| Aerobic granular sludge technology is an innovative biological wastewater treatment process for industrial and sewage wastewater treatment because of its characteristics such as compact sludge structure, excellent settling property and high biomass and microbial enrichment. However, as a special kind of microbial aggregates, aerobic granular sludge has issues such of easy to granular disintegration and unclear formation mechanism, which limits its industrial application. Focused on the granular characteristic, key components of EPS and functional microorganism, novel processes with effluent recycle and influent OLR regualtion are built in this thesis, and composition changes of EPS, succession of microbial community and identification of key functional microbes are studied during aerobic sludge granulation with technologies like illumine-masiq and qPCR. The main conclusions are as follows:1. In order to solve the problems of low OLR sewege wastewater and difficult sludge granulation, three SBR reactors were established to investgate the effect of effluent recycle and granular fragment addition on formation of aerobic granules. Compared with R1 (Blank), R2(Effluent recycle)and R3(Granule fragment addition) reactors achieved sludge granulation on 40d and 55d, repectively. The EPS contents increased from 104.83±11.87 mg-gVSS-1 to 127.65±9.31 mg·gVSS-1 and 179.88±15.77 mg·gVSS-1, and SVI reached 35 mL·g-1 and 45 mL·g-1, respectively. It was found that the granular sludge in R2 and R3 were more compact and had higher pollutants removal efficiencies. Results showed that excessive secretion of PS led to granular sludge disintegrated in R1 and R3, while R2 kept stable indicating that the effluent recycle favors the start-up and stability of aerobic granular sludge process.2. Researches on the succession of microbial communities in aerobic granule sludge processes showed that Proteobacteria gradually replaced Bacteroidetes during the sludge granulation and became the dominant bacteria. However, Bacteroidetes became the dominant specy again when system performance deteriorated significantly and lots of granular sludges were washed out in R1 and R3. Results showed that abundance of microbial communities in R2 kept increasing and Zoogloea spp. With function of EPS secretion was enriched in mature aerobic granules. Furthermore, signaling molecules such as C6-HSL, C8-HSL,3OC6-HSL and C12-HSL were also enriched in R2 indicating that the effluent recycle process can accelerate sludge granulation and favor stable operation by quorum sensing.3. The start-up and operation characteristics of aerobic granular sludge process with different influent OLR modes were studied. Results showed that the sludge in R1 (increased influent OLR) and R3 (stable OLR) floated on the top of reactor and was washed out in 55d and 40d, respectively. At the same time, the removal efficiencies of TN and COD decreased to below 87% and 54%, respectively. EPS analysis showed that the PS content increased significantly while PN/PS ratio decreased to below 0.60 which caused the sludge bulking and granular structural instability. In comparison, the sludge in R2 (decreased influent OLR) achieved complete sludge granulation in 35d and the structure of granule sludge was compact. The hydrophobic angle increased from 85.5° to 102.1° and the removal rate of TN and COD in R2 kept higher than 96% and 73%, respectively. EPS analyzing showed that the PN content increased significantly while PS content remained stable. The PN/PS ratio kept above 2.3 in R2, and efficient operation of aerobic granule sludge reactor was achieved finally.4.The microbial community of different OLR regulating processes were studied, and results showed that the microbial community structure in three reactors have significant difference, indicating that different OLR regulation processes lead to succession of different microbial community. In the inoculation sludge, Bacteroidetes accounted for 70.4%. Along with the sludge granulation, the proportion of Proteobacteria increased from 20.6% to 36.8%,41.2% and 37.9% while the proportion of Bacteroidetes decreased. When the granular sludge lost the stability in R1 and R3, the proportion of Bcteroidetes increased again, confirming that excessive Bacteroidetes proliferation does not favor the stable structure of aerobic granule sludge. It is worth noting that Zoogloea spp. and Thauera spp.which belong to Proteobacteria were enriched in R2. Thereinto, Zoogloea spp. favors sludge granulation by secreting EPS, while Thauera spp. has the ability of nitrogen and refractory organics removal. In summary, the novel processes with effluent recycle and influent OLR regulation could improve the formation and structural stability of aerobic granular sludge and fuctional microorganism enrichment... |
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