Research On Nitrogen And Phosphorus Removal In An Aeration Tank With High Activated Sludge

With the development of economy and improvement of people’s living,surfacewater has been seriously polluted in China. Nitrogen（N） and phosphorys（P） are thekey nutrients that stimulate the growth of algae and other photosyntheticmicroorganisms,and must be removed from wastewater to avoid eutrophication inaquatic water systems.Around the world,a growing awareness of the need tocontrol N and P emissions, which is reflected in increasingly stringent regulations,has made N and P removal widely employed in wastewater treatment. A great manywastewater treatment plants have to face with the advanced removal of N and P. Theaeration tank with high biomass concentrations promotes the removal of N and Pfrom wastewater with less energy consumption and low sludge production, whichhas great reference value for the other wastewater treatment plants.The aeration tank running under low dissolved oxygen（0.3⁰.5mg/L）and highmixed liquor suspended solids（MLSS,5000⁸000mg/L）,has achieved the removal ofN and P in the same time. It has some advantages of the plug flow and the completemixing,because of the high internal mixed liquor recirculation. The gradient ofpollutants is very low along the flow. Microorganisms will be inhibited in theconditions of low dissolved oxygen and high MLSS, growing lowly in the time ofendogenous respiration. As a result，it won’t appear the sludge bulking phenomenon.Dissolved oxygen and MLSS do have a great influence on the system. Theresults show that the increase in oxygen supply might give a positive effect onnitrification and denitrification, but inhibited the removal of P. The high MLSSenhanced the removal of N and P. The aeration tank can get the best N and Premoval in the conditions with dissolved oxygen（0.3⁰.5mg/L） andMLSS（6000⁷000mg/L）.The average removal rates of COD_Cr, TN and TP are92%,81%,97%. The average effluent concentrations of COD_Cr, TN and TP are26.54mg/L,8.63mg/L,0.12mg/L.The system has good resistance to fluctuations of the water yield,waterquality and temperature.