Effect of different heat treatments of inoculum on the production of hydrogen and volatile fatty acids by dark fermentation of sugarcane vinasse

Abstract

Vinasse the main residue of bioethanol production can be used as a substrate in microbiological processes to obtain value-added products. However, it is necessary to use a microbial consortium with high capacity to produce hydrogen (H2) and volatile fatty acids (VFA). There is no consensus on the best inoculum pretreatment to eliminate hydrogen-consuming bacteria. Thus, the present study evaluated the influence of three methods of heat pretreatment of the inoculum: T1 = 90 °C/10 min; T2 = 105 °C/120 min; T3 = 121 °C/20 min for the production of H2 and VFA using vinasse as substrate. The effect of the concentration of vinasse and the initial pH (5, 6 and 7) were also evaluated. The highest hydrogen production (821.34 mL) and yield (4.75 mmol H2 g−1 COD) was obtained using undiluted vinasse at pH 6 and T1 pretreatment. The highest number of copies of the Fe-hydrogenase genes confirms the higher H2 production. The presence of Clostridium and facultative anaerobic microorganisms Bacillus and Enterobacter in the microbial consortia were confirmed by isolation and PCR-DGGE. The highest production of VFA was obtained at pH 7 and T3 pretreatment. This study showed that dark fermentation could be driven by the inoculum pretreatment and pH selecting different process either for the production of H2 or VFA from vinasse in natura, without addition of supplements.