88    PRETREATMENT LIMITS FOR FATS, OIL AND GREASE
Peter V. Cavagnaro, Senior Engineer
Kenneth E. Kaszubowski, Senior Engineer
Howard Needles Tammen & Bergendoff
Milwaukee, Wisconsin 53224
INTRODUCTION
A discrepancy exists between the information available in the literature regarding oil and grease and
the information used to establish discharge limits for this material. The goal of this chapter is to
present information and recommendations that will be useful in the establishment of pretreatment
limits for the discharge of oil and grease material to publicly owned treatment works (POTW's). The
recommendations are intended to facilitate the development of regulations that will result in efficient
use of POTW treatment capacity while minimizing the cost of pretreatment for industry. The chapter
is organized as follows:
• Oil and Grease in Domestic Wastewater
• Physical and Chemical Characteristics of Oil and Grease
• Operational Problems
• Pretreatment Regulations
• Regulatory Approaches
• Pretreatment Technology
• Summary
• Recommendations for Oil and Grease Limits
The first sections address the amount and the character of oil and grease that is present in waste
water, the nature of the pollutant, and the reasons for implementing discharge limitations for oil and
grease. The next sections describe the approaches used to establish pretreatment limits, the recommendations of the federal government and professional guidance manuals and the results of a survey of
local discharge limitations. The last sections address the treatability of oil and grease followed by a
summary and the recommendations.
OIL AND GREASE IN DOMESTIC WASTEWATER
Environmental engineers and wastewater treatment plant operators are primarily aware of oil and
grease in wastewater by the presence of grease balls and blockages in the collection system and by the
presence of floating scum on sedimentation tanks. The oil and grease concentration for weak,
medium and strong wastewaters is 50, 100, and 150 mg/L, respectively.1 Rudolfs2 conducted oil and
grease analysis on a number of raw wastewater samples and found that the concentration ranged from
8.4 to 220.8 mg/L. Skimming volumes from primary treatment have been reported to range between
0.1 and 6.0 cf/MG.3 A value of 2 cf/MG would correspond to an oil and grease concentration of 14
mg/L, for an assumed specific gravity of 0.95. An analysis of a raw wastewater containing 45 mg/L
oil and grease4 indicated that over half the oil and grease was colloidal, and that most of the oil and
grease was in the form of glycerides of fatty acids (i.e. food fats and oils). The colloidal designation
was established by the process used to separate the solids.
A number of researchers have demonstrated that the concentration of oil and grease in industrial
and untreated municipal wastewaters and the effluent from biological treatment follows a log-normal
frequency distribution.5'6 The range of maximum to minimum values commonly varies from 5 to 1.
This type of variability is not commonly addressed in pretreatment regulations. Municipal ordinances
commonly require that industrial discharges not exceed a specified limit, and use grab samples taken
at infrequent intervals to monitor compliance. The degree of confidence required to meet such a limit
may exceed 99%. The corresponding average operating level required to meet this condition may be
20% of the regulated limit.
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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