Improving dark fermentative biohydrogen production of food waste hydrolysate by balancing metal availability through inoculum heat pretreatment duration and inoculum-to-substrate ratio

Abstract

This study investigates how anaerobic granular sludge (AnGS) heat pretreatment duration (HPD, 0–1.5 h) at 100 °C and inoculum-to-substrate ratio (ISR, 0–0.5 v/v) interact to regulate Fe, Mg, and Ca availability and enhance hydrogen yield (HY) in the dark fermentation (DF) of food waste hydrolysate (FWH). A glucose solution (10 g/L) is used to assess HPD, while FWH evaluates ISR. ANOVA showed significant treatment effects for HY, and the Tukey test identified 0.5-h HPD and ISR 0.3 as optimal. 0.5-h HPD released Fe (35.50 mg/L), Mg (5.80 mg/L, and Ca (22.65 mg/L) from AnGS, yielding 0.53 mol H₂/mol glucose. Under optimal combined conditions, the initial DF contains Fe (18.77 mg/L), Mg (73.00 mg/L), and Ca (346.62 mg/L), reflecting contributions from the inoculum and FWH. This condition improved HY to 0.60 mol H₂/mol glucose equivalent, with butyric acid (3.43 g/L), acetic acid (0.68 g/L), and ethanol (0.11 g/L). Results highlight inoculum preparation and loading strategies to enhance DF-based waste-to-energy conversion.