Nitrogen and phosphorus are key nutrients causing eutrophication in water body, and they are required to be removed from water resources in many countries. Biological nutrient removal (BNR) can be accomplished by nitrification, denitrification, and enhanced biological phosphorus removal (EBPR). However, these systems often encounter several difficulties including the sludge bulking due to proliferation of filamentous organisms, requirement for a long sludge age to ensure stable nitrification as well as requirement for a large space if multistage systems are employed.
In the past few years, aerobic granules for organic carbon removal had been developed in sequencing batch reactors (SBR) (Beun et al., 1999; Peng et al., 1999; Etterer and Wilderer, 2001; Tay et al., 2001). Compared to conventional activated sludge flocs, aerobic granular sludge has regular, dense, and strong physical structure, good settling ability, high biomass retention, and the ability to withstand shock load. Recently, research attention has been given to the development of granules capable of removing nitrogen and phosphorus (Beun et al., 2001; Lin et al., 2003; Yang et al., 2003; de Kreuk and van Loosdrecht, 2004; Qin et al., 2005). Evidence shows that the problems encountered in the suspended growth nutrient-removal system, such as sludge bulking, large treatment plant space, washout of nitrifying biomass, secondary P release in a clarifier, higher production of waste sludge, would be overcome by developing and applying N-removing and P-accumulating granules (Lin et al., 2003; Yang et al., 2003). A more compact and efficient granule-based biotechnology would be expected for high-efficiency N and P removal. Therefore, this chapter presents up-to-date information with regard to the development of microbial granules for the nutrient removal processes.
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