Process optimization of biogas recovery from giant reed (Arundo donax) alternatively pretreated with acid and oxidant agent: experimental and kinetic study

This study focused on biogas production from anaerobic co-digestion of grinded giant reed (Arundo donax) (GGR). The performance of co-digestion process was evaluated in bench-scale digesters operated in batch mode at different conditions. The effect of GGR particle size, pretreatment method, inoculum type, and thermal conditions were studied. The results demonstrated that biogas production was affected by the size of GGR particles and it was in the order of small (0.3–0.6 mm) > medium (0.6–1.18 mm) > large (1.18–2.36 mm). Maximum cumulative biogas productions were 94.24, 73.60, and 69.82 for small, medium, and large particle size of GGR, respectively. Biogas generation from H2O2-pretreated GGR and H2SO4-pretreated GGR exceeded its amounts from chemical-free GGR by 200% and 36%, respectively. The results indicated that biogas production from chemical-free GGR, H2SO4-pretreated GGR, and H2O2-pretreated GGR at thermophilic conditions exceeded its recovery rate at mesophilic conditions by 11%, 17%, and 26%, respectively. A relatively, higher rates of biogas generation of 67%, 56%, and 100% were observed from the co-digestion of GGR with chicken dung compared with cattle manure for the chemical-free GGR, H2SO4-pretreated GGR, and H2O2-pretreated GGR, respectively. The kinetic study of the co-digestion process was carried out using modified Gompertz model. A significant agreement was observed between the predicted and measured values of biogas recovery with determination coefficients ≥ 0.96 indicating favorable conditions for the co-digestion of inoculated GGR.