Enhanced thermophilic bioenergy production from food waste by a two-stage fermentation process

Purpose The objective of research was emphasized on the optimal conditions (initial pH and C/N ratio) for enhancing bioenergy from food waste by a two-stage fermentation process. Methods Bioenergy production from food waste was operated by mixed culture under thermophilic temperature in batch reactor. Thermophilic biohydrogen production was optimized in terms of initial pH (5.0–9.0) and then was optimized in terms of C/N ratio (10–50) in the first stage. After that, thermophilic biomethane production was optimized in terms of initial pH (6.0–10.0) in the second stage. Results The results revealed that the thermophilic biohydrogen production from food waste at an initial pH 7.0 presented the maximum hydrogen yield of 176.10 mL H2/ g COD. At this optimal initial pH, the maximum hydrogen yield of 214.88 mL H2/ g COD was achieved at C/N ratio 30. Subsequently, the effluent from the first stage of thermophilic biohydrogen production from food waste under the optimal initial pH of 7.0 and the optimal C/N ratio of 30 was used as a substrate in the second stage of thermophilic biomethane production. Thermophilic biomethane production from hydrogen fermentation effluent provided the maximum methane yield of 310.77 mL CH4/ g COD at initial pH 7.0. At these optimal conditions, COD removal was achieved at 70–90%. Conclusion Therefore, a two-stage thermophilic fermentation process could effectively enhance biohydrogen and biomethane production, including reduction of organic waste at the same time.