Development of photolysis enhanced oxidation technologies for the removal of polycyclic aromatic hydrocarbons from offshore produced water

Abstract

Offshore Produced Water (OPW) represents the largest volume waste stream from offshore oil and gas (OOG) production activities. It poses major environmental and operational challenges to offshore petroleum industries for requiring more efficient and environmental friendly on-site management. This is true particularly under growing regulatory and economic pressure to reduce the impact of waste discharges. Conventional on-site OPW monitoring and treatment is mainly focused on the oil and grease portion for meeting the regulatory standards, while limited efforts have been given to dissolved compounds especially including Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are proved as one of the most significant contributors to the ecological hazard posed by OPW discharges because of their toxicity, persistency, and potential for bioaccumulation even at a trace level. As a result, effective measurement of PAHs in OPW is imperative, and advanced on-site treatment of the effluent is desired to improve the conventional systems. This dissertation research focused on the development of new analytical testing methods and photolysis and its enhanced oxidation technologies for treating PAHs in OPW. They are composed of the key tasks including: a) refining of solid-phase extraction (SPE) and liquid-phase microextraction (LPME) pretreatment systems to extract PAHs from OPW; b) enhancement of gas chromotography-mass spectrometry (GC-MS) analytical methods for background and residual PAHs analysis; c) design and fabrication of photochemical oxidation reactors for batch- and bench-scale experiments; d) systematic one-factor-at-a-time (OFAT) analysis of key parameters and factors in the course of direct photolysis and photocatalysis; e) investigation of efficacy, parameters/factors interactions, kinetics and mechanisms of the enhanced hybrid oxidation systems by integrating photolysis and ozonation (O₃) and/or hydrogen peroxide (H₂O₂); and f) development of central composite design (CCD) based response surface modeling (RSM) models for process simulation and optimization. The major contribution of this research is the development of compact, efficient, and eco-friendly technologies for on-site OPW testing and treatment. The developed technologies are proved technically sound by lab experiments with high efficiency in detection and removal of PAHs. The research outcomes bring significant environmental, economic and social benefits to industry, government and academia by providing not only effective but also environmentally benign methods for treating OPW generated from OOG production.