Nitrogen and phosphorus are the primary causes of eutrophication. One of the common symptoms of eutrophication is thealgal bloom that can cause hypoxia especially in deep water as a consequence of settled algae and its decay. The limiting nutritional element in water body is depending on the location, but typically phosphorus is more limiting than nitrogen since phosphorus is delivered only from organic matters containing phosphorus while ammonium nitrogen is synthesized by many different microorganisms that can fix gaseous nitrogen in the air.
Nutrient removal has been practiced for more than five decades in conventional activated sludge (CAS) process (Gujer, 2010). Numerous physico-chemical and biological process designs have been devised, but primarily biological methods are used for both nitrogen and phosphorus with some complementary chemical phosphorus removal. Though the biological nutrient removal (BNR) processes used for CAS can be adapted to MBR, some modifications are inevitable due to the unique characteristics of MBR that differs from CAS. Moreover, the efficacy of chemical phosphorus removal in MBR differs from that in CAS primarily due to the longer solids retention time (SRT).
In this chapter, principles of BNR processes and chemical phosphorus removal are discussed with process examples. Emphases are given to how the unique characteristics of MBR affect the mechanisms and performance of the nutrient removal processes.
© Seong Hoon Yoon