Current technologies and future directions for the treatment of wastewater from petroleum refineries and petrochemical plants (PRPP) are discussed without mentioning microplastic pollution [96]. Water scarcity and wastewater treatment are a serious challenge for petroleum refineries and petrochemical plants. The growing demand for petroleum products, in addition to technological development, requires new water management strategies that encourage (i) the reduction of water consumption, (ii) the reuse of treated wastewater, and (iii) the remediation of environmental impacts (R3). New innovations and design of PRPP wastewater treatment plants (WWTPs) are needed to incorporate R3 principles in order to meet industrial water demands and environmental regulatory requirements. The review summarizes the status of wastewater treatment technologies in PRPP to identify areas for future development. First, a systematic assessment of water quality characteristics of PRPP discharges and regulatory requirements for wastewater is discussed. Next, the current PRPP wastewater treatment technologies, configuration, and operation are investigated, followed by an overview of PRPP wastewater treatment plants in Iran. Finally, based on the identified shortcomings, an outlook on our future opportunities to improve the design and operation of PRPP wastewater treatment plants is presented. Specifically, new hybrid technologies are proposed to increase treatment capacity, improve wastewater quality, and manage shock loads of toxic and organic substances.

As for the industrial sector, hydrocarbon processing in petroleum refineries and petrochemical plants (PRPP) uses the largest amount of water and also generates a large amount of wastewater, about 0.4 to 1.6 times the volume of processed crude oil. Wastewater can come directly from production processes (e.g. steam condensate, process water, cracking and aromatics sections), cooling tower blowdown, pump and compressor cooling, stormwater drains contaminated with petroleum, chemical solvents, and petroleum product spills, and sanitary wastewater from large PRPPs. In the wastewater quality and discharge guidelines of PRPP, a wide variety of unique and common organic and inorganic pollutants are listed.

Current PRPP wastewater treatment technologies (WWTP): In the PRPP wastewater treatment technologies currently used worldwide, the well-known methods of WWTP (coagulation/flocculation, flotation, biological phenol removal, oxidation, and sedimentation; biological activated sludge process, hollow fiber ultrafiltration [UF], reverse osmosis [RO], etc.) are used. Current PRPP wastewater treatment plants are similar in design to the municipal wastewater treatment plants (primary, secondary, and tertiary treatment or polishing); it is unique that primary and secondary oil and water separation is used in primary wastewater treatment. During secondary treatment, a biological purifier is used to break down the residual dissolved oil and other organic pollutants, and membrane bioreactors (MBR) are also used. MBR technology can be successfully used to treat PRPP wastewater, but its application is not common and not sufficiently cost-effective. The use of MBR technology in PRPP wastewater treatment plants is increasing as membrane costs are reduced. Tertiary treatment or polishing is traditionally performed by sand filtration, activated carbon filtration, or chemical oxidation. More recently, membrane separation technologies such as ultrafiltration (UF) and RO have been used to improve wastewater quality for discharge or recycling. Other advanced treatment technologies, including ion exchange, electrodialysis (ED), and electrodialysis reversal (EDR), are recommended. Advanced oxidation processes (AOPs: hydrogen peroxide/ultraviolet [H2O2/UV] light, ozonation, Fenton and photo-Fenton processes, heterogeneous photocatalysis, electrochemical oxidation, wet air oxidation [WAO], and supercritical water oxidation [SCWO]) have also been proposed or tested in the laboratory to remove resistant chemical contaminants. Most of these advanced processes have not been applied in industrial-scale PRPP wastewater treatment plants.

PRPP WWTP design and configuration: technology and configuration may vary from site to site, the treatment efficiency and effluent quality of different technologies and design configurations have not yet been compared globally. Four Iranian technologies are presented in detail.

Development of PRPP wastewater treatment plants and future trends: new technologies require a fundamental change in thinking about wastewater discharge, recycling and reuse within the industry. New technologies should include online control and intelligent feedback. Examples include: the PACT system designed by Siemens Water Technologies (combines biological treatment and carbon adsorption in a single, synergistic treatment step); the first membrane-based PRPP wastewater treatment plant (General Electric [GE], 2012), advanced GE ZeeWeed UF and MobileRO units; and GE’s integrated ZeeWeed MBR, EDR and RO technologies (Russian oil company Bashneft, 2014). In the coming years, membrane-based technologies are likely to become more prevalent, thereby significantly improving wastewater quality to meet reuse and environmental protection requirements. There are great opportunities to incorporate membrane separation technologies such as MBR, forward osmosis (FO), which separates water from salt and organic matter with minimal energy requirements and low membrane fouling, in advanced oxidation processes (recommended to remove toxicity and resistant organic matter). PRPP wastewater treatment plants often do not have sufficient resources to implement technological improvements. The final selection of treatment technologies should consider a balance between economic, environmental, and technical feasibility and regulatory constraints.