Passivation Effect Of Hydroxy Sulfate Iron Sludge-based Biochar On Arsenic Contaminated Soil

Arsenic-contaminated soil is a widely concerning environmental problem.In this paper,two different sludge-based biochars,ordinary municiple sludge-based biochar(as S-biochar)and hydroxy sulfate iron sludge-based biochar(as Fe-biochar),are applied as passivation/stabilizers to remediate As(III)contamined soil at different concentrations of exogenous arsenic(III)from 20-200mg/g.The species and content of As(III)of contaminated soil were monitored after one year stabilization by sludge-based biochar to investigate the remediation efficiency on arsenite contaminated soil.The physical and chemical properties of the soil were measured to find out whether they have an effect on remediation process.And to study the changes in the structure of the flora in the entire repair system after the application of exogenous arsenic and biochar.And using the plant marker method to determine the total arsenic content in plants,as a basis for evaluating whether biochar is effective for immobilizing arsenic.After the application of biochar,the content of the available As(III)reduced drastically,correspondingly the content of the fixed and residual arsenic were increased.It could be deduced that the arsenite toxity in soil were reduced because the decrease of available arsenic restrain the As(III)mobility and toxicity.The existence of aluminum iron phosphorus,calcium and silicon,,has an effect on the species and content of fixed arsenic.As to aluminum-arsenic,the S-biochar treatment has higher aluminum content and less phosphorus content comparing with Fe-biochar which result to the higher aluminum-arsenic content in S-biochar soil.As to iron-arsenic,S-biochar and Fe-biochar soil differentiated little although Fe-biochar contained much more iron than S-biochar.However phosphorus content in Fe-biochar soil is also much more than that in S-biochar,which inhibits the adsorption of iron on arsenic due to phosphorus stronger affinity to iron than As.The presence of silicon makes arsenic easier to convert to an active state.After the application of biochar,the pH of the soil decreased slightly,but it was still in the neutral range,which made the soil have a better fixation effect on arsenic.Nitrogen,phosphorus and sulfur are the indicators for evaluating soil fertility.The application of Fe-biochar has higher phosphorus content.It competes with arsenic for adsorption sites;the sulfur elements of both biochars are greatly increased,and sulfur causes arsenic to be converted to an inactive state.Manganese also affects the species of arsenic like iron and aluminum,but the content of manganese is very low,which is difficult to play a decisive role.After testing the flora structure of the repair system,it was found that there were 12 dominant bacteria.After the addition of exogenous arsenic and the application of biochar,microbial diversity increased at the OTU level,but decreased at the Phylum level.Environmental factors also affect the diversity of microorganisms.For environmental factors,carbon is positively correlated with nitrogen,negatively correlated with sulfur,phosphorus,and pH,and the relative contribution of sulfur is large,followed by pH,then carbon,and finally phosphorus and nitrogen.The rapeseed was selected as a plant marker.Arsenic may stimulate the growth of plants.After the application of biochar,the plants grow vigorously,which may be an increase in the content of nutrients such as phosphorus and sulfur.As the concentration of exogenous arsenic increases,the amount of arsenic absorbed by plants from the soil also increases significantly.After the application of biochar,the arsenic content in the plants decreases.The decrease first increased and then decreased.The maximum decrease occurred in group C(normal carbon:83.89%,iron carbon: 84.55%).The decrease to the F group was significantly reduced.The application of biochar was better in the low concentration arsenic treatment group,and also effective in the middle and high arsenic concentration treatment groups,but the effect was not as good as the low concentration arsenic treatment group.In addition,the treatment effects of the two different biochar treatment groups were not much different.