Engineering strategies for the enhanced photo-H₂ production using effluents of dark fermentation processes as substrate

The major obstacle of combining dark and photo fermentation for high-yield biohydrogen production is substrate inhibition while using dark fermentation effluent as the sole substrate. To solve this problem, the dark fermentation broth was diluted with different dilution ratio to improve photo-H₂ production performance of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5. The best photo-H₂ production performance occurred at a dilution ratio of 1:2, giving a highest overall H ₂ production rate of 10.72 ml/l/h and a higher overall H₂ yield of 6.14 mol H₂/mol sucrose. The maximum H₂ content was about 88.1% during the dilution ratio of 1:2. The photo-H₂ production performance was further improved by supplying yeast extract and glutamic acid as the nutrient. The results indicate that the overall H ₂ production rate and H₂ yield increased to 17.02 ml/l/h and 10.25 mol H₂/mol sucrose, respectively. Using a novel solar-energy-excited optical fiber photobioreactor (SEEOFP) with supplementing tungsten filament lamp (TL) irradiation, the overall H₂ production rate was improved to 17.86 ml/l/h. Meanwhile, the power consumption by combining SEEOFP and TL was about 37.1% lower than using TL alone. This study demonstrates that using optimal light sources and proper dilution of dark fermentation effluent, the performance of photo-H₂ production can be markedly enhanced along with a reduction of power consumption.