Effect of Ni2+ concentration on fermentative hydrogen production using waste activated sludge as substrate

The influence of Ni²⁺ concentration on biohydrogen production was investigated using waste activated sludge as substrate. The degradation of substrate, accumulation of volatile fatty acids (VFAs) and distribution of microbial community were analyzed to provide information for influencing mechanisms of Ni²⁺ addition. The experimental results demonstrated that the efficiency of hydrogen fermentation from waste activated sludge could be significantly improved. The optimal Ni²⁺ concentration was 5 mg/L, and under this concentration, the cumulative hydrogen production was 1.29 times of the control group. The degradation of soluble chemical oxygen demand (SCOD) increased from 25.21% to 27.69% when the added Ni²⁺ concentration was 5 mg/L. The analysis of microbial community distribution revealed that Ni²⁺ decreased the microbial diversity, and provided more suitable condition for the microbial growth and activity of hydrogen-producers. Citrobacter was the dominant hydrogen-producers in the control group, they changed into Enterococcus when 5 mg/L Ni²⁺ was added. Besides, the proportion of Clostridium_sensu_stricto_1, which is regarded as the primary hydrogen-producing bacteria under numerous operating conditions, was also significantly increased in the presence of Ni²⁺.