A review on the application of different treatment processes for emulsified oily wastewater

Oily wastewater, one of the major threats to environment nowadays, mainly originates from petrochemical, heavy metal, food processing, paint, automobile industrial premises. This oil contaminated wastewater is mutagenic and carcinogenic to human health as well as inhibitory to plant growth. Without any proper treatment if such oily water stream disposed into water bodies, apart from increasing the BOD and COD, it also imparts a sunlight impervious layer at the top of the stream restricting the entrance of sunlight followed by disruption of aquatic ecosystem. Hence proper treatment of oily wastewater before its discharge to environment is one of the primary concerns. Researchers have used several technologies such as, gravity sedimentation, coagulation, flotation, coagulation composite flotation, demulsification, membrane separation, flocculation, chemical precipitation and bioremediation have been explored to purify this oil contaminated wastewater to a desired level. Especially, the uniqueness of the treatment will require a through merit analysis of the process, when the wastewater comprises of oil-water emulsion. Hence, in this review an analytical insight on the merits of the process for the treatment of such emulsified system has been provided. The review article also discusses different microorganisms that are required for bioremediation of either oil spill over a large aquatic zone or oil-water emulsion at source point. Finally, the manuscript highlighted some of the effluent treatment plants' operational process from different industries, which might provide a typical understanding of a comparative view between different treatment processes.