Mercury Enrichment And Transfer Of Several Herbs And Application Of Mercury-contaminated Soil Remediation

Mercury-contaminated soil has great harm to human beings and other animals and plants. Mercury in the soil may also enter the aquatic ecosystem to pollute the water body and the aquatic organism. So the remediation of mercury-contaminated soil is a problem all over the world. Phytoremediation of heavy metal contaminated soil has the advantages of low investment, simple operation, no secondary pollution, in situ remediation, potential or significant economic benefits. Green phytoremediation has good social and ecological benefits. The results of the treatment of heavy metal contaminated soil are permanent, which meets the requirements of environmental protection. Phytoremediation technology will become a sunrise industry in the field of environmental protection in the future. Preliminary screening of plants of phytoremediation for mercury-contaminated soil and the application of phytoremediation have been studied in the paper. The aim is to find a kind of plant with strong ability of enrichment and translocation of mercury, to explore ways of promoting the effect of phytoremediation for mercury-contaminated soil and reduce the time of remediation, and to explore the prevention measure of volatile mercury secondary pollution in the phytoremediation process. Important scientific basis and technical support for phytoremediation for mercury-contaminated soil has been provided by the paper. The main research conclusions in the paper are as follows:(1) In the Hoagland medium experiment, only the absorption amount of mercury by shoots(stem+leaf) is larger than the absorption amount of mercury by roots of Oxalis corniculata. The transfer rate of Hg by Oxalis corniculata is the largest of five plant species under the same condition. Mercury translocation rates of the same plant species are different in the medium with different concentrations of mercury. Opuntia stricta and Aloe vera are most suitable for accumulating and transferring 2?g/L Hg. Setcreasea purpurea, Chlorophytum comosum, Oxalis corniculata are most suitable for accumulating and transferring 10?g/L Hg. In the Hoagland culture, the chemical accelerator Na2S2O3 can not promote the plant to absorb the absorbed mercury, but have a certain inhibitory effect.(2) In the experimental time period, normal watering is most conducive to the growth of Aloe vera; Lv Yebao is most conducive to the growth of Setcreasea purpurea; normal watering is most conducive to the growth of Chlorophytum comosum; normal watering occasionally using Green cake fertilizer is most conducive to the growth of Oxalis corniculata. Oxalis corniculata has strongest resistance to mercury; Aloe vera and Setcreasea purpurea have strong resistance to mercury; the resistance to mercury by Chlorophytum comosum is poor.(3) In this study, the polluted soil is weak acidity and the mercury in the soil is mainly in the residual state, however, the exchangeable content is the least. In the soil without chemical accelerator, the absorption amount of mercury by roots is more than the absorption amount of mercury by shoots of Aloe vera, Setcreasea purpurea and Chlorophytum comosum after 60 days. Only the absorption amount of mercury by shoots(stem+leaf) is larger than the absorption amount of mercury by roots of Oxalis corniculata after 60 days. The maximum transfer rate of Hg by Oxalis corniculata is 128.16%, however, the transfer rate of Hg by other three plant species is far less than Oxalis corniculata. Only the enrichment coefficient of Hg by Oxalis corniculata is more than 100% after 60 days comparing other three plant species. The maximum enrichment coefficient of Hg by Oxalis corniculata is 136.67% after 60 days. With the extension of the time of planting in the soil, the residual rate of mercury in soil decreased continuously. The residual rate of mercury in soil by four plant species after 60 days is: Oxalis corniculata(81.73%)<Setcreasea purpurea(81.78%)<Chlorophytum comosum(83.52%)<Aloe vera(88.77%). The residual rate of mercury in soil by Oxalis corniculata is lowest with best repair effect. The absorption amount of mercury in soil adding EDTA?DTPA?Na2S2O3 and(NH4)2S2O3 by roots and shoots of four plant species all increases after 60 days. It shows that the chemical accelerator is beneficial to the absorption of mercury by four plant species and good for phytoremediation. Na2S2O3 is the most favorable for phytoremediation of all the four kinds of chemical accelerator.(4) The study analyses the dominant species of rhizosphere microorganisms according to different standards from Kingdom, Phylum, Class, Order, Family and Genus. The dominant species of Oxalis corniculata rhizosphere microorganisms in soil adding EDTA is k__Archaea; p__Crenarchaeota; c__Thaumarchaeota; o__Nitrososphaerales; f__Nitrososphaeraceae; g__Candidatus. The dominant species of rhizosphere microorganisms in background soil is k__Archaea; p__Crenarchaeota; c__Thaumarchaeota; o__Nitrososphaerales; f__Nitrososphaeraceae; g__Candidatus. The dominant species of Oxalis corniculata rhizosphere microorganisms in soil adding Na2S2O3 is k__Archaea; p__Crenarchaeota; c__Thaumarchaeota; o__Nitrososphaerales; f__Nitrososphaeraceae; g__Candidatus. The dominant species of Oxalis corniculata rhizosphere microorganisms in soil without chemical accelerator is k__Archaea; p__Crenarchaeota; c__Thaumarchaeota; o__Nitrososphaerales; f__Nitrososphaeraceae; g__Candidatus. The dominant species of Oxalis corniculata rhizosphere microorganisms in soil adding(NH4)2S2O3 is k__Bacteria; p__Bacteroidetes; c__Cytophagia; o__Cytophagales; f__Cytophagaceae; g__. The dominant species of Oxalis corniculata rhizosphere microorganisms in soil adding DTPA is k__Bacteria; p__Bacteroidetes; c__Cytophagia; o__Cytophagales; f__Cytophagaceae; g__. The microbial diversity index of Oxalis corniculata rhizosphere microorganisms in soil without chemical accelerator is the highest with highest uniformity. The microbial diversity index of Oxalis corniculata rhizosphere microorganisms is higher than background soil showing that planting Oxalis corniculata can promote the survival and activity of some microbial species. On the other hand, the microbial diversity index of Oxalis corniculata rhizosphere microorganisms in soil adding Na2S2O3 is the highest with highest uniformity of the addition of four kinds of chemical accelerator. EDTA,(NH4)2S2O3 and DTPA can inhibit the survival and activity of some microbial species. But Na2S2O3 don't inhibit the survival and activity of the microbial species.(5) Activated carbon and zinc powder are powder with large specific surface area. Cation exchange resin is granular with smaller specific surface area than activated carbon and zinc powder. The adsorption effect of different adsorption materials on volatile mercury is different. The adsorption of mercury by activated carbon is the best in the three kinds of adsorption materials, the second is cation exchange resin and the worst is zinc powder. The adsorption effect of Hg by adsorption materials is different also depending on the different weight of the adsorption material. When the weight of the adsorption material is 4g, the adsorption effect is best. With the increase of the distance between the Hg source and the adsorption material, the adsorption amount of the volatile mercury the adsorbed material decreased and the adsorption effect is getting worse. Through the range analysis of the orthogonal experiment, the effect of the type of adsorption material on the adsorption is the most and the influence of the distance between the Hg source and the adsorption material on the adsorption is the least.