EPA 904/9/76/004
TECHNICAL ASSISTANCE PROJECT
AT THE
WINSTON-SALEM/ NORTH CAROLINA
WASTEWATER TREATMENT PLANT
NOVEMBER 1375
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Environmental Protection Agency
Region TV
Surveillance and Analysis Division
Athens, Georgia
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TECHNICAL ASSISTANCE PROJECT
AT THE
ARCHIE ELLEDGE WASTEWATER TREATMENT PLANT
WINSTON-SALEM, NORTH CAROLINA
NOVEMBER, 1975
ENVIRONMENTAL PROTECTION AGENCY
REGION IV
SURVEILLANCE AND ANALYSIS DIVISION
ATHENS, GEORGIA
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TABLE OF CONTENTS
Page
INTRODUCTION 1
SUMMARY 2
RECOMMENDATIONS 4
TREATMENT FACILITY 6
TREATMENT PROCESSES 6
PERSONNEL 9
STUDY RESULTS AND OBSERVATIONS 11
FLOW 11
WASTE CHARACTERISTICS AND REMOVAL
EFFICIENCIES 13
DISSOLVED OXYGEN 14
AERATION BASIN . 19
PREAERATION BASIN 25
TRICKLING FILTERS . 25
CLARIFIERS 26
DISINFECTION 28
DIGESTER AND DRYING BEDS . . 28
EXAMINATION OF MICROSCOPIC ORGANISMS 28
OXYGEN UPTAKE RATES 29
LABORATORY 32
REFERENCES 33
APPENDICES
A-CHEMICAL LABORATORY DATA ^ 34
B-DISSOLVED OXYGEN PROFILES - . 52
C-DISSOLVED OXYGEN PROFILE THROUGH WTP .... 55
D-GENERAL STUDY METHODS 56
E-OXYGEN UPTAKE PROCEDURE 58
F-DESIGN DATA 60
FIGURES
1 - ARCHIE ELLEDGE WASTEWATER TREATMENT PLANT . 7
2 - STAFFING PLAN 10
3 - WASTEWATER AND RETURN SLUDGE FLOW 12
4 - BOD5 PROFILES THROUGH PLANT 15
5 - AVERAGE COD & TOTAL SUSPENDED SOLIDS
PROFILE THROUGH PLANT 16
6 - AMMONIA AND NITRATE-NITRITE
PROFILES THROUGH PLANT 17
7 - AERATION BASIN DISSOLVED OXYGEN 18
8 - AERATION BASIN DISSOLVED OXYGEN 20
9 - AERATION BASIN DISSOLVED OXYGEN .• 21
10 - PLANT DISSOLVED OXYGEN PROFILE 22
11 - SETTLOMETER TEST 24
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Table of Contents (continued)
Page
TABLES
1 - WASTE CHARACTERISTICS AND REMOVAL
EFFICIENCIES 13
2 - ACTUAL AND RECOMMENDED PARAMETERS FOR
THE COMPLETE MIX ACTIVATED SLUDGE
PROCESS 23
3 - ACTUAL AND RECOMMENDED FILTER LOADINGS ... 25
4 - OXYGEN UPTAKE RATES 31
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INTRODUCTION
A technical assistance study of operation and maintenance
problems at the Archie Elledge Wastewater Treatment Plant
(WTP) serving Winston-Salem, NC', was conducted November 10-18,
1975, by the U. S. Environmental Protection Agency, Region IV.
Assistance was requested by the City of Winston-Salem through
the North Carolina Department of Natural and Economic Resources
(NC-DNER). Operation and maintenance technical assistance
studies are designed to assist local wastewater treatment plant
operators in maximizing treatment efficiencies as well as assist
with special operational problems.
The specific study objectives were to:
o Optimize treatment via control testing and operation •
and maintenance modifications,
o Determine influent and effluent waste characteristics,
o Assist laboratory personnel with any possible laboratory
procedural problems, and
o Compare design and current loadings.
A follow-up assessment of plant operation and maintenance
practices will be made at a later date. This will be accomplished
using data generated by plant personnel and, if necessary,
additional facility visits. The follow-up assessment will
determine if the recommendations made in this report were
successful in improving plant operations and if further assis-
tance is required. Close contact has been maintained by phone
with plant personnel since the study in order to relate pre-
liminary study findings and stay abreast of process changes
and results. Some of the recommendations made in this report
have already been implemented.
The cooperation of the NC-DNER is gratefully acknowledged.
The technical assistance team is especially appreciative of
the cooperation and assistance received from Archie Elledge
WTP personnel.
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SUMMARY
The 36 mgd, activated sludge WTP serves the entire Winstor.-
Salem area. The plant originally constructed as an 18 mgd
trickling filter system was redesigned in 1969 as a 36 mgd
activated sludge system with roughing filters.
During the study, plant influent flow rates varied between
15 and 38 mgd with the lower flows occurring on the weekend
due to the absence of industrial discharges. The decreased
volume and strength of the waste on the weekend caused con-
siderable variations in food supplied to the biological treat-
ment units. This upset the activated sludge system since the
food to microorganism (F/M) ratio continually fluctuated.
Even though the sewer excludes stormwater, infiltration causes
considerable problems with flows of 60 mgd being reported during
wet periods. Influent flow in excess of 38 mgd is presently
bypassed untreated to prevent upset of the activated sludge
system.
The wastewater entering the WTP is a strong waste with
an average BOD5 of 380 mg/1, COD of 1,078 mg/1 and TSS of
236 mg/1. The wastewater is considerably stronger during
the weekdays than on weekends (BOD^ 520 versus 270 mg/1).
The primary clarifiers and roughing filters were performing
satisfactorily; however, the activated sludge process did not
achieve acceptable BOD5 reduction.
Aeration basin dissolved oxygen (DO) profiles indicated
large areas where DO concentrations were zero, or approaching
zero. These conditions were observed with six of the ten
aerators operating. The profiles also indicated poor mixing
in the basins with zones of low DO observed a short distance
from the aerators. The DO concentration at the three to five
foot depth was sometimes considerably less than at the one
foot level. A DO profile, collected through the different
plant treatment units, also indicated septic conditions at the
primary clarifier effluent.
The trickling filters performed well except for frequent
mechanical failures. The most common problem was failure
of the cables supporting the distributor arms due to corrosion.
One cable failed during the night of November 10, 1975. Plant
personnel reported that this occurred frequently. The filters
accounted for approximately 50 percent of the BOD5 removed
through the complete treatment process.
-2-
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Effluent chlorine residual was excessive each time it
was measured.
The sludge age was young (3.7 days) and most of the sludge
was lost in the effluent. The average MLSS was 752 mg/1 and
settled poorly. Profuse growths of filamentous fungi were
present in the mixed liquor. The low MLSS produced a food
to microorganism ratio above acceptable limits.
The primary clarifiers performed well in removing settle-
able solids; however, the effluent wastewater was septic. The
detention time is excessive (3.4 hours) at the average weekday
flow of 25 mgd. The solids loading on the intermediate clari-
fiers is low due to the small amount of biological solids
sluffed from the trickling filters. The final clarifier's
surface settling rate is 800 gpd/ft^ for average design flow
(36 mgd) and 11,200'gpd/f t^ for peak design flow (54 mgd) which
are the extreme upper recommended limits. The corresponding
design weir overflow rates were 23,900 and 35,800 gpd/ft.
With the overflow weirs located on the periphery of the
clarifiers in the upturn zone, the maximum recommended rate
is 20,000 gpd/ft. During the study, excessive solids were lost
over the effluent weir, and there was no sludge blanket in
the clarifiers. The final clarifiers are not equipped with
surface skimmers.
-3-
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RECOMMENDATIONS
o Mixed liquor solids should be increased by using
polymers in the final clarifier or addition of digested
solids to the aeration basins. Digested solids should
be aerated for a day or two before addition if possible.
In order to maintain a reasonable F/M ratio, a mixed
liquor concentration of approximately 2", 000 mg/1 is
desirable.
o Dissolved oxygen concentrations in the aeration basins
should not normally be permitted to fall below 1.0 mg/1.
This will necessitate running all ten aerators during
normal weekday flow conditions.
o Dissolved oxygen profiles should be run periodically
in the aeration basins to insure that minimum DO concen-
trations are being maintained, and that proper mixing
is accomplished.
• o The use of draft tubes on the mechanical aerators should
be considered in order to improve circulation and mixing
in the aeration basins.
o The possibility of utilizing all, or a portion of, the
intermediate clarifiers as final clarifiers to relieve
the overloaded conditions on the existing clarifiers
should be investigated.
o Industrial wastewater flow equalization should be encouraged
and implemented if possible.
o During low flow periods intermediate clarifier or filter
effluent should be recirculated back to the primary clari-
fier to reduce detention times and septic conditions in
the primary clarifier. Chlorine or peroxide additions
could be used to freshen the wastewater.
o A sludge reaeration basin or anaerobic digester could be
used to maintain a larger volume of activated sludge.
The old, abandoned chlorine contact chamber or the unused
sludge conditioning unit may be suitable.
o As a temporary measure to improve plant operation until
remedial action can be taken to correct the collection
system infiltration problem, excessive wastewater flow
should bypass the activated sludge system to prevent
washout of the sludge. It is suggested that, with the
present clarifier arrangement, flows through the system
be limited to the peak design flow of 54 mgd during per-
iods of good sludge settleability and to approximately
-4-
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36 mgd during periods of poor sludge settleability.
Before this recommendation is implemented, the City of
Winston-Salem must obtain the concurrence of the US-EPA
Region IV Enforcement Division and the NC-DNER.
o Chlorine residuals should be determined by use of an
Amperometric titrator or the iodimetric titration method.
The orthotolidine colorimetric titration is not an
accepted method for determining chlorine residuals in
wastewater. The use of a continuous residual chlorine
analyzer and control system would reduce chlorine costs.
o Effluent chlorine residual should be reduced to an
acceptable level of approximately 0.5 mg/1.
-5-
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TREATMENT FACILITY
TREATMENT PROCESSES
A schematic diagram of the 36 mgd WTP is presented in
Figure 1. Plant design data is shown in Appendix F. The
WTP was originally designed in 1956 as an 18 mgd, high rate
trickling filter facility. In 1969 the plant was redesigned.
An activated sludge process was added.and the trickling filters
were converted to roughing filters.
The WTP, which serves the entire Winston-Salem area,
receives wastewater via the Schlitz, Kimel and Salem outfalls.
The Schlitz outfall contains predominately brewery waste with
very little domestic wastewater. The Schlitz wastewater flow
(1.2 - 1.5 mgd) is passed through a small aeration basin prior
to combining with the other two outfalls. These two outfalls
contain domestic and industrial wastes from tobacco processing,
textile finishing, metal products, dairies, and soft drink
bottling plants.
The combined influent flow enters the plant via a
60 inch diameter concrete pipe into an influent box. This
box also receives digester supernatant, sludge drying bed under-
flow, and septic tank cleaning truck discharges. Influent
wastes pass through three automatically cleaned bar screens
and longitudinal velocity controlled grit chambers in route
to the primary pump station. Screenings and grit are conveyed
to refuse containers. Grit chamber velocity is controlled
by the combined effect of trapezoidal channel bottoms and
Parshall flumes, which also measure influent flow. Four
propeller type, vertical shaft pumps (3 - 22 mgd, 1-13 mgd)
lift the wastewater into a discharge box where it flows by
gravity into the primary clarifiers.
Settled primary sludge is collected by scraper collecting
equipment and flows by gravity into a sump from which the sludge
is pumped (4 - 700 gpm pumps) into anaerobic digesters. The
pumps are controlled by time clocks and sludge density gaug-
ing equipment. Scum is removed from the clarifier by manually
controlled, rotating, slotted pipes and is conveyed by gravity
to a scum box. The thickened scum is subsequently pumped to
the digesters.
-6-
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Anaerobic
D i t; e s L c r s
PRIM
RY
U
3
CLAR1
IERS
2
1
jO IS Composite nnmpli'r location
o Crab sample location
sludge
!)-(> mil! U-/ ,ire ra-i nml.-iry Llnriricrs
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The clarifier effluent flows by gravity to the intermediate
pump station located in the central control building. Two 25
mgd, variable speed pumps lift wastewater to the two primary
trickling filters (TF #1 and £2). Effluent .from these two
filters can flow either directly into the wet well for the
secondary trickling filters (TF #3 and #4) or into the inter-
mediate clarifiers. Recirculation from the intermediate
clarifier can go to either of the intermediate pump station
wet wells for subsequent pumping onto the trickling filters
(see Figure 1).
All four trickling filters are covered by concrete domes
to control the filter environment and to permit control of
odors produced in the filters. Ozone, odor control units, lo-
cated between each set of filters, eliminate odors from the
air drawn through the filters. Effluent air discharges
through a chimney to the atmosphere.
The intermediate settling tanks discharge over two
separate sets of weirs, one at the influent end, and the other
at the effluent end. The length of the weirs at the influent
end is one half that of the weirs at the effluent end. As long
as the filter recirculation is less than 0.5:1, almost all of
the recirculated flow originates from the influent end. At
ratios greater than 0.5:1, additional recirculation is taken
from the overflow of the weirs at the effluent end of the tanks.
The remainder of the flow, which is approximately equal to
the plant influent, flows by gravity to the aeration basins.
Intermediate clarifier sludge flows by gravity into the
primary pump station wet well where it is mixed with plant
influent, and pumped into the primary clarifiers. A sludge
conditioning building equipped with diffused aeration is
available, for conditioning intermediate clarifier sludge,
but is no longer used.
Intermediate clarifier effluent and return sludge (RS)
from the final clarifiers enter the two aeration basins through
butterfly valves located below the center walkway of the basins.
The walkway covers the two distribution channels and the wall
between the basins. The upper channel conveys return sludge;
the lower conveys wastewater. Five sets of valves are located
along the walkway to control wastewater RS distribution. Aera-
tion is provided by five 100 hp mechanical surface aerators
in each basin. Aerator operation is controlled by manually
programmed clock timers. The aeration basin discharge is over
wooden weirs at one end of the basins.
-8-
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Aeration basin effluent flows into four, center fed,
circular clarifiers operated in parallel. These units are not
equipped with any means for removing floatable solids. Settled
sludge is continuously removed through suction type sludge
collectors and pumped to the aeration basins or wasted to
the primary clarifiers for subsequent pumping to the digesters,
along with primary sludge.
Final clarifier effluent flows through a chlorine mixing
box where a flash mixer blends the chlorine solution with the
effluent. A portion of the chlorinated effluent is diverted
into the wet well of the plant effluent pump station; pumps
deliver pressurized effluent to the plant wide distribution
system for washing and cooling where potable water is not
required.
The chlorine contact chamber allows 30 minutes retention
at design flow before discharging into Salem Creek. Chlorine
feed rates are manually controlled.
Two stage, anaerobic digesters treat all primary, inter-
mediate, and waste activated sludges. Influent sludge to the
primary digesters is preheated, and each primary digester is
continuously mixed and heated to approximately 95° F. Secondary
digesters are unheated, but are mixed.
Digested sludge flows by gravity or is pumped from the
digesters to sand drying beds. Dried sludge is either removed
manually or lifted by a sludge mechanism onto a belt conveyor
which loads it onto trucks. Trucks deliver sludge to an
adjacent site where the sludge is available to the public.
Eventually an on site processing plant for further drying
and conditioning will be used.
Digester gas, supplemented by natural gas and/or fuel
oil, is used to power the five, dual fuel, diesel driven genera-
tors which furnish all electrical power used at the treatment
plant. There is no outside electrical connection to the plant.
PERSONNEL
The City of Winston-Salem employs approximately 55 people
to operate the WTP. The employees serve several functions in
support of maintenance and operation (Figure 2).
-9-
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FIGURE 2
STAFFING PLAN
ARCHIE ELLEDGE WTP
WINSTON-SALEM, NC
NOVEMBER, 197 5
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The employees are certified and/or classified from
supervisory Grades IV through technician Grade I. At the
time of the study there were two Grade IV operators, 12 Grade
III operators, 12 Grade II operators and 5 Grade I operators.
STUDY RESULTS AND OBSERVATIONS
A complete listing of all anlaytical data and study
methods are presented in the Appendices. Significant results
and observations made during the study are presented in the
following sections.
FLOW
Figure 3 presents the wastewater flow variation during
the study. The weekday flow averaged 27 mgd and varied from
15 to 38 mgd. During the weekend, when the tobacco, brewery,
and other industrial operations were minimal, the flow ranged
from 12 to 24 mgd and averaged 19 mgd.
Wastewater influent flows of 26-30 mgd are typical during
dry weather periods; however, excessive infiltration occurs
during periods of heavy rainfall, and flows to the plant can
exceed 60 mgd. Although the plant was designed for a hydraulic
peak flow of 54 mgd, these high flows usually cause a washout
of the activated sludge system. Therefore, the mode of operation
has been modified to allow no more than 38 mgd of influent wastes
to be pumped through the plant. Influent wastewater in excess
of 38 mgd is bypassed untreated to Salem Creek.
Influent wastewater flow is measured with three parallel
Parshall flumes; the effluent with a propeller type meter.
Both have chart recorders and totalizers located in the control
building. The influent flumes are subject to flooding. Therefore,
during the study, effluent flow measurements were used.
Trickling filter recirculation is measured with three
Parshall flumes. One measures the flow from TFs #1 and #2;
one measures flow from the influent end of the intermediate
clarifier, and the third measures flow from the effluent end
of the intermediate clarifier.
Total return sludge flow is measured by a propeller type
meter located on the combined sludge return line from the final
clarifiers. A second propeller type meter, at the influent
end of the aeration basins, measures waste activated sludge
flow. The difference in these two meter readings is the
volume of sludge returned to the aeration basins. Digester
supernatant flow is also measured with a propeller type meter.
-11-
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FIGURE 3
WASTEWATER AND RETURN SLUDGE FLOW
WINSTON SALEM, N. C.
Il/ll 11/12 11/13 11/14 11/15 11/16 11/17 11/18
TIME KFV
plant effluent flow
RETURN SLUDGE FLOW
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Magnetic flow meters are used to measure flow between the
preheaters and the digesters and from each set of digesters
to the drying beds.
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES
Waste characteristics and removal efficiencies are pre-
sented in Table 1. Sample station locations are depicted in
Figure 1.
The data in Table 1 are based on 24 hour, flow proportional,
composite samples from stations 1-3 and E-l. These stations
represent the plant influent and effluent with differences
showing treatment plant removal efficiencies.
Samples from station C-l reflect the digester supernatant
return and show the increased loading on the plant from the
supernatant.
Table 1
Waste Characteristics and Removal Efficiencies
Influent* Effluent
Parameter (mg/1) (mg/1) % Reduction
BODc
380
(400)
45
88
COD
1075
(1048)
362
66
TSS
236
(343)
129
45
TKN
19.8
(30.5)
17 .8
10
nh3
11.3
(17.3)
11.8
—
NO3-NO0
0. 21
(0.29)
0.43
—
Total-P
9.0
(10.8)
8.1
10
Pb
. 158
. 130
18
Cr
. 186
. 164
12
Cu
.751
.536
29
Cd
< . 020
< . 020
—
Zn
.386
.320
17
*Values in () are samples from station C-l and include
influent plus supernatant return.
-13-
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Wastewater entering the plant was relatively strong with
an average BOD^ of 380 mg/1, a COD of 1,078 mg/1, and a TSS
of 236 mg/1. The C:N:P nutrient ratio of the waste, after
supernatant return, was roughly 100:8:3.
Concentration profiles' of BOD^, COD, TSS, and nitrogen
through the plant are presented in Figures 4 through 6.
From these curves, the efficiency of each unit process can be
calculated. Increased concentrations between stations 1-3
and C-l were attributed to supernatant return. The two BOD^
curves (Figure 4) on 11/11-12/75 and 11/13-14/75 reflect the
weekday industrial and domestic waste loads. The other two
curves were representative of a weekend period with reduced
industrial discharge. Figure 4 shows that the primary clari-
fiers and trickling filters were effecting significant B0D5
removal while the activated sludge system was performing
poorly. The trickling filters were shut down during most
of the weekend period of November 15-16, 1975, reducing
the efficiency of those units during that time period.
Figure 5 shows a TSS removal in the primary clarifier of
approximately 250 mg/1 (72 percent) and then essentially no
change through the rest of the plant. Figure 6 shows a sizable
increase in ammonia between stations 1-3 and C-l. This was
due to supernatant return to the waste stream. There
appeared to be a small amount of nitrification occurring in
the trickling filters and slightly more occurring in the
activated sludge system. Very little nitrification was ex-
pected from the activated sludge system due to the young
sludge age which was caused by washout of solids. The average
ammonia concentrations in the effluent were almost identical
to the average influent concentration. The N02~N0g curve in
Figure 6 shows some decrease between stations C-l, C-2 and
C-3. This was probably due to biological denitrification
caused by septic conditions in the primary clarifier. An
increase in N02-N0g in the activated sludge system was caused
by the slight arfiount of ammonia nitrification.
DISSOLVED OXYGEN
All dissolved oxygen (DO) measurements taken in the
aeration basins are presented in Appendix B. Figure 7 depicts
the mean DO concentrations throughout the basins under the
most common aerator configuration (six of 10 aerators operat-
ing) during the study. A significant portion of the basins
exhibited less than 0.5 mg/1 DO (shaded area in Figure 7).
The highest DO concentrations were observed nearest the basin
effluent in Bays A6 and A12. A number of stations (Al-f,
Al-g, A3-b, A3-c, A3-d, A8-f, A9-c, AlO-c, All-d) showed
significant differences in DO at the one and five foot depths,
indicating poor mixing. Extremely low DO concentrations were
often observed at distances of approximately 20 feet from
operating aerators at depths of three to five feet. This
condition seems to indicate dead spots created by the mixing
-14-
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600 —
bod5 profiles through plant
WINSTON SALEM, N.C.
H / 13- 14/ _7_5_.. %
C - 2 S C - 3 T- I
SAMPLING STATION
T-2
-------
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too
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FIGURE 5
AVERAGE C.O-D. 8 TOTAL SUSPENDED SOLIDS PROFILE THROUGH PLANT
WINSTON SALEM, N.C.
J I I I I I
1-3 C-l C-28C-3 T-1 T-2 E-l
SAMPLING STATION
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28
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24
22
20
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10
8
AMMONIA AND NITRATE-NITRITE PROFILES THROUGH WTP
WINSTON SALEM, N.C.
NH,
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1-3
C-2 8C-3 T-1
SAMPLING STATION
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pattern of the aerators. Slightly higher DO concentrations
were measured along the basin walls due to flow patterns
created by the surface aerators.
Additional testing should be performed in the aeration
basins to determine the extent of poor mixing. Consideration
should be given to the installation of draft tubes to attain
better mixing. This could be tried on one or more aerators
when one of the basins is shut down for servicing.
Dissolved oxygen concentrations for aeration configura-
tions which were used experimentally are presented in Figures
8 and 9. Even with-eight aerators operating, numerous areas
of low DO were evident. With all aerators on (Figure 9),
excessive DO concentrations (4.3 - 5.5 mg/1) were observed;
however, the MLSS in the basins were extremely low (approxi-
mately 500 mg/1), and the plant waste load was relatively low
since it was on a weekend.
These data for normal aerator operations indicate
unacceptably low dissolved oxygen and poor mixing in the
aeration basins. Low DO levels have been found to be the
major cause of sludge bulking. Dissolved oxygen concentrations
in aeration basins of 2-4 mg/1 are recommended (3).
For the past year, this plant has been plagued with profuse
filamentous growths in the aeration basins. These growths
can sometimes be controlled by reducing the dissolved oxygen
concentration in the aeration basins to the bare minimum. How-
ever, low DO concentrations had been maintained for an extended
period without showing any decrease in the amount of filamentous
growth. Also, careful monitoring throughout the basins is
required when maintaining low DO levels to prevent the occurrence
of septic zones in the basins. DO was monitored continuously
at the basin effluent.
Figure 10 presents a profile of the average effluent DO
from each unit process in the WTP; a Complete listing of this
data is presented in Appendix C. Zero DO was always measured
in the primary clarifier. Less than 0.5 mg/1 DO was measured
in the combined influent (station 1-3).
AERATION BASINS
Grab samples were taken at the discharge from each of
the two aeration basins (stations A-13 and A-14). Settlometer,
TSS, VSS, and percent total solids by centrifuge tests were run
on each sample.
The average mixed liquor suspended solids (MLSS) and
mixed liquor volatile suspended solids (MLVSS) were 752 and
613 mg/1, respectively. The percent solids by volume, as
-19-
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WINSTON-SA
IeRT^north^carolina
PLANT DISSOLVED OXYGEN PROFILE
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SAMPLING STATION
-------
determined by centrifuge, ranged from 1.4 to 2.5 percent.
Based on a design flow of 36 mgd and an influent BOD- of
200 mg/1 in the aeration basins, an MLVSS concentration of
approximately 2,000 mg/1 should be maintained in order to have
a food to microorganism (F/M)s ratio from 0.2 - 0.6 (7).
Presented in Table 2 are various activated sludge
operating parameters calculated during the study and corres-
ponding recommended values for the complete mix activated
sludge process.
Table 2
ACTUAL AND RECOMMENDED PARAMETERS FOR THE COMPLETE MIX
ACTIVATED SLUDGE PROCESS
Actual
Weekday
Weekend
Recommended
Hydraulic Detention
Time (hours)
5.7
7.5
4-8
Sludge Age (Days)
3.7
—
3.5-7
Lbs. BOD/Lbs. MLVSS
.54
.44
0.2-0.4
Lbs. COD/Lbs. llLVSS
1. 57
.92
0.5-1.0
Lbs. BOD/1000 cu. ft.
aeration basin
22.3
13.6
20-40
MCRT
3.5
13.6
5-15
The mean cell residence time (MCRT) and sludge age were
less than recommended values. The F/M ratio was near maximum
recommended limits based on BOD and exceeded maximum recommended
values based on COD. This condition was due to low MLVSS in
the aeration basins.
Wastewater flow equalization for the major industrial
customers would greatly benefit operation of the activated
sludge system. By retaining a portion of the weekday industrial
wastewater flow and discharging it over the weekend, the weekday,
shock load would be reduced. A reasonably constant F/M ratio
could then be maintained. Currently, the weekday BOD load
is approximately four times greater than the weekend load.
Another method of controlling the F/M ratio to handle the
cyclic waste load would be to maintain a larger volume of
sludge either in an aerobic digester or in a sludge reaeration
basin. This would enable the operatar to rapidly increase the
MLSS when heavy load conditions w?rrant. The abandoned chlorine
contact basin could be equipped with a surface aerator and
used for this purpose.
The average, maximum and minimum readings of all settlometer
tests are presented in Figure 11. The average volume of settled,
mixed liquor sludge, after 60 minutes of settling, was 46 per-
cent. The results shown in Figure 11 indicate an activated
sludge with poor settling characteristics.
-23-
-------
FIGURE 11
SETTLOMETER TEST
WINSTON SALEM, N.C.
SETTLING TIME (MINUTES)
-24-
-------
PREAERATION BASIN
Wastewaters discharged from the Schlitz brewery flow
into a 1.3 mg preaeration basin at the WTP. The basin has
a 16-18 hour detention time and is equipped with six 100 hp
floating surface aerators. The purpose of the basin is to
satisfy a portion of the high BOD5 of the waste that ranges
from 1,000 to 2,500 mg/1. The flow from the brewery varies
from 1.2 to 1.5 mgd during weekdays. Piping is arranged so
that either all or a portion of the brewery waste can be passed
through the basin. Urea is added to supply nitrogen to the
brewery waste. The objective of this pretreatment basin
is to reduce the total brewery waste to a BOD^ concentration
of approximately 1,000 mg/1. During the study, all of the
waste was passed through the basin, and the average BOD5
concentration of the effluent was 1,160 mg/1.
TRICKLING FILTERS
The four domed trickling filters were operated as a pair
of primary filters in series with two secondary filters.
(Figure 1). The system is arranged to provide the operator
the option of operating all filters in series, in parallel,
or in combination. The actual and recommended filter loadings
are presented in Table 3. The filters, originally designed
as high-rate filters, are now utilized as roughing filters
to reduce the organic load on the activated sludge system.
The filters were shut down on November 16-17, 1975. This
was a relatively low flow weekend period. The operator felt
that this was necessary in order to strip excessive biological
growth from the filters and to possibly reduce the fungi
concentration in the aeration basin. There is no evidence
to show that the fungi are produced in the trickling filters.
During the study, the two primary filters were receiving
the total plant influent plus from one to ten mgd of recircu-
lated flow for a total of 25 to 35 mgd. Recirculation rates
were controlled to load the secondary filters at approximately
25 mgd. The organic loading to the two primary filters was
above the recommended level for high-rate filters placing
them in the roughing filter category.
TABLE 3
ACTUAL AND RECOMMENDED FILTER LOADINGS
Actual Recommended (7)
Primary Filters
Hydraulic (gpd/ft^)
Organic (lbs. BOD5/IOOO
400-560
ft3-day) 195-270
230-920
23-115
Secondary
Hydraulic (gpd/ft^)
Organic (lbs. BOD5/IOOO
400
ft^-day) <194*
230-920
23-115
~No samples taken at intermediate filter stations.
-25-
-------
The filter system is an integral part of the biological
process and breakdown or upset of one or more filters has
a deteriorating effect on the activated sludge unit. Changes
in BOD5, COD, TSS, and nitrogen concentrations can be seen
from the profiles in Figures 4 through 6. The filters are
between sampling stations C-2 and C-3 and Tl. The BOD5
reduction for the two day period (November 12 and 13) when
the filters were in full operation, amounted to 54 percent
of the filter influent BODc or 46 percent of the total BOD5
removed through the complete process.
Frequent mechanical problems have been experienced with
the filters. Cables supporting the distributor arms fail
frequently in the corrosive environment under the domes. As
recirculation rates increased, mechanical failures were more
common.
CLARIFIERS
The four rectangular primary clarifiers are operated in
parallel and receive raw influent plus return waste sludge from
the intermediate and final clarifiers. The clarifiers were
designed for an overflow rate of 800 gal/ft^/day at the
design flow of 36 mgd with a detention period of two hours
and twenty minutes. Plant inflows, during the study, ranged
from 12 to 38 mgd which produced loadings within the design
limits. The detention time was 3.5 hours at .a plant flow
of 24 mgd.
Wastes flowing into the primary clarifiers had a DO of
2.5 mg/1 and the effluent DO was zero (Figure 10). Evidence
of this anaerobic condition can be observed from Figure 6 which
shows a decrease in NO2-NO3. The decrease is probably due to
denitrification. Figure 5 shows a 72 percent reduction in
suspended solids and a 40 percent reduction in COD. Figure 4
shows an average 23 percent reduction in BOD5 in the clarifier.
The intermediate clarifiers are similar in design to the
primary clarifiers. These basins are designed to settle
biological solids that have sluffed off the trickling filters.
Figures 4 through 6 indicate that these clarifiers had little
effect upon the wastewater quality. Suspended solids and
BOD,- concentrations were unchanged. A small volume of thin
sludge (500-1,000 mg/1) was returned from the intermediate
to the primary clarifier.
Plant flow and return sludge flow rates are shown in Figure
3. The return rate during the study averaged approximately
88 percent of plant flow. The final clarifiers are designed
for a surface settling rate of 800 gpd/ft^ at the average design
-26-
-------
flow of 36 mgd, and 1,200 gpd/ft^ at the design peak flow of
54 mgd. Corresponding weir overflow rates are 23,900 and
35,800 gpd/ft, respectively. These rates are at the upper
limit of the recommended range and leave very little room
for satisfactory operation during process upsets. The ten
state standards criteria (6) recommend a maximum loading of
800 gpd/ft^ during "significant flow periods' and a preferable
maximum weir overflow rate of 15,000 gpd/ft." The US-EPA (2)
recommends a loading of 400-800 gpd/ft^ during average flow
conditions and 1,000 to 1,200 gpd/ft^ for peak flow conditions.
Metcalf and Eddy (7) recommend a surface settling rate of
800 gpd/ft^ for activated sludge, peak flow conditions with
a MLSS concentration of 3,000 mg/1 and a recirculation rate
of 50 percent. A maximum weir overflow rate of 30,000 gpd/ft
is recommended if the weir is located away from the upturn
zone and 20,000 gpd/ft if located in the upturn zone. The
weirs on the final clarifiers are located on the outer wall
of the clarifiers in the upturn zone.
Solids carryover occurred in the final clarifiers
continually during the survey and had been occurring for
several months prior. Settleability of the mixed liquor was
poor (Figure 11) due to profuse filamentous growth. High
sludge return rates were creating additional turbulance in
the clarifier. Turbidity measurements were taken at the effluent
weir of each clarifier (station FC-1 through FC-4). Turbidity
values ranged from 1 to 215 standard turbidity units (STU).
Most of these samples, after a 30 minute quiescent settling
time, produced values of less than 5 STU. This test indicated
that clarifier performance was poor, and that additional
settling time would significantly improve the effluent.
Considering the overloaded condition of the final clari-
fiers and the underused condition of the intermediate clari-
fiers it would appear reasonable to investigate using all
or a portion of the intermediate clarifiers for final settling.
This modification would require pumping and some repiping
but should be much less costly than constructing additional
clarifiers.
On November 16 at 2:00 p.m., a small amount of Rhodamine
WT fluorescent dye was dumped into the aeration basin effluent
to observe flow distribution in the clarifiers. The waste
appeared to be distributed fairly evenly in all four clari-
fiers .
-27-
-------
DISINFECTION
Disinfection of the treated wastewater effluent is
accomplished by the introduction of chlorine gas into the
final clarifier effluent, upstream from the chlorine contact
tank. The vacuum operated duplex chlorination system fed an
average of 3,067 pounds of liquified chlorine per day to the
wastewater stream. Chlorine usage for the study period ranged
from 1,800 lbs/day to 4,300 lbs/day. The resulting chlorine
residual at the chlorine contact tank overflow weir ranged
from 2.3 ppm to 16.0 ppm. The high of 16.0 ppm was measured
on Sunday, November 16, 1975, during a period of extremely
low flow, and was due to a malfunction of the automated
chlorinator. Plant personnel use the orthotolidine colori-
metric test for free chlorine residual as a central measure
in the chlorination process. Combined chlorine residual,
rather than free chlorine residual, should be measured for
control purposes. The amperometric or iodimetric titration
method for total chlorine residual should be used.
DIGESTERS AND DRYING BEDS
Immediately prior to the study the solids content of
all digesters had been reduced considerably in order to store
solids during the coming wet months. This was done in order
to avoid the problem which occurred at the plant last year,
when all drying beds were full of wet sludge .and the emergency
sludge holding pond had to be used. Because of this condition,
digester sampling during the survey was limited, and the data
obtained are not typical of digesters operated under steady,
fill and drain conditions. The results are more typical of
start-up conditions. The total solids content was less than
one percent in the six primary digesters and about five percent
in the two secondary units. Gas produced from the primary
units was utilized in the onsite power plant. The pH was
above the desirable 6.8 to 7.2 range in four of the primary
units, and the volatile acid/alkalinity ratio of digester
D-2 was 0.53 which is approaching the danger zone (8). This
condition can be corrected by reducing the raw feed rate or
by recirculating solids from the secondary units to buffer
the volatile acids in the primary units.
EXAMINATION OF MICROSCOPIC ORGANISMS
Slide samples of return sludge, aeration basin mixed
liquors, floating clarifier solids, and influent samples
were observed.
Return sludge and mixed liquor from the aeration basin
had a very high concentration of filamentous growth and a high
density of free-swimming ciliates and flagellates. No
specific organism dominated since all types were well represen-
ted. The stalked ciliates with a limited number of rotifer
and higher animal forms' were present in lower concentrations.
-28-
-------
Floating clarifier solids were primarily filamentous
and of the same general protozoan makeup as the mixed liquor
and return sludge.
Examination of the influent waste showed a limited number
of protozoan types. Free-swimming bacteria, yeast cells, and
macrofilaments were present in large numbers.
Sludge samples from the primary and intermediate units
showed good mass flocculation, few protozoans, numerous fibers,
and large fungal filaments. In the intermediate unit, numer-
ous fly larvae, nematodes, flagellates, and the very small
filamentous growth were observed.
The protozoan population of the activated sludge system
was indicative of a waste system with a high organic load.
Flagellates are the dominant organisms under these conditions.
Free-swimming ciliates are found when there are a large
number of free-swimming bacteria. Together, flagellates and
free-swimming ciliates are found normally at the low side
of the efficiency scale. Stalked ciliates which indicate
an activated sludge which will produce low BOD effluent
arise as a result of the number of available bacteria being
reduced below the demands of the free-swimming ciliates (4).
From these observations, the source of innoculation of
the small bulking filamentous growth cannot be ascertained.
The small filamentous growth encountered appeared to be
sheathed with separate individual cells enclosed. The
mycelium did not branch, and fragmentation was not observed.
Bacteria and flagellates were observed adhering at right
angles to the filaments. These filaments, except for size
of the mycelium, are similar to' the Sphaeratilus organisms.
Dr. Pfaender, of the Mycology Dept., University of
North Carolina at Chapel Hill, made an identification and
enumeration of the filamentous growth. The growth was
identified as fungi of the family Moniliaceae and genus
Monilia. These organisms ranged from 2 to 5 x 10^ cells
per milliter of activated sludge.
OXYGEN UPTAKE RATES
General sludge activity can be measured by determining
the difference in Oxygen (O2) uptake rates of the sludge
before and after introduction of raw waste. The ratios of
these two variables or "load ratio" is calculated as follows:
d „+-,•„ - ADO/min. fed sludge
Load Ratio = —: t—-3
ADO/min. unfed sludge
-29-
-------
The test procedure and its significance are presented
in Appendix E.
Table 4 is a listing of the O2 uptake rates and calcu-
lated load ratios for each type of waste. As shown in the
table, O2 uptake rates were determined on the three sewers
entering the WTP as well as for the combined influent.
The calculated load ratios for the combined waste ranged
from 1.14 Sunday morning, November 16, to 5.90 Sunday evening,
to 6.67 Monday, November 17. On the morning of November 16,
total plant inflow was very low; industrial process waste
loads were low, and the trickling filter units had been shut
down at 8:30 a.m. These conditions may have resulted in the
one conspicuously low ratio. The afternoon of November 16
showed a calculated ratio of 5.9 which was attributed to the
shutdown of all trickling filters. On Monday, the trickling
filters were also down, and flow was again normal.
The aerated brewery waste, as opposed to the brewery
waste before aeration, is very readily biodegradable, while
the nonaei'ated brewery waste was slowly biodegradable. This
was shown by average O2 uptake rates for aerated and non-
aerated brewery waste of 0.75 ppm and 0.13 ppm, respectively.
Calculated load ratios for the Salem and Kimel wastewaters
were comparable to that of the combined waste.
These load ratios indicated a readily biodegradable
waste and a fairly active sludge. The oxygen uptake rates
for the unfed return sludge was somewhat lower than might
be expected due to the low solids concentration (low micro-
organism density) in the sludge.
-30-
-------
TABLE 4
OXYGEN UPTAKE RATES
Average 09 Uptake , Load Ratio
1/ PPM/Min. PPM/Min.—i FRS/URS£/
Date Time % .RS URS FRS
Combined Plant Wastewater
11/11/75
2: 30
p.m.
100
0. 20
0.84
4.2
11/12/75
3:00
p.m.
70
0.20
0.68
3.4
11/13/75
11:00
a.m.
55
0.11
0.44
4.0
11/14/75
2: 20
p.m.
77
0.15
0. 55
3.7
11/16/75
10: 15
a.m.
78
0. 14
0. 16
1.14
11/16/75
2:00
p.m.
78
0.10
0. 59
5.9
11/17/75
2:15
p.m.
100
0. 12
0.75
6.25
Schlitz Wastewater
11/12/75
3: 00
p.m.
70
0.20
1. 34
6.7
11/13/75
11:00
a.m.
55
0.11
0.75
6.8
11/14/75
2:2-0
p.m.
77
0. ] 5
0.40
2.7
11/16/75
2:00
p.m.
78
0. 10
0.45
4.5
Salem
Wastewater
11/12/75
3: 00
p.m.
70
0.20
0.70
3.5
11/13/75
11:00
a.m.
55
0.11
0.44
4.0
Kimel
Wastewater
11/12/75
3: 00
p.m.
70
0.20
0.68
3.4
11/13/75
11:00
a.m.
55
0.11
0.40
3.6
\f - RS - Return activated sludge
2/ - URS - Unfed return sludge (sludge plus final effluent)
3/ - FRS - Fed return sludge (sludge plus raw influent from the
intermediate settling basin).
-31-
-------
LABORATORY
The laboratory at the Winston-Salem WTP is located within
the main control building. The lab was neat and appeared to
be operated efficiently. Observations of lab records revealed
a well organized data handling system.
The laboratory staff included a plant chemist, responsible
for control testing and plant monitoring analyses, and an
industrial chemist in charge of monitoring industrial dis-
chargers. The staff also included six laboratory technicians.
During the study a discrepancy in the results of TKN
analyses was observed. In comparing plant data with EPA data
it was discovered that EPA data on TKN samples were consistently
30-40 percent lower than data run by the WTP personnel. Sub-
sequent split samples also confirmed this variation. EPA
normally uses an automated procedure for TKN analysis and
the WTP uses a manual procedure. On the split samples the
problem was isolated to the comparability of the manual and
automated TKN procedure for this particular waste. The EPA
Laboratory Services Branch is continuing to investigate and
will identify the problem.
-32-
-------
REFERENCES
1. "Operation of Wastewater Treatment Plants", A Field Study
Training Program, US-EPA, Technical Training Grant No.
5TT1-WP-16-03.
2. "Process Design Manual for Suspended Solids Removal",
US-EPA Technology Transfer, January 1975.
3. "Process Design Manual for Upgrading Existing Wastewater
Treatment Plants", US-EPA Technology Transfer, October
1974.
4. Ross E. McKinney and Andrew Gram. "Protozoa and Activated
Sludge", Sewage and Industrial Wastes, 28 (1956):1219-1231.
5. "Sewage Treatment Plant Design", American Society of
Civil Engineers, Manual of Engineering Practice - No.
36, 1959.
6. "Standards for Sewage Works", Upper Mississippi River
Board of State Sanitary Engineers, Revised Edition, 1971.
7. "Wastewater Engineering", Metcalf and Eddy, Inc., 1972.
8. "Operation of Wastewater Treatment Plants", A Field
Study Training Program, US-EPA, Technical Training
Grant No. 5TT1-WP-16-03, 1970.
-33-
-------
Appendix A
Chemical Laboratory Data
Archie E3ledge STP
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Appendix A, Chemical Laboratory Data, Archie Elledge STP, Winston-Salem, NC (continued)
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Appendix A, Chemical Laboratory Data, Archie Elledge STP, Winston-Salem, NC (continued)
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Appendix A, Chemical Laboratory Data, Archie Elledge STP, Winston-Salem, NC (continued)
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Appendix A, Chemical Laboratory Data, Archie Elledge STP, Winston-S^lem, NC (continued)
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Appendix A, Chemical Laboratory Data, Archie Elledge STP, Winston-Salem, NC (continued) ^
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Appendix B
Dissolved Oxygen Profiles
Winston-Salem, NC
Date
Station (1975)
1/ Temp.
Il/i I
Time
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Date 2/
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9.
-------
Appendix B (continued
Dissolved Oxygen Profile
Kinston-Salem, NC
I Date iy)
Station
===== 2/_
Tempi DO
(°C) '(mg/l)_l
| Date [ 3/|Temp.
Station (1975),' Time .'(°C)
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-------
Appendix B (continued)
Dissolved Oxygen Profiles
Winston-Salcm. NC
J s.tat
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-------
Appendix C
Dissolved Oxygen Profile through WTP
Winston-Salem, NC
R Date
i!" (1975)
11
12
13
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-------
Appendix D
General Study Methods
To accomplish the stated objectives outlined in the
introduction, the study necessitated extensive sampling
physical measurements, daily visual observations and dis-
cussions with the plant operator (5).
The plant influent stations I—1, 1-2, 1-3; the primary
unit process stations C-l, C-2 & 3; intermediate unit process
station T-l, T-2; and the effluent stream station E-l, were
sampled for seven consecutive 24 hour periods with ISCO Model
1392-XG automatic samplers. Aliquots of sample were pumped
at hourly intervals into individual refrigerated glass
bottles which were composited proportional to flow at the
end of each sampling period.
Effluent from each trickling filter unit, stations TF-1,
TF-2, TF-3, and TF-4 were grab sampled on four equal]y spaced
time periods between 8 a.m. and 6 p.m. for five consecutive
days. Nine hundred milliters were composited for each time
period into a'gallon jug.
Each digester was grab sampled once daring the study
period and supernatant flow was grab sampled once per day
for six consecutive days.
Standard operational control tests were run twice
daily, once in the morning and once in the afternoon for
seven consecutive days. The control tests consisted of:
o sludge settleability as determined by the 60 minute
settlometer test,
o percent solids by centrifuge on the mixed liquor and
return sludge,
o TSS and VSS analyses on mixed liquor and return sludge,
o depth of clarifier sludge blanket and
o turbidity of the effluent from the final clarifiers.
The return sludge flow was grab sampled twice per day
for six days to determine sludge activity. Sludge activity
was measured by the oxygen uptake procedure presented in
Appendix E. The rate of oxygen uptake for fed and unfed
sludge was determined and a loading factor was calculated.
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Microscopic examinations were made on influent, primary
sludge, intermediate sludge, return sludge, and trickling
filter slime.
Physical observations of individual unit processes and
flowmeter readings were recorded daily and whenever operational
changes were made.
The BODg analysis was modified in that the incubation
temperature was not maintained at exactly 20°C during the 6-hour
transit time from Winston-Salem to Athens. Currently, compara-
tive tests are being run to determine what effect, if any,
temperature variation and agitation has upon BOD^ results.
This is being done by setting up duplicate samples at selected
plants. One sample is then returned to Athens for analysis
and the other is analyzed by the plant.
Mention of trade names does not constitute endorsement
or recommendation by the EPA.
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APPENDIX E
OXYGEN UPTAKE PROCEDURE3
A. Apparatus
1. Electronic DO analyzer arid bottle probe
2. Magnetic stirrer
3. Standard BOD bottles (3 or more)
4. Three wide mouth sampling containers (approx. 1 liter each)
5. DO titration assembly for instrument calibration
6. Graduated cylinder (250 ml)
7. Adapter for connecting two BOD bottles
B. Procedure
1. Collect samples of return sludge, aerator influent and final
clarifier overflow. Aerate the return sludge sample promptly
2. Mix the return sludge and measure that quantity for addition
to a 300 ml BOD bottle that corresponds to the return sludge
proportion of the plant aerator, i.e. for a 40% return sludge
percentage in the plant the amount added to the test BOD
bottle is:
300 X .4 = 120 = 86 ml
1.0 + .4 1.4
3. Carefully add final clarifier overflow to fill the BOD bottle
and to dilute the return sludge to the plant aerator mixed
liquor solids concentration.
4. Connect the filled bottle and an empty BOD bottle with the
BOD bottle adapter. Invert the combination and shake vigorously
while transferring the contents. Re-invert and shake again
while returning the sample to the original test bottle. The
sample should now be well mixed and have a high D.O.
5. Insert a magnetic stirrer bar and the previously calibrated
DO probe. Place on a magnetic stirrer and adjust agitation
to maintain a good solids suspension.
6. Read sample temperature and DO at test time t=0. Read and
record the DO again at 1 minute intervals until at least 3
consistent readings for the change in DO per minute are
obtained (A DO/min). Check the final sample temperature.
This approximates sludge activity in terms of oxygen use
after stabilization of the sludge during aeration (unfed
sludge activity).
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APPENDIX E (Cont)
7. Repeat steps 2 through 6 on a replicate sample of return
sludge that has been diluted with aerator influent (fed
mixture) rather than final effluent. This A DO/minute
series reflects sludge activity after mixing with the new
feed. The test results indicate the degree of sludge
stabilization and the effect of the influent waste upon
that sludge.
The load factor (LF), a derived figure, is helpful in evaluating
sludge activity. It is calculated by dividing the DO/min of fed sludge
by the DO/min of the unfed return sludge. The load ratio reflects the
conditions at the beginning and end of aeration. Generally, a large
factor means abundant, acceptable feed under favorable conditions. A
small LF means dilute feed, incipient toxicity, or unfavorable conditions.
A negative LR indicates that something in the wastewater shocked or
poisoned the "bugs."
(3) Taken from "Dissolved Oxygen Testing Procedure," F. J. Ludzack and
script for slide tape XT-43 (Dissolved Oxygen Analysis - Activated Sludge
Control Testing) prepared by F. J. Ludzack, NERC, Cincinnati.
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Appendix F
Design Data
Archie Elledge Wastewater Treatment Plant
Winston-Salem, North Carolina
DESIGN FLOWS
Average 36 mgd
Peak 54 mgd
SCREENING AND GRIT REMOVAL
Designed to handle flows and process screenings and
grit from flow of 100 mgd. Velocities through the bar screens
range from 1.7 - 2.5 ft./sec., and velocities in the grit
channels range from 0.8 - 1.0 ft./sec.
PRIMARY PUMP STATION
Pumping Capacity variable 0-80 mgd maximum
Control valve recirculation 0-18 mgd
Capacity, variable
PRIMARY CLARIFIER
Number of hydraulically separate 4
tanks
Dimensions
Length
Width
Depth
Wetted volume
869,000 gal. each
465,000 ft.3 total
3,477,000 gal. total
140 ft.
83 ft.
10 ft.
116.200 ft.3 each
Detention time at 36 mgd
Surface overflow rate
Sludge collector's rate of
travel
Main collector
Cross collector
Sludge pumps
Number
Capacity, constant
2 hours 20 minutes
800 gal/sq ft/day
2 ft/minute
4 ft/minute
700 gpm @ 90' TDH
1 gpm @ 90' TDH
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Appendix F (continued)
INTERMEDIATE PUMP STATION
Number of pumps
Pumping capacity, variable
TRICKLING FILTERS
Number
Dimensi ons
0-25 mgd each
0-100 mgd total
Diameter
Depth
200 ft.
5.25 ft
Area
Volume
Hydraulic, capability of
distributors
Estimated BOD removal
capability
INTERMEDIATE CLARIFIERS
Number hydraulically separate
tanks
.72 acre, each
2.9 acre, total
3.8 acre ft. each
15.1 acre ft. total
25,000 gal. each
100,000 gal. total
110 lb/1000 cu. ft./day or
72,500 lb/day
12
Dimensions
Length
Width
Depth
Volume
124 ft.
31 ft. 6 inches
8 ft. 10 inches
Detention time without
recirculation
Detention time with 100%
recirculation
Surface overflow rate
Sludge collector's rate of
travel
34,500 ft. each
258,100 gals, each
414,000 ft.3 total
3,100,000 gals, total
@ 36 mgd 2 hrs.
1 hr.
770 gal/ft2/day
1 ft/min.
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Appendix F (continued)
AERATION BASINS
Number of basins
Dimensions each
Length
Width
Depth
525 ft.@ surface
105 ft.@ surface
14.5 ft. @ center
Volume
752,000 ft. each
5,625,000 gals, each
1,504,000 ft.3 total
11,250,000 gals, total
Detention time without recirculation
@ 36 mgd
Detention time with 25% recirculation
Estimated BOD removal
assuming adequate final settling and
1700 - 2000 mg/1 MLSS, 70% MLVSS,
65°F., SVI 100-200
Aerators
Number
Horsepower
Calculated 02 requirement
Rated total O2 transfer capacity
FINAL CLARIFIERS
Number
Dimensions
Diameter 120 ft.
Depth 11 ft.
weir length 378 ft.
7.5 hrs
6 hrs
44,000 lbs/day
10
100 each
77,000 lbs/day
82,000 lbs/day
Volume
124,300 ft.3 each
929,800 gals, each
497,200 ft.3 total
3,719,000 gals, total
Detention time without recirculation @ 36 mgd
Detention time with 25% recirculation
hrs.
2 hrs.
Surface overflow rate
-62-
800 gal/ft /day
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Appendix F (continued)
CHLORINE CONTACT TANK
Number 1
Dimensions
Length 120 ft.
Width 84 ft.
Depth 10.5 ft.
Volume 105,800 ft3 or 791,700 gals.
plus approx. 1300 ft. 190,800 gals.
of 60 inch pipe to CCT 982,500 gals.
Detention time @ 36 mgd approx. 40 minutes
RETURN SLUDGE PUMP STATION
Number of pumps 3
Capacity, variable 0-36 mgd total
DIGESTERS
Number 8
Volume old digesters 153,000 ft.^ each
1,144,000 gals, each
Volume new digesters 200,000 ft.^ each
1,496,000 gals, each
Total digester volume 1,412,000 ft.3
10,560,000 gals.
Volume of primary digesters 1,012,000 ft.^
7,569,800 gals.
Volume of secondary digesters,
2 new 400,000 ft.3
2,992,000 gals.
Estimated design loading @ 36 mgd
55,000 lb/day primary sludge
60,000 lb/day TF sludge
25,000 lb/day Waste AS
140,000 Total 140,000 lb/day
Estimated volatile content 60% 84,000 lbs/day
Loading on primary digesters 83 lb. MLVSS/1000 ft.
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Appendix F (continued)
SLUDGE DRYING BEDS
Number
Dimensions
69
Length
Width
100 ft.
100 ft.
Area
10,000 ft.„ each
690,000 ft. total
15.8 acres total
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