Two-stage anaerobic digestion of fruit and vegetable waste: optimization of dark fermentation through thermal pretreatment and co-digestion with sugar-rich wastewater

Fruit and vegetable waste (FVW) poses environmental challenges but can be valorized via dark fermentation (DF) and two-stage anaerobic digestion (TSAD) to produce H2 and CH4. This study evaluated the effects of culture medium and thermal pretreatment of inoculum in DF, testing various sugars and jam wastewater (JWW) as a renewable sugar source. Thermal pretreatment at 60 °C for 30 min enriched H2-producers, while culture medium had no significant effect. Glucose and sucrose allow H2 yield of 6.5 and 45.8 N mL/gVS, respectively. JWW proved suitable for DF of both raw and pretreated FVW, achieving H2 yields of 67.1 and 99.5 N mL/gVS, respectively. Volatile fatty acids after DF indicated active fermentation pathways reaching 7.2 g/L in JWW_FVW_1:1. In the TSAD, CH4 production reached 184 N mL/gVS, surpassing conventional single-stage digestion. These results demonstrate the potential of TSAD systems using FVW and JWW for efficient simultaneous H2 and CH4 production.