Hydrogen production using amino acids obtained by protein degradation in waste biomass by combined dark- and photo-fermentation

•Five amino acids produced limited hydrogen but abundant SMPs in dark-fermentation.•C conversion efficiencies of alanine and serine were 85.3–94.1% in dark-fermentation.•Dark-fermentation effluent of alanine gave a high H2 yield in photo-fermentation.•HVCE of alanine to hydrogen by combined dark- and photo-fermentation was 25.1%.

The biological hydrogen production from amino acids obtained by protein degradation was comprehensively investigated to increase heating value conversion efficiency. The five amino acids (i.e., alanine, serine, aspartic acid, arginine, and leucine) produced limited hydrogen (0.2–16.2 mL/g) but abundant soluble metabolic products (40.1–84.0 mM) during dark-fermentation. The carbon conversion efficiencies of alanine (85.3%) and serine (94.1%) during dark-fermentation were significantly higher than those of other amino acids. Residual dark-fermentation solutions treated with zeolite for NH4+ removal were inoculated with photosynthetic bacteria to further produce hydrogen during photo-fermentation. The hydrogen yields of alanine and serine through combined dark- and photo-fermentation were 418.6 and 270.2 mL/g, respectively. The heating value conversion efficiency of alanine to hydrogen was 25.1%, which was higher than that of serine (21.2%).