Nitrogen removal performance and characteristics of gel beads immobilized anammox bacteria under different PVA:SA ratios.

Although polyvinyl alcohol and sodium alginate gel (PVA/SA) cell immobilization technology has been successfully applied in anaerobic ammonium oxidation (anammox) processes, there is no comprehensive evaluation of the PVA:SA ratio in PVA/SA gel beads. Therefore, to determine the optimal PVA:SA ratio, the nitrogen removal performance and structure of PVA/SA anammox gel beads under different PVA:SA ratios were studied through batch experiments. The results suggested that cell immobilization technology could significantly improve the nitrogen removal rate (NRR). PVA concentration was positively correlated with the proportion of -macropore in the gel beads but negatively correlated with mechanical strength. Despite having poor mechanical strength, PVA/SA (12%/2%) gel beads had the highest NRR owing to the increased pore size and were experimentally determined to be the most suitable concentration of immobilized carrier. UASB reactor tests showed that compared with anammox granular sludge, the response time of anammox PVA/SA (12%/2%) beads to increased nitrogen load was shorter and the specific anammox activity was higher. Candidatus "Jettenia" was the dominant bacterium in anammox gel beads, accounting for 37.96% of the community. This study provides a reference for preparing PVA/SA cell immobilization. PRACTITIONER POINTS: Increasing the concentration of PVA can reduce the apoptosis of microorganisms during the gel process. The macropore of PVA/SA beads increased with the increase of the PVA:SA ratio. This study provides a reference for preparing PVA/SA gel beads immobilized anammox bacteria.