Effect of combined chemical and thermal pretreatments on biogas production from lignocellulosic biomasses

Anaerobic digestion of lignocellulosic biomass like crop residues have gained attention due to their surplus availability in rural areas. However, anaerobic digestion of such biomass feedstock require pretreatment to increase their digestibility. A combination of chemical (banana peel ash and calcium hydroxide) and thermal treatments (60-90 °C for time intervals of 2, 6 and 10 h) is investigated to understand the degradation behavior of two agro-residue biomasses viz. rice straw and corn stalk. Various analytical methods like FTIR, SEM and degradation of fiber (lignin, cellulose and hemicellulose) were employed to assess the efficacy of the pretreatment technique. Post pretreatment, biogas production is also investigated from the pretreated biomass along with the degradation of volatile solids during anaerobic digestion. Longer duration and higher temperature improved biodegradability as compared to short duration and low temperature treatments with differentiated results on both samples. Lignin of corn stalk (∼47%) degrades better than rice straw (∼39%) under identical pretreatments. The biogas production in cubic meter per unit kilogram of volatile solids of rice straw and corn stalk pretreated at 90 °C for 6 h was enhanced by 62% and 66%, respectively as compared to untreated rice straw and corn stalk. The know-how generated form the study will be useful to explore the potential benefits of banana peel ash as a pretreatment source for energy recovery via anaerobic digestion from surplus biomasses in rural India.