## 1 Introduction  
Water is the most essential substance for all living things on earth. Reliable access to clean and affordable water has become a world-wide problem due to the continuous growth in water demand [1]. In the last century, the global population quadrupled and the world water demand increased sevenfold [2]. The World Water Council also estimates that by 2030, 3.9 billion people will live in regions characterized as \"water scarce\" [3]. With extensive industrial development, water quality has worsened over the years. A large volume of oily wastewater has been discharged indiscriminately from oil and gas fields, food and beverage, petrochemical and metal processing industries [4]. Oily wastewater discharge can cause pollution to surface water, underground water and soil. The low molecular weight hydrocarbon and petroleum fraction can evaporate to the air and thus cause unpleasant smell and air pollution. Many countries are setting the regulatory limits on the maximum oil concentration in oily wastewater discharge to be within the range of 5-40 mg/L [5]. Thus, the treatment of oily wastewater is a crucial environmental issue. Conventional methods such as gravity separation, de-emulsification, dissolved air flotation, coagulation and flocculation were studied and used to treat the oily wastewater. However, several drawbacks such as high operation cost, ineffective rejection of smaller emulsified oil droplets with size less than 20 um, corrosion of the equipment and recontamination were faced in these methods [6]. In this regard, the membrane-based oily wastewater cleaning techniques such as microfiltration, nano-filtration, ultrafiltration and pervaporation are being studied extensively by researchers worldwide [7; 8; 9]. The membrane technology has large potential to remove oil-water emulsion due to its advantages in term of energy efficiency, easy process and low maintenance cost [10; 11; 12]. In spite of that, the main obstacles for the commercial use of membrane filtration in oily wastewater treatment were discovered to be low chemical resistance and the trade-off effect between permeation flux and rejection rate [13]. [PERSON] et al. reported 98.2% rejection rate of emulsified kerosene in oily wastewater with permeation flux of only 153.2 Lm\({}^{-2}\)h\({}^{-1}\)[14]. Poly(vinyl chloride)-bentonite membrane could reject 97% emulsified oil from saline oily wastewater but the permeation flux was only reported as 186 Lm\({}^{-2}\)h\({}^{-1}\)[15]. [PERSON] et al. reported 97.2% removal of oil-grease content from refinery oily wastewater using polyacrylonitrile (PAN) ultrafiltration membrane with a permeation flux of 96.2 Lm\({}^{-2}\)h\({}^{-1}\)[16]. The high rejection rate of oil and low corresponding permeation flux were reported in many other research works as well [17; 18]. Low permeation flux leads to a low volume of wastewater being treated daily, and economically this is not feasible. Moreover, current polymeric membranes possess low mechanical strength, and chemical resistance which can limit their applications in oily wastewater treatment [19]. In this research, nitrile butadiene rubber latex (NBR)/graphene oxide (GO) membrane was fabricated to overcome the tradeoff effect. NBR latex was chosen as the membrane material due to its superior chemical resistance and structural integrity [20]. The mechanical strength and chemical resistance of NBR could be tailored through the three-dimensional sulfur cross-linking network. In industry, NBR is used in a wide variety of application areas requiring oil, fuel, and chemical resistance [21]. However, the primary concern of using NBR membrane for oily wastewater filtration is its hydrophobic profile which compromises permeation flux. Thus, GO is incorporated to impart water affinity to the membrane surface [22; 23]. GO was selected because it has large surface area, various oxygen-containing functional groups and exhibits good compatibility with polymers [24; 25].