Performances of anaerobic co-digestion of fruit & vegetable waste (FVW) and food waste (FW): Single-phase vs. two-phase

The co-digestion of fruit & vegetable waste (FVW) and food waste (FW) was performed at various organic loading ratios (OLRs) in single-phase and two-phase system, respectively. The results showed that the ethanol-type fermentation dominated in both digestion processes when OLR was at low levels (<2.0 g(VS) L−1 d−1). The propionic acid was rapidly accumulated as OLR was increased to higher levels (>2.0 g(VS) L−1 d−1), which could cause unstable anaerobic digestion. Single-phase digestion was better than two-phase digestion in term of 4.1% increase in CH4 production at lower OLRs (<2.0 g(VS) L−1 d−1). However, at higher level of OLR (⩾2.0 g(VS) L−1 d−1), two-phase digestion achieved higher CH4 production of 0.351–0.455 L (g VS)−1 d−1, which were 7.0–15.8% more than that of single-phase. Additionally, two-phase digestion presented more stable operation, and higher OLR treatment capacity. Furthermore, comparison of these two systems with bioenergy recovery revealed that two-phase system overall presented higher bioenergy yield than single-phase.