Study On Heavy Metal Contaminated Soil In E-waste Dismantling Site Combined With Sludge High-temperature Treatment Residue And Plants

The irregular dismantling of electronic waste in my country in the early days caused ecological and environmental problems such as heavy metal pollution and vegetation destruction in the soil of the dismantling site.It is difficult for the soil to quickly restore vegetation depending on its own conditions.Sludge high-temperature treatment slag is a harmless product of sludge,which can be used as soil conditioner and heavy metal passivator,which not only realizes the utilization of sludge resources,but also provides favorable conditions for accelerating the restoration of soil vegetation.In this paper,two kinds of sludge high-temperature treatment residues（pyrolysis residue and aerobic fermentation residue）were taken as the research object,and the physical and chemical properties,organic matter and mineral composition were analyzed;then the soil of an electronic waste dismantling site in Taizhou City,Zhejiang Province was taken as the research object,through the pot experiment,the plants that can grow well in the soil were screened;based on the screening results,the pot experiment was continued to study the effect of applying two kinds of sludge high temperature treatment residues on soil properties and plant growth;finally through the toxicity leaching（Toxicity characteristic leaching procedure,TCLP）and fuzzy mathematics method were used to study the effect of heavy metal leaching and comprehensive improvement of soil after remediation.The main results are as follows:（1）The physical and chemical parameters were measured and characterized by infrared spectroscopy,three-dimensional molecular fluorescence spectroscopy and X-ray diffraction for the two kinds of sludge high-temperature treatment residues.The results showed that the sludge fermentation residue was acidic,mainly containing SiO₂ and MoS₂ crystal phases,which dissolved Fulvic acid-like and humic acid-like substances were detected in the organic matter,and their electrical conductivity,organic matter,available phosphorus,available potassium,total nitrogen content and infrared absorption peak intensity of oxygen-containing functional groups were higher than those of pyrolysis slag;Alkaline,mainly containing SiO₂,AlPO₄ and K（FeAl）₂（SiAl）₄O₁₀（OH）₂ crystal phase,humic acid-like substances were detected in the dissolved organic matter,and its carbon-hydrogen ratio and heavy metal content were higher than those of fermentation residue;The pH,moisture content,organic matter and heavy metal content of the two kinds of sludge high-temperature treatment residues all meet the requirements of"Mud Quality for Land Improvement for Sludge Disposal in Urban Sewage Treatment Plants"（GB/T 24600-2009）,which can be used in saline-alkali land and sandy land.and requirements for soil improvement in abandoned mines.（2）For the soil of the dismantling site of electronic waste,a pot experiment（30 days）was arranged to observe ryegrass（Lolium perenne Linn.）,vetiver（Vetiveria zizanioides（Linn.）Vach）,Shanghai green（Brassica chinensis Linn.）),Leek（Allium tuberosum Rottler ex Spreng.）,Amaranth（Amaranthus spinosus Linn.）,Nepeta cataria Linn.,Elsholtzia splendens Nakai ex F.Maekawa,Chicory（Sonchus oleraceus Linn.）),the growth of shepherd’s purse（Capsella bursa-pastoris（Linn.）Medic.）and dandelion（Taraxacum mongolicum Hand.-Mazz.）.The results showed that seven species of leek,amaranth and nepeta had few buds,slow growth or pathological growth.Ryegrass,vetiver and Shanghai green have a large number of buds and grow rapidly,and can be used as pioneer plants for vegetation restoration in polluted sites.（3）For the soil of the dismantling site of electronic waste,a pot experiment（45 days）was arranged to explore the effect of applying two kinds of sludge high temperature treatment residue on soil properties,heavy metal migration and transformation and plant（rye grass,vetiver grass,Shanghai green）growth Impact.The results showed that:overall,compared with the control,the two sludge high temperature treatments significantly（P<0.05）increased soil conductivity（32%-218%）,cation exchange capacity（33%-84%）,organic matter（17%-218%）%～36%),available phosphorus（142%～245%）and available potassium（40%～96%）;increased soil Cu（14%～20%）,Zn（9%～20%）,Pb（10%-18%）and Cd（6%-11%）in steady state;significantly（P<0.05）increased plant fresh weight（32%-101%）,plant height（18%-30%）,phosphorus uptake（33%～48%）and potassium uptake（22%～45%）;significantly（P<0.05）decreased plant Cu（8%～34%）,Zn（5%～12%）,Pb（17%）～32%)and Cd（30%～38%）enrichment;inhibited the ability of plants to transport heavy metals from underground to shoots;new heavy metal crystalline phases were detected in soil,and detected in soil dissolved organic matter Humus composition.（4）The leaching amount of heavy metals and the soil improvement effect of the nine treatments were comprehensively evaluated by the toxicity leaching test（TCLP）and the construction of the fuzzy membership function for the soil after two kinds of sludge high-temperature treatment residues and plants.:The two sludge high-temperature treatment residues reduced the TCLP leaching amount of Cu（11%-19%）,Zn（8%-20%）,Pb（7%-15%）and Cd（5%-17%）,However,it is still over the GB/T 14848-2017".Overall,the comprehensive effect of fermentation residue on soil improvement is better than that of pyrolysis residue.To sum up,ryegrass,vetiver grass and Shanghai green can be used as pioneer plants for soil vegetation restoration at e-waste dismantling sites.Although there are differences in the properties and soil remediation effects of the two kinds of sludge high-temperature treatment residues,they both promote the improvement of soil quality,the stabilization of heavy metals and the growth of plants to a certain extent,and have the potential to be combined with plants for ecological restoration of soil.Since the leaching amount of heavy metal TCLP in soil after remediation still exceeds the category IV index stipulated in my country’s GB/T 14848-2017"Groundwater Quality Standard",further research is required.