Inhibitory effect of zinc on fermentative hydrogen production: Insight into the long-term effect

This study explored the inhibitory effect of zinc (Zn) on fermentative hydrogen production. Results showed that hydrogen production was stimulated by 75% in the presence of 200 mg/L Zn and inhibited by 67.5% when Zn concentration reached 500 mg/L. Further increase of Zn concentration to 1000-2000 mg/L induced the complete inhibition of hydrogen production. When the inhibited microorganisms were got rid of high Zn concentration, hydrogen production was recovered in all inhibited groups, and the recovery rate was increased with the increase of inhibiting Zn dosage. Microbial analysis exhibited that Zn stimulated hydrogen production by enriching genus Clostridium sensu stricto 1, while the inhibited hydrogen production was induced by the dominance of genus Pseudomonas. Recovery of hydrogen production was achieved with the enrichment of genus Klebsiella and Clostridium sensu stricto 1 in Zn inhibited groups. Metabolic analysis showed that 200 mg/L Zn stimulated hydrogen production by strengthening pyruvate formation and formate decomposing, while high dosages of Zn inhibited hydrogen production by weakening the pyruvate and Acetyl-CoA formation.