Improved performance of single-stage partial nitritation-anammox membrane bioreactor (PN/A MBR) by adding biofilm carriers: start-up, membrane operation and microbial structure

Abstract

Serious sludge washout is a bottleneck in the partial nitritation-anammox (PN/A) process that needs to be addressed urgently. A membrane bioreactor (MBR) is suitable for the PN/A process because of its 100 % biomass retention ability. Therefore, this study establishes a single-stage PN/A MBR and a PN/A moving bed membrane reactor (PN/A MB-MBR) for investigating the operation performance, membrane fouling behavior, and effect of biofilm carrier addition. The results demonstrate that the PN/A MB-MBR achieves a significantly shorter start-up time and substantially higher maximum nitrogen removal rate (NRR) of 17 days and 1.02 g N/L/d, respectively, compared to that of PN/A MBR (61 days and 0.19 g N/L/d, respectively). Further, the PN/A MB-MBR exhibits a lower membrane fouling of 0.023 kPa/L compared to that of 0.050 kPa/L in PN/A MBR because of the integration of the biofilm carrier. The biofilm in PN/A MB-MBR shows a higher relative abundance of Candidatus Kuenenia (18.90–25.10 %), which is a major AnAOB, compared to that observed in the suspended sludge of PN/A MB-MBR (10.30–14.32 %). Furthermore, the relative abundance of Candidatus Kuenenia absorbed on the membrane surface of PN/A MB-MBR (8.6 %) was lower than that on PN/A MBR (15.5 %). This study presented a promising method for enhancing the performance of PN/A MBR, which can serve as a valuable reference for its extensive implementation.