EPA-908/3-77-005
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U. S. ENVIRONMENTAL PROTECTION AGENCY
ROCKY MOUNTAIN — PRAIRIE REGION
REGION VIII
Plant evaluation at fishing
BRIDGE WASTEWATER
TREA TMENT PLANT
YELLOWSTONE NATIONAL PARK
OPERATION & MAINTENANCE SECTION
WATER DMWON
AUGUST, 1977
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EPA-908-77-005
PLANT EVALUATION
AT
FISHING BRIDGE WASTEWATER TREATMENT PLANT
YELLOWSTONE NATIONAL PARK
AUGUST 1977
Owen K. Boe, Project Engineer
Leon Malloy, Engineering Technician
Control Technology Branch
Water Division
Region VIII
U.S. Environmental Protection Agency
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DISCLAIMER
This report has been reviewed by the Region VIII Office of the
Environmental Protection Agency, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement
or recommendation for use.
Document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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TABLE OF CONTENTS
I. INTRODUCTION
II. SUMMARY AND CONCLUSIONS
III. RECOMMENDATIONS
IV. DESCRIPTION OF PLANTS
V. OPERATIONS EVALUATION
A. PROCESS CONTROL
B. TREATMENT UNITS
1i
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LIST OF TABLES
TABLE 1 DESIGN FLOWS FOR FISHING BRIDGE WWTP
TABLE 2 DESIGN CRITERIA FOR FISHING BRIDGE WWTP
TABLE 3 ADDITIONAL DESIGN INFORMATION FOR FISHING BRIDGE WWTP
1 i i
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LIST OF FIGURES
FIGURE 1 FLOW SCHEMATIC OF THE FISHING BRIDGE WWTP
FIGURE 2 FISHING BRIDGE PLANT LAY-OUT
FIGURE 3 SETTLEOMETER TRENDS AT THE FISHING BRIDGE WWTP
FIGURE 4 BOD PERFORMANCE OF THE FISHING BRIDGE WWTP
FIGURE 5 TOTAL SUSPENDED SOLIDS PERFORMANCE OF THE FISHING
BRIDGE WWTP
FIGURE 6 pH AND ALKALINITY DATA
FIGURE 7 EFFLUENT pH AND NH3 REMOVAL AT FISHING BRIDGE WWTP
FIGURE 8 PERCENT NITRATE REMOVAL AT THE FISHING BRIDGE WWTP
iv
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I. INTRODUCTION
The National Park Service (NPS) has recently constructed several new
waste water treatment facilities at the Yellowstone National Park. These
facilities represent a major commitment by the Park Serivce to ensure that
the high quality of water 1n the Park 1s not degraded by the presence of
man.
To ensure that their new facilities perform as expected, the Super-
intendent of Yellowstone National Park requested assistance from EPA to
train Park personnel in process control procedures and to provide performance
evaluations of treatment facilities. Specific technical assistance was
requested for the nitr1ficat1on-den1trif1cation facility located at Fishing
Bridge. Additional assistance was provided for the Old Faithful facility.
Two weeks of troubleshooting on-site technical assistance was conducted
1n August 1976 and extensive follow-up through telephone calls continued
for the remainder of the operating season.
The intent of this report 1s to document the technical assistance
activities and to provide recommendations to the Park Service relating
to the problems that were encountered.
II. SUMMARY AND CONCLUSIONS
An operations evaluation and process control training program was provided
to the National Park Service (NPS) at Yellowstone National Park. Process
control training was given to four NPS Engineers (one from Glacier National
Park), three NPS operators (one from Mount Rushmore National Park) and
six part-time-summer employees.
Operations evaluations were conducted at the Fishing Bridge waste water
treatment facility. Various deficiencies were noted during these evaluations
and are discussed 1n this report.
Several problems were of such magnitude that the facility was not capable
of producing the degree of treatment that was expected.
The NPS has already Initiated appropriate action for reducing Infiltration
problems and for increasing the area available for percolation. Other
actions, however, are still needed to ensure that efficient and reliable
treatment will be provided. Recommendations for these actions follow.
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III. RECOMMENDATIONS
1. Continue using the Process Control Plan as Instituted. Especially
utilize trend charts to chart plant process characteristics.
2. Provide permanent staff and seasonal employees with refresher training
prior to start-up of plants.
3. Expand the plant monitoring program to Include a complete nitrogen
profile of the treatment plant and periodically run a profile of the plant
loading fluctuations for a typical day.
4. Evaluate the addition of inert media to the denitriflcation ponds. A
pilot study could be especially useful for determining appropriate design
cf*1 terl si •
5. Strongly consider providing the capability to add alkalinity to the
wastewater to support the sto1ch1metr1c requirements for nitrification.
6. Correct flow controller and flow measuring equipment problems.
7. Take appropriate measures to ensure that gasoline or other toxic
substances do not get Into the sewer system.
8. Evaluate and correct the problem of solids separation 1n the oxidation
ditches.
9. Operate the return sludge system to minimize sludge detention time
1n the final clarlfler. If this cannot significantly reduce the solids
loss associated with denitriflcation, then, consider installing surface
skimmers.
10. A permanent scum collection system should be Installed on the final
clarlflers to eliminate nuisance problem from septic scum.
11. Construct a permanent return sludge flow splitting and flow measuring
box 1n the headworks.
12. Ensure that the percolation ponds are operated so that one pond 1s
allowed to dry out every two to three weeks.
13. Closely monitor the dissolved oxygen 1n the basins to determine if
aerators are supplying sufficient dissolved oxygen.
14. Consider adding recycle capability to the denitriflcation ponds.
15. Consider adding an aerobic digester for waste sludge and scum.
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IV. PLANT DESCRIPTION
A schematic flow diagram of the treatment facilities 1s presented 1n
Figure 1. The use of this figure 1n conjunction with the following
brief description of the various processes will aid in understanding
the overall treatment system. Figure 2 shows the overall treatment plant
layout and piping.
1. Headworks: Wastewater receives comminution at the pump station
and then enters the plant through a 12-inch force main which
is an extension of the parallel 8-inch force main from the Fishing
Bridge pump station. Flow entering the plant passes through a
9-inch Parshall flume to a distribution box, which splits the
flow to either or both oxidation ditches. At the inlet box,
flow may also be diverted to the clarifier or directly to the
evaporation-percolation ponds.
2. Oxidation Ditch: In the oxidation ditch, the incoming wastewater
is brought into intimate contact with the micro-organisms (mixed
liquor suspended solids, MLSS). Initially, the biodegradable
organic matter is adsorbed on the surface of the micro-organisms.
Then, over a period of hours, the organic matter 1s absorbed by
the micro-organisms causing the growth of more organisms. The
oxidation ditch contents, flow over an adjustable weir and to
the clarifier by means of a I4-1nch pipe.
3« Clarifier: The mixed liquor from the oxidation ditch Is transferred
to the clarifier where the most of the micro-organisms are separated
by gravity. The mixed liquor enters the clarifier along the perimeter
of the basin and flows inward to the weirs at the center. The
sol Ids settle to the bottom and are scraped toward a hopper by
means of a rotating arm assembly. Settled sludge 1s pumped from
the bottom of the clarifier by the return sludge pumps (located
in the control building) back to the headworks.
Scum which collects 1n the clarifier is collected Into a slotted
pipe and falls Into the sump at the east side of the clarifier.
It is pumped back to the headworks by means of a pump located
1n the control building.
4. snlids Disposal: Solids from the clarifier are returned to the
oxidation ditch with a portion being periodically wasted to the
sludge drying beds or the sludge lagoon to prevent an excessive
build-up of sol Ids 1n the ditch. Biological solids generated
in the anaerobic denitrlflcation ponds will be allowed to pass
to the disposal (evaporation-percolation) ponds where they will
be filtered out in the soil.
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FIGURE I
planl bypo««
^lojrvoporotlon-ptrcolation ponds
DENITRIFICATION
PONDS
OXIDATION DITCH
CLARIPIER
[mixing basin
METHANOL
SLUDGE DRYING
BED
OXIDATION DITCH
SUJOGE LAGOON
J
FLOW DIAGRAM
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7789
WS 7781 00
WS. 7776.00 7780
WS, 777700
WS. 777*73
DWORKS
OXIDATION PITCH
7775
EVAPORATION - PERCOLATION
PONOS
7770
CLARIFIER
DENITRIFICATION
HYDRAULIC PROFILE
FLOW SCHEMATIC OF THE FISHING BRIDGE WWTP
4
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FIGURE II
BOX NO. 4
EVAPORATION-PERCOLATION PONO NOl 2
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EFFLUENT
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FISHING BRIDGE PLANT LAYOUT
5
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5. Denitrification: Flow from the clarifier can be directed to
either the evaporation-percolation ponds or the deep denltriflcation
ponds. Methanol addition to the denitrification ponds provides
the carbon source necessary to allow for partial denitrification
of the effluent prior to discharge into the groundwater through
the evaporation-percolation ponds. A series of monitoring wells
are monitored as a means of verifying any detrimental build-up
of nitrates and their migration to the river.
6. Chlorination and Disposal: Clarified effluent flows to either
the denitrification ponds or to the evaporation-percolation ponds
with effluent chlorination provided at flow control box Number 3
before final disposal. This box directs effluent flow from the
denitrification ponds to either of the two evaporation-percolation
ponds. Evaporation-percolation ponds are provided to help stabilize
the effluent as well as perform their primary purpose of effluent
disposal and storage.
Tables 1, 2, and 3 summarize the design criteria and physical
dimensions of the major plant units.
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TABLE I
DESIGN FLOWS FOR FISHING BRIDGE WWTP
Average Daily Flow (ADF) 0.6 mgd
Macimum Peak Flow (3 X ADF) 1.8 mgd
Minimum Peak Flow (.25 x ADF) 0.15 mgd
Design Flow (1.3 x ADF) .78 mgd
7
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TABLE II
DESIGN CRITERIA FOR FISHING BRIDGE WWTP
Infl uent Effluent
Average Design From Clarifier From Denitrification
Constituent
mg/1
lbs/day
mg/1
Ponds, % Removal
BOD
250
1625
15 - 25a ,b
—
Suspended Solids
140
910
15 - 30b
—
Ammonia Nitrogen
25
163
—
—
Nitrite Nitrogen
0
—
—
--
Nitrate Nitrogen
0
—
15 - 25
20 - 25c
40 - 45d
60 - 95e
a - Typical BOD removal in excess of 90 percent
b - Each year there will be a 2 to 4 week period during plant start-up that
the effluent will be of lower quality than shown.
c - Estimated nitrogen removal for the existing uncovered denitrification
ponds without mixing.
d - Estimated nitrogen removal for a hypalon covered, unmixed pond
e - Estimated nitrogen removal for a denitrification system complete with
pond covers, mixing and solids separation with recycle
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TABLE III
ADDITIONAL DESIGN INFORMATION FOR FISHING BRIDGE WWTP
UNIT SIZE
Headworks
Parshall Flume, In. 9
Oxidation Ditch
Number of basins 2
Volume (total), gallons 810,000
Water depth, ft. ,5
Width of channel, ft., top 36
" " " ", bottom 24
Hydraulic detention time, hrs. (at 0.78 mgd
0% sludge
return) 24.8
Loading Rate
lb BOD/1000 cu.ft./day !5
F/M ratio, lb BOD/1b MLVSS/day .05-. 15
Maximum MLSS concentration, mg/1 3,000-6,000
Mean cell residence time, days 30
Aeration Equipment
Number of aerators (rotor assemblies) 4
Length of rotor assembly, ft. 20
Blade diameter, in. 27.5
Submergence, in.
Average design 6
Maximum (at peak flow) 10
Unit rpm 85
Horsepower, each aerator 25
Total horsepower 100
Clarifier
Number 1
Diameter, ft. 41
Surface area, sq.ft. 1,300
Side water depth, ft. 10
Volume, gallons 97,500
Weir Length, ft. 116
Surface loading rate, gpd/sq.ft.
Design flow 600
Peak flow (3.0 x ADF at 0% sludge return
rate) 1,385
Weir loading rate, gpd/lin. ft.
Design flow 6,720
Peak flow (3.0 x ADF) 15,000
Detention time @ design flow, hrs. 3.0
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Unit Size
Sludge Handling Facilities
Estimated sludge load, lb. dry solids/day 600
Sludge lagoons
Number 1
Volume, cu.ft. 25,000
Sludge drying beds
Number 2
Surface area (total), sq. ft. 3,500
Loading rate, lb/sq.ft./year 26
Denitrification Pond
Number 2
Total volume, cu.ft. 380,000
Side water depth, ft. g
Detention time, days (at 0.78 mgd) 3,6
Average methanol dosage 75 mg/1 (70 gal/day)
Evaporation-Percolation Ponds
Number 2
Total area, acres 73
Evaporation-percolation rate, ft./day *25
Water depth @ 15 day detention time, ft. ' 3
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V. OPERATIONS EVALUATION
Operational considerations of a wastewater treatment plant are dependent
on three general conditions. The first condition is that the plant be
designed appropriately to provide the degree of treatment that is necessary.
The second condition 1s that the sewage characteristics are compatible
with plant design and that theplant equipment perform as the designer
intended. Thirdly, the operations staff have an adequate process control
plan and that they have the expertise, laboratory support and budgetary
support to perform the operational duties.
In evaluating and assisting in plant operations at Yellowstone National
Park, various deficiencies were noted pertaining to each of the three
general conditions just identified. It is important that the three
categories be identified and kept in mind and in perspective when corrective
action is implemented 1n order for these actions to be effective. For
example, process control on deni trification can only be administered to a
limited point because the design of the unit is so limiting. Consequently,
the major corrective emphasis needs to be placed at identifying the
design limitations and then, correcting or eliminating the design limitation.
A. PROCESS CONTROL
Process Control 1s one area of concern at Yellowstone. Generally,
the Park operators are seasonal help and are inexperienced 1n plant
operations. Part of the assistance that the Environmental Protection
Agency provided was to train Park personnel in operational conditions and
to Implement a Process Control Plan. Written as well as verbal guidelines
were provided the Park Service staff on Process control. The seasonal
operating situation and the extensive use of seasonal personnel dictates
that Process Control procedures be as straight-forward as possible and that
operating procedures be developed into well defined routines. One of the
major recommendations that this report gives 1s that a thorough review of
operating procedures and process control techniques be given to the
operational staff each year, just prior to start-up of the treatment
facilities.
A second recommendation is that emphasis be put on giving to plant
operators Instructions on the need to keep detailed daily logs of operating
conditions and trend charts depicting process performance. These are normal
considerations for efficient plant operations; but they are especially
Important for the situation at Yellowstone, where several facilities
have to be operated for short seasonal uses. Efficient use of trend
charts should greatly help the Park Environmental Engineer to quickly
observe and evaluate operating condition over any given period of time.
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B. TREATMENT UNITS - HEADWORKS
Considerable miscellaneous problems were experienced with headwork systems.
The flow controller system did not work properly which caused hydraulic
surges in the treatment units. The flow recording instrument was not
operable which made it difficult to assess plant loadings and plant
hydraulic characteristics. The chlorinator and the methanol feed systems
were also limited as they were designed to be paced to the influent flow
through the flow monitoring system.
All flow measurements were consequently made by visual observations of
the staff gage in the parshall flume. This as well as other problems
adds an additional work load to the operators. The full extent of the
headwork problems was not within the scope of this study but these
problems do need to be evaluated and resolved.
SECONDARY TREATMENT
Secondary treatment is provided by two oxidation ditches. The key
parameters which significantly affect secondary treatment performance are
dissolved oxygen (D.O.), mixed liquor suspended sol Ids (MLSS), return
sludge (RS) and clarification.
DISSOLVED OXYGEN (D.O.)
Generally, D.O. levels should be about 2.0 mg/1 in order to provide an
adequate aerobic environment. D.O. 1s controlled by chanqinq the
immersion of the aerators in the mixed liquor. The change 1n liquid
level is accomplished by raising or lowering the mixed liouor overflow
m 1rs at the end of each ditch. Proper D.0° levels Se esp«1al?J
important at the Fishing Bridge Plant in order to maintain an adequate
number of the highly sensitive nitrifying bacteria. Several times
during the summer the operators noted a complete absence of D.O. In
the system. Although no real supportive data 1s available, this lack
pe,r1ods ^tensive nitrification. However,
fact°rs which could produce this same effect are short periods
of high organic loading, periods of high nitrogen loading, or possibly
an operational change which could affect the activity of the micro-organisms.
In order to properly analyze this an extensive montrolng program needs
to be maintained to monitor such parameters as organic loading, nitrogen
loading, and oxygen uptake rates of the activated sludge.
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MLSS
Mixed Liquor Suspended Solids is a mass measurement of the quantity of
micro-organisms in the aeration tank. The function of the micro-organisms
1s to biologically remove soluble and colloidal organic matter from the
wastewater. Since MLSS measures only the mass of the micro-organisms,
the operator still needs a process control system which evaluates the
quality of the activated sludge. The process control system which
was Introduced to the Park Service staff provides this control.,
Settleometer trends on Figure 3 provides some insight to the system's
ability to adequately control MLSS. The plotted curves represent sludge
settling concentrations (SSC) for a given period of time (5 minutes,
etc.) in a Mallory settleometer. The other values shown are the return
sludge concentration (RSC) and the aeration tank concentration (ATC).
All concentration values on this graph are measured in terms of percent
by volume.
The first characteristic this graph shows is that in the latter part
of July a significant change 1n sludge settling characteristics occurred.
The exact reason for this change is not known but the operators did observe
the appearance of gasoline in one lift station on at least two occasions.
The introduction of toxic substances such as gasoline could easily produce
this response, a deterioration of sludge quality. Park Services employees
identified one instance of gasoline contamination and initiated steps to
prevent 1t from recurring. During future operating seasons, Park Service
employees will need to make very careful checks on lift station operation
to ensure that such incidents do not recur. The presence of gasoline in
the collection system is also very hazardous and could result in the
formation of explosive vapors. Numerous explosive incidents have occurred
in other systems because of gasoline in the collection system.
After EPA's arrival the sludge settling characteristics improved
dramatically. The major reason was probably due to the elimination of
gasoline from the sewage, but at the same time closer attention was provided
to the plant operations due to the increased manpower that was then available.
Consequently, more responsive process control was provided and timely
changes were made 1n plant operations. This example illustrates the needs
for maintaining efficient process control aids such as the trend chart shown
in Figure 3.
Another problem with controlling the MLSS was discovered at the end of
the EPA technical assistance period. At that time all the sludge from
one oxidation ditch was transferred to the remaining ditch. This was
done 1n an attempt to provide a more optimum food-to-m1cro-organ1sm ratio
1n hopes of improving nitrification. However, the MLSS measurements, as
found at the overflow weir, did not correspond with the anticipated
results. Further checking revealed that some sol Ids separation was occurring
in the ditch. It also appeared that this separation occurred only after
the MLSS rose above 2000 mg/1 as no discrepencies 1n MLSS data were observed
13
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Figure 3 Settlometer Data - Fishing Bridge - 1976
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15
20
July
25
30
14
10
August
15
20
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at values below this level.
Examination of the plans revealed that a potential dead zone appeared at
the outlet structure from the ditch. The design of the outlet structure,
therefore, could have caused the solids separation problem.
Another potential reason for the solids separation problem may be
attributed to the placement of the flow direction baffle. This baffle is
located horizontially in front of the rotors and its purpose is to change the
direction of the velocity gradient in order to prevent solids from
separating. In either case this problem needs further evaluation during
the next operating season and the assistance of the equipment manufacturer
and the design engineer will probably be needed to correct this problem.
Sludge wasting 1s the primary operational tool for ultimately controlling
MLSS levels. The Fishing Bridge plant was provided with both sludge drying
beds and sludge lagoons for dewatering sludge. Due to the short operating
season there was no limitation experienced with sludge wasting. The
Park Service is cautioned, however, that because the wasted sludge has a
high percentage of volatile solids odors from the sludge drying beds and
sludge lagoons may be present each Spring.
CLARIFIER OPERATION
Final clarification 1n an activated sludge plant has the dual objective
of separating solids from the treated sewage and concentrating activated
sludge so 1t may be returned to the aeration tank. The hydraulic design
characteristics of the clarlfier meet established criteria, yet significant
problems were still experienced with solIds carry over.
The most significant problems were experienced during the periods of
poor sludge settling quality, as shown in Figure 3 and, therefore, were not
attributed to clarlfier design. But problems were still encountered
after significant improvement in sludge settling was obtained. These
problems were attributed directly to denitrlflcation and Indirectly to
the efficiency of sludge removal from the clarifier. The clarlfier system
used at Fishing Bridge requires that activated sludge be scraped to a center
well and from which it is pumped back to the aeration system. This type
of sludge removal system minimizes the ability to rapidly remove sludge
which has settled in the outer portions of the clarifier and consequently,
makes the clarifier system very susceptable to denitrlflcation. Once
the sludge denitrifies there 1s an uncontrolled loss of solids because
there are no surface skimmers on the clarlfier. There 1s very little
the operators can do about this problems, except to maintain a close watch
on the solids inventory 1n the clarifier and try to keep 1t to a minimum.
If the problem persists then surface skimmers may be required to collect
the floating solids.
15
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Another problem encountered with the clarification system was with the
rim feed and scum removal system. Scum that entered the feed channel did
not move around the periphery to the scum collector. Consequently,
scum collected 1n the channel, went anaerobic and produced odor and other
nuisance problems. Either a water spray system or a mechanical scum
scraper system should be installed.
RETURN SLUDGE SYSTEM
Returning activated sludge to the aeration tank is necessary 1n order
to provide sludge residence times greater that the hydraulic detention
time of the system. The return sludge system has to be flexible and highly
efficient in order to minimize any adverse effects from the low oxygen
concentration environment of the clarlfier and to counter changes 1n
sludge settling characteristics.
As discussed previously, the sludge collection system is somewhat
limited in Its ability to efficiently remove sludge from the clarlfier,
and also has limited flexibility. Since there are two aeration tanks,
there are times that the return sludge should be split to each tank
independent of the raw sewage flow split. This was not possible with the
plant design. A flow control box was constructed and placed in the head-
works channel to provide temporary return sludge control flexibility. It
1s recommended that a permanent structure be constructed to provide
additional flexibility and also to facilitate the measurement of return
sludge flow. Any permanent structure should have the capability to regulate
and measure return sludge to each basin Independently of the other basin.
Sliding V-notch gates have been shown to be very effective for this.
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SECONDARY PERFORMANCE
The primary objective of secondary treatment is to remove BOD and
total suspended sol Ids from the wastewater. Figures 4 and 5 respectfully
show influent and effluent trends of BOD and total suspended solids from
the summer operating period. Data, based on composite samples, shows
that influent BOD strength increased steadily until July, where 1t leveled
out at about 150 - 175 mg/1.
The effluent BODc stayed below 30 mg/1 until about July 10. At this
time the effluent quality deteriorated very rapidly. This period coincides
with the previously discussed disruption 1n sludge settling and is attributed
to the gasoline that was found in the sewer system. Problems continued for
the rest of July but by August 12, the effluent BOD was reduced to 34 mg/1.
Due to manpower limitations no more BOD5 data was taken after this time.
Figure 5, as stated, shows weekly averages of the total suspended solids
at the plant. Influent total suspended solids values increased much faster
than the B0D5 values and also exhibited a very high degree of variability.
The total suspended solids effluent values were also quite good until
July 10. The effluent total suspended solids climbed to over 100 mg/1
as the plant performance deteriorated. Unlike the BOD, however, the effluent
suspended levels never did return to expected ranges despite the Improved
settling characteristics of the sludge. The poor suspended sol Ids capture
1n August coincide with a fairly active nitrification process 1n the oxidation
ditches, so 1t 1s suspected that the solids carry over was from denitrlfication
1n the final clarlfler. The floating solids also had the gray-brown color
that is associated with denitrifying sludge.
Except for the den1trif1cat1on problems, the oxidation ditch effluent BOD5
and total suspended solids level are expected to be much better than were
found. Elimination of toxic substances from the sewer system and Improve-
ment In operations should ensure that the plant does significantly better
next summer. As recommended earlier, 1f denitrification cannot be
controlled then surface skimmers may need to be installed on the final
clarlfler.
17
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Figure 4 BOD Performance
200
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in
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co
150
Influent
Q.
_
Effluent
10
20
June
30
10
20
July
18
30
10
20
August
30
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Figure 5 Suspended Solids Performance
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Influent
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LABORATORY CONTROL
Appropriate laboratory facilities are important to provide good infor-
mation for process control, process performance, and for any special plant
evaluations. The lab at the Fishing Bridge plant was spacious and fairly
well supplied with necessary glassware and equipment. The major deficiency
found was the inability to measure total organic nitrogen. Kjeldahl
equipment was purchased for the purpose but it did not arrive in time
to be useful.
The second problem was with the manpower available for doing extensive
monitoring. The operator was essentially responsible for both operations
and laboratory work, so extensive laboratory work was not possible due to
other Important duties.
The limited manpower 1s also compounded by the use of seasonal employees
and by the start-up and shut-down operations each year. These conditions
necessitated the need for very systematic operations, pre-train1ng of
new and returning employees and considerable planning before plant start-
up commences.
NITRIFICATION
Nitrification is the bacterial process of converting ammonia (NH3) to
nitrate (NOq )• Specific bacteria are needed for this process and the
"principal genera of Importance 1n biological nitrification are Nltrosmonas
and Ntirobacter."* Nitrification wastewater treatment plants utilizing
biological nitrification have to be specifically designed to provide an
environment suitable for these specific bacteria. Specific limits are required
for such parameters as temperature, pH, alkalinity, and dissolved oxygen.
The nitrifying bacteria are generally considered as very sensitive to changes
1n environmental conditions. A slight deviation from an ideal condition
may produce a significant change in process performance.
Levels of nitrification achieved at the Fishing Bridge plant averaged
70% during the month of August. More critical, however, Is the observation
that the apparent percent of nitrification ranged from a low of 14% to
a high of 92%. Factors which cause this range 1n efficiencies, are not
totally understood, but the following discussion attempts to analyze
these factors.
Sewage Influent temperatures ranged from 10 - 17 degrees Celsius during
the summer. The rate of nitrification 1s very sensitive to temperature
and reaction rates reduce quite appreciably as temperatures are reduced.
It would appear, however, the long detention times afforded by the
20
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extended aeration process minimized any temperature related problems.
Dissolved oxygen has, likewise, been reported as being very critical for
nitrification. Generally, it is felt that D.O. levels of at least 2.0 mg/1
are needed to support nitrification. Nitrification can occur at lower
D.O. levels but again, it 1s believed long detention times limit any adverse
effect on reaction rates of low D.O. levels.
The operators reported that at times the D.O. fell to 0 mg/1. This
1s unacceptable for maintaining any degree of nitrification. The reason
for the total depletion of D.O. is not clearly understood. The operators
attempted to regulate the D.O. levels by adjusting the immersion level
of the rotors, but this was not always successful. Part of the problem
may be attributed to excessive loadings of total nitrogen and B0Dv Due
to the nature of the facilities served, it 1s possible that very strong
wastes were received periodically.
pH 1s another parameter which influences nitrification reaction rates.
Generally, 1t has been found that pH's of 7.0 to 8.5 are needed to support
nitrification. Occasionally nitrification has been observed at a pH of
6.5, but 1f the pH drops much lower nitrification may be drastically
reduced.
pH control is not generally a problem unless there are industrial loads
to the facility or unless the wastewater has very little alkalinity. When
low alkalinity water is encountered, careful control has to be exerted
because for every milligram of ammonia oxidized, 7.14 milligram of
alkalinity is removed.
F1g1re 6 1s a profile of the pH data and alkalinity data taken at the
Fishing Bridge facility. As can be seen when the plant first started
up the plant influent pH and effluent pH were nearly the same. However,
by July, when the plant was 1n full operation, the effluent pH fluctuated
quite significantly from the influent values and by late July the effluent
pH appeared to be cycling from high of 7 to a low of 6.
Since pH is a function of the alkalinity in the water it is important
to look at this parameter. It is especially important considering the
sto1ch1metr1c requirement of alkalinity 1n the nitrification process.
The alkalinity data noted 1n Figure 6 shows a similar pattern as the
effluent pH, 1n that at high alkalinity values the pH 1s not suppressed,
but at low alkalinity values the pH drops off very quickly. This data
strongly supports the contention that alkalinity is limited 1n the natural
water to such an extent that the buffering ability of the wastewater is lost.
Figure 7 shows the effluent pH data for July and August with the percent
ammonia removal superimposed. This data shows quite clearly that within
a few days after the pH was suppressed the nitrification efficiency dropped
off very rapidly. Likewise, when the pH returned to a much more acceptable
range of 6.5 - 7.0 the nitrification efficiency climbed to 90%.
21
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Figure 6 pH and Alkalinity Profiles
Influent pH
>-
H-
M
I—H
—I
C
Effluent pH
Influent
Alkalinity-
Effluent Alkalinity
June
July
August
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Figure 7 Nitrification as
Influenced by pH
^ K
^ % Nitrification
\
AN
*
August
7.5
7.0
6.5
6.0
5.5
1976
23
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It 1s recommended, therefore, that the Park Service initiate plans to
add alkalinity to the wastewater 1n order to maintain the nitrification
efficiency at optimum levels. Alkalinity additions usually Involve
adding lime, sodium hydroxide or sodium bicarbonate. Liquid sodium
hydroxide is probably the easiest to handle but 1t 1s probably more
expensive than lime. Sodium bicarbonate 1s also more expensive than lime
but it would require less chemicals and would be relatively easy to handle.
It 1s recommended that extensive monitoring be maintained on
nitrogen loading to the plant. The conclusions drawn from this
evaluation are limited to some degree because a nitrogen blance cannot
be made due to the unavailability of organic nitrogen data and because
the alkalinity data is very limited.
24
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DENITRIFICATION
The denitrificatiori process 1s the bacterial reduction of nitrates (NO3)
to nitrogen gas (Ng). In order for this process to proceed sufficient
numbers of appropriate bacteria are necessary and an environment free of
dissolved oxygen must be available. The denitrlfication process at the
Fishing Bridge plant utilizes two covered lagoons.
During the month of August nitrate reduction averaged 38%. As is shown
in Figure 8 this reduction was not achieved consistently. Part of the
problem was obviously related to the fluctuating nitrification process.
However, a critical look must also be given to the facilities available
for nitrification. At no time was the D.O. found to be less than 0.5 mg/1
1n the effluent from the denitrificatlon ponds. This is significant
because as was stated earlier, denitrification can only occur in the
absence of D.O.
The inability to provide a D.O. free environment can probably be
attributed to several reasons. The Instability of the preceding nitrification
process certainly would not lend to a stable denitryfying process and the cold
sewage would inhibit denitrificatlon. However, since both BOD and D.O.
were available, there should have been sufficient aerobic activity to
deplete the dissolved oxygen. In fact, the BOD leaving the ponds was
always so high that no attempt was made to add methanol to the ponds.
Since the dissolved oxygen was not depleted it was suspected that the ponds
had either significant short circuiting or that the design was not
adequate to maintain a sufficient population of denitrifying micro-organisms.
One possible solution, or at least an Improvement over the existing
system would be to recycle pond effluent back to the pond influent structure.
This would have the effect of providing a continuous seed of organisms
to the pond Influent and thus add to the population of organisms and
possibly enhancing the growth rates of the organisms. This solution
would not be expected to provide much more than a 10 - 20% increase
1n NO3 removals but 1t also should act as a way to make the denitrificatlon
performance more consistent.
Another possible solution would be to fill the ponds with some inert
material such as rock, redwood, or plastic to convert the system to a fixed
growth denitrificatlon process. This modification would be significantly
more expensive, but if designed properly, 1t should be very effective in
converting all the nitrate to nitrogen gas.
25
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Figure 8 % NO3 Removal
In Denitrification Pond
August
-------
It is recommended that Park Service employees or their consultant
fabricate a pilot plant to operate and study fixed growth denitr1f1cat1on.
011 drums and rock could be used to simulate the environment that would be
expected 1n the ponds. Key parameters that need to be studied and related
to the existing ponds would be hydraulic detention t1meo(measured without
media), volumetric loading rates (pounds NO3-N/IOOO ft. of media),
surface loading rates (pounds N0o-N/ft.2 of media), recycle rates,
temperature effects, and methanol feed rates.
PERCOLATION PONDS
The two evaporation-percolation ponds were designed to dispose of final
effluent without a direct discharge to the Yellowstone River. The critical
parameters for effective performance are a design based on reliable
percolation rates and the ability to maintain the percolation rates at
optimum conditions.
Recommended operating practices call for periodically drying of the cells
to ensure an aerobic environment. Slime layers on the bottom of the
cell when the cells are dry can be removed or rototilled into the soil.
One major problem found at Fishing Bridge was that early spring Infil-
tration completely filled both ponds faster than the water was being percolated
Into the soil. Later, when the infiltration subsided, water did not
percolate fast enough to keep up with the incoming sewage. Consequently,
the ponds filled to the point where sewage was backing up into the plant and
the dikes were 1n danger of being flooded. Because the cells never were
able to operate as Intended (with a drying period) an accurate assessment
of the percolation rates was not available. However, having only two cells
does not provide much operational flexibility.
The Park Service, decided by the end of the summer to construct an
additional cell and to Initiate major correction activities of the
Infiltration problem. Both activities should greatly Improve the
operabllity and reliability of the percolation system.
The Park Service, also has a contract with the U. S. Geological Survey
to monitor the groundwater around the ponds.
The groundwater monitoring was initiated prior to the operation of
the ponds and continued through the first operating season. Results from
this study should reveal information about the impact of the pond operation
on the level and quality of the groundwater.
27
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¦ turiltiwnL iikrwn i wnin
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-908/3-77-004
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE Report Ufl The
Plant Evaluation at Fishing Bridge Wastewater
Treatment Plant - Yellowstone National Park
5. REPORT DATE
August 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Owen Boe and Leon Ma Hoy
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Protection Agency
1860 Lincoln Street
Denver, Colorado 80295
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The National Park Service (NPS) has recently constructed several new wastewater
treatment facilities at the Yellowstone National Park. These facilities represent
a major commitment by the Park Service to ensure that the high quality of water in
the Park is not degraded by the presence of man.
To ensure that their new facilities perform as expected, the Superintendent of
Yellowstone National Park requested assistance from the EPA to train Park personnel
in process control procedures and to provide performance evaluations of treatment
facilities. Specific technical assistance was requested for the nitrification-
denitrification facility located at Fishing Bridge. Limited additional assistance
was provided at the Old Faithful facility. Two weeks of troubleshooting on-site
technical assistance was conducted in August 1976 and extensive follow-up through
telephone calls continued for the remainder of the operating season.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. IDENTIFI ERS/OPEN ENDED TERMS
c. COSATI Field/Group
Nitrification
Denitrification
Sewage Treatment
Oxidation Ditch
Activated Sludge
Yellowstone National Park
Fishing Bridge WWTP
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report/
21. NO. OF PAGES
44 inr.l t.itlp
20. SECURITY CLASS (This page)
22. PRICE
EPA Form 2220-1 (R«v. 4-77) previous edition is obsolete
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11Mb I KULI IUIN&
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