Development of Effective Biological Treatment Process of Organic and Nitrogenous Substances in Wastewater

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In biological wastewater treatment process, organic compounds are generally removed by aerobic microbes, while nitrogenous substances are removed by a combination of aerobic nitrification and anaerobic denitrification. Nitrification carried out by nitrifiers transfers ammonia to nitrite and nitrate, and denitrification reduces the nitrogen oxides to nitrigen gas. The present research aims to develop an effective biological process for simultaneous removal of organic and nitrogen substances in wastewater by cohabitation of aerobic and anaerobic microbes in porous particle carriers. This research made clear the factors related to the simultaneous removal of organic and nitrogenous substances, and laid the engineering foundation of developing such process. The research results obtained in the present research were summarized as follows.Using a model bioreactor installed with porous sheets of definite thickness, spatial distribution of microbial species in the porous sheets was analyzed qu … More antitatively. The organic oxidizing bacteria, nitrifiers and denitrifiers showed a unique distribution pattern in the porous sheets. A mathematical model taking microbial growth and death kinetics into account was proposed and successfully explained the microbial distribution. These results showed that cohabitation of aerobic and anaerobic microbes could be formed artificially.In order to obtain the basic engineering data for the simultaneous removal of organic and nitrogen substances in wastewater, a continuous-flow fluidized-bed bioreactor consisting of porous particle carriers was constructed to treat artificial sewage. The reactor was operated aerobically by aeration with a sparger (DO=6-7ml/L), and the sewage was fed continuously at a hydraulic retention time of 8h. Ratio of Carbon concentration to nitrogen concentration (C/N ratio) in the wastewater varied from 2.5 to 10. At the steady state, total nitrogen removal ratio increased from 50% to 85% with C/N ratio in case of influent nitrogen concentration = 20 mg/L,while in case of influent nitrogen concentration = 40 mg/L,the total nitrogen removal ratio was between 40 - 50%, independent of C/N ratio.Based on the experimental results, a kinetic analysis of the microbial reactions related to simultaneous removal of organic and nitrogenous substances was performed. The rate constants of orgainc oxidation, nitrification and denitrification were obtained and found to be dependent on the organic loading and influent nitrogen concentration. At low C/N ratio, denitrification contributed largely to the nitrogen removal, while nitrogen removal was mainly dependent on the nitrogen uptake by microbial growth at high C/N ratio. Less