Advanced oxidation processes in the removal of organic substances from produced water: Potential, configurations, and research needs

Produced water is the main by-product generated by fossil fuel extraction activities. This wastewater is often heavily contaminated and associated with significant health, safety, and environmental risks; thus, adequate treatment systems are required to bring these streams to a quality that may be suitable for their recycling, reuse, or discharge into the environment. Advanced oxidation processes (AOPs) are increasingly studied to purify produced waters, and specifically for the removal of organic pollutants in the aqueous and non-aqueous phases. This review evaluates Fenton-based oxidation, heterogeneous catalysis, electro-oxidation, photo-assisted processes, and homogeneous advanced oxidation processes to remove organic contaminants in produced water. The efficiency and applicability of the reviewed approaches are discussed with particular attention to the configurations within the water purification train. Ozonation, Fenton-based techniques, heterogeneous photocatalysis, and anodic oxidation techniques are the most widely researched AOPs in produced water treatment. Photo-assisted processes and electrochemistry have been shown to significantly improve the effectiveness of decontamination of more traditional processes. Oxidation can be exploited as polishing stage of already pre-treated effluents with the final goal of reuse with closing of the water cycle, or as a primary/secondary treatment step to facilitate subsequent biological processes and membrane separation steps. The combination of two oxidation approaches or the oxidation with a membrane-based treatment within the same hybrid system is particularly promising. Challenges, research needs, and future perspectives are thus examined to guide efforts aimed at improving the application of advanced oxidation in produced water treatment and accelerate its implementation at real scale.