High-strength distillery wastewater treatment using catalytic sub- and supercritical water

•Hydrothermal condition effectively destructed organic compounds of distillery wastewater as well as its color.•CuO and MnO2 catalysts greatly increased COD removal efficiency.•The optimum COD removal efficiencies of 74.4% and 75.1% were obtained by CuO (10wt%) and MnO2 (10wt%), respectively, at 400°C and 30min.•MnO2 could remove the color of wastewater up to 98.2% at temperature of 400°C and reaction time of 30min.•Optimal value of reaction temperature, residence time, catalyst type and catalyst loading was determined. In the current research, we have studied the catalytic sub- and supercritical water (SCW) treatment of distillery wastewater (DWW) in a batch tubular reactor. Experiments were conducted in the temperature range of 250–400°C, reaction time of 30–120min at constant pressure of 25MPa with the aim of chemical oxygen demand (COD) and color removal. The initial COD concentration was 60,000mgl−1, regarded as high-strength wastewater. The experiments were performed in the presence and absence of different homogeneous (MnSO4·7H2O, ZnSO4·7H2O) and heterogenous (TiO2, CuO, MnO2) catalysts. The obtained results showed that increasing the temperature from 250°C to 400°C has a positive influence on both COD reduction (18.3–50%) and color removal (up to 48.5%) within 30min and without catalyst, while reaction time has no significant effect. By applying both homogeneous and heterogeneous catalysts, COD and color removal efficiencies were considerably increased. The optimum COD removal efficiencies of 74.4% and 75.1% were obtained by CuO (10wt%) and MnO2 (10wt%), respectively at 400°C and 30min, while the highest COD removal efficiency was 80.9% at 400°C, 120min and 5wt% of CuO. Addition of catalysts also greatly influenced color removal, such that MnO2 could remove up to 98.2% of wastewater color at 400°C in 30min.