The effect of CO2 sparging on high-solid acidogenic fermentation of food waste

Carbon dioxide (CO₂), a by-product of acidogenic fermentation, also acts as a reactant that affects carboxylic acid metabolism in reactors. However, the effect of headspace CO₂ in an acidogenic leach bed reactor (LBR) is unclear. In this study, high-solid acidogenic fermentation of food waste (FW) in LBRs with different fractions of CO₂ (CK: self-generated headspace, T1: 100% N₂, T2: 30% CO₂ + 70% N₂, and T3: 90% CO₂ + 10% N₂) was performed. CO₂ sparging significantly increased the acidogenic performance of FW, with T3 showing the highest soluble product yield of 0.81 g chemical oxygen demand per 1 g volatile solid removal (gCOD/gVS_removal). CO₂ sparging prolonged the fermentation of ethanol and lactic acid in T2 and T3 while it hindered the evolution of butyric and caproic acids. The relative abundance of the genus Limosilobacillus was enhanced by CO₂ sparging, reinforcing the ethanol and lactic acid metabolic pathways. However, sparging excessive CO₂ (≥30% CO₂) inhibited the colonization of the genus Clostridium sensu stricto 12, which suppressed the reverse β pathway with butyric and caproic acids as the metabolites. This work provides valuable insights into the targeted production of carboxylic acids from the acidogenic fermentation of FW via CO₂ regulation.

Graphical abstract