Porous ceramsite catalytic ozonation for the treatment of pulp and paper mill wastewater in a continuous-flow reactor

The pollutants in wastewater can be degraded effectively by heterogeneous catalytic ozonation due to the production of hydroxyl radical (center dot OH) with strong oxidation power. For the natures of low weight, large specific surface area, excellent physical strength and stable chemical characteristics, the porous ceramsite was chosen for catalytic ozonation of wastewater in the present study, and the practical application parameters of the system were investigated for the actual pulp and paper mill wastewater (PPMW) in the continuous-flow reactor including temperatures, feeding flow rate, O3 flow rate and O3 dosage. The optimum experimental conditions were obtained (T = 25 celcius, feeding flow rate = 0.25 L/min, O3 flow rate = 0.5 L/min, O3 dosage = 15 g/L) for the process of catalytic ozonation. The results show that the effluent concentration of COD decreases from about 200 mg/L to 10 mg/L, namely the removal efficiency is about 95 %. The stability of the catalyst over time was tested in the continuous-flow reactor for 48 days, confirming that the porous ceramsite exhibits good performance in 30 days. The reusability of the catalyst was studied after the used catalyst was washed with Milli-Q water and ethanol, exhibiting good catalytic activity of the regenerated catalyst in three cycles. The fluorescent excitationemission matrix (EEM), UV-vis analysis and GC-MS analysis were used for analyzing the organic pollutants in raw PPMW and after treatment. These results indicate that the process of catalytic ozonation with porous ceramsite has a high treatment efficiency on PPMW, and the continuous-flow reactor can be more practically used for a full-scale community PPMW application at a mill level.