EPA. 904/9-76-07
TECHNICAL ASSISTANCE PROJECT
AT THE
THOMAS P. SMITH
WASTEWATER TREATMENT PLANT
TALLAHASSEE/ FLORIDA
Environmental Protection Agency
Region IV
Surveillance and Analysis Division
A then s, Georg'i a
February 1976
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TECHNICAL ASSISTANCE PROJECT
AT THE
THOMAS P. SMITH
WASTEWATER TREATMENT PLANT
TALLAHASSEE, FLORIDA
Environmental Protection Agency
Region IV
Surveillance and Analysis Division
Athens, Georgia
February 1976
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TABLE OF CONTENTS
Page
INTRODUCTION I
SUMMARY 2
RECOMMENDATIONS 3
TREATMENT FACILITY 4
TREATMENT PROCESSES 4
PERSONNEL - 6
STUDY RESULTS AND OBSERVATIONS 7
FLOW 7
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES 7
AERATION BASINS 12
OXYGEN UPTAKE RATES 14
CLARIFIERS 14
DISINFECTION 18
DIGESTER AND DRYING BEDS 18
LABORATORY 18
REFERENCES 19
APPENDICES
A - CHEMICAL LABORATORY DATA 20
B - GENERAL STUDY METHODS 26
C - OXYGEN UPTAKE PROCEDURE 28
D - DESIGN DATA 30
FIGURES
1 - THOMAS P. SMITH - SOUTHWEST TREATMENT PLANT .... 5
2 - ACTIVATED SLUDGE PLANT EFFLUENT AND RETURN
SLUDGE FLOWS 8
3 - FLOW STRIP CHARTS : 9
4 - SETTLOMETER TEST 13
5 - DYE CONCENTRATION CURVE 17
TABLES
1 - WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES -
THOMAS P. SMITH WTP 7
2 - WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES -
TRICKLING FILTER PLANT 11
3 - ACTUAL AND RECOMMENDED PARAMETERS FOR CONVENTIONAL
AND CONTACT STABILIZATION ACTIVATED SLUDGE PROCESS 12
4 - ACTUAL AND RECOMMENDED PARAMETERS FOR SECONDARY
CLARIFIERS 16
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INTRODUCTION
A technical assistance study of operation and maintenance problems
at the Thomas P. Smith Wastewater Treatment Plant (WTP) serving Tallahassee,
Florida was conducted during February 8-13, 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 treat-
ment 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.
Historically, the Thomas P. Smith plant had BOD5 removal efficiencies
in the 75-85 percent range. This was much less than optimum, especially
for a facility with little or no influent industrial wastewaters. This
study was conducted at the request of plant personnel to:
Optimize treatment through control testing and recommended
operation and maintenance modifications,
Determine influent and effluent wastewater characteristics,
o 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 has been maintained with plant
personnel since the study in order to relate preliminary study findings
and stay abreast of process changes and results. Most of the recommenda-
tions in this report have been implemented since the study and a visit
to the plant on April 14 indicated significantly improved removal
efficiencies.
1
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SUMMARY
The Thomas P. Smith activated sludge WTP was designed for an average
flow of 7.5 mgd. On site with the activated sludge facility is an older
2.5 mgd trickling filter plant. With pump station controls, the trickling
filter plant is used to relieve the activated sludge plant when total
inflow exceeds 7.5 mgd. Flows to the Thomas P. Smith plant averaged 6.35
mgd during the study and average 0.6 mgd at the trickling filter plant
The influent wastewater was relatively weak with an average BOD^ of 152 mg/1
and COD of 333 mg/1. This produced a food to microorganism (F/M) ratio of
about half the minimum recommended levels.
The two aeration basins were constructed for capabilities of plug
flow, step feed or contact stabilization; however, the step feed mode
could not have been utilized since the motorized butterfly valves on the
raw waste lines could not be maintained in a partially open position. At
the time of the study, the plant was being operated in the contact
stabilization mode. Good mixing and oxygen transfer was accomplished by
four fixed mechanical aerators in each basin.
Based on present loading conditions, the aeration system contained
excess solids. Even though the mean cell residence time (MCRT) was within
accepted limits, the characteristics of an old sludge were apparent.
Effluent quality during the study period was typical of removal
efficiencies in recent months. BOD^ and suspended solids removals were
88 and 84 percent respectively. Approximately one-half of the ammonia
nitrogen was oxidized to nitrate-nitrite nitrogen. Turbidity of the
clarifier effluents averaged 6 NTU.
The two secondary clarifiers were not hydraulically overloaded during
the study. Dye used to observe the flow patterns revealed even disperse-
ment of wastewater throughout the basins.
Return sludge is pumped from the clarifiers back to the aeration
basins; however, the lines were inadvertently crossed in a design revision.
Sludge from the north aeration basin and west clarifier is returned to the
south aeration basin and visa versa (Figure 1).
Disinfection of the treated wastewater was with chlorine gas in a
contact tank with 30 minutes detention at the design flow of 7.5 mgd.
Residual chlorine concentrations in the effluent were higher than necessary
to attain proper disinfection.
Sludge handling facilities include two aerobic digesters with
mechanical aerators. Conditioned sludge is placed on drying beds and then
spread on OTP property.
The laboratory was well arranged and had all required analytical
capabilities.
2
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RECOMMENDATIONS
The following recommendations are made to improve treatment and plant
operations:
1. Switch the operational mode back to conventional plug flow.
If the scum problem reappears temporarily switching to contact
stabilization should increase the oxidation pressure on the
waste and breakdown the scum.
2. Switch the return sludge lines so that sludge is returned
back to the proper aeration basin.
3. Waste mixed liquor suspend solids down to 2000 to 2500 mg/1 level
or until the food to microorganism (F/M) ratio reaches
the minimum recommended range of 0.2.
4. Shut off one aerator in each aeration basin if the reduced
oxygen demand due to the reduction in mixed liquor solids
permits. Check to see that adequate mixing is maintained.
5. Monitor food to microorganism, mean cell residence time, sludge
settleability and other process control parameters. Establish
historical operating data and maintain trend charts where
cause and effect relationships can be easily determined.
6. Repair or replace the motorized butterfly valves on the raw
waste lines to the aeration basin so that they can be held
in the partially open position.
7. The pump stations should be regulated to deliver a smoother
flow to the plant.
8. A good operation and maintenance manual is a useful
operational tool and would be useful at the Thomas P.
Smith WTP.
3
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TREATMENT FACILITY
TREATMENT PROCESSES
A schematic diagram of the Thomas P. Smith activated sludge WTP
is presented iri Figure 1. Also located on the same site is the older
Southwest WTP, a trickling filter facility designed for 2.5 mgd. These
two plants receive all of the waste from the. City of Tallahassee except
for the 4.5 mgd treated at the Lake Bradford Road WTP. Future plans are
to expand the Thomas P. Smith plant to treat all of the wastewaters
from the City of Tallahassee. There are no major industrial wastewater
discharges into the system.
Raw sewage is pumped to the plant site from a pump station
located on Spring Hill Road. A manually cleaned bar screen is located
at the pump station. Approximately 150 lbs/day of chlorine is added
for odor control. The pump station contains 3 two-speed pumps rated
at 3,600 gpm at low speed and 7,200 gpm at high speed at 57 feet total
dynamic head. Water level in the wet well is monitored and transmitted
to a recorder on the plant control panel. On site, the wastewater flows
through a bar screen, grit chamber, and Parshall flume into the pump
station wet well. From this point the wastewater is split and pumped
to the two wastewater treatment plants, which contain three 5,500 gpm
pumps and one 1,800 gpm pump. All pumps discharge to a common header
with a control valve provided to regulate flow to the trickling filter.
Under the present mode of operation, the pump station is controlled to
maintain a flow as constant as possible through the activated sludge
system and the trickling filter handles a portion of the excess flow over
8 mgd. This is done by isolating the small pump during the daytime to
pump to the filter when the plant inflow exceeds 8 mgd. Approximately
1 mgd is recirculated to keep the filter wet during low flow periods.
At night, the small pump is switched back to pump to the activated sludge
plant. The trickling filter receives no flow during this period. The
flow rate to the activated sludge plant is measured by an in-line
magnetic flow meter.
The aeration basins are designed to offer considerable flexibility
in operational modes. Each basin contains four 50 hp fixed mechanical
aerators. The fourth bay of each basin is segregated from the rest of
the basin with a wall and sluce gate. Raw wastewater can be fed into
all four bays of each basin by automatically controlled butterfly valves
and return sludge can be fed into the first and fourth bays. This
permits the system to be operated in either conventional plug flow,
step feed or contact stabilization modes.
Mixed liquor flows over a weir at the end of each aeration basin
into two final clarifiers. The circular clarifiers are rim feed and rim
take-off type. Two in-line propeller type flow meters are used to measure
the discharge from each clarifier to the chlorine contact tank and the
effluent from the contact tank is measured by a rectangular weir.
4
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FIGURE I
THOMAS SMITH - SOUTHWEST TREATMENT PLANT
TALLAHASSEE, FLA.
5
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Settled sludge from each clarlfier is removed by vacuum pick-up
into separate sludge sumps. The sludge is pumped back into the aeration
basins by 7 5 hp duplex pumps. A sluce gate is provided in the common
wall between the sludge sumps. In a design revision, the sludge return
lines were inadvertently crossed. This takes away the option of opera-
ting each side of the system independently. Sludge from the north
aeration basin and west clarifier is returned to the south aeration
basin and visa versa. Flow meters are provided on each return sludge
line. Sludge can be wasted to the two aerobic digesters by turning a
manually controlled valve on either return sludge line. Each digester
is equipped with a 100 hp fixed mechanical aerator.
Effluent wastewater from each clarifier passes through a flow meter
and into a rectangular baffled chlorine contact chamber. Chlorine gas,
added at the basin influent, is used for disinfection. After chlorination,
the wastewater is discharged into a polishing pond where a portion is
spray irrigated on a test plot and the remainder is discharged to Munson
Slough. Spray irrigation of the total plant effluent on the municipal
airport property is planned.
PERSONNEL
The plant is well staffed with two Class A, one Class B and six
Class C operators plus three trainees. The plant is manned 24 hours per
day, 7 days per week.
6
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STUDY RESULTS AND OBSERVATIONS
A complete listing of all analytical data and study methods are
presented in the Appendices. Significant results and observations made
during the study are presented in the following sections.
Figure 2 presents the wastewater flow variation during the study.
The weekly flow averaged 6.35 mgd and varied from near zero to 12 mgd.
An additional 0.6 mgd was treated in the trickling filter plant
Surges in flow are created when rags are periodically removed from
the manually cleaned bar screen at the Spring Hill Road Pump Station.
Wastewater stored in the sewer flows into the wet well which causes an
additional pump to be activated. This surge is reflected throughout
the treatment unit as Figure 3 demonstrates.
The lower curve (contact chamber) is the sum of the two clarifier
curves. The wrong type of strip chart paper was used in the lower two
curves. The scale on all three charts should be the same as the top
curve (west clarifier).
Raw wastewater is repumped into each bay of the aeration basins
from a common header through separate butterfly valves. Any differences
in water surface elevation in either aeration basin produces a disproportion-
ate split in waste flow to the basins.
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES
Table 1 presents a chemical description of the activated sludge
plant influent and effluent with calculated average percent reductions.
The removal efficiencies were calculated using data from Stations 1-1
and E-l which were collected on a 24-hour proportional to flow composite
basis for the period February 9-12, 1976.
FLOW
TABLE 1
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES
THOMAS P. SMITH WTP
Parameter
Influent
Effluent % Reduction
B0D5 (mg/1)
COD (mg/1)
Suspended Solids (mg/l)
Total Solids (mg/1)
TKN-N (mg/1)
NH3-N (mg/1)
N03-N02-N (mg/1)
Total Phosphorus (mg/1)
Pb (yg/1)
152
333
70
454
23.3
18.9
.01
8.4
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I
12
11
10
9
8
7
6
5
4
3
2
1
I
2/9/76 2/10/76 2/11/76 2/12/76
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AM 3
AM 7
F/GUR£
FLnio <.t/p / f> r*///j a? h 3
6 PM 7
io P?.( n
SPARLING
EL MONTC. C^u.POitN.A
CHART S-SO
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TABLE 1 (Cont)
Parameter
Influent
Effluent
% Reduction
Cr (yg/1)
Cd (ug/1)
Cu (yg/1)
Zn (yg/1)
< 80
< 20
63
246
< 80
< 20
25
80
60
67
It is apparent from the data in Table 1 that nitrification was taking
place in the plant. Approximately one-half of the ammonia in the influent
was oxidized to nitrate-nitrite nitrogen. The remaining one-half was
discharged in the effluent. In plants where partial nitrification is
accomplished, special precautions must be taken in running and interpreting
the BOD^ results. Much of the oxygen demand in the BOD5 test may result
from the oxidation of ammonia. In these situations, nitrification can
be expected to exert a demand for the entire 5-day period rather than
exhibiting the characteristic 8-12 day lag time. The lag time is normally
required to build up an effective population of the relatively slow growing
nitrifying organisms. In plants where partial nitrification is accomplished,
an effective population of nitrifiers is already present in the sample.
Clair N. Sawyer^ stated that BOD tests run on the effluents of plants
accomplishing partial nitrification will have a considerable nitrogenous
BOD superimposed upon the small remaining residual carbonaceous BOD. He
also stated that "it is theoretically possible for plant effluents which
are in the so-called "incipient nitrification stage" to exhibit greater
5-day BOD values than those shown by the untreated sewages."
At the Thomas P. Smith plant, the average BOD5 of samples collected from
the two clarifier effluents (before chlorination) stations C-l and C-2
was 33 mg/1. The average results from station E-l (chlorine contact
chamber effluent) was 19 mg/1. This amounts to a 42 percent reduction
or 740 lbs/day of BOD5 at the average flow of 6.35 mgd. Chlorine application
during the study ran about 220 lbs/day. Assuming a one for one destruction
of BOD5 due to chlorine oxidation^ this leaves 520 lbs/day of BOD5 which
is apparently due to nitrification.
The samples collected from station E-l were reseeded with final
clarifier effluent. Each bottle contained 0.9 ml of clarifier effluent
per 300 ml. This volume evidently did not provide enough nitrifying
bacteria to provide significant nitrification.
In the clarifier effluent samples 10 and 25 percent dilutions for
the BOD5 test were set up. This gave 30 and 75 ml of clarifier effluent
per 300 ml sample bottle, providing a sufficient nitrifying bacteria r
population for nitrification to occur. The 10 and 25 percent dilutions
gave comparable values indicating that the additional bacteria in the
25 percent dilution did not further increase the oxygen demand due to
nitrification.
10
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The effects of nitrification on the BOD5 test can be avoided by
collecting effluent samples after chlorination (as shown by the results
of this study) or sterilizing the sample with heat and reseeding. The
degree of nitrogenous demand can be monitored and separated from the
carbonaceous demand by measuring the relative amount of ammonia and
nitrate-nitrite in the BOD bottles as the test progresses.
The trickling filter plant's efficiencies were determined using
samples from the influent and effluent station E-2. Analyses were made
on grab samples since there were periods of no flow from the trickling
filter plant. Table II lists an average of the data
on the influent and effluent with calculated percent reduction.
TABLE II
WASTE CHARACTERISTICS AND REMOVAL EFFICIENCIES
TRICKLING FILTER PLANT
Parameter
BOD5 (mg/1)
COD (mg/1)
Suspended Solids (mg/1)
Total Solids (mg/1)
TKN--N (mg/1)
NH3-N (mg/1)
N03-N02-N (mg/1)
Total Phosphorus (mg/1)
Pb (yg/1)
Cr (yg/1)
Cd (yg/1)
Cu (yg/1)
Zn (yg/1)
Influent Effluent % Reduction
152 22 86
333 60 82
70 11 84
454 332 27
23.3 9.0 61
18.9 5.6 70
<.01 8.4
8.4 7.5 11
<80 <80
<80 <80
<20 <20
63 25 60
246 68 72
11
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AERATION BASINS
During the study, the system x^as operated in the contact stabilization
mode. The plant had operated previously, with some success, in the conven-
tional "plug flow" configuration. Due to the development of a scum problem,
contact stabilization was initiated and the scum dissipated. Under contact
stabilization, the oxidative pressure on the waste is increased and the scum
is biodegraded.
Table III lists actual and recommended parameters for both the
conventional and contact stabilization process.
TABLE III
ACTUAL AND RECOMMENDED PARAMETERS FOR THE CONVENTIONAL AND
CONTACT STABILIZATION ACTIVATED SLUDGE PROCESS
Actual Recommended (5) (6)
Hydraulic Retention Time (hrs.)
Conventional Contact
Contact Basin
2.8
4-8
0.5-1
Stabilization Basin
7.4
3-6
Mean Cell Residence Time (days)
13.0
5-15
5-15
Sludge Age (days)
24.0
3.5-10
3.5-10
Lbs B0D5/day/lb MLVSS (F/M)
0.11
0.2-0.4
0.2-0.6
Lbs COD/day/lb MLVSS
0.25
0.5-1.0
Lbs BOD /day/1000 cu. ft.
25.0
20-40
60-75
Return Sludge Rate (% of average
design flow)
54.0
15-75
Average Flow (mgd)
6.35
7.5 (Des
Aeration and mixing in the basins were efficiently accomplished by
the 50 hp mechanical aerators. Dissolved oxygen concentrations of 2.0
mg/1 or greater were measured throughout the aeration basins with no dead
spots or solids blanket observed.
Solids concentrations in the aeration system were determined by
analyzing for suspended solids, volatile suspended solids and percent
solids by centrifuge. Settleability of the sludge was determined by the
sixty minute settlometer test (see Figure 4). Samples for these tests
were taken from the stabilization zone discharges (stations A-3 and A-4)
and from the contact zone discharge (Stations A-l and A-2).
Samples from the contact zone contained from 1,200 to 2,400 mg/1
total suspended solids. The varying solids concentrations are attributed
to the influent flow, i.e., samples in the afternoon had a lower total
suspended solids concentration since the flows were higher, effectively
diluting the solids. The solids settled rapidly with maximum compaction
attained in most cases in less than twenty minutes.
12
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FIGURE 4
SETTLOMETER TEST
NORTH BASIN
0)
a
p
r\
o
>
CD
M
X3
2
r~I
CO
13
CD
rH
+->
-P
CD
CO
\ Contact zone
v
X
s
-a.
¦-©-
10
100
South Basin
Nv Contact zone
""a.
s9.
- -0 __
-is
floated
0
5 10 15 20 25 30 35 40 45 50 55 60
TIME IN MINUTES
13
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OXYGEN UPTAKE RATES
The oxygen uptake rate is a measure of the general sludge activity,
i.e., the biodegradability of a particular waste by a particular activated
sludge. This activity is measured by mixing return activated sludge with
influent (fed) and nonchlorinated effluent (unfed) and determining the up-
take rates and calculating the load ratio.
Load Ratio =
&DO (ppm/min) fed sludge
A DO (ppm/min) unfed sludge
Details of the procedure and the significance of the test are presented
in Appendix B.
The following lists the oxygen uptake data and the calculated load ratio:
Date
Time
Station
% RS
2-10-76
1500
RS-2
63%
2-11-76
0830
A-3
36%
2-12-76
1400
A-3
36%
Average Oxygen Uptake
ppm/min ppm/min
URS^y
0.6
0.16
0.36
FRS
3/
1.1
0.35
0.60
Load
Ratio
1.83
2.23
1.67
1/ RS - Return Activated Sludge
2/ URS - Unfed Return Sludge
3/ FRS - Fed Return Sludge
On February 10, the return sludge sample was taken from the west
return sludge well (station RS-2). Since the plant was operated in the
contact mode, this sludge contained a large amount of undigested waste
which had been adsorbed in the contact tank. This was essentially a "fed"
sludge sample. On February 11 and 12, the activated sludge sample was
taken from the discharge of the stabilization zone where the organisms had
completely digested the adsorbed waste (Station A-3). Although the load
ratios are fairly consistent, the uptake rates show significant difference.
This is most likely due to the different concentrations of solids in the
activated sludge and the one supposedly "unfed" sample which actually con-
tained a considerable amount of food. Calculated load ratios indicate a
well acclimated sludge and a readily biodegradable waste.
Clarif iers
Clarifier effluent turbidity ranged from 6.5 to 9.0 nephelometric
turbidity units (NTU) based on grab samples collected each day. Occasional
clumps of rising sludge deteriorate the aesthetic and physical quality of
the effluent. This condition is caused by sludge collecting under the
influent troughs and weir pans, becoming septic, and rising to the surface
to flow over the weir. The problem is more severe when the plant is opera-
ted in the contact mode, since the settled sludge becomes septic rapidly
and tends to rise to the surface.
14
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Denitrification in the contact zone samples, with the resultant
floating of the sludge, occurred in AO to 75 minutes. Deoxygenation
of the sludge occurs very rapidly in the clarifier when using the contact
stabilization mode of operation. The operators must maintain close con-
trol on the return sludge rate to prevent denitrification and rising
sludge in the clarifier.
Samples taken from the stabilization zone had a fairly consistent
suspended solids concentration of 4,200-4,500 tng/1. Denitrification
occurred and the solids floated to the surface in 80 to 90 minutes. Ob-
servations of the settlometer indicated that the sludge settled slower,
leaving a much clearer supernatant, indicating that conventional plug
flow would likely produce a better effluent than contact stabilization.
Plug flow would also slow down denitrification of solids in the clarifier
and make for generally easier operation.
If a scum problem reappears, the contact mode has been proven effective
in correcting the problem at this plant. Other modes of operation, such
as step feed,(feed waste into number 2, 3, and 4 bays) may be effective in
controlling scum and should also produce a good effluent.
Food to microorganism ratios (F/M) using BOD^ and COD concentrations
were calculated using the total pounds of volatile suspended solids in the
aeration system. The BOD5 F/M ratio was 0.11 and the COD, F/M ratio was
Q.25. These ratios are about half the recommended minimums.^
Motorized automatic butterfly valves on the raw waste lines feeding
the aeration basins were inoperative. The valves could not be maintained
in a partially open position. For step feed operations, it is essential
to be able to operate the individual valves and make exact settings. Prop-
er operation of the valves would also help to prevent uneven splitting of
flow into the basins.
15
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The clarifiers were designed for an overflow rate of 590 gal/day/
ft^ at the design flow of 7.5 mgd and a weir overflow rate of 9,375 gal/
day/ft (14,600 gal/day/ft without weir pans). The actual and recommended
hydraulic loading, solids loading, and weir overflow rates for final
clarifiers following activated sludge wastewater treatment are presented
in Table IV.
TABLE IV
ACTUAL AND RECOMMENDED PARAMETERS FOR SECONDARY CLARIFIERS
Actual Recommended (2)(3)(6)
Hydraulic Loading (gpd/ft^) 480 400-800
Solids Loading (lbs/day/ft ) 120 20-30
Weir Overflow Rate (gpd/ft) 7,700, 12,000* <15,000
Hydraulic Detention Time (hrs.) 5 2-3
*Extra weir length due to weir pans not included
Calculations in Table IV are based on an average flow of 6.35 mgd.
From Figure 2 it can be seen that a sustained flow of approximately
8 mgd occurs each day. This flow is only slightly above the average
design flow of 7.5 mgd and does not produce overloading. Maximum peak
flow during the study was 12 mgd caused by irregular pump cycling.
This produced a weir overflow rate of 12,300 gpd/ft or 19,000 gpd/day/ft^
not considering the extra weir length due to weir pans. These loading
rates should not present any problems; however, the flow surging in
the clarifiers due to pumping may cause problems.
As mentioned above, the weir pans provide several additional feet
of weir length and are some improvement over the single peripheral weir.
However, the additional weir length is not equivalent to the same length
of peripheral weir. Approach velocities to the weir are the critical
factor. A small volume of dye was added to the west clarifier influent
to determine flow patterns and distribution in the clarifier. The dye
was added at 1340 hours on February 11, 1976 when the clarifier was
receiving a waste flow of 3.75 mgd (7.5 mgd for both clarifiers).
Samples were collected at the clarifier effluent and results are shown
in Figure 5. The first traces of dye appeared in the effluent in 20
minutes with a peak concentration in 45 minutes. The centroid of the
dye curve appears to be between one and two hours. This point (centroid)
represents the average detention time in the clarifier. Visual observa-
tions indicated that the dye was well dispersed throughout the entire
area of the clarifiers. The average detention time as measured by the
dye study approaches the recommended detention time.
16
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Researchers (2) have shown that the rim feed, rim take-off clarifier
generally performs better than the center feed clarifier. Similar
dye studies conducted on a number of clarifiers by the EPA team indicate
that the flow distribution in the west clarifier is better than in most
clarifiers observed.
DISINFECTION
Disinfection of the treated wastewater was accomplished by the
injection of chlorine gas at the entrance to the contact chamber. At
an average dosing rate of 220 lbs/day, an average residual of 2.48 mg/1
was observed at the overflow weir. Automatic chlorine feed and monitor-
ing equipment is being installed and should provide better chlorine
control.
DIGESTERS AND DRYING BEDS
The two aerobic digesters are operated on a fill and draw basis.
Normally waste sludge is pumped to each digester once or twice per day.
The procedure takes approximately two hours. First, the fixed surface
aerator in the digester is shut off and the sludge is allowed to settle.
Then approximately 20 inches of supernatant is drawn off and returned
to the on-site lift station. Waste activated sludge is then pumped
to the digester to bring the water surface up to operating level and
the aerator restarted.
Sludge is discharged on drying beds or spread on the plant site.
A centrifuge unit is available for sludge dewatering, but has not been
used.
LABORATORY
The laboratory is well organized and has many analytical capabilities.
The facility serves as a central laboratory, performing analyses for all
Tallahassee water and sewerage facilities. The staff included a chief
chemist, one biologist arid three laboratory technicians.
In general, analytical techniques were good. In the BODr test,
however, the routine procedure at the time of the study for chlorinated
samples was to dechlorinate without reseeding. It was suggested by
EPA personnel that seeding be performed per "Standard Methods for the
Examination of Water and Wastewater", 13th Edition, 1971. At the
conclusion of the study, plant personnel were adding this step to their
routine procedure.
18
-------
REFERENCES
1. "Process Design Manual for Suspended Solids Removal", US-EPA
Technology Transfer, January 1975.
2. "Process Design Manual for Upgrading Existing Wastewater Treatment
Plants", US-EPA Technology Transfer, October 1974.
3. "Sewage Treatment Plant Design", American Society of Civil Engineers,
Manual of Engineering Practice No. 36, 1959.
4. "Standards for Sewage Works", Upper Mississippi River Board of
State Sanitary Engineers, Revised Edition, 1971.
5. "Wastewater Engineering", Metcalf and Eddy, Inc., 1972.
6. "Operation of Wastewater Treatment Plants", A Field Study Training
Program, US-EPA, Technical Training Grant No. 5TT1-WP-16-03, 1970.
7. "Standard Methods for the Examination of Water and Wastewater",
13th Edition, 1971.
8. "Modernization of the BOD Test for Determining the Efficiency of
Sewage Treatment Processes", Sawyer and Bradney, Reprinted from
Sewage Work Journal, Vol. XVIII, No. 6, November, 1946.
19
-------
APPENDIX A' .
LABORATORY DATA
THOMAS P. SMITH| WTP
TALLAHASSEE, FLORIDA
Influent and Effluents
-------
APPENDIX A ' (continued)
LABORATORY DATA
THOMAS P. SMlTII WTP
TALLAHASSEE, FL
Effluents (continued)
-------
APPENDIX A- (contlct)
LABORATORY DATA
TH.OMAS P. SMITH ij/TP
TALLAHASSEE. FLQRIDA
Aeration Basins
-------
APPENDIX A (cont'd)
LABORATORY DATA
THOMAS P-. SMITH WTP
TALLAHASSEE, FLORIDA
Aeration Basins (continued)
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APPENDIX A'(continued)
LABORATORY DATA!
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-------
APPENDIX A- (con-CId)
LABORATORY DATA
¦THOMAS P. SM'ITH WTP
TALLAHASSEE, FLORIDA
Return Sludge and Aerobic Digestors
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-------
Appendix B
GENERAL STUDY METHODS
To accomplish the stated study objectives, extensive sampling was
conducted, physical measurements taken, and daily observations recorded
during the study.
Automatic ISCO samplers, Model 1392-X, were installed on the plant
influent, activated sludge plant effluent, trickling filter plant effluent,
and polishing pond effluent (stations 1-1, E-l, E-2, and E-3, respectively)
to sample for three 24-hour periods. Aliquots of sample were pumped at
hourly intervals into individual glass bottles on ice which were composited
proportional to flow at the end of each sampling period. Twenty-four
hour composite samples were collected by plant personnel, from stations
C-l and C-2 by pouring equal volumes of hourly grab samples into an
insulated sample container.
Flows were determined from totalizer readings on the main plant
control panel. Additional instantaneous flows were acquired by measuring
the head on each individual flow device. A Stevens Model F stage recorder
was installed at the effluent of the chlorine contact chamber serving the
activated sludge unit to check totalizer and flow chart accuracy.
A series of standard operational control tests were run daily. These
tests consisted of:
e Sludge settleability as determined by the settlometer test;
o percent solids by centrifuge determined on the reaeration and
contact basins, return sludge and aerobic digester;
© TSS and VSS analysis on the reaeration and contact basins,
return sludge and aerobic digester;
c turbidity of the effluent from the activated sludge section;
e depth of clarifier sludge blanket.
Dissolved oxygen was determined at all sampling stations using a
YSI model 51A dissolved oxygen meter.
The BOD^ test deviated from standard procedure. The samples were
set up at the study site and then transported, within the -mobile laboratory
incubator, to Athens, Georgia. The samples were then removed from the
mobile laboratory and placed in an incubator at the Athens facility. The
time of travel was 7 hours and the temperature at arrival was 20.5°C.
26
-------
(the temperature was measured using a calibrated thermometer placed in
a BOD bottle of distilled water and incubated along with the samples.)
Sludge activity was determined using the. oxygen uptake procedure
presented in Appendix C. The oxygen uptake rate for fed and unfed sludge
was determined and a load factor was calculated. The load factor reflects
the conditions at the beginning and end of aeration and is helpful in
assessing sludge activity for plant operation.
. All chlorine residuals were determined using the Fisher and Porter
Model 17T1010 amperometric titrator.
Physical observations of individual unit processes were recorded
daily.
The mention of trade names does not constitute endorsement or
recommendation by the EPA.
27
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APPENDIX C
OXYGEN UPTAKE PROCEDURE 8
A. Apparatus
1. Electronic DO analyzer and 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 (ADO/min). Check the final sample temperature.
This approximates sludge activity in terms of oxygen use
after stabilization of the sludge duripg aeration (unfed
sludge activity).
28
-------
Appendix C (cont'd)
7. Repeat steps 2 Lhrough 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 ]arge
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."
(8) 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.
29
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APPENDIX D
DESIGN DATA
THOMAS P. SMITH WASTEWATER TREATMENT PLANT
TALLAHASSEE, FL
DESIGN FLOWS
Average 7.5 mgd
SPRING HILL ROAD LIFT STATION
Pumping capacity - 3, two speed 150 hp pumps
Bar screen - 2 inch centers, manually cleaned
Chlorination - 200 lbs. high flow, 50 lbs. low flow
Bar screen - manually cleaned
INFLUENT UNITS
BAR SCREEN
Bar screen on 2 inch centers, mechanically cleaned
equipped with belt conveyor
AERATED GRIT CHAMBER
Dimensions
Length - 36 ft.
Width - 14 ft. 2 inches
Depth - 9.5 ft.
Mechanically cleaned - screw conveyor for transfer to
trash container
Aerated - 7 1/2 hp blower
PLANT FLOW MEASURING DEVICES
Influent - 3 ft. Parshall flume with recorder and totalizer.
Aeration tank influent - magnetic meter with totalizer and
recorder.
Clarifier effluents - individual propeller meters with
totalizer and recorder.
Return activated sludge - propeller meter with dial flow
control and totalizer.
A/s effluent (chlorine contact chamber) - 4 ft. rectangular
weir with totalizer and recorder.
Sludge wasting - propeller meter with totalizer.
Trickling filter effluent - 1 ft. Parshall flume with
recorder and totalizer.
30
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APPENDIX D
(CONTINUED)
STABILIZATION BASINS
Number - 2
Dimensions
Length (inside) - 162 ft.
Width (inside) - 54 ft.
Depth - 13.5 ft.
Volume - 115,832 ft.3, 869,000 gal.
Detention time - w/50% return sludge - 3.8 hrs.
Aerators - 3 fixed 50 HP surface each basin
CONTACT BASINS
Number - 2
Dimensions
Length - 54 ft.
Width - 54 ft.
Depth - 13.5 ft.
Volume - 38,300 ft.3, 287,000 gal.
Detention time - 2/50% return sludge - 1.3 hrs.
Aerator - 1 fixed 50 HP surface each basin
CLARIFIER
Number - 2 circular, rim-feed, rim take-off
Dimensions
Diameter (Inside) - 90 ft.
Depth - 13.4 ft.
Surface Area - 6,358 ft.
Volume - 85,204 ft.3, 639,000 gal.
Weir length with pans - 400 ft.
without pans - 258 ft.
Weir overflow rate - with pans - 9,375 gal/day/ft.
without pans - 14,565 gal/day/ft.
Detention time - 50% return sludge - 2.7 hrs.
Surface loading - 590 gal/day/ft. -J
DIGESTORS - 2 circular aerobic basins
Dimensions
Diameter - 80 ft.
Depth - 16.7 ft.
Volume - 83,900 ft.3, 629,000 gal.
Aerator - Fixed surface - 1,100 hp
CHLORINE CONTACT CHAMBER
Dimensions
Length - 52.8 ft.
Width - 50 ft.
Depth - S ft.
Volume - 21,120 ft.3, 158,000 gal.
Detention time - 0.5 hrs.
31
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APPENDIX D
(CONTINUED)
RETURN SLUDGE PUMPS
Number - 4, 75 hp variable speed
Capacity - 5,250 gpm
Sludge recirculation - 0-100%
SLUDGE DRYING BEDS
Number - 12
Dimensions
Length - 450 ft.
Width - 250 ft.
Total area - 112,500 ft.
32
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