Refinery wastewater biological treatment: A short review

Introduction Petroleum refining utilize large quantities of water for desalting, distillation, thermal cracking, catalytic and treatment processes to produce useful products [liquefied petroleum gas (LPG), gasoline, jet fuel, diesel, asphalt and petrochemical feedstock] 1-3. Refining process generates wastewater (0.4-1.6 times the volume of crude oil processed)4. Discharge of untreated petroleum refining wastewater (PRW) into water bodies results in environmental and human health effects due to release of toxic contaminants (hydrocarbons, phenol and dissolved minerals)5,6. Hydrocarbons [benzene, toluene, ethyl benzene and xylenes (BTEX)] are of serious concern due to their toxicity and as carcinogenic compounds3,7,8. High exposure for long periods to these compounds can cause leukemia and tumors in multiple organs3. Phenol and dissolved minerals are also toxic to aquatic life and lead to liver, lung, kidney and vascular system infection9,10 . Therefore, according to Environmental Protection Agency (USEPA), PRW have to be sufficiently treated for quality to meet the established regulations11. Physical and chemical treatments of PRW have been carried out using different methods [electrocoagulation (93% of sulfate and 63% of COD removal)12, electrochemical oxidation (92.8% for COD removal and low salinity of 84μScm-13 and dissolved air flotation (BOD and COD removal efficiencies of 7694% and 72-92.5% respectively)14]. However, physical and chemical methods are costly due to high price of chemicals and equipments, and excessive amounts of sludge production. Thus, biological methods are preferred due to simple, cheap and environmentally friendly operations3,15. This review presents characteristics of PRW and biological treatment technologies.