Research On High-ammonia Nitrogen Domestic Wastewater Treatment By Step-feed A/O Process

The step-feed A/O process was used to treat high ammonia nitrogen domestic wastewater, aeration rate and C/N ratios were researched to investigate the effect on property of nitrogen and phosphorus removal. Water quality in each reaction tank was measured to analysis the reason of difference between actual nitrogen removal efficiency and the theory of nitrogen removal efficiency. Moreover, study of cooperative phosphorus removal by chemical and biological process was carried out to find a approach to improve the phosphorus removal efficiency, which used the adsorption saturation phenomenon of PAC, so the nitrogen and phosphorus removal can be improved simultaneously. Results are as follows:First, COD, total nitrogen and total phosphorus removal had little difference under different aeration rate, and carbon source was the limiting factor of nitrogen and phosphorus removal. Better nitrification efficiency could be obtained with optimal distribution in the aerobic tank when the aeration rate was0.5m3/h, the ammonia removal efficiency was more than95%and the total nitrogen removal was improved to some extent because of simultaneous nitrification and denitrification. The COD and ammonia nitrogen removal had little dierence under different C/N ratios on condition of ammonia nitrogen concentration was constant. Total nitrogen and total phosphorus removal efficiency were improved as the C/N ratio were increased, so nitrate nitrogen and phosphorus were low. When take nitration into consideration, C/N ratio was not the higher the better, and there was a optimal range of C/N.Second, after researching pH, DO, COD, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total nitrogen and MLSS, we found that most easily biogradable organic mater was removed after getting through the anoxic tank because of dilution, assimilation and denitrification, and the COD concentration was below40mg/L. Ammonia nitrogen could be nitrified completely under high aeration rate, and the effluent concentration was below0.5mg/L. The denitrification was incomplete because of the limit of carbon source, so nitrate was more and more. Total nitrogen was decreased in the aerobic tank, and it proved that there was simultaneous nitrification and denitrification. MLSS reduced gradually because of dilution, but the average MLSS was high, and the treatment efficiency could be improved more than30%when the solid load of secondary sedimentation tank was not increased.Third, the cooperative phosphorus removal by chemical and biological process showed that compound was optimal not only in effect but also in economy. The average phosphorus efficiency was91.95%and the effluent concentration was below0.5mg/L, which met the fist grade A diacharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002). Chemical phosphorus removal could improve COD removal efficiency, but reduce ammonia nitrogen removal. The optimal adding quantity and reaction condition of different flocculant were necessary to be researched so that there will be a higher nitrogen and phosphorus removal efficiency.