Effect of H2O2 oxidation on the properties and heavy metals of sludge biochar fabricated at different temperatures
To investigate the ecological risk of sludge biochar(SBC),H2O2 oxidation was used to simulate the chemical ageing process of the SBC.In this way,the effects of the different concentrations of H2O2 on the physicochemical properties of SBC,the total amount of heavy metals,and morphology of the heavy metals(Cr,Ni,Pb,Zn)in SBC were explored.Furthermore,the ecological risk of these four metals in SBC was evaluated by the risk assessment index method(RAC).The results showed that the C content in SBC decreased overall,and the O content and the H/C ratio increased overall,along with the increase of H2O2 concentration.This led to a decrease in the aromaticity of SBC.Low H2O2 concentration(5％volume fraction)treatment resulted in a decrease of specific surface area(SSA)of SBC fabricated at 400 ℃(SBC-400),while an increasing SSA of SBC-600 and SBC-800.High H2O2 concentration(20％volume fraction)treatment led to the opposite result.Compared with the raw sludge,the four kinds of heavy metals were enriched in the sludge biochar after pyrolysis.The BCR step extraction showed that the percentage of bioavailable metals in SBC was significantly lower than that in raw sludge.Moreover,the heavy metal forms of SBC-600 and SBC-800 were less susceptible to H2 O2 oxidation than that of SBC-400.Combined with the RAC analysis,the ecological risk of these four heavy metals was the lowest with the pyrolysis temperature of 600 ℃.This study is beneficial for the reuse and recycle of municipal sludge.
sludge biochar chemical ageingH2O2 oxidationheavy metalsBCR step extractionecological risk assessment
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