Two distinct patterns for advanced simultaneous nitrogen and phosphorus removal treating low C/N wastewater in a low...

The anaerobic/aerobic/anoxic-aerobic granular sludge (AOA-AGS) process possesses capacity for efficient external carbon usage and potential to enrich autotrophic anammox bacteria. However, how do these two distinct ways perform under low dissolved oxygen (DO) in treating low carbon to nitrogen (C/N) wastewater remains largely unknown. An AOA-AGS system was therefore configured treating wastewater with a C/N of 4.5 ± 0.5 and low DO of 0.5 ± 0.2 mg/L over a long period of 126 days. Results showed that admirable and stable TIN and TP removal efficiency up to 90.75% and 95.16% on average was maintained over operation. Two distinct microbial patterns were found, i.e., simultaneous nitrification, endogenous denitrification and phosphorus removal (SNEDPR) pattern via dominant Defluviicoccus (23.57%) and Candidatus Competibacter (10.17%) in transitional phase, and enhanced SNEDPR pattern coupled with anammox (SNAEDPR) via in-situ self-enriched Candidatus Brocadia (0.01%) in terminal phase. The dynamics of functional microbial communities optimized the allocation of limited carbon sources, with the proportion of COD utilized for denitrification and phosphorus removal in influents COD increasing from 27.98% and 42.02% to 40.30% and 49.48%, respectively. This study finally proposed a possible mechanism for AOA-AGS process treating low C/N wastewater with low DO via dynamic microbial interactions, providing theoretical and technical supports for the practical engineering application.