Denitrifying phosphorus removal and microbial community characteristics of two-sludge DEPHANOX system: Effects of COD/TP ratio

Abstract

Two Lab-scale ANOXic DEPHosphation (DEPHANOX) bioreactors, in the continuous flow (DEPHANOX-CFR) and sequencing batch reactor (DEPHANOX-SBR) modes, were successfully operated and compared with varying influent C/P ratios. A decrease of influent chemical oxygen demand (COD)/total phosphorus (TP) feeding ratio from 250/4 to 250/14 generally did not significantly affect the nutrient removal performances. However, the overall microbial community structure and composition significantly shifted in the both two DEPHANOX bioreactors. Quantitative polymerase chain reaction results revealed that denitrifying phosphate-accumulating organisms (DPAOs) dominated and accounted for around 78.8 % of phosphorus accumulating organisms (PAOs). High-throughput sequencing results further suggested that the most three prominent phyla identified in the DEPHANOX system under different COD/TP ratio conditions included Proteobacteria (38.8–68.7 %), Bacteroidetes (10.3–12.3 %) and Chloroflexi (12.2−1.9 %). In addition, Dechloromonas and Pseudomonas spp. were identified as the dominant DPAOs. Furthermore, PICRUSt prediction analysis suggested that functional genes related to diverse metabolism pathways, including tricarboxylic acid cycle, electron transport, and nitrogen metabolism, were predicted to be actively involved with simultaneous phosphorus and nitrogen (SPN) removal. This study optimized the influent constituent characteristics and operating conditions of the DEPHANOX system, and provided novel insights into key metabolism functions of DPAOs in the DEPHANOX system.