| China has been a primary electrical waste(e-waste) importing country where the pollution of e-waste has exerted harmful impacts on environment and human health. Based on the background above, the river sediments in proximity of one of the major e-waste dismantling areas-Longtang Town in Qingyuan City, were sampled and analyzed. First, indexes including the basic physicochemical properties, heavy metal contents and concentrations of polychlorinated biphenyls(PCBs) of the sediment were determined and then an ecological risk assessment around these indexes was made. Moreover, aiming at the combined contamination of heavy metal and PCBs in practical sediment, impact of sulfate reducing bacteria(SRB) on heavy metal species formation in anaerobic environment was studied, along with the impact of different strengthening methods on dechlorination of PCB153 by anaerobic microorganisms.(1)The results show that the organic content of sediment increased as it went deeper from 0 to 30 cm but with small variation around the value of 2%, while for the heavily contaminated drainage spot 1 and 2, the organic content reached 11.73% and 11.34%, respectively. The concentration of SO42-in the spot flanked the river was 320 mg·kg-1 and the contents of Cd, Pb and Zn manifested extremely ecological toxicity with high RI value more than 5000, besides the high concentrations of Ca2+ and Mg2+ may compound the situation of increasing the concentrations of available heavy metals. In superficial layer zone(0~40 cm), the concentration of PCBs increased with the decrease of depth, ranging from 0.36 μg·g-1 to 3.160 μg·g-1 and 3~5 chlorine congeners accounted for about 70%. Two risk assessment methods yield the identical results that the ecological risk of this PCBs contaminated zone is more than 50% and the toxic risk is relatively high.(2) The results of heavy metal affected by SO42-of different concentrations are listed as follows. After anaerobic incubation, the species of Cu, Pb, Zn and Cd were all transformed, while no change was observed in sterile treatment. Furthermore, for the naturally anaerobic treatment, the transformation ratios of Cu, Pb, Zn and Cd from unstable forms to stable ones were 7%, 5%, 11% and 5%, respectively. Compared to the naturally anaerobic treatment, the impact of SO42-addition on the heavy metal transformation ratios was in the order of Cu>Cd>Zn>Pb. After 28-day anaerobic incubation, there were relatively large changes of risk for Cu and Zn but not for Pb and Cd. When SO42-concentration was 660mg·kg-1, the ecological risks of Cu and Zn were decreased from high level to middle level. And the ecological risk of Pb was also decreased, but it remained in the middle level. Although the amount of Cd was small, however, it possessed very high ecological risk due to its high concentration of acid-soluble form. Apart from the above chemical analysis, methods of molecular biology were also applied to detect the content of SRB, which proved its important role in the process of heavy metal species transformation.(3) Although after one and a half year incubation, the dechlorination process of PCB153 under different strengthening methods was not that obvious. The degradation rate of PCB153 were 6%, 10%, 9.5%, with sodium lactate, VFA, ZVI. The degradation rate were 7.5% adding 4,4-BB. Thus it needs further investigation. |
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