found with other insoluble matter, presenting relevant problems with safe and convenient separation. The legal discharge of oil-water emulsions is a complex process. [4] Thus, environmental authorities have established stringent regulations to cope with it. [5] Depending on countries, the oil limits are concentrations below 40 ppm as in Vietnam, [6] and in other countries like Korea, the maximum is only five ppm of oil in discharge. [7] Generally, the oil phase in water has three forms, based on oil droplets, size of more than 150 micrometers is called free oil, but that size found from 50 to 150 micrometers is the dispersed oil, [8] finally, the emulsified oil less than 20 µm. There is an increasing interest in employing membrane technology for filtering smaller size oil droplets. In this review, oil-water emulsion problems are highlighted with oil-water separation techniques selection and their performance with varied oil concentration and composition of other immiscible or miscible components. [9] Membrane technology is known formerly to economically advantageous for oily wastewater (OWW) treatment compared with other conventional technologies. [9] Based on the literature, the membranebased treatment cost estimation was about 1 and 3 $ m −3 , [10] lower than for dissolved air floatation (DAF) treatment (cost was 3.65 $ m −3 ). Generally, the treatment cost depends on OWW sources, as each industry has its specific blends for oil and grease jointly with other membrane foulants. [11] For example, oil-water emulsions treatment from the fatty acid industry has a total capital cost (costs of membranes, electricity, labor, cleaning, and maintenance) of 2.65 $ m −3 , compared with the railroad industry (it was ranged from 1.03 to 1.48 $ m −3 ). These costs for the metalworking OWW using UF were 2.8 $ m −3 . In microfiltration (MF) membrane, the OWW membrane-based treatment for oil concentration of 50 ppm annual cost was estimated as 0.098 $ m −3 with a feed rate of 100 m 3 day −1 . [9] The cost of membrane-based treatment of OWW is generally varying but is lower than conventional technologies. [12] 1.1. Oil-Water Emulsions Sources, Environmental Hazard, and Discharge Limits An oil-water emulsion is either a waste stream product, or secondary product. These effluents are generated from different areas and industrial sectors like the petroleum& gas sector, food processing, shipping facilities and maritime, and many others Oily wastewater is generated by various industries in extraordinary growing volumes, such as oil refineries, petrochemicals, metallurgical, food & beverages, and dairy industries, which need oil removal for safe discharge to the environment. Lower cost of production with high oil removal and efficient performance compared to classical methods for treating oil-water emulsions attributed to the alleviation of operation. That emphasizes membrane modification to enhance wettability, hydrophilicity with the antifouling property such as membranes dealing with tiny oil emulsions to be the key parameters to im...
