Optimization of Methane Production from Rice Straw and Buffalo Dung by H2O2 and Ca(OH)2: Pretreatments and Its Kinetics

Abstract

Rice straw (RS) residue consists of lignocellulosic biomass and is being mostly burned in the open air after harvesting in Pakistan. The atmospheric burning of RS is causing environmental degradation. While, the buffalo dung (BD) is suitable for production of methane because of containing various microbes and nutrients. In this study, the methane potential of anaerobic co-digestion of RS and BD was investigated. The RS was pretreated with hydrogen peroxide (H2O2) and calcium hydroxide (Ca(OH)2) prior to use in anaerobic digestion (AD) batch reactors. The ratio of RS to BD on the basis of the volatile solids (VS) was taken as 30:70, whereas the RS was shredded to particle size of 4 mm. The batch reactors were pretreated in serum cultural bottles with the separate H2O2 and Ca(OH)2 concentrations of 0.1, 0.2, 0.3, 0.4 0.5 and 0.6%. The co-digestion experiment was conducted in Semi-Automatic Methane Potential Test System (SAMPTS) under mesophilic conditions i.e., 37 ± 1 °C. The results show that both pretreatments remarkably degrade the RS and increases the production of methane as compared to the control. The highest methane was observed from the pretreatment concentration of 0.3% in case of H2O2 and 0.4% in the case of Ca(OH)2, whereas the methane production of 331.6 and 346.7 mL CH4 g−1 VS was observed, respectively. Moreover, in order the check the AD process dynamics, the kinetic coefficients were determined by using S-Gompertz and Cone models. On the basis of coefficient of determination, S-Gompertz model was better fitted as compared to the Cone model.