Synergistic effect of TiO₂ photocatalytic advanced oxidation processes in the treatment of refinery effluents

Different types of photolytic and photocatalytic advanced oxidation processes (AOPs) were used for treatment of refinery effluents from bitumen production. The treatment efficiency was evaluated by analyzing chemical oxygen demand (COD), biological oxygen demand (BOD₅), volatile organic compounds (VOCs) and sulfide ions concentration. The studies revealed a synergistic effect of application of external oxidants (O₃, H₂O₂, O₃/H₂O₂) with TiO₂ and UV applied for improved COD and BOD₅ reduction as well as the degradation of the VOCs present in the effluents. Among studied processes a photocatalytic process combined with peroxone (TiO₂/UV/O₃/H₂O₂) was the optimal and the most economical technology. It allows to reduce 38 and 32% of COD and BOD₅ respectively and degrade 84% of total VOCs in 280 min of treatment. At this conditions the reduced COD exceeds over 30% a theoretical value based on the dose of oxidants, which proves the importance of photocatalysis in the developed technology. The sulfide ions were completely depleted in all experiments in the first 30 min of treatment. The addition of TiO₂ in the AOPs technology revealed a decrease in the process cost using less amount of chemicals achieving similar treatment efficiency when comparing with photolytic and non-catalytic technologies. The application of these technologies can be conducted in two alternative scenarios; whether to deplete the sulfides ions concentration or to maximize the treatment efficiency. In both options, the technologies studied are promising as a pre-treatment before other types of AOPs effective at neutral/acidic pH values or before a biological treatment stage. Further studies should be developed, by scaling up the process to a pilot scale in a real case scenario to check the possibility of its implementation in the industrial practice.