Removal of naphthalene from offshore produced water through immobilized nano-TiO 2 aided photo-oxidation Bo Liu, Bing Chen, Kenneth Lee, Baiyu Zhang, Yinchen Ma and Liang Jing ABSTRACT In order to increase the applicability of photocatalysis in treating offshore produced water (OPW), an immobilized catalyst was introduced into the UV irradiation system and its performance on the degradation of organic compounds in OPW was evaluated. Naphthalene was selected as the target pollutant owing to its abundance in produced water and its chemical property as a typical polycyclic aromatic hydrocarbon. Aeroxide ® P25 nano-scale TiO 2 powder was immobilized on glass slides by a heat attachment method and its photocatalytic capacity was compared to that of the original powder in terms of naphthalene removal efficiency. The results of adsorption showed that the reduction of catalysts’ surface area by immobilization was similar to that by agglomeration. The photocatalytic reaction rate constants in the homogeneous and immobilized systems were 0.00219 min À1 and 0.00305 min À1 , respectively, indicating that the immobilized catalyst had a better performance in photo-oxidation. The fouling of catalyst surface during the irradiation process came from the deposition of insoluble particles, organic matter, and the scaling of calcium. The immobilization of catalysts was more resistant to the substrate effects of OPW, indicating a promising alternative in treating OPW. Bo Liu Bing Chen (corresponding author) Baiyu Zhang Yinchen Ma Liang Jing The Northern Region Persistent Organic Pollution Control (NRPOP) Laboratory, Faculty of Engineering and Applied Science, Memorial University, St. John’s A1B 3X5, Canada E-mail: bchen@mun.ca Kenneth Lee The Oceans and Atmosphere Flagship, Commonwealth Scientific and Industrial Research Organisation, Kensington, WA, Australia Key words | immobilization, naphthalene, offshore produced water, photocatalysis INTRODUCTION Offshore produced water (OPW) is one of the largest waste streams produced during the exploitation and production of oil and gas at sea ( Jaji ; Zheng et al. ). The annual generation of OPW is approximately 14 billion barrels worldwide (Hawboldt et al. ; Jaji ). The composition of OPW is site specific and usually includes suspended solids, salt, petroleum hydrocarbons, organic acids, heavy metals, radionuclide and treating chemicals (Li et al. ). Without proper treatment, the discharge of OPW can cause long-term negative impacts on marine and coastal environments. OPW is usually treated on-site prior to being reinjected or disposed. The conventional on-site treatment technologies are mainly physical separation, such as hydro- cyclone, skimming, and dissolved air flotation; however, they have difficulties in efficiently removing the dissolved petroleum hydrocarbons from OPW (OGP ; Fakhru’l- Razi et al. ). These hydrocarbons may cause severe deterioration of marine environments. Particularly, polycyc- lic aromatic hydrocarbons (PAHs) are among the most toxic components in OPW due to their strong mutagenic and car- cinogenetic effects on marine biota and the resistance towards biodegradation (OGP ). With the presence of insoluble particles, the removal of PAHs by membrane tech- nologies could be more problematic because of easily jamming the membrane modules (Fu et al. ). Further- more, there is a growing need for more stringent regulations when the petroleum industry is marching toward the Arctic and deep waters. For example, the ‘Zero Discharge’ policy has been required by the Arctic Waters Pollution Prevention Act in Canada, which means that no contaminants shall be discharged into Arctic waters. A simi- lar policy has also been enforced by the Oslo and Paris 246 © IWA Publishing 2016 Water Quality Research Journal of Canada | 51.3 | 2016 doi: 10.2166/wqrjc.2016.027