TECHNICAL ASSISTANCE PROJECT
AT THE
COLUMBIA, KENTUCKY
WASTEWATER TREATMENT PLANT
April 1976
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Environmental Protection Agency
Region IV
Surveillance and Analysis Division
Athens, Ceorgia
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TECHNICAL ASSISTANCE PROJECT
AT THE
COLUMBIA, KENTUCKY
WASTEWATER TREATMENT PLANT
April 1976
«T: Proiedscs Ageacy
2iZ Cuir>-3;^ Sired
Gsccgia 30365
Environmental Protection Agency
Region IV
Surveillance and Analysis Division
Athens, Georgia
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TABLE OF CONTENTS
Page
INTRODUCTION
SUMMARY 2
RECOMMENDATIONS 3
TREATMENT FACILITY 4
TREATMENT PROCESSES 4
PERSONNEL 4
STUDY RESULTS AND OBSERVATIONS 7
FLOW 7
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES 7
AERATION BASINS 8
DISSOLVED OXYGEN 8
SECONDARY CLARIFIER 10
SLUDGE WASTING AND AEROBIC DIGESTION 11
LABORATORY H
REFERENCES 12
APPENDICES
A - LABORATORY DATA 13-14
B - GENERAL STUDY METHODS 15
FIGURES
1 - COLUMBIA, KENTUCKY WASTEWATER TREATMENT PLANT 5
2 - PLANT FLOW 6
TABLES
I - DISSOLVED OXYGEN PROFILES 9
II - ACTUAL AND RECOMMENDED PARAMETERS FOR SECONDARY 10
CLARIFERS
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INTRODUCTION
A technical assistance study of operation and maintenance problems
at the wastewater treatment plant (WTP) serving Columbia, Kentucky, was con-
ducted April 19-20, 1976, by the Region IV, Surveillance and Analysis
Division, U.S. Environmental Protection Agency. Operation and maintenance
technical assistance studies are designed to assist local WTP operators in
maximizing treatment efficiencies as well as assisting with special
operational problems. Municipal wastewater treatment plants are selected
for technical assistance studies after consultation with state pollution
control authorities. Visits are made to each prospective plant prior
to the study to determine if study efforts would be productive.
The major problem at the Columbia, Kentucky, facility was periodic
solids losses which resulted in a poor quality effluent. This study was
conducted at the request of state and plant personnel in an effort to:
o Optimize, treatment through control testing and recommended
operation and maintenance modifications,
9 Introduce and instruct plant personnel in new operational
control techniques,
• Determine influent and effluent waste characteristics,
6 Assist laboratory personnel with any possible laboratory
procedure problems, and
e 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 by utilizing
data generated by plant personnel and, if necessary, subsequent visits
to the facility will be made. The follow-up assessment will determine
if recommendations were successful in improving plant operations and if
further assistance is required. Contact by phone has been maintained with
plant personnel since the study in order to relate preliminary study
findings and stay abreast of process changes. Some of the recommendations
contained in this report have already been implemented.
The cooperation of the Kentucky Department for Natural Resources
and Environmental Protection in planning the study is gratefully acknow-
ledged. The technical assistance team is especially appreciative of
the cooperation and assistance received from plant personnel.
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SUMMARY
The Columbia, Kentucky Wastewater Treatment Plant (WTP) is a 0.395
mgd activated sludge facility. The facility was found not to be hydrau-
lically or organically overloaded. According to plant personnel, there
are no industrial wastewaters discharged into the Columbia sewerage
system.
The influent magnetic flow meter, which is the only flow measuring
device in the plant, was inoperative during the study. Plant flows
measured utilizing EPA equipment ranged from .13 mgd to .42 mgd, with an
average of .25 mgd.
The plant was designed with two rectangular aeration basins, however,
one of the two aerobic sludge digesters was being operated as an additional
aeration basin. The suspended solids data collected during the study
indicated that an unequal loading was being placed on this third basin.
Settlometer analyses revealed poor settleability in all basins with apparent
denitrification and subsequent floating sludge after 75 to 90 minutes.
Initial dissolved oxygen (D.O.) profiles indicated low levels of
oxygen present in the aeration basins. This profile was taken at peak flow
conditions. Later, the aeration rate was increased with subsequent increase
in D.O. concentrations as revealed by a later D.O. profile. This indicated
the need for additional aeration during peak loading conditions.
The rectangular final clarifier had floating solids and subsequent
carryover during high flow periods. Return sludge was removed from the
sludge hopper by an airlift system.. The major problem at the facility,
in addition to a poor quality sludge, seems to be inadequate sludge
removal from the clarifier.
Laboratory operations were very limited at the Columbia WTP. Training
is badly needed in laboratory procedures.
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RECOMMENDATIONS
1. Plant personnel should receive training in laboratory procedures and
plant operations so that an effective process control testing routine
can be established and utilized. This training will be necessary in
order to implement some of the following recommendations.
2. Flow measuring equipment should be installed to monitor total plant
flow, return sludge flow to each influent stream, and waste sludge
flow.
3. Dissolved oxygen should be monitored and maintained in the aeration
basins, preferably from 1.0 rag/1 to 2.0 mg/1. It will be necessary
to run both blowers to the diffusers and increase the mechanical
aeration speed during periods of higher flow. A portable dissolved
oxygen meter and probe should be used to monitor the dissolved oxygen
levels in the aeration basins.
h. Sludge wasting should be decreased in order to increase mixed liquor
volatile suspended solids to approximately 2,000 mg/1, thereby
obtaining a food to microorganism ratio within recommended ranges.
5. A portable sludge pump, rated at approximately half the average
daily plant flow, would be useful as a temporary measure to aid in
removing sludge from the secondary clarifier.
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TREATMENT FACILITY
Treatment Processes
A diagram of the Columbia WTP is presented in Figure I. The activated
sludge facility was designed for a flow of 0.395 mgd and has both mechani-
cal and diffused aeration. Presently, the facility treats no industrial
wastewater.
Wastewater flow is received from the city collection system in a wet
well at the plant. The wastewater is pumped by two 250 gal/min. pumps
from the wetwell into the influent channel. Wastewater influent flow is
ultimately split into three unmetered portions for each of the three aera-
tion basins. A Foxboro magnetic flow meter, installed on the influent
stream, was inoperative during the study.
The aeration system was operated as an extended aeration process during
the study. Two of the aeration basins have diffused air supplied by two
25 h.p compressors. The third aeration basin was originally designed as
an aerobic digester. This basin is smaller than the other aeration basins
and has one 7.5 h.p. mechanical aerator.
Clarification is achieved in a rectangular clarifier with a mechanical
flight sludge collection system. Return sludge is pumped by an airlift
system from a hopper on the effluent end of the clarifier to a splitter
box where the flows are separated into each influent stream. There was no
flow measurement on the return sludge. Accumulated scum from a surface
skimmer in the clarifier is pumped back to the aeration basins. Clarified
effluent flows over four 12 ft. weirs into troughs where it is ultimately
discharged unchlorinated into Russell Creek.
Waste sludge is conditioned in one aerobic digester with a 7.5 h.p.
mechanical aerator and subsequently discharged onto one of two drying
beds.
Personnel
The plant staff includes a superintendent (class II operator certified)
and one operator (class III operator certified). The superintendent's
duties are divided between the WTP and the city water plant.
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FIGURE I
COLUMBIA WASTEWATER TREATMENT PLANT
COLUMBIA, KENTUCKY
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.50
.40
T3
hO
. 10
7 8 9 10 11 12
PM 4/19/76
FIGURE II
PLANT FLOW
4 5 6 7 8 9 10 11 12 1 2 3
AM 4/20/76 PM
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STUDY RESULTS AND OBSERVATIONS
A complete listing of all analytical data and study methods are
presented in Appendices A and B respectively. Significant results and
observations made during the study are presented in the following
sections.
Flow
EPA personnel determined plant flows during the study by placing
an 8-inch rectangular weir in the effluent channel and measuring gage
height with a Stevns Model-F stage recorder. Figure II gives a graphic
representation of the flows measured. The peak flow was .42 mgd
measured at 11:00 a.m. on April 20, and the minimum flow at 4:00 a.m.
on April 20 was .13 mgd. The average plant flow for the 24-hour period
was .254 mgd.
Waste Characteristics and Removal Efficiencies
The following gives a chemical description of the plant wastewater
influent and effluent along with treatment efficiencies. The data is
based on one 24-hour proportional to flow composite sample.
Parameter
Influent
Effluent
% Reduction
COD (mg/l)
Suspended Solids (mg/l)
TKN-N (mg/l)
NH3-N (mg/l)
NO3-NO2 (mg/l)
Total P (mg/l)
Pb (ug/1)
Cr (ug/1)
Cd (ug/1)
Cu (ug/1)
Zn (ug/1)
537
133
30.6
19.5
.03
10.5
120
<80
<20
64
260
197
122
14.5
3.8
,26
11.6
<80
<80
<20
41
190
63
8
53
80
36
27
The nitrogen data indicates that the nitrification stage of treatment
had been reached, with almost complete denitrification taking place in the
final clarifier.
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Aeration Basins
A detention time of 21.8 hours was calculated using the average
plant flow and an assumed 50% return sludge rate. Recommended extended
aeration detention times are 18-36 hours (1). During the study, sludge
was wasted for a total of 90 minutes per day, but the flow rates were
unknown. A mean cell residence time (MCRT) of 11 days was calculated
assuming a waste rate of 50 percent of total plant flow for the 90
minute period. The recommended MCRT for extended aeration is 20-30
days (1). Large amounts of solids lost in the effluent, as well as
the high sludge wasting rate, caused the low MCRT. At present, sludge
wasting needs to be decreased in order to increase the MCRT. As the
sludge settleability improves, wasting rates may have to be increased
to maintain a workable MCRT.
Mixed liquor suspended solids (MLSS) concentrations in the basins
averaged 2020 mg/1 for Basin //I (A-l), 1810 mg/1 for Basin //2 (A-2),
and 3090 mg/1 for Basin #3 (A-3) (See Figure 1) with corresponding mixed
liquor volatile suspended solids (MLVSS) concentrations of 1515 mg/1,
1320 mg/1, and 2240 mg/1. A food to microorganism ratio (F/M) of .
.25 lb COD per day/lb MLVSS was calculated for the sludge based on the
influent COD value. The recommended F/M for extended aeration using
COD values is <0.2 lb COD per day/lb MLVSS (2). Based on these results,
MLVSS levels need to be increased to approximately 2000 mg/1 in
Basin ill and #2 and maintained at the 2000 mg/1 level in Basin //3.
Basin //3 (A-3) contained a disproportionate amount of solids at the
time of the study. This was probably caused by an excessive amount of
return sludge. Flow measuring equipment is badly needed to measure the
influent streams and return sludge flows. With this capability, unequal
loading to the aeration basins can be prevented.
Settleability of the activated sludge was determined by the 60-minute
settlometer test. The sludge slowly settled to 60, 64 and 87 percent
of the original volume in 60 minutes for stations A-l, A-2, and A-3
respectively. After a period of 75 to 90 minutes, the solids floated
to the surface, indicating that denitrification was taking place-
Dissolved Oxygen
Dissolved oxygen (D.0.) profiles in the aeration basins were run
once in the morning and once in the afternoon on April 20, 1976. The
initial profile was made during peak loading conditions, with one
compressor supplying air to Basins //I and 112. At 11:00 a.m., the
additional blower was started and the mechanical aerator speed in Basin
#3 was increased. A list of all data is given in Table I. The data
clearly indicated that it was necessary to increase the aeration during
higher loading conditions. As the flow decreases at night, a single
blower may maintain adequate D.0.
A check of the D.0. in the aerobic digester and final clarifier re-
vealed a sufficient supply of oxygen in the digester and only a trace
of D.0. in the clarifier.
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TABLE I
DISSOLVED OXYGEN PROFILES
COLUMBIA Y/ASTrJV-ATElt TREATMENT PLANT
COLUMBIA, KENTUCKY
e
A-3
AERATION
BASIN
#3
0
A-2
9A-13 ? r
A-S
•
A-l
°A-8 •
A-4
FINAL
CLAKIFIER
AERATION
BASIN
nuikn a
BASIN
® C-l
•
AD-1
IT 2
AEROBIC
DIGESTER
BA-12 A-l(
© 0
A-7 A-5
0
A-ll
A-0
»
C-2
• #
Dissolved Oxygen (ng/1) Dissolved. Oxygen (mg/I*
4-20-76 4-20-76 4-20-76 4-20-76
Station Depth (ft) 1015 1400 Station Depth (ft) 1015
A-l 1 - .8 a-2 1 .2 1.2
5 - .8 5 .3 la
10 " .6 10 .4 1.0
13 - .6 13 .4 9
A-4 1 .2 1.2 A-9 1 .2 1.6
5 ** 5 .2 1.3
10 .2 1.1 10 .3 1.2
13 .2 1.1 13 .3 1.2
A~5 1 -2 -5 A-10 1 ,2 1.4
10 .2 .6 10 .3 1.4
13 -2 -5 13 .3 1.4
A-6 1 .4 1.0 A-U 1 .5 .8
5 .2 .6 5 .3 .9
10 .3 .5 10 .4 .9
13 .3 .6 13 .4 *7
A-7 1 .2 . .8 A-12 1 .2 10
5 .2 .8 5 .4 1.0
10 .2 .7 10 .7 1.0
« .2 .8 13 .6 1.6
A-8 1 .3 1.1 A-13 1 .4 l.l
5 .2 .8 5 .4* l.l
10 .2 .8 10 .4 l.l
13 -2 -8 I3 .5 1.1
AD-1 1 1.5 - A-3 1 .2 .2
5 1.4 - 5 .2 *2
10 1.7 - 10 .3 .3
13 1.8 - 13 .3 .4
C-l 1 .3
5 .2
8 .2
C-2 1 .4
5 .3
8 - .3
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Secondary Clarlfier
Surface loading and the weir overflow rates are within recommended
design criteria, as shown in Table II.
TABLE II
ACTUAL AND DESIGN PARAMETERS FOR SECONDARY CLARIFIERS
Actual Recommended (3) (4) (5)
Hydraulic Loading (gpd/sq. ft.)
Average 480 200-400 ; 600
Peak 583 800
Weir Overflow rate (gpd/liri. ft.) 6,125 <15,000
Detention Time (hrs.) 2.6 * 3 ; 2.0-2.5
* The detention time was calculated assuming a return sludge flow of 50
percent of the average plant flow.
With the exception of the early morning hours on April 20, 1976,
floating sludge with subsequent solids carryover was observed. Poor
sludge settleability is part of the problem. Denitrification, as
exhibited in the settleometer test, further compounds the problem.
During the study, the return sludge system was being operated at the
maximum return rate, however, this system was unable to get the sludge
out of the clarifier before the dissolved oxygen (D.O.) was depleted,
resulting in denitrification and a floating sludge blanket. This is
more prevalent as the organic loading increases with the increased
flow. The operation of both diffused air blowers during high loading
periods should help increase the D.O. and delay denitrification in the
clarifier. With increased D.O., sludge quality should improve and
ultimately, settleability, should increase. As this occurs, the
removal system will become more efficient, i.e., will return a thicker
sludge.
As a temporary measure a portable sludge pump should be installed
in the final clarifier to aid in returning sludge. A pump flow rated
at about half the average daily flow should be sufficient. If this
measure proves successful, installation of a permanent unit should
be considered.
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Sludge Wasting and Aerobic Digestion
During the study activated sludge was routinely wasted from the
system for two 45 minute periods per day. Wasted sludge flows by
gravity into the aerobic digestor. Stabilized sludge was ultimately
placed on one of two drying beds. Dewatered solids were then disposed
of by hauling to a sanitary landfill.
Laboratory
Laboratory operations at the Columbia facility are very limited.
The analyses being conducted routinely at the time of the study were
BOD5(using a manometric procedure), solids by centrifuge (using a hand
turned centrifuge), sludge settleability (using a liter graduated
cylinder) and D.O. in the aeration basins by the Winkler titration.
It should be noted that the manometric BOD^ test is not an approved
procedure per the Federal Register of approved procedures, volume 38,
number 199, October 16, 1973.
The sodium thiosulfate titrant used in the Winkler D.O. determination
was checked by EPA personnel and found to be inaccurate. New reagent
was prepared and standardized. Plant personnel were instructed on
proper procedure in preparing fresh titrant.
At present, there is limited understanding by plant personnel of
laboratory procedures. Training is badly needed for the WTP staff in
this area.
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REFERENCES
1. "Wastewater Engineering", Metcalf and Eddy, Inc., 1972.
2. "Operation of Wastewater Treatment Plants", A Field Study Training
Program, US-EPA, Technical Training Grant No. 5TT1-WP-16-03.
3. "Process Design Manual for Suspended Solids Removal", US-EPA
Technology Transfer, January 1975.
A. "Standards for Sewage Works", Upper Mississippi River Board of
State Sanitary Engineers, Revised Edition, 1971.
5. "Sewage Treatment Plant Design", American Society of Civil Engineers,
Manual of Engineering Practice. No. 36, 1959.
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I
A?PcX"DiX A
LABORATORY DAT A
COLUMBIA, KENTUCKY
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A?r li.N'DlX A
LABORATORY DATA .
C0LCM31A, KENTUCKY
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APPENDIX B
General-Study Methods
To accomplish the stated objectives, the study included sampling,
physical measurements, visual observations, and discussions with the
plant operator.
One 24-hour proportional to flow composite sample was taken from
the influent (Station 1-1) and from the effluent (Station E-l) by an
ISCO model 1392-X automatic sampler. These samples were used to charac-
terize the waste being treated by the facility and to observe treatment
efficiencies.
Grab samples were taken throughout the system for routine control
testing. These 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 the mixed liquor and return sludge,
o depth of the clarifier sludge blanket.
The aerobic digester was grab sampled for total solids and total
volatile solids.
Dissolved oxygen in the aeration basins and aerobic digester was de-
termined using a YSI model 51A dissolved oxygen meter with field probe,
standardized against a Winkler titration.
Plant flow was determined by placing an 8-inch rectangular weir
in the effluent channel and measuring gage height with a Stevens model F
stage recorder.
Mention of trade names does not constitute endorsement or recommen-
dation by the Environmental Protection Agency.
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