Comparison of Acetate‑butyrate and Acetate‑ethanol Metabolic Pathway in Biohydrogen Production

Abstract

Hydrogen gas is the cleanest energy carrier and could be produced by biological process. Dark
fermentation is one of the biohydrogen production methods that carried out just on organic wastes
conversion. In this study, the batch tests were conducted to compare the biohydrogen production
and glucose fermentation via acetate‑butyrate and acetate‑ethanol metabolic pathway induced by
NaOH and KOH (10 M) pretreatment. In batch test, the glucose concentration in the feed was varied
from 3.75 to 15 g/L under mesophilic conditions (37°C ± 1°C). In order to sludge pretreatment,
NaOH and KOH (as an alkaline agent) was used. Batch tests showed that maximum biohydrogen
production under NaOH (2.7 ± 0.5 L) and KOH (2.2 ± 0.7 L) pretreatment was achieved at 15 g/L
of influent glucose. In the batch test, with increasing influent glucose concentration, the lower yields
of hydrogen were observed. The biohydrogen reactions had good electron closure (5.2%–13.5%) for
various glucose concentrations and pretreatments. For NaOH and KOH pretreatment, the biohydrogen
yield decreased from 2.49 to 1.63 and from 2.22 to 1.2 mol H2/mol glucose, respectively, when
glucose concentration increased from 3.75 to 15 g/L. By applying alkaline sludge pretreatment by
NaOH and KOH, the glucose fermentation was followed with acetate‑butyrate and acetate‑ethanol
metabolic pathway, respectively. The lower biohydrogen yields were observed under acetate‑ethanol
metabolic pathway and related to metabolically unfavorable for biohydrogen production.