| Environmental pollution has been a growing problem. As stricter environmental regulations are imposed, advanced and cost effective techniques for nitrogen removal from wastewater become more and more important. In view of the advantages of denitrifying phosphorus removal and aerobic granular sludge (AGS), it is considerable to combine these two technologies, cultivateing aerobic granular sludge possessing enrichment of denitrifying phosphate-accumulating organisms (DPAO). This study focuses on the startup and domestication of denitrifying phosphorus removal AGS in a sequencing batch reactor (SBR) and the impacts of various environmental factors on the denitrifying phosphorus removal performances, characteristics of AGS and microbial community succession in the reactor.The methods using strong hydraulic selection pressure and strong hydraulic selection pressure combined with adding soil particles have been introducesed to accelerate the procees of granulation. Granules fed with overstressed organic loading rate appeared on 7 d with short cycle time(3 h) and settling time(5 min) to strengthen the hydraulic selection pressure under aerobic conditions. And AGS with average particle size of 0.92 mm was obtained on 11 d. Granules appeared in the reactor operated with the strategy of strong hydraulic selection pressure combined with adding soil particles on 4 d. AGS with average diameter of 1.06 mm was obatained on 11 d. The granular sludge formed with the two startup strategys exhibited good effect on the removal of COD with the removal the removal rate over 93%. The effluent NH4+-N concentrations were maintained at 0.25-1.26 mg/L and 0.41-0.41 mg/L, respectively. There is no accumulation of NO2-N. The reactor performed a excellent removal of COD and NH4+-N.Denitrifying phosphate-accumulating organisms were enriched in AGS with low strength water under A/O/A model. The reactor possessed excellent capability of nutrient removal after 47 d. The COD concentration of effluent was lower than 20 mg/L, and the average ammonia nitrogen concentration is 0.53 mg/L. TP concentration was always below 1 mg/L. There was no accumulation of NO2--N and NO3--N. Investigated the typical cycle of the reactor and found simultaneous nitrification and denitrification(SND) during aerobic phase. Anoxic phosphorus absorption phenomenon was observed. Based on Miseq high-throughput sequencing analysis, Proteobacteria replaced the dominant place of Firmicutes and Candidate division TM7 gradually.When pH was 6.5-8.5, the change of pH did not have a significant impact on the reactor. Only at pH 6.5, the system of TP removal efficiency declined, average removal rate fell to 78.72%. MiSeq sequencing results show that the reactor had high microbial diversity at different pH values. And the microbial diversity was highest when pH was 6.5. Proteobacteria was the dominant phylum in the reactor during the experiment and Bacteroidetesfollowed.The performane of the reactor was better using sodium acetate(NaAc) or sodium succinate as sole carbon source. The concentration s of COD, ammonia nitrogen, TIN, and TP in effluent rose when glucose was the sole carbon source, which indicated that the types of carbon source had significant effects on the system. Proteobacteria was the dominant phylum when the carbon source type changed,with relative abundance over 50%. The change of the carbon source led to the obvious changes of microbial community. Candidatus Competibacter was the dominant genus in the granules using NaAc and glucose as carbon source, while Saprospiraceae uncultured and Thauera were dominant genera (abundance were 8.18% and 8.71% respectively)with sodium succinate as carbon source..When COD concentration was 200-400 mg/L with invariable COD/N/P, the system showed ideal removal performance. The concentrations of COD, ammonia nitrogen, TP in effluent increased when the influent COD concentration rose to 600 mg/LThe microbial diversity rose as the increase of organic loading rate(OLR). the whole process of Gammaproteobacteria is dominant class in the system. Acinetobacter and Saprospiraceae uncultured occupy a big proportion in the system and the relative abundance decreased as the OLR increased. The AOB Nitrosomonas and Nitrosomonadaceae uncultured were suitable for low OLR conditions.The C/N ratio was changed by changing the concentration of ammonia nitrogen tin influent. The changes of C/N had little effect on the removal of COD, ammonia and TP when C/N was among 5-20. The increase of NOx--N caused by the decrease of C/N led to the lack of PO43--P. Meanwhile, the amount of organic matters was little, which inhibited the reduction of NOx--N and impaired the removal of nitrogen. The microbial diversity decreased as the C/N reduced. Proteobacteria and Bacteroidetes had always been the dominant phylum in the system.As the reduction of the C/N DPAO Candidatus Accumulibacter gradually became the dominant genus of the system. AOB Nitrosomonas and NOB Rhodocyclaceae unclassified had maintained a certain proportion in the system, which was the biological basis for the stable operation of the system.The C/P varied in the range of 16.7-50 by changing the concentration of PO43--P in influent. The removal of COD and TIN were always excellent. Microbial diversity decreased a little when C/P increased and Proteobacteria and Bacteroidetes was the dominant phylum in the in the reactor. The relative abundance of Candidatus Accumulibacter and Thauera rose with the decrease of C/P and Thauera became one of the dominant genera in the reactor. The decrease of C/P promote the growth of PAOs and DPAOs.Finally, the toxicity of phenol on the aerobic granular sludge system was investegated. When the concentration of phenol was below 50 mg/L, granules removed phenol completely and kept excellent denitrification and phosphorus removal performance during the study of shock effects of phenol on the AGS. When the concentration of phenol was above 100 mg/L, granular sludge could only degradate part of the phenol with the concentrations of ammonia nitrogen, TP and NO3--N increased. The results indicated that the system could tolerate the phenol Hess than 50 mg/L. With the long-term effct of phenol(0-100 mg/L), the removal performance of nutrent fluctuated a little at the initial days of change phenol concentration and became stable gradually. Reactor has always maintained good denitrification and phosphorus removal effect and degraded the phenol completely. Phenol could not be used by PAOs and DPAOs at anaerobic phase to synthesis PHA. Both of the abundace and microbial diversity of the microbial community decreased when the concentration of phenol increased from o to 100 mg/L gradually. Proteobacteria and Bacteroidetes have always been the dominant phylum in the system. Thauera and Zoogloea, which were capable of degrading phenol, became the dominant genus of the microbial community successively, while the growth of them was inhibited slightly when the concentration of phenol reached 100 mg/L. In addition, Flavobacterium, Gracilibacteria norank and Candidatus Accumulibacter also had a certain resistance to phenol and played an important role in the system. |
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