| At present,most municipal wastewater treatment plants have some shortcomings,such as high aeration,high sludge product and high CO2 emission.With the continuous improvement of Energy Conservation and Pollution Emissions Reduction requirements for wastewater treat-ment plants in China,it is urgent to reduce the energy consumption of wastewater treatment.Microaerobic biological wastewater treatment technology can effectively reduce aeration and sludge production by controlling the dissolved oxygen concentration to 0.3-1.0 mg/L,and enriching activated sludge with multiple functional bacteria to treat carbon and nitrogen pollu-tants in wastewater,microalgae can assimilate nutrients such as CO2 and NH4+-N in wastewater through photosynthesis,then synthesize their own cellular material and release O2.Microalgae and bacteria symbiosis wastewater treatment system came into being.In view of the problems of poor stability and difficulty in harvesting microalgae in the wastewater treatment system with microalgae and bacteria symbiosis,a new microalgae aeration and reflux coupled with micro-aerobic sludge blanket(MMSB)was constructed in this study,which was a separate microalgae and bacteria symbiosis system and can realize the attachment and film formation of microalgae,reduce the difficulty in harvesting microalgae,as well.The effluent of microaerobic sludge blanket was deeply removed of carbon and nitrogen pollutants by microalgae,and a part of reoxygenation water after microalgae photosynthesis was back-flowed to the microaerobic sludge blanket to supply oxygen.The dissolved oxygen gradient in the reactor can lead to shortcut nitrification,ANAMMOX and partial denitrification.The process realized independent control of microalgae and activated sludge functional flora,and microalgae had dual functions of oxygen supply and deep denitrification.In this study,the feasibility of microalgae reoxygenation was investigated around the new MMSB process.The microaerobic sludge blanket(MSB)was started under different C/N ratios,and the effects of pollutant removal,sludge performance and changes of flora structure were analyzed.The MMSB was constructed to investigate the pollutant removal effect、changes in the performance of sludge and microalgae under different C/N ratios as well as analyze the changes in the bacterial community structure and the carbon and nitrogen removal mechanism.The results of microalgae aeration ability showed that the average oxygen production rate of high microalgae concentration(0.94 g/L)was the highest under 3000,5000,7000 and 10000 lux light intensity,which were 0.69,1.61,1.60 and 2.07 mg(O2)/(g(algae)·h)respectively.The MSB was started under the condition of municipal wastewater with different C/N ratios.when the influent NH4+-N concentration was 60 mg/L and the C/N ratio ≥5,the effluent NH4+-N and TN concentrations are lower than 5.40 mg/L and 9.41mg/L respectively.When C/N=5,the particle size of granular sludge was the largest,with clear outline and dense structure.The flora structure of seed and domesticated sludge was analyzed by high-throughput sequencing.NOB in domesticated sludge samples were inhibited and elutriated.The abundance of ANAMMOX bacteria,mainly Candidatus Kuenenia,was negatively correlated with C/N ratios,and the relative abundance were 0.55%,0.23%,0.13%and 0.03%,respectively.Heterotrophic denitri-fying bacteria decreased significantly in domesticated sludge,and with the increase of C/N ratios,the relative abundance were 5.73%,4.17%,5.43%and 6.13%,respectively.The results of MMSB operation under different C/N ratios showed that the pollutants were removed best after 15 days of operation,and the effluent NH4+-N and TN concentration were 6.87 and 16.51 mg/L,3.13 and 9.15 mg/L,7.82 and 9.33 mg/L and 4.37 and 5.92 mg/L,respec-tively,and the COD removal load were 0.05 and 0.16,respectively.However,in the subsequent operation,when C/N>5,microalgae grew too fast and produced self-shading,so the effects of NH4+-N and TN in effluent became worse.After 7 days of microalgae and bacteria coupling,the concentration of suspended microalgae in the pool decreased steadily by 40.00%,66.67%,76.27%and 84.48%respectively compared with the initial concentration,and the flocculation rate of microalgae on the filler increased from 44.18%to 88.25%,87.91%,80.96%and 78.06%respectively.The microbial flora analysis of sludge from microalgae and bacteria of nitrogen removal function coupling system showed that with the increase of C/N ratios,the abundance of hetero-trophic denitrifying bacteria gradually increased,while the abundance of ANAMMOX and autotrophic denitrifying bacteria gradually decreased.The main way of nitrogen removal was shortcut denitrification-ANAMMOX when C/N<5,while autotrophic-heterotrophic denitrifi-cation occurred when C/N=5,and the whole process nitrification and denitrification occurred when C/N=7.60.73%of COD was used for denitrification while only 9.03%was removed by carbon mineralization when C/N=1,which showed that the low C/N ratio microaerobic system made full use of organic carbon source.The ratio of nitrogen source consumed by sludge growth to influent reached the maximum at C/N=7,which was 5.93%. |
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