Current Practice for Treatment of Petroleum Refinery Wastewater and Toxics Removal

Current practice and experience in the treatment of petroleum refinery wastewater is reviewed briefly, with emphasis on the fate of toxic contaminants. The sources and composition of the wastewater are described in terms of the parameters adopted for evaluating the performance of individual treatment units. The parameters include oil and grease content and sulphide concentration for evaluating the primary treatment units: sour water stripping, API separation and dissolved air flotation (DAF). COD, BOD, suspended solids and “listed” trace contaminant concentrations are considered in the description of biological activated sludge secondary treatment. Current treatment technology achieves a significant reduction in toxic contaminants and other pollutants generated in the petroleum refining process, with the principle reduction occurring in the activated sludge system. The removal mechanisms considered in activated sludge are biological degradation, nitrification, stripping of VOC’s, biosorption, bioaccumulation of heavy metals and heavy metal precipitation. A number of potential problems associated with activated sludge treatment are identified; amongst others, high effluent COD’s, presence of toxic contaminants (at low concentrations) in the treated effluent, inhibition, poor sludge settleability, and waste sludge disposal.