| Since the discovery in aerobic up-flow sludge blanket reactor in 1990s, aerobic granular sludge has drawn worldwide attention due to its adavantages of compact structure, excellent settling ability, high biomass retention, and enrichment of multi-functional microorganisms. However, the long sludge granulation period and unstable granular structure are the bottlenecks which limits its industrial application. In order to optimize granular size distribution and reduce energy consumption, the effects of different pore sizes of internal screen and mode of aeration device setting on the performance of aerobic granular sludge process are studied in this paper. At the same time, the microbiological mechanism of enhanced aerobic granluar sludge process is revealed. Main conclusions are as follows:1. Four sequencing batch reactors were built to explore the effect of pore sizes of internal screen on the performance of aerobic granular sludge reactor. Thereinto, R1 was the control group without the screen, while R2, R3 and R4 were imbedded with screens of 1.5 mm,2.5 mm and 3.5 mm pore size, repectively. After 120 days of operation, R3 achieved the highest sludge concentration (MLSS of 8.2±0.1 mg·L-1) and best settling ability (SVI of less than 30mL·g-1), and the mean granular diameter in R3 was 1850±28um. R2 had a lower MLSS of 6.1±0.2 mg·L-1 and the mean diameter of granular sludge was 900±19μm, while R1 and R4 collapsed due to the granule broken. For the pollutant removal, removal efficiencies of COD, NH4+-N and TN in R3 were 96.1±1.6%,98.6±0.8%, and 83.9±1.2%, and R2 had lower removal efficiencies of COD, NH4+-N and TN. In R1 and R4, removal efficiencies of COD, NH4+-N and TN were only 73.4%-75.5%,25.6%-40.3%, and 22.4%-28.2%, respectively.Results of nitrogen vatiation during one cycle showed that influent NH4+-N was almost degraded after 120 min, while NO3--N was accumulated at different levels in four reactors. R3 had the minimum accumulation ammount of NO3--N (2.3±0.1mg·L-1), and there were 8.1-13.4 mg·L-1 in the other reactors. TN removal efficiencies were as follows:R3(83.9±1.2%)>R2(75.6±1.6%)>R1(65.3±1.7%)> R4(22.4±3.1%), suggesting size control, simultaneous nitrification and denitrification (SND) were achieved in R3 with internal screen of 2.5mm pore size.2. In order to reduce energy consumption and increase pollutant removal efficiency, three reactors with 2.5mm screen were built with different modes of aeration device setting. Compared with R1, R2 had better pollutant removal efficiency and increasing velocity. TN and NHU+-N removal efficiencies in R1 were 82.3±0.3% and 98.5±0.1%, while there were 83.1±1.1% and 99.1±0.2% in R2 on day 20, respectively. Mean diameter and bottom diameter analysis indicated that bigger granules were withhoeld in the bottom of R2, speeding up the granulation process. These results showed that the new aeration strategy in R2 has high efficient pollutant removal and enegy-saving.The analysis of oxygen saturation of different position in three reactors showed that oxygen saturation reached 37.2±0.5% in the bottom of R1, while it was completely anaerobic in the bottom of R3. And in the bottom of R2, oxygen saturation reached 20.1±0.1%, which was the optimal oxygen saturation for SND. Aeration consumption in three reactors were 17.25W,14.60W and 11.55W, respectively. Aeration comsumption in R2 was only 66% of that in R1, and results showed that the new aeration strategy in R2 was high efficient and enegy-saving.3. The analysis of microbial community in four reactors with different pore sizes of screen showed that R3 had the rishest species of microbial community, which has Shannon index of 6.91. Analysis of the microbial community structure showed that Proteobacteria and Bacteroidetes were the dominant microbes in four reactors. Proteobacteria had increased from 40.2% of seed sludge to 59.6%,59.0%,70.2% and 42.1%, respectively. Bacteroidetes had varied from 35.4% in seed sludge to 29.8%, 20.3%,17.4% and 40.3, respectively. Heatmap analysis of major microbes illustrated that there was 50.5% proportion of Zoogloea spp.,6.1% of Thauera spp. and 3.6% of Paracoccus spp.. Furthermore, high content of Leadbetterella spp. was found in R1 and R4, reaching 15% and 35%. Its enrichment often leads to granule collapse due to excessive polysaccharide secretion.The analysis of microbial community succession of aerobic granular sludge reactor with optimal aeration strategy showed that its Shannon index was 6.83. Proteobacteria was the dominant microbe, with the proportion of 74.5%. Heatmap showed that the proportion of Zoogloea spp. was 40.4%, and an obvious enrichment of Paracoccus spp., was observed. It’s indicated that the new aeration strategy had created facultative anaerobic condition which favors the growth of Paracoccus spp.. The proportion of Thauera spp. also had noteble increase from 2.6% to 7.9%. The directional enrichment of these functional microbes could increase granular stability as well as pollutant removal efficiency.Focused on granule size optimization and energy-saving., the optimal operation condition with the addition of screen and different aeration mode was developed for enhancing granule stability and pollutant removal. At the sme time, the microbial mechanism was also explored, providing theoretical support for the full-scale application of aerobic granular sludge process. |
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