICT
                                                        10. WHEATRIDEE
                                                        11. SOLDEN • COORS
                                                        12. AURORA  SINITtTIQN  DISTRICT
                                                        U. flUlAitl DIM HtLO
                                                        14. GLENDALE SANITATION DISTRICT
                                                        15  FITZSIMONS HOSPITAL
    Figure 1.  Municipal Wastrualer  Treatment  Facilities Metropolitan Denver Area

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                     WASTE SOURCE EVALUATIONS

NORTH DENVER WASTEWATER TREATMENT PLANT

General

     The North Denver plant is a primary wastewater treatment facility

with a design capacity of 120 million gallons per day (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.

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
                                                             2
evaluated during the South Flatte 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 for this facility is shown in Figure 2.]  The Northside

flow constitutes about 75 percent of the total flow to Metro.
* 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 I!B" certification at Northside.

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INFLUENT
 GRIT
REMOVAL


PREAERATION



 GREASE
FLOTATION
  AND
 REMOVAL
                                                  GREASE TO
                                                  RENDERING
                                                  COMPANY
                     SECONDARY
                     DIGESTION
                      PRIMARY
                      DIGESTION
                                                                        EFFLU NT TO
                                                                          METRO
                                          DIGESTED
                                          SLUDGE TO
                                          METRO

                                           LEGEND
                     STATION              DESCRIPTION
                        E      DENVER NORTHSIDE INFLUENT
                        G      DENVER NORTHSIDE PRIMARY
                                 [SAMPLED AT DENVEI METRO PLANT)
             Figure 2. Flow  Diagram North  Denver Waslewaler  Treatment  Plant.

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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 August




1-9, 1971.  Influent samples were collected upstream from the point of




supernatant return [Figure 2-Station £].  Effluent samples from the




Northside plant were collected where they enter the Metro plant [Figures




2 and 3-Station G].  All wastewater samples were analyzed at the DFI-DC




laboratory for BOD, 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 to ascertain if concentrations were at levels which could affect



biological processes.




     According to plant officials, 130 industries discharge wastewater




to the 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

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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.  A contract has been let to install additional interceptor

capacity by June 1972.

     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 efficiencies

averaged between 22 and 36 percent for BOD, and between 39 and 60 per-

cent for suspended solids liable 2].  Concentrations of heavy metals

were low and would not affect biological treatment processes.  Plant

officials do not know the source of these heavy metals.
* The negative BOD removal is attributed to carryover of solids from
  the primary clarifiar-.

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                                               TABLE 1

                    SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE
                             DENVER NORTHSIDE WASTEWATER TREATMENT PLANT
                                          August 1-9, 1971
Parameter Measured
Flow (MGD)-
Value
Influent Effluent
76.7-92.5
Percent
Reduction (Range)
•v«v
pH (Units)
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
105-310
 30-300
 30-160
0.2-0.7
160-270
UD-'-sa
  6-96
 67-96
 86-90
 73-85
J/ Flow measured at Metro plant.  Northside effluent samples collected at Metro (Station G-Figure 3).
   Flow recording equipment at Denver Northside not considered accurate.

2/ Numbers in parentheses are negative numbers.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

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                                   TABLE 2

              MONTHLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
                      SUSPENDED SOLIDS REMOVALS AT THE       j/
             NORTH DENVER WASTEWATER TREATMENT PLANT FOR 1971-
21
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
_!/ Efficiencies calculated on the basis of data provided by Northside officials.

2f Supernatant was returned upstream of the pre-aeration chambers
   January-April and returned upstream of the bar screens May-June
   [Figure 2].
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

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METROPOLITAN DENVER SEWAGE DISPOSAL PLANT




General




     The Metro plant is a secondary treatment facility that began opera-




tion in May 1966.  It has a primary and secondary design capacity of 27




and 117 mgd, respectively.  The design BOD load is 166,350 Ibs/day.  The




estimated population served by- this plant is 870,000.




     The operating staff includes 9 shift supervisors (5 with Class "A"




certification) and 40 operators (most have Class "C" and "D" certifica-




tions) .  In addition, the laboratory has 12 employees (chemists, micro-



biologists, and technicians) to collect and analyze in-plant and stream




samples.




     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 of less than 1 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 Sanitation District) is diverted to Metro



also. [Figure 1]  The average waste flows treated and the average waste




flows diverted at each  of these plants during the evaluation period are




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 requirement of 80 percent BOD removal.



     District members are charged according to the amount of BOD, suspended




solids, and flow received by the Metre plcnt.  These charsss, accord ir.~ to

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                                                     TABLE  3

                                WASTE TREATMENT FLOWS AND COSTS AT SELECTED PLANTS
Map"
Key
7

9
Name of Plant
Baker Sanitation
District.
Clear Creek
River Mile
305.5/3.0

305.5/7.0
Design
Capacity
mgd
1.0

2.2
2/
Flotf-
Ob served
mgd
0.9

!.«*>
Flow
Diverted
to Denver
mgd
0.8

H ^
None
Cost of . .
Treatment-*-
$/mil gal
63

185
Metro
Cost of jj/
Treating—
$/mil gal
6/
155-

123-192^-
       Sanitation 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

                                                                       o.o/'
102

168
     8/
  173-

123-192^-
 I/  See Figure 1 for location.
 2/  Treated  flow observed during plant evaluation.
 ^/  Receives waste from Sigman Meat  Company.
 k_l  Based  on design flows and annual operation cost  figures provided by  plant  officials.
 _5/  Metro  officials estimate the charge  to  customers for  each million gallons  delivered as  $112/nil gal*  The exact
    charge is based on $53/mil  gal flow, $46/ton BOD, and $40/ton suspended solids.
 £/  Based  on annual cost figures of  $45,000 provided by plant officials  and assuming 0.8->nigd diverted to Metro.
 ]_l  Based  on influent BOD and suspended  solids concentrations of  200-350.
 JJ/  Based  on annual cost figures of  $221,000  provided by  plant officials and assuming  3.5 -mgd  diverted to Denver.
 9/  Plant  officials indicate that flow is diverted to Metro approximately  10 minutes twice  a day  (between 0800-0900
    ar.d 1500-1600) to facilitate cleaning of  headworks.
1Q/  Presently are not connected to Metro facility.   Plant located in near  proximity  to Clear Creek Interceptor.
 Water  Quality  Investigations
 in  the South Platte River  Basin
 1971 - DFI-DC

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                                                                       11






plant officials, are $46.43/ton BOD, $40.23/ton suspended solids, and




$53.13/mil gal.  This combined cost amounts to approximately $112/mil gal




delivered.  The cost per family is about $15/year.  Officials of the four




treatment plants contend they can treat wastewaters at a cost less than




at Metro.  Some of these plants attempt to treat flow in excess of design




capacity to avoid sending the excess wastewater to Metro.  Based on in-




fluent BOD and suspended solids concentrations, treatment costs for Wheatridge




and Clear Creek Sanitation District are similar to the Metro treatment




cost rate.




     The estimated operation and maintenance costs at the Arvada and the




Baker plants were provided for 1971 [Table 3].  It appears wastewater can



be treated at these plants at much less cost than at Metro.  The cost of




expanding these plants to take all incoming flows would increase the treat-




ment 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 ex-




pectancy, the annual cost of construction is estimated at $47,000.  If




the community receives a 30 percent Federal grant, the annual cost would




be about $33,000.  At design flow, the cost to treat 1 mgd varies from     ^




$90 without a grant to $130 with a grant.  When labor, chemical, and other   '




costs are added, the cost per million gallons treated is comparable to that




of the Metro plant cost.




     In addition to these four plants, nine plants operate independently




of the Metro system [Table 4 and Figure 1].  The South Lakewood Sanitation




District, for example, operates as a contact stabilization plant located




at 700 Depew Street, Lakc'.;cod, Colorado.   Effluent frons this plant is

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                                                      TABLE 4

                       OTHER WASTEWATER TREATMENT FACILITIES IN THE METROPOLITAN DENVER AREA
Map-
Key
   I/
Name
 Flow Observed
    During
Evaluation (mgd)
Receiving Stream   River Mile
     Remarks
12   Aurora Sanitation District
                                       2/
                     Sand Creek
                   306.8/5.5/1.15  Discharges  sludge to
                                   Metro.
13   Buckley Air Field

 5   Englewood Sanitation District



15   Fitzsimons General Hospital
14   Glendale Sanitation District

11   Golden - Coors
 6   Littleton Sanitation District

 1   Souch Adams Sanitation District

 4   South Lakewood Sanitation District
_!/ Sec Figure 1 for location.
21 Not avaluated.
Water Quality Investigations
in the South Platte River Basin
1971 - JVI-DC
                                      1.25
                                      3.0 Coors
                                      2.0 Golden
                                      2.3

                                      1.85

                                      1.2
                     Sand Creek

                     South Platte
                       River
                                                      Toll Gate Creek
                                                      Tributary to
                                                      Sand Creek
                     Cherry Creek

                     Clear Creek
                   306.8/11.9

                   319.7
                   305.5/15.5
                     South Platte River 323.5

                     South Platte River 301.2

                     South Platte River 314.1/2.1W
Additional treat-
ment facilities
under construction.

Treated wastewater
is used for irri-
gation on the hospital
grounds,  excess is dis-
charged to Sand Creek.
Interceptor has been
constructed to deliver
Coors Porcelain Plant
and Golden wastes to
Metro.

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                                                                       13
discharged to the South Platte River.  The facility is designed for




1.2 mgd, but presently receives 1.8 mgd.  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 5], none were



meeting the State requirement of 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 grant




should be provided to these plants for further construction unless it




can be shown that such an expansion will provide for the continued pro-




tection and enhancement of the South Platte River.




Wastewater Treatment Facilities




     The principal components for this treatment facility are as follows




[the flow diagram for the Metro plant is presented in Figure 3]:




     1.  Preliminary treatment - bar screens, grit chambers, grease




         flotation and removal.




     2.  Primary clarifiers (4) - each 106 feet in diameter with an




         8-foot, 9-inch side water depth.   Each clarifier has a




         skimmer to remove floating solids.




     3.  Activated sludge units - 12 aeration basins each consisting




         of 3 tanks 210 feet long, 30 feet wide, and 15 feet deep.

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CLEAR CREEK
INTERCEPTOR
EFFLUENT FROM
NORTHSIDE PLANT
PACKAGING '
B


CORPORATION I
CrCIIICMT 1 _ I
BAR
SCREENS


GRIT
REMOVAL
                                                           /^~*\     G
                                                           / PRIMARY \
SAND CREEK
INTERCEPTOR
SOOTH 1"
PL1TTE ,
RIVER -» •'
i
CHLORINE
CONTACT
CHAMBER
POMP
TO BORLINGTON
DITCH











STATION
A
B
C
D
F
G
H
1
J

H

LEGEND
DESCRIPTION
CLEAR CREEK RAW INFLUENT
PACKAGING CORPORATION EFFLUENT
SAND CREEK RAW INFLUENT
COMBINED RAW INFLUENT TO METRO
METRO PRIMARY EFFLUENT
DENVER NORTHSIDE PRIMARY EFFLUENT
INFLUENT TO SECONDARY UNITS
INFLUENT TO C12 CONTACT CHAMBER
METRO FINAL EFFLUENT











    Figure  3.-Flow Diagram Metropolitan Denver Sewage  Treatment  Plant

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                                                                       15






     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,




functionsas a separate secondary plant.  In effect, there are four sec-




ondary treatment facilities at Metro which are operated separately.  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 combined effluent channel




before and after chlorination.




Discussion of In-Plant Survey and Findings




     The Metro plant was evaluated August 1-9, 1971.  All samples were




analyzed at the DFI-DC laboratory for BOD, TOG, COD, and solids (total,




suspended, volatile suspended, and settleable)-.  Samples from 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




from the final effluent [Table 7].  Field measurements of the Metro




effluent showed:  pH, 7.0-7.8; temperature, 19.0°-23.0°C; and conduc-




tivity, 875-1,200 ^mhos/cm.




     Daily, during the survey, large amounts of suspended solids were




observed passing over cue rinai ciarifier weirs during periods of peak
* Tables B-l, B-2, and B-3 are located in Appendix B.

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                                                                         TABLE 5

                                           SUMMARY 0? ORGANIC AND NUTRIENT  DATA FOR NORTHSIDE AND METRO PLANTS'
                                                                     August 1-9, 1971
Station Description
A Clear Creek Raw Influent
B Packaging Corporation
Affluent
C Sand Creek Raw Influent
E 1'enver Northside Influent
G ):enver Northslde Prlnary
Uf fluent
I Influent to C^ Contact
Chamber
J Final Effluent from
Metro
Flow
med
IS. 9
0.4
10.3
86.7
86.7
116.3
116.3
BOD
rng/1
187
398
211
295
175
41
31
Susp.
Solids
me/1
334
344
349
680
120
98
123
Vol.
Susp.
Solids
nut/1
283
287
305
620
80
100
117
I/
Settl. Total (KJ)
Solids COD NH-i N NOj+NOj P
mg/1 mK/1 rag/1 ng/1 mR/1 mg/1
5.3 475 18 27
1030 1.4 5.8
6.2 695 19 30
5.9 1250 17 25
1.0 230
0.9 213
1.7 160 15 20
0.04 10.5
2.2 0.9
0.11 13.0
0.08 9.4
-
-
0.73 7.1
I/  Values listed are averages.
2j  KJeldahl nitrogen.
Water Quality Investigations
In the South Platte River Basin
1971 - DFI-DC

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                                                 TABLE 6

                       SUMMARY OF HEAVY METALS DATA FOR METRO AND NORTHSIDE 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
Hg/1
Average
< 0.30

< 0.57

0.55

0.58

0.53

-

0.50

< = Less Than
WaLer Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

-------
                                                                18
                              TABLE 7

             BACTERIOLOGICAL AND CHLORINE RESIDUAL DATA
             METROPOLITAN DENVER SEWAGE DISPOSAL PLANT
Date/Time
August 2




August 3





August 4






August 5


August 6






Sampled
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
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

-------
                                                                       19




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.


     Removal efficiencies observed at the Northside and Metro facilities


[Table 8] show 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 efficien-


cies ranged from 42 to 86 and 39 to 94 percent before and after chlori-


nation, respectively.  The BOD removal efficiency was below State stan-


dards 33 percent of the time.  If the Northside plant is considered as


part of the overall Metro system, the range of BOD efficiencies increases


to 66 to 91 percent before chlorination and to 63 to 96 percent after


chlorination.  The daily BOD removal efficiency was below State standards


20 percent of the time.  Metro was designed for a BOD load of 166,350


Ibs/day.  During the survey period, the influent BOD varied from 92,000


to 279,000 Ibs/day with an average of 182,000 Ibs/day.  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 flows periods.  The


combined chlorine residual in the effluent varied from 0.01-G.64 mg/1,


significantly lower than the level (1 mg/1 after 15 minutes detention)

                                               3
specified by the Colorado Department of Health.   Fecal coliform concen-


trations in the effluent ranged from 230-430,000/100 ml, indicating




* The negative BOD removal was due to sludge blanket losses from the
  secondary clarifiers.

-------
                                                 TABLE 8
                                                                                      I/
                 REMOVAL EFFICIENCIES FOR DENVER METRO AND DENVER NORTHSIDE FACILITIES"
Degree of
Treatment for
Norths ide
Metro before Clj
Mei.ro after Cl-
Meirro plus Northside
BOD
Range
%
UD-'-SS
42-86
39-94
66-91
Susp. Solids
Range
%
6-95
UD-'-SS
2/
(16)~ -78
27-97
Vol. Susp. Solids
Range
%
66-95
(36)- -BO
(36)~ -66
32-96
Settleable Solids
Range
%
11-81
89-91
(50)~ -91
92-98
  before Cl_

Metro plus Northside
  .ifter C10
                          63-96
39-95
31-95
54-96
_!/ Overall efficiencies were calculated by summing the load into and out of the plant.

2J Numbers in parentheses are negative numbers.  These negative values are due to sludge blanket
   losses from clarifiers.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

-------
                                                                       21






inadequate disinfection [Table 7].  According to plant officials, about




1 ton/day of chlorine is used (2 mg/1 dosage rate at design flow).   The




Colorado State Criteria recommends a minimum dosage rate of 8 mg/1 for




activated sludge plant effluents.




     Concentrations of heavy metals discharged in the final effluent




were insignificant.  The mercury concentrations discharged, for example,




ranged from 0.2 to 1.0 yg/1 (0.18 to 0.87 Ibs/day), with an average of




0.5 yg/1 (0.48 Ibs/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 Ibs/day, respectively.




     Bi-weekly operational data for the period May 30 - December 31, 1971




[Table 9] were obtained from Metro officials.  The data for the period




July 25, 1971, through August 7, 1971, show  average BOD and suspended




solids removals of about 84 and 1 percent, respectively.  Plant officials




indicated that during this 2-week period, the sludge furnaces were shut




down  and the digesters were loaded to capacity.  Sludge that had built




up in the final clarifiers was scoured from these clarifiers during peak-




flow periods.



     During twelve of the sixteen bi-weekly periods [Table 9], the plant




was operating below the minimum 80 percent BOD removal requirement speci-




fied in the Colorado State Water Quality Standards.  These standards also




require chat adequate disiniieccion be provided.

-------
                                                                  22
                               TABLE 9

BI-WEEKLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND SUSPENDED SOLIDS
      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
BOD 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
Percent Suspended
Solids Removal
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
 j./ Data provided by Metro officials.
 Water Quality Investigations
 in the South Platte River Basin
 1971 - DFI-DC

-------
                                                                       23






     Operation of Che 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




officials indicated 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.




     An in-plant study was conducted by EPA investigators from Region VIII




and DFI-Cincinnati Center, during the period October 1969-February 1970,




in order to evaluate plant operations and provide technical assistance.




Weirs on the final clarifier are inadequately placed [Appendix C], allowing




"scouring" velocities to be obtained.  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, thus it is




difficult to obtain a balance.  Surface skimmers were also recommended.

-------
                                                                       24






     During the October-February study, the 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 accomplished 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.

-------
                                                                     25
                          STREAM SURVEYS


General


     In August 1964, December 1964 through March 1965, September and


October 1965 surveys of the South Platte River were conducted by the


South Flatte River Basin Project.  Stream flows at the 19th Street


station averaged 140, 50,-380, and 305 cfs, respectively, during these


periods.  The average dissolved oxygen values during these surveys


ranged from 6 to greater than 10 mg/1 at 19th Street; from 1.5 to


3 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 1 million total and fecal coliform organisms/100 ml at York


Street and 88th Avenue.  The average BOD concentrations ranged from


10-20 mg/1 at 19th Street; from 50-170 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

                                                 5
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.

-------
                                                                      26
     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
                                               6
Federal Water Pollution Control Act, as amended , classified the South

Platte River and established water quality standards [Appendix D] for

the following reaches:

         South Platte River from Exposition Avenue (RM 321.9)
         to York Street (RM 313.4) -

              B2 - Warm Water Fishery
              C  - Industrial Water Supply
              DI - 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) -

              C  - Industrial Water Supply
              DI - Irrigation Water Supply

-------
                                                                      27






     The discharge from the Metro plant enters the South Flatte River




downstream from the Burlington Ditch.  Facilities are available to




pump the effluent to Burlington Ditch if, at the point of diversion,




there is 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 Northside (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 pre-




sently a controversy over the ownership of the Metro effluent.  The




Fanners Reservoir and Irrigation Company, et al, have filed suit against



the Metropolitan Sewage Disposal District No. 1, contending 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.




     During the period August 30 to September 2, 1971, a water quality



survey was conducted by DFI-DC on the South Platte River from Waterton



to Platteville, Colorado.  A bacteriological survey was conducted during




November 17-21, 1971, to determine quality of the South Platte River




upstream of and downstream from the Metro discharge (19th Street-RM 317.3,




Colorado 224-RM 310.9) and to evaluate the Burlington Ditch.  Sampling




was conducted at selected stations to determine whether or not Salmonella




were present.  Another stream survey was conducted in the same reach




during December 13-17, 1971, to determine chemical quality [Figure 4].

-------
                                                                -N-
                                                l E 6 E N D
                                      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 AYE
                                      10.  DENVER METRO  EFFLUENT
                                                             NOT TO SCALE
Figure 4.  South Plalle  Kiver from  I9lh  Si  to  88th Ave

-------
                                                                      29
     The total Metro effluent was discharged to the South Platte River




during the in-plant survey and during the three stream surveys and




comprised about 30 to 35 percent, 65 to 95 percent, and 95 percent




of the flow in the South Platte River, respectively, at the point of




discharge.  Flow conditions in the South Platte River were above




normal from August 30 to September 2.  Survey findings are discussed




below.




Findings of August-September Survey



     The August survey showed 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 sludgewortns 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).  Water samples collected at York Street were severely




contaminated by fecal matter.  The number of fecal coliform bacteria




was greater than 13,000/100 ml (log mean value); concentrations of




total coliform exceeded 100,000/100 ml.  The levels of organic matter




and suspended solids also were high in this reach.  The dissolved oxygen




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 Ibs/day), and 85 mg/1 sus-




pended solids (88,000 Ibs/day) [Table 10].  Total coliform bacteria




levels during the in-plant survey ranged from 6,600 to 14,000,000 per




100 ml, 230 to 430,000 per 100 ml of which were fecal coliforcs [Table 7]

-------
                                                      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
SPR at 19th
St. (RM 317.3)
SPR at York
St. (RM 313.2)
Denver Macro
Effluent-
(RM 312.2)
Sand Creek
at Mouth
(RM 312.1/0.1)
Clear Creek
at York Street
(RM 311.1/0.3)
SPR at 88th
Date
8/30-9/2/71

8/30-9/2/71

8/30-9/2/71

8/30/9/2/71


8/30-9/2/71


8/30-9/2/71
Flow
CFS
Avg.
413

210^'

192

100T


21


700-
Temp.
°C
Range
17-24

17-22



17-21


16-21


18-22
pH
S.U.
Range
7

7



7


7


7
.2-8.3

.4-8.1



.5-8.0


.3-8.4


.3-7.6
Cond.
umhos/cm
Range
375-600

360-580



420-600


470-600


600-800
DO
mg/1

Range Avg .
6.0-7.6 7

5.7-7.4 6



6.4-7.3 6


4.8-8.7 6


3.3-5.7 4
.0

.9



.8


.7


.5
BOD5
mg/1
Average
6

7

56

8


4


29
Total Solids
mg/1
Average
405

543



570


383


690
Susp. Solids
mg/1
Average
< 80

260

85

203


< 30


233
Avenue.
(RM 308.8)
I/ Estimated flow.
2J Flow taken at gage located downstream of York Street near Sand Creek.
J}/ Da fa provided by Denver Metro personnel.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

-------
                                                                 31






     During the August survey, the flow in Sand Creek (KM 312.1/0.1)




was comprised primarily of overflow from the Burlington Ditch.   The




creek swelled of sewage and was gray in color because Burlington Ditch




carried by-passed raw municipal sewage.  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 inverte-




brates, 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 river mile 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 benthos community was reduced to seven kinds and consisted mostly



of pollution-tolerant sludgeworms and snails.




     Clear Creek intersects the South Flatte River at river mile 311.1.




Pollutants carried by this creek contributed to the degradation of




quality of the South Platte River waters.




     The pollutants discharged to the South Platte River from the sewage




treatment facilities and from polluted Sand Creek and Clear Creek,



settled to the river bottom forming sludge beds that were evident




from Clear Creek downstream - approximately 23 river miles.  Throughout




this river reach, water quality was degraded severely.  The densities

-------
                                                                 32


of coliform bacteria were equivalent to those of many sewers; 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 sludgewonns.

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 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 no bacterialstandards for the South Flatte 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 the Burlington Ditch at York Street to determine

if enteric pathogenic bacteria were present.  The results at all three

stations were positive.  Particular serotypes isolated were Salmonella

anatum (Burlington Ditch) and Salmonella senftenberg (South Platte River
* The Colorado Water Pollution Control Commission adopted bacterial
  water quality standards for the South FlaLte River, downstream frcni
  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 DFI-DC conducted a survey in November,
  to determine if the bacterial standards were being violated.
  However, 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 BACTERIAL ANALYSES-SOUTH PLATTE RIVER STREAM SURVEY
                                               November 17-21, 1971
Map~
Key
   I/
                       Total Coliform
                        Count/100 ml
Station
                            Fecal Coliform          % 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
      at 19th St. bridge

 2    South Platte River    3,000-440,000     15,000
      at Denver Northside
      plant
                        2/
 3    South Platte River"   5,000-270,000     21,000
      at York St.
                      21
 4    Burlington Ditch-     3,200-210,000     16,000
      at York St.

 6    South Platte River    7,000-6,200,000  340,000
      at 1-270 Bridge

 7    South Platte River    7,100-5,400,000  200,000
      at Colorado 224
 8    Clear Creek at York     600-190,000
      St.
10    Denver Metro
      effluent-^'
                  9,200-14,000,000
_!/ See Figure 4 for location.
2_l Isolated salmonella at this station.
^/ Data from in-plant survey August 1-9, 1971.

Water Quality Investigations
in the South Platte River Basin
1971 - OFI-DC
                                             170-4,000
                                             310-2,600
                                        490
                                        620
                                              61-10,000      790
                                             410-6,500
                                        850
                                              70-70,000   >7,000
                                             160->60,000  >3,300
                                     7,100   <10-5,300      <190
                        230-430,000
                                      10


                                      10



                                      20


                                      20


                                      70


                                      60


                                      20
160-27,000     1,600
330-39,000     2,100
                                                              360-87,000     3,800
570-77,000     3,500
                                                              150-160,000   14,000
                                                              980-98,000     8,200
                                                              220-190,000    1,800

-------
                                                                 34






stations).  The presence of these pathogenic bacteria, in attendance




with fecal conforms, proves 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 densities exceeded 7,000 downstream from Metro




at the 1-270 bridge  (KM 312.0).  Concentrations exceeding 3,300 (log




mean) were observed at Colorado 224 (EM 310.9).




     Clear Creek at York Street does not have a bacterial standard.




The fecal coliform concentration (log mean) was low (<190/100 ml);




however, more than 20 percent of the samples exceeded 2,000/100 ml.




     Survey results showed some improvement in the bacterial quality



of the South Platte River downstream from 19th Street since the 1964-65




studies.  Total and fecal coliform concentrations were markedly lower




in November than those observed in 1964-65.  Downstream from York Street,




the log mean total and fecal coliform concentrations 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.




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 dissolved

-------
                                                                 35






oxygen [Table 12].  The average BOD concentration at the background




station (19th Street) was 18 mg/1.  The level decreased to 14 mg/1




at Denver Northside.  At York Street the average concentration was




9 mg/1, about 50 percent less than the BOD measured in the Burlington




Ditch at York Street.  A factor that could account for this difference




is that the flow of the South Platte River at York Street was primarily



made up of seepage because the entire river was being diverted to the




Burlington Ditch.  Consequently, it 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 500 percent higher than the average observed at York



Street.  At this station, the river was mostly Metro effluent, which




contained an average BOD concentration of 44 mg/1.




     The BOD level at the next downstream station (Colorado 224) re-




mained at 40 mg/1.  This station is downstream from the confluence of




Clear Creek, which had an average BOD concentration 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




69 to 94 percent of saturation upstream of the Metro discharge and 55




to 85 percent downstream at 1-270 and Colorado 224.




     In summary, the survey results indicated an improvement in the




South Platte River quality downstream from Denver Northside compared




to the 1964-65 studies.  Obvious improvements include better BOD and




DO values as a result of the elimination of the Northside primary




effluent.  However, the BOD load discharged by the Metre plant still

-------
                                                      TABLE 12

                   SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE  SOUTH PLATTE  RIVER
                                             19th Street to ,88th Avenue
                                                December 13-17, 1971
Station
SPR at 39th
St. (RM 317.3)

SPR at Denver
Date
12/13-17/71


12/13-17/71
Flow
CFS
Avg.
107

I/
135~
Temp.
°C
Range
3-6


3-6
PH
S.U.
Range
7.6-7.9


7.4-7.9
Cond . DO
Umhos/cm mg/1
Range Range Avg.
775-875 8.5-10.0 9.4


825-1000 7.8-9.8 8.9
BODc
mg/1
Average
18


14
Total Solids
mg/1
Average
675


750
Susp. Solids
mg/1
Average
40


30




Northslde plant
(RM 314.5)

SPR at York
St. (RM 313.2)

Burlington
Ditch at
York St.
Denver Metro
effluent
(RM 312.2)

SPR at 1-270
bridge
(RM 312.0)


12/13-17/71


12/13-17/71


12/13-17/71



12/13-17/71



l/
2~

2/
142^


153


I/
160-




3-5


3-5






15-15




7.7-7.8


7.5-7.8






7.1-7.4




750-1000 7.8-9.4 8.7


850-1000 7.7-9.6 8.8






1000-1100 6.0-6.4 6.1




9


14


44



44




755


725






890




30


40






95

















I/ Estinated flow.
2J Flow taken at gage located downstream of York Street near Sand Creek.

Water Quality Investigations
in the ::outh Platte River Basin
1971 - IJKI-DC
                                                                                                                  ON

-------
                                                TABLE 12  (Continued)

                   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
S.U.
Range
Cond.
umhos/cm
Range
DO
mg/1
Range
Avg.
BOD5
mg/I
Average
Total Solids
mg/1
Average
Susp. Solids
mg/1
Average
Clear Creek   12/13-17/71
at York St.
(RM 311.]/0.3).

SPR at Colo.  12/13-17/71
224 (70tl. Ave.)
(RM 310.9)
    at 88th   12/13-17/71
Ave. (RM 308.8)
I/ Estimated flow.
54
                            220~
                               I/
       0.3-2
                                            7.7-8.0   825-1000    9.2-10.5  9.8
         8-9    7.3-7.6   950-1050   7.4-8.0   7.8
200~     3-12   7.4-7.7   775-1100   6.7-7.3   7.0
15
                                                        40
            820
45
70
Water Quality Investigations
in the South Platte River Basin
1971 - DKl-DC
                                                                                                                   CO

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                                                                 38






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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                                                                 39






                WATER QUALITY IMPROVEMENT MEASURES






     Water quality conditions could be improved by diverting the Metro




effluent  to the Burlington Ditch and allowing normally diverted South




Flatte 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 35,000 acre feet 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, 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.



     A study done on Barr Lake in 1964-65  concluded  that  the  lake was




a large wastewater stabilization lagoon.  The BOD, Total N, and Total




PO^ concentrations in the water entering Barr Lake ranged from 55-150;




12-37; and 11-21  mg/1, respectively.  This study recommended that the




'Metro plant provide 90 percent BOD removal, which would be  equivalent




to about  20 mg/1.




     During the irrigation season water demands would require flows




in excess of the  Metro effluent  to be diverted from the South Platte




River.  Direct use of the MeLro effluent un crops should have no detri-




mental effect, if adequate disinfection is provided.

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                                                                 40
     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 seven-day, ten-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 mg/1 DO.  The BOD loading to the river is 29,100 Ibs/day




with a residual stream BOD of an additional 810 Ibs/day (includes BOD




loading from Sand Creek and Clear Creek).   Calculations were made at




25°C.  The minimum DO which would occur is approximately 0.5 mg/1 which




is below the approved water quality standard of 3 mg/1 [Figure 5].



     The same procedures were utilized 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].




     Based on the above calculations, the effluent 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 treatment



facility to provide at least 95 percent BOD reduction.




     In summary, the Metro plant must provide:  (1) a minimum BOD




removal of 90 percent when all effluent is pumped to Burlington Ditch,




(2) a minimum BOD removal of 95 percent of all the effluent is dis-




charged to the South Platte River assuming a low flow in the river of




20 cfs at 19th Street, and (3) minimum BOD removals between 90-95




percent when a portion of the effluent is being discharged to the




river.

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  7-
  6-
» 5.
C9
  4-
CO
CO
  2-
  1-
                           Saturation at  25°c
                                                                   Proposed Dissolved Oxygen Standard
                                                               Present Dissolved  Oxygen Standard
                                                                         LEGEND

                                                                Profile for present Metro effluent
                                                                (BOD Concentration of 30mg/l)

                                                                Profile of Metro  effluent for
                                                                .BOD  Concentration of 10mg/l
             •        i    •    I       I        i        i        i        i        i        i
    0      0.2      0.4      0-6     0.8      1.0      1.2      1.4      1.6      1.8      2.0

                                               TIME-days


 FIGUl.:  -   DISSOLVED  OXYGEN PROFILE FOR SOUTH  PLATTE  RIVER  DOWNSTREAM  OF DENVER METRO

            EFFLUENT.

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                                                                 42
     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 (B2) classification




is feasible if adequate flow is maintained in the river (25 cfs).

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                                                            43
                      CONCLUSIONS






1.  The Metro plant is overloaded hydraulically and organically.




    The plant is designed for 117 mgd.   Peak flows of 180 mil gal




    were recorded during the survey.   Average BOD loading of 182,000




    Ibs/day was 110 percent of the design loading.




2.  Adequate treatment was not being  provided by the Metro plant




    for BOD and suspended solids removal.  Moreover, adequate




    disinfection was not provided, as shown by the low chlorine




    residuals and the high bacteria concentrations in the effluent.




    The chlorine dosage rates were about 2 mg/1, whereas the




    criteria of the Colorado Health Department recommend  8 mg/1




    minimum for an activated sludge effluent.




3.  Scouring velocities occurred in the final clarifiers at the




    Metro plant during peak flows due to the hydraulic overload




    and to the inadequate placement of the weirs.  The lack of




    skimmers on the final clarifiers  resulted in floating solids




    being discharged into the receiving waters.




4.  The Metro and Northside plants are under different management




    making effective operation difficult.  The Northside plant




    effluent constitutes the major input to Metro and operational




    difficulties at Northside affect  Metro significantly.




5.  Small treatment plants in the metropolitan area treat flows




    that are about 12 percent of the  present flow treated at Metro.




    Of nine plants evaluated, seven were not meeting the State




    requirement of 80 percent BOD removal.  These plants could be

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                                                             44
     phased out and the entire flow diverted to Metro.  The cost




     of expansion at these plants is about 50 percent greater per




     mgd design capacity than expansion of the Metro plant.




 6.  Sludge handling capacity at Metro continues to be a problem;




     its inadequacy affects plant performance in producing




     a satisfactory effluent.



 7.  Mercury discharges vary from 0.2 to 0.9 Ibs/day.  The majority




     of the mercury comes from the Denver Northside wastewater




     treatment facility but plant officials do not know its source(s).




 8.  Minor changes in NH_ and the sum  of NO- and NO- occur  during




     treatment.  Total phosphorus is reduced approximately 28 percent.




     The total nitrogen and phosphate loads discharged to the South




     Platte River during the survey averaged 34,700 and 6,900 Ibs/day,




     respectively.




 9.  Metro personnel were observed washing an insecticide tank.




     The wash water entered the South Platte River through a storm




     drain.  This practice has been discontinued.




10.  Raw sewage discharges were observed at 47th Avenue and Franklin




     Street.




11.  Since the studies conducted by the South Platte River Basin




     Project in 1964-65, there has been some improvement of water



     quality conditions in the South Platte River.   Lowering of BOD




     and coliform concentrations and the increase in DO levels is




    .due mainly to the elimination of the Denver Northside primary




     effluent.

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                                                             45






12.  Violation of the bacterial standard occurred in the South




     Platte River at York Street.   Salmonella were isolated in




     the South Flatte River and Burlington Ditch, indicating




     fecal contamination in the River.




13.  The South Flatte River quality could be enhanced by the ex-




     pansion of the Metro plant and improvement in plant operation.



     Pumping Metro effluent to Burlington Ditch would supplement




     these improvement measures by allowing normally diverted river




     water to continue downstream from York Street.

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                                                                 46






                          RECOMMENDATIONS






It is recommended that:




     1.   The planned expansion at Metro include a capacity for waste-




         waters now being treated by small plants.  A time schedule




         be developed to phase out these small plants when the expansion




         at Metro is completed.




     2.   The expansion provide for an effluent which contains no more




         than 10 mg/1 BOD.




     3.   The effluent be pumped to the Burlington Ditch to supplement




         irrigation and storage demands.




     4.   The final clarifiers be equipped with skimming devices and



         additional weirs be placed on these clarifiers to diminish




         the generation of scouring velocities.



     5.   The chlorine feed rate be increased to provide adequate dis-




         infection on a continuous basis and to maintain a combined




         chlorine residual of 1 mg/1 after 15 minutes detention in




         accordance with Colorado Health Department criteria.




     6.   Adequate sludge treatment and disposal be -provided in con-




         junction with the plant expansion.




     7.   The Northside and Metro plants be placed under the same manage-




         ment so that the combined operations can be effectively con-




         trolled; and the offer of a construction grant be predicated




         on the development of a single agency responsible for operations




         in both plants.

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                                                             47
 8.   Immediate steps be taken by the City and County of Denver




     to eliminate all raw sewage discharges to the South Flatte




     River in the metropolitan area.




 9.   Flow augmentation be practiced to insure a minimum of 25 cfs




     of water in the South Platte River from just upstream of




     Littleton to the Colorado-Nebraska state line.




10.   Consideration be given to upgrading the water quality standards




     of the South Flatte River downstream from York Street to in-




     clude potable water supply and warm water fishery classifications;




     thus, encouraging water quality enhancement.

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                                                                 48
                            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]  Criteria Used in the Review of Wastewater Treatment Facilities,
     Colorado Department  of Health, Denver, Colorado, 1969.

[4]  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.

[5]  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.

[6]  Federal Water Pollution Control Act,  Public Law 84-660,  U.  S.
     Department of the Interior, Federal Water Pollution Control
     Adminis trat ion.

[7]  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.

-------
     APPENDIX A




SAMPLING PROCEDURES

-------
                                                                 A-l




Appendix A




                        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 DFI-DC laboratory and analyzed



for BOD, total and suspended solids, volatile suspended solids, settle-




able solids, total organic carbon (TOG), chemical oxygen demand (COD),




nitrogen series, total phosphorus, and selected heavy metals.




     Samples of the final effluent from the Denver Metro facility




were analyzed for total and fecal coliform.  These bacterial samples




were iced and delivered to the DFI-DC mobile bacterial laboratory for




analyses.  At the time of collection, field measurements and chlorine




residual was measured.

-------
                APPENDIX B

                 DATA ON
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
                   AND
 NORTH DENVER WASTEWATER TREATMENT PLANT

-------
APPENDIX B
TABLE B-l
SUMMARY OF ORGANIC DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
I/
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 EfEluent from
Flow BOD
MGD mg/1
17.3-21.2 140-250
0.4-0.6 280-480
9.5-11.0 140-290
27.2-32.6 190-250
76.7-92.5 180-430
27.2-32.6 120-160
Total Susp.
Solids Solids
mg/1 mg/1
930-1300 210-480
1120-2130 220-480
890-1200 240-440
1120-1640 300-620
920-1440 320-1240
980-1060 60-180
Vol.
Susp. Settl.
Solids Solids
mg/1 mg/1
180-440 3.5-7.0
150-400 19-100
(est)
180-420 5-8
160-540 5-9
240-1200 3.5-10
60-140 Trace-1
COD TOC
mg/1 mg/1
320-700 64-150
890-1200 80-320
350-1560 66-190
480-870 66-360
590-1800 84-340
250-290 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
  H
Influent to Secondary
Units
103.9-124.0   75-210   780-890    50-140    40-130   0.1-0.5  200-270   33-80
          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
\J For location see Figures 2 and 3.

Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC

-------
                                                    APPENDIX B
                                                    TABLE B-2

          SUMMARY OF HEAVY METAL DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
                                                 August 1-9, 1971
Station-
    Description
 Cadmium
  me/1
Chromium     Copper
  mg/1        me/1
Lead
mg/1
Zinc
mg/1
Mercury
 Jig/1
  A

  B


  C

  E

  J
Clear Creek Raw Influent

Packaging Corporation
Effluent

Sand Creek Raw Influent

Denver Northside Influent

Final Effluent from
Metro
<0.02-0.05    <0.02-0.07   0.05-0.10    0.05-0.20   0.17-0.21   <0.2-0.6


<0.02-<0.02    0.03-0.37   0.07-0.26    0.29-2.3    0.26-6.1    <0.02-1.0

<0.02-<0.02    0.09-0.A3   0.13-0.58    0.06-0.14   0.13-0.43    0.02-1.2

<0.02-0.04     0.03-0.26   0.16-0.23    0.09-0.22   0.69-1.9     0.2-1.-3


<0.02-<0.02    0.03-0.11   0.04-0.24    0.03-0.10   0.06-0.49    0.2-1
_!/ For location see Figures 2 and 3.
  Water Quality Investigations
  in the South Platte River Basin
  1971 - DFI-DC
                                                                                                                7
                                                                                                                ro

-------
APPENDIX B
TABLE B-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
A. 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
_!/ For location see Figures 2 and 3.
Water Quality Investigations
in the South Platte  River Basin
1971 - DFI-DC

-------
            APPENDIX C
            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

-------
The Superintendent of Documents
classification number is:

      EP 2.2:  D43

-------
                                     TABLE OF CONTENTS
                                                                                  PAGE NO.
I.      Introduction	      *
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

-------
                                      LIST OF TABLES
TABLE NO.                                  TITLE                                  PAGE NO.

    1        A Summary of Various Parameters Associated with the Selected
             "Steady State" Periods	     17
    2        Calculated Values of ec and qgoDs  -  Selected Periods of
             Operation  -  Areas #2 and #3	     19
    3        Average Settled Sludge Volumes for "Steady State" Periods 	     22
    4        Zone Settling Rates (Vs) and Equivalent Surface Overflow
             Rates (Or) for "Steady State" Periods 	     25
    5        Waste Sludge Flow Required to Remove an Equivalent Amount of
             Solids with Varying Underflow Concentrations	     28
                                             11

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                                      LIST OF FIGURES
FIGURE NO.                                  TITLE                                  PAGE NO.
1
2
3
4
5
6

Influent BODs Loadings and Seven Day Moving Average, Effluent
Weekly Average Percentage Reduction of BODs and TSS
Waste Sludge Concentration in mg/1 vs Time 	
Net Growth Rate (l/8c) vs Substrate Removal Rate (o,R0nc) 	
Determination of Zone Settling Rate (Vs) - Height of Sludge
4
8
10
14
20

             Interface vs Time  -  Area #3 Period:  2/9 - 2/16/70 Average
             9:00 A.H	     24
                                            iii

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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
1n 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 speci-al 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 Joslin 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 recoirmendations 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 Commerce 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 grec.se 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 (6005) 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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       r sn
ARE/H,
                                   FEDERAL ASSISTANCE PROJECT
                           METROPOLITAN DENVER SEWAGE TREATMENT PLANT
                                  OCTOBER 1969  -  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 SI and 82) 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 aata also

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         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 skimned 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
  id  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
  low meters and to  collect grab  and composite samples so that the plant performance could be
monitored.

u.   Performance Evaluation-Procedures and Results
     The Metro plant laboratory conducted various analyses on the collected samples to provide addi-
  ional data for the project.   Influent and effluent samples for the secondary treatment portion of
*-he  plant were composited and determinations were made for BOD5 and TSS.  In addition to overall
  lant 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 BOD5 applied to the
  econdary treatment (activated sludge) portion of the Metro Denver plant, as well as  the seven  day
moving average of the overall plant effluent concentrations of BODg and TSS.
    The seven day moving average BOD5 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
 •elationship 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
                                                  6,

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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 BODj 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 BODr 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 converUd 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
BODg 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 82 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  BOD^ per day.   The
dotted line represents the design average day loading (166,350 Ibs. BODg 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 BOD5 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 BODjj 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 Jar.uary end e:-pec:;ny the psz'f. Icai cr- -January 1C., 1970.
    Another trend that is not as apparent is the relationship between loading  and effluent quality.

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   C9
00 £1
  " .a
  »«
  «- 3
 320-
 280
 240
 200<
 1£0
 120-
 80-
 90'
• 80<
i 70'
 60'
 SO'
 40'
 30-
 20'
 10 ,J
                                           FIGURE 2
                                     FEDERAL ASSISTANCE PROJECT
                               METROPOLITAN DENVER SEWER TREATMENT PLANT
                                    OCTOBER-1969 to FEBRUARY-1970
                                     INFLUENT BODS LOADINGS AND
                                  7 DAY MOVING AVERAGE, EFFLUENT BODS
                                       ANDTSS CONCENTRATIONS
                                              VS
                                             TIME
            /    ^'\  7 DAY MOVING £AVG.TSS
           /        ^....^
           •
                                                                                                                 AVERAGE DAY DESIGN
                                                                                                                            LBS
                                                                                                                              DAV
                           Xrx/   V
     i .-i i ^nt'iYnifi i ivni'm i-rn'rhfrnrn m m f m n n itrnn'ir
                                                           i i (  i rr
tiivrttm-i'h-irhwiTf'trfiffti'i
                                                                                             . i     nnaui am-
                                                         TIME IN DAYS

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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 BODg 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 BOD,- and TSS achieved by the
Metro Denver plant.  The percentage removal of BOD5 is a better indicator than effluent BOD5 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 BODg reduction in conjunction with the fluctuating effluent
BODg concentrations can be explained by the variations in the incoming BODg load.  An increasing
BODg load was accompanied by increased effluent concentrations and thus a relatively constant rela-
tionship as far as percentage removal.
    The average reduction of BODg 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
BODg 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 BOD5 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, dai ly 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 settlcability of the sludge.  Also established was the trena outlining cne

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  90-
  80-
  70-
  60-
z
o
  50-
u>
cc
  40-
   30-
  20>
  10-
            /\A
                                                                             NX \
                                                                                     FIGURE 3


                                                                               FEDERAL ASSISTANCE PROJECT
                                                                        METROPOLITAN DENVER SEWAGE TREATMENT PLANT


                                                                             OCTOBER - 1969 to  FEBRUARY - 1970


                                                                        WEEKLY AVERAGE PEPCENTAGE REDUCTION OF BOD s

                                                                                AND TSS ( SECONDARY ONLY )

                                                                                        VS

                                                                                       TIME
   _ , _ _ _ . __ _ _ w ___ _ ___ .   _        ........
'.'I £H OF 9 JO I 10 "6 I 10 111  0 20llO 17 III jlll Ifllil i7'n 14l •! I  IllSlll lillj 2]ll! J»I I S ll II I I 19 I I 26
                                                                                        1/16 • 2/23

                                                  TIME IN WEEKS    I96» - 1970

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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 well1 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 BODg 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 BODg 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 82 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

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        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 B 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 BOD5 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
daca on the waste sludge total suspended solids concentration are  available for the early phases of
                                                  12

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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 cf 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  BOD-.
                                                  13

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   7.
8
«  6


z
o

Jr
<
ee
»-
z  >
Ul
u
z
o
u

Ul

o
                           • DAILY CONCENTRATION



                           O WEEKLY AVC. CONCENTRATION
                                                      .,     J    M
                                                                                             FIGURE 4


                                                                                     FEDERAL ASSISTANCE PROJECT
                                                                             METROPOLITAN DENVER SEWAGE TREATMENT PLANT

                                                                                   OCTOBER-1969 (o FEBRUARY - 1970


                                                                              WASTE SLUDGE CONCENTRATION IN MG /L «s TIME
   L^,^ffl.tfj.B,.v^foi.n
      "»»»•.'"-*^3fl___    Ilia.-^M               .             IIMICI-»»

                    10EC.
                                                                                  1 KB. •

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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 tne 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(Sp ~ sl)  =  Substrate removal rate                   Equation 1
                           X,V
                   v - K
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                   WHERE:
                         q • substrate removal  rate, pounds  of substrate  removed  per pounds  of cells
                             In the system per day
                        SQ = Influent substrate concentration
                        Sj = 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
                        Kd = 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
                        Xr • 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 1s 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 02 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 (1/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 Kd have been determined.  Heukelekian, Oxford
and Manganelli (6) have presented values of Y = 0.5 milligrams volatile suspended solids produced
per milligram of waste (BOD,-) removed and values of K. = -0.055 as  being  representative, while
Middlebrooks and- Corlir:i (7) have presented values cf Y =  0.67 milligrams volatile tcspen-^d solids
                                                  16

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                                              TABLE 1
                                    FEDERAL ASSISTANCE PROJECT
                            METROPOLITAN DENVER SEWAGE TREATMENT PLANT
                                  OCTOBER 1969  -   FEBRUARY 1970
                            A Sumnary 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)
X 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 BOD5 Concentration - mg/1
Effluent TSS Concentration - mg/1
AREA n
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 #3
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

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produced per milligram of waste (BODg) removed and values of Kd = -0.048.
    The value of Y (slope) and Kd (Intercept) can be graphically determined by determining the value
of ec (Equation 4) and q (Equation 1) and plotting 1/e  versus q.  Values  of the removal  rate (q)
and the mean cell residence time (ec) 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 6C 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 qBQD  and l/ec determined from the project data have been plotted in Figure 5.
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 Kj = -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 (Kd) of the esti-
mated line was assumed to be zero to minimize any increase in slope.  Since Kj must be negative, a
value of K(j other than zero will produce a line of a greater slope if the  line is constructed
through the centroid.  It is stressed that this line is only an attempt to estimate a yield factor
for the Metro Denver waste, although the scatter of the points may not warrant its location on the
graph or even its construction.  The estimated line has a slope slightly greater than that normally
expected.   However, the variation between the two slopes is not great enough to warrant  a conclusion
that the sludge production at Metro Denver is greater than that of typical domestic sewage.
    Figure 5 also shows that those points representing values from Area #2 are generally lower or
closer to the "typical" line than those of Area #3.  The reason for this fact is not apparent.
However, Area #2 was using only two aeration basins while Area #3 was using three.
    The average influent 8005 to the secondary process was 161,560 pounds  8005 per day for the
entire project.  The average effluent BOD5 load for the same period was 23,700 pounds BOD5 per day.
This represents a daily average reduction of 137,900 pounds of 8005, or about 86 percent removal.
If the yield coefficient (Y) for typical  domestic sewage is applied (Y = 0.60), the amount of excess
                                                  18

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                  TABLE 2

        FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
       OCTOBER 1969 - FEBRUARY 1970

     Calculated Values of ec and qBQD.

       Selected Periods of Operation
              Areas #2 and #3
AREA #2
Day
Mon
Tues
Wed
Thurs
Fr1
Sat
Sun

Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Frl
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


















iBODs
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


















6C
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
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Sat
Sun
Mon
Tues
Tues
Wed
Thurs
Frl
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 HO
2/10/70
2/11/70
2/12/70
2/13/70
2/14/70
2/15/70
2/16/70
qsoos
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
O.i66
0.348
0.330
0.339
0.354
0.307
0.354
0.302
0.458
«c
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
l/ec
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

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        0.9'
        0.8 >
         0.7-
         0.6.
        0.5*
cxi

   CO
   — i  0.4«
         0.3.
         0.2°
         0.1*
                               •*
                                                                 FIGURE 5

                                                          FEDERAL ASSISTANCE PROJECT
                                                  METROPOLITAN DENVER SEWAGE TREATMENT PLANT
                                                        OCTOBER 1969 TO FEBRUARY 1970


                                                            NET GROWTH RATE  (%e)
                                                                    vs
                                                        SUBSTRATE REMOVAL RATE (qBOD5)
                                                                                                             • AREA - 3
                                                                                                             O AREA - 2

0.1       0.2
                                       0.3
0.4
0.7
      0.5       0.6


SUBSTRATE  REMOVAL RATE   QB005
Q&       0.9       1.0       1.1


  Ib. BOD5  REMOVED PER DAY
1.2
1.3
1.4
1.5
                                                                                         Ib. VSS IN SYSTEM

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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) 1s 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 Clarlflers
    Eckenfelder and O'Connor (8) have stated that the size of secondary  clarlflers In biological
systems Is 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 clarlfiers and the return
sludge pumping capacity was generally satisfactory to allow rapid removal of the sludge.
    The clarification and thickening capacities for a secondary clarlfier 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 daily 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 in 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 cf  the lew
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

«

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
Settling
Time (Mln)

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 1n a clarifler 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 In the plant effluent If  the settling rate
Is exceeded by the clarifler overflow rate.

                   0_ • V. x 7.5 gallons per cubic foot x 24 hours per day
                    r    s                                                     Equation 6
                      » Vs x 180
                   WHERE:
                        Or = Equivalent Surface Overflow Rate (gal/sq ft/day)
                        V$ = 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 (V$) was established.  An example determination of V$ is shown In Figure 6.  The values of the
zone settling rates (V$), as well as the associated equivalent overflow rates (Or),  are shown in
Table 4.
    The zone settling rate (V$) varied throughout the "average" day for the selected periods.  This
Is to be expected since the zone settling rate is a function of the Initial MLSS concentration and of
the loading rate. I.e. pounds of BOD 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 in 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 1n 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
clarifiers 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 clarifler overflow rates for  the periods
Investigated.  However, this is based on maximum zone settling rates compared with average clarifler
overflow rates.  If the maximum flow is assumed to occur at 1:00 P.M. and the design ratio of
I"averagehday1?atete a 2 CSee Henningson, Durham and Richardson (11)] is applied to the clarifler
overflow rates, then in every case the equivalent surface overflow rate derived from Vs values at
                                                 23

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10 «
                                                           FIGURE 6

                                                  FEDERAL ASSISTANCE PROJECT
                                          METROPOLITAN DENVER SEWAGE TREATMENT PLANT
                                                OCTOBER. 1969 - FEBRUARY. 1970

                                            DETERMINATION OF ZONE SETTLING RATE ( Vs )

                                              HEIGHT OF SLUDGE INTERFACE vi TIME

                                            AREA #3   PERIOD: 1/V- 2/16/70  AVG.9:OOAM
                                        SFTTLING TIME  -  ( 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 (Qr) For "Steady State" Periods
Area and "Steady
State" Period
#2
January 5, 1970
to
January 11 , 1970
fz
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
i
* Vs values are given on top and Or values on bottom.
                                              25

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1:00 P.M. 1s exceeded by the clarlfler 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
clarlflers at the outer edge of the clariflers.  This allowed  localized high upflow velocities to
occur 1n 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 1n 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:

                   A = ^                                                     Equation  7
                       £ o
                   WHERE:
                          A = cross section required to obtain a layer  of a  desired concentration
                              -- ft*
                          q = flow rate of the mixed liquor entering the final  clarifier ~ ft3/sec.
                                                  26

-------
                        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 cludge
                              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 wM! 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 o* 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 B005 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 affluent representing  increased
removals of BOD5 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 atterot was roade to develop a sludge that would concentrate or dewater better tlv.n
                                                  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 (Vs) 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 wsir 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  mete red
        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)
                                                   83

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              APPENDIX A
 A RESOLUTION ADOPTED BY METROPOLITAN
DENVER SEWAGE DISPOSAL DISTRICT NO.  TS
          BOARD OF DIRECTORS
               ENTITLED
 "Concerning the Federal Government's
 Responsibilities in Constructing and
 Operating Sewage Disposal  Facilities"
             July 11, 1969

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                                            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 comnunity, 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,
Bear 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
environment;
    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 can be implemented, since the
        Federal government has set up the standards the District is required to meet.
    4.  Recognize that antipollution standards adopted by the Congress and enforced by federal and
        state as well as local government agencies are placing unprecedented and unbearable financial
        responsibilities on local governments and their constituents, thus making it mandatory that
        the Federal government assist local communities in meeting costs involved not only in con-
        structing adequate sewage facilities but of operating them as well.
                                                  35

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APPENDIX B
REFERENCES

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 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 Mater 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)

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    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 • F*So " S1}       [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 SQ (12/15/69 for Area #3, S  - 198 mg/1).
            S. = effluent substrate concentration  -  For Metro Denver a BOD. value based on a
                 composite sample was used to represent S. (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. BODg removed/day
    2.  Determination of VX,
        WHERE:
             V = volume of aeration plus secondary sedimentation basins
            X  = MLSS or MLVSS concentration
        NOTE:
            VX1 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
            (Xj).   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 S3 and the
    average VSS/TSS ratio was 0.840.  Another refinement was also used in obtaining VX1,
    which will be outlined below.
APPROACH:
    A value comparable to VX1 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 VX1 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)]
    CUD = 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).
                                          39

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    BIT = sludge blanket thickness  -  This  value  is  equivalent  to  CWD -  DOB  (11.7  - 9.7 =
          2.0 feet (BLT) 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  =
          11.252}
    CMC = clarifier mean sludge concentration   -   This value is  obtained  by the equation
          ATC + RSC^  jhis 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 = 7iOZ (Q^C)  for Area #3 on 12/15/69)
OTHER FACTORS:
    CVG = 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  ikl  ( 2i° = 0.171  (CSP) for Area #3 on
                                              CWD   11.7
          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 IDS, of total suspended solids  or sludge in clarifier
b.  Determination of Aerator Sludge Units (ASU)
    ASU = AVG x ATC
                                         40

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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 S3
                  on 12/15/69).
            ATC = 2.75% for Area 13 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 =
        IX 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 basin
    c.   Determination of TSU
            Using the modifications outlined above the value of  TSU is assumed to  be equivalent
        to the value VXr
        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 = VX1 in Ibs. of VSS
                                     = 106,220 x 0.840
                                     = 89.220 Ibs. of volatile suspended  solids  in system
3.   Example Determination of q
    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 lb.  of 6005 removed per day
                               Ib.  of VSS in system
        [q for conventional activated sludge normally has  a value of 0.2 to 0.5,  see  Jenkins  (3)]

B.  Determination of the Net Growth Rate l/ec
    l/ec » FX2 * wxr          [See Jenkins (3)]

    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 1/9C it is not necessary to convert from a TSS basis  to a VSS
        basis since both the numerator (FXg + WXr) and denominator (VX]} in the calculation can  be
        determined on a total suspended solids basis.  Therefore, VX] 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
            WXp 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
                                                  42

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3.  Determination of FX2
        FX£ represents the cells lost from the system per day in the plant effluent.
    WHERE:
         X- = effluent TSS or VSS concentration  -  At Metro Denver the effluent ISS concentra-
              tion was determined for each area based on the analysis of a composite sample
              (12/15/69 for Area 13 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
    1/ec ' -n^
    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:
        I/a  - 10.180*51.310
         '  c       106,220
             = •  61.490
               106,220
             = 0.581 Ibs. TSS wasted or lost per day
                         •  Ibs.  TSS in__sy_s.t;enfi
        The reciprocal  of l/oc is equal  to f»c or the mean cell  residence time (sludge age).  For
    Area #3 on December 15, 1969. BC = 1.72 days.
        Similar calculations were rnade for the other days included in the selected "steady state"
    periods for Areas #2 and #3.  The results of these analyses are presented in Table 2 in text.
                                              43

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           APPENDIX
COLORADO WATER QUALITY STANDARDS

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                                                                    D-l

Appendix D

                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 otlier 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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                                                                    D-2
         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 - me/1

                   Arsenic	0.05
                   Barium	1.00
                   Cadmium	0.01
                   Chromium (Hexavalent)	0.05
                   Cyanide	0.20
                   Lead	0.05
                   Selenium	0.01
                   Silver	0.05

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                                                               D-3
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
    net 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 58F.

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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                                                               D-4
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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