Anaerobic digestion of elephant grass hydrolysate: Biogas production, substrate metabolism and outlet effluent treatment

Elephant grass (Pennisetum purpureum) acid hydrolysate was used as substrate for anaerobic digestion for the first time. Within short period (ten days), the organic materials (sugars and organic acids) in the elephant grass hydrolysate could be utilized efficiently for stable biogas production that the COD removal, biogas yield, and CH4 content were 91.3 +/- 2.0%, 0.561 +/- 0.014m(3)/kg COD consumption, and 68.1 +/- 4.6%, respectively throughout this bioprocess. During anaerobic digestion, almost no volatile fatty acids (VFAs) was accumulated (merely< 0.1 g/L acetic acid was found) and the outlet pH was very stable (7.3 +/- 0.1). Meanwhile, the furans including furfural and 5-hydroxymethylfurfural (HMF) existing in the inlet substrate could be degraded. After anaerobic digestion, the outlet effluent was treated by combination of Fe-C micro-electrolysis and Fenton reaction to remove 93.1% of residual COD and 98.6% of color. Considering the performance, cost, operation, and environmental influence, this technology is suitable for industrial treatment of waste elephant grass.