BIOLOGICAL TREATMENT
OF
WASTE WATER
1970 STATUS
DOI/FWQA-0001
ROBERT A. TAFT WATER RESEARCH CENTER
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
FEDERAL WATER QUALITY ADMINISTRATION
U.S. DEPARTMENT OF THE INTERIOR
CINCINNATI, OHIO
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FORWARD
This report covers only projects funded under subprogram element 1705,
"Dissolved.Biodegradable Organic Removal", of the Planning-Programming-
Budgeting-System (PPB3).
Information on sludge disposal and nutrient removal as related to bio-
logical treatment will be found in the yearly status reports of sub-
program elements IT07 and 1701.
Robert L. Bunch
Program Chief, PPB 1705
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PUKE OXTGEN AERATION OF ACTIVATED SLUDGE
Linde Division of Union Carbide, under contract to FWQA., has completed a
comparison of pure oxygen aeration and air aeration in the conventional
activated sludge process. The study was carried out in identical parallel
trains at the 2.5 mgd Batavia, New York Plant. Inefficient utilization of
costly pure oxygen has discouraged similar full-scale operation in the past.
The covered-staged oxygen injection and dissolution concepts developed by
Linde overcome this obstacle and 90-95$ utilization of the input oxygen was
achieved.
The oxygenation system used employed sealed covers on the aeration tanks
and intertank "baffles to form a series of staged compartments. Each com-
partment or stage is equipped with a submerged turbine-rotating sparger
unit and a recirculating gas compressor located on the top of the tank
cover.
The three points demonstrated by this study with the greatest potential
for reducing the cost of waste treatment are:
1. The substantial reduction in aeration volume possible with oxygen
aeration while maintaining efficient carbon and solids removal.
The oxygen train achieved better treatment in 1-1/2 hours aeration
detention time than the air train at 3 hours.
2. The high solid content of the waste activated sludge achieved by
the oxygen system; thereby, possibly eliminating the need for a
separate thickener operation. Oxygenated sludge had a Sludge
Volume Index of ^0 and concentrated to about 3$ i~i the final
clarifier underflow.
3- The reduced quantity of waste sludge produced with oxygen.
Significant reduction in the quantity of waste activated sludge
produced by the oxygen system was noted. The best estimates at
this time are that the reduction, by,weight was 30-^0$. Better
data on the exact amount will be obtained this summer.
The economic substitution of pure oxygen for air may eventually prove to
be one of the most significant breakthroughs in the history of the activated
sludge process. The pure oxygen process, in addition to offering potential
reduction in new plant construction, is also applicable to many existing
high-rate or overloaded plants which are performing poorly.
A large scale R&D demonstration grant application Is currently in Washington
for funding consideration.
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For more information, see report "Investigation of the Use of High Purity
Oxygen Aeration in the Conventional Activated Sludge Process" by Linde
Division of Union Carbide Corporation, Contract No. 1^-12-465, or contact:
Mr. Richard C. Brenner
Advanced Waste Treatment Research laboratory
Ohio Basin Region
Cincinnati, Ohio 45226
TRICKLING FILTERS
There has been no major breakthrough in the past two years. This process
is capable of producing a good quality effluent having a BODc of less than
20 mg/1 if lightly loaded. In the United States, the tendency is to load
the filter at a much higher rate than is done in England. Thus, we find
today many installations that will have difficulty in meeting the more
stringent water quality standards.
It is not enough to just look for completely new processes, but attention
and action must be given immediately to applying known technology to up-
grading present treatment plants. All the needed new plants and plant
expansion cannot be built in a short time. Substantial amounts of pollu-
tion can be prevented from reaching our surface waters by upgrading present
plants. There are several ways of achieving higher removals. There is
probably no one solution that will work at all installations, for each
plant is different. If a plant is not getting good removal and the impair-
ment is not due to toxic or grossly atypical waste, then it is usually due
to either hydraulic overload, organic overload, or poor final liquid-solids
separation. The following are suggested ways of alleviating these conditions,
Easing hydraulic overload
1. Find and reduce needless sources. Infiltration, downspouts, and
cross connection can contribute greatly to the flow.
2. Use large interceptors as holding tanks. Many towns use their
main interceptor to the plant to back-up the flow during the day
and treat it at night when the flow is low.
3. Construct an equalizing or surge tank to smooth out the high peak
flows. An equalization tank will mix and dilute toxic wastes,
giving better downstream settling and lessen load fluctuations.
Aiding organic overloaded plants
Most organically overloaded plants can be aided by the same methods
suggested for hydraulic overloads since they commonly occur con-
currently. Additional methods are:
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1. Have industry program the load for slow release. In smaller towns,
most industries are willing to program extremely high organic waste
flows.
2. Have industry treat at source using a roughing filter or other
appropriate means to relieve part of the load.
3- Treat digester supernatant return "by alternate methods or program
return load to time of low load.
k. Remove more material in the primary tank "by using iron or aluminum
salts and polymers in the incoming waste. This will also remove
phosphorus.
Lessen final solids discharge
One of the greatest improvements that can "be made in secondary treat-
ment is reliable solid removal from effluents. For efficient overall
removal, the final settler must remove better than 98$ of the solids.
If overflow weirs are submerged several inches with the present flow,
then there is no recourse except to increase settler capacity. For
less hopeless cases, the following can be tried.
1. Chemical flocculation or precipitation in process or final effluent
treatment.
2. Improve inlet and/or overflow design.
3. Install a xaicroscreener.
k. Install mixed media filters.
5. Install tube settlers.
If a town has a trickling filter that is water tight or can be made so, the
filter unit can be simply converted to an aeration tank. This can be done
by removing the filter media and installing a surface aerator. The existing
primary and final clarifiers can be utilized with minimal structural and
piping changes. This type of conversion will usually increase the capacity
of the plant twofold for a fraction of the cost of a completely new plant.
All the methods discussed are not new, but are well-proven processes. Thus,
there are answers to the question on how a town can meet the new water quality
standards. All that is needed is an awareness of the fundamentals involved
and a willingness to pay for and use all the technology that is known.
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ROTATING BIOLOGICAL DISCS
The rotating biological disc method of treating vaste has been used in
Europe for at least the last five years. The system basically consists
of closely spaced rotating discs alternately submerged in wastewater and
exposed to air. Wastewater continuously flows parallel to the discs. The
waste level is slightly less than half the disc diameter. The units are
usually arranged in series or stages.
The discs are molded of low-density expanded polystyrene. The entire
downward load is offset by the buoyancy of the discs. Thus, the only power
required to rotate the discs is that needed to overcome bearing friction.
Microorganisms attach themselves to the discs and perform the same function
as in a trickling filter. The biomass sloughed off the discs is removed in
a final clarifier. In short, the rotating biological disc method is a modern
version of the "Immersion Filter" developed by Buswell in the middle twenties.
IWQA has funded a grant (IT01 EBfl) with Rutgers University to assess the
degree of treatment and to obtain operating data on this method of treatment.
The pilot plant used in this study is a ten-staged unit with a design flow
of 8 gpai. This gives a detention period of 5 minutes per stage or a 50-
minute overall detention time for the disc unit. The plant has been in oper-
ation for about one year at the Jamaica Treatment Plant in New York City near
the Kennedy International Airport. Data obtained thus far show that the unit
is oxidizing about 93$ of the biodegradable carbonaceous matter and 80$ of
the ammoniacal nitrogen in the primary effluent being trea,ted. A report on
the work is not available at this time.
A demonstration grant (11010 EBX) has been awarded to the Village of Pewaukee,
Wisconsin to evaluate the effectiveness and efficiency of the rotating bio-
logical disc method for treating municipal wastes on a full-scale community
level. The performance of the unit will be compared directly with an existing
trickling filter under identical conditions. The design flow of the disc unit
is 0.46 mgd. The unit is scheduled to be on^-stream the latter part of this
year.
The rotating disc system has an advantage over a trickling filter unit in
that recycle is not necessary at night to keep the biological mass wet be-
cause the trough always contains liquid. It seems quite possible that the
method can produce an effluent in quality some place between that of a trick-
ling filter and an activated sludge unit. It is conceivable that the system
would find application at some of our Federal installations, such as small
parks or rest stations where there is a wide variation in the flows. There
is a small two-stage unit available that handles population equivalents of
12 to 200 persons.
The main disadvantages of the method are that it must be housed to protect
it from storms, hail, etc. and the large disc surface area required. For
90$ removal, the unit load is 2.7 gal/day/ft2 of disc surface area. Normally
the discs are ten feet in diameter and the disc spacing is 0.846 inches.
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DTSTKUMEHTATIOH OF WASTE TREATMENT PLANTS
Instrumentation and control have not yet caught up with the basic require-
ments of waste-water plants. There are several reasons for the limited use
of continuous automatic analysis and control. Some of these are the absence
of sensors to measure some of the most important factors directly, the fairly
high cost of instruments available, and the willingness of those in the waste
treatment field to decide that automatic operation is necessary and to take
all the steps required to bring it to fruition. In the past, the cost of
instrumentation has eliminated them from consideration by managers of small
and medium-sized plants.
Recent emphasis on water quality standards is bringing about a natural in-
crease in the extent of automatic control. This is especially evident in
newer facilities where instrumentation is no longer an "afterthought", but
an integrated part of plant design. Unfortunately, some engineers engaged
in designing new plants have not kept up with the improved processing tech-
niques . The design of a modern plant for treatment of wastewater requires
a considerably broader knowledge of treatment and control techniques than
in the past.
Many sensors cannot be used in treating wastewater because they become fouled
by the gross solids, greases, oil, and aquatic growths. Despite the encum-
brances inherent in the physical makeup of raw wastewater and sludge drawoff,
measuring devices and instrumentation are now available that can monitor and
control most of the secondary plant flow systems. The real problem in auto-
mating the various flow regimes is not a lack of flow controlling equipment,
but the inability to rapidly measure biological activity or "state-of-health"
of the system. For instance, wasting of activated sludge could logically
be based on the active mass of microorganisms in the system. However, the
closest we can come now to determining active mass is mixed liquor volatile
suspended solids and this has been estimated to represent 50 to 100 percent
more active solids than are actually present. Thus, the difficulty in con-
trolling the treatment plant is directly attributable to the inability to
model constantly changing life processes.
It would appear that the best index for understanding and controlling the
activated sludge process would be the amount of living cells in the aeration
tank. No method now exists which permits determination of the microbial
activity in a manner useful to process control. Adenosinetriphosphate (ATP)
is present in and essential to all living cells. Measurement of ATP would
be a rapid and unequivocal method for active microbial mass. Biospherics
Incorporated is under contract (14-12-1^9) to design and fabricate an in-
strument for use in the ATP assay. In addition, they will adapt the fire-
fly bioluminescent method to determine the ATP of activated sludge which is
directly proportional to the biomass. E.I. DuPont is now producing commer-
cially the reagent^ needed for the test; therefore, there will not be any
difficulty in obtaining the reagents if the method becomes a reality. This
method probably can be automated. The time to perform the tests should be
about 15 minutes if done manually.
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Biological process efficiency is now measured by various laboratory analytical
techniques. The time required to collect, transfer samples, and perform the
analyses may take anywhere from three hours to five days. The time involved
in obtaining data seriously hinders rapid and effective process control. On-
line instrumentation designed to yield reliable, useful information in terms
of minutes instead of hours would contribute significantly to improving plant
operation. Contracts are now being let to develop an on-line instrument to
measure the organic strength of influent and effluent streams at a waste treat-
ment plant. The instrument will be capable of analyzing both filtered and un-
filtered samples. This will entail developing an on-line macerating device
as well as a,n on-line filter. Within the next year, it is hopeful that a
full automatic on-line COD and TOG analyzer will be available to treatment
plants.
A wastewater treatment plant can have too much instrumentation and auto-
mation or it cannot have enough. Most wastewater treatment plants now have
too little instrumentation to give adequate control. The new pilot plant
at AWTRL in Cincinnati will test new process control equipment and instru-
ments in the coming year. The aim here is to operate them under controlled
conditions to determine durability, performance, and limitation. This in-
formation will then be made available to construction grants people and con-
sultants so that new plants can be operated more efficiently.
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