COD removal from petrochemical wastewater by UV/hydrogen peroxide, UV/persulfate and UV/percarbonate: biodegradability improvement and cost evaluation

The petrochemical industry has been highly considered by environmentalists since it can affect the environment through the production of high strength wastewater. This study investigates chemical oxygen demand (COD) removal from petrochemical wastewater by ultra violet (UV)/oxidant systems with varying dosages of oxidants, initial pH values and reaction time. Hydrogen peroxide (H2O2), persulfate (PS) and percarbonate (PC) were used as oxidants. The results showed that pH = 3.0 was suitable for H2O2 and PC, while PS had the best performance at pH = 7.0. The presence of ferrous ions improved the removal efficiency, especially in the case of UV/PC. However, COD removal efficiencies of UV/PS and UV/H2O2 were more effective than that of the UV/PC system. The biochemical oxygen demand (BOD)/COD ratio achieved >0.4 by UV/PS/Fe2+, UV/H2O2 and UV/H2O2/Fe2+ systems. Complete decolorization occurred for all the UV/oxidant systems after only 30 min reaction time. Besides the effective performances of PS and H2O2 in COD removal, PC was considered as an inexpensive oxidant. The order of total costs based on kg COD removed was: UV/PS/Fe2+ > UV/PS > UV/H2O2/Fe2+ > UV/H2O2 > UV/PC/Fe2+ > UV/PC. In conclusion, UV/H2O2 displayed an effective, applicable and clean process for petrochemical wastewater treatment.