Performance and nitrogen removal mechanism in a novel aerobic-microaerobic combined process treating manure-free piggery wastewater.

[Display omitted] • A novel SBR-UMSR process was constructed to treat manure-free piggery wastewater. • The front-end SBR functioned as a COD remover to get an effluent with a COD/TN ≤ 1. • Partial nitrification – anammox process was well performed in the back-end UMSR. • Effective synchronous removal of COD and TN was achieved in the combined process. • COD, NH 4 +-N and TN in effluent all well met the strict discharge standard of China. A novel combined sequencing batch reactor (SBR) – up-flow microaerobic sludge reactor (UMSR) process was developed to treat manure-free piggery wastewater characterized by low COD/TN ratio and high NH 4 +-N. The front-end SBR was designed to get an effluent with COD/TN ≤ 1 by removing COD, allowing the back-end UMSR to practice anammox for the simultaneous removal of TN and NH 4 +-N. Fed with the raw piggery wastewater, the combined SBR-UMSR process was started up at 27℃ with a reflux ratio of 15:1 in the UMSR. After 230-days running, the removal of COD, TN, and NH 4 +-N in the combined SBR-UMSR process reached 78.41%,85.05%, and 92.21%, respectively. 50.22% of COD in the wastewater was removed in the SBR, while 87.11% of NH 4 +-N and 79.69% of TN were removed in the UMSR. Stoichiometry and bacterial function analysis revealed that the partial nitrification – anammox process was the dominant nitrogen removal approach in the UMSR. [ABSTRACT FROM AUTHOR]