Development And Large Scale Application Of The Key Techniques For The Treatment Of Lake Sediments Contaminated By Heavy Metals

Hangu sewage reservoir is located in the Sino-Singapore Tianjin Eco-City and has been discharging the sewage for more than thirty years.The deposition of heavy metal leads to the serious environmental pollution of the reservoir sediments,which is a h?ge hidden danger to the human health in the surrounding area.The purpose of this project is to deal with the heavy metal contaminated sediments.The main aspects and conclusions were displayed as follow:1.The environmental investigation and risk assessment of the sediments.After the sediment sampling,the mechanical parameters,physicochemical properties of the sediment,and the content,speciation and spatial distribution of the pollutants in the sediment were determined.Furthermore,the risk assessment of the heavy metals in sediment was conducted.The results show that 29 pollutants are determined in the sediment,among them,the content of the Hg,As,Cd,Cu is higher than the values in the national standard.It is worth mentioning that part of mercury existed in methylmercury,which is highly harmful to the environment.Additionally,most of arsenic and cadmium is in the exchangeable and carbonate form,leading to release into water.2.The stabilization of heavy metals in the sediments.The stability of heavy metals in the presence of the different stabilizers,including calcium oxide,sodium sulfide,ferrous sulfate,disodium hydrogen phosphate,ES,and chitosan,was investigated.The results show that ES possess the good performance in the stabilization of heavy metals.At a 5% of the ES loading,pH 8,1.2: 1 of the ratio of liquid to solid,the stability ratio of Hg,As,Cd and Cu were 61.2%,87.7%,86.4% and 85.6%,respectively.Additionally,the speciation of heavy metal in sediments before and after ES treatment was measured.The results show that the percentage of the residual and oxidation state form increased after ES treatment,indicating the stability of heavy metals was significantly enhanced.3.Development and application of key techniques for the sediments treatment.The GIS-based spatial distribution library of heavy metals in the sediment was constructed.The precise dredging and the control strategy of secondary pollution were also proposed.Furthermore,the geotextile tubes-based dewatering technology was developed in the lab-scale and pilot scale.The packaged technologies featuring the environmental dredging,the stabilization of heavy metals during the pipeline transportation,and the dewatering of sediments using geotextile tubes were thus developed,which is successful applied to the dealing with the sediments in the Hangu sewage reservoir with a reduced capital investment.4.The environmental investigation and risk assessment of the sediment landfill.The pollutant in the leachate,groundwater,and atmospheric environment were determined.The results show that the content of pollutant is lower than the values in the national standards.The risk assessment results indicate that the probability of leachate leakage is very low,specially,which is above the level of once in a decade.Even if the leakage of leachate occurred locally,the level of both non-carcinogenic and carcinogenic risk is also acceptable.