IVi-1 r r :i I mr M t R i-q u i rr in ruts
for Oil iiiul (Jri'iisc1
TREATABILITY OF OIL AND GREASE
DISCHARGED TO PUBLICLY OWNED
TREATMENT WORKS
U.S. I.NVIRONMI N I Al. PRO I l.( I ION A(;i N( Y
APRIL IV75
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TREATABILITY OF OIL AND GREASE
DISCHARGED TO PUBLICLY OWNED TREATMENT WORKS
Russell Train
Administrator
James L. Agee
Assistant Administrator for Water & Hazardous Materials
2 JTB o
ussy
Allen Cywin
Director, Effluent Guidelines Division
Raymond C. Loehr
Program Adviser
April 1975
Prepared for
Office of Water and Hazardous Materials
Effluent Guidelines Division
U.S. Environmental Protection Agency
Washington, D.C. 20460
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TREATABILITY OF OIL AND GREASE
DISCHARGED TO PUBLICLY OWNED TREATMENT WORKS
The Effluent Guidelines Division recommends that the
following pretreatment requirements be established for existing
point sources discharging into publicly owned treatment works for
the listed categories of oil and grease:
animal and vegetable origin no limitation
petroleum or mineral origin 100 mg/1
Introduction
The need for pretreatment cf any industrial waste is related
to the ability of a publicly owned treatment works to remove
pollutant parameters in the waste. The Federal Water Pollution
Control Act Amendments of 1972 (the Act) contains sections which
required EPA to take specific actions regarding pretreatment of
industrial waste introduced into municipal systems. The
pretreatment sections of the Act were intended to prevent
intoduction of pollutants into publicly owned treatment works
which interfere with, pass through, or are otherwise incompatible
with such works.
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Oil and grease is a pollutant parameter which has been
considered to interfere with the performance of publicly owned
treatment works. Factors affecting the establishment of
pretreatment requirements include the constituents and their
biodegradability in a publicly owned treatment works.
Method of Analysis
Unlike some pollutant parameters, such as distinct chemical
elements, oils and greases are defined by the method used for
their determination. An absolute quantity of a specific
substance is not measured. Ratherr groups of substances with
similar physical characteristics are determined quantitatively,
based on their mutual solubility in the solvent used,, The term
oil and grease will include fatty acids, soaps, fats, waxes,
petroleum products and any other material which is extracted by
the solvent and which is not volatilized during evaporation of
the solvent. Both hexane and freon (trichlorotrifluoroethane)
are the recommended solvents (1, 2, 3) . A method using activated
alumina is available to separate polar (primarily hydrocarbon)
and non-polar (fatty acids and esters) constituents of oil and
grease (1) . This method provides information on the proportion
of oil and grease composed primarily of fatty matter from animal
and vegetable sources and of hydrocarbons from mineral oil and
petroleum sources.
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Constituents
Oil and grease in waste waters or natural waters result from
the introduction of animal and vegetable fats and oils and from
petroleum products. Animal and vegetable fats and oils are
present in significant concentrations in household sewage. They
are also present in the waste waters from the refining of these
materials for preparation of shortening, soap, and from other
industries such as meat packing,, slaughterhouse, leather tanning,
and food processing operations.
Petroleum products in waste water result from losses of
petroleum oils during refining or other processing in refineries
and petrochemical plants. Oil also may be lost during cleanup of
metal machining and metal working operations, from lubricating
operations, and in the case of service stations some may be
deliberately disposed of to the sewer system. Oil, though
basically insoluble in water, may become emulsified or dispersed
in waste waters through pumping and other agitation. Emulsified
oils may also be discharged from certain industrial operations.
The majority of greases or oils in food or animal fat exist
as glycerides. Glycerides may bo hydrolyzed in waste water
collection and treatment systems to yield glycerol and the
alkalyzed salts of the fatty acid. These compounds constitute
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the major faction of grease in normal domestic sewage. The
principle constituents of these glycerides and soaps are the
long-chain saturated fatty acids—lauric, myristic, palmitic, and
stearic acids—and the long-chain unsaturated fatty acids—oleic
and linoleic acids. Palmitic, stearic and oleic acids usually
constitute over 80% of the fatty acids in most municipal waste
waters. Vegetable oils discharged to sewerage systems will be
absorbed onto other suspended material in sewage and are unlikely
to be in liquid form entering waste water treatment facilities.
Oil and greases of petroleum origin consist primarily of
long-chain, saturated hydrocarbons that are relatively non-
reactive. These compounds can be degraded to various degrees
especially if the microorganisms are acclimated to use the
compounds as a substrate.
Removal by Waste Treatment Processes
Waste treatment processes are utilized, among other reasons
to reduce the oxygen demand of waste waters prior to discharge.
The total oxygen demand and the rate of the demand of a compound
is related to the ability of microorganisms to metabolize the
compound. Long chain, saturated, reduced organic compounds, such
as hydrocarbons, generally are oxidized more slowly but require
more oxygen per unit weight than short chain, unsaturated,
oxidized compounds such as organic acids.
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Grease in waste water can be in three forms a) free, b)
attached to other solids, and c) semi-colloidal. Free grease can
float and be skimmed from primary sedimentation tanks. Grease
attached to other particles can settle with these particles or
remain in suspension if the resultant specific gravity is not
greatly different from that of water. Much of the grease
attached to other solids and that in the semi-colloidal state is
not removed in a primary sedimentation tank and flows to a
secondary treatment unit, such as an activated sludge unit or a
trickling filter. The microorganisms in the secondary biological
treatment unit will metabolize the entering greases. The energy
from such metabolism is used for both maintenance of organisms
and for synthesis of additional organisms. It can be expected
that biological waste treatment will not only decrease the
quantity of grease in waste waters but will also change the
relative proportion of grease components as the easily
metabolized greases are removed, the less easily metabolized
greases remain, and microbial oil and grease extractable
compounds are synthesized. Such material forms a significant
fraction of microorganisms.
All greases are not metabolized at the same rate in microbial
systems. Fatty acids, glycerides, and methyl esters are more
readily oxidized than hydrocarbons. The less easily metabolized
greases and the greases in microorganisms discharged in the
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effluent represent the major part of the organic matter
discharged from secondary treatment facilities„
Investigations of oil and greases in waste water and their
removal in waste water treatment processes have shewn that
hydrocarbons, sterol esters, glycerides, fatty acids, compound
lipids, and possibly sterols were found in the oil and grease
extractable material from untreated waste water and activated
sludge samples. Oil and grease extractables from influent waste
water samples indicated that fatty acids were the predominant
extractable components, followed by hydrocarbons, triglycerides,
and compound lipids. In some samples, hydrocarbons and compound
lipids were the predominant extractable components (4,5).
The general pattern of hexane soluble material in influent
waste water was shown to change as the degree of treatment
increased. Compounds more resistant to biological degradation
remained in the waste water for a longer period of time. Whereas
fatty acids were a predominant oil and grease component in the
effluent from an activated sludge treatment facility (4, 5).
A waste water treatment plant receives a heterogenous group
of organic compounds, the mix being a function of the commercial,
manufacturing and domestic contribution of the community.
Bacteria will adapt to degradation of each category of material.
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i.e., proteins, carbohydrates, and greases, since these compounds
are normally found in waste water. No problems concerning
adaptability or acclimation would be expected until a specific
compound suddenly appeared in abnormally high concentrations.
Analysis of oil and grease at waste water facilities is not
as routine as it is for EOD, COD, or solids. Available
information indicates the following total grease removals at
activated sludge plants: SUE - Topeka, Kansas; 85.7% - Cleveland
easterly plant; 94% - Madison, Wisconsin. The Cleveland data
represents a yearly average with the average influent grease
concentration being 80.3 ir.g/1 and the average effluent
concentrations being 11.5 mg/1 (6) .
The Topeka study was done to investigate grease removal patterns
at a secondary treatment facility (7) . Grease removal by primary
treatment was U5%, by secondary treatment 7U%, and by complete
treatment 84%. The average BOD and suspended solids removal at
this time was 85 and 82* respectively. Other results from the
study showed that there was a reasonable correlation between the
grease and the suspended solids concentrations in the effluent
from treatment plant.
When the suspended solids concentration was low, the
concentration of grease was also low. Grease in the effluent
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from the activated sludge plant averaged 22 mg/1 with hourly
samples having concentrations that ranged from 7-68 mg/1.
A summary of one years data, 1968, at the three major Chicago
sewage treatment plants indicated that the West Southwest,
Calument, and North Side plants failed to meet an effluent oil
and grease concentration of 15 mg/1 36, 34, and 3% of time
respectively. During the same period, the three plants failed to
meet a BOD effluent standard of 20 mg/1 and a total suspended
solids effluent standard of 25 mg/1 40 and 55*r 60 and 40X, and
20 and 1H% of the time respectively. The data was based on daily
2«l hour composite samples. The summary indicates that the oil
and grease removals were on the same order Two research studies
have provided additional insight into the removal of oil and
grease by biological treatment processes.
One study investigated the effect that wastes from processing
vegetable and animal fats and oils had on treatment systems
involving biological degradation and sludge filtration (8). The
results indicated that these wastes were readily degraded by the
activated sludge process even at temperatures as low as 12.25°C,
that they were readily degraded by anaerobic treatment with
removal efficiencies of from 82 to 92 percent, and that the
presence of the wastes, with one minor exception, had no adverse
effect on oxygen transfer in the activated sludge process.
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An EPA supported study determined the tolerance of biological
treatment systems to various oily materials which included
crankcase oil, crude oil, refinery waste, vegetable oil, benzene,
and benzene derivateive (9). The study indicated that the
failure of activated sludge systems due to oily materials is
physical rather than biochemical. The oily compounds are
absorbed in the sludge floe but are only slowly metabolized. The
result of the oil accumulation is a lowering of floe density
which results in a loss of sludge settling properties. An
activated sludge system will perform satisfactorily with a
continuous loading of oil and grease of 0.1 pounds per pound of
mixed liquor suspended solids. For conventional plant
operations, the influent to the biological system was suggested
to contain less than 75 mg/1 oil and grease and preferably less
than 50 mg/1. None of the compounds studied interfered with the
oxygen transfer in the system.
The above information indicates that different oil and grease
components in waste water have different removal and
biodegradation rates in waste treatment facilities. Hydrocarbons
and complex greases associated with microbial cells are likely to
be the main components in secondary treatment plant effluent.
Fats and oils of vegetable and animal origin are more readily
metabolized. Although data is not excessive, grease removal
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efficiencies in primary facilities appear to be about 40-5055 and
in secondary treatment facilities about 80-90%.
Grease removal efficiency correlates with BOD and suspended
solids removal efficiency. Grease concentrations in an activated
sludge effluent appears to correlate with high suspended solids
in the effluent. This indicates that one mechanism to minimize
oil and grease discharged to surface waters is to provide for
better suspended solids removal from the effluent. Because
vegetable and animal fats and oils can be metabolized by micro-
organisms, they will be removed in secondary biological treatment
facilities and their effect will be observed in the BOD test.
Control of excess grease in an effluent, especially that from
vegetable and animal sources, should be accomplished by
implementation of BOD and suspended solids effluent standards at
the secondary treatment plant. Additional constraints by a
pretreattnent limitation on these compounds would be redundant. A
pretreatinent limitation on the less biodegradable compounds, such
as those of petroleum or mineral origin, may be advisable.
Currently Acceptable^Concentrations
Specific limitations on oil and grease discharges to municipal
treatment plants were published in 1949 when the Federation of
Sewage Works Associations first presented its Manual of Practice
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on Municipal Sewer Ordinances. The recommended maximum
concentration of oils and greases in the manual was 100 mg/1. In
the intervening years there has been considerable disagreement on
such a rigid limitation. The concern has been with the non-
specificity of the oil and grease components that may interfere
with the performance of a publicly owned treatment works. As
noted earlier, numerous investigations have more clearly
identified the problem components. The most recent manual of
practice (10) suggests the following limitations on oil and
grease discharged to municipal treatment systems:
"Waste water containing more than 25 milligrams per liter of
petroleutrt oil,, nonbiodegradable cutting oils, or product of
mineral origin"
"Waste water from industrial plants containing floatable
oils, fats, or grease."
The manual notes that oils .and grease of mineral origin
(primarily nonpolar substances) are essentially nen-biodegradable
either in aerobic or anaerobic processes and that animal and
vegetable oils and greases (polar substances) are readily
degradable in these processes. It further notes that "if oils
and greases are biodegradable and in a physical state that does
not cause clogging or undue maintenance problems in the waste
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water facilities, the discharge of these substances can be
accepted in a wastewater treatment system." Many municipal sewer
ordinances have been based on the material in the editions of the
above Manual of Practice and include a statement to the effect
that waste water discharges having oil and grease concentrations
in excess of 100 mg/1 are prohibited. Examples can be found in
the sewer ordinances of the metropolitan St. Louis Sewer District
(11) and of Jefferson County, Alabama (12).
Oils and greases are a normal constituent of municipal waste
waters and information on the concentrations currently in the
untreated waste water of municipalities should provide an idea of
the concentration currently being accepted, and thus by
inference, able to be handled by municipal treatment plants.
Information in the Manual of Practice (10) indicated that oil and
grease concentrations of 16 to 105 mg/1 were found in waste water
free of industrial wastes.
Summary and Conelusigns
1. Available information indicates that oil and grease of
animal and vegetable origin can be metabolized by microorganisms
in secondary waste treatment facilities and would be reduced in
concentration along with other organics. The oils and grease in
the effluent from secondary treatment plants is related to the
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suspended solids content of the effluent. Low concentrations of
oil and grease in the effluent can be obtained by achieving low
suspended solids concentration thus, oils and grease of animal
^
and vegetable origin are not expected to pass through or
interefer with a publicly owned treatment works. Pretreatment
requirements for these compounds are not needed.
2. In the event that excessive quantities of oils and
grease are discharged to a publicly owned treatment works such
that they do cause obstruction to the flow in sewers or interfere
with the operation of such works, or are in such slugs that they
upset the treatment processes and result in a loss efficiency,
such discharges are subject to the general prohibitions of
section 128.131 of the General Pretreatment Regulation (40 CFR
128) published on July 19, 1973. No other pretreatment
requirements are needed to control such discharges.
3. Oils and grease of mineral or petroleum origin are less
biodegradable in secondary treatment plants, one of the above
studies has noted that the influent ot biological treatment
systems should contain less than 75 mg/1 and preferably less than
50 mg/1 oil and grease. Varying degree of dilution occur in an
municipal sewer system due to household and commercial
contributions. A dilution of a least two occurs, thus a limit of
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100 mg/l on the discharge of oils and grease of petroleum or
mineral origin is realistic.
This concentration is greater than that currently recommended
in the Manual of Practice (10)„ however the available information
justifies a number higher than that noted in the Manual of
Practice. Because of the dilution the does occur in sewers as
industrial and other waste waters are mixed, it is expected that
the concentration of petroleum or mineral oils in the influent to
the publicly owned treatment works will be less than 50 mg/1 and
thus will not interfere with the performance of such works.
These requirements do not preclude a municipality or other
agency from establishing more stringent pretreatment requirements
where it can be shown that they are needed for the protection of
the publicly owned treatment works. Thus the recommended
requirements for oils and grease of petroleum or mineral origin
are not contradictory to the recommendations in the Manual of
Practice.
References
1. Standard Methods for the Examination of Water and; Waste
Vfatey f 13th Ed, (1971) , American Public Health
Association, Washington, D.C.
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2. Environmental Protection Agency, "Methods for Chemical
Analysis of Water and Waste—1971", National Environmental
Research Center, Cincinnati, Ohio.
3. CFR 38, 199, 10/16/73.
t|. Loehr, R. C. and Kukar, T. J. (1965) "Removal of Lipids by
Conventional Waste Treatment", Intl. Jour. Air and Waste
Poll, 9,479-485.
5. Loehr, R. C. (1969) "Aerobic Microbial Degradation of Lipids"
Final Project Report, June 1963 - January 1968, to the
Federal Water Pollution Control Administration.
6. Ellms, J. W. arid Werts, J. J. (1943) "Extracts from the 1940
Report of Division of Sewage Disposal, Cleveland, Ohio," Sew.
Journal 15, 100-109.
7. Loehr, R. C. and the de Navarra, C. T, (1969) "Grease Removal
at a Municipal Treatment Facility," JWPCF 41 R 142-154.
8. McCarty, P. L., Hahn, D. J., McDermott, G. N., and Weaver, P.
J. "Treatability of Oily Waste Water from Food Processing
and Soap Manufacture" (1972), Presented at the 27th Annual
Purdue Industrial Waste Conference, Lafayette, Indiana.
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9. "Impact of Oily Materials on Activated Sludge Systems, "
(1971) Environmental Protection Agency, Project 12050 DSH,
March 1971.
10. Water Pollution Control Federation (1973) "MOP No. 3:
Regulation of Sewer Use" JWPCF 45 1985-2235.
11. Metropolitan St. Louis Sewer District, Ordinance No. 2289,
St. Louis, Missouri.
12. "Rules and Regulations for Discharge of Waste into Sanitary
Sewerage System, Jefferson County, Alabama," Birmingham,
Alabama.
* U.S. COVERNMENT PRINTING OFFICE: 1975-628-875/590 3-1
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