Effect of pH on the performance of hydrogen production by dark fermentation coupled denitrification

High concentration nitrogen-containing organic wastewater is a potential substrate for hydrogen production by dark fermentation. In this study, the effect of initial pH on the performance of hydrogen production by dark fermentation coupled denitrification was investigated. The hydrogen production, liquid metabolites, nitrate, nitrite and microbial community were monitored under the condition of pH varying from 4 to 11. Results showed that the highest hydrogen production (70.94 ± 4.750 mL/g VSS), chemical oxygen demand (COD) removal rate (37.13 ± 1.86%) and nitrate reduction rate (1.57 ± 0.27 mg/L/h) were obtained at pH of 5. Under this condition, the nitrate was mainly reduced to N₂ with hydrogen as the electron donor. When the initial pH was 6-11, nitrate mainly reduced to N₂ through co-action with acetate. Microbial community analysis revealed that as the initial pH increased from 4 to 11, the main hydrogen-producing microorganisms were gradually converted from Clostridium sensu stricto 12 sp. into Clostridium sensu stricto 1 sp, which leaded to changes in the hydrogen production process.