Abstract:

The acceleration of urbanization brings increasing pressure on sludge disposal. Pyrolysis is an effective means of resourceful sludge disposal, and heavy metals are a kind of pollutants that need extra attention in the disposal process. In this paper, the co-pyrolysis experiments of sludge and agroforestry wastes were carried out in a horizontal fixed-bed reactor to investigate the effects of different pyrolysis temperatures (500℃, 700℃), types of agroforestry wastes (rice hulls, wood chips, corn stover) and blending ratios (25%, 50%) on the migration and transformation characteristics of heavy metal elements, Co, Cr, Cu, Mn, Ni, Pb and Zn, in the biochar. It was found that with the pyrolysis temperature increasing from 500℃ to 700℃, the residual rate of heavy metals in biochar reduced. The co-pyrolysis with agroforestry wastes would be beneficial to the enrichment of Co, Cr and Mn in biochar. By studying the morphology of the heavy metals, it was found that increasing the pyrolysis temperature would be beneficial to the transformation of the heavy metals towards the stable morphology in most cases, and the co-pyrolysis with agroforestry wastes would facilitate the transformation of the heavy metals into more stable morphology in biochar. However, it should also be noted that at 700℃, co-pyrolysis with agroforestry wastes was not conducive to the stabilization of Ni. Generally, co-pyrolysis with agroforestry wastes reduced the potential ecological risks of biochar. The results of this paper would provide a valuable reference for the control of heavy metal emissions in the thermal disposal of sludge in practical industrial production.

Key words: sludge, agroforestry wastes, co-pyrolysis, heavy metals, biochar

摘要：

城镇化的加速推进导致污泥处置压力不断增大。热解法作为资源化处置污泥的有效手段，重金属是处置过程中需要格外关注的一种污染物。本文在水平固定床反应器中开展污泥和农林废弃物的共热解实验，探究不同热解温度下（500℃、700℃）农林废弃物种类（稻壳、木屑、玉米秸秆）以及掺混比例（25%、50%）对重金属元素Co、Cr、Cu、Mn、Ni、Pb、Zn在生物炭中迁移转化特性的影响。研究发现，随着热解温度由500℃升至700℃，重金属在生物炭中的残余率呈现下降趋势，而掺混农林废弃物共热解则会使生物炭中Co、Cr、Mn的残余率上升。对重金属赋存形态的研究发现，热解温度的升高以及掺混农林废弃物共热解在大部分情况下可以使重金属以更稳定的形态赋存在生物炭中，但也应注意700℃时掺混农林废弃物共热解不利于生物炭中Ni向稳定形态转化。总体上看，掺混农林废弃物共热解会使生物炭的潜在生态风险系数呈下降趋势。本文期望为实际工业生产中污泥热处置重金属排放控制方面提供有价值的参考。

关键词: 污泥, 农林废弃物, 共热解, 重金属, 生物炭