water Review Oily Wastewater Treatment: Overview of Conventional and Modern Methods, Challenges, and Future Opportunities Khaled Abuhasel 1 , Mohamed Kchaou 1,* , Mohammed Alquraish 1, Yamuna Munusamy 2 and Yong Tzyy Jeng 2 1 Department of Mechanical Engineering, College of Engineering, University of Bisha, P.O. Box 001, Bisha 67714, Saudi Arabia; [email protected] (K.A.); [email protected] (M.A.) 2 Department of Petrochemical Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Petaling Jaya 31900, Malaysia; [email protected] (Y.M.); [email protected] (Y.T.J.) * Correspondence: [email protected] Abstract: Industrial developments in the oil and gas, petrochemical, pharmaceutical and food sector have contributed to the large production of oily wastewater worldwide. Oily wastewater pollution affects drinking water and groundwater resources, endangers aquatic life and human health, causes atmospheric pollution, and affects crop production. Several traditional and conventional methods were widely reported, and the advantages and limitations were discussed. However, with the technology innovation, new trends of coupling between techniques, use of new materials, optimization of the cleaning process, and multiphysical approach present new paths for improvement. Despite these trends of improvement and the encouraging laboratory results of modern and green methods, many challenges remain to be raised, particularly the commercialization and the global aspect of these solutions and the reliability to reduce the system’s maintenance and operational Citation: Abuhasel, K.; Kchaou, M.; cost. In this review, the well-known oily wastewater cleaning methods and approaches are being Alquraish, M.; Munusamy, Y.; Jeng, highlighted, and the obstacles faced in the practical use of these technologies are discussed. A critical Y.T. Oily Wastewater Treatment: review on the technologies and future direction as the road to commercialization is also presented to Overview of Conventional and persevere water resources for the benefit of mankind and all living things. Modern Methods, Challenges, and Future Opportunities. Water 2021, 13, Keywords: oil; wastewater; methods; emergent nanotechnology; commercialization; performance 980. https://doi.org/10.3390/ w13070980 Academic Editor: Cidália Botelho 1. Introduction Clean water and sanitation were one of the sustainable development goals (SDG) set Received: 13 February 2021 by the United Nations General Assembly in 2015. According to the UN, water scarcity Accepted: 29 March 2021 Published: 2 April 2021 could displace 700 million people by the year 2030, and in 2017, 2.2 billion of the world’s population still lacked access to safe drinking water. Rapid urbanization and industrial- Publisher’s Note: MDPI stays neutral ization have made matters worse by the discharge of large volumes of wastewater, which with regard to jurisdictional claims in needs to be treated carefully before being released to natural water bodies [1]. published maps and institutional affil- Wastewater from industry can contain toxic chemicals, heavy metals, microorganisms, iations. biological substances, microplastics, oil and viruses [2]. The United Nations Educational, Scientific and Cultural Organization (UNESCO) reported that more than 80% of this wastewater is not being treated at all before being released to the water body [3]. Wastewa- ter treatment is not being properly adopted by industries due to high wastewater treatment facility setup costs, high operational cost, large space requirement in the area near the Copyright: © 2021 by the authors. industry, less legislative enforcement of discharge limit and less technical understand- Licensee MDPI, Basel, Switzerland. This article is an open access article ing of wastewater treatment systems. Some countries have taken a serious approach to distributed under the terms and water-saving and water pollution control. For instance, in China, a Water Pollution Control conditions of the Creative Commons Action Plan was enforced starting January 2015, where the focus was given on water Attribution (CC BY) license (https:// resources conservation and protection. Industry must comply with this plan by designing creativecommons.org/licenses/by/ wastewater treatment systems to separate pollutants from water, recycle the water and 4.0/). reuse [4]. Water 2021, 13, 980. https://doi.org/10.3390/w13070980 https://www.mdpi.com/journal/water Water 2021, 13, x FOR PEER REVIEW 2 of 36 In the EU, reclaimed wastewater usage is included in the circular economy strategy and governed by Water Framework Directive (2000/60/EC) (WFD). WFD has led to the secondary treatment of 88% of EU wastewaters, but the reuse is still low [5]. In Latin America and the Caribbean, the World Bank, through its “Wastewater: From Waste to Resource “initiative, had created awareness among governing parties on the potential of converting wastewater to valuable resources, such as energy, reusable water, nutrients and bio-solids [6]. Oily wastewater is one of the major constituents of wastewater dis- Water 2021, 13, 980 charged by industry. A large volume of oily wastewater is being generated by food2 and of 35 beverage, but the majority of oil mixed in water is coming from petrochemical and metal processing industries, in terms of fats, hydrocarbons, and petroleum fractions like diesel oil, gasoline,In the EU, and reclaimed kerosene. wastewater These constituents usage is exist included in the in form the circularof oil-in-water economy emulsions strategy [7].and In governed 2002, U.S by National Water Framework Research Council Directive reported (2000/60/EC) that 1.3 (WFD).million WFDtons of has oil led were to there- leasedsecondary to the treatment sea annually of 88% from of known EU wastewaters, sources [8]. but the reuse is still low [5]. In Latin AmericaOily andwastewater the Caribbean, is carcinogenic the World and Bank, mutagenic through to human its “Wastewater: health and From could Waste also in- to hibitResource plant “initiative, growth. Oily had wastewater created awareness discharg amonge without governing proper treatment parties on can the increase potential the of biologicalconverting oxygen wastewater demand to valuable (BOD) and resources, chemical such oxygen as energy, demand reusable (COD) water, of the nutrients water body, and reducebio-solids sunlight [6]. Oily penetration wastewater into is the one water of the by major forming constituents a layer ofon wastewaterthe water surface discharged and thusby industry. disrupt Athe large aquatic volume ecosystem of oily wastewater[9]. Thus, treatment is being generatedof oily wastewater by food and is crucial beverage, to reducebut the its majority effect ofon oilthe mixed environment in water and is coming humans; from recovery petrochemical of oil fr andom metaloily wastewater processing treatmentindustries, could in terms also of provide fats, hydrocarbons, economic benefits and petroleum [10–13]. The fractions overview like of diesel oily oil,wastewater gasoline, resources,and kerosene. impact These and constituents benefit of trea existtment in theare formsummarized of oil-in-water in Figure emulsions 1. [7]. In 2002, U.S NationalMany technological Research Council advances reported in wastewater that 1.3 million treatment tons of have oil were been released achieved to thein the sea pastannually three from years known from sources2018 onwards. [8]. The main reasons for these achievements are the multidisciplinaryOily wastewater approach, is carcinogenic advancement and mutagenicin material to science, human healthparticularly and couldin nano- also materialinhibit plant and integration growth. Oily of technology. wastewater In discharge this paper, without a comprehensive proper treatment review can of the increase work donethe biological using conventional oxygen demand technologies (BOD) and and th chemicale advancement oxygen in demand modern (COD) technologies of the water from thebody, period reduce of 2018 sunlight onwards penetration are being into discussed the water in by detail. forming The areview layer onalso the includes water surface future directionsand thus disruptin the development the aquatic ecosystem of modern [ 9technologies]. Thus, treatment for further of oily commercialization. wastewater is crucial The reviewto reduce is expected its effect onto thebenefit environment researchers and and humans; industry recovery to identify of oil the from gaps oily for wastewater practical usetreatment of oily couldwastewater also provide treatment economic systems benefits and lead [10– 13their]. The effort overview in the ofright oily direction wastewater for betterresources, output impact of treatment. and benefit of treatment are summarized in Figure1. FigureFigure 1. 1. OilyOily wastewater wastewater resources, resources, physical form, impact and benefit benefit of treatment. Many technological advances in wastewater treatment have been achieved in the past three years from 2018 onwards. The main reasons for these achievements are the multidisciplinary approach, advancement in material science, particularly in nanomaterial and integration of technology. In this paper, a comprehensive review of the work done using conventional technologies and the advancement in modern technologies from the period of 2018 onwards are being discussed in detail. The review also includes future directions in the development of modern technologies for further commercialization. The review is expected to benefit