Nitrogen and phosphorus removal by activated sludge process: A review

This paper describes the mechanism of nitrogen and phosphorus removal by activated sludge process, and introduces several conventional nitrogen and phosphorus bioremoval processes, namely sequencing batch reactor (SBR), anaerobic-anoxic-aerobic (AAO), oxidation ditch, and bio-doubling process (BDP). Many improved technologies were invented to compensate for the defects of conventional activated sludge process Nitrogen and phosphorus bioremoval by activated sludge process have many similarities and conflicts, including different sludge characteristics and competition for carbon sources that affect the results of the simultaneous nitrogen and phosphorus removal. Therefore, a series of countermeasures to resolve such conflicts are reviewed. Economy, sefficiency and low energy consumption will be the developing trends of wastewater treatment in the future.