Treatment of Oily Wastewater by Membrane Hybrid Processes

Abstract

Oily wastewaters are usually treated by physical, chemical and biological methods. Most conventional methods (coagulation, sedimentation, centrifugation and filtration) are not efficient in treating stable oil-in-water (O/W) emulsions, especially when the oil droplets are finely dispersed and the concentration is very low. These techniques can reduce oil concentrations by no more than 1% by volume of the total wastewater and cannot efficiently remove oil droplets below 10 μm. Hence, further treatment is needed to meet effluent standards. Membrane processes have found an increasing number of applications in the treatment of complex oily wastewater. However, sometimes it is not desirable or even possible to use a membrane system to carry out the entire separation because of the effluent nature that may cause severe fouling of the membrane. In those situations a pretreatment of the effluent by conventional methods may be suitable for a better process performance. These membrane-based hybrid processes combine a conventional process (mechanical, chemical or thermal) with a membrane separation. In this review lecture the design parameters and performance of conventional processes for the treatment of oily wastewater are summarized and several membrane hybrid processes and chosen examples are presented.