The technically feasibility of converting organic pollutants in wastewater into hydrogen by a continuous two-step process was demonstrated. Two carbohydrates, i.e. glucose and sucrose, in wastewater were respectively acidified by dark fermentation at pH 5.5 with 6–6.6 hours of hydraulic retention in a 3-l fermentor, producing an effluent containing mostly acetate and butyrate, and a methane-free biogas comprising mostly hydrogen. The acidified effluent was then further treated by photo fermentation for hydrogen production. The overall yield based on the substrate consumed was 31–32%, i.e. 17–18% for dark fermentation and 14% for photo fermentation. It was found that under certain dark fermentation conditions, hydrogen-producing sludge was agglutinated into granules, resulting in a higher biomass density and increased volumetric hydrogen production efficiency. DNA-based analysis of microbial communities revealed that the respective predominant bacteria were Clostridium in dark fermentation and Rhodobacter in photo fermentation. Further investigations are warranted, particularly, in areas such as improving reactor design, treating protein and lipid rich wastewaters, and studying sludge granulation mechanisms and controlling factors.
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