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 H 2, with anaerobic acidogenic bacteria is an ideal option for efficient H 2 production from wastewater. In the present work, H 2 production by Rhodopseudomonas capsulata from three individual VFAs, i.e. acetate, propionate and butyrate, and a mixture of the three, was investigated. H 2 yields were 0.65 for acetate, 0.28 for propionate and 0.24 for butyrate, respectively, whereas the corresponding maximum H 2 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 H 2 production. In contrast, a higher butyrate concentration favoured cell growth, but was detrimental to H 2 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 H 2 production with a yield of 0.34 and maximum H 2 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.