| Remediation of black-stinking rivers is the key work to improve the urban water environment improvement.Effective control of endogenous pollution is very important when exogenous pollution is effectively intercepted.Dredging is the main means to repair the sediment pollution at present,which can effectively relieve the internal pollution load of the water body.However,the engineering cost is large,the dredging depth is difficult to grasp,and the sediment ecosystem is destroyed.Recently,the technology of in-situ ecological restoration of sediment,such as environment-friendly physical,chemical and nutritional preparations,has gradually emerged,which stimulating the purification ability of microorganisms to pollutants by improving the physicochemical and biological environment of sediment,thus restoring the ecological chain of water body and realizing the continuous recovery of water quality.In this paper,the characteristics of the bacterial community in five rivers with different levels black-stinking were compared by high-throughput sequencing technology,and the relationship between bacterial community composition and environmental factors was analyzed.Besides,the high-efficiency denitrifying bacteria were screened,and the composite microbial agents was constructed.Different chemical remediation agents and composite microbial agents are adopted to carry out in-situ remediation simulation test of the sediment,and comprehensive physical,chemical and biological methods were used to carry out in-situ remediation test of the black-stinking river sediment.The results are as follows:(1)The dominant phyla of sediment bacteria with different degrees of black-stinking were Proteobacteria(43.71%-60.14%),Chloroflexi(9.90%-19.22%)and Bacteroidetes(4.19%-10.42%).The dominant genus were Halomonas(8.76%-19.13%)and Pseudomonas(6.24%-13.08%).The relative abundance of Proteobacteria and Chloroflexi in the sediment of severe black-stinking rivers is higher than that of a slight black-stinking river,while Bacteroidetes showed the opposite trend.Potential deodorizing bacteria(Halomonas,Pseudomonas,Smithella etc.)widely exist in the sediment of black and stinking rivers,and the relative abundance of these microbial in the sediment of severe black-stinking rivers is higher than that of mild black and stinking rivers.The bacterial community structure and diversity of sediment with different levels of black-stinking are closely related to organic matter and nutrients.(2)The effects of Ca(NO3)2,CaO2,Na2S2O8 and remediation agent on the degradation of organic matter and the release of nitrogen and phosphorus were studied in sediment by laboratory simulation tests.The results show that:1)Different chemical remediation agents can reduce organic matter and total nitrogen in the sediment.After 56 days,the degradation rate of organic matter in sediments ranged from 12.94%to 24.42%,and the overall trend was Ca(NO3)2>CaO2>Na2S2O8>commercial remediation agent>blank,and the removal rate of total nitrogen ranged from 7.44%to 20.46%,and trend was CaO2>Ca(NO3)2>Na2S2O8>commercial remediation agent>blank,and the chemical remediation agent has no significant effect on the total phosphorus in the sediment.2)Different chemical remediation agents have different effects on the quality of the overlying water under short-term.COD and TP in the overlying water continued to rise with the addition of CaO2 and reached 69.2mg/L and 0.47mg/L after 56 days,which were 2.47 and 2.94 times of the blank group,respectively.Ca(NO3)2 obviously controlled the contents of COD and TP in the overlying water,but increased the content of TN,and TN was 10.39 times that of the blank group after 56 days.Na2SO8 can not only effectively reduce the TP of overlying water in the early stage,but also maintain a high DO level continuously.Remediation agent can inhibit the release of organic matter and nitrogen from sediment,and generally reduce COD and TN in overlying water.In general,the addition of Ca(NO3)2 and CaO2 has a better effect on the in situ repair of sediment.(3)Three strains of high-efficiency denitrifying bacteria were screened from river sediments,which were identified by molecular biology and the highest similarity with Acinetobacter(K38,K42)and Pseudomonas(K99),respectively,and these microorganisms and Lactobacillus are combined into a composite microbial agent.Furthermore,the remediation effect of combined chemical remediation agent and composite microbial agent on sediment was analyzed.The results showed that:1)The combined application of compound microbial agent and chemical remediation agent can promote the reduction of organic matter and total nitrogen in the sediment.Compared with the commercial microbial agent,the removal efficiency of the composite microbial agent to the total nitrogen in the bottom mud is increased by 13.82%?29.70%,but the degradation ability to the organic matter is decreased.In a simulated experiment,the composite microbial agent reduces the pH and DO of the overlying water and improves the NH4+-N level of the overlying water.2)Compared with Ca(NO3)2 and Ca(NO3)2+Na2S2O8,Ca(NO3)2+CaO2 group is more effective to promote decomposition of sediment organic matter,and the degradation rate of organic matter is increased by 3.53%?14.48%and 41.52%?65.54%respectively compared with the other two groups when combined with two kinds of microbial agents respectively.3)The removal efficiency trend of chemical remediation agent to total nitrogen in sediment is as follows Ca(NO3)2+CaO2>Ca(NO3)2>Ca(NO3)2+Na2S2Os,and chemical remediation agents have little effect on phosphorus content in sediment.4)Compared with Ca(NO3)2,the Ca(NO3)2+CaO2 and Ca(NO3)2+Na2S2O8 reduced the TP level of the overlying water in the early stage,but increased the levels of TP and NH4+-N of the overlying water in the later stage,and increased the levels of COD in the whole experimental period.In general,the adding mode of Ca(NO3)2+CaO2 combined with compound microbial agents is better in situ remediation effect on sediment.(4)Treatment of black-stinking river was carried out by using chemical combined biological in situ sediment repair method,and supplemented by zeolite,artificial aeration and other materials and technical means.The results showed that:1)these measures have effectively eliminated the black-stinking phenomenon in the rivers.After 30 days treatment,NH4+-N,TN,TP and COD of overlying water decreased from 2.53 mg/L,19.47 mg/L,11.27 mg/L and 173.67 mg/L to 1.22mg/L,2.11mg/L,0.33mg/L and 24.13mg/L,respectively,and TP of the overlying water continued to decrease after 90 days,while the other indexes recovered but were still significantly lower than the pre-treatment level;2)Available Phosphorus and NH4+-N in the sediment increased significantly after treatment,and increased from 20.93 mg/kg and 24.42 mg/kg to 135.53 mg/kg and 128 mg/kg,respectively.And other physical-chemical indicators in sediment showed an increase-decrease trend in the whole process.The increase of Available Phosphorus and NH4+-N in sediment has little effect on water quality,indicating the application of zeolite and sediment remediation agent may inhibit the release of nitrogen and phosphorus from sediment to overlying water.3)The dominant phyla of sediment bacteria in the whole process were Proteobacteria(47.72%-77.67%)and Chloroflexi(7.89%?19.21%).The relative abundance of Proteobacteria continued to increase with prolonged the treatment time,while Chloroflexi showed the opposite trend.Halomonas(11.97%-40.76%)and Pseudomonas(9.04%?28.30%)were the dominant genus in the process of treatment,and their relative abundance was significantly increased. |
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