| In recent years,the effluent from wastewater treatment plants(WWTPs)containing high concentrations of nitrogen and phosphorus has been discharged into surface water constantly.At the same time,pharmaceuticals and personal care products(PPCPs)as one kind of emerging contaminants,also have been detected frequently in the WWTPs effluent,which seriously affect the safety of water ecology and drinking water health of human and livestock.Therefore,the research of enhanced biological treatment technology for nitrogen,phosphorus and PPCPs removal are urgent in the world.Aerobic sludge granulation is a novel wastewater treatment technology with promising features including compact granular structure,excellent setting ability and diverse microbial community,and has the advantages in enhanced removal of nitrogen,phosphorus and refractory organics.Several lab-scale sequencing batch aerobic bioreactors were built in this thesis,and the effect of COD/TN ratio on structure stability and nitrogen removal of aerobic granular sludge(AGS),typical PPCPs removal in AGS and its structural stability,and possible mechanism for synergistic nitrogen and PPCPs removal of AGS were studied using three-dimensional fluorescence spectroscopy(3D-EEM),laser scanning confocal microscope(CLSM),liquid chromatography-mass spectrometry(LC/MS),and high-throughput sequencing technology.The main results are as follows:1.The effect of COD/TN ratio on structure stability and denitrification performance of aerobic granular sludge was studied.The results showed that the phenomenon of uneven granular size distribution(Span value 6.53)with excessive proliferation of flocs and loose structure of large granules with excessive growth of filamentous bacteria appeared in the reactor operating under the condition of COD/TN 15,and eventually the performance deteriorated along with sludge washed out.In contrast,the average granular size of sludge in the reactor operating under reduced COD/TN from 15 to 5 increased to 647±28 ?m and the granular structure was dense.At the same time,the removal efficiency of COD and TN were stable at 98.5%and 75%,respectively.Analysis of sludge extracellular polymeric substances(EPS)showed that the ratio of extracellular protein(PN)and polysaccharide(PS)was maintained at 4.17-5.16 under low COD/TN condition,and the high levels of tryptophan protein,tyrosine protein and hydrophobic humic acid in sludge EPS were favorable for stable granular structure.Further analysis of sludge microbial community structure showed that the abundance of Proteobacteria in steady-state granular sludge of the reactor with low COD/TN ratio was 74.9%,and denitrifying microorganisms such as Paracccus spp.,Pseudoxanthomonas spp.,Rhodobacter spp.were enriched.The abundance of amoA,narG,nirS,nirK and nosZ maintained at higher levels,indicating that low COD/TN ratio favors the enrichment of denitrification microbes and stability of granular sludge.2.The effect of roxithromycin(ROX),sulfamethoxazole(SMZ)on the properties of aerobic granular sludge and their removal performance were studied.The addition of PPCPs significantly inhibited the growth of granular sludge in both reactors under high COD/TN condition,and the PS content of granular sludge increased and the granular structure tended to be loose.In comparison,the reactor operating under the condition of low COD/TN continued to be stable for more than 2 months after PPCPs addition,and the average granular sludge size reached 1268±21 ?m,and the abundance of tyrosine protein,tryptophan protein and hydrophobic humin acids in sludge EPS were relatively high,which maintained the stability of granular structure.The TN removal efficiency was also stable at 82.4±2.9%.The analysis of typical PPCPs removal performance of three reactors showed that the removal efficiency of ROX and SMZ in the reactor operating under low COD/TN ratio was 95.2±0.5%and 92.9±0.3%,respectively,which were obviously higher than those in the reactors with COD/TN 30(65.6±1.4%,62.9±0.6%)and COD/TN 15(74.5±2.3%,69.6±0.8%).Consequently,the granular sludge formed under the condition of low COD/TN has the better ability to resist the impact of PPCPs combined with higher PPCPs removal ability.Further analysis of sludge microbial community found that the abundance of Proteobacteria in the both systems with high COD/TN ratio decreased significantly with typical PPCPs addition,while the abundance of Proteobacteria in the granular sludge of the system with low COD/TN ratio gradually increased to 72.4%.At the genus level,the dominant bacteria in the granular sludge were Thauera spp.(31.4%),Rhodocyclaceae spp.(6.4%),Xanthomonadaceae spp.(5.8%),Sphingobacteriales spp.(4.3%)and Nitrospira spp.(3.2%),given the system better secretion of EPS,denitrification and PPCPs degradation.Comparatively,the proportions of Defluviicoccus spp.and Chryseolinea spp.increased in the presence of ROX and SMZ,which affected the stability of granular sludge.3.The removal of ROX and SMZ by aerobic granular sludge was mainly via sludge adsorption and biodegradation in batch experiments.Granular sludge formed under low COD/TN had higher biodegradability to ROX and SMZ,and the proportions were 39.1%and 42.1%,respectively.Combined with the previous results of granular characteristics,pollutant removal,EPS composition and dominant microbial community,the PPCPs removal was significantly correlated with nitrogen removal and PN content.At the same time,the aerobic granular sludge formed under the condition of low COD/TN could enrich Thauera spp.,Rhodocyclaceae spp.,Nitrospira spp.and other functional microorganisms for nitrogen removal and EPS producing,which favored the stability of granular sludge.Furthermore,the dominant microbes in the stable granular sludge cooperated with each other,and the synergistic removal of nitrogen and PPCPs could be realized by their cometabolism. |
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