Conversion of individual and mixed volatile fatty acids to hydrogen by Rhodopseudomonas capsulata

A combination of photosynthetic bacteria, which can utilize volatile fatty acids (VFAs) as a carbon source for growth and production of H2, with anaerobic acidogenic bacteria is an ideal option for efficient H2 production from wastewater. In the present work, H2 production by Rhodopseudomonas capsulata from three individual VFAs, i.e. acetate, propionate and butyrate, and a mixture of the three, was investigated. H2 yields were 0.65 for acetate, 0.28 for propionate and 0.24 for butyrate, respectively, whereas the corresponding maximum H2 production rates were 17.7, 16.0 and 5.8 ml l−1 h−1. A higher acetate and propionate concentration was beneficial for both cell growth and H2 production. In contrast, a higher butyrate concentration favoured cell growth, but was detrimental to H2 production. A mixture of 1.9 g l−1 acetate, 0.4 g l−1 propionate and 0.8 g l−1 butyrate was readily utilized by R. capsulata for H2 production with a yield of 0.34 and maximum H2 production rate of 14.5 ml l−1 h−1. The consumption rate for individual and mixed VFAs by R. capsulata followed the order acetate>propionate>butyrate.