An Investigation of the Treatment and Recycling of Oil Refinery Wastewater

Abstract

The objective of the present investigation was a high level of purification of the wastewater from an oil refinery achieved by using some improved methods yielding an effluent suitable for recycling into the process. All the investigations were carried out on a continuous laboratory pilot system consisting of the following units: dissolved air flotation (DAF), sedimentation, double-stage microbiological reactor, and adsorption columns filled with granular biologically activated carbon (GBAC). A high degree of COD reduction close to 100% (precisely, 99.95 %), as well as removal of nitrogen compounds of 72% was achieved during a relatively short retention time within the range of 15-16.5 hrs. The DAF technique combined with gravitational separation was used to achieve the recovery of free oil matter up to 98%, without any preliminary conditioning. After the sedimentation of coagulated and flocculated dispersed oils, the microbiological oxidation of dissolved matter was accomplished by using two kinds of activated sludge for easy and hard degradable organics. Using the continuously bioregenerating GBAC, an effluent having a lowered COD value to about 9 was obtained. At the same time, the denitrification process took place. According to the obtained results the treated oil refinery wastewater can be recycled into the process, or discharged into a water recipient of a low self-purifying capacity.