2.3. Batch fermentation
The two stage batch fermentation system including H2 fermentation in the first stage and CH4 fermentation in the second stage was set up in 500 mL screw-cap bottles with a working volume of 500 mL (375 mL of food waste and 125 mL of inoculum). The microbial seed inoculum in all conditions was fixed at 4.75 g total volatile solids (VS) per batch. The food waste was added at varying concentrations between
23.75 and 95.0 g VS L 1, corresponding to F/M ratios of
2.5-10. The initial pH in the H2 fermentation was adjusted to 6.0 with 6 N NaOH or concentrated H3PO4. The system was flushed with nitrogen gas to generate anaerobic conditions. H2 fermentation was conducted at 37 C with rotary shaking at 150 rpm. After H2 fermentation was exhausted, the non-heat pretreated seed of 4.75 g VS per batch was added, the initial pH was adjusted to 7.0, and the system was reflused with nitrogen gas, and the CH4 fermentation was conducted at 37 C. All experiments were setup in duplicate. During the fermentation experiment, total gas volume and composition were periodically monitored by gas
counters and gas chromatography, respectively. The liquid samples were analyzed for pH and volatile fatty acids (VFAs) every 4-6 h.