Investigating metal, glucose, and inhibitory compound levels through food waste hydrolysate dilution and pH adjustment to enhance dark fermentation performance.

Food waste hydrolysate (FWH) produced by dilute H2SO4 thermohydrolysis is a promising substrate for dark fermentation (DF), but its performance can be unstable due to interactions among nutrients (metals and glucose) and inhibitory compounds such as 5-hydroxymethylfurfural (HMF) and furfural. This study investigates the effects of FWH dilution (D0-D4) and initial pH (6-9) on its composition and DF performance. Key parameters included the level of metal ions (Fe, Mg, and Ca), glucose equivalent, HMF, and furfural, which influence hydrogen yield (HY). ANOVA showed that FWH dilution and initial pH significantly affected HY (p < 0.05). Tukey's post hoc test identified D2 and an initial pH of 8 as the adequate conditions. At D2 and pH 8, DF system contained 14.21 g/L glucose, 27.97 mg/L Fe, 35.60 mg/L Mg, and 148.77 mg/L Ca, while HMF and furfural levels were 32.19 mg/L and 97.86 mg/L. This condition achieved the highest HY of 0.60 mol H2/mol glucose equivalent, accompanied by the formation of butyric acid (2.92 g/L), acetic acid (0.76 g/L), and ethanol (0.01 g/L). These findings highlight the importance of investigating substrate dilution and initial pH to enhance DF performance and improve waste-to-energy conversion efficiency.