Effects of nitrate concentration on biohydrogen production and substrate utilization in dark-fermentation

Batch experiments were conducted to investigate the effect of the nitrate (NO3−) concentration on the hydrogen production and substrate utilization in a dark fermentation process. The nitrate concentration was varied from 0 to 5,000 mg L−1 in experiments with a mixed culture of anaerobic sludge. Anaerobic sludge was treated with 2 M HCl at pH 2 for the enhanced biohydrogen production. With added NO3− concentration of 0 g/L, the maximum hydrogen production was 2.2 mol-H2 mol- glucose−1. But, an increase in NO3− concentration, the hydrogen production decreased to 0.3 from 2.2 mol-H2 mol- glucose−1 at 4,000 mg NO3− L−1. But, in all conditions, more than 90 % of initially added glucose (10 g L−1) was removed and the microbial community structures were observed similarly in every condition and main germinated species was detected as Clostridium perfringens by DNA cloning. As a result, it was confirmed that the high nitrate concentration at the initial stage, glucose was utilized for nitrate removal reaction than hydrogen production.