Methane fermentation and kinetics of wheat straw pretreated substrates co-digested with cattle manure in batch assay

Abstract

Lignocellulosic biomass contains high percentages of lignin, which is hard to biodegrade and therefore, pretreatment is required to enhance energy recovery yield. In this study, five types of pretreatments, i.e., dilute acid, alkali, acid–alkali combination and calcium hydroxide–sodium carbonate combination, and grinding were applied on wheat straw to enhance the efficiency of methane fermentation. Methane fermentation of untreated and pretreated substrates was evaluated at 35 °C temperature in 5 L glass bottle reactors. Cumulative CH4 yields of these pretreated substrates were found as 0.125±0.002, 0.370±0.02, 0.003±0.005, 0.380±0.017 and 0.241±0.005 m3/kg of VS (volatile solids), respectively for, T1, T2, T3, T4 and T5 treatments compared to that of untreated treatment T0 as 0.191±0.004 m3/kg of VS. Alkali (2% NaOH on weight/volume ratio basis) and calcium hydroxide–sodium carbonate combination (3% Ca(OH)2+3% Na2CO3 on weight/volume ratio basis) pretreatments have been found to improve biogas and CH4 production yields by 94.0% and 99.0%, respectively, in comparison to the untreated wheat straw substrate. Gompertz model used to analyze the kinetic behavior of anaerobic digestion process in present study. Kinetic study indicates that Gompertz equation best describe the cumulative gas production as a function of the digestion time.