S&A-TSB-21
TECHNICAL ASSISTANCE PROJECT
VAIL WASTEWATER TREATMENT FACILITY
VAIL, COLORADO
MARCH - APRIL, 1973
.ECHNICAL SUPPORT BRANCH
SURVEILLANCE AND ANALYSIS DIVISION
U. S. ENVIRONMENTAL PROTECTION AGENCY
REGION VIII
-------
TABLE OF CONTENTS
SECTION PAGE NUMBER
I. INTRODUCTION 1
II. DESCRIPTION OF PLANT 1
A. BACKGROUND 1
B. PLANT FACILITIES 2
III. SUMMARY OF LABORATORY ASSISTANCE 4
IV. SUMMARY OF OPERATIONAL ASSISTANCE •• 6
A. CONTROL TESTING 6
B. PROCESS MODIFICATIONS 7
C. PERFORMANCE RESULTS 18
V. SUMMARY AND CONCLUSIONS 22
VI. RECOMMENDATIONS 25
-------
LIST OF FIGURES
FIGURES PAGE NUMBER
1. PLANT FLOW SCHEMATIC 3
2. TURBIDITY VS TIME 19
3. EFFLUENT BOD5 VS TIME 21
4. PERCENT REDUCTION OF BOD5 VS TIME 23
-------
I. INTRODUCTION
On September 14, 1972 Region VIII of the Environmental Protection Agency
(EPA), received a letter from the Colorado Department of Health requesting
assistance concerning the operation of the Vail Wastewater Treatment Facility.
An initial evaluation of the Vail plant was made on October 26 and 27, 1972.
Various plant deficiencies were observed during the initial evaluation and
recommendations were made to correct the observed problems. After the plant
had been modified a formal technical assistance project was initiated on
March 19, 1973.
The first objective of the assistance project was to improve effluent
quality from the Vail facility by initiating a series of operational control
tests and analyses. In addition, those portions of the facility which hindered
or limited successful operation were to be identified. This report summarizes
the results and findings of the technical assistance project and proposes
several recommendations for future consideration at the Vail plant.
II. DESCRIPTION OF PLANT
A. BACKGROUND.
Vail .and the surrounding area is provided wastewater treatment by two
separate Sanitation Districts. The Vail Sanitation District (VSD) serves
primarly the Town of Vail and discharges its effluent into Gore Creek. The
Upper Eagle Valley Sanitation District (UEVSD) serves localities upstream
(The Big Horn Area) and downstream of the Town of Vail. The UEVSD discharges
its effluent to the Eagle River downstream of the confluence of the River
with Gore Creek.
-------
Since a portion of the area served by the UEVSD is located upstream of
the Vail facility, an agreement between the two districts was reached pro-
viding for a portion of Vail's collection lines to be used by the UEVSD to
transport sewage to the Upper Eagle treatment plant.
Flow from the Big Horn area is measured prior to entering the Vail
interceptors. This flow is transmitted to the Vail plant along with sewage
from Vail. At the Vail facility the flow is split and an amount approxi-
mately equal to that flow measured from the Big Horn area is directed to the
UEVSD plant. Vail is required to pay the UEVSD for all wastewater sent to
the UEVSD plant in excess of that measured at the Big Horn metering station.
It is noted that the interrelationship that exists between the plants pro-
vides a means to adjust flows to a desired quantity between the two facilities
and therefore must be considered an important operational tool.
B. PLANT FACILITIES
Figure 1 shows the plant flow schematic for the Vail Wastewater Treat-
ment facility. A brief discussion of each unit and its interrelationship
with other units is described below.
Flow enters the plant and is directed through a parshall flume, bar
screen, and grit channel before entering the aeration basins. Flow may enter
the aeration basins at the head end, near aerator #3, half way down, near
aerator #2, or at the far end of the basin, near aerator #1. A concrete wall
is located near the end of the aeration basins, and physically separates
aeration basin #1 from basins #2 and #3. During the initial EPA evaluation
made at the Vail plant it was recommended that an opening be provided in the
wall between basin #1 and basins #2 and #3 to allow for series operation.
-------
grit channel and
grease removal
FIGURE 1
TECHNICAL ASSISTANCE PROJECT
VAIL WASTEWATER TREATMENT FACILITY
VAIL, COLORADO
MARCH-APRIL, 1973
PLANT FLOW SCHEMATIC
parshall flume
waste sludge pump
polymer feed tank
sludqe to incinerator
T or landfill
grease separation I
screen ^ I
return sludge
pumps
ickened i I i
udge |_J floatation
± 1 1 unit
:al
clarifiers
(scum
separation
zone)
-------
Dissolved oxygen is introduced and mixing is provided in the aeration
basins by three fixed surface mechanical aerators. After flow passes through
the aeration basin it is directed to two rectangular final clarifiers. Flow
to the clarifiers may be varied by manually adjusting the inlet gates. The
clarifier effluent is chlorinated and discharged to Gore Creek.
Both final clarifiers are separated into two zones, a scum separation
zone and overflow zone. Once each day, the scum is drawn off the front
portion of the final clarifier, screened and incinerated. Settled sludge
in the clarifiers is pulled by scrapers back to the head end of each clar-
ifier. Sludge is removed from the clarifiers through four telescoping valves
and is collected in a return sludge wet well. Return sludge flow rates are
varied by adjusting the height of the telescoping valves. Sludge may be
returned directly to aeration basin #3 or can be returned to the influent
sewage channel.
Excess activated sludge is removed from the process (wasted) to a
flotation type thickening unit. Polymer addition is used to affect the
separation and flotation of the waste activated sludge. Thickened sludge
is held in a storage tank and then dewatered on a vacuum filter. The filter
cake can be either incinerated or buried. Supernatant from the sludge
thickener and vacuum filter is recycled to the aeration basins.
III. SUMMARY OF LABORATORY ASSISTANCE
The major emphasis of the assistance project was to improve plant
operational control and effluent quality. In addition, plant personnel
were taught the procedures used in collecting, storing, and analyzing
samples for the biochemical oxygen demand (BOD^) and suspended solids tests.
-------
Prior to the assistance project, plant personnel at Vail had infrequently
collected grab samples of plant influent and effluent (prior to chlorination)
and had performed a BOD^ analysis on these samples using a proprietary method.
Attempts were also made to conduct suspended solids analysis on these samples;
however, adequate laboratory equipment was not available at the Vail plant.
During assistance all plant personnel were taught the proper techniques used
to collect, composite and store treatment plant influent and effluent (prior
to chlorination) wastewater samples. Both influent and effluent samples were
collected every two hours through the operational day (i.e. 8:00 am to 10:00
pm). No attempt was made to composite the samples proportional to flow.
Samples were stored in a refrigerator until the following day.
Suspended solids and BODg analyses were performed on the composited
influent and effluent samples. Due to the nature of these analyses, the
emphasis on plant operational controls, and the limited number of plant oper-
ators at the facility only two plant operators were given insturctions in
the procedures used to run the 8005 and suspended solids analyses. Both
operators were taught the proper techniques required to analyze wastewater
samples for BOD5 using the cylinder dilution technique as outlined in
Standard Methods for the Examination of Water and Wastewater (1). Instruction
was also given in determining the dissolved oxygen concentrations in the BOD^
analysis using the azide-modification to the dissolved oxygen method again
as listed in Standard Methods. The techniques used in conducting the
suspended solids analysis using the gooch crucible and glan fiber filter method
as listed in the manual entitled Operation of Wastewater Treatment Plants (2)
was also explained to the operators.
-------
As a result of the laboratory assistance all personnel at the Vail plant
are capable of properly collecting, compositing and storing wastewater samples
for the BOD5 and total suspended solids analyses. Two operators are capable
of properly performing the BODg and total suspended solids analyses.
Conducting the laboratory tests; however, placed an additional respon-
sibility on the Vail plant operators. In order to release the plant operators
to do their other tasks and to provide for consistent laboratory data it is
suggested that additional personnel be hired to perform primarily the laboratory
functions. Consideration should also be given to sharing such a laboratory
technican with the Upper Eagle Wastewater Treatment Facility.
IV. SUMMARY OF OPERATIONAL ASSISTANCE
A. CONTROL TESTING
In addition to instruction in conducting various laboratory tests, plant
personnel were given instruction in conducting and interpreting various "control"
tests. Centrifuge tests, turbidity, settleability tests, and sludge blanket
depth were the control tests that were initiated. All except the settleability
tests were conducted seven times per day seven days a week during the project.
The settleability tests were conducted twice a day seven days a week.
Centrifuge tests were used to determine variations in solids concentrations
from day to day. Tests were conducted on samples of mixed liquors taken at the
discharge end of the aeration basin and on samples of return sludge. The centri-
fuge test values are expressed in percent solids by volume. Although it is not
necessary for control, a correlation between percent solids by volume and solids
by weight was made. The results of this correlation indicated that during the
-------
project one percent by volume was approximately equal to 690 mg/1 by weight.
This correlation will vary as the characteristics of the sludge vary. For this
report all solids concentrations by weight were determined by using the corre-
lation of one percent by volume equal to 690 mg/1 by weight.
Turbidity tests were performed on samples of the effluent from the final
clarifier. In all cases attempts were made to exclude any solids in the samples
since test results were used to monitor the performance of the actived sludge
process (i.e. the ability of the activated sludge to convert colloidal and
dissolved BOD^ to sludge solids).
Settleability tests were conducted on samples of the mixed liquor collect-
ed at the discharge end of the aeration basins. Settleability tests were used
to monitor and observe sludge settling characteristics.
Sludge blanket depth determinations were made on the final clarifiers.
Results were used to monitor changes in the depth of the blanket and to deter-
mine the amount of sludge that was accumulating in the final clarifier.
Data obtained from the various control tests were used to perform cal-
culations and develop various graphs. The calculations and graphs were used
to interpret plant performance and control plant operations. Since the termi-
nation of the Federal assistance project, Vail has purchased the equipment
necessary to run the control tests and are using these tests to control plant
operations.
B. PROCESS MODIFICATIONS
Many process modifications were made at the Vail Wastewater Treatment
Facility as a result of the technical assistance effort. These modifications
are outlined below:
-------
A major deficiency which limited plant flexibility was noted during the
October 26 and 27, 1972 on-site evaluation survey. The plant could not be
operated in a "contact stabilization" mode nor could effective use of all the
aeration basins be provided if the plant was operated in a "conventional" mode.
The location of the opening in the concret wall which separates aeration basin
#1 from aeration basins #2 and #3 allowed flow from these basins to be directed
only to the final clarifiers. In order for the plant to be operated in the
"contact stabilization" mode the effluent from basins #2 and #3 should have been
directed to basin #1, the contact zone. For the plant to be operated in the
"conventional" mode all the sewage had to be entered into basin #3. However, if
all the sewage were entered into aeration basin #3, basin #1 could not be used,
thereby eliminating one third of the aeration capacity.
To eliminate the inadequacies posed by the concrete wall it was recommended
that a second opening be placed in the concrete wall to enable flow from basins
#2 and #3 to pass directly to basin #1. Plant personnel acted on this recommen-
dation and a second opening in the wall was made prior to the beginning of the
formal technical assistance project.
In order to discuss process modifications made during the formal technical
assistance project it will be necessary to briefly outline operation of the
plant prior to assistance. It is noted that approximately one week before
assistance began significant process control changes were made. These changes
are also outlined.
Using the new opening in the concrete wall, the Vail facility was operating
in the "contact stabilization" mode. The major empahsis of plant operation was
to control bulking and thereby eliminate the numerous citizen complaints that
-------
were received when bulking did occur. As a result of this operational emphasis
little sludge bulking occurred; however, plant effluent quality was not
completely satisfactory. The method used by plant operators to stop the
bulking sludge was to decrease the return sludge flow rate (i.e. raise the four
telescoping valves). Since the mode of plant operation at that time was contact
stabilization the decreased return sludge flow rate served to decrease the quan-
tity of sludge entering the re-aeration zone (basins #2 and #3) and thereby
decrease the suspended solids being "displaced" to the contact zone. This
decrease in "displacement" of solids resulted in a. decrease in the mixed liquor
suspended solids concentration (MLSS). The decreased MLSS concentrationrin the
contact zone resulted in a lower solids loading to the final clarifiers and had
the short term effect of stopping the sludge bulking. Plant effluent quality
continued to be unsatisfactory; however, due to the larger quanities of
colloidal and dissolved BODs in the effluent caused by the inability of the
lower concentrations of sludge in the contact zone to effectively convert BODg
to sludge solids. The practice of decreasing the return sludge flow rate at
Vail in order to eliminate sludge bulking without considering other factors in
plant operations such as sludge wasting, long term effects, aerator operation,
etc., was unsatisfactory.
During the week before the assistance project a second factor, the volume
of sludge wasted, was used as a means of controlling plant operation and speci-
fically the sludge bulking problem. During this week the volume of sludge to be
wasted was determined as a percentage of the volume of sewage flow received at
the plant and was wasted irrespective of the waste sludge solids concentration.
Using this approach, large quantities of sludge were wasted during this week,
March 12-17, 1973. As the wasting was substantially increased, the return
-------
sludge flow rate was for the most part set at a low flow rate and maintained.
This combination of large quantities of sludge wasted and low return sludge
flow rates greatly reduced the MLSS concentration in the contact zone of the
contact stabilization process. At the beginning of the assistance project the
MLSS concentration in the contact zone had decreased to about 1000 mg/1. This
low MLSS concentration in the contact basin greatly reduced the solids loading
to the clarifier and no problems with sludge bulking occurred; however, plant
effluent quality was unsatisfactory. Colloidal and dissolved BODs remained in
the effluent because the low concentration of sludge in the contact zone was
inadequate to convert this BOD to removable sludge solids. The practice of
controlling the quantity of sludge wasted and not adjusting the rate of return
sludge flow also proved to be an unsatisfactory mode of operation.
At the beginning of the assistance project plant effluent quality was
unsatisfactory. No problems with sludge bulking occurred, but large quantities
of colloidal and dissolved 6005 were present in the plant effluent (effluent
turbidity was about 20 JTU). The major emphasis at this point of the assistance
project was to increase the MLSS concentration in contact with the sewage.
Operational flexibility at Vail enabled the plant to be operated in either of
three different modes of operation; contact stabilization, step loading, or
conventional. Prior to formal assistance and after the opening between aeration
basins #2 and #3 and basin #1 has been provided, the plant has been operated in
the contact stabilization mode. The advantages of this mode of operation are
claimed to be decreased plant upsets due to wide variations in hydraulic load
and decreased operational controls required because of the relative insensitivity
to changing hydarulic loads.
At the beginning of the assistance project the plant mode of operation
10
-------
was changed from contact stabilization to conventional. The change was made
primarily to take immediate advantage of the sludge solids that were "stored"
in the re-aeration zone (basins #2 and #3). For example the suspended solids
concentration in the contact zone was about 1000 mg/1 and the suspended solids
concentration in the re-aeration zone was about 5000 mg/1. By distributing
these solids throughout the system a desirable MLSS concentration of about
2700 mg/1 throughout all the basins was achieved. In addition to the MLSS
increase, the sewage detention time in the aerators also increased from about
7.3 hours to 21.9 hours (average flow of 1,703 cu m/day(450,000 gal/day).
Immediately after the change in the mode of operation sludge bulking
occurred for approximately four days. Reasons for the bulking were high solids
loading to the clarifiers and a relatively young and undeveloped sludge that
exhibited poor settling characteristics. During this bulking period, every
attempt was made to minimize solids lost and allow time for the settling
characteristics of the sludge to improve. Close control over the return sludge
flow rate was provided and the volume of sewage received at the plant was
reduced by diverting flow to the Upper Eagle facility. After four days of
maintaining the relatively high MLSS concentration coupled with a longer sewage
detention time in the aerator, the settling characteristics as well as the
removal characteristics of the sludge began to improve; (i.e. turbidity decrease
from 20 JTU to 5 JTU).
The volume of sewage received at Vail prior to the assistance project was
approximately 2,650 cu m/day(700,000 gal/day). During the four day period when
problems with sludge bulking occurred the volume of flow received at Vail was
reduced to about 1,628 cu m/day(430,000 gal/day). When the sludge began to
settle better the flow rate to Vail was increased by 379 cu m/day(100,000 gal/day)
11
-------
Additional flow was not accepted at Vail because of problems encountered with
the operation of the final clarifier and continued sludge bulking. It should
be pointed out that the ability to decrease the sewage flow to the Vail
facility during the troublesome period greatly reduced the total pollutional
load to the receiving stream and was a significant factor in maintaining a
required high MLSS concentration. This interrelationship between the Vail plant
and the Upper Eagle plant must continue to be used as an operational tool in
future difficulties with either plant.
Numerous problems were encountered with the final clarifiers and attempts
to improve their performance were attempted. The effect of poor clarifier
performance was to allow solids to be lost in the plant effluent and although
effluent quality was significantly improved it never reached an optimum because
of the clarifier performance.
The major problem with the final clarifiers at Vail was inadequate control
over flow splitting to the two clarifiers. Flow to the clarifiers was adjusted
by opening or closing rectangular inlet gates. These adjustments; however,
were not precise enough to attain equal flows to each clarifier. Also, rags
and other debris would routinely clog the gate openings. High flow would be
directed to one clarifier causing sludge bulking in that clarifier while the
other clarifier would maintain a deep sludge blanket. Many different methods of
splitting the flow equally to each clarifier to include using a butterfly split-
ter, 2x6 boards, etc., were tried to eliminate the splitting problem. However,
all the methods tried required that the plant operators adjust and control the
flow to each clarifier and balance the sludge blanket depth. Problems occurred
during the night when plant operators were not on duty. Unequal flow to the
clarifier continued unchecked and solids bulked over one or the other clarifier.
12
-------
Major modifications to the Vail plant must be made in order to control
adequately flow splitting to the two clarifiers. These modifications should
provide for positive direct control over the flow to each clarifier. An
intermediate solution would be to provide 24-hour operation so that the plant
operators can make the necessary adjustments to prevent solids losses during
the night.
The other major problems with the final clarifiers at Vail resulted from
inadequate design features. The clarifiers are rectangular in shape and are
separated into two zones. The first zone is a scum flotation zone where grease
and other floating material is removed. The second zone is a weir overflow
zone where the effluent weirs are located. Flow in the final clarifiers is
directed through the scum removal zone to the overflow weir zone and discharges
to the chlorine contact basin. The settled sludge in the clarifier is pulled
countercurrent to the flow back to the head end of the clarifier and returned
to the aeration basins. These countercurrent flow patterns have a tendency to
create shear stresses in the sludge blanket and cause lower return sludge
concentrations than would normally be expected, especially because of the
shallow depth of the clarifier (approximately 9 feet). A through investi-
gation of the proposed shear stresses in the final clarifier was not made,
however, the effects of the stresses were observed in the results of the control
tests. A method to correct the inadequate design features of the final clarif-
iers would be to complete major modifications (i.e. deeper clarifiers, co-
current sludge removal, etc.). A second and more immediate method would be to
reduce the flow to the clarifiers. Reduced flow would reduce the effects of the
shallow depth and countercurrent flows. It is recommended that the second
approach to reduce the flow to the final clarifiers, be considered. The maximum
13
-------
volume of flow these clarifiers are capable of accepting should be determined
by a trial and error procedure.
Another problem encountered with the clarifiers at Vail was caused by a
series of baffles that had been installed in the clarifiers. Four baffles had
been placed in each clarifier with the intent of keeping the majority of the
settled sludge in the head end of the clarifier. In actuality the baffles
increased the flow velocity past each baffle (the cross-sectional area of the
clarifier was decreased at that point) and hindered the settling of the
activated sludge flow. Also/ each baffle acted like a hydraulic "barrier" to
inhibit pulling the sludge back to the head end of the clarifiers. The result
of these "barriers" was to force sludge to accumulate in the weir overflow
section of the clarifiers and aggravate the sludge bulking problems. The
baffles were removed and the sludge bulking problem was reduced substantially.
During the assistance project, various other modifications to plant operation
were made and recommendations for future modifications were given. Modifications
to control the return sludge flow rate, control of the waste sludge operation,
measurement of the return sludge flow rate, measurement of the waste sludge
flow rate, control of the aerator operation, and control of the waste sludge
thickening unit were made during the assistance project. Suggestions for future
modifications to control the vacuum filter operation were also made. Each of
these modifications are briefly discussed in this report.
The modification to controlling the return sludge flow rate involved drastic
changes in the operators approach. Prior to the assistance project, the rate of
return sludge flow was varied to control sludge bulking. This approach was in-
adequate. During assistance, the return sludge flow rate varied throughout the
day as the incoming flow rate varied and was varied from day to day based on
14
-------
results of the control tests. Direct control over the rate of return sludge
flow was maintained and positive control over plant operation from this stand-
point was achieved.
Modifications to procedures for wasting excess activated sludge were
made. A method of determining the quantity of sludge to be wasted and a change
in the location of the sludge wasting draw off point were initiated. Prior to
the assistance project the quantity of sludge to be wasted was not used as
a tool for plant operation. A specific volume of sludge was wasted each day
based on the influent flow rate. Since this volume was wasted irrespective of
its solids concentration the quantity of sludge wasted could vary significantly
and drastically change the quantity of sludge in the activated sludge system.
During assistance the quantity of sludge wasted was determined based on the
results of the control tests. Both the volume and concentration of sludge wasted
was included in the calculations. Using this method, complete control over the
quantity of sludge in the activated sludge system was achieved disregarding the
uncontrolled sludge bulking problems that existed. The location of the sludge
wasting draw off point had to be changed after the plant mode of operation was
switched from contact stabilization to conventional. Prior to assistance, sludge
was wasted from aeration basins #2 and #3, the re-aeration zones of the contact
stabilization mode of operation. After the mode of plant operation was changed
to conventional the mixed liquor from aeration basins #2 and #3 was too thin
for wasting. Initially attempts were made to waste return sludge using the
return sludge pumps. This method resulted in decreasing the rate of return
sludge flow to the head end of the aeration basins and an alternative method of
sludge wasting had to be provided. An alternative method was provided by
modifying the separate waste sludge pump piping arrangement so that return
15
-------
sludge could be directed to the separate waste sludge pump and wasted without
disrupting the return flow to the head of the aeration basins.
Measurement of the return sludge flow rate was initiated by developing a
flow chart for the four telescoping return sludge valves. Prior to assistance
the four telescoping valves had been adjusted to control the rate of return
sludge flow; however, the volume of sludge returned was not determined. No
return sludge flow meters are provided at the Vail facility. During assistance
an indication of the rate of flow of return sludge was made by determining the
time required to fill a specific volume in the return sludge wet well and
calculating the corresponding flow rate. Flow rates were determined for various
settings of the telescoping valves and a graph showing the telescoping valve
setting versus the flow rate was developed. This method of determining the
rate of return sludge flow is satisfactory as an interim measure. It is
recommended that future plant modifications include a return sludge flow meter
in order to attain more precise return sludge flow measurements.
A method of measuring the waste sludge flow rate was also initiated. A
waste sludge flow meter is provided at Vail, but was not calibrated properly
at the time of assistance. During assistance the waste sludge flow rate was
determined by measuring the time required to fill a specific volume in the
sludge thickening unit. It is recommended that this method of determining the
waste sludge flow rate be used until the available flow meter is properly
calibrated.
Aerator operation was modified at the same time the plant mode of operation
was switched from contact stabilization to conventional. The modifications
involved changing the operation of the three surface mechanical aerators from
an on-off time clock operation to a continuous operation. Prior to assistance
16
-------
various on-off time cycles for all three aerators were tried in order to
improve plant effluent quality. During assistance all three aerators were
operated continuously. It was felt that continuous operation would provide for
better mixing conditions and better mixing would yield a higher quality plant
effluent. It is recommended that all three surface mechanical aerators
continue to be operated on a continuous basis.
The modification made concerning control of the sludge thickening operation
involved adjusting the quantity of polymer added to the selected quantity of
sludge entering the flotation unit. At Vail sludge is wasted to a flotation
unit and a polymer is mixed with the wasted sludge causing the sludge to float
and thicken. The supernatant (clear liquid) from the flotation is recycled to
the aeration basins. An adequate quantity of polymer must be mixed with the
sludge or a clear supernatant cannot be attained. When attempts were first
made to waste sludge to the flotator, a clear supernatant could not be
attained. The polymer feed rate was checked and was found to be inadequate
due to a clogged line. After the line was flushed, adjustments were made in
the quantity of polymer added to the flotator per quantity of sludge added to
the flotator by adjusting the polymer concentration, polymer pump rate, poly-
mer pump stroke, and sludge feed rate to the flotator. Prior to assistance,
these adjustments were not varied and a consistently clear supernatant from
the flotator could not be maintained. During assistance all adjustments were
varied and a consistently clear supernatant was obtained. Time during the
assistance project; however, did not permit an extensive analysis of the
flotator portion of the sludge handling system. Additionally an extensive
analysis was not made of the vacuum filter portion of the sludge handling system.
In both cases suggestions regarding possible alternative investigations to op-
17
-------
timize the sludge handling operation were given. It is recommended that inves-
tigations be continued to determine the most efficient operational method for
both the sludge flotator unit and vacuum filter. The results of these investi-
gations should give the methods of operation necessary to achieve the desired
thickener and vacuum filter operation at the most economical cost.
C. PERFORMANCE RESULTS
Prior to the technical assistance project effluent water quality data was
incomplete and questionable. During assistance, BOD^ and suspended solids
analyses were conducted on composited samples of plant influent and clarifier
effluent each day. In addition turbidity tests were conducted on the clarified
effluent seven times per day. After assistance BOD^ analyses were conducted on
composited samples of plant influent and clarifier effluent periodically, tur-
bidity tests were conducted on the clarified effluent seven times per day, and
the suspended solids analyses were conducted infrequently. For this report only
the 6005 and turbidity data are discussed quantitatively.
Figure 2 shows the daily average turbidity values of the clarified effluent
during and after the assistance project. It should be noted that in all cases
attempts were made to exclude suspended solids in the turbidity sample. The
purpose of the turbidity test was to indicate the ability of the mixed liquor
suspended solids in the aeration basin to convert colloidal and dissolved BODs
in the waste stream to sludge solids. A high turbidity normally indicates a
larger quantity of colloidal and dissolved BODs present in the clarifier
effluent and low turbidity normally indicates smaller quantities of colloidal
and dissolved BODs in the clarifier effluent. It is noted that a low turbidity
value reported as outlined above does not necessarily mean low effluent total
18
-------
I
X
a
EH
5
u
g
2
8
w
U)
15
TECHNICAL ASSISTANCE PROJECT
VAIL WASTEWATER TREATMENT FACILITY
10
3/20
23
25
27
29 5/1
TIME
-------
values because of the possible presence of suspended solids in the
clarifier effluent.
Figure 2 shows a dramatic decrease in the turbidity within one week after
the beginning of the assistance project and a continued decrease in turbidity
until formal assistance was completed. The dramatic decrease in turbidity was
the result of the changes in plant operation as discussed earlier in the report,
(e.g. changed plant mode of operation, changed return sludge flow operation,
changed aerator operator operation, etc.). The continued slower decrease in
turbidity after the initial drop indicates the length of time required for the
activated sludge biological system to change and develop. After the formal
technical assistance project was completed the turbidity increased, then decreased,
and then increased again. These changes in turbidity indicate the continued
problems encountered with the final clarifiers and the resultant solids loss due
to uncontrollable "sludge bulking". Sludge bulking occurred primarily because of
inadequate flow distribution to the two final clarifiers. The uncontrolled
solids loss caused lower MLSS concentrations resulting in additional colloidal
and dissolved BODs in the plant effluent.
Figure 3 shows the daily composited secondary clarifier effluent BODg test
results. At the beginning of the assistance project most of the BOD^ in the
effluent was due to the colloidal and dissolved organic matter, (refer to
Figure 2 for an indication of amount of colloidal and dissolved organic matter
in the effluent as measured by turbidity). During assistance less of the BODg
was due to colloidal and dissolved organic matter and more of the 6005 was due
to suspended solids "lost" in the effluent. As can be seen from Figure 3, a
drastic reduction in the BOD^ occurred during the assistance project (i.e.
approximately 110 mg/1 to 45 mg/1) and an even further reduction occurred after
20
-------
I
in
D
ij
£
W
5
u
S
a
8
W
CO
150
140
120
100
80
60
40
20
FIGURE 3
TECHNICAL ASSISTANCE PROJECT
VAIL WASTEWATER TREATMENT. FACILITY
VAIL, COLORADO
MARCH-APRIL, 1973
EFFLUENT BOD5 VS TIME
Periodic BOD,- Test Results
Daily BOD5 Tests Results
11 13 15 17 19 21 23 25 27 29 5/1
3/20 22
24 26
MARCH
-------
formal assistance was completed (i.e. approximately 45 mg/1 to 30 mg/1). However,
the present Colorado Water Quality BOD^ Standard (30 mg/1) was not consistently
being met. The primary reason this standard was not met was the continued
problems associated with the final clarifier. If the problems with the final
clarifiers are eliminated, it is felt that the Vail treatment facility will be
capable of consistently discharging BOD^ and suspended solids concentrations
less than 30 mg/1.
The reduction in clarifier effluent BOD^ due to technical assistance re-
presents nearly a 73% reduction in BOD5 or a reduction of about 136.2 Kg
(300 Ibs.) of BOD^ per day in the effluent (assume average plant flow of 1,703
cu m/day (450,000 gal/day) during assistance). Figure 4 shows that the present
reduction in BOD^ through the Vail facility increased from about 45% to about
75% due to assistance.
Greater reductions can be expected with appropriate modifications to the
secondary clarifiers.
V. SUMMARY AND CONCLUSIONS
Region VIII of the Environmental Protection Agency (EPA) received a letter
from the Colorado Department of Health requesting assistance concerning the
operation of the Vail Wastewater Treatment Facility. An initial evaluation of
the Vail plant was made on October 26 and 27, 1972. Various plant deficiencies
were observed during the initial evaluation and recommendations were made to
correct the observed problems. After the plant had been modified, a formal
technical assistance project was initiated on March 19, 1973.
During assistance, plant personnel.were taught the proper techniques used
in collecting, compositing, and storing wastewater samples for the BOD5 and total
22
-------
100
in
Q
§
B
z
w
u
w
o.
Daily BOD Test Results
Periodic BOD Test Results
FIGURE 4
TECHNICAL ASSISTANCE PROJECT
VAIL WASTEWATER TREATMENT FACILITY
VAIL, COLORADO
MARCH-APRIL, 1973
PERCENT REDUCTION BOD5 vs TIME
3/20
29 5/1
TIME
-------
suspended solids analyses and were given instructions in the procedures used to
run the 6005 and total suspended solids tests. However, limited manpower in-
hibited obtaining consistent analytical test results. Future plant considerations
should include a position for a laboratory technician to insure consistent moni-
toring of plant performance by analytical tests.
Plant personnel were also given instructions in conducting and interpreting
various "control" tests. Initiation of the control tests and data interpretation
methods aided in solving problems encountered when controlling plant operation.
The operators should be able to use these methods to solve future operational
problems.
Prior to technical assistance, the Vail facility had been operated with the
major emphasis on eliminating sludge bulking. As a result of this emphasis,
little sludge bulking or loss of solids occurred, but effluent quality was not
satisfactory. The procedures that had been used to control bulking resulted in
low concentrations of sludge solids in contact with the sewage and ineffective
conversion of colloidal and dissolved BOD^ to "activated" sludge solids.
Numerous process modifications were made at the Vail plant in conjunction
with the results of the control tests and data interpretation. The most sig-
nificant modifications were the conversion from the contact stabilization mode
to the conventional mode of activated sludge operation and the initiation of
continuous aerator operation. As a result of these modifications, as well as
others, effluent quality was substantially improved; however, optimum performance
was not achieved due to various design deficiencies that existed.
Several plant deficiencies were corrected during the project including; the
removal of baffles from the final clarifiers, the changing of the location for
withdrawing waste or excess activated sludge, and the adjustment and cleaning of
24
-------
the polymer feed equipment. Other deficiencies which were noted were not
modified during the project. These included the shallow rectangular final
clarifiers which were designed to remove sludge by returning it to the head of
the clarifiers (countercurrent to the sewage flow) and the inadequate method of
splitting flow to the final clarifiers.
All modifications to the Vail facility combined to drastically reduce the
clarifier effluent 6005 from about 110 mg/1 to about 45 mg/1 during assistance
and to about 30 mg/1 after formal assistance was completed. The percent reduc-
tion in BODg through the plant increased from about 45% to about 75%. Even
though the BOD^ was reduced significantly, the Vail facility was not consistently
meeting the Colorado Water Quality BOD5 Standard of 30 mg/1. The primary reason
why the BOD^ standard was not met consistently was the continued problems
associated with the secondary clarifiers. If these problems are eliminated, it
is felt that the Vail facility will be capable of consistently discharging BOD,.
and suspended solids concentrations of less than 30 mg/1.
VI. RECOMMENDATIONS
Based on the results of the assistance project, the following recommendations
are made:
1. Methods of operational control and control testing outlined during the
assistance project should be continued.
2. The relationship between the Vail treatment facility and the Upper Eagle
treatment facility should continue to include flow splitting capability
so that the Upper Eagle facility can accept additional flow while the
Vail facility is experiencing operational problems or the Vail facility
can accept additional flow while the upper Eagle facility is experi-
'-. encing operational problems.
25
-------
3. All three surface mechanical aerators should be operated continuously.
4. Plant modifications should be made to provide for positive flow split-
ting capability to e'ach final clarifier.
5. Lower flows should be accepted at 'the Vail facility to reduce the
problems associated with the existing clarifiers. The maximum volume
of flow that clarifiers are capable of accepting and adequately
treating, should be determined by a trial and error procedure.
6. The clarifier capacity as established by a trial and error procedure
should be considered in future designs if increased plant capacity
is desired.
7. Plant modifications should be made to provide for more precise return
sludge flow measurements.
8. The method of determining the waste sludge flow rate as established
during assistance should be used until the waste sludge flow meter
is properly calibrated.
9. Investigations should be continued to determine the optimum flotation
unit and vacuum filter operation.
10. A separate laboratory technician should be considered to perform all
analytical work. If one technician at Vail is not feasible, consid-
eration should be given to sharing a technician with the Upper Eagle
treatment facility.
11. The plant should be operated on a twenty-four hour basis to allow
manual adjustments to the present flow splitting devices on the final
clarifiers. This interim activity should continue until an adequate
automatic flow splitting device can be installed.
26
-------
REFERENCES
1. Standard Methods for the Examination of Water and
Wastewater, 13th Edition, American Health Associ-
ation, 1015 Eighteenth Street, N.W. Washington,
D.C., 20036
2. Operation of Wastewater Treatment Plants, A Field
Study Training Program, prepared by Sacramentao
State College for the Environmental Protection
Agency, Office of Water Programs, Division of
Manpower and Training.
27
------- |