| With the development of industrial economy, the society is under increasing pressure of resource shortage. Hence, electrical and electronic waste (e-waste) dismantling industry grows rapidly in the last century. However, the irrational industrial distribution and backward dismantling technique has caused serious pollution to the environment and high risk to human beings and the ecosystem. Therefore, it is necessary to conduct a thorough investigation of e-waste dismantling contaminated sites and develop applicable soil remediation technologies to deal with this type of contaminated sites.A typical e-waste dismantling contaminated site in southeast China was chosen as the research subject. A site investigation and health risk assessment was conducted according to the "Site Environmental Investigation Technical Guideline" (HJ25.1-2014) and "Contaminated Site Risk Assessment Technical Guidelines" (HJ25.3-2014). Then, soil was collected from the site for further research. By composting the artificial organic pollutants-heavy metals contaminated soil in a lab-scale, the transformation and degradation of organic pollutants and heavy metals were studied. At last, a pilot-scale site remediation experiment was conducted. The main results and conclusions are as follows:(1) Site investigation results show that there is serious organic-heavy metals contamination in the topsoil of this site. The concentration of certain pollutants has exceeded the criterion value according to the "Technical Guidelines for risk assessment of contaminated sites in Zhejiang Province" (DB33/T 892-2013), which means the risk assessment should be done. According to the risk assessment, polychlorinated biphenyl (PCBs) and copper have the highest risk. And the highest cancer risk and hazard quotient value were 1.69×10-4 and 122 respectively, which exceed the acceptable level. Therefore, this site needs to be restored.(2) The lab-scale composting experiment was conducted. It was found that indigenous soil bacteria of this site has a strong ability of degradatiing PCB28 (2,4,4’-Trichlorobiphenyl) and phenanthrene. After 120 days of natural composting, PCB28 had a rate of 80.5% reduction, phenanthrene 71.2%. Turning, adding organic fertilizer and degradating bacteria promoted the degradation of highly chlorinated PCBs and pyrene significantly. In the natural composting treatment, PCB52 (2,2’, 5,5’-Tetrachlorobiphenyl) removal rate was 32.6%, and pyrene was 65.5%, while that was 41.3%(PCB52) and 89.4%(pyrene) in the strengthened composting treatment. In addition, the composting system will change the bioavailability of contaminants, adding degrading bacteria and manure improved biological effectiveness ratio of PCBs by 19.5%, while the blank treatment only increased 4.1%. Composting treatment can reduce the bioavailability of heavy metals in the soil, thereby reducing its risk. Adding manure composting can increase the content of non-bioavailable Pb and Cu significantly.(3) Based on the results of the lab-scale experiment, a small plot of this e-waste contaminated site was selected to conduct a pilot-scale composting experiment. The concentration of PCBs in this area is 0.88 mg/kg, higher than the restoration target value (0.23 mg/kg). The results show that the static strengthened composting technology can effectively remove PCBs, after 195 days of composting treatment, the total PCBs was reduced to 0.22 mg/kg with an removal rate of 79.2%.Based on these studies, composting bioremediation is a potential technique to be applied in brown field soil remediation in e-waste recycling areas. |
