Acidogenic biorefinery of rice straw for volatile fatty acids production via sequential two-stage fermentation: Effects of pre-treatments

Abstract

The physical and chemical effects of the hydrothermal, acid and alkali pretreatment methods of rice straw were investigated to be used in volatile fatty acids (VFAs) production through two-stage anaerobic fermentation. The effects of two-stage acid production and fermentation process parameters of different pretreated straws under the fermentation temperature conditions of 35°C, 55°C, and 70°C were analyzed. The results showed that The hydrothermal, 2% HCl, and 1% Ca(OH)2 increased the specific surface area of the rice straw by 12.20%, 52.62% and 37.81%, respectively. The alkali pretreatment increased the macro and mesopores of the rice straw while the hydrothermal and acid pretreatments increased the small and micropores. The primary fermentation did not affect significantly the infrared spectrum peaks of pretreated rice straw. The rate and total VFAs production was enhanced significantly after the 1% Ca(OH)2 pretreatment compared with 2%HCl and hydrothermal pretreatments respectively. Based on the initial mass of 100 g raw straw, when pretreated with 1% Ca(OH)2 and fermented at 35°C, the primary and the secondary acid production were 12.23 g and 16.54 g, respectively, and the total acid production was 28.77 g. This study provides an optimum condition for the best pretreatment and process parameters for acidogenic biorefinery of rice straw for enhanced VFAs production.