Denitrification characteristics and community distribution of glycogen accumulating organism granules

Abstract

This study aimed to investigate the denitrification ability and microbial ecological characteristic of glycogen-accumulating organisms (GAOs) during sludge granulation. A combined method of reactor process, batch test, microscale techniques and fluorescence in situ hybridization (FISH) was employed to evaluate the denitrification ability of GAOs, to reveal the micro structure of microbial communities and to characterize the distribution of GAOs and polyphosphate-accumulating organisms (PAOs) in different size granules. The results indicated that the adsorption rate of organic compound by sludge was over 92%. The SVI10 of granules stabilized at 30-50 mL g -1, a very low value compared to those measured for inoculating sludge (108.2 mL g-1). The nitrogen removal rate of nitrate and nitrite by GAOs granules reached 65% and 70% respectively, with N2 as the main gaseous product. The granules were tightly packed with a large amount of tetrad-forming organisms (TFOs), with flamentous bacteria serving as the supporting structures for the granules. FISH demonstrated that GAOs were distributed evenly throughout the granular space, whereas PAOs were severely inhibited and presented only in the edge of granules. A lab-scale sequencing batch reactor (SBR) could be successfully operated for cultivating GAOs granules in alternating anaerobic stirring-discharge-aerobic modes, with the GAOs granules showing excellent denitrifying capability. Therefore GAOs are the predominant member of the microbial population in granules.