Insights of enhancing methane production under high-solid anaerobic digestion of wheat straw by calcium peroxide pretreatment and zero valent iron addition

Recent investigations verified CaO 2 accelerated hydrolysis of lignocellulose, but its residue caused a harmful oxidizing environment. This study therefore proposed the combined CaO 2 pretreatment and zero-valent iron (ZVI) addition to enhance high-solid anaerobic digestion of wheat straw, trying to eliminate negative effect of residual oxides . Effects of CaO 2 pretreatment without/with ZVI addition on digestion performance were investigated. Results showed that in non-ZVI added digesters, as CaO 2 dosage increased, total production of SCOD and VFAs increased linearly, while activities of coenzyme F 420 and electron transport system were negatively correlated. Pretreatment using appropriate CaO 2 dosage indirectly increased biogas production by promoting hydrolysis and acidification. Comparably, initial ORP in ZVI-added digesters sharply declined below −350 mV, which was suitable for methanogen growth. ZVI significantly improved activities of cellulase , hemicellulase , acetic kinase and coenzyme F 420 , with the highest improvement percentages of 138%, 48%, 35% and 58%, respectively. Since ZVI could provide electrons for conversion of CO 2 to CH 4 , compared with non-ZVI added digesters (R0-R4), methane content in ZVI-added digesters (RZ0-RZ4) increased by 8.1%, 9.0%, 11.2%, 17.0% and 18.0% successively. Consequently, 0.6 g/g VS CaO 2 pretreatment combined with 0.4 g/g VS ZVI addition achieved the maximum methane production, increasing by 35.6% compared to control digester.