Effect of copper on fermentative hydrogen production from sewage sludge: Insights into working mechanisms

The effect of Copper (Cu) on fermentative hydrogen production from sewage sludge (SSL) was firstly explored, and glucose was chosen as typical substrate to make a comparison. Results showed that the stimulative dosages of Cu on hydrogen production from glucose and SSL were 20–60 mg/L and 20–100 mg/L, respectively. The stimulation was more significant to SSL (6.3–43.8 %) than glucose (4.8–16.1 %). 500–1000 mg/L Cu posed obvious inhibition to hydrogen production, and the inhibition was more significant to glucose (80.6–91.9 %) than SSL (25.0–37.5 %), which was due to the protective effect of SSL to hydrogen producers from adsorbing Cu. The exposure enriched the Cu-resistant microorganisms like genus Aeromonas, Comamonas, Pseudomonas and Dechloromonas. Metabolic analysis shows that low dosages of Cu stimulated hydrogen production by strengthening the formate decomposition process, and weakening the lactate formation and homoacetogenesis processes, while high dosages of Cu inhibited hydrogen production by weakening all hydrogen-producing processes including formate decomposition, ferredoxin hydrogenation and glucose decomposition processes.