Effects of Alkali Pre-treatment, Total Solid Content, Substrate to Inoculum Ratio, and pH on Biogas Production from Anaerobic Digestion of Mango Leaves

The present study investigated the effects of five parameters [alkali (NaOH) pretreatment (doses and durations), total solid (TS) content, substrate to inoculum ratio (S/I), and pH] on biogas production from anaerobic digestion of mango leaves. To evaluate these parameters effects 26 batch experiments were conducted. Which included: NaOH pretreatment (doses: 0, 0.1, 0.2, 0.3, and 0.4 mol/L and durations: 4, 6, 8, 10, and 12 h), TS content (4, 6, 8, 10%), S/I (15, 20, 25, and 30%), and pH (6.5, 7.0, 7.5, and 8.0). Also, the kinetics of biogas production was studied by using three models: first order kinetic, Cone, and modified Gompertz models. It was found that the optimum conditions were: NaOH dose with 0.2 mol/L, NaOH duration for 10 h, TS content with 8%, S/I ratio with 20%, and pH of 7.5. These optimum situations gave the highest production with 616.2, 644.0, 1968.4, 1467.2, and 1488.6 mL/gVS, respectively. Cone model showed the best fit followed by modified Gompertz model and finally first order kinetic model. These results proved the applicability of mango leaves as a good source for renewable methane-rich energy, and the impact of NaOH pretreatment, TS, S/I, and pH on the biogas/methane yield.