Experimental study finds highest hydrogen yield at D2 and pH 8

An experiment comparing five dilution levels and initial pH values found that D2 food waste hydrolysate at an initial pH of 8 produced the highest hydrogen yield, reaching 0.60 mol H₂ per mol of glucose equivalent. The study examined dark fermentation of food waste hydrolysate made by dilute sulfuric acid thermohydrolysis, testing dilution levels D0 through D4 and initial pH values from 6 to 9. Analysis of variance showed that both dilution and initial pH significantly affected hydrogen yield, with p-values below 0.05, and Tukey’s post hoc comparison identified D2 at pH 8 as the adequate condition.

The researchers investigated the composition of the fermentation systems, including iron, magnesium, calcium, glucose equivalent, 5-hydroxymethylfurfural and furfural. These measurements were considered in relation to dark fermentation performance because the hydrolysate contains nutrients and inhibitory compounds that can interact and contribute to unstable hydrogen production. The supplied study results report composition and hydrogen yield for the selected D2 and pH 8 condition; they do not show that any one metal, glucose concentration or inhibitory compound independently caused the higher yield.

At D2 and an initial pH of 8, the dark fermentation system contained 14.21 g/L glucose, 27.97 mg/L iron, 35.60 mg/L magnesium and 148.77 mg/L calcium. Concentrations of 5-hydroxymethylfurfural and furfural were 32.19 mg/L and 97.86 mg/L, respectively. The highest observed hydrogen yield therefore occurred in a fermentation mixture that retained measurable concentrations of both investigated furans.

The experiment tested operating conditions rather than isolating the contribution of individual chemical components, so its result supports a combined condition rather than a single-factor mechanism. The selected condition also produced measurable quantities of organic products. Butyric acid was present at 2.92 g/L, acetic acid at 0.76 g/L and ethanol at 0.01 g/L. These reported concentrations show that hydrogen production at D2 and pH 8 coincided with the formation of butyric and acetic acids and a much smaller measured concentration of ethanol.

The abstract does not provide the concentrations of these liquid products for every dilution and pH combination, so the data do not establish that dilution or pH changed their overall distribution across the experiment. The study provides laboratory evidence that operating conditions matter when food waste hydrolysate is used for dark fermentation, but its findings are bounded by the tested matrix of five dilution levels and initial pH values between 6 and 9. The reported optimum applies to the hydrolysate and conditions examined; it does not establish that D2 and pH 8 will deliver the same hydrogen yield in hydrolysates with different glucose, metal or inhibitor concentrations.

Subject of Research: Effects of dilution and initial pH on hydrogen yield from food waste hydrolysate during dark fermentation

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

Article References: Julkipli, J., & Babel, S. (2026). Investigating metal, glucose, and inhibitory compound levels through food waste hydrolysate dilution and pH adjustment to enhance dark fermentation performance. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38328-0

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38328-0

Keywords: dark fermentation, food waste, hydrogen production, food waste hydrolysate, dilution, initial pH, 5-hydroxymethylfurfural, furfural, butyric acid, waste-to-energy, Investigating, metal