Effects Of Biochar On Bioavailability And Bioremediation Of PAHs And Heavy Metals In Combined Polluted Soils

Combined pollution is a common phenomenon in contaminated soil.The PAHs-heavy metal combined contamination of soil is often the result of either simultaneous or successive entry of PAHs and heavy metals.Adding biochar,which has the ability to adsorb PAHs and heavy metals,to combined pollution soil has an impact on the effective state content of pollutants in soil and certain bioremediation effect for combined contaminated soil.Existing researches on remediation of contaminated soil by biochar are mainly focused on the single pollutant pollution of soil,while the research on combined pollution of soil is comparatively limited in amount.Moreover,for existing researches the use of soil with pollutants artificially added under laboratory conditions is more common than that of field contaminated soil.In this paper,PAHs-heavy metal combined contaminated soil is used.Plants and cultured earthworms are cultivated in soil with different proportions(0%,2%,5%,10%)of added rice husk biochar(300BC and 600BC),under different temperatures(300?and 600?).The phytoremediation effects of PAHs and heavy metal with different biochar treatments on soil are studied.The differences in the amounts of PAHs and heavy metal effective state contents in soil before and after the addition of biochar is analyzed.A scientific basis for the remediation of combined polluted soil with biochar as additive is thus established.The main results are as follow:1.Compared with the control without added biochar,the PAHs content in the soil with added 600BC and 300BC has not been significantly changed in phytoremediation of alfalfa.Under different treatments of adding 300BC and 600BC to soil,the content of 2-3 rings PAHs in plant roots are significantly lower than the control without added biochar(P<0.05).Under different treatments of adding 10%300BC,2%,and 10%600BC to soil,the content of total PAHs and 5-6 rings PAHs in plant roots are significantly lower than the control without added biochar(P<0.05).Under the treatment of adding 300BC to soil the content of PAHs in aboveground part of plants has not been significantly changed compared with the control and experiments with different proportions of added biomass carbon(0%,2%,5%,10%).The content of PAHs in aboveground part of plants with added 600BC in soil has no significant differences with the other treatments except the treatment with addition proportion of 10%,under which the PAHs content is lower than that of the control(P<0.05).The contents of Cr,Cu,As,Cd,Pb in soil in treatment of adding 5%,10%300BC to soil are significantly lower than those of the control(P<0.05).The content of Zn in soil in treatment about adding 2%300BC to soil were significantlyhigher than which on control(P<0.05).The contents of heavy metal in soil without significant difference between in the other treatments and control without adding biochar.The content of as in soil that added 600BC is lower than which on control(P<0.05),and the contents of heavy metal in soil in other treatments were no significant differences.The content of Cr,Cd,Pb in plant roots and aboveground parts in soil added 10%600BC were significantly lower than those of the controls(P<0.05).But the content of Cr in plant roots in soil added 2%300BC was significantly higher than that of the controls(P<0.05).The content of Cr in above ground part of plants in soil added 10%300BC was significantly lower than that of the controls(P<0.05).About phytoremediation of ryegrass,the content of 2-3 rings PAHs in soil added 5%,10%600BC were significantly higher than that of the control without adding biochar(P<0.05).The content of PAHs in other treatments are not significant difference compared with that of the control without adding biochar(P<0.05).In treatments that add 300BC,600BC to soil,the content of 4 rings PAHs in plant roots in soil added5%600BC was significantly higher than that of control,and the content of PAHs in plant roots were not significant differences between in the other treatments.The content of total PAHs and 5-6 rings in aboveground part of plants in soil added 5%600BC were significantly lower than that in the control(p<0.05),and the content of PAHs in aboveground part of plants in other treatments was no significant difference compared with that in control.The content of Pb in soil added 5%,10%300BC was significantly lower than those in control without adding biochar(P<0.05),and the content of As in soil added 2%300BC was significantly higher than those in control without adding biochar(P<0.05),and the content of heavy metal in other treatments had no significant difference compared with that in control.The content of Pb in soil added 10%600BC was significantly lower than those in control without adding biochar(P<0.05),and the content of As in soil added 2%600BC was significantly higher than those in control(P<0.05),and the content of heavy metal in other treatments had no significant difference compared with that in control.The content of Cr,As in plant roots in soil added 5%,10%300BC was significantly lower than those in control without adding biochar(P<0.05),and the content of Cu in plant roots in soil added 2%,5%600BC was significantly lower than those in control(P<0.05),but the content of Pb in plant roots in soil added 5%600BC and Zn in plant roots in soil added 10%600BC was significantly higher than those in control(P<0.05),and the content of Cr,As in aboveground part of plants in soil added 300BC was significantly lower than those in control without adding biochar(P<0.05).Overall,adding biochar to soil has a trend of decreasing accumulation of PAHs and heavy metal in plants about phytoremediation of combined contaminated soils.2.In the earthworm culture experiments of the control(without earthworms,add biochar),the content of total PAHs and 4 rings PAHs in soil added 5%300BC were significantly lower than those of control without respectively adding biochar(p<0.05),and the content of 4 rings PAHs in soil added 2%,5%300BC and 5%600BC were significantly lower than that of the control(P<0.05),and there is no significant differences between in other treatments.When earthworms are put in the soil,there was no significant difference in the contents of PAHs in soil with adding different amounts(2%and 5%)of 300BC and 600BC.When 300BC and 600BC put in the soil,the content of 4 rings PAHs in earthworm bioaccumulation were significantly lower than those of control without adding biochar(p<0.05),the content of 5-6 rings PAHs in earthworm bioaccumulation in treatment with adding 2%300BC in soil were significantly lower than those of control without adding biochar(p<0.05).The content of total PAHs and 5-6 rings PAHs in earthworm bioaccumulation in treatment with adding 5%600BC in soil were significantly lower than those of control without adding biochar(p<0.05).In addition,the content of 4 rings PAHs in earthworm bioaccumulation in treatment with adding 5%600BC in soil were significantly lower than those in treatment with adding 2%600BC in soil(p<0.05).The content of 5-6 rings PAHs in earthworm bioaccumulation in treatment with adding 5%600BC in soil were significantly lower than those in treatment with adding 5%300BC in soil(p<0.05).The content of Cu,Zn,Pb in earthworm bioaccumulation in treatment with adding 5%300BC in soil were significantly higher than those in control without adding biochar in soil(p<0.05).The content of Cu in earthworm bioaccumulation in treatment with adding 5%600BC in soil were significantly higher than those in control without adding biochar in soil(p<0.05).The content of Pb in earthworm bioaccumulation in treatment with adding 2%600BC in soil were significantly higher than those in control without adding biochar in soil(p<0.05).However,the content of Zn in earthworm bioaccumulation in treatment withrespectively adding 2%600BC,5%600BC in soil were significantly lower than those in control without adding biochar in soil(p<0.05).Overall,adding biochar to soil in general will reduce the content of PAHs in earthworm bioaccumulation for combined contaminated soil.The preparation temperature of biochar is higher,the more the amount of biochar adding,the content of PAHs in earthworm bioaccumulation is lower.But adding the biochar to soil promoted the accumulation of heavy metals in earthworm.3.The effective state contents of PAHs and heavy metal in combined contaminated soilin the experiment of planting and earthworm culture were studied by polyoxymethylene solid phase extraction(POM-SPE)and 0.1 M HCl.The effective state contents of 5-6 rings PAHs in planting alfalfa soil with adding 10%300BC and 10%600BC were significantly lower than the control group without biochar(P<0.05).The effective state contents of total PAHs and 4 rings PAHs in planting ryegrass soil with adding 10%300BC and 10%600BC were significantly lower than the control group without biochar(P<0.05).The effective state contents of total PAHs and different ring-number PAHs in earthworm culture soil with adding 300BC and 600BC were significantly lower than the control group without.biochar(P<0.05).In the experiment of planting alfalfa,the effective state contents of Cd and As in soilwith 300BC and As in soil with 300BC were significantly higher than the control group without biochar(P<0.05).The effective state contents of Zn in soil with 2%300BC,10%300BC,5%600BC and Cu in soil with 5%300BC were significantly higher than the control group without biochar(P<0.05).The effective state content of Cd in soil with 5%600BC,10%600BC was significantly higher than the control group without biochar(P<0.05).But the effective state content of Cr in soil with 5%300BC,10%300BC,5%600BC,10%600BC was significantly lower than the control group without biochar(P<0.05).In the experiment of planting ryegrass,the effective state contents of as in soil with 300BC and 600BC were significantly higher than the control group without biochar(P<0.05).The effective state contents of Cd in soil with 10%300BC were significantly higher than the control group(P<0.05).The effective state contents of Cr in soil with 300BC and 600BC was significantly lower than the control group(P<0.05).The effective state contents of Zn in soil with 10%600BC was significantly lower than the control group(P<0.05).The effective state contents of Cu in soil with 5%600BC and 10%600BC was significantly lower than the control group(P<0.05).In the experiment of earthworm culture,the effective state contents of Cu,Zn in soil with 5%300BC and Zn in soil with 2%600BC was significantly higher than the control group(P<0.05).The effective state contents of As,Cd in soil with 2%300BC,5%300BC,2%600BC,5%600BC was significantly higher than the control group(P<0.05).The effective state contents of Cr in soil with 2%300BC,5%300BC and 5%600BC was significantly lower than the control group(P<0.05).In general,adding biocha to soil decreased the effective state contents of PAHs.Effects of biochar on the effective state contents of heavy metal are different because of the metal elements and the experimental treatment varies.