| The black-odorous river in rural areas has high nitrogen and phosphorus content,and its purification efficiency is insufficient,which can easily lead to the accumulation of black and odorous substances.Once the water environment condition change,pollutants released from polluted sediment will aggravate the deterioration of water quality.In order to solve the problems of limited effect and high cost during rural river sediment remediation,the study investigated the sediment pollution situation and distribution characteristics of typical rural river and analyzed,and evaluated the pollution status.Straw-based biochar had been innovatively applied to the sediment remediation and habitat construction of rural river,and the effects of straw-based biochar types,microbial adding methods and submerged plant species on sediment remediation have been explored.On this basis,the composite microecosystem of straw-based biochar,microorganisms,submerged plants and benthic animal was constructed and its dynamic remediation effect on sediment was explored.The main research conclusions are as follows:According to the investigation of the sediment pollution of rural river in China,TN,TP,and OM are generally at the level of severe pollution and have high ecological risk.Therefore,the ecological effect should be considered comprehensively in the remediation process.Bioecological technologies can be adopted to achieve sustainable optimization of the sediment quality.The effects of straw-based biochar,microorganism and submerged plant on sediment remediation were investigated.The results showed that the 200-mesh straw-based biochar promoted the nitrification and inhibited the release of nitrogen and phosphorus from sediment at the initial stage,but the release of nitrogen and phosphorus from biochar was obvious at the later stage.By investigating the effects of raw materials and particle size on nitrogen and phosphorus release,it was found that the TN release of corn straw biochar was only about 50%of that of rice and wheat.Compared with 200-mesh biochar,the nitrogen and phosphorus release of 50～100 mesh biochar decreased by more than 90%.After adding biochar immobilized denitrification bacteria,the removal rates of TN in overlying water and sediment were 58.56% and 70.07%,respectively,which were higher than adding biochar or denitrification bacteria separately.The submerged plants had a good removing effect on nitrogen and phosphorus in the overlying water.The concentration of TN decreased to less than0.7mg/L.The concentration of TP was less than 0.2mg/L.Vallisneria natans was the best for removal of nitrogen and phosphorus in overlying water,and the removal rates of TN and TP were 86.77% and 92.80%,respectively.Hydrilla verticillata was the best for phosphorus remediation of sediment,removal rates were 84.42%.A sediment-water interface microecosystem with corn straw biochar immobilized denitrification bacteria-Vallisneria natans and Elodea nuttallii-snail was constructed,and the dynamic remediation effect of the system was studied.The results showed that the microecosystem can effectively remove nitrogen and phosphorus pollution from sediment,and the removal rates of TN and TP in sediment were 77.40% and 54.91%,respectively.Within 90-day operating period,the sediment of TN,TP and OM with serious pollution levels can be remediated to light pollution,moderate pollution,and clean levels respectively.The microecosystem had a synergistic effect on the removal of nitrogen and phosphorus in the overlying water.The removal rates of TN and TP in the overlying water were 84.27% and87.55%,and the water quality was better than the limit of the Environmental Quality Standard for Surface Water(GB3838-2002)Ⅲ class water standard.Submerged plants increased the microbial diversity of sediments and the relative abundance of functional bacteria such as Verrucomicrobia. |
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