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, mercaptans, sulfides, ammonia, and cyanides. The wastewater treatment of the reported oil refinery is based on several treatment stages, consisting of gravity separation, chemical coagulation-flocculation 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.
