H_(2)O_(2)氧化对不同温度制备的污泥炭特性及重金属的影响

Effect of H_2O_(2) oxidation on the properties and heavy metals of sludge biochar fabricated at different temperatures

为探究污泥炭的生态风险,利用H_(2)O_(2)氧化模拟污泥炭的化学老化过程,探究不同浓度的H_(2)O_(2)对污泥炭理化性质及其重金属(Cr、Ni、Pb、Zn)总量和形态变化的影响,并利用风险评价指数法(RAC)对污泥炭中这4种重金属的生态风险进行评价。结果表明,随着H_(2)O_(2)浓度升高,污泥炭含C量总体下降,含O量总体上升,H/C比总体增大,芳香度降低。低浓度的H_(2)O_(2)(体积分数5%)氧化使得400℃制备的污泥炭比表面积降低,600、800℃制备的污泥炭比表面积增大,高浓度的H_(2)O_(2)(体积分数20%)氧化与之结果相反。与原污泥相比,热解后各重金属均富集在污泥炭中,BCR分级提取后发现,污泥炭中重金属生物有效态占比显著降低,且600、800℃制备的污泥炭重金属形态更不易受H_(2)O_(2)氧化影响。结合RAC分析,当热解温度为600℃时,污泥炭中4种重金属的生态风险最低,可为污泥的资源化安全利用提供参考。

To investigate the ecological risk of sludge biochar(SBC),H_(2)O_(2)oxidation was used to simulate the chemical ageing process of the SBC.In this way,the effects of the different concentrations of H_(2)O_(2)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 H_(2)O_(2)concentration.This led to a decrease in the aromaticity of SBC.Low H_(2)O_(2)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 H_(2)O_(2)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 H_(2)O_(2)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.