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Siv 'or
Athens, Georgia
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TECHNICAL ASSISTANCE PROJECT
AT THE
CADIZ, KENTUCKY
WASTEWATER TREATMENT PLANT
April 1976
CSV
Environmental Protection Agency
Region IV
Surveillance and Analysis Division
Athens, Georgia
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TABLE OF CONTENTS
Page No.
INTRODUCTION 1
SUMMARY 3
RECOMMENDATIONS 4
TREATMENT FACILITY . 5
TREATMENT PROCESSES 5
PERSONNEL 5
STUDY RESULTS AND OBSERVATIONS 7
FLOW 7
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES . . 7
AERATION BASIN AND DISSOLVED OXYGEN 9
SECONDARY CLARIFIER 11
DISINFECTION 12
SLUDGE REAERATION AND WASTING 12
LABORATORY 12
REFERENCES 14
APPENDICES
A - LABORATORY DATA 15
B - GENERAL STUDY METHODS 17
FIGURES
1 - CADIZ, KENTUCKY WASTEWATER TREATMENT PLANT . . 6
2 - PLANT FLOW 8
TABLES
I - DISSOLVED OXYGEN PROFILES 10
II - OBSERVED AND RECOMMENDED PARAMETERS FOR
SECONDARY CLARIFIERS 11
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INTRODUCTION
A technical assistance study of operation and maintenance problems
at the wastewater treatment plant (WTP) serving Cadiz, KY, was
conducted April 21-22, 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 to assist with special operational problems. Municipal waste-
water 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 assistance is desired and if study efforts would be productive.
The major problem at the Cadiz WTP was a rising sludge blanket with
solids carryover in the plant effluent. At the request of the state
and plant personnel, this study was conducted in an effort to:
® Optimize treatment through control testing and recommended
operation and maintenance modifications,
c Introduce and instruct plant personnel in new operational
control techniques,
a Determine influent and effluent wastewater characteristics,
e Assist laboratory personnel with any possible laboratory
procedure problems, and
9 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.
The ass-is tance and cooperation of the Kentucky Department for Natural
Resources and Environmental Protection in planning and conducting the
study is gratefully acknowledged. The technical assistance team is
especially appreciative of the cooperation and assistance received
from WTP personnel.
Since the study, close contact has been maintained by phone with WTP
personnel in order to relate preliminary study findings and keep
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abreast of process changes. Some recommendations in this report
have already been implemented. The WTP operator related in June
1976, that the operation of two blowers during high flow periods
has been successful in preventing the rising sludge blanket.
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SUMMARY
The EIMCO package wastewater treatment plant (WTP) serving Cadiz,
KY, is a .32 mgd facility treating domestic wastewater from a
population of approximately 1,800. During the study, wastewater
flow to the plant averaged .125 mgd. According to the plant
operator, the WTP receives no major industrial wastewater; however,
the COD test indicated organic loadings higher than would be
expected for domestic wastewater.
The major problem was a rising sludge blanket in the final clarifier
during periods of higher wastewater flow. This caused significant
solids losses in the effluent for periods of about 4 to 6 hours
daily.
Other problems detected during the study included poor mixed liquor
solids settleability, no dissolved oxygen (DO) in the aeration
basins, and inadequate return sludge rates (via airlift system)
for existing conditions. The standard practice of operating only one
blower was found to be inadequate to supply sufficient DO and lift
return sludge at an acceptable rate. Increased aeration by operat-
ing both blowers gave positive results, indicated by an increase in
DO concentrations and reduced solids losses.
The construction of the air diffusers made cleaning of the headers
very difficult; consequently, the diffusers have not been cleaned
since the plant began operation in 1962.
With DO maintained in the basins, sludge condition and settleability
should improve, and the rising blanket should not be a problem.
Laboratory operations were limited due to lack of equipment and
training.
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RECOMMENDATIONS
1. Dissolved oxygen must be maintained in the aeration system for
proper operation. Both blowers should be operated during
daily peak flows.
2. The air diffusers and headers should be cleaned, and if possible,
modified to facilitate easier access for periodic cleaning.
3. A daily control testing program should be initiated. Tests
should include at a minimum:
o Mixed liquor suspended solids settleability
as determined by the settlometer test,
o Suspended solids and volatile suspended solids
on the mixed liquor, return sludge, and reaerated
sludge.
o Dissolved oxygen throughout the treatment system,
preferably with a portable meter and probe, and
o Sludge blanket depth in the clarifier.
4. The plant operator should receive additional training in
laboratory operations.
5. The plant flowmeter should be recalibrated.
6. Due to the high influent COD concentration, the city sewer
collection system should be checked for possible discharge
from an unknown source with high organic wastewater.
7. The mixed liquor volatile suspended solids (MLVSS) should be
maintained at approximately 2^300 mg/1.
-4-
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TREATMENT FACILITY
Treatment Processes
The watewater treatment plant serving Cadiz, KY, is a package
facility manufactured by Process Engineers, Inc., a subsidiary of
EIMCO Corporation, and has a design flow of .32 mgd. The WTP was
constructed in 1962 and serves a population of approximately 1,800.
According to the plant operator, the WTP receives no industrial
wastewaters.
Wastewater enters the WTP from the city collection system at an
aerated grit chamber equipped with barscreen and comminutor. All
subsequent treatment units are in compartments of one large basin
(see Figure I). Approximately three-fourths of the outer rim of
the basin serves as the mixed liquor aeration basin (206,052 gal.
capacity), with the remainder utilized for return sludge reaeration
(74,183 gal. capacity). The center of the larger basin serves as
a final clarifier and.has a volume of 47,548 gallons. The chlorine
contact chamber is adjacent to the clarifier and has a volume of
4,950 gallons.
Influent wastewater flow is pumped to the aeration basins by two
Fairbanks-Morse 5 hp, variable-speed pumps, rated at 400 gpm each
at maximum output. Raw wastewater mixes with reaerated return
sludge and is then aerated in the aeration basin with diffused
air supplied by two 25 hp blowers. Mixed liquor flows around
the basin and subsequently into a four-foot circular influent
baffle located in the center of the clarifier. Scum from the
clarifier is pumped back to the sludge reaeration compartment via
an airlift system. Clarified effluent flows over 78.5 ft. of
peripheral weir into the chlorine contact chamber and thence about
300 yards into the Little River.
Return sludge is airlifted from a hopper in the bottom of the
clarifier and can be returned directly to the aeration basin or
sludge reaeration basin. Waste sludge flows from the reaeration
basin to one of four drying beds.
Personnel
The Cadiz WTP is staffed by one Class III certified operator.
-5-
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FIGURE 1
CADIZ WASTEWATER TREATMENT PLANT
CADIZ, KY
Effluent
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STUDY RESULTS AND OBSERVATIONS
A complete listing of all analytical data and general study
methods is presented in Appendices A and B, respectively. Signi-
ficant results and observations made during the study are discussed
in the following sections.
Flow
The Cadiz WTP flow transmitter, manufactured by BIF, is installed
at the chlorine contact chamber effluent 90° V-notched weir. The
recorder is located in the main control building. EPA flow measure-
ments were made with a Stevens stage recorder installed at the
effluent weir. Three instantaneous flow determinations by EPA
personnel were 16-29% greater than wastewater flow indicated by
the WTP recorder. EPA measured maximum and minimum wastewater
flows of .246 and .035 mgd respectively during the study period,
with an average flow of .125 mgd. Figure II gives a graphic
representation of the wastewater flow measured by EPA during the
s tudy.
Waste Characteristics and Removal Efficiencies
The following is a chemical description of the WTP influent and
effluent wastewater treatment with calculated treatment efficiencies.
The data is based on one 24-hour proportional to flow composite
sample from each station.
Parameter Influent
Effluent
% Reduction
COD (mg/1)
803
417
48
Total Suspended
Solids (mg/1)
330
428
—
Total Volatile Sus-
pended Solids (mg/1)
258
311
—
TKN-N (mg/1)
46
42.4
7.8
NH3-N (mg/1)
32
28.5
11
NO3-NO2-N (mg/1)
.01
.09
—
Pb (ug/1)
120
100
17
Cr (ug/1)
<80
<80
—
Cu (ug/1)
126
190
—
Cd (ug/1)
<20
<20
—
Zn (ug/1)
580
740
—
The influent COD data reveals high organic loading for a domestic
wastewater. At present, low average flows prevent organic over-
loading; however, it would be beneficial to make an inspection
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.30
FIGURE II
PLANT FLOW
, 2C
•o
60
I 6
00 ^
1
g
63
.10
6 7 8 9
PM i/21/76
10 11 12
4 5 6
AM A/22/76
10 11 12
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of the city sewer collection system to check for possible infil-
tration or discharge from an industrial source.
Aeration Basin and Dissolved Oxygen
The hydraulic detention time of the aeration basins was calculated
to be 26.4 hours at the average WTP flow of .125 mgd. Since there
was no measure of return sludge flow, an assumption of 50% of total
WTP flow was used in the calculations. At peak wastewater flow,
the detention time was 16 hours. Recommended detention times range
from 18-36 hours (l)for extended aeration processes.
The suspended solids concentration in the aeration basin was 3(150
mg/1 with a volatile fraction of £350 mg/1. Using the COD value
of the incoming raw wastewater (803 mg/1) and the volatile suspended
solids, a food-to-microorganism ratio (F/M) of .21 was calculated.
The recommended value is less than 0.2(2). To maintain an F/M
ratio of <0.2, the volatile suspended solids need to be increased
to about ^500 mg/1.
The settleability of the mixed liquor solids was determined using
the 60-minute settlometer test. The solids settled slowly, leaving
a clear supernatant. The average 60-minute settled sludge volume
(SSV) reading was 74 percent. For best results, compaction to a
SSV of 30 to 40 percent is desired. The solids gave no indication
of floating after a period of 2.5 hours.
A mean cell residence time (MCRT) was calculated at 18.8 days,
somewhat lower than the recommended 20-30 days (1) . The lower
than recommended MCRT was due to tremendous solids losses in the
effluent during the study.
Aeration was accomplished in the treatment system by diffused
aerators with two 25-hp blowers. Standard operating procedure
at the time of the study was to operate one blower using the second
as a back-up.
Dissolved oxygen (DO) profiles were run to check for oxygen con-
centrations throughout the system. The first profile was deter-
mined at 3:00 p.m. on April 21, 1976, with the WTP in the normal
operational mode, and wastewater flow at about .three-fourths of
peak rates. As can be seen by Table I, there was essentially no DO
at any station in the system. At 9:00 a.m., on April 22, 1976, a
DO profile revealed traces of oxygen present. This DO profile was
measured just after a low flow period. The additional blower
was put on line at 10:00 a.m., and an additional profile at peak
-9-
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StaiIon
A-2
A-4
A-5
A-6
A-8
A-9
A-l
All-2
AD-1
TABI.E I
DISSOLVED OIIYGEII PROFILES
A-8
A-9
AERATION
BASIN
Dopth (ft)
1
5
1
5
1
5
1
5
1
5
1
5
1
5
1
5
Raw
Influent
Dissolved Oxygen (mre/1)
4/21/76
1500 F..S.T.
0
0
0
0
0.2
0
0.2
0
0.2
0
0
0
0.2
0
0
0
3
0
-10-
4/22/76
0000 E.S.T.
.2
.2
.2
.2
.4
.4
.4
.3
.4
.4
. 2
0
.2
0
.1
0
0
o
4/22/7R
lion K.S.T
0.2
0
0.4
0.2
0.6
0.4
0.6
0.5
0.9
0.7
0.6
0.4
0.8
0.7
0.8
0.5
0.5
O.fi
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flow conditions (11:00 a.m.) revealed the presence of dissolved
oxygen, although still low. These data indicate the need for
operating both blowers during peak wastewater flow periods.
According to the WTP operator, the diffusers are mounted in the
basins so that removal and cleaning of the headers is very
difficult. Consequently, the headers have not been cleaned since
the plant began operation. Cleaning of the diffusers should make
the aeration system more efficient, thereby increasing the DO
concentrations in the basins. If possible, modification of the
diffuser mountings to facilitate easier access would be desirable.
If this were accomplished, periodic cleaning of the diffusers
could be incorporated into routine WTP operations.
Secondary Clarifier
The secondary clarifier is circular with center feed. Hydraulic
loading and weir overflow rates were within recommended ranges,
while the detention time was exceeded. Table II gives the actual
and recommended parameters.
TABLE II
OBSERVED AND RECOMMENDED PARAMETERS
FOR SECONDARY CLARIFIERS
Actual Recommended (3,4,5)
Hydraulic loading
(gpd/sq. ft.)
Average 255 200 - 400;
Peak 501 600 - 800
Weir overflow rate
(gpd/lin. ft.) 1,592 <15,000
Detention Time (hrs.) 6.1* 3;2.0-2.5
* - The detention time was calculated assuming return sludge
flow rate of 50 percent of average plant flow.
The major problem observed in the final clarifier was a rising
sludge blanket with increased wastewater flow and subsequent solids
carryover into the effluent. According to the WTP operator, the
sludge blanket surfaced daily from approximately 10:00 a.m. until
3:00 p.m.
Return sludge is removed from the clarifier by an air lift system.
With one blower in operation, it was suspected that the return
sludge rate was not sufficient. The operation of two blowers kept
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the sludge blanket down, with the exception of a two-hour period
on April 22. The benefit of using two blowers during increased
wastewater flow periods is reinforced by these observations. As
the condition of the sludge improves, settling and compactability
should increase to the point that the sludge blanket in the clari-
fier should not rise to the surface.
Disinfection
Chlorine gas is used for disinfection, at the rate of 7 lbs./day.
A portion of this (approximately 40%) is used for influent pre-
chlorination to control odor. Station 1-2 (see Figure I) was
grab sampled to check for any residual chlorine in the influent
entering the aeration basin. The concentration was measured at
<.05 mg/1.
The effluent (Station E-l) had essentially no residual chlorine
(<«05 mg/1) during the period of solids carryover, but had 0.7
mg/1 on April 22 when no solids were being lost. The chlorine
contact chamber has a single baffle and a capacity of 4,950 gallons
resulting in a detention time of 58 minutes at the average waste-
water flow measured during the study.
Sludge Reaeration and Wasting
Assuming a return sludge flow of 50% of the total WTP flow, the
sludge reaeration compartment had a detention time of 4.5 days.
Solids are periodically wasted from the system by shutting down
the aerators, allowing the solids to settle in the basin and drawing
the sludge off to one of the four drying beds. Dewatered solids
are disposed of at a sanitary landfill.
Laboratory
Laboratory functions at the Cadiz WTP were limited due to a lack
of equipment and a lack of training in some procedures.
A daily control testing program is needed at the WTP. Additional
training for the operator in laboratory testing would be extremely
beneficial so that control testing could be initiated and the data
utilized in making process changes. Control testing should include
mixed liquor suspended solids settleability as determined by the
60-minute settlometer test; suspended solids and volatile suspended
solids in the mixed liquor, return sludge, and sludge reaeration
basins; dissolved oxygen through the treatment systems (preferably
with a portable meter and probe); sludge blanket depth in the
clarifier; and percent solids volume to volume (V/V) by centrifuge
on the mixed liquor, and return sludge (preferably with an electrically
powered centrifuge)). With a basic understanding of the significance
-12-
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of each test, an operator can keep firm control of plant opera-
tions and make adjustments in unit processes as necessary to
maintain a quality effluent.
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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 Tech-
nology Transfer, January 1975.
4. "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.
-14-
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LABORATORY DAT.-i
Cadiz, Kentucky
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APPENDIX A
LABORATORY DATA
CADIZ, XENTliCKY
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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 characterize the waste being treated by the WTP and to deter-
mine treatment efficiencies.
Grab samples were taken throughout the system for routine control
testing. These control tests consisted of:
s Sludge settleability as determined by the 60-minute
settlometer test,
e Percent solids by centrifuge on the mixed liquor and
return sludge,
e TSS and VSS analyses on the mixed liquor and return
sludge,
e Depth of the clarifier sludge blanket.
Dissolved oxygen in the aeration basins and sludge reaeration basins
was determined with a YSI Model 51A dissolveld oxygen meter with field
probe, standardized against a Winkler titration.
WTP flow was determined by measuring gage height at the final
effluent weir with a Stevens Model F stage recorder.
Mention of trade names does not constitute endorsement or recommenda-
tion by the Environmental Protection Agency.
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