Study On Further Denitrification Of Composite Carbon Filler

The cooked corncob was pretreated by 1.5%Na OH, 1%H2SO4, 1.5%H2O2 and alkaline hydrogen peroxide(caustic soda solution with 1.5%H 2O2) combined with ultraviolet radiation to solve the problems including low of denitrification rate, the high concentration of TOC in the effluent, the filter layer easy to block. These problems existed commonly in adding cellulose carbon source of advanced denitrogenation in low C/N ratio effluent from municipal wastewater treatment plant(WWTP). Optimum pretreatment method of cooked corncob was selected through analyzing the characteristics of carbon released and denitrification. The polyethylene float ball diameter of 80 mm packed with zero-valent iron, corncob and activated carbon was made as composite carbon filler. And the appropriate filling ratio of zero-valent iron, corncob and activated carbon was determined by the orthogonal test in three factors and three levels. The combined process of composite carbon denitrifying nitrogen bio-filter and facultative anaerobic bio-filter(DN/AF) was developed. The operation characteristics and the diversity of microbial community in the combined process were researched.And the characteristics of carbon released, denitrification and bio-attachment capability of using pretreated corncob were studied in carbon released and denitrification experiments in laboratory scale. The results show that when the nitrate removal loading of unit mass corncob, the removal efficiency of nitrate and surface characteristics of corncob were considered together, the corncob pretreated by alkali was suitable for biodegradation and utilization by denitrifying microorganism.The corncob pretreated by alkali, zero-valent iron and activated carbon were used as composite carbon filler. The affecting factors of denitrification system were investigated by the orthogonal experiments in three factors and three levels of zero-valent iron species, the corncob and total zero-valent iron and activated carbon of mass ratio and the mass ratio of zero-valent iron and activated carbon. The results show that the optimum condition for orthogonal test was iron wire, 5:1 for the corncob and total zero-valent iron and activated carbon of mass ratio and 1:2 for the mass ratio of zero-valent iron and activated carbon by the accounting standards of nitrate removal efficiencies, ammonia nitrogen and nitrite nitrogen accumulation and pH.The stable operation of combined process was researched from macroperspective and micro-perspective. For one thing, the denitrification characteristic of combined process was studied by the water quality index of total nitrogen, nitrate nitrogen and pH in the effluent of denitrifying nitrogen bio-filter and TOC in the both bio-filters. For another, the Miseq high-throughput sequencing technology and scanning electron microscope were applied to analyze the microbial community structures and morphology in the denitrifying nitrogen bio-filter biological film system. The experimental results indicate that the combined process of composite carbon denitrifying nitrogen bio-filter and facultative anaerobic bio-filter could effectively remove nitrate and obtain low concentration of TOC to keep a good perceptual effects. The denitrifying nitrogen bio-filter run 159 days had afforded one kilogram of nitrate nitrogen per kilogram of corncob pretreated by alkali and the effluent TOC could be less than 10mg/L. The lack of carbon source had an effect on the accumulation of nitrogen accumulation in the late stage. From the corncob structure SEM pictures, we could obviously see that the surface of corncob before using was raspy and had many holes. While the surface of corncob after using had more holes and formed a dense biofilm which coccus and bacilli were the main bacteria. Miseq high-throughput analysis revealed that at the genus level the genera related to denitrifying and degradation of cellulose was accounted for 40.35% and 29.04% which were related to known bacteria, respectively. So,the masses of denitrifying bacteria and cellulolytic bacterium in the sludge made it feasible to denitrify of composite carbon filler efficiently.The article had the advantage of strong novelty on the contrast and selection of pretreatment method of corncob as carbon source for denitrification, preparation of composite carbon filler and microbial sequencing technology. Therefore, this study is of significance for WWTP effluent further denitrification, advancing the process of wastewater reuse and improving the quality of the reclaimed water.