Research On In-situ Remediation Of Urban River Sediment Based On Oxygen Mass Transfer Membrane

River sediment pollution is the most important endogenous pollution of black and odorous rivers,and its treatment plays a vital role in the regulation of black and odorous water bodies and the optimization of urban environment.In this paper,the oxygen mass transfer membrane has the characteristics of low-pressure and bubble-free oxygen mass transfer,and it is applied to the treatment of urban river sediments,which can avoid the internal source pollution of the river caused by bubble aeration.The oxygen mass transfer membrane continuously provides oxygen to the sediment around the membrane,improves the microenvironment of the sediment,and can also avoid secondary pollution caused by sediment disturbance.This paper first conducts surveys on urban river sediments,detects the total nitrogen and organic matter content of the sediments,and conducts a risk assessment on the urban river sediments.Secondly,two oxygen mass transfer membranes A and B with different membrane filament intervals and membrane filament amounts were used to treat the sediment,and the blank group C was not treated.Analyze the changes in sediment properties before and after treatment,the diversity and community structure of sediment microbial species,and the changes in overlying water pollutants.Finally,observing the law of static release of pollutants from the improved sediment to the overlying water and the removal effect of pollutants on the overlying water when subjected to high-concentration pollution loads,the conclusions are as follows:(1)Among the thirteen river sections sampled,the proportions of river sections with sediment total nitrogen content less than 1500mg/kg,1500mg/kg～3000mg/kg,3000mg/kg～5000mg/kg,and more than 5000mg/kg were respectively 23%,46%,23%and 8%.The proportions of river sections with sediment organic matter content lower than 1%,1%-2% and higher than 2% were 46%,15% and 39%,respectively.As for the risk assessment of sediment pollution,77% of the river section is heavily polluted by total nitrogen;there is one section of river heavily polluted by organic pollution.(2)The oxygen mass transfer membrane continuously supplies oxygen to the sediment through 40 days,and the removal of organic matter and total nitrogen in the sediment by the oxygen mass transfer membrane with different membrane filaments is not much different.The reduction rates of sediment organic matter in the experimental group A,B and blank group C devices were 35%,31.4%,and 5.6%,respectively.The reduction rates of total nitrogen in sediment were 22.3%,17.8%,and 6%,respectively.The color of the bottom mud in the experimental group changed from black to yellow,and the smell changed from pungent smell to earthy smell.The color and smell of the blank group did not change significantly.The number,richness,and principal components of the sediment microbial communities in the experimental groups A and B were similar,and the similarity with the sediment microorganisms in the blank group C was low.The proportion of obligate aerobic bacteria in the sediments in A and B was equal higher than C.(3)By monitoring the static release pattern of pollutants after the improvement of the substrate,it was concluded that the dissolved oxygen content of the overlying water in the three devices A,B and C reached 7.25 mg/L,4.88 mg/L and 2.27 mg/L,respectively,within 20 days,and the release rates of total nitrogen,ammonia nitrogen,COD and total phosphorus from the improved substrate in device A were the slowest,followed by the substrate in device B.The release rates of total nitrogen,ammonia nitrogen,COD and total phosphorus from the substrate in device C were the fastest,The release rate of total nitrogen,ammonia nitrogen,COD and total phosphorus was the fastest in plant C.(4)When the oxygen mass transfer membrane supplies oxygen to the sediment with high pollution load,the dissolved oxygen level in the overlying water is at a low level.The removal rates of COD,ammonia nitrogen and total phosphorus in experimental groups A and B can reach more than 80%,but the removal rate of total nitrogen is low.Combining the oxygen mass transfer membrane with the microbial agent to enhance nitrogen removal,compared with before adding the agent,the total nitrogen removal rates of A and B devices before adding the agent were 74.8% and66.3%,and after adding the agent,the A and B devices The removal rates of total nitrogen in the overlying water were 95.4% and 88.8%,which were increased by 20.6%and 22.5% respectively.The oxygen transfer membrane continuously provides oxygen molecules to the surrounding substrate,which improves the microenvironment of the substrate,not only can effectively avoid endogenous pollution caused by bubble aeration disturbance,but also enhances the degradation ability of the substrate pollutants,and the microbial community of the improved substrate has changed and can maintain a better health state after stopping oxygen supply,which is important for the in-situ restoration of river substrate.