Effect of energy grass on methane production and heavy metal fractionation during anaerobic digestion of sewage sludge

• Published in: Waste management (Elmsford) Vol. 58; pp. 316 - 323
• Main Authors: Zhang, Min, Yang, Changming, Jing, Yachao, Li, Jianhua
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.12.2016
• Subjects: Anaerobic co-digestion; Anaerobic digestion; Energy grass; Fractionation; Grasses; Heavy metal speciation; Heavy metals; Lead (metal); Methane; Pennisetum alopecuroides; Sewage sludge; Sludge; Stabilization process; China, People's Rep; Stabilization process; VFA; Anaerobic co-digestion; AD; C/N; Heavy metal speciation; MFs; Sewage sludge; VS; Energy grass; TS
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2016.09.040

•The addition of P. alopecuroides could increase methane production and improve anaerobic digestion performance of sewage sludge.•The presence of P. alopecuroides considerably reshaped the distribution characteristics of the heavy metal species.•The energy grass addition significantly enhanced the stabilization process of heavy metals during anaerobic digestion.•Anaerobic co-digestion of sewage sludge with the energy grass may greatly benefit efficient energy recovery and safe land application. 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.