In-situ Remediation Of River Sediment Based On Microhabitat Improvement

The sediment of rural river is affected by domestic sewage discharge and agricultural nonpoint source pollution,and the accumulation of nitrogen,phosphorus and organic matter is serious.When the external conditions change,the pollutants released from sediment will lead to the deterioration of river water quality.In view of the limited effects of existing sediment remediation technologies and difficulties in restoring aquatic ecosystems,this study enriched and cultured indigenous microorganisms in overlying water and sediment of river,and screened specific bacterial communities for typical pollutants.On this basis,micro-nano aeration technology was coupled with a microecological system composed of immobilized microorganism,submerged plant and benthic animals.The restoration effect of micro-nano aeration and microecosystem on overlying water and sediment in rural river was investigated,and the restoration mechanism was explored from the changes of submerged plants and the community structure of microorganisms.The main research conclusions are as follows:The COD degrading bacteria,nitrifying bacteria and denitrifying bacteria were screened from the overlying water and sediment of the river.The orthogonal test was used to compound the three bacteria,and the optimal dosage of different bacteria was determined by investigating the removal effect of pollutants.The results showed that the overall removal rate of pollutants reached the best when the overlying water cultured bacteria dosage was 2%,1% and 2%,respectively.The removal rate of pollutants reached the best when the sediment cultured bacteria dosage was 0.5%,0.5% and 0.5%,respectively.The micro-nano aeration and microecosystem restoration technology was constructed.The results showed that in the static release stage of sediment,the removal effect of TN and TP from overlying water in the micro-nano aeration and microecosystem group was obviously better than that in the other groups.The TN removal rate of overlying water in the stable stage(50-74d)was 85.88%,which could meet the requirements of class Ⅲ surface water,and TP could meet the requirements of class Ⅲ surface water after 10 days of operation.The micro-nano aeration and microecosystem could effectively reduce the nutrient and organic matter contents of sediment.After 90 days of remediation,the contents of TN and TP in sediment were reduced to 0.82 g/kg and 0.56 g/kg,respectively.TN and TP pollution level in sediment was restored from severe to mild,and TP pollution level was restored from severe to moderate.The organic matter content of sediment decreased from 1.59% to 0.54%,and recovered from severely polluted to clean level.After the microecosystem was constructed,the purification capacity of each group under the input of exogenous pollution was investigated,the results showed that at low concentrations exogenous pollution type(COD: 70.0 mg/L,TN: 3.37 mg/L,TP: 0.69 mg/L),the overlying water TN,TP removal effect of micro-nano aeration and microecosystem group was superior to the other group.The TN removal rate at the end of stage was 66.86%.At the end of the stages,TP concentration of overlying water was stable below 0.3 mg/L,which could satisfy the requirements of the class Ⅳ surface water.When high concentration of exogenous pollution was imported(COD: 107.5mg /L,TN: 13.11 mg /L,TP: 1.35 mg/L),the removal efficiency of TN and TP in overlying water was the best in micro-nano aeration and microecosystem group,and the removal rates were 88.79% and 85.61%,respectively.After 30 days of restoration,they all reached the requirements of surface Ⅳ water stably.In order to explore the mechanism of micro-nano aeration and micro-ecosystem restoration of rural river sediment,the changes of submerged plants and sediment microbial community structure during the restoration process were measured.The results showed that the soluble protein content in the micro-nano aeration and microecosystem group was significantly higher than other groups,and the malonaldehyde content was significantly lower than other groups.After treatment,the dominant bacterial community remained unchanged,but the relative abundance of Flavobacterium,Acinetobacter and Arcobacter,which have the function of nitrogen and phosphorus removal at the genus level,decreased,and the relative abundance of Thiobacillus,which can simultaneously reduce sulfur and nitrate of sediment,increased.The correlation analysis of microorganisms and environmental factors in the sediment showed that TN and TP contents had a significant effect on the microbial community structure at the genus level.Flavobacterium and Arcobacter were positively correlated with TP content,while Thiobacillus was negatively correlated with TN content.The results showed that the micronano aeration and microecosystem could change the microbial community structure by reducing the pollutant content in sediment.