Kinetic Study of Biogas Production from Raw and Solid-State Organosolv Pretreated Rice Husk

Abstract

Solid-state organosolv pretreatment was carried out on rice husk (RH) at various concentrations and temperatures for biogas enhancement. Pretreatments were conducted at 100 and 120°C for 60 min with acid-catalysed ethanol at 1, 3 and 5% concentration. Samples pretreated with 3% ethanol at 100 and 120°C for 60 min produced more biogas compared with raw RH, although the difference between the 3% pretreated sample at 120°C was not significant. The samples were designated in accordance with the ethanol concentration and reaction temperature. 3E100 produced 5545 ml of biogas followed by 3E120 with 2550 ml, whereas the control RH produced 2500 ml. First-order kinetic model and the modified Gompertz model were used to determine biodegradability constants and predicted cumulative biogas production. The Chen and Hashimoto model was used to determine the critical hydraulic retention time (HRTcritical) for 3E100 to determine the minimum retention time needed to prevent washout when biogas production was run on a continuous basis. The biodegradability constant (ko) ranged between 0.2688 and 0.9185 d–1 with 3E100 having the highest value for ko which confirmed optimum utilisation of substrate. Comparison between experimental and predicted data revealed that Gompertz model showed a good fit in describing cumulative biogas production of RH and pretreated RH at different concentrations and temperatures. HRTcritical for 3E100 was calculated to be approximately 10 days. Pretreatment of RH at 3% concentration of ethanol at 100°C for 60 min greatly enhanced cumulative biogas production with 121.80% increase in comparison with the raw sample.