Main Article Content
The chemical and biological oxygen demands, COD and BOD considered as an important indicator for organic pollution of water and soil, This research aims to reduce the biological and chemical demands for oxygen ( COD and BOD ) of Al Najaf oil refinery final wastewater which located in medium western of Iraq before discharging it to the environment , by biodegradation process using two isolates of gram negative bacteria, Pseudomonasaeuroginosa and Alcaligenesfaecalis, which isolated from refinery wastewater . The percentage of poly-aromatic hydrocarbons (PAH) removal were 85.84 % by Ps.aeuroginosa and 76.13 % by A. faecalis. The percentage of COD reduction were 60%, 40 % and BOD reduction 53.13 %, 42.34 % for two isolates respectively. This proves the efficiency of both bacterial isolates in treatment of petroleum contaminants found in the wastewater.