Pilot Study On The Technological Characteristics Of Catalytic Ozonation And Garnular Activated Carbon Filtration For The Purification Of Drinking Water

Drinking water sources are now suffering ever severe organic pollution, and the presence of organics in water is not only harmful to human being by itself, but also responsible for the formation of disinfection by products (DBPs) after chlorination, and the organics may also decrease water biostability, leading to the propagation of microorganism in drinking water distribution system, so the organics in water is supposed to be removed as much as possible. The traditional water treatment processes is less capable on the removal of organics, which calling for more economic and efficient water treatment processes. Based on the advantage of ozone oxidation, catalytic ozonation may initiate the formation of hydroxyl radicals (·OH), whose oxidation potential is much higher than ozone. Therefore, refractory micropollutants may be effectively degraded and the ozonation byproducts may be restrained by catalytic ozonation, which shows a promising application on drinking water treatment.Ceramic honeycomb catalytic ozonation (CH catazone) and activated carbon catalytic ozonation (carbozone) were proved to be efficient on the removal of certain micropollutants in bench experiments, while the operation character of carbozone-GAC processes remains to be explored, so in this study, the operating characteristics of CH catazone, carbozone and their following granular activated carbon (GAC) filtration were investigated by pilot experiments.Under the study condition, the gas-liquid mass transfer efficiency of CH contactor was slightly lower than that of ozone contactor unless gas-liquid ratio was larger than 0.15. At a flow rate of 0.1 m³/h, the gas holdup (εg) of ozone and CH contactor was 0.19% and 0.15% respectively, thus the bubble size was relatively larger in CH contactor, which was adverse on gas-liquid mass transfer. Calculated by liquid pulse tracer input test, the Pe number of ozone and CH contactor was 3.14 and 5.25 respectively, thus the portion of plug flow was relatively larger in CH contactor, which was positive on gas-liquid mass transfer. The increase of gas flow rate may promote gas-liquid mass transfer more obviously in CH contactor.The oxidation degradation efficiency of CH catazone was higher than ozonation, and the highest TOC and CHCl₃FP removal rate of CH catazone was 2 times higher than that of ozonation in batch experiment. The advantage of CH catazone on UV₂₅₄ removal was more pronounced at lower ozone dose in continuous flow experiment, and at an ozone dose of 1 mg/L, the UV₂₅₄ removal rate of CH catazone was 16.7% higher than that of ozonation, which was the result of the larger portion of plug flow and faster increase of dissolved ozone concentration in CH contactor. The BrO₃^- was better controlled by CH catazone, and the BrO₃^- concentration was 38.8% lower in CH catazone effluent comparing with that of ozonation at an ozone dose of 1 mg/L.Activated carbon catalyst may promote ozone decomposition. The dissolved ozone consumption ratio of 2nd carbozone process was 71.2% higher than that of ozonation process in long-term continuous flow experiment. Analysis on the relationship between ozone consumption and organic content in 2nd carbozone process proved the ozone decomposition and radical initiation effects of activated carbon, and those effects were more obvious at lower organic concentration. The MIB removal rate of 2nd carbozone was 1 times higher than that of ozonation at an ozone dose of 1 mg/L. BrO₃^- concentration decreased 0.04 mg/L in 2nd carbozone and process, when dissolved ozone concentration was about 1.5 mg/L.The water purification performance of catazone-GAC filtration process was better than its counterpart. The UV₂₅₄ removal rate of catazone subsequent GAC and ozonation subsequent GAC was 30% and 21% respectively, at an dissolved ozone concentration of 0¹.0 mg/L and influent UV₂₅₄ of 0.020⁰.030 1/cm. The UV₂₅₄ and DOC decreasing effect of GAC filtration was most obvious when both influent organic content and dissolved ozone concentration were in their moderate levels, and the highest DOC removal efficiency of GAC filtration appeared at a specific dissolved ozone dose (O₃/DOC) of 0.3. Organic and ozone concentration were both lower in the influent of GAC following catazone, which was helpful to the maintenance of adsorption capacity and the delay of surface oxidation. Moreover, metal oxides eluted from catalyst may be adsorbed by GAC, contributing to the decomposition of ozone on GAC surface.