Section Eleven
OIL AND PETROCHEMICAL WASTES
41    CHARACTERIZATION OF HYDROCARBONS
REMOVALS IN WASTEWATER FROM AN
INTEGRATED OIL REFINERY
Noah Galil, Dafna Zeira-Blum and Menahem Rebhun
Technion - Israel Institute of Technology
Faculty of Civil Engineering
Haifa 32000, Israel
ABSTRACT
The wastewater from an integrated oil refinery is characterized by a diversity of pollutants including hydrocarbons, in free and emulsified form, phenols, including cresols and xylenols. mer-
captans, sulfides, ammonia, and cyanides. The wastewater treatment of the reported oil refinery
is based on several treatment stages, consisting of gravity separation, chemical coagulation-floc-
culation followed by dissolved air flotation, and a combined biological treatment based on two
aerated ponds in series and lime flocculation-sedimentation. The effluent is recycled and reused
as makeup to the recirculated cooling water system of the refinery. The aim of this study was to
identify and quantify the main hydrocarbons groups after the different treatment stages. API separators provided substantial removal of hydrocarbons from about 1,000 mg/L to less than 100
mg/L. Chemical flocculation and dissolved air flotation (DAF) enabled further removal of about
70 mg/L of the hydrocarbons, to 20 mg/L, based on average values. This removal included
aliphatics, phenols, naphtalens, and benzenes. This process involved mechanisms of coagulation-
flocculation accomplished by physical separation, as well as binding of hydrophobic compounds
to nonpolar fractions and stripping of volatile compounds. The combined biological-chemical
treatment (BCT) provided removal of hydrocarbons to average values of less than 4 mg/L, and
efficient removals of over 90% of the phenols, naphtalens, and benzens.
INTRODUCTION
An integrated oil refinery is characterized by a diversity of production processes including distillation, catalytic cracking, platforming. ethylene production, sulfur recovery, and others. The
results of these various processes is the diversity of pollutants found in wastewater, which contains hydrocarbons, phenol, methyl and di-methyl phenols (cresols and xylenols) mercaptans.
sulfides, and ammonia. Spent caustic streams from washeries. especially from gasoline wash-
eries, are characterized by very high concentrations of phenols. Acid water at the bottom of stripping towers contains high concentrations of organic matter, sulfides, and cyanides.
The wastewater is usually treated in order to achieve the appropriate effluent quality for either
discharge to natural recipients or to be reused by the industry. While a substantial part of the hydrocarbons can be removed from the aqueous phase by gravity separation and by dissolved air
flotation, all the other organic materials, including residual hydrocarbons, phenols, and other dissolved organics, can be removed only by biological treatment processes.
The adopted solutions in order to achieve reliable cost-effective wastewater treatment and
reclamation1-2 was based on several treatment stages which include the following elements:
52nd Purdue Industrial Waste Conference Proceedings. 1997. Ann Arbor Pre*,s. C'heKca. Michigan 48118. Printed in
U.S.A.
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