Produced water treatment by advanced oxidation processes

Highlights: • An integrated PW treatment is aimed for increasing sustainability of O&G sector. • PW treatment can include a pretreatment, an AOP and a RO unit. • Acetic acid is one of the most recalcitrant compounds of PW. • With photocatalysis a low TOC removal percentage is achieved. • The highest TOC removal percentages are achieved combining ozone and H₂O₂. -- Abstract: Different Advanced Oxidation Processes (AOPs) such as photocatalysis, Fenton-based processes and ozonation were studied to include one of these technologies within an integrated solution for produced water (PW) polishing. Synthetic PW was prepared adding toluene, xylene, naphthalene, phenol, acetic and malonic acids to a seawater matrix. Despite that in all AOPs studied in this work BTEX and naphthalene were removed, the efficiency (in terms of TOC removal) of each treatment varied largely. Among these techniques, photocatalysis was found to be the less effective for the treatment of PW, as TOC removals lower than 20% were obtained for the best scenario after 4 h treatment. In the contrary, best results were obtained by ozonation combined with H₂O₂, where all the organic components were removed, including a high percentage of acetic acid, which was not abated by the rest of the AOPs studied. The optimum conditions for ozonation were 4 g h⁻¹ O₃ and 1500 mg L⁻¹ H₂O₂ at pH 10, where after 2 h a 74% of TOC removal was achieved and the acetic acid elimination was 78%. This condition enabled that ozonation process accounted for the lowest electric energy consumption per order of target compound destruction regarding total organic carbon (TOC).