玉米秸秆与污泥混合热解对生物碳特性及重金属的影响

Effects of maize stovers and sewage sludge co-pyrolysis on characteristics and heavy metals in biochar

利用热解装置开展不同质量比例玉米秸秆(0,25%,50%和75%)与污泥混合热解实验,分别得到4种生物炭(SCB0,SCB25,SCB50和SCB75),研究了生物炭性质、重金属(Cu,Zn,Pb,Ni,Cr,Mn和As)含量、BCR形态和TCLP浸出毒性特征,并开展潜在生态风险评估。结果表明,随着玉米秸秆添加比例的增加,生物炭产率、灰分、H/C和N/C比显著降低,p H值显著增大,生物炭芳香化程度明显提高。添加玉米秸秆与污泥混合热解可以促进重金属向更稳定的形态(F4态)转化。4种生物碳中重金属浸出均未超出GB5085.3-2007浸出毒性鉴别标准规定的限值,生态风险均明显降低至轻微风险水平,在玉米秸秆添加量为50%时达到最低风险水平,该研究为污泥与玉米秸秆资源化和无害化利用提供了理论依据。

Maize stovers were mixed with sewage sludge at different proportions(0, 25%, 50% and 75%) and treated in a pyrolysis device up to 600 ℃ via a co-pyrolysis process. Four kinds of biochars(SCB0, SCB25, SCB50 and SCB75) were obtained respectively. The properties of biochars, heavy metals(Cu, Zinc, Pb, Ni, Cr, Mn and As)contents, BCR forms and TCLP leaching toxicity characteristics were studied and the potential ecological risks were evaluated. The results showed that with the increase of maize stover content, the biochar yield, ash content, H/C and N/C ratios were significantly reduced while the p H value and the aromatization degree of biochar were significantly increased. After co-pyrolysis with maize stovers, the morphology of heavy metals in the resultant biochar changed significantly. The residue fraction ratio of Cu, Zn, Ni and Cr was significantly increased, indicating that pyrolysis might promote the transformation of heavy metals into more stable forms. All the heavy metals leached from biochars obtained by mixed pyrolysis did not exceed the limit stipulated by GB5085.3-2007 leaching toxicity identification standard and the overall potential risk index was further reduced. The ecological risk was significantly reduced from the moderate to the slight risk level and the minimum risk level reached when the addition amount of maize stover was 50%. The current study might provide a theoretical basis for the resource utilization and harmless utilization of sewage sludge and maize stovers.