19    ANOMALIES IN OIL AND GREASE ANALYSES OF
PETROLEUM WASTEWATERS AND THEIR
IMPLICATIONS
Paul T. Sun, Staff Engineer
Shell Oil Company
Houston, Texas 77252-2099
Cheerie L. Price, Research Technician
Joseph C. Raia, Senior Research Chemist
Rafael A. Balderas, Technician
Shell Development Company
Houston, Texas 77251-1380
INTRODUCTION
Several components in petroleum wastewaters are shown to cause varying degrees of interference in
oil and grease analytical procedures. These compounds have been identified through GC/MS analyses
as phenolics, short-chain carboxylic acids, naphthenic acids, and other compounds. The interferences
can bias the data, and lead to erroneous conclusions in interpretations of in-plant source control
studies and in evaluations of oil and grease removal processes. More importantly, these interferences
can have a profound impact upon compliance to certain discharge regulations for the petroleum
industries. This article delineates the mechanisms of these interference phenomena and provides
technical background for proper interpretation of oil and grease analytical results.
OIL AND GREASE ANALYTICAL PROCEDURES
Numerous analytical procedures have been devised to measure the oil content of petroleum wastewater samples.1 All of them essentially consist of two major steps. In the first step, after the sample
has been acidified to pH 2, it is then contacted with an appropriate amount of solvent (usually freon).
The second step, determination, can be accomplished by either weighing the residue of the extract
after evaporating the low boiling point solvent or by infrared spectroscopy.
As the name implies, these analytical procedures are for the measurement of insoluble hydrocarbons or animal grease and vegetable oils. However, other substances are also extracted during the
analysis. For instance, in petroleum refinery wastewaters, phenolics, short-chain acids, naphthenic
acids, complex aromatics, and sulfur and nitrogen containing hydrocarbon derivatives can interfere
with the oil and grease determination to varying degrees.1 Because these interfering compounds are
dissolved, they have been erroneously called "soluble oil and grease". Figure 1 shows a typical chro-
matogram of acid extractable soluble components in a Shell West Coast refinery effluent which is
discharged to a public owned treatment work (POTW). Most of these compounds have been identified by mass spectroscopy (MS) as oxygenates, with low molecular weight acids and phenolics eluting
"1  I" •Inwtfl
Figure 1. GC chromatogram, soluble oil and
grease components, West Coast Refinery discharge sample.
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