Microbial Population Dynamics During Sludge Granulation in a Simultaneous Nitrogen and Phosphorus Removal System

Abstract

In this study, domestic sewage was utilized to cultivate aerobic granular sludge (AGS) in a simultaneous nitrogen and phosphorus removal (SNPR) system. The bacterial population dynamics during the aerobic sludge granulation were investigated to reveal the granulation mechanisms using Illumina MiSeq PE300 high-throughput sequencing. Quantitative real time polymerase chain reactions (PCR) were used to investigate shifts in the abundance of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), nitrite-oxidizing bacteria (NOB) and polyphosphate accumulating organisms (PAOs). After cultivation for 100 d, the AGS was compact and demonstrated good SNPR performance. During the AGS formation process, extracellular polysaccharides obviously increased, while extracellular proteins kept relatively stable. The abundance of AOA significantly decreased during the formation of AGS process, while the abundance of PAOs increased. The bacterial diversity increased at first and then decreased during the formation of AGS. The bacterial community changed dramatically during aerobic sludge granulation. Persistent operational taxonomic units (OTUs) accounted for 92.70% of the total sequences. Proteobacteria (31.07%-53.67%), Bacteroidetes (6.70%-16.50%) and Chloroflexi (7.84%-13.36%) were the dominant phyla. Candidatus competibacter was obviously enriched in the AGS formation process (increased from 0.11% in the seed sludge to 35.33% in the AGS) and may play an important role in the formation of AGS.