TREATMENT OF OILY WASTES-OIL RECOVERY PROGRAMS
Dale Bauer, Engineer
Liquid/Solids Separation
Betz Laboratories, Inc.
Trevose, Pennsylvania 19047
INTRODUCTION
In the last few years, stricter environmental controls have forced industry to remove
oily wastes from wastewater before discharging it to a municipal system or to a receiving
stream.   Wastewater discharge criteria generally limit oil concentrations to 50 to 100 mg/l
prior to discharge in municipal sewer systems.   Criteria for discharge to a surface stream
limit   oil concentrations to 5 to 15 mg/l and further stipulate that this oil cannot be
floating or visible [ 1,2].
The problem of oily wastes is enormous.   The Environmental Protection Agency (EPA)
estimates that approximately 150 million gal of metal-working oils were consumed by industry in 1974.   Of this total, it is estimated that two-thirds (or 100 million gal) is potentially recoverable; however, less than 50 million gal are currently being recovered [3].
Rising oil prices, coupled with stringent disposal regulations, are providing the incentive
to recover this valuable oil for reuse while cutting the overall costs of an oily waste treatment program.
Most of the work conducted for this chapter has been in the automotive and industrial
vehicle categories.   However, the technology involved also applies to other metal-forming
and finishing operations, steel mills and the hydrocarbon processing industry.
The purpose of this chapter is to investigate the processes, chemical technology and
economics of breaking soluble oil emulsions and the subsequent cooking for oil recovery.
THEORY OF EMULSIONS
Emulsified (soluble) oils are purposely stabilized for use in industry as cutting, rolling
and hydraulic oils.   With time, solids contamination and biological activity render an oil
"spent" and it is then disposed of or discharged to a waste treatment plant.   Each oily
waste is unique and may contain various emulsifiers, biocides, metallic and nonmetallic
solids, antioxidants and other chemical additives.
An emulsion is defined as two immiscible liquids, one of which has been dispersed in
the other as droplets and stabilized by electrical charges and emulsifying agents.   A stable
emulsion is one that will not break down without some form of treatment.   To form a
stable emulsion, three conditions are necessary:   (a) an emulsifying agent must be present;
(b) the two liquids must be immiscible; and (c) there must be sufficient agitation to disperse one liquid in the other as droplets [4,5].
Types of Emulsions
Automotive and metal-forming wastewaters are typically oil-in-water (O/W) emulsions.
Oil is the dispersed or internal phase and water is the continuous or external phase.   The
oil content is normally in the 500 to 10,000 parts per million (0.05 to 1.0%) range.   A
water-in-oil (W/O) emulsion has water as the dispersed phase and oil as the continuous or
external phase.
Free oil or tramp oil is oil that floats to the top of an equalization or holding tank
with the retention time provided in the system.   In the automotive industry, such oil is
generally present as a W/O emulsion.
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