| As the main form of surface waters,the water source reservoir has been identified an important source of drinking water.Eutrophication is the most serious problem of the water pollution,and nitrogen is one of the most critical factors that lead to eutrophication.In this paper,high-efficiency aerobic denitrifier communities were isolated and screened from the sediments fetched from Lijiahe Reservoir.Community composition,denitrification characteristics and nitrogen balance of the communities were analyzed.Response surface methodology was used to construct the nitrogen removal model of the aerobic denitrification bacteria to obtain the optimal nitrogen removal efficiency.The combination of aerobic denitrification technology and immobilization technology explored the effect of immobilization system on the denitrification efficiency of aerobic denitrifier communities.The main conclusions were shown as the following:(1)Three groups of oligotrophic aerobic denitrifier communities A1,A2,and A3 were successfully screened from reservoir sediment.Illumina MiSeq PE300 high-throughput DNA sequencing was used to analyze the composition of the bacterial group.The results showed that the structural composition of the A2 was most complicated.The dominant bacteria of the three groups of mixed bacteria were all Pseudomonas,accounting for 83.65%,73.00%,and 93.30%,respectively.The results showed that the three groups of bacteria could remove nitrogen with high efficiency.After 18 h of reaction,the nitrate-nitrogen removal rates of the mixed flora A1,A2,and A3 were 93.44%,90.06%,and 91.35%,respectively,and the total nitrogen removal rates were 51.96%,47.88% and 50.21%,respectively.There was no accumulation of nitrite nitrogen observed during the entire denitrification process.(2)Explore the nitrogen conversion pathways of aerobic denitrifying bacteria in the process of denitrification.According to the principle of conservation of quality,about 45%,44%,and 46% of the nitrate-nitrogen in the mixed bacteria A1,A2,and A3 were removed as gas product.The single-factor experiment results showed that the best carbon sources for the three groups of aerobic denitrifier communities were sodium acetate and sodium succinate.Under low temperature or weakly acidic environment,the nitrogen removal efficiency was suppressed.The change of dissolved oxygen had no obvious effect on the aerobic denitrification process.(3)Response surface method was used to determine the optimal conditions of aerobic denitrification mixed bacteria denitrification.The optimal condition for the oligotrophic mixed flora A1 were carbon-to-nitrogen ratio 9.96,temperature 22.69°C,shaking speed with 91 r/min,initial p H value 8.01;optimal conditions for flora A2 were carbon-nitrogen ratio 10.05 and temperature 24.00°C,shaking speed with 103 r/min,the initial pH value was 8.14;the optimal operating conditions for the mixed flora A3 were carbon-to-nitrogen ratio with 10.27,temperature with 29.90°C,shaking speed with 57 r/min,initial pH value 8.40.(4)Immobilization technology enhances the denitrification characteristics of aerobic denitrification bacteria.The results of scanning electron microscopy showed that the three groups of aerobic denitrification mixed bacteria were well fixed on the surface or inside of the four carrier materials.Under the same volume conditions,the amount of microorganisms on the carrier was greater than that under free conditions;Recycle and tolerance experiments of the immobilization system showed that the combination of loofa sponge and polyvinyl alcohol(PVA)had the best effect among the four carrier materials,and the carrier material can buffer and protect the three groups of highly effective aerobic denitrifier communities under low temperature and weakly acidic conditions. |
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