An innovative strategy for regenerating anammox granule sludge: Nitrogen removal performance, sludge characteristics, and microbial community

Abstract

To prevent sludge floating, a new strategy known as "breaking-collecting-recovering" has been proposed, which involves adding filler to the reactor, breaking the floating granules, and recycling them into the reactor. This allows the broken granules to be recovered and settle on the surface of the filler. In this study, granules were divided into three categories according to location: granules that remain attached to the surface of the filler after breaking (FFG), granules attached to the surface of the filler that floated after some time (MFG), and settling granules (SG). The characteristics of the regenerated granules were studied through their morphology, structure, and microbial community. The experimental results indicated that the "breaking-collecting-recovering" strategy was effective. When the nitrogen loading rate (NLR) returned to 8.4 kg N·m-3·d-1, the number of floating granules was greatly reduced. Scanning electron microscopy showed that MFG contained more filamentous bacteria, while microbes on FFG and SG were smoother. As the setting performance deteriorated, the extracellular polymeric substance (EPS) content of granules increased, though the polysaccharide content of MFG was higher. The microbial community characterization of FFG and SG was similar. Additionally, the relative abundances of Candidatus_Kuenenia were 27.96% and 37.38%, respectively, while abundance in MFG was only 16.26%. Unclassified_Deltaproteobacteria and Gp3 rapidly aggregated in MFG, which may be the microbial cause of sludge floating.