Research On Efficiency Of Municipal Wastewater Treatment By Biological Flocculation-pre-denitrification Biological Aerated Filters Process

With the increase of the urbanization level, the volume of sewage discharge is increasing,and being low carbon and nitrogen ratio. Which make it difficult to standard in the traditional sewage treatment plant. At the same time,the expenses of excess sludge disposal takes more larger proportion in sewage plant operation costs. In order to solve the denitrification of low carbon and nitrogen ratio sewage and disposal of WAS in wastewater treatment plant effectively,the research and development of new treatment process is imperative.According to the above problems, the biological flocculation adsorption-pre-denitrification BAF combined process was employed in this topic, and the hydrolysis-acidification liquor of flocculation/adsorption sludge was used as addition carbon source at the same time. At the first stage in the experiment, the removal effect of COD, NH₄⁺-N and TN were analyzed on the reflux ratios and gas-water ratio. At the second stage in the experiment, the hydrolysis-acidification liquor of flocculation/adsorption sludge was used in pre-denitrification BAF system as addition carbon. Studying on the influences of the denitrification performances by pre-denitrification BAF system. At the last stage, the new combined process-the biological flocculation adsorption/pre-denitrification BAF system/Hydrolysis-acidification was employed to improve the content of biodegradable carbon source in sewage wastewater at the optimal conditions. The main results of this study are as follows:?1? In the pre-denitrification biological aerated filters process, the way of hanging membrane is sludge inoculation firstly and then continuous training by which we can research the biofilm culturing.After 25 days, the biofilm culturing in C/N filter and D/N filter were successful. At the 15 th day of Starting hanging membrane, the removal rate of COD is about 60%.But it needs 20 days when the the removal rate of NH₄⁺-N reached about 65%. With the pre-denitrification BAF system operating in design parameters, the removal rate of COD, NH₄⁺-N in final effluent were about 70% and 80%.?2? When the pre-denitrification BAF system in the reflux ratio was 150%, gas water ratio was 4:1 under the condition of stable operation, the sewage denitrification performance achieved the best. The average concentration of COD, NH₄⁺-N and TN in final effluent were 17.57mg/L, 1.02mg/L and 10.21mg/L, and the average removal rates were 77.91%, 95.45% and 64.52%. The results show that the removal of NH₄⁺-N mainly happened in the C/N filter, and the removal of TN mainly happened in the D/N filter in the pre-denitrification BAF system.?3? When the pre-denitrification BAF system operatied stability in the reflux ratio was 150% and gas water ratio was 4:1, comparativing with three kinds of the ratio of flow rates of carbon source to influent to the influences of the denitrification performances by pre-denitrification BAF system in 1:70, 1:60 and 1:50. As the results : when the ratio of flow rates of carbon source to influent was 1:60,then the average concentration of COD, NH₄⁺-N and TN in final effluent were 24mg/L, 0.87mg/L and 5.87mg/L, and the average removal rates were 75.24%, 96.12% and 79.80%.?4? The new combined process operatied stability in the reflux ratio was 150%,the gas water ratio was 4:1 and the ratio of flow rates of carbon source to influent was 1:60.The results show that, in the stable running period of the process, the concentration of COD, NH₄⁺-N and TN in raw water were 209mg/L,29.41mg/L and 36.28mg/L.The concentration of COD, NH₄⁺-N and TN in effluent after the bio-flocculation and adsorption process were 95mg/L, 22.50mg/L and 28.98mg/L, and the average removal rates were 55%, 23% and 20%. Then the Sewage went into the pre-denitrification BAF system,and the average concentration of COD, NH₄⁺-N and TN in final effluent down to 24mg/L, 0.87mg/L and 5.87mg/L. So the total removal rate of COD, NH₄⁺-N and TN were 90%, 97.04% and 83.75% in the combined process.Compositing the concentration of COD, NH₄⁺-N and TN in final effluent after the combined process, the effluent water quality can achieve the standard of “urban sewage treatment plant pollution emissions standards”?GB 18918-2002? A level.