Realization of microbial community stratification for single-stage nitrogen removal in a sequencing batch biofilter granular reactor

•Nitritation-anammox process successfully started up in SBBGR.•The SNAP process performance was gorgeous with ammonium removal efficiency >90% and TN removal efficiency >80%.•The observed specific microbial stratified distribution in SBBGR contributed to the co-existence of AOB and anammox.•Proteobacteria and Planctomycetes were dominant functional organisms on the phylum level.

A permanent microbial stratified nitrogen removal system coupling anammox with partial nitrification (SNAP) in a sequencing batch biofilter granular reactor (SBBGR) was successfully constructed for the treatment of ammonia-rich wastewater. With a nitrogen loading rate of 0.1 kg N m−3·d−1, the maximal ammonia and total nitrogen removal efficiencies could reach up to 96.08% and 84.86% on day 108, respectively. The pH, DO profiles revealed a switch of functional species (AOB and anammox) at a typical intermittent aeration cycle. qPCR and high throughput analyses certified a stable spatial microbial stratified community structure. Although, anammox preferred strict anaerobic environment while AOB needed oxygen, a special stratified community structure contributed to conquer this obstacle. Moreover, Bacteroidet, Chlorobi, OD1, Planctomycetes, and Proteobacteria were the dominant species in the SBBGR. Although we have predicted the possible pathways of nitrogen transformation, further studies are needed to validate the pathways in enzymology.