Improved phototrophic H₂ production with Rhodopseudomonas palustris WP3-5 using acetate and butyrate as dual carbon substrates

An indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 was used to produce hydrogen phototrophically from acetate (HAc) and butyrate (HBu), which are the major soluble products from acidogenic dark fermentation. Statistical experimental design methodology was applied to identify optimal composition of the two carbon substrates in the medium, leading to better H₂ production performance of R. palustris WP3-5. Three performance indexes were used to assess the effectiveness of the phototrophic H₂ production; they were H₂ yield (Y_H2), maximum H₂ production rate (R_max) and maximum cumulative H₂ evolution (H_max). An overlay contour plot was used to determine the optimal concentration range of HAc and HBu, taking into account all three performance indexes (i.e., R_max, H_max, and Y_H2) simultaneously. With the response surface analysis, R. palustris WP3-5 could produce H₂ efficiently with the best R_max, H_max, and Y_H2 of 39.5 ml/h, 2738 ml, and 51.6%, respectively. This performance is superior to most reported values in the literature, indicating that the statistical experimental design is an effective tool to improve phototrophic H₂ production with R. palustris WP3-5.