Study on granule size control strategies in a novel continuous flow system for Anammox

This study, employed a novel, patented twin-reactor self-recirculating system to explore the granule size control strategies and its controlling mechanisms of anaerobic ammonium oxidation (Anammox) granular sludge based on granules size recirculation approach. By adjusting internal recirculation locations, the strategy aimed to control the size of granules through introducing sludge of varying sizes into regions with high substrate concentration and mechanical shear. The result demonstrated that this strategy effectively increased granule size, and maintained it within an appropriate range. Furthermore, it enhanced sludge concentration, settling characteristics, and nitrogen removal performance. Specifically, recirculating larger granules proved to be highly effective, keeping the size of granular sludge within the optimal range of 0.5~1.6mm, with a median size of 948µm, SVI of 35.6mL/g, and an enhanced total inorganic nitrogen (TIN) removal efficiency of 88.59%. Analysis of extracellular polymeric substances (EPS) revealed that proteins (PN) in the tightly bound EPS (TB-EPS) played a crucial role in granule size control. Stratification experiments revealed that PN in the outer layer of the sludge primarily influenced settleability, while PN in the TB-EPS of the inner layer strengthens the granule structure. High-throughput sequencing showed a significant increase in the abundance of anammox bacteria (AnAOB) Candidatus Kuenenia, mainly located in the inner layers of the sludge granules. These findings have significant implications for the engineering application of anammox granular sludge technology. © 2024 Chinese Society for Environmental Sciences. All rights reserved.