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FIGURE 7
MAXIMUM GROWTH RATE OF NITRIFYING BACTERIA
AT VARIOUS TEMPERATURES
2.0
O -4
DC
. 3
2
2.2
X
.1
FROM KNOWLES ET AL(I4)
x
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8 10 12 14 16
TEMP ERATUR E •C
18
20
22
SAWYER ETAL (12)
GUYER AND JENKINS (13)
KNOWLES ET AL (14)
PRAKASAM a LOEHR (|7) •
THIS STUDY O
87
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DESIGN CONSIDERATIONS
Determination of the Design SRT
In our opinion, the importance of incorporating a reason-
able degree of flexibility (i.e., margin of safety) into the
design of a combined carbon oxidation-nitrification system was
clearly demonstrated by the results obtained during this study.
This requirement for an adequate safety factor cannot be over-
emphasized as the key to successfully maintaining nitrification
during periods of high strength waste loadings or sustained low
temperature conditions. Thus, in general, the major considera-
tions to be made in the determination of the safety factor, and
therefore in the selection of the design SRT, are with respect
to aeration temperature and waste strength, with DO and other
environmental factors assumed not to be limiting. Consequently,
since the maximum growth rate of the nitrifying bacteria is
primarily affected by temperature, determination of the design
SRT required in order to achieve the desired NH4~N removals
should be predicated on the lowest temperatures expected to be
encountered in the aeration tanks.
Based on historical data, the lowest sustained aeration
temperature likely to be experienced at W-SW is 10°C. As may
be recalled from Figure 6, Battery D successfully maintained
nitrification throughout the winter at temperatures ranging from
11-13°C (averaging 12°C), with SRTs being about 8-10 days. On
the other hand, Batteries A, B and C achieved only marginal
88
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nitrification during this period as average SRTs equalled 5.0,
4.4 and 4.5 days, respectively. Therefore, on the basis of
these results and the published literature previously cited
with regard to SET and temperature considerations, it would
appear that a design SRT of 10 days at 10°C should be adequate
for treating the W-SW influent wastewater.
A 10-day design SRT for the expanded and improved W-SW
Plant also provides sufficient flexibility to accommodate
significant increases in waste loadings in terms of BOD, sus-
pended solids and NH.-N, which could otherwise result in de-
terioration of the effluent quality. In fact, NH.-N break-
throughs in response to transient increases in NH.-N loading
were recorded on several occasions in Batteries A, B and C,
being indicative of the generally insufficient nitrifying
populations maintained in these batteries. However, this
occurred on only one occasion in Battery D (documented in
Figure 4), and resulted in the future effluent NH.-N daily
standard of 4.0 mg/1 being exceeded on two consecutive days.
As was pointed out, with the notable exception of the estab-
lished SRT, Battery D was maintained at roughly equivalent
operating conditions as the other three batteries.
With the anticipated implementation of the MSDGC's Tunnel
and Reservoir Plan (.TARP) for pollution and flood control, it
is expected that hydraulic shock loadings to the W-SW Plant
will be substantially reduced but not completely eliminated.
89
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Estimation of Suspended Solids Production
As mentioned, it was revealed in a previous publication
by Obayashi et al(ll) that the suspended solids loading to the
(Battery D) aeration tanks, rather than the total 5-day BOD
applied, was more indicative of the suspended solids produc-
tion rate in the system. This observation was attributed to
the relatively low soluble BOD concentration (approximately 30
mg/1) which was found in both the West Side Imhoff primary ef-
fluent and the Southwest preliminary effluent, with most of
the total BOD being associated with the suspended solids. Fur-
ther, owing to the combined stormwater — domestic sewer system
in use in the MSDGC service area—the BOD to SS ratio was
highly variable, ranging from 1;1 during dry weather to about
1:2 or 3 during storm flow periods.
The report also indicated that the percent volatile con-
tent of the suspended solids significantly affected the sus-
pended solids production, with approximately 30-40 percent
less solids being produced per Ib of influent suspended solids
from the Southwest primary effluent (73 percent volatile) than
from the West Side Imhoff effluent (64 percent volatile). The
lower solids production obtained was accounted for by an over-
all greater destruction of the more easily biodegradable sus-
pended solids in the SW primary effluent, as evidenced by the
90
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volatile content being reduced from 70-75 percent to 60-65
percent in the activated sludge process. In comparison, the
volatile content of the influent suspended solids and the
mixed liquor was about the same (60-65%), thus reflecting lit-
tle or no biological oxidation, when the primary effluent was
from the West Side,
Based on the average results of the study, a suspended
solids yield coefficient of 0.9 Ibs of SS produced per Ib of
influent SS was obtained and was subsequently used to estimate
future SS production at W-SW. This value (0.9 Ibs/lb) repre-
sents the average of Phases 1 and 2, and is in agreement with
earlier MSDGC studies conducted at both the North Side and
West-Southwest Plants.
Aeration Tank Volume Requirements for Single Stage Nitrification
At West-Southwest
Table 9 lists several design alternatives, along with the
basic assumptions on which the design aeration tank volume re-
quirements for single-stage nitrification at West-Southwest are
predicated. These assumptions reflect projected conditions at
the W-SW Plant for the 1990 design year, and were obtained from
the results of a solids study(7) conducted by the Engineering
Department projecting future solids loadings.
Following the completion of TARP, the winter design sewage
flow of 1315 mgd (1358 mgd~summer) should essentially constitute
the maximum flow to the aeration tanks. Therefore, with the
(assumed) average influent suspended solids concentration to the
91
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TABLE 9
An Evaluation of Various Design Parameters for
Nitrification at West-Southwest
Assumptions:
1. design flow (winter) = 1315 MGD
2. average influent TSS = 105 mg/1
3. solids yield coefficient = 0.9 Ibs/lb inf. TSS
4. solids recycle rate = 50 percent
5. design flow (summer) = 1358 MGD
6. design final tank surface settling rate = 800 gpd/sq ft
SRT, MLSS, HRT, Solids Loading Rate to
days mg/1 Required Volume, MG hrs Clarifiers, Ibs/ft2/day
10 2500 493 9.0 25.0
3000 411 7.5 30.0
3500 352 6.4 35.0
9 2500 444 8.1 25.0
3000 370 6.8 30.0
3500 317 5.8 35.0
8 2500 394 7.2 25.0
3000 329 6.0 30.0
3500 282 5.1 35.0
7 2500 345 6.3 25.0
3000 288 5.2 30.0
3500 246 4.5 35.0
6 2500 296 5.4 25.0
3000 247 4.5 30.0
3500 211 3.8 35.0
92
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aeration tanks being 105 mg/1, the anticipated design solids
loadings should equal about 575 tons/day. Accordingly, given
a solids yield coefficient of 0.9 Ibs of solids produced per
Ib of influent suspended solids, the daily quantity of sus-
pended solids to be wasted would amount to 518 tons. Thus, in
order to achieve the recommended design SRT of 10 days, the
solids inventory (mixed liquor suspended solids under aeration)
would have to be equivalent to approximately 5180 tons. Prac-
tically speaking, this requirement can only be met by sub-
stantially increasing the aeration volume above the present
204 million gallon capacity. Consequently, by maintaining MLSS
at approximately the 3,000 mg/1 level as recommended, although
operation at higher MLSS concentrations would not be precluded,
411 million gallons of total aeration volume will be needed.
The resulting design HRT at 411 MG of aeration volume is
7.5 hours (with the design sewage flow being 1315 mgd). Al-
though this design value exceeds the average HRT of 5.5 hours
that was observed in Battery D during Phase 1 at a comparable
SRT of 10 days, this can be attributed to the relatively low
solids yield coefficient of 0.72 Ibs/lb obtained during this
period while treating Southwest preliminary effluent. In
other words, if a higher solids yield coefficient had been
obtained during Phase 1, for example 0.9 Ibs/lb, then Battery D
could not have operated at 10 days SRT due to higher solids
wastage requirements. Given this particular situation, provid-
93
-------
ing a larger aeration volume would consequently permit main-
taining the desired 10 day SRT. However, the corresponding
HRT would then be increased in proportion to the increase in
the aeration volume.
Summarizing the above, the required aeration volume needed
to achieve desired levels of nitrification and carbon oxidation
in the future West-Southwest Plant is 411 million gallons, an
expansion of approximately 207 million gallons over the present
aeration capacity of 204 MG. As discussed and shown in Table 9,
the required volume is based on the following design criteria:
1. SRT = 10 days
2. MLSS = 3;000 rag/1
3. Suspended solids produced = 0.9 Ibs SS produced
Ib influent SS
4. Sewage flow = 1315 mgd
5. 1990 influent suspended solids = 105 mg/1.
It should be clear that the success of the nitrification
design depends on the existing older facilities (Batteries A,
B and C) being sufficiently rehabilitated, as planned, to the
extent necessary to affect carbon oxidation and NH.-N removal
consistent with the demonstrated performance of Battery D.
Further, the scheduled rehabilitation of the West Side Imhoff
tanks must also be completed.
Estimated Construction Costs
The estimated construction costs for implementing the
indicated expansion and improvements to the West-Southwest
94
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Plant are about $475 million, based on an Engineering News
Record (ENR) Chicago area January, 1980 construction cost
index of 3300(18). Included in this cost estimate are approx-
imately $61.3 million for a new blower facility.
95
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References
1. "Rules and Regulations of the Illinois Pollution Control
Board," Chapter 3, Water Pollution, Rule 406, 1972.
2. Sawyer, B., A.W. Obayashi, and C. Lue-Hing, "Full-Scale
Single Stage Nitrification Study at the North Side Sewage
Treatment Plant," MSDGC Research- and Development Report,
75-26, October, 1975.
3. Washington, B., A.W. Obayashi, C. Lue-Hing, and D.R. Zenz,
"Single Stage Nitrification Study at the West-Southwest
Treatment Plant," MSDGC Research and Development Report,
76-2, November, 1975.
4. Prakasam, T.B.S., C. Lue-Hing, E. Bogusch, and D.R. Zenz,
"Pilot-Scale Studies of Single-stage Nitrification," Jour.
Wat. Poll. Con. Fed., Vol. 51, p. 1904 (1979).
5. Lawrence, A.W., and P.L. McCarty, "Unified Basis for
Biological Treatment Design and Operation," J. Sanitary
Engr. Div. Amer. Soc. of Civil Engr., Vol. 96, p. 757
(1970).
6. "Process Design Manual for Nitrogen Control," U.S. EPA, Of-
fice of Technology Transfer, Washington, D.C., October,
1975.
7. "Design Criteria, Expansion and Improvement, West-Southwest
Sewage Treatment Works, Rev. No. 4," Department of
Engineering, Metropolitan Sanitary District of Greater
Chicago, June, 1975.
8. Beckman, W.J., et al, "Combined Carbon Oxidation Nitrifica-
tion," Jour. Wat. Poll. Con. Fed., Vol. 44 p. 1916 (1972).
9. Smith, J.I., "Investigation of a Rapid Method for Sludge
Solids Estimation," Sewage Works J., Vol. 6, p. 908 (1934).
10. "Standard Methods for the Examination of Water and Wastewater,"
American Public Health Assn., Inc., 13th Ed., New York, N.Y.U971).
11. Obayashi, A.W., B. Washington, and C. Lue-Hing, "Net Sludge
Yields Obtained During Single Stage Nitrification Studies
at Chicago's West-Southwest Treatment Plant," Proc. of the
32nd Annual Purdue Industrial Waste Conference, p. 759
(1978).
12. Sawyer, B., A.W. Obayashi, C, Lue-Hing and D.R, Zenz
"Estimation of the Maximum Growth. Rate of Ammonia Oxidizing
Nitrifying Bacteria Growing in Municipal Wastewater," Paper
presented at the 52nd Annual WPCF Conference, Houston, Tex.,
October, 1979.
96
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References (Cont'd)
13. Gujer, W., and D. Jenkins, "The Contact Stabilization Pro-
cess-Oxygen and Nitrogen Mass Balances," San-Engr. Res.
Lab. Rept No. 74-2, Univ. of Calif. Berkeley (1974).
14. Knowles G., A.L. Downing, and M.J. Barrett, "Determination
of Kinetic Constants for Nitrifying Bacteria in Mixed
Culture, with the Aid of an Electronic Computer," J. Gen
Microbiology, Vol. 38, p. 263 (1965).
15. Lawrence, A.W., and C.G. Brown, "Design and Control of
Nitrifying Activated Sludge Systems," J. Water Poll. Con.
Fed., Vol. 48, p. 1779 (1976).
16. Poduska, R.A., and J.F. Andrews, "Dynamics of Nitrification
in the Activated Sludge Process," Jour. Water Poll. Con.
Fed., Vol. 47, p. 2599 (1975).
17. Prakasam, T.B.S., and R.C. Loehr, "Microbial Nitrificaiton
and Denitrification in Concentrated Wastes," Water Res.,
Vol. 6, p. 859 (1972).
18. "Master Design Program for Treatment Facilities," Department
of Engineering, Metropolitan Sanitary District of Greater
Chicago, January, 1980.
97
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PHOSPHORUS REMOVAL WITH IRON SALTS AT BLUE PLAINS
Edgar R. Jones, P.E.
Chief Process Engineer
Bureau of Wastewater Treatment
District of Columbia Government
Washington, D.C.
BACKGROUND AND INTRODUCTION
The District of Columbia's Wastewater Treatment Plant at Blue Plains
is a regional treatment plant located along the Potomac Estuary in the
nation's capital. (See Figure 1.) The plant's service area is approximately
725 square miles with a population equivalent of 2,200,000. An average
flow of 330 mgd of medium strength sewage from primarily residential and
office complexes is treated daily. Flows from the District of Columbia
and Maryland account for 95% of the flows received with the balance coming
fram Virginia. (See Figure 2.) The wastewater treatment scheme
incorporates primary sedimentation followed by a modified aeration activated
sludge process (See Figure 3.). On-going expansion will add nitrification
and multi-media filtration to the wastewater train in the early 1980's.
Sludge processing operations include gravity and flotation thickening,
anaerabic digestion and elutriation, vacuum filtration and sludge disposal
by an amalgram of composting, trenching, incineration and land spreading
methods. (See Figure 4.)
Discharges to the Potomac Estuary are regulated by an NPDES permit and an
Order of Compliance. Effluent quality criteria is designed to enhance the
water quality in the Estuary. Maximum pound loadings for various pollutants
under various flow conditions in the Estuary were developed by EPA in 1971
(1). In their study, EPA noted a 12-fold and 9 -fold increase in phosphorus
and nitrogen loadings to the estuary from 1913 to 1970. The algae population
98
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N
-ANACOSTU HIVCR
LEGEND
• MAJOR WASTE TREATMENT PLANTS
A GAGING STATION - WASHINGTON, O.C.
A DISTRICT OF COLUMBIA
B ARLINGTON COUNTY
C ALEXANDRIA SANITATION AUTHORITY
D FAIRFAX COUNTY - WESTGATE PLANT
E FAIRFAX COUNTY - LITTLE HUNTING CREEK PLANT
F BMRFAX COUNTY - OOGUE CREEK PLANT
G WASHINGTON SUBURBAN SANITARY COMMISSION - PISCATAWAY
H ANDREWS AIR FORCE BASE - PLANTS ONE. FOUR
I FORT BELVOIR - PLANTS ONE. TWO
J PENTAGON
K FAIRFAX COUNTY - LOWER POTOMAC PLANT
Source - EPA TR 35, Ref. 1
Figure 1. Potomac Estuary
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became unbalanced with dominance by blue-greeen algae coincident with
the phosphorus and nitrogen increases. Since wastewater loadings increased
from 42 mgd to 325 mgd during that same period, EPA concluded that
unfavorable ecological changes were due to the phosphorus and nitrogen
loadings from wastewater treatment plant discharges.
To maintain algal standing crops below nuisance levels under severe
summer conditions, EPA concluded that phosphorus concentrations should
be limited to 0.03 to 0.1 mg/L as P in the estuary. Similar limitations
were imposed on nitrogen concentrations. Consequently, discharge limitations
for Blue Plains were formulated that would effect the necessary nutrient
restrictions in the Estuary. Table 1 summarizes Blue Plains NPDES
limitations along with Order of Compliance iterim requirements staged to
coincide with construction events.
To meet the stringent effluent quality criteria established for the Blue
Plains wastewater treatment facility, numerous unit processes were reviewed
in an extensive pilot plant program. The research effort was carried out
jointly by the District of Columbia Government and the EPA. Various process
combinations were compared in terms of process reliability, relative costs,
land requirements, chemical availability and treatment capabilities of
existing facilities during and after construction. The process scheme
selected utilized the existing modified aeration activated sludge process
for secondary treatment to conserve limited site aera and to produce an
effluent compatible with the subsequent biological nitxificaticm-denitrification
process. Denitrification has been held in obeyance pending additional
estuary studies. Alum or ferric chloride is designed for phosphorus removal
in the modified aeration system.
103
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Iron salts, either FeCL, or FeSO. are used, at Blue Plains because of
costs and local availability. Both chemicals are industrial waste by-
products from major sources within 150 miles of the plant. FeClo is added
prior to secondary clarification. When used in lieu of FeCL,, FeSO. is
added in the aeration basin for ferrous iron to ferric iron conversion by
oxidation. Anionic polymers are added with the iron salts to improve
the settling characteristics of the mixed liquor suspended solids.
The purpose of this paper is to present on analysis of Blue Plains operating
data showing phosphorus removal efficiencies, chemical sludge quantities
and costs related to phosphorus removal. Full-scale process performance
data will be compared to pilot plant data, plant design criteria and NPDES
and compliance order requirements.
CHEMICAL ADDITION IN SECONDARY
During the initial compliance period, effluent limitations were met by
adding 35 mg/1 of FeCl- to half of the secondary process. The 35 mg/1
was a criteria established in the pilot plant studies. The 35 mg/1 dose
was quickly recognized as too sludge intensive for full plant application.
A polyelectrolyte was substituted for part of the metal salt dosage. Full
plant addition of 25 mg/1 FeCl., and 0.3 mg/1 of an anionic polymer minimized
the amount of chemical sludge generated and achieved the desired phosphorus,
BOD_ and suspended solids removals during the Interim I period.
Once Region III EPA recognized phosphorus discharges were as low as 1.6
mg/1 routinely, the Order of Compliance was revised to restrict phosphorus
discharges to that lower level. Table 2 summarizes plant performances under
three degrees of compliance.
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A decline in phosphorus influxes to Blue Plains has reduced chemical
demands below original projections. Phosphorus reduction trends are
shown in Figure 5. Better than expected phosphorus discharges are
attributable to the lower phosphorus influxes.
Rate of phosphorus insolubilization by FeCl- was separated from the
biological phosphorus uptake and quantified. Figure 6 is a plot of
phosphorus removal in the secondary process as a function of FeCl,
addition. Each point plotted represents a monthly average as sunmarized
in Appendix A. The slope of the line of best fit is 0.0926 pounds of
phosphorus removed per pound of FeClo added. Inversely, 10.8 pounds of
FeCl., is required to remove one pound of phosphorus. The Fe/P molar
ratio was 1.8. The Y - intercept, 2.1 mg/1, represents the biological
phosphorus uptake occurring in the activated sludge process. The phosphorus
to volatile suspended solids ratio (P/VSS) in the secondary waste sludge
was 0.029 and is consistant with the P/VSS ratio of 0.03 calculated for
the waste sludge in 1970 and 1971 when Fedo was not added.
By far, the most alarming problem associated with phosphorus removal with
iron salts is the inability of feed systems to resist the process chemical.
Blue Plains has experienced over 30 failures in sections of rubber lined
pipes and fittings. Those failures have occurred in suction, discharge,
and transmission lines. On one occasion, an 8-inch PVC transmission
line burst sending fragments of PVC flying 50 feet in all directions and
spilling approximately 3000 gallons of FeCl-,, m addition, no less than
20 FeCl., measuring cylinder heads in the metering pumps have failed
spilling FeCL. in the pump vicinity. As a result of the many failures in
various system components, spilled FeCL, has seriously injured three
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employees and caused extensive damage to the equipment.
Faulty rubber lined pipe is normally replaced by PVC or fiberglass pipe
as ruptures occur. The permanent fix on the measuring cylinders was to
replace the kynar coated cylinders with, solid polypropylene ones. Slight
microscopic imperfections in the egg-shell thin kynar coating were suspected,
allowing FeCl3 to attack the aluminum core.
Since effluent phosphorus concentrations are well within permit limitations,
the phosphorus analyzers installed to trim the metering pumps are not
utilized. As tolerances decrease, the analyzers will be put on-line to
support the flow pacing mechanising built into the metering pumps.
SOLIDS GENERATION WITH FeCl.,
One adverse consequence of chemical addition for phosphorus removal is the
increased sludge mass. Besides the chemical precipitates of FePO. and
Fe(OH)-. complexes, improved suspended solids captures add to the amount
of waste sludge requiring disposal. Data and procedures predicting
quantities of chemical sludge as a function of chemical added or phosphorus
removed are scarce. In their design manual for phosphorus removal (2),
EPA estimates solids generation rates using simple stoichiometric relationships
and then allowing for extra sludge by multipling the stoichiometric result
times a 35% safety factor, i.e. 1.35 multiplier. The following analyses
of Blue Plains data will support at least a 35% safety factor.
The observed chemical solids generation rate was 1.12 pounds of solids
per pound of FeCl3 added. The major device used to measure the chemical
sludge quantities generated was a mass balance around the point of chemical
addition. As a check, mass balances with and without chemical addition
110
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Mass balances were performed for four, two-year periods as summarized in
Table 3. Background data without chemical addition was codified for the
period between January 1969 through December 1970. Mass balances during
a two year period of Alum and FeCl- trials were reduced in a mass balance
for January 1372 through December 1973. Another mass balance for the period
between January 1975 through December 1976 was produced for the period where
reduced FeCl3 dosages were tolerated while a polymer was used to aid MLSS's
settleability. The mass balance for January 1977 through December 1978
reveals the effect of heavy recycled solids from gravity thickening. The
mass balance for each period is enclosed in Appendix B.
Figure 7 is a bar graph of total waste activated solids for the four
periods identified in Table 3. Chemical solids (ChemS) are shown
in perspective with biological waste activated solids (EWAS). BW&S equals
inert waste activated solids (IWAS) plus volatile activated solids (VWAS).
Bar C shows the pronounced increase of inert solids due to chemical solids
while Bar D reflects an increase in solids loadingA/asting effects due
to the plant recycled solids situation.
FeCl- addition appears to have little effect on the biology in the high
rate secondary process at Blue Plains. The biological solids production
factors were relatively consistent before and after FeCl., addition. Table
4 summarizes the observed solids yields. Also, as shown in Table 5, the
%VS (BWAS) data provides additional credence to the biological growth factors
and the mass balances. Table 6 presents Blue Plains chemical solids production
factors for both FeCl and Alum.
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were compared for similarity of non-chemical related parameters. Following
is a recap of the generalized solids generation formulas used in the
Blue Plains secondary process:
(1) TWAS = BWAS + ChemS = WASTE + SSrff
(2) BWAS = TWAS + VWAS
(3) IWAS = ^ x SSinf
(4) I/SET = k2 x F/M
(5) VWAS = k3 x BODr
(6) ChemS = k. x FeCl^
(7) F = BCD ._ - BCDeff + 0.68 x 1.42 x VSS
(8) % VS (TWAS) = VWAS x 100 = %MLVSS
TWAS
(9) %VS (BWAS) = VWAS x 100
BWAS
Where:
TWAS = Total waste activated solids
BWAS = Biological waste activated solids
ChemS = Chemical waste solids
IWAS = Inert waste activated solids
VWAS = Volatile waste activated solids
WASTE = Waste secondary sludge
SS. ,. = Suspended solids in secondary influent
BODV^p = BOD_ in secondary influent
SS =Suspended solids in secondary effluent
VSS .p, = Volatile suspended solids in secondary effluent
BCD _f = BODj. in secondary effluent
FeC?3 = FeCl- added in secondary
SET = Solids residence time
F/M. = Food to mass ratio
F = BCD5 insolubilized in secondary
BCD = BCD,, removed in secondary
M = Mixed Liquor volatile suspended solids mass
k,, k«, k., k. = Solids production factors derived
ffon actual operating data
%MLVSS = Per cent mixed liquor volatile suspended solids
117
-------
The stoicniometric factor can range fron 0.94 to 0.66 Ibs solids/Ib
FeCl3 as the Fe/P molar ratio varies from zero to infinity. An adjusted
estimated range of values for the solids/FeCl., ratio using the EPA
multiplier of 1.35 is 1.27 to 0.89. The 1.12 Ibs chemS/lb FeCl3 factor
correlates well with EPA estimates.
POSTS
Recent O&M costs for the past three fiscal years (FY 77-79) are presented
in Appendix C. FeCl., requirements in the period were 58,000 Ibs/day for
phosphrous removal. To properly identify the costs associated with
phosphorus removal, the cost for chemicals must be added to the extra cost
for handling and disposal of the chemical sludge. For the three year period,
FeCL, costs were 6.8^/lb. Raw sludge disposal costs by trenching were $35/ton.
Filter cake production of chemS's as a function of phosphorus assuming
chemical condition requirements of 8% FeCl- and 27% lime on a vacuum filter
producing a 22% cake are as follows:
1.12 x 1.35 x 58,000 _ _._ wet tons
0.22 x 2000 Day
Ignoring the chemical conditioning costs and combining the two major cost
items, the average annual cost for phosphorus removal during the past three
years was as follows:
ITEM Daily Quantity Annual Cost
$ 10bAear
FeCl3 58,000 Ibs/Day $1.44
Raw Sludge 217 wet ton/day 2.77
$4.21
Since the phosphorus removed chemically in the past three years was
0.0926 x 58,000 = 5370 lbs/t>ay, the O&M cost to remove phosphorus chemically
was greater than two dollars per pound, i.e. 4,210,000/365 = $2.15/lb P .
5370
Figure 8 shows the O&M costs for
FeCl and sludge disposal as a function of phosphorus removed.
118
-------
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Utilizing FeSO. will reduce the costs by a third since FeSO. will be
supplied at no costs.
RECOMMENDATIONS
Following are suggested reconmendations for future investigations:
1) To reduce sludge requirements, biological phosphorus
removal mechanisms should be further evaluated to reduce
chemical requirements and sludge generation in the phosphorus
removal process.
2) Where commercial grade chemicals are being used for phosphorus
removal, cleaper industrial waste by-products should be examined
for possible use.
CONCLUSION
In the modified aeration activated sludge process at Blue Plains, FeCl3
is added to remove phosphorus and enchance SS's and BOD_ removal efficiencies.
Concern over increasing solids generation rates due to chemical sludge
resulted in a substitution of polymer for a portion of the FeCl^ dose. A
significant quantity of costly sludge production has been avoided at a
substantial saving. One pound of FeCl, creates 1.12 pounds of chemical
sludge but only removes 0.0926 pounds of phosphorus in the process. Cost
to remove phosphorus with FeCl, is over two dollars per pound. Eventual
O&M costs to remove phosphorus will drop once FeSO, is used since FeSO.
will be provided free of charge.
BIBLIOGRAPHY
1. Jaworski, N.A., Leo J. Clark, and Kenneth D. Feigner, "A Water
Resource - Water Supply Study of the Potomac Estuary,"
Technical Report 35, April 1971.
120
-------
2. "Process Design Manual for Phosphorus Removal," USEPA,
Technology Transfer, April 19.16.
121
-------
APPENDIX A
INSOLUBILIZATION OF PHOSPHORUS IN THE EAST
SECONDARY PROCESS AT BLUE PLAINS
PHOSPHORUS CONCENTRATIONS, MG/L
MONTH
JUN 77
JUL77
AUG 77
SEPT 77
OCT77
NOV 77
DEC 77
JAN 78
FEB 78
MAR 78
APR 78
MAY 78
JUN 78
JUL 78
AUG 78
SEPT 78
OCT 78
MEAN
STAN-
DARD DEV
0-IN
MGD
173
173
193
215
168
172
199
202
174
193
201
213
214
228
243
231
207
200
t
FeCI3
KIP/DAY
40.7
38.5
44.2
47.8
47.4
44.3
49.8
40.0
39.5
46.0
38.2
31.2
35.1
40.0
40.8
42.1
36.2
41.9
MG/L
28.2
26.7
27.5
26.7
33.8
30.9
30.0
23.7
27.2
28.6
22.8
17.6
19.7
21.0
20.1
21.9
21.0
25.1
4.56
TOTAL
PIN
(A)
5.7
6.0
5.3
5.5
5.9
5.4
4.7
4.6
5.3
5.2
5.1
4.8
4.7
5.0
4.9
4.6
5.2
5.2
0.45
TOTAL
POUT
(B)
1.7
2.2
1.9
1.9
1.6
2.0
1.3
1.4
1.9
1.2
1.5
1.8
1.9
2.1
1.7
1.7
2.0
1.8
0.28
DIS-
SOLVED
POUT
(0
0.9
1.1
0.9
0.8
0.5
0.7
0.3
0.3
0.5
0.3
0.8
1.0
1.0
1.1
1.0
0.7
0.9
0.76
0.273
INSOLU-
BILIZED
P
(A-C)
4.8
4.9
4.4
4.7
5.4
4.7
4.3
4.3
4.8
4.9
4.3
3.8
3.7
3.9
3.9
3.9
4.3
4.42
0.492
WASTE VSS
KIPS/DAY
103
90
138
125
109
99
112
123
101
134
145
136
109
115
110
128
176
121
NOTES: BIOLOGICAL P UPTAKE: P/VSS RATIO
1) 2.1 • 8.35 * 200/121 - 0.029
2) W/0 FeCI3 (CY 70 & 71) » 0.029 TO
003
122
-------
APPENDIX B
SECONDARY SOLIDS PRODUCTION MASS BALANCE FOR
nAss B
CY
SS
225
BOD
32O
N
MOD Secondary Influent
mg/1
kips/day
Kips/day I - %VS
MGD Reactor Loading
j/2/7 Kips/day | 7f./_%VS_
3/.O MG D " Ret" uf n
Secondary Reactors
MLSS = 60? mg/1
Reactor Vol. = 2S_ MG
Kips/dayNet Growth
i*t 92 Kips/day ] 20.2 %VS
MGD Reactor Effluent
Secondary Clarifiers
Surf. Area =230X/0*SF
Clar. Vol. =2O MG
W12 Kips/day | - gVS
MGD Discharge
/63 Kips/day
/. fr 3 MOD
Waste
SS
BOD
57
//O
N
262 MGD Secondary Effluent
SR~= O,V7 Days
F/M= 2.% /Day
Chemical
Polyner
kips/day
ng/1
kips/day
1) TV/AS = Total Waste Act. Solids = Waste + SSeff = 275
TV/AS = Biological Waste Act. Solids (BWAS) + Chemical Solids
ChemS = 1.12 * FeCl = Q Kips/Day
BWAS = TWAS - ChemSj= 27f Kips/Day
BWAS = Volatile Solids (VWAS) + Inert Solids (IWAS)
= 55MLVSS * TWAS/100_= 221 Kips/Day
= BWAS -
Kips/Day
(ChemS)
IWAS = BWAS - VWAS =
= IWAS/SSinf = _J
Kips/Day
VWAS/BWAS
,8 62
2) 1/SRT = k.
F/M
= VWAS/F
0.75
SRT = Solids Residence Time = M/VWAS
kp = Observed Yield F/M = Food to Mass Ratio
F = BODlnf - BODpff +0.68 * 1.H2 * VSSpff
VWAS/BODR
/. 05
M
^MLVSS * 8.35
M =
123
Kips/Day
Kips
-------
SECONDARY SOLIDS PRODUCTION MASS BALANCE FOR CY 72 i 73
HAS5 BALANCE "B*
Kips/day | 6S.S %VS
•5 MGD Return
Kips/day
O/7«? MOD
Waste
SS
222
BOD
287
7.7
/7.7
N
277 MOD Secondary Influent
mg/1
kips/day
Kips/day I — %VS
MOD Reactor Loadin
Secondary Reactors
MLSS * 75"3 mg/1
Reactor Vol.=20.£MG
f3g Kips/day 'Net Growth
if53 KipsTday | 7f,3 %VS>
3/t MOD Reactor Effluent
Secondary Clarif iers
Surf. Area ~230*IO*S?
Clar. Vol. = ^O MG
7973 Kips/day \ -%VS
MOD Discharge
SS BOD
J7
96
N
XX
276MGD Secondary Effluent
SRT=
kips/day
ry
kips/day
1) TWAS
TV/AS
Total Waste Act. Solids = Waste + SSoff = Z77 Kips/Day
Biological Waste Act. Solids (BWAS) + Chemical Solids (ChemS)
ChemS « 1.12 * FeCl^= 2O Kips/Day
257 Kips/Day
BWAS = TWAS - ChemS-
BWAS = Volatile Solids (VWAS) + Inert Solids (IWAS)
VWAS = 55MLVSS * TWAS/100 = 209 Kips/Day
IWAS = BWAS - VWAS «
= IWAS/SSlnf = Q.22
Kips/Day
VWAS/BWAS = 0,813
2) 1/SRT = k2 * F/M
k0 = VWAS/F = 0
SRT = Solids Residence Time = M/VWAS
Observed Yield
= VWAS/BODR
= /.O?
F - BODinf -
M = VA *MLVSS * 8.35
252
F/M = Food to Mass Ratio
0.68 * 1.42 * VSS
-------
SECONDARY SOLIDS PRODUCTION MASS BALANCE FOR
HAS5 BALANCE "£NS
75
\20/6 Xips/day
MOD
_
Return
256 Kips/day
6f.7 ^VS
0,70 MGD Waste
SS
BOD
213
5,7
N
MGD Secondary Influent
mg/1
kips/day
Kips/day I - %VS
320 MGD Reactor Loading
Secondary Reactors
MLSS = 8S& mg/1
Reactor
i~SZ Kips/day Net Growth
22 ?O Kips/day T 6SP
Clar. Vol. = 3-Q MG
^y Kips/Day
IWAS
k, =
= BWAS - VWAS «
IWAS/SSinf = Q.2O
Kips/Day
VWAS/BWAS = O.fZS"
2) 1/SRT = k2 * F/M
k0 = WAS/F = 6
SRT = Solids Residence Time = M/VWAS
k0 = Observed Yield F/M = Food to Mass Ratio
0.68 * 1.42 * VSS.
= VWAS/BODR
= /.OS
F = BODlnf - BODftff -
M « V. *MLVSS * 8.35
F «
M »
125
eff
1/3
Kips/Day
Kips
-------
SECONDARY SOLIDS PRODUCTION MASS BALANCE FOR CY77
MASS BAM MCE "D
l%
SS . BOD
N
135
339
tto
352
2*.*}
3O/ MOD Secondary Influent
mg/1
kips/day
Kips/day | - %VS
MOD
Return
Kips/day 6f,7 SVS
MGD
Waste
Kips/day | - %VS
351 MGD_... React or Loading
Secondary Reactors
MLSS = /bVff mg/1
Reactor
Kips/day Net Growth
Kips/day
357 MOD Reactor Effluent
Secondary Clarifiers -f 71
Surf. Area = *N0x/o* SF
Clar. Vol. =5? MG
-" %VS
MGD Discharge
SS BOD
N
217 MGD Secondary Effluent
SRT=^77 Days
F/M=-/5'j'/Day
Chemical
Polymer
kips/day
ng/1
kips/day
1) TWAS = Total Waste Act. Solids = Waste + SSpfy = ^^2 Kips/Day
TV/AS - Biological Waste Act. Solids (BWAS) + Chemical Solids (ChemS)
ChemS • 1.12 * FeCl = 7/ Kips/Day
TWAS - ChemS -_J?7//_ Kips/Day
Volatile Solids (VWAS) + Inert Solids (IWAS)
WAS = $MLVSS * TWAS/100 = 2?O Kips/Day
<5V
BWAS
BWAS
IWAS = BWAS - VWAS
1^ = IWAS/SSinf =
Kips/Day
VWAS/BWAS = 0,182
2) 1/SRT = k2
F/M
VWAS/F = 0,2$
SRT = Solids Residence Time = M/V\VAS
k = Observed Yield F/M = Food to Mass Ratio
VWAS/BODR
/,03
F = BODinf - BODPff +
M = VA *MLVSS * 8.35
0.68 * 1.42 * VSS
ff
F = 322 Kips/Day
M =
126
Kips
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NITRIFICATION AT LIMA, OHIO
Felix F. Sampayo
Member
Jones & Henry Engineers, Limited
INTRODUCTION
The City of Lima, located in northwestern Ohio (40°45? lati-
tude), has a population of approximately 53,000. The City is
an important industrial center with an excellent rail and high-
way network. Average monthly temperatures range from 2.4 C
in January to 23.2 C in July.
A substantial part of the City is served by combined sewers.
Combined sewer overflows and wastewater treatment plant efflu-
ent are discharged to the Auglaize River. During dry weather,
treatment plant effluent constitutes the majority of the stream
flow.
In the late 1960s, the City began planning a pollution control
program to reduce combined sewer overflows and to improve the
existing secondary treatment plant. The program called for the
first flush of the combined sewer overflows to be collected and
transported to the treatment plant where the wastewaters would
receive at least primary treatment and chlorination. In late
January 1970, the City of Lima authorized Jones & Henry
Engineers, Limited to prepare a report recommending improve-
ments to the treatment plant. In May 1971, a report covering
phosphorus removal and miscellaneous improvements was submitted
to the City. Shortly after the report was completed, the City
129
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was requested by the State regulatory agency to investigate the
possibility of producing a nitrified effluent in order to
reduce the ammonia concentration in the Auglaize River.
This paper summarizes the results of the pilot studies used in
the design of the nitrification facilities, discusses the
selected treatment process, and presents operating results and
costs for three years of full-scale operation. Overall nitro-
gen control efficiency, process reliability, operational con-
trols and problems, and capital costs are also discussed. The
paper concludes with recommendations directed to more cost-
effective second generation facilities and suggests areas for
additional research.
PILOT STUDIES
Several processes were considered for possible use in producing
a nitrified effluent. The use of a one-stage or two-stage
activated sludge for nitrification was investigated and aban-
doned as impractical. During wet weather, nitrifying organisms
were washed out of the system due to high flows from the com-
bined sewers. Laboratory studies verified that one-stage and
two-stage activated sludge were ineffective, and that break-
point chlorination of the effluent would have been very cost-
ly. A decision was made to investigate nitrification towers
rollowing the existing activated sludge. This concept appeared
to offer advantages such as low area requirements, stable per-
formance, and easy operation. The possible disadvantages
130
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included high capital and operation costs required to pump the
secondary effluent to the nitrification tower.
The studies were conducted in 1972-73 using a pilot unit con-
sisting of a steel shell 3 feet in diameter and 30 feet high
with 21.5 feet of plastic filter media. The media used in the
study was Surfpac, a product marketed at that time by Dow
Chemical.
The experiments showed nitrification towers could produce very
low ammonia levels during the summer months. Winter ammonia
levels would be higher because the ammonia concentration in the
tower effluent increased as the waste and air temperatures
decreased.
No net reduction in BOD^ was obtained which pointed to the
development of very specific nitrifying cultures in the tower.
Changes related to suspended solids concentration and pH were
negligible. No substantial sloughing of solids occurred at any
time as the high application rates kept solids from accumu-
lating on the surface of the media.
Study results showed nitrification units should be designed on
the basis of Total K-N (Kjeldahl) Nitrogen loading. Within the
flow ranges investigated, the hydraulic application rate did
not appear to be a significant parameter. The report of the
pilot studies recommended that nitrification towers be designed
for a TK-N loading of 0.18 pounds per square foot per day.
This loading was expected to produce an effluent containing
131
-------
2 mg/1 NH -N during the summer months and 7 mg/1 NH3 during
the winter. Another study recommendation was not to include
either post-nitrification settling tanks or effluent polishing
filters since the tower effluent contained an average of only
15 mg/1 suspended solids.
THE PLANT
Construction of the improvements to the wet stream processes
began in January 1974 and was essentially completed in the fall
of 1976. The expansion of the anaerobic digesters and dewater-
ing facilities began in the fall of 1977 and was completed in
mid-1979.
The plant is designed for an average dry weather flow of 18.5
mgd and for a peak flow of 53 mgd. Under normal conditions,
the secondary and advanced treatment portions of the plant
operate at a peak rate of 33 mgd.
The improved activated sludge plant includes screening, grit
removal, primary settling, aeration, final settling, nitrifi-
cation towers, chlorination, and phosphorus removal. The
chemicals used for phosphorus removal are ferric chloride and
anionic polymer. Sludge treatment and disposal consists of
gravity thickening, anaerobic digestion, vacuum filtration,
sludge cake storage, and land spreading. Normal sludge
treatment/disposal uses thickening, digestion, and land spread-
ing of liquid sludge. Vacuum filtration and sludge storage is
used to provide backup to the landspreading program. Figure 1
132
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Ferric
Chloride
Polymer
Raw
Sewage
Screenings
p
To Disposal To Disposal
To Sludge Treatment
and Disposal
Recycle
To Auglaize River
Figure 1. City of Lima, Ohio
Wastewater Treatment Plant
Wet Stream Process Diagram
133
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illustrates the wet stream treatment process. Figure 2
diagrams sludge handling and disposal.
The activated sludge process was designed on organic loadings
ranging from 22 to 53 pounds BOD per 1,000 cubic feet of aera-
tion tank capacity. The precise loading is dependent on flow.
Over the range of organic loadings, BOD removals ranging from
92 to 66 percent were anticipated. The suspended solids remov-
als in secondary were projected to be between 75 and 60 per-
cent, depending on the flow to the system.
Two nitrification towers, each with a diameter of 106 feet,
were designed in accordance with the experimental results. The
media used in the full-scale installation was supplied by
Goodrich. The basis of design for the treatment plant, the
description of the individual treatment units, and the pro-
jected plant effluent are shown in Table 1.
THE NPDES PERMIT
The plant operates under a National Pollutant Discharge Elim-
ination System (NPDES) Permit issued on September 19, 1977 that
expires on June 30, 1980. The pertinent conditions of the Per-
mit may be summarized as follows:
Concentration (mg/1)
Parameter 30-Day 7-Day
Suspended Solids 14 20
BOD5 9 13
Ammonia (N) 2 4
Total Phosphorus 1 1.5
134
-------
Primary
Sludge
Gravity
Thickeners
Waste
Activated
Sludge
Anaerobic
Digesters
Overflow
Supernatant
To Primary Settling Tanks
Land Application
Vacuum
Filters
Filtrate
Filtrate
Holding
Tank
Filtrate
To Primary Settling Tanks
Landfill
Figure 2. City of Lima, Ohio
Wastewater Treatment Plant
Sludge Process Diagram
135
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Table 1
City of Lima, Ohio
Wastewater Treatment Plant
DESIGN CRITERIA AND DESCRIPTION OF PLANT
Average Daily Flow: 18.5 mgd
Peak Flow Through Secondary and Tertiary Facilities: 33 mgd
Peak Flow Through Primary Treatment: 53 mgd
Unit
Bar Screens (2)
Grit Removal Basins (2)
Primary Settling
Tanks (7)
Aeration Tanks (5)
Aeration Blowers (5)
Size
1 @ 5' wide
Ii6' wide
1 @ 20' x 20'
1 @ 24' x 24'
2 @ 2,964 sf
2 @ 3,600 sf
2 @ 4,803 sf
1 e 4,900 sf
730,250 cf total
3 @ 9,300 SCFM
2 @ 10,100 SCFM
Final Settling Tanks (4) 115' dia. x 14' swd
Capacity and/or
Operating Conditions
53.0 mgd
16.0 mgd
23.1 mgd
53.0 mgd @ 1,900 gpd/sf
33.0 mgd @ 1,200 gpd/sf
18.5 mgd @ 650 gpd/sf
7.1 hrs @ 18.5 mgd
4.0 hrs @ 33.0 mgd
1,760 cf air/lb BOD applied
33.0 mgd @ 794 gpd/sf
18.5 mgd @ 445 gpd/sf
Nitrification Towers (2) 106' dia. x 21.5' deep 18.5 mgd @ 0.73 gpm/sf
18.5 mgd @ 0.18 Ibs TK-N/sf
33.0 mgd @ 1.30 gpm/sf
33.0 mgd @ 0.32 Ibs TK-N/sf
Chlorine Contact
Tanks (2)
37,970 cf total
Phosphorus Removal Chemical Pumps
FeCl3 (2)
Polymer (2)
Sludge Thickeners (2)
Anaerobic Digesters
Primary (2)
Secondary (1)
210 gph each
210 gph each
75' dia. x 11' swd
85' dia. x 22' swd
85' dia. x 22' swd
18.5 mgd @ 24 minutes contact
33.0 mgd @ 15 minutes contact
25 mg/1 Fe
0.2 mg/1
21.4 Ibs/sf primary sludge
2.4 Ibs/sf chemical sludge
3.9 Ibs/sf secondary sludge
21 days detention
136
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Table 1
City of Lima, Ohio
Wastewater Treatment Plant
(Continued)
Unit Size
Sludge Holding Tanks (2) 70' dia. x 32' swd
Vacuum Filters (3) 12' dia. x 10'
Supernatant and Filtrate
Holding Tank (1) 25' dia. x 8' swd
Design Effluent Quality
BOD: 9 mg/1 @ 18.5 mgd
SS: 14 mg/1 @ 18.5 mgd
NH3-N: 2 mg/1 (summer) - 30-day average
7 mg/1 (winter) - 30-day average
P: 1 mg/1 - 30-day average
Capacity and/or
Operating Conditions
103,000 cf total
1,130 sf total
4,000 cf
137
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These conditions apply to the secondary and tertiary treatment
effluent. The winter NH--N limitation in the Permit is more
restrictive than the plant was designed for.
STARTUP
The nitrification facilities began operating in late summer,
1976. Startup progressed on schedule after damage to the plas-
tic media in one of the towers was repaired. Damage resulted
from mechanical failure of one of the distributor arms. The
facility began nitrifying in about eight weeks, and by early
November was producing the expected effluent values. The time
required for the start of nitrification was essentially the
same as that found in the pilot studies. The startup for the
rest of the plant, including phosphorus removal, presented no
particular problems.
OPERATING CHARACTERISTICS, OPERATING
PROBLEMS, AND CORRECTIVE MEASURES
During 1978 the plant removed approximately 96 percent of the
BOD and 94 percent of the suspended solids in the wastes. The
aeration system operated at a loading of 12.61 pounds BOD per
1,000 cubic feet and used 2,786 cubic feet of air per pound of
BOD removed. During 1979 the BOD removal was about 97 percent
while that for suspended solids was 93 percent. The aeration
system operated at a loading of 21.72 pounds BOD per 1,000
cubic feet and used 1,334 cubic feet of air per pound of BOD
removed.
138
-------
Operation of the nitrification facilities has been remarkably
free of problems. The towers are operated at 100 percent
recirculation throughout the year with no attempts made to
optimize recirculation rates. The operational simplicity of
the system is greatly appreciated by the plant personnel.
The towers have sloughed off solids once since they began oper-
ating. This occurred late in the summer of 1979 and lasted for
a period of approximately two hours. No decrease in process
efficiency was reported following slough-off.
The nitrification facilities have not experienced significant
operating problems during about 3.5 years of operation. The
plant superintendent reported icing problems two or three times
during the winters of 1977 and 1978, two of the coldest winters
on record for the Lima area. During these occurrences, ice
along the filter walls built up and stopped the distributor
arms. The operators broke the ice and the towers were put back
into operation.
At the beginning of the winter of 1979, operating personnel
capped the end nozzle in each of the distributor arms, elimina-
ting ice formation from splashes on the walls. No icing prob-
lems were experienced this past winter.
RESULTS
The results for BOD, suspended solids, ammonia, and dissolved
oxygen during the first three full years of treatment facili-
ties operation are shown in Tables 2, 3, and 4. Of special
139
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Table 2
City of Lima, Ohio
Wastewater Treatment Plant
RAW WASTEWATER AND EFFLUENT CHARACTERISTICS (1977)
Flow (mgd) Average Raw Wastewater Average Final Effluent
Month
Jan.
Feb.
March
April
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Avg.
Day
13.64
13.67
14.41
15.50
15.21
15.20
16.75
16.30
16.34
14.16
15.25
22.85
High
Day
16.31
23.06
26.86
25.28
28.26
21.96
20.11
23.75
31.28
26.08
24.77
48.60
Low BOD
Day (mg/1)
10.39 102
8.37
9.26
7.75
8.60
9.90
12.92
11.50
10.97
8.20
9.48
10.30
82
53
93
116
119
102
80
90
103
109
96
SS
(mg/1)
93
97
85
110
160
124
103
87
98
122
130
124
P
(mg/1)
11.4
6.0
2.4
6.0
5.8
6.5
4.2
12.0
16.3
14.6
15.4
12.4
BOD
(mg/1)
3.1
2.9
3.1
4.0
2.0
2.1
2.1
1.5
1.7
1.2
1.3
2.4
SS
(mg/1)
3.6
7.0
10.0
6.0
8.4
8.3
4.7
2.8
2.9
1.9
2.5
5.6
P NH3-N
(mg/1) (mg/1)
1.2
0.4
0.0
1.0
0.7
0.8
0.7
4.0
4.3
3.9
4.0
1.7
4.0
4.6
1.2
1.5
1.0
1.7
1.2
1.4
0.1
0.1
0.1
0.0
D.O.
(mg/1)
9.5
9.0
8.9
10.2
10.0
9.3
9.2
9.2
9.3
9.7
9.9
11.6
140
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Table 3
City of Lima, Ohio
Wastewater Treatment Plant
RAW WASTEWATER AND EFFLUENT CHARACTERISTICS (1978)
Flow (mgd) Average Raw Wastewater Average Final Effluent
Month
Jan.
Feb.
March
April
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Avg.
Day
14.93
12.99
27.55
19.80
10.76
9.29
8.85
9.17
8.06
8.53
8.93
11.94
High
Day
35.57
17.69
60.83
36.67
19.98
16.37
21.41
16.28
15.15
23.64
24.52
36.50
Low
Day
9.50
9.17
9.30
7.80
6.95
5.35
5.76
9.17
5.65
5.74
5.47
6.60
BOD
(mg/1)
71
131
82
64
89
86
93
102
105
127
135
145
SS
(mg/1)
117
146
96
75
116
143
128
164
150
145
147
139
P
(mg/1)
5.4
5.6
3.6
2.9
4.8
5.2
5.3
6.6
6.5
7.3
7.3
6.1
BOD
(mg/1)
1.3
1.3
5.2
3.2
1.6
4.1
4.1
4.2
5.9
3.5
4.9
6.2
SS
(mg/1)
4.4
4.2
6.9
6.7
2.8
6.8
5.5
6.9
8.2
6.0
5.6
19.9
P
(mg/1)
0.17
0.18
0.33
0.24
0.42
0.61
0.96
1.50
1.20
0.63
0.70
0.98
NH3-N
(mg/1)
2.14
2.80
3.05
0.37
0.45
0.54
2.00
1.23
1.97
1.14
1.93
1.13
D.O.
(mg/1)
11.3
10.6
10.6
10.6
9.9
9.1
9.7
8.6
8.7
9.9
9.2
10.0
141
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Table 4
City of Lima, Ohio
Wastewater Treatment Plant
RAW WASTEWATER AND EFFLUENT CHARACTERISTICS (1979)
Flow (mgd) Average Raw Wastewater Average Final Effluert
Month
Jan.
Feb.
March
April
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Avg.
pay_
12.31
14.58
21.60
23.31
16.47
10.89
13.20
17.31
14.16
10.65
19.11
18.15
High
Day
41.72
39.53
47.73
45.11
48.76
20.32
30.50
42.22
38.74
20.36
47.02
48.00
Low BOD
Day (mg/1)
7.47 145
6.35
11.12
9.11
8.64
8.23
7.88
10.08
8.22
6.90
8.38
9.41
116
115
170
202
246
208
139
158
129
147
116
SS
(mg/1)
159
157
147
110
141
108
122
128
105
129
102
112
P
(mg/1)
5.8
6.2
4.4
3.4
5.4
6.0
5.0
4.5
5.7
6.2
4.4
4.4
BOD
(mg/1)
4.7
10.1
6.2
7.1
6.5
5.3
5.4
3.0
2.3
2.1
4.8
5.5
SS
(mg/1)
7.8
8.5
12.8
10.5
16.6
12.8
5.6
6.6
5.4
6.3
9.6
9.2
P
(mg/1)
0.42
1.23
0.57
0.72
0.89
0.75
0.67
0.60
0.90
0.71
0.74
1.23
NH3-N
(mg/1)
1.24
3.92
1.40
0.85
1.15
1.09
1.90
0.45
0.80
0.68
1.38
0.59
D.O.
(mg/1)
10.7
11.9
11.1
10.0
10.6
10.7
10.9
10.7
10.7
11.8
13.4
13.2
142
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significance were the results obtained during the exceptionally
cold winter of 1977-78 and 1978-79. The Tables show the quali-
ty of the effluent is generally better than required by the
NPDES Permit. The only parameter the plant has had difficulty
meeting consistently is phosphorus.
Effluent COD, pHf and nitrate nitrogen are shown in Table 5.
Table 6 shows the variations in effluent NEU-N concentrations
and effluent temperatures for 1978 and 1979.
During 1979, plant personnel began taking approximately four
measurements per month of TK-N in the nitrification towers
influent and effluent. The average for these values is shown
in Table 7. Table 8 shows loading to the tower (Ibs TK-N/sf/
day) and the resulting effluent NH..-N concentration for the
year 1979.
In February 1980, samples were collected upstream and down-
stream of the nitrification towers, and analyzed for BOD and
suspended solids. The average of the seven samples analyzed
are as follows:
BOD - 11 mg/1 upstream; 2 mg/1 downstream
SS - 22 mg/1 upstream; 10 mg/1 downstream
SLUDGE PRODUCTION
The nitrification towers are not followed by settling tanks,
therefore no sludge is collected. The pilot studies leading to
the design showed a sludge collection system would not be
required. The findings of the pilot studies have been largely
confirmed during operation. The towers have sloughed off
143
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Table 5
City of Lima, Ohio
Wastewater Treatment Plant
COD, pH, AND NH3-N IN PLANT EFFLUENT
(1978-1979)
COD (mg/1)
PH
1978
1979
Avg.
35
38
High
65
66
Low
21
22
High
8.1
7.8
Low
7.0
7.2
Avg.
11.7
16.8
High
14.1
26.3
Low
8.1
8.1
Table 6
City of Lima, Ohio
Wastewater Treatment Plant
VARIATIONS IN EFFLUENT AMMONIA
CONCENTRATION AND TEMPERATURE (1978-1979)
Month
1978
January
February
March
April
May
June
July
August
September
October
November
December
1979
January
February
March
April
May
June
July
August
September
October
November
December
NH^-N (mg/1)
Avg.
2.14
2.80
3.05
0.37
0.45
0.54
2.00
1.23
1.97
1.14
1.93
1.13
1.24
3.92
1.40
0.85
1.15
1.09
1.90
0.45
0.80
0.68
1.38
0.59
High
3.40
5.00
10.00
1.70
2.20
1.40
7.90
6.06
5.46
4.50
6.89
4.17
2.82
9.52
2.80
3.40
8.50
4.18
8.10
1.12
2.60
2.60
4.45
2.20
Low
1.00
0.40
0.00
0.00
0.00
0.00
0.10
0.15
0.27
0.22
0.18
0.13
0.25
0.89
0.10
0.15
0.32
0.14
0.12
0.16
0.19
0.17
0.11
0.12
Temperature (°C)
Avg.
9.3
6.9
9.7
11.5
15.5
21.2
23.6
23.4
22.8
22.3
18.5
18.1
10.0
9.0
12.3
14.9
17.3
21.4
23.6
23.9
22.3
18.6
14.2
11.1
Hicjh
12.1
9.4
15.0
15.6
20.0
24.4
26.1
25.6
25.0
24.4
23.3
23.3
12.0
13.9
18.9
18.9
20.6
23.3
26.1
25.6
25.6
21.7
17.8
13.9
LOW
6.1
5.0
4.4
7.8
12.8
19.4
20.6
20.6
20.6
19.4
14.4
6.1
1.0
3.9
6.7
11.1
13.3
19.4
20.6
22.2
18.9
16.1
10.0
8.9
144
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Table 7. City of Lima, Ohio
Wastewater Treatment Plant
AVERAGE TK-N CONCENTRATION IN
NITRIFICATION TOWERS INFLUENT AND EFFLUENT (1979)
Month
January
February
March
April
May
June
July
August
September
October
November
December
TK-N Concentration (mg/1)
Tower
Influent
13.70
17.15
9.34
7.58
23.90
14.58
9.33
4.82
2.41
2.71
2.82
Tower
Effluent
3.48
8.43
4.18
2.30
5.59
7.92
7.78
3.81
1.68
1.62
2.10
2.14
1.97
Table 8. City of Lima, Ohio
Wastewater Treatment Plant
TK-N LOADING VERSUS NH3-N IN EFFLUENT (1979)
Month
January
February
March
April
May
June
July
August
September
October
November
December
Flow
(mgd)
12.31
14.58
21.60
23.31
16.47
10.89
13.20
17.31
14.16
10.65
19.11
18.15
Tower
TK-N
(mg/1)
13.70
17.15
9.34
7.58
23.90
14.58
9.33
4.82
2.41
2.71
2.82
2.14
Influent
TK-N
(Ibs/day)
1,406.5
2,085.4
1,682.5
1,473.6
3,282.9
1,324.2
1,027.1
695.8
284.6
240.7
449.4
323.7
Tower Loading
Ibs TK-N/
sf/day
0.08
0.12
0.10
0.08
0.19
0.08
0.06
0.04
0.02
0.01
0.03
0.02
* Tower
Effluent
NH^-N (mg/1)
1.24
3.92
1.40
0.85
1.15
1.09
1.90
0.45
0.80
0.68
1.38
0.59
*Total area of towers = 17,650 sf.
145
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solids only once for a period of about two hours during the
three and one-half years of operation.
CONSTRUCTION COST
The improvements to the wet stream portion of the plant were
built for a construction cost of $11,295,000. The major
improvements included: a new administration building and
laboratory, reconditioning of existing primary and final set-
tling tanks, additional aeration tanks and blowers, new final
clarifiers, new secondary effluent pumping station, nitrifica-
tion towers, equipment to store and feed phosphorus removal
chemicals, improvements to chlorination facilities, new sludge
thickeners, and extensive piping changes. The project was bid
in 1973 and completed in the fall of 1976.
The major improvements to sludge treatment and disposal includ-
ed additional secondary digester capacity, vacuum filters and
vacuum filter building, a sludge cake storage area and build-
ing, supernatant and filtrate storage tank, and a garage for
sludge trucks. The project was bid in 1976 and completed in
1979. The total construction cost was approximately $3,582,000.
Both projects received Federal EPA grants for 75 percent of the
eligible portions.
OPERATION AND MAINTENANCE COST
Operation and maintenance costs averaged $142.55 per million
gallons in 1978 and $138.93 per million gallons in 1979. Total
146
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operation and maintenance costs for both years are shown in
Table 9.
TABLE 9
CITY OF LIMA, OHIO
WASTEWATER TREATMENT PLANT
OPERATION AND MAINTENANCE COST FOR
WASTEWATER TREATMENT PLANT (1978 AND 1979)
Item
Payroll
Power
Chlorine
Chemicals**
Miscellaneous
1978
$356,666.58
172,208.54
3,833.08
55,367.50
66,346.64
$654,422.34
1979
$415,957.31
217,028.92*
5,545.90
74,604.53
97,228.62
$810,365.28
* The cost for power
** Ferric chloride and
DISCUSSION
Figures 3 and 4 show the data
and used for design, and the op
results predicted by the pilot
under actual operation. This
designing nitrification towers on
ferived from the pilot studies
crating results for 1979. The
studies have been confirmed
stjrongly supports the concept of
the basis of TK-N loads.
The nitrification efficiency of
expectations. For part of the y
was nitrifying well as evidenced
dary effluent. During that time
polishing facilities. When the
not nitrifying well, the towers
oxidation. Stable performance ha
averaged 0.0213/KWH.
polymer.
the total system meets design
?ar (1979) , the secondary plant
by the low TK-N in the secon-
the towers functioned as
econdary was not nitrifying or
provided the necessary ammonia
been achieved with a minimum
as
147
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of operational adjustment to the nitrification facility. The
operators simply set the recycle rate to 100 percent.
The plant has produced the desired results while treating the
highly variable wastewaters generated by a partially combined
sewerage system. In any single month the flow can range from
less than half to more than twice the design average. The
monthly average for BOD in the raw sewage has ranged from
53 mg/1 to 246 mg/1. The monthly average for suspended solids
in the raw sewage has ranged from 87 mg/1 to 164 mg/1.
SUGGESTED AREAS OF ADDITIONAL RESEARCH
The following areas for additional research are suggested:
1. Potential for reducing the height of the media. No
information has been developed on the minimum
height that will give the desired results.
2. Performance of nitrification towers when operated
as a combination of carbonaceous BOD removal and
nitr ification.
3. The influence of the surface area per unit volume
of media.
4. The effect of forced air ventilation on the per-
formance.
POTENTIAL AREAS FOR COST SAVINGS
The only area identified where the design could be made more
cost-effective is in the material of construction for shells
housing the trickling filter media. Metal or fiberglass panels
could probably be substituted for the concrete used at Lima.
150
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CONCLUSIONS
The stability of the nitrification process under highly vari-
able flow conditions is evidenced in Tables 2, 3, and 4. The
flow to the plant in any one day can range between about twice
and half the average for the month. Hourly variations are con-
siderably greater. The process produces the high degree of
nitrification projected from the pilot studies.
The use of nitrification towers following activated sludge con-
sistently produces a high quality effluent. The BOD, suspended
solids, and NH--N values have been low for the first three
years of operation. Final settling following the towers has
not been necessary as the effluent contains very low suspended
solids.
A secondary benefit derived from the use of nitrification
towers is the high dissolved oxygen concentration in the efflu-
ent. The plant effluent is normally saturated with oxygen.
The performance of the full scale plant has confirmed the
design criteria derived from pilot studies. Very low ammonia
concentrations can be obtained even during the cold winters
experienced in midwestern United States. The process used at
Lima, Ohio, single-stage activated sludge followed by nitrifi-
cation towers, is relatively easy to operate and reliably pro-
duces a high quality effluent.
151
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ACKNOWLEDGMENTS
The author gratefully acknowledges the operating and data col-
lecting efforts of the Superintendents for the Wastewater
Treatment Plant. Mr. Roland Nevergall, now retired, assisted
greatly during the pilot and startup phases. Mr. Jerry Coffey
has been of great assistance in the recent past.
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OPERATING EXPERIENCE WITH A 30 MGD TWO-STAGE
BIOLOGICAL NITRIFICATION PLANT
Earl W. Knight
Assistant Chief Engineer
Metropolitan Sanitary District of Greater Chicago
INTRODUCTION
The Metropolitan Sanitary District of Greater Chicago is located
within the boundaries of Cook County in Illinois. The District
encompasses an area of 866 square miles, has a present population
of approximately 5,400,000; and serves 124 member municipalities.
The District owns and operates seven treatment plants with a total
treatment capacity of 1869 MGD: 1755 MGD secondary and 114 MGD
tertiary.
The John E. Egan Water Reclamation Plant (WRP) one of the seven
plants, is located in Northwest Cook County in an unincorporated
area of Schaumburg and serves an area of approximately forty-four
square miles. This area encompasses most of the upper Salt Creek
drainage basin and includes all or parts of Palatine, Schaumburg,
Hoffman Estates, Arlington Heights, Roselle, Schaumburg, Elk Grove
Village, Rolling Meadows and Inverness. Construction of the plant
began in 1971 and the plant started treating sewage on December 16,
1975. The plant was constructed at a cost of $43 million.
The plant is designed as a 30-million gallon per day (MGD), two-stage
activated sludge system with dual media filtration. The plant con-
sists of control, maintenance, pretreatment, filter, digester, labo-
ratory, and thickener buildings; three pump houses; four aeration
tanks, four digesters, and twelve settling tanks. The plant is
capable of providing complete treatment for flows as high as 50 MGD.
153
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Primary treatment can be provided for an additional 75 MGD. All
effluent flows are chlorinated.
The facilities provided (Figure 1) comprise coarse screening; pump-
ing; fine screening; grit removal; two stages of aeration each fol-
lowed by settling; gravity filtration through dual-media filters;
and chlorination. Provision has been made for the addition of
aluminum salts in the first aeration stage for reduction of phos-
phorous and the addition of methanol in the filter influent for
the reduction of nitrogen if these reductions become necessary.
Facilities for handling waste activated sludge from the two aera-
tion stages include flotation thickeners and anaerobic digesters.
A centrifuge building to provide dewatering of the digested sludge
before disposal is currently under construction. Until the centri-
fuge facilities are completed the digested sludge is being pumped
to a sewer to the District's Northside Sewage Treatment Works.
TREATMENT REQUIREMENTS AND DESIGN CRITERIA
The bases for the degree of treatment provided in the design of the
John E. Egan Water Reclamation Plant were the Illinois Sanitary
Water Board Rules and Regulations which were in force at the time
of design. Since the flow of Salt Creek downstream of the plant
outfall is dominated by the Egan Plant effluent flow, the most
stringent effluent requirements were applied in the design of the
plant. The most pertinent effluent requirements were as follows:
BOD 4 mg/1
Suspended Solids 5 mg/1
154
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03
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Ammonia Nitrogen 2.5 mg/1
Nitrate Nitrogen 45 mg/1
Fecal Coliforms 2000 per 100 ml.
The design criteria provided for an average flow of 30 MGD with a
range of 15 MGD to 50 MGD for complete treatment. An additional
requirement was for a peak wet weather flow of 125 MGD to receive
a minimum of primary treatment. Sludge treatment was to be pro-
vided by flotation thickening and high rate anaerobic digestion.
The aeration tanks (first and second stage) were to be designed
to provide three hours detention at 50 MGD with diffused air aera-
tion and were to be capable of conventional, contact stabilization,
or step aeration processes. The settling tanks were to be designed
for an overflow rate of 1430 GPD/S.F. and a detention time of two
hours at 65 MGD. The storm water settling tanks were to be designed
for an overflow rate of 1660 GPD/S.F. and a detention time of 1.7
hours at 75 MGD. The sand filter loading for design was 5 GPM/S.F.
at 50 MGD. The digesters were to provide a fourteen-day detention
time. Figure 1-A documents the success of the design.
PLANT START UP
The John E. Egan WRP began receiving sewage for treatment on
December 16, 1975. The plant had been seeded with 100,000 gallons
of waste activated sludge from the District's Hanover Park WRP.
The limited supply of solids available made it necessary to mini-
mize the flow entering the plant until a population of organisms
adequate to provide treatment had grown in the aeration tank. This
procedure allowed better control of plant processes during the
156
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QUALITY DESIGN ACTUAL AVERAGE ANNUAL PERFORMANCE
PARAMETER AVERAGE
1976 1977 1978 1979
BOD
(MGA)
SS
(MGA)
NH4-N
(MGA)
FLOW
(MGD)
4
5
1.5
30
4
4
2.4
12.2
3
2
.8
15.4
4
3
1.7
18
4
2
1.1
18
Figure 1-A. Comparison of Design Treatment Quality
With Actual Effluent Quality
157
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shakedown period and accomplished the following:
(1) Minimized the discharge of pollutants during biological
conditioning.
(2) Minimized the discharge of ammonia until the slow growing
nitrifiers could be established to provide treatment.
(3) Minimized waste sludge production. The digestion facility
was not operational until the end of February, 1976.
Flow into the plant was controlled by removal of the bulkheads from
only one of the two intercepting sewers entering the plant. This
limited the flow to approximately one third of that available.
Mixed liquor suspended solids (MLSS) was less than 300 mg/1 from
the start-up on December 16, 1975, until January 23, 1976. In spite
of the low MLSS, effluent BOD5 ranged from 1 to 39 mg7l and effluent
suspended solids ranged from 3 to 31 mg/1. Both parameters averaged
approximately 20 mg/1. First stage MLSS increased steadily to more
than 2000 mg/1 by February 5, 1976. As the MLSS increased the
effluent quality steadily improved until it was consistently able
to meet the 4 mg/1 BOD5 and 5 mg/1 suspended solids criteria 55 days
after start-up.
The difficulty in obtaining a sufficient MLSS concentration was
unexpected but the problem was attributed to low plant flows allow-
ing the settling of some of the solids in sections of channels and
aeration tanks. The presumption was that the settling of solids
would not allow an increase in MLSS until the sections trapping
solids reached an equilibrium rate of gain and loss. This rate was
attained in January, 1976, when MLSS started to increase.
158
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Significant nitrification was first observed in the first stage
aeration effluent on February 2, 1976. Nitrification continued
to improve as the solids in the first stage increased. Ammonia
nitrogen in the first stage effluent was reduced to less than
1 mg/1 by February 29, 1976, just seventy-four days after plant
start-up. Solids from the first stage were used to seed the second
stage on March 2, 1976, and, on April 16, 1976, the remaining
bulkheads blocking flow to the plant were removed. This addi-
tional flow did not affect the effluent quality.
PLANT OPERATIONS AFTER START-UP 1976 - 1980
The John E. Egan Water Reclamation Plant serves a rapidly develop-
ing suburban area of approximately forty-four square miles. The
average daily flow, increasing yearly since the plant opened in
1975, was approximately eighteen million gallons during 1979.
This flow is sixty percent of the design flow for the plant.
Figure (2) shows actual average daily flow compared to average
daily flow estimates for design purposes.
now
IKU)
1S75IJrt 1977 I'll
Figure 2. A comparison of Estimated Sewage Flows
with the Actual Flows
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The aeration systems are operated as conventional activated sludge
systems and solids are wasted from the first stage as necessary.
Normally, solids are not wasted from the second stage. Table 1
presents data showing 1979 plant performance, treatment efficiency,
and permit requirements.
Table 1
Plant Performance, 1979
Sample
Raw
Final Efficiency
Effluent (%)
Permit Limits
BOD5
SS
NH3-N
129 mg/1
180 mg/1
14.6 mg/1
4 mg/1
2 mg/1
1.1 mg/1
96.9
98.9
92.5
(1975)
4 mg/1
5 mg/1
1.5 mg/1
(1979)
10 mg/1
12 mg/1
*
* 1.5 mg/1 April 1 - November 1
4.0 mg/1 Nov. 1 - April 1
OPERATIONAL PROBLEMS
Beginning in December, 1977, one-half of each aeration system was
taken out of service to test the treatment systems at design flow.
This test continued through September, 1978, and flow through the
plant averaged eighteen million gallons per day during this period.
Excluding September, the effluent ammonia averaged 0.9 mg/1 for the
one-tank operations with an influent concentration of 14.5 mg/1
representing a removal efficiency of 93.8%.
MLSS levels of 1000 - 2000 mg/1 were maintained during the period
from initial start-up until September, 1978. Nitrification was
maintained with little difficulty except for periods when power
160
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outages or mechanical problems caused lowered D.O. concentrations
and inhibited growth of the nitrifying organisms. However, these
problems were transient and caused no prolonged upset of the treat-
ment process. Major repair work was performed on the aeration tank
weirs in September, 1978. This work required a shutdown of the
entire plant for several hours, and also required that one first
stage aeration tank be drained. This operation apparently caused
the growth of nitrifying organisms to be inhibited as there was a
noticeable increase in the concentration of ammonia nitrogen in
the plant effluent for several days after the plant was restored
to service. Figure 3 shows percent ammonia nitrogen removal com-
pared to MLSS for the period September, 1978 to December, 1978. The
decrease in ammonia nitrogen removal efficiency shown on Figure 3
in December, 1978, was attributed to a four-hour power failure.
The effect of this power failure lasted well into February, 1979,
when ammonia nitrogen removal efficiency was restored.
An analysis of plant operating data was undertaken to determine
what factors caused the upset of nitrification. This analysis showed
that past power outages and low D.O. periods had caused little or
no disruption of treatment processes, but that the MLSS in the
second stage aeration tanks had been less than 500 ppm when the
upset of the nitrification process occurred. Further analysis of
the data led to the development of Table 2 which shows the relation-
ship between MLSS and nitrification relative to efficiency and
reliability. This table shows 1978 data and uses 1.5 mg/1 as the
maximum allowable ammonia nitrogen in the plant effluent. Based on
the relationship shown in Table 2, 500-600 mg/1 MLSS range was
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selected for operational purposes as the minimum level for reliable
maintenance of the nitrification process at the Egan Plant.
Table 2
2nd Stage
MLSS (mg/1)
<100
100 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700
700 - 800
800 - 900
900 - 1000
>1000
Nitrification Process at Egan Plant
(Efficiency)
Average %
Nitrified
32.4
53.0
67.0
70.2
90.1
83.6
91.2
81.5
91.8
94.0
94.7
(Reliability)
% within each
range below 1.5 mg/1
100
82.6
58.0
56.8
17.1
29.7
20.0
36.4
16.1
11.8
7.5
Maintenance of second stage MLSS is a continuing problem at the
Egan Plant. Three possible reasons for this problem, all related
to current underloading of the plant, are given below:
(1) The long retention times in first stage cause much of the
nitrification to occur in that stage leaving a negligible
amount of ammonia nitrogen for growth of the nitrifiers in
second stage. This problem is most apparent in the warm
summer months.
(2) The first stage produces an effluent which has a suspended
solids concentration of 5 - 10 mg/1 on a regular basis
163
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causing little solids to enter second stage.
(3) The long solids retention times in the second stage cause the
development of pin flock which carries over the weirs into
the filters thus removing solids from the second stage.
The first problem has been overcome by running only half of the
first stage system during the warm months. This reduces the deten-
tion time, and the amount of nitrification occurring in first stage,
thus providing nutrients for the nitrifiers in second stage.
The second and third problems are interrelated. The suspended
solids concentrations for second stage influent and effluent are
nearly equal, or, what solids, enter the system leave the system.
In addition, some portion of the solids are utilized within the
tanks by the nitrifying bacteria and are "lost". The solution to
the first problem provided little or no relief for problems (2) or
(3). Two possible solutions to these problems would be to increase
the second stage influent solids or to reduce the effluent solids.
These alternatives were rejected because it would be undesirable
to try to produce a poorer quality effluent in first stage to
increase the solids in the second stage influent and to reduce the
SET in second stage by reducing the MLSS thus reducing effluent
solids carryover would cause the nitrification to suffer as was
indicated by the previous analysis.
An acceptable solution to this problem has been found to be transfer
of solids directly from first stage MLSS, to second stage MLSS. The
first stage solids contain nitrifiers to assist in the development
of nitrifiers in the second stage and provide a net influx of
164
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solids to second stage. The transferred first stage solids also
exhibit better settling characteristics and provide more capture
of the pin flock in the second stage settling tanks.
OPERATIONAL CONTROL
Several automatic control loops are designed into the second stage
system. These include such parameters as Dissolved Oxygen (DO) and
Return Sludge.
The DO is a set point controller allowing for more air to enter the
tank if the DO falls below the set level. Each pass of the aera-
tion system has a DO probe indicating the DO level in that pass
which is the basis for determining if more air is required.
The return sludge can be set at a fixed return rate or as a percent-
age of the current sewage flow rate. In either case the automatic
valves open or close to maintain the requested sludge flow rate to
the air lifts.
Measurements of other parameters used for operational control are
made manually. These include MLSS, settleability, and ammonia
nitrogen.
In the second stage system, the nitrifying organisms are sensitive
to the dissolved oxygen level and, thus, the DO is maintained above
2 mg/1 at all times to prevent an upset of these organisms. The
required DO level is tapered upward from first through third pass
to insure adequate oxygen for nitrification.
An adequate solids retention time (SRT) must be maintained in the
165
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second stage to allow for growth of nitrifying organisms. The second
stage SRTs1 are normally greater than twenty days which should be
adequate for nitrification to occur.
CAPITAL AND OPERATING AND MAINTENANCE COSTS
The contract for the construction of the John E. Egan Water Recla-
mation Plant was awarded on November 4, 1971, for $43,259,000, or
$1,442,000 per MGD (based on 30 MGD design flow). Although the
average daily design flow is 30 MGD, portions of the plant, speci-
fically the pretreatment phase, the stormwater settling tanks, and
the thickener building were constructed to meet some or all of the
future year 2020 average design flow of 90 MGD. In addition, por-
tions of the plant were designed to handle service areas greater
than the sewage treatment service area. These include the sludge
thickening and digestion facilities which will handle the sludge
produced by the nearby 72 MGD O'Hare WRP, which began operating
May 12, 1980; the maintenance shop and storeroom areas which service
the entire Northwest area; and the laboratory which performs analysis
and research for the whole north area comprising four treatment
plants. Extracting these portions from the contractor's item by
item bid listing yields a construction cost of $37,764,700 for a
30 MGD, 2-stage activated sludge sewage treatment plant, or
$1,258,900 per MGD.
The cost for nitrification, specifically the second stage aeration
and settling tanks and associated piping and equipment is estimated
to be $5,818,900 for nitrification, or $195,000 per design MGD.
The annual maintenance and operations (M & 0) cost for the plant
166
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is obtained from data compiled from all personnel timesheets,
purchase invoices and material distribution records. The total
M & 0 cost for 1979 for the entire plant was $2,051,599 or $112,601
per MGD (based on the 1979 average treated flow of 18.22 MGD).
The breakdown by phase of treatment shows maintenance and operation
cost for 1979 for nitrification to be $362,862, or $19,916 per MGD
for the 1979 yearly average flow of 18.22 MGD.
Table 3 summarizes the extracted capital cost and the 1979 main-
tenance and operations cost for the J.E. Egan W.R.P.
167
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Table 3
John E. Egan Water Reclamation Plant
Capital and Maintenance and Operations Cost
CONSTRUCTION COST
A. TOTAL $43,259,000 OR $1,442,000/MGD*
B. 30 MGD PLANT 37,764,700 OR 1 ,258,900/MGD*
C. NITRIFICATION 5,848,900 OR 195,000/MGD*
MAINTENANCE AND OPERATIONS COST - 1979
A. TOTAL $2,051,599 OR $112,601/MGD**
B. NITRIFICATION 362,862 OR 19,916/MGD**
* BASED ON DESIGN FLOW OF 30 MGD
** BASED ON 1979 AVERAGE TREATED FLOW OF 18.22 MGD.
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CONCLUSIONS AND RECOMMENDATIONS
(1) Means of readily transferring MLSS from first stage to second
stage should be incorporated into the design of a two-stage
system.
(2) A minimum solids level must be maintained in the second stage
aeration tanks to provide reliable nitrification. The MLSS
required, however, can be much lower than that required in the
first stage carbonaceous system.
(3) Once nitrifying organisms are established in the second stage,
the nitrification occurs very rapidly in the aeration tank,
usually in the first half. This indicates that the second
stage aeration tanks may be designed smaller than those in
the first stage. This area requires further research.
eld
169
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NITRIFICATION-DENITRIFICATION IN FULL-SCALE
TREATMENT PLANTS IN AUSTRIA
N. F. MATSCHE
Assistant Professor
Technical University,Vienna,Austria
INTRODUCTION
Austria is situated in the center of Europe with the main part
of the country north-east of the Alps. The country has many na-
tural lakes which are of prime importance for recreation in a
country that is economically dependent to a large extent on
tourism. The decreasing \vater quality in some of these lakes in
the past years could be stopped by means of big investments in
sewers and treatment plants. Vhen it was possible all effluents
were diverted from the catchment of the lakes or the plants dis-
charging to lakes were equipped with phosphorus removal which
in most cases means simultaneous precipitation. The removal of
nitrogen from waste water will be more important in the future
with an increasing amount of surface water being used for water
supply and an ever increasing number of hydroelectric plants on
the rivers which increases the tendency of algal nuisances under
certain climatic conditions. At the moment nitrogen removal is
mainly an operational advantage, saving a significant amount of
170
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energy in treatment plants \vith nitrification. On example of 3
different treatment plants with simultaneous nitrification-deni-
trification the process will be discussed. In conclusion the
conditions for simultaneous nitrogen removal and the advantages
of the process will be dealt with.
TREATMENT PIANTS WITH mTRIETGATION-DENITEIFICATIQN
VIE1WA BLUMENTAL
Nitrogen removal on a large scale single stage activated sludge
plant was reported for the treatment plant Vienna Blumental for
the first time in 1971 • In this plant waste water of approxima-
tely 200 000 PE is treated without primary sedimentation in 2
aeration tanks with mammoth rotor aeration (Figure 1). Besides a
high BOD removal a significant removal of nitrogen of up to 90%
could be obtained. The mechanism of this single stage activated
sludge process for BOD-removal, nitrification and denitrifica-
tion could be explained by the simultaneous presence of aerobic
and anoxic zones in the aeration tanks (MATSCHE 1977, MATSCHE
and SPATZIERER 1977). In order to keep these conditions which
are essential for the simultaneous nitrification and denitrifi-
cation the oxygenation capacity had to be adjusted according to
the specific oxygen demand of the mixed liquor. This could be
performed with an automatic control system (USRAEL 1977) where
ML from the aeration tank is pumped to an aerated control tank
with a fixed rate. It could be shown that the DO in this control
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EXCESS ACTIVATED
SLUDGE ,
1
u
t
UESINGTAL
SEWER
AERATION
TANKS i
RETURN SLUDGE
PUMPI STATION
GRIT CHAMBER
FINAL SETTLING
TANKS
SCREEN
^-i
PUMP STATION
OPERATORS
BUILDING
Figure 1. Treatment Plant Vienna-Blumental
Aeration Tanks:
Total Volume 12000 m3; 2 tanks,
each 150 x 17 x 2,5 m; each tank
equipped with 6 pairs of mammoth
rotors, each 75 kW, 15 m long.
Final Tanks:
Total volume 9400 m3
2 tanks of 45 m 0
172
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tank was inversly proportional to the oxygen uptake rate of the
ML and could be used for the continuous control of the aeration
of the plant.This control scheme has been successfully in opera-
tion for 4 years turning the aerators on and off according to
the actual demand in the aeration tanks. In order to improve
the use of this system a series of investigations was performed in
which the performance of the plant under different operating
conditions was studied. The main operating conditions that
differed in the distinct investigations were
Food Microorganism-Ratio F/M
MLSS M
Oxygen Supply OC/OU
Temperature
The main results of the experiments are given in Table 1. The
F/M-ratio varied within a range of 0,12-0,29 kg BOD^/kg MLSS.a
and was mainly influenced by the varying MLSS.
During Period 1 MLSS were kept as high as 6,8 g/1 which redu-
ced the F/M ratio to 0,12 kg/kg.d. The plant was nitrifying
nearly completely under these conditions and denitrification
was working satisfactorily as well. The removal of TKN amounted
to 96 % whereas total nitrogen (TN) was removed to 86 %. The
total nitrogen content of the effluent was as low as 3,5 mg/1
of which 2,5 mg/1 were present as nitrates.
A reduction of the MLSS to 3 g/1 during Period 2 caused an in-
crease of the F/M-ratio to 0,29 kg/kg.d. In spite of the low
173
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Table 1. Results of Operation, Vienna-Blumental
Period 1
Qd-Flow 5^,5
F-Vol.Load. 0,84
M-MLSS - 6,8
F/M-SL.Load. 0,12
BODc-Inf. , 194
BOD.-Eff. 9
COD-Inf. . 355
COD-Eff. 31
rJKN-Inf. : 25
NH^-N-Inf . . 13
NH4-N-Eff. 0,2
org.N-Eff. ! 0,8
TI-TKN 96
NOv-N-Ef f . ; 2,5
I ri-TK ' 86
; EN./F 0,98
OC/F 1,76
OC/OUR 1,15
T 20
2
58,2
0,86
3,0
0,29
186
9
342
41
24
14
2
1,5
85
6
60
0,79
1,42
1,19
20
I 3 i
61,2
1,08
5,7
0,19
223
11
369
39
28
15
7
0,3
74
1
70
0,52
0,94
0,76
20
4
75,5
0,98
6,8
0,14
._„
5
394
28
27 I
17
1,7
0,4
92
3
81
0,80
1,44
1,12
12,5
Dim.
~~10^7d
kg BOD/m^.d
kg/m^
kg/kg. d
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
/°
mg/1
%
kWh/kg BODc
kg Op/kg BOD
kg/ kg
°C
174
-------
sludge age nitrification was still nearly complete as the HH^-N
in the effluent was only 2 mg/1. However the TN-removal decreased
to 60 % since the NCU-N in the effluent increased to 6 mg/1.
Due to the low MISS the anoxic zones were not sufficient to
achieve a satisfactory denitrification.
During the following Period 3 the control system was adapted to
a lower energy level and the specific energy supply was reduced
to 0,52 kWh/kg BODr. Nitrification was significantly reduced
bringing the NH^-N in the effluent to ? mg/1. With full deni-
trification the TN removal could be kept at 70 % however.
An increase in the energy supply and in the MLSS in Period 4-
could again improve the plant performance and nearly complete
nitrification was obtained even under winter conditions (12,5°C).
A comparison of the different investigations shows that at a
volumetric loading of roughly 1 kg BOD,-/m .d the BOD,- removal
amounted to 95 % with a BOD,- below 10 mg/1 in the effluent in
most cases. The varying energy for aeration between 0,5 and
1,0 kWh/kg BODc--load did not show a significant influence on
the BODc-removal efficiency and so did the change in tempera-
ture. There was no significant difference between results at
12°C and 20°C.
With an increase of the P/M ratio the COD removal efficiency is
only slightly reduced from 91 % (l/M = 0,12) to 88 % (F/M =
= 0,29). As a consequence variations in the load hardly have
115
-------
an influence on the COD removal efficiency. A continuous regis-
tration of TOG in the influent and effluent of the plant could
confirm these results. Variations "between 50 and 200 mg TOC/1 in
the influent of the plant resulted only in values from 8 to 12
mg TOC/1 in the effluent.
A significant influence of the operation parameters was effec-
tive for the TKN removal. A reduction in efficiency was obser-
ved with both decrease in applied energy for aeration and in-
crease in F/M ratio. The use of only 0,52 kWh/kg BOD^ reduced
the TEN removal to 74- % leaving 7 mg of NH^-N in the effluent.
As compared to Period 1 the low temperature in Period 4 only
caused a minor reduction from 96 to 91 % of TEN with NH^-N in
the effluent below 2 mg/1
The most significant differences between the different modes of
operations can be demonstrated with the TN-removal. The TN-re-
moval of 86 % under optimal conditions during Period 1 compares
well with results of earlier investigations and seems to be the
upper limit of the removal efficiency under present loading
conditions. With an operation at a low F/M-ratio of 0,12-0,13
kg/kg.d the low temperature of 12,5 °C did not significantly
affect the TN-removal which amounted to 81 %. A reduction in the
MLSS from 6,8 g/1 (Period 1) to 3,0 g/1 (Period 2), however, re-
duced the TN-removal from 86 % to as low as 60 %. In this case
the oxygen uptake in the anoxic zones was not sufficient for
the complete reduction of the produced nitrate and the NO^-N in
176
-------
the effluent rose to 6 mg/1.
The reduction of energy for aeration in Period 3 had a positive
influence on the denitrification. Nearly the whole nitrate pro-
duced is eliminated, however, the nitrification was incomplete
leaving 7 mg NH^-N in the effluent and reducing the TN-removal
to ?0 %.
FELDKIRCH-KEININGEN
The treatment plant at Heiningen is a regional plant that re-
ceives the waste water of the town of Feldkirch and some surroun-
ding communities. The whole area is situated in the catchment of
Lake Constance, which means that beside a BOD,- below 20 mg/1 in
the 24 hour composite sample the total P in the same sample has
to be below 1 mg/1.
The design is based on the load that is expected for the year
2000 with a BOD<- of 15000 kg/d. The conception of the plant is
very similar to Vienna-Blumental exept the presence of primary
sedimentation. The plant consists of
Pumping Station: 3 screw pumps, 640 1/s each
Screens , width 25 mm
Aerated grit chamber
Primary sedimentation: 2 rectangular tanks (60x15x2 m)
1800 m^ each
Aeration: 2 tanks (160x17x2,8 m) 7500 m^ each, 8 mammoth
rotors, length 7,5 m per tank
177
-------
Final sedimentation: 2 circular tanks (ft 45 m) 5100 nr
each
Return sludge pumping: 2 variable speed screw pumps,
100-400 1/s each
Simultaneous precipitation: addition of FeCl-,
At present one aeration tank is used for stabilization of the
excess sludge which is afterwards stored in one of the primary
and final clarifiers for agricultural application.
The plant is in operation since one year and a recent investiga-
tion (April 1980) could show the excellent performance of the
process, With a total flow of 12 000 nr/d the BOD,- load amoun-
ted to approximately 3800 kg/d which is only 25 % of the design
load. The results of this investigation are summarized in Table 2,
The oxygenation capacity of the rotors is controlled by the
immersion depth using DO probes in the tank. The mean DO was
kept at 0,8 mg/1. Based on the chemical results the total oxygen
uptake was calculated including nitrification-denitrification
and amounted to 4400 kg O^/d. With approximately 4600 kg/d of
oxygen transferred into the aeration tank the ratio of OC/OU
was 1,05. The experience from Vienna Blumental to keep this
ratio slightly above 1 resulted in an even improved nitrogen
removal in this treatment plant with primary sedimentation.
178
-------
Table 2. Results of Operation, Feldkirch-Meiningen
(Flow 12120 m3/d)
(MLSS 3,8 kg/m3)
r " ' — " 1
COD
TN
NH4-N
NO^-N
TP
PO^-P
Influent
310
773
7
6,9
-
5,8
4,6
Primary
Effluent
261
519
14,8
8,7
-
4,2
3,9
Final
Effluent
5
27
2,6
<0,1
2,5
0,1
<0,1
mg/1
mg/1
mg N/l
mg N/l
mg N/l
mg P/l
mg P/l
179
-------
ZELLERBECKEN
The treatment plant Zellerbecken has "been designed for the
treatment of sewage from Zell am See and Kaprun. Both places
are well known tourist resorts for winter and summer. As a con-
sequence the load of the plant can vary in the range of 6:1.
The design of the plant was based on a variation in the BODc
load between 560 and 3150 kg/d. Biological treatment with sepe-
rate aerobic sludge stabilization has been chosen as treatment
process.
The plant consists of:
2 screens (width 25 and 10 mm)
Aerated grit chamber
Aeration: 4- tanks, 600 nr each
7.
Final sedimentation: 2 tanks, 2050 nr each
Return sludge pumping: 2 variable speed screw pumps,
80-190 1/s each
•z
Stabilization: 2 tanks, 1000 nr each
-z
Sludge thickener, 300 nr
The aerobically stabilized excess sludge is either used in
agriculture or can be dewatered and composted together with
garbage. The aeration of the 4 aeration tanks and the 2 stabi-
lization tanks is performed by cone aerators which can be ope-
rated at two different speeds. By means of an adjustable weir
at the effluent of the aeration tanks the immersion depth of
the aerators can be controlled so that the oxygenation capacity
180
-------
can be changed in the range of 6:1. The plant was put into oper
ration "1976 and after a short starting period a number of in-
vestogations on nitrogen and phosphorus removal started (Table 3)
(v.d.ET'IDE, SPATZIEEER). The plant is very flexible and can be
operated with one, two, three or four aeration tanks (Fig.2).
It is also possible to operate in two seperate lines, each con-
sisting of two aeration tanks and one final sedimentation tank.
For the investigations on nitrogen removal the system with pre-
denitrification was used. Instead of an internal recirculation
the return sludge was used the flow of which could be varied
between 80 and 380 1/s. The waste water and the return sludge
were fed to the first aeration tank which should serve as the
denitrification tank. Therefore the aerator was operated at the
lower speed in this tank to keep the oxygen input as low as
possible. Under these conditions approximately 50 % nitrogen
removal was achieved (Period 1). In order to obtain increased
denitrification the oxygen input in aeration tank 4- was de-
creased and as a result the nitrogen removal reached 75 % with
(Period 2) the same BOD and COD removal as in the previous
period.
During the following investigation (Period 3) it was tried to
adjust the oxygen input according to the oxygen consumption. This
could be met by keeping the DO between 1 and 2 mg/1 in aeration
tank 3. The application of this control decreased the power
consumption under otherwise unchanged conditions from 1800 kWh/d
to 1300 kWh/d. The TN-removal increased over 80 %. During this
181
-------
Table 3. Results of Operation, Zellerbecken
'"-'— •"••"•"•" '— ' —.-.—"•' .'- -- -.--L- -.
Period | 1
Qd-Plow 4750
P-Vol.Load 0,47
! M-MLSS 9,4
P/M 0,051
BOD5-Inf. 229
BOD5-Eff. 5
COD-Inf. 431
COD-Ef f . 28
TN-Inf. 35,8
NH4-N-Eff. 0,2
NO,-N-Eff. 15,4
TN-Eff. 15,9
TP-Inf. 11,4
TP-Eff. 8,6
EN/F 1,69
OC/P I 2,67
T j 17
2
4390
0,43
9,1
0,047
236
6
502
28
44,6
0,2
10,3
11,0
13,1
9,9
1,82
2,83
18
3
4900
0,40
9,6
0,043
201
5
428
36
39,2
4,0
3,3
7,6
11,6
4,0
1,38
I 2,16
| 17
4
4610
0,47
9,1
0,054
241
4
463
26
4-1,3
0,9
2,3
3,4
11,7
3,0
1,27
2,00
16
5
4300
0,35
8,8
0,030
196
4
349
24
35,9
0,2
3,9
3,4
8,9
4,3
1,56
2,45
15
m3/d
kg BOD/m5.d
kg/nr
kg/kg, d
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
kWh/kg BOD5
kg O^kg BOD^
°C
182
-------
UJ
u.
u_
UJ
to
2
t—
a
|
UJ
1
1
o
cr
UJ
o
X
<
o
LL
o:
c
0)
0)
A
^
OJ
0)
[S3
4J
C
a;
4->
to
OJ
!N
-------
period the phosphorus removal without chemical precipitation
amounted to 65 % as compared to 20-30 % during Periods 1 and 2.
A comparatively high concentration of ammonia (4 mg IsTH^-N/l)
in the effluent indicated, that nitrification was limited by a
lack of oxygen. In order to get full nitrification DO in tank 3
was increased to 1,5-2,5 mg/1 (Period 4). As a result the energy
demand increased to 1400 kVh/d. Nitrogen removal exceeded 90 %
and 73 % of total phosphorus was removed. The return sludge
flow was kept constant at 100 1/s during Periods 1-4. An increase
in flow to 160 1/s (Period 5) left the nitrogen removal at the
90 % level, however, the phosphorus removal dropped to 50 %•
On the basis of a nitrogen mass balance the processes in the
denitrification tank could be studied. It could be shown that
besides denitrification simultaneously also nitrification
occured in this tank. Oxygen supplied to this tank is utilized
not only for the oxidation of carbonaceous compounds but also
for nitrification (Table 4). In addition to the determination of
nitrogen compounds measurements of the oxygen uptake rate of
the ML with and without inhibition of nitrification (addition
of allylthiourea) were performed. From the results one could
expect that the high oxygen demand for carbon oxidation and ni-
trification (^UQ N) compared to the relatively small oxygen in-
put (01) would result in a high amount of denitrification. In
order to decide whether nitrification or denitrification is pre-
dominant, the difference between oxygen uptake for carbon oxi-
dation (OU^) and oxygen input (01) has to be calculated.
184
-------
In case the difference of OI-OUC is positive nitrification will
be predominant; if this difference is negative denitrification
will be predominant. The observed results (Table 5) agree well
with the nitrogen mass balance.
During the whole year 1977 the performance of the plant was in-
vestigated. The BOD,--loading and the F/M-ratio during this year
varied between 0,3-0,6 kg BOD5/m5.d and 0,04-0,12 kg/kg.d re-
spectively. With COD concentrations of 300-550 mg/1 in the in-
fluent a mean value of 25 mg COD/1 in the effluent was obtained
indicating a COD removal of more than 90 %. The total nitrogen
concentration in the effluent was most of the time significant
below 10 mg/1 (mean value 6,6 mg/1). With a TN concentration
of 30-55 mg N/l in the influent the removal amounted to more
than 80 % (Figures 3,4-)-
CONDITIONS FOR SIMULTANEOUS NITROGEN REMOVAL
nitrification can only be performed by the specialized nitri-
fying bacteria. On the other side a great number of aerobic
bacteria in the ML is able to use nitrate instead of DO as an
oxygen source. As a consequence the process of denitrification
is closely related to the activity of the bacteria which in case
of ML can best be expressed by the oxygen uptake rate (OU). The
OU of the ML depends on a number of influencing parameters like
F/M-ratio, temperature and addition of substrate. The denitrifi-
cation rate is influenced by the same parameters as could be
demonstrated with several measurements (MATSCHE 1979). For
185
-------
Table 4. Nitrogen Mass Balance of Aeration Tank 1
Date
| 12.8.
.
15.8.
Time
14.00
17.00
19.00
21.45
9.30
13.00
. NH4-N N07,-N
(mg N/l)
4,8
I 2,5
2,6
5,4
1,6
1,5
(mg N/l)
8,2 !
4,4 |
6,6 ;
8,7
0,3
3,3 !
Table 5. Oxygen Uptake Rate with (OU£+N) and without
Nitrification (OUC) Compared to Oxygen Input (01)
Date '. Time •
12.8. ; 14.00
: 16.30
13.8.
18.45
21.45
9.30
13.30
ouc
OU« TT Ul
(mg02/l .h) (mg027l .h) j (mgO^/1 .
37 : 100 ! 32,5
38 | 94 36,0
41 92 j 35,0
34 j 78
22
33
75
82
33,5
27,5
30,0
UJ.-UUC ;
h): (mgO^/l.h)
-4,5
-2,0
-6,0
i -o,5
| +5,5
j -3,0
186
-------
50
COD (Effluent)
TOC mg/l
COD-Influent
300.7550 mg/l
COD
TOC
8
10
-1-—* Month
12 (1977)
BR(kg.BOD5/m-d)
0,2 -
0
F/M
kg BOD 5
kgMLSSd
•0,12
-0,08
-0,04
J - Month
(1977)
12
Figure 3. Treatment Plant Zellerbecken,
Results of Operation in 1977
COD, TOC in Effluent and Organic
Loading
187
-------
Total N Influent
30-r55mg/L
5 -
0
N03-NE
NI-U-NE
Month
8 10 12 (1977)
kWh/kgBOD5
Temperature = 10,4
8 10 12
•> Month
(1977)
Figure 4. Treatment Plant Zellerbecken,
Results of Operation in 1977,
Nitrogen Concentrations in
Effluent, Specific Energy
Consumption and Temperature
in Aeration Tank
188
-------
practical purposes it is recommended to use 70-75 % of the oxygen
uptake for carbonaceous compounds (OU^) for the estimation of
the denitrification.
This estimation method takes care of all situations in the plant
excess organic substrate at peak loads or carbon limitations
under endogenous conditions . Depending on the carbon-nitrogen
ratio in the influent the ratio of the oxic and of the anoxic
part of plants with simultaneous nitrification and denitrifica-
tion can be estimated and varied accordingly in order to obtain
optimal process performance. The volume of the aeration tank
(V,m) can be devided in an anoxic fraction a . V,^ and in an
oxic fraction (1-a) "V^T* In order to achieve full denitrifica-
tion the oxygen uptake in the anoxic fraction must exceed the
amount of oxygen supplied by nitrate. The required oxygen up-
take can be expressed by
OU ^ 2,9 . N
The available oxygen uptake is
OUay = a . OUC . 0,75
ouc = 0,7 - n . COD
For extensive denitrification OU has to be equal to OU
av ^ re
a . 0,7 . 0,75 - T) COD0 = 2,9 . NT,
N J'
c c E
a a 5,5 -
Tl COD0
189
-------
where NQ CODg nitrogen, COD in influent
ND nitrogen for denitrification
N-gg nitrogen in excess sludge
N-g-p nitrogen in effluent
a anoxic fraction of aeration tank
r) COD removal efficiency
The anoxic fraction of the aeration tank depends on the ratio
of nitrogen and COD in the waste water. Since this ratio changes
between different days and within the course of a day it would
be necessary to have a flexible partition well for a denitrifi-
cation stage for optimal performance. Plants with simultaneous
nitrification-denitrification can approach this demand by tur-
ning on or off the aerators which influences the oxic and an-
oxic fractions in the tank.
SUMMARY AND CONCLUSIONS
The demand of energy for an activated sludge plant is mainly
influenced by the energy for aeration (v.d.EMDE). Nitrification
and denitrification have a significant influence on the oxygen
demand of the process (Table 6). With full nitrification (30 mg/1
NOv-N in effluent) a process operated at a F/H-ratio of 0,2 kg/
/kg.d uses 65 % more oxygen as compared to the same process
without nitrification. In case the 30 mg NO--N/1 are denitri-
fied, however, the additional oxygen demand is reduced to 24- %.
The DO that is kept in the aeration tank has an even higher in-
fluence on the energy for aeration (Table 7)« In case a DO of
190
-------
Table 6. Relative Oxygen Demand as a Function
of Nitrification and Denitrif ication
(F/M = 0,2 kg/kg. d, 17 = 40 mg/1,
= 10 mg/1)
V/ith Nitrification
N05-NEF
mg/1
0
10
20
30
relative oxygen
demand
1
1,22
1,43
1,65
' V/ith Denitrification
NT,
denitrified N
mg/1
0
10
20
30 ;
, _ _ '
relative osqygen
demand
1
1,08
1,16
1,24
Table 1. Relative Demand for Oxygenation as a
Function of DO in Aeration Tank
DO in
Aeration Tank
mg/1
0
1
t~*
4
6
relative
OI/OU
1
1,13
1,29
1,80
191
-------
4 mg/1 is kept in the aeration tank the necessary oxygenation
exceeds the oxygen demand by 80 %. One should therefore operate
a plant with a DO as low as possible because this can save most
of the energy. Depending on the geometry of the system with a
low DO denitrification can in many cases be obtained as well
which results in a further saving of energy for aeration. Due
to the variations in oxygen uptake the aeration system should
be as flexible as possible. This is true for aeration tanks
with circulating ML and mammoth rotor aeration that are used in
Vienna Blumental and in Feldkirch-Meiningen. However, it could
be shown that under proper operating conditions excellent ni-
trogen removal was possible in an aeration tank cascade (treat-
ment plant Zellerbecken) as well. In Vienna Blumental and in
the treatment plant Zellerbecken the process works without
primary sedimentation which instead of the presence of filamentous
organisms in the sludge results in a well settling sludge and
the possibility to work with high MLSS. To keep a high ML3S is
advantageous for denitrification. The application of the same
concept is, however, also possible with primary sedimentation
as could be shown in the plant Feldkirch-Meiningen.
For the optimal performance of a denitrification plant the
adaptation of the oxygen supply according to the oxygen uptake
is essential. With low loaded plants (volumetric loading below
-7
0,5 kg BODr/m^.d) a control by means of DO measurements in the
aeration tank seems to be sufficient. The application of a
continuous device for the measurement of oxygen uptake rates
192
-------
seperated from the aeration tank is a suitable method for
higher loaded plants.
LITERATURE
v.d. EMDE V. (1980): Untersuchungen iiber Energieeinsparungen
beim Belebungsverfahren. Abwassertechnisches Seminar,
TU Hiinchen, April 1980
v.d. EliDE V., SPATZIERER G. (1978): Das Klarwerk Zellerbecken.
Osterr. Wasserv/irtschaft J>0, 85-94
HATSCHE N. (19.72): The Elimination of Nitrogen in the Treatment
Plant of Vienna Blumental. Water Research 6, 485-4-86
HATSCHE IT. (1977): Removal of Nitrogen by Simultaneous Nitrifi-
cation-Denitrification, Progr.Wat.Techn. Vol.8, Nos. 4/5,
625-637
HATSCHE N., SPATZIERER G. (1977): Investigations towards a Con-
trol of Simultaneous Nitrogen-Elimination in the Treat-
ment Plant Vienna-Blumental. Progr.Wat.Techn. Vol.8, No.6,
501-508
11ATSCHE II. (1979) : Influencing Parameters on the ITitrification-
Denitrification Performance of a Single Stage Activated
TC\
Sludge Plant. 3XU IAWPR Workshop, Vienna Sept. 1979
U3RAEL G. (1977): Control of Aeration at the Treatment Plant
Vienna-Blumental, Progr.Wat.Techn., Vol.8, No.6, 245-2^9
193
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SINGLE-STAGE NITRIFICATION-DENITRIFI CATION
AT OWEGO, NEW YORK
BY D. E. SCHWINN AND D. F. STORRIER
INTRODUCTION
In some areas of the United States, water quality criteria require
the removal of nitrogen from wastewater treatment plant effluents. Facili-
ties for nitrogen removal can cost considerably more to construct and
operate than conventional secondary treatment facilities. This increased
cost results from the fact that the most reliable biological system
available necessitates three separate stages of activated sludge treatment
with different types of process control in each of the three stages. Addi-
tionally, methanol must be added to multi-stage systems for nitrogen
removal. Within the past few years the energy situation has resulted in
methanol shortages and much higher costs.
Recent research has demonstrated that the functions of the three
different stages can be combined in a single treatment stage under con-
trolled operating conditions to achieve 75 percent or more nitrogen removal
without the addition of methanol. However, there is a lack of detailed
design and operating data for engineers and operators to implement single-
stage nitrification-denitrification. The major objective of this study was
to operate a full-scale plant to determine the feasibility and reliability of
the process, to identify design features needed to be incorporated by engi-
neers, and to develop operating techniques to ensure optimum performance.
Schwinn is partner and Storrier is project engineer with Stearns & Wheler,
Civil and Sanitary Engineers, Cazenovia, New York.
194
-------
Because nitrification-denitrification can become more difficult to control
under extremely cold wastewater temperatures, a full-scale plant at Owego,
New York, was selected which performs under wastewater temperatures
ranging from 8° to 22 °C.
195
-------
BACKGROUND
Considerable research has been reported on biological processes
for nitrification and denitrification to provide nitrified effluents or nitro-
gen removal from wastewater. Three basic classes of organisms are
required to achieve the removal of carbonaceous and nitrogenous materials
in a suspended growth biological reactor. Aerobic heterotrophs provide
carbonaceous removal by microbial assimilation and oxidation. Aerobic
autotrophs, collectively known as nitrifiers, provide oxidation of nitrogen
in a two-step microbial reaction: first, ammonia is converted to nitrite
by Mtrosomonas; and then, nitrite is converted to nitrate by Nitrobacter.
Facultative heterotrophs provide denitrification by nitrate respiration,
i. e. , the microbial reduction of nitrate to nitrogen gas. The nitrate
radical acts as the electron acceptor and organic carbon sources serve
as electron donors under anaerobic or anoxic conditions. Facultative
organisms are also capable of oxidizing carbonaceous material under
aerobic conditions.
Optimum environmental and operating conditions for each of these
classes of bacteria differ from one another. Nitrifying bacteria have more
specific environmental requirements than the heterotrophic bacteria
responsible for carbon removal. The nitrification rate in the activated
sludge process reportedly reaches a maximum at dissolved oxygen (DO)
concentrations of approximately 2 mg/1 or above, and decreases to zero
as the DO concentration decreases to zero. Although some denitrification
can occur in aerobic systems, maximum denitrification rates occur at DO
concentrations near zero, when ample organic carbon is available. Because
of the varying conditions best suited for each type of bacteria, two-stage and
196
-------
three-stage systems for nitrification-denitrification with supplemental
carbon addition received the most attention initially. However, because
multi-stage systems have high capital and operating costs, the search
for more economical alternatives has intensified.
197
-------
DESCRIPTION OF TREATMENT FACILITIES
Owego Water Pollution Control Plant No. 2 (Figure 1) is located
in the Hamlet of Apalachin, Town of Owego, in the southern portion of
Central New York State near Binghamton. The Town of Owego and the
treatment plant itself are located on the banks of the Susquehanna River.
The plant was designed for a year 1990 flow of 7, 600 cu m/day (2. 0 mgd)
and was placed in operation in 1971.
Flexibility was provided in the design to allow operation during
the initial low flow years as an extended aeration plant and operation in
the conventional activated sludge or contact stabilization mode as waste-
water flows increase over the design life of the plant. During the year
previous to start-up of the single-stage nitrification-denitrification study,
the plant had been operated as a low-loaded conventional activated sludge
treatment plant. Currently, plant flow is approximately 1, 900 cu m/day
(0. 5 mgd). A schematic flow diagram of the treatment facilities is shown
in Figure 2. A summary of key plant components is presented in Table 1.
The wastewater at Owego is typically domestic in character. While
operating in the conventional activated sludge mode prior to initiation of
this study, the plant had been consistently achieving BOD and suspended
0
solids (SS) removals above 90 percent.
198
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FIGURE 1. OWE GO WATER POLLUTION CONTROL PLANT NO. 2
199
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TABLE 1. MAJOR PLANT COMPONENTS
Component
Bar Rack, Hand Cleaned
No. of Units
Unit Capacity
Commlnutor
No. of Units
Unit Capacity
Grit Separators
Cyclone Degritter, Primary Sludge
Cyclone Size
Flow Meters
Parshall Flume
Flow Range
Flow Tube (Return Sludge)
Flow (Waste Sludge)
Flow Tube (Thickened Sludge)
Pr1f?'-y Settling Tanks
No. of Units
Total Surface Area
Diameter
Average Depth
Aeration Tanks
No. of 'Tanks
No. of Compartments Per Tank
Volume of Compartments
First Compartment (N-l and S-l)
Second Compartment (N-2 and S-2)
Depth
No. of Mechanical Aerators Per
Compartment
Aerator Horsepower
Return Sludge Rate
Final Settling Tanks
No. of Rectangular Units
Length
Width
Average Depth
Surface Area
Total Volume
Chlorine Contact Tanks
No. of Rectangular Units
Length
Width
Depth .
Total Volume
Sludge Digestion Tanks
No. of Units
Diameter
Sldewall Operating Depth
Sludge Thickening Tank
No. of Units
Diameter
Sldewater Depth
Sludge Disposal
Tank Truck
Tank Capacity
Emergency Open Sludge Drying Areas
Total Area
ISU
1 1
19,000 cu m/day 5 mgd
1 1
19,000 cu m/day 5 mgd
1
0.3 m
0.23 m
0-19,000 cu m/day
1
1
1
230 sq m
12 m
2.7 m
2
2
1,190 cu m
760 cu m
3.7 m
1
11 kw
1,900-5,700 cu m/day
2
26 m
4.4 m
2.6 m
240 sq m
630 cu m
1
27 m
4 m
1.8 m
200 cu m
2
12 m
9 m
7.3 m
2.4 m
1
7.6 cu m
2
4,050 sq m
12 1n.
9 In.
0-5 mgd
1
1
1
2,500 sq ft
40 ft
9 ft
2
2
42,000 cu ft
27,000 cu ft
12 ft
1
15 hp
0.5-1.5 mgd
2
85 ft
14.5 ft
8.5 ft
2,600 sq ft
167,000 gal
1
88 ft
13 ft
6 ft
52,000 gal
2
40 ft
30 ft
1
24 ft
8 ft
1
2,000 gal
2
1 acre
201
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PROCESS MODIFICATIONS
To achieve single-stage nitrification-denitrification in an activated
sludge system utilizing wastewater organics as the carbon source for deni-
trification, the operational plan was to provide sufficient solids retention
time (SRT) to obtain a stable nitrifying population and to provide alternating
aerobic-anoxic conditions within the reactor. To increase the concentra-
tion of solids, and thereby increase the SRT, it was anticipated that the
sludge wasting rate would have to be significantly reduced. Automatic
timers were installed to cycle the mechanical aerators in Compartments
N-l and S-l (see Figure 2) to provide the alternating aerobic-anoxic condi-
tions. No additional equipment was added to provide mixing during the
anoxic stage when the aerator was off. It was anticipated that the residual
rolling action caused by mechanical aeration would keep the mixed liquor
solids suspended to a reasonable extent if the anoxic cycle was kept rela-
tively short. Mechanical aerators in Compartments N-2 and S-2 were
allowed to provide continuous aeration to oxidize residual ammonia (NH -N)
and carbonaceous material and to prevent sludge bulking in the secondary
clarifiers caused by denitrification of nitrified mixed liquor.
In preparation for the change to the single-stage nitrification-
denitrification process, the mixed liquor suspended solids (MLSS)
concentration was increased. Starting in November 1974 sludge wasting
was discontinued. The MLSS concentration increased from 1, 000 mg/1 in
mid-November to 3, 600 mg/1 in early January 1975. Both aeration tanks
were put into service to fully establish the extended aeration process. The
hydraulic retention time (HRT) in the aeration tanks increased from approxi-
mately 12 hours to 24 hours. The process of building up the MLSS inventory
was continued.
202
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A major operating modification necessary to initiate the study was
the bypassing of raw wastewater directly into the aeration tanks, rather
than through the primary settling tanks as normally done. The influent
was piped directly to the aeration tanks to enhance the carbon/nitrogen
ratio entering the aeration tanks. This was done to maintain a relatively
high BOD/TKN ratio for effective denitrification.
One of the most important features of process development and
operation was the creation of alternating periods of aerobic and anoxic
conditions. Computations indicated that the aerators installed at Owego
could supply the oxygen required for carbonaceous oxidation and for
nitrification, even when operating on a 50 percent on-off cycle. This
would then allow adequate time for denitrification to occur during the off
cycle. As the aerators are of the variable submergence type, the oxygen
required can be provided in a short aerobic cycle at high submergence, or
during a long aerobic cycle at low submergence. Therefore, the duration
of the aerobic and anoxic cycles could be balanced, if desired, in accordance
with nitrification and denitrification kinetic rates.
The following equipment and process modifications were also made:
a. Installed automatic sampler housings.
b. Repaired aeration tank weir drives.
c. Installed manual bar screen at aerator influent channel
to minimize rag accumulations on aerator blades.
d. Installed flow splitter at aerator influent.
e. Balanced flows to final tanks.
f. Repaired solenoids on return sludge suction valves.
g. Installed laboratory equipment and minor electrical
and physical equipment.
h. Wasted activated sludge to control MLSS at 3, 000 mg/1.
203
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i. Modified recycle rate to optimize clarifier performance
and reduce rate if possible when excess supernatant
appeared in 30-minute return sludge settling sample.
The study was divided into two phases: warm weather operation and
cold weather operation. Shorter HRT's were investigated during each phase
of the study once the process had been established at longer HRT's, assuming
that sufficient SRT was provided throughout. Operation in the winter was of
particular interest because cold weather was considered to be the critical
controlling environmental factor of the study.
The timers on the aerators in Compartments S-l and N-l were
pulsed on a 30-minute staggered on-off cycle to begin Phase I (warm
j
weather operation) of the study. The aerators in Compartments S-2 and
N-2 were set to remain running continuously. Figure 3 shows a typical
aerobic-anoxic cycle. This initiated the denitrification phase of the single-
stage nitrification-denitrification process utilizing wastewater organics as
the carbon source for denitrification. The process was operated in this
manner for the remainder of the study period, varying only the aeration
tankage in service and the submergence of aerator blades. No attempt
was made to fine tune the process by optimizing the aerator on-off cycles.
Sludge disposal was as normally practiced, employing two-stage digestion
of thickened sludge followed by ultimate disposal to the land.
The critical phase of the project, Phase II, took place during the
late winter and spring of 1976 when cold temperature performance was
studied.
Table 2 lists the sequence of events for the entire study period.
204
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TABLE 2. SEQUENCE OF EVENTS
Pre-Study
November 1974
January 7, 1975
January 27, 1975
March 1, 1975
Phase I Start-Up
March 18, 1975
March 24, 1975
April 18, 1975
Phase IA
May 5, 1975
May 28, 1975
June 13, 1975
Phase IB
July 17, 1975
August 1975
September 8, 1975
October 1975 thru
January 1976
January 28, 1976
Phase II Start-Up
February 3, 1976
February 12, 1976
Phase IIA
March 10, 1976
March 1976
Phase IIB
May 1, 1976
May 28, 1976
Sludge wasting discontinued
Second aeration tank put in service
Primary clarifiers taken off line
Grant funded
Initiation of operational and equipment modifications
Nitrogen series analysis started
Changed labs (Technicon Auto-Analyzer to wet chemistry)
Air pulsed on 30-minute cycle
Aerator blade submergence increased to 5 inches
Aerator blade submergence increased to 7 inches
North aeration tank (N-l and N-2) taken out of service
Primary digester malfunction—taken out of service
Discontinued study until cold weather period
Monitored on random basis
Hydraulic washout of solids
Aerator blade submergence decreased to 5 inches
Measures taken to reestablish process; north aeration
tank put in service; all aerators placed in continuous
operation
Pulsing started; resumed monitoring program
Began cleaning out primary digester
North aeration tank (N-l and N-2) taken out of service
Study terminated
206
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DISCUSSION OF RESULTS
Single-stage biological nitrification-denitrification was shown to be
a viable nitrogen removal process under full-scale plant operation for both
summer and winter conditions. Suitable environmental conditions for
nitrogen removal were created by simple operational changes and without
the supplemental addition of methanol. Wastewater organics proved to be
adequate as a carbon source for denitrification in lieu of methanol. By
operating at sufficiently low F/M ratios and correspondingly high SRT's
under warm and cold weather conditions at HRT's of about 13 to 16 hours
and 20 to 24 hours, respectively, stable carbonaceous-oxidizing, nitrifying,
and denitrifying bacterial populations were maintained. As shown in Table 3,
the largest constituent of Total-N in the effluent was generally NO3~N.
Influent and effluent NO2~N concentrations were negligible. With the
exception of the latter part of Phase II, effluent NH.-N levels varied from
0. 3 to 2. 2 mg/1, indicating a high degree of nitrification. Good removals
of Org-N were also consistently achieved. Except for a two-week period
in Phase I when too little available carbon impaired denitrification, nitrogen
removals during Phase I averaged 76 to 81 percent with both aeration tanks
in service and 77 to 86 percent with one aeration tank in service. In
Phase II, with two tanks in operation, nitrogen removals averaged about
78 percent. Nitrogen removal was initially good in Phase II with one
tank in operation but rapidly dropped to about 50 percent because of strong
supernatant returns from the anaerobic digester. One digester had to be
removed from service because of a structural failure, leaving one digester
in operation and that became increasingly overloaded.
Careful operational control Qf solids inventory was found to be a
major factor in obtaining efficient year-round nitrogen removal. Other
207
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important factors were influent characteristics and loadings, including
wastewater temperature, COD/TKN ratio, excessive wet weather waste-
water flow rates and excessive solids in digester supernatant returns.
In early summer in Phase I, the combination of a higher bacterial
metabolism rate resulting from increasing temperature, and a lower
COD/TKN ratio, resulted in a deficiency of available carbon for denitri-
fication. To reduce the rate at which carbon was consumed during the
aerobic cycle, and thus to increase the amount of carbon available during
the anoxic cycle, the north aeration tank was removed from service. This
resulted in an immediate return of denitrification and previously observed
effluent values.
Some problems were encountered in attempting to restore nitrifica-
tion following a solids washout due to high settling tank loading rates that
resulted from infiltration/inflow problems in the collection system prior to
the start of Phase IL Although solids were rapidly built back up and the
biomass responsible for carbonaceous removal was quickly reestablished,
the nitrifiers were not reestablished until approximately four weeks after
the washout. Conversely, denitrifying bacteria were found to be highly
responsive and readily established. It appeared that when conditions were
favorable for good nitrification efficiency, a high degree of denitrification
was readily achievable by providing an anoxic period and an adequate
carbon source.
The failure of the process to efficiently remove nitrogen in the
latter part of Phase II is believed to be primarily attributable to digester
problems causing a return of excessive inert solids in digester supernatant
and not to temperature effects at lower retention times. Data from the
period between Phase I and Phase II suggest that single-stage nitrification-
denitrification at SRT's of less than 20 days is feasible during winter
conditions with adequate operational control. Spot checks indicated that
nitrification-denitrification at such SRT's was maintained at wastewater
temperatures as low as 11°C with one aeration tank in service until the
209
-------
hydraulic washout of solids occurred. Insufficient data, however, were
collected during this period prior to the washout to fully evaluate the
process under such conditions. Additional research is needed to deter-
mine minimum reactor volume under winter conditions.
Process modifications and operational changes performed to
create suitable environmental conditions for the nitrification-denitrification
process did not adversely affect the plant's ability to remove BOD, COD,
and SS. Removal efficiencies were equal or superior to previous plant
performance. As shown in Table 4, excellent removals of these three
pollutants were consistently achieved throughout the study period until
near the end of Phase n when strong digester supernatant returns caused
a slight decrease in treatment efficiency. BODr removal efficiency
normally ranged from 94 to 97 percent, except late in Phase n when the
efficiency decreased to 86 percent. Effluent COD values over various
time periods averaged between 35 and 78 mg/1. As effluent BODg values
were consistently less than 10 mg/1, the data suggest that residual COD
consisted of mostly refractory material. SS removals generally exceeded
95 percent. On many occasions, equipment and piping objects located
6 to 8 feet below the water surface of the final settling tanks could clearly
be seen.
There are many existing extended aeration plants in the nation
which have the capability for nitrification and denitrification, as well as
many such plants under design or construction. This study demonstrated
that a significant improvement in national water quality could be achieved
at very little increased cost by the use of single-stage nitrification-
denitrification, especially in water quality limited areas where nitrogen
removal is mandatory.
210
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ACKNOWLEDGMENTS
The interest and support of Mr. William E. Engelhard, Supervisor
of the Town of Owego, and the members of the Town Board are acknowledged
with sincere thanks. Employees of the Water and Sewer Department of the
Town of Owego who carried out the major share of plant operation and
control included Mr. Daniel G. Thome, Chief Plant Operator, and
Mr. Burton E. Schoonover, Laboratory Technician. This study was
partially sponsored by a grant from the United States Environmental
Protection Agency, Grant No. 803618-01.
212
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REFERENCES
1. Barth, E. F. , R. C. Brenner, and R. F. Lewis. Chemical Control of
Nitrogen and Phosphorus in Wastewater Effluent. J. Water Pollution
Control Federation, Vol. 46, No. 12, 2040, 1968.
2. Bishop, D. F. , J. A. Heidman, and J. B. Stamberg. Single-Stage
Nitrification-Denitrification. J. Water Pollution Control Federation,
Vol. 48, No. 3, 520, 1976.
3. Heidman, J. A. , I. J. Kugelman, and E. F. Barth. Plug Flow Single-
stage Nitrification-Denitrification Activated Sludge. Presented at:
49th Annual Conference of the Water Pollution Control Federation,
Minneapolis, Minnesota, October 3-8, 1976.
4. Kugelman, I. J. Status of Advanced Waste Treatment. Presented at:
Long Island Marine Resources Council, Hauppauge, Long Island,
New York, June 10, 1971.
5. Lawrence, A. L. , and C. G. Brown. Biokinetic Approach to Optional
Design and Control of Nitrifying Activated Sludge Systems. Presented
at: Annual Meeting of the New York Water Pollution Control Association,
New York, New York, January 23, 1973.
6. Ryan, R W., and E. F. Barth. Nutrient Control by Plant Modification
at El Lago, Texas. EPA-600/2-76-104, U. S. Environmental Protection
Agency, Cincinnati, Ohio, 1976.
7. U. S. Environmental Protection Agency, Office of Technology Transfer.
Nitrification and Denitrification Facilities. Prepared by: Metcalf &
Eddy, Consulting Engineers, Boston, Massachusetts, August 1973.
8. U. S. Environmental Protection Agency, Office of Technology Transfer.
Process Design Manual for Nitrogen Control. Prepared by: Brown and
Caldwell, Consulting Engineers, Walnut Creek, California, October
1975.
9. U. S. Environmental Protection Agency, Office of Technology Transfer.
Process Design Manual for Upgrading Existing Wastewater Treatment
Plants. Prepared by: Metcalf & Eddy, Consulting Engineers, Boston,
Massachusetts, October 1974.
213
•/us GOVERNMENT PRINTING OFFICE igeo -657-165/0078
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