Enhanced H2 fermentation of organic waste by CO2 sparging

This study aimed to improve the productivity of dark fermentative hydrogen production from organic waste. An anaerobic sequencing batch reactor was used for hydrogen fermentation and it was fed with food waste (VS 4.4 ± 0.2% containing 27 g carbohydrate-COD/L) at various CO2 sparging rates (40–120 L/L/d), hydraulic retention times (HRTs; 18–42 h), and solid retention times (SRTs; 18–160 h). CO2 sparging increased the H2 productivity by 5–36% at all the examined conditions, confirming the benefit of the replacement of headspace gas by CO2. The maximum H2 production was obtained by CO2 sparging at 80 L/L/d, resulting in the H2 productivity of 3.18 L H2/L/d and the H2 yield of 97.3 mL H2/g VSadded. Increase of n-butyrate and isopropanol yields were concurrent with the enhanced H2 yield by CO2 sparging. Acidogenic efficiency, the sum of H2, organic acid, and alcohol, in the CO2-sparged reactor ranged from 47.9 to 56.0%, which was comparable to conventional acidogenesis. Thermodynamic analysis confirmed that both CO2 sparging and CO2 removal were beneficial for H2-producing reactions, but CO2 sparing has more profound effect than CO2 removal on inhibiting H2-consuming reactions.