Effects of rice straw/wood sawdust addition on the transport/conversion behaviors of heavy metals during the liquefaction of sewage sludge

• Published in: Journal of environmental management 2020-09, Vol.270, p.110824-110824, Article 110824
• Main Authors: Xiao, Xiao-feng, Chang, Yan-chao, Lai, Fa-ying, Fang, Han-sun, Zhou, Chun-fei, Pan, Zi-qian, Wang, Jia-xin, Wang, Yu-jie, Yin, Xin, Huang, Hua-jun
• Format: Article
• Language: English
• Subjects: Co-liquefaction; Heavy metals; Rice straw; Sewage sludge; Wood sawdust
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2020.110824

Lignocellulosic biomass has been widely introduced into the liquefaction process of sewage sludge (SS) to improve the yield/quality of liquefaction products (bio-oil/biochar). This study explores the effect of adding rice straw (RS) and wood sawdust (WS) on the transport/conversion behaviors of heavy metals (HMs) during the liquefaction of SS. The introduction of lignocellulosic biomass, especially for RS, substantially lowers the total content of HMs in biochar. Most HMs (except Cd) still remain in biochar, although the introduction of RS/WS enhances the transport of HMs into bio-oils. The addition of RS/WS raises the percentage of HMs in active form, but the contents of bioavailable/leachable HMs are not considerably increased and even decreased in some cases, especially when RS is introduced. The overall pollution degree and environmental risk of HMs in biochars are lowered to a certain extent with the addition of RS/WS. Considering that the pollution degree and environmental risk of HMs present in biochars are still at a considerable level, appropriate pollution management measures should be undertaken when using such biochars for agricultural use. [Display omitted] •Addition of RS/WS during SS liquefaction reduces the total content of HMs in biochar.•The transport of HMs into bio-oil is enhanced but most of HMs still exist in biochar.•Proportions of HMs in active chemical form in biochar are generally risen.•Overall, the leaching ability of HMs in biochar is improved to some extent.•The pollution risk/degree of HMs in biochar is reduced to some extent.