Effects Of Vermicomposting With Biochar On Heavy Metals In Industry Sludge

Sludge is a kind of organic solid waste,it can be used as resource in a certain extent by vermicomposting.At present,the research of vermicomposting mainly focuses on domestic sludge and less on industrial sludge.In this study,heavy metals fraction and bioavailability in the industry sludge from Maanshan steel sewage treatment plant was investigated to assess the combination of earthworm and biochar(Rice husk charcoal,bamboo charcoal,straw charcoal)on the sludge during compost.Different proportions of biochar(2%,4%,8%)were added in industrial sludge during sludge composting with biochar and vermicomposting.After composting,the indexes of organic matter,pH,electrical conductivity(EC),nutrient elements and heavy metals in each experimental group were studied,and compared the differences of sludge composting effect with adding different biochar,so as to provide certain basic data and reference for the application of vermicomposting.Specific conclusions are as follows:(1)aerobic composting of sludge with adding biochar increased pH value,EC,TP,TK as well as decreased TOC,TN,while vermicomposting with biochar increased TN,and further increased EC,TP,TK,but significantly decreased pH and TOC in the sludge.The optimum proportions of rice husk carbon,bamboo carbon and straw carbon were 4%,8%and 2%in aerobic composting and vennicomposting,At the same time,the compost effect of adding bamboo charcoal was better than rice husk charcoal under the same composting conditions,and the compost effect of adding straw charcoal was worst.(2)The contents of heavy metals Zn,Cu,Pb and Cd in aerobic composting with biochar increased due to the concentration effect.At the same time,the bioavailable heavy:metals extracted by DTPA in aerobic composting decreased with the increase of the proportion of biochar.However,the heavy metals con centration of vermicomposting with biochar decreased significantly.At the same time,the minimum heavy metals contents appeared under adding 4%rice husk charcoal with values of 856.64,137,10,158.92 and 15.48mg·kg-1,for Zn,Cu,Pb and Cd,respectively.When 8%bamboo charcoal was added,the contents of heavy metals Zn,Cu,Pb andCd reached the minimum values with 954.95,146.97,155.61 and 15.73mg·kg-1,respectively.And added 2%straw charcoal the minimum heavy metals contents appeared with values of 1084.23,162.25,166.05 and 17.483mg·kg-1 for Zn,Cu,Pb and Cd,respectively.Compared with the control group,the reduction ratio of heavy metals contents was Zn>Cu>Cd>Pb,at the ratio of 4%rice husk charcoal,8%bamboo charcoal and 2%straw charcoal,the synergy between earthworm and biochar was the strongest,and the bioavailable heavy metals extracted by DTPA was the lowest.(3)After the end of the experiment,compared with the control group,the heavy metals of aerobic composting the exchangeable and carbonates fraction increased and the residual fraction decreasing with the increase of the biochar ratio.In contrast,sludge vermicomposting with charcoal transformed exchangeable,carbonates,Fe-Mn oxide fraction and organic fraction of heavy metals in the sludge to the residual fraction.adding 4%rice husk charcoal,8%bamboo charcoal,and 2%straw charcoal were added,the earthworm activity was relatively stronger than other ratios,which promoted the reduction of the heavy metals mobility.At the same time,the compost treatment results of several biochars were found to be heavy passivation effect of bamboo charcoal>rice husk charcoal>stalk charcoal.(4)The risk assessment of the heavy metals in the compost after the test,whether it was a potential risk assessment or a RAC assessment,the risk of heavy metals in vermicompost was lower than that of aerobic composting.The potential ecological risk of vermicomposting with biochar reduced.the RAC evaluation had the lowest risk of Adding 4%rice husk charcoal,8%bamboo charcoal,and 2%straw charcoal in vermicomposting.The high ecological risk of heavy metal Cd would be medium risk,and the medium risk of Zn,Cu,and Pb will be low risk.The RAC value of the best suitable ratio of vermicomposting with biochar could be seen that the treatment effect of adding bamboo charcoal was better than rice husk charcoal,and the last was straw charcoal.Figure[17]table[18]reference[136]...