title: Effect of energy grass on methane production and heavy metal fractionation during anaerobic digestion of sewage sludge.
abstract: Anaerobic digestion (AD) is one of the most widely used processes to stabilize waste sewage sludge and produce biogas as renewable energy. The relatively low organic matter content and high heavy metal concentrations in sewage sludge have severely restricted the application and development of AD technology in China. In this study, the effect of energy grass (Pennisetum alopecuroides) addition on methane production and heavy metal fractionation during the AD of sewage sludge was evaluated. Methane production was enhanced by 11.2% by the addition of P. alopecuroides. The addition of P. alopecuroides significantly reduced the percentages of the water-soluble and exchangeable fractions of the target heavy metals in the sewage sludge after AD, and the dominant species were concentrated in Fe-Mn oxide-bound and organic- and sulfide-bound fractions of the digested sludge. The addition of P. alopecuroides at a dosage of 0.3kg significantly (P<0.05) decreased the mobility factors (MFs) of the target heavy metals after AD. In particular, the MFs of Cr and Ni were 61% and 32% lower, respectively, relative to the control. The increase in the added dose did not necessarily lead to further decreases in the MFs of the heavy metals. These results demonstrate that an appropriate addition of energy grass could enhance AD, decrease the mobility of heavy metals and promote heavy metal stabilization in sewage sludge during AD, which is beneficial for the subsequent land application of sewage sludge.
authors.affiliation: Key Laboratory of Yangtze River Water Environment of the Ministry of Education, Tongji University, Shanghai 200092, China. Electronic address: zimuwanqing@163.com.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Yangtze River Water Environment of the Ministry of Education, Tongji University, Shanghai 200092, China. Electronic address: cmyang@tongji.edu.cn.
authors.forename: Changming
authors.initials: C
authors.lastname: Yang
authors.affiliation: Key Laboratory of Yangtze River Water Environment of the Ministry of Education, Tongji University, Shanghai 200092, China. Electronic address: jingyachao@qq.com.
authors.forename: Yachao
authors.initials: Y
authors.lastname: Jing
authors.affiliation: Key Laboratory of Yangtze River Water Environment of the Ministry of Education, Tongji University, Shanghai 200092, China. Electronic address: lijianhua@tongji.edu.cn.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Li
keywords: Anaerobic co-digestion; Energy grass; Heavy metal speciation; Sewage sludge; Stabilization process