稻壳与污泥共热解对污泥炭特性及其重金属生态风险的影响

污泥热解过程中,辅料是影响热解产物性质的主要因素之一.本文研究了添加废弃生物质辅料——稻壳(0、25%、50%)对污泥炭性质、结构和重金属含量、生物有效性及生态风险的影响.实验结果表明,稻壳添加比例为50%时,污泥炭产率及其H/C和O/C比均为最小值,而其pH值和比表面积均达到最大值,污泥炭芳香化程度明显提高.同时,添加稻壳致污泥炭所含重金属存于生物有效态的含量显著降低.通过RAC风险评估,稻壳添加比例为25%时,较原污泥,污泥炭中Cu、Zn、Mn和Ni 4种元素风险水平均有不同程度的减小,而当添加比例为50%时,污泥炭中除Cu元素以外,其余各重金属风险等级均为低风险或无风险.表明污泥与稻壳共热解可有效降低污泥中重金属潜在生态风险水平,且当稻壳添加比例为50%时处理效果最优,本研究结果为污泥与稻壳资源化和无害化利用提供了理论依据.

Effects of rice husk and sewage sludge co-pyrolysis on characteristics of the sludge biochar and its ecological risk of heavy metals

Auxiliary materials may dramatically influence the characteristic properties of the final product through the pyrolysis of sewage sludge. This paper studied the effects of the addition of rice husk (0, 25% and 50%), a kind of agricultural wastes,on the characteristics including structure and heavy metal contents as well as their bioavailability and relevant ecological risk. The results show that the biochar production rate and ratio of H/C reached the lowest point when the addition dosage of husk was 50%, however, the pH value and total surface area got the maximum values. The addition of rice husk significantly improved the aromatic degree of biochar compared with no husk addition control. Meanwhile, the addition of husk led to a remarkable reduction of the bioavailable heavy metals fractions in the sludge biochar. According to RAC risk assessment, there was no risk level variation of Pb and Ni among the raw sewage sludge, the sludge biochar and the sludge-husk co-pyrolyzed biochar. When the addition rate of rice husk was 25%, the risk level of Cu and Mn was reduced to the middle-risk level from the high-risk level, and Zn and Ni was reached to the low-risk level compared to the raw sludge. When the proportion of risk husk reached to 50%, the risk of Mn declined to the low level. It is shown that the co-pyrolysis of sludge and rice husk could effectively reduce the potential ecological risk level of heavy metals in sludge, and the optimal addition rate of risk husk was 50%. The results of this study may provide theoretical basis for the recycling and harmless utilization of sludge and rice husk.