The wastewater from petroleum industries contains high organic matter content, oil and grease,

dissolved solids and turbidity. The petroleum wastewater normally treated in a plant comprising of primary, secondary and tertiary treatments.

The high organic loading needs to be treated in biological treatment step.

Biological treatment can be suspended growth or attached growth type.

Activated sludge process is one of the major treatment methods used. The anaerobic treatments have advantages such as reduction in sludge content, reduction in diffuser and aeration cost and generation of gas with high hydrocarbon.

Many investigators have investigated biological treatments for treatment of petroleum refinery wastewater.