Investigation of the Photoheterotrophic Hydrogen Production of Rhodobacter sphaeroides KCTC 1434 using Volatile Fatty Acids under Argon and Nitrogen Headspace

In this study, the photo fermentative H₂ production of Rhodobacter sphaeroides KCTC 1434 was investigated using acetate, propionate and butyrate under argon and nitrogen headspace gases. The highest H₂ yield and Substrate Conversion Efficiency (SCE) were observed from butyrate (8.84 mol H₂/mol butyrate consumed, 88.42% SCE) and propionate (6.10 mol H₂/mol propionate consumed, 87.16% SCE) under Ar headspace. Utilization of acetate was associated with low H₂ evolution, high biomass yield and high final pH, which suggest that acetate uptake by the strain involves a biosynthetic pathway that competes with H₂ production. The use of N₂ in sparging resulted to a decreased H2 productivity in propionate (0.49 mol H₂/mol propionate consumed, 7.01% SCE) and butyrate (1.22 mol H₂/mol butyrate consumed, 1.04% SCE) and was accompanied with high biomass yield and radical pH increase in all acids. High H₂ generation had shown to improve acid consumption rate. The use of the three acids in a mixed substrate resulted to a drastic pH rise and lower H₂ generation. This suggests that a more refined culture condition such as additional control of pH during fermentation must be kept to enhance the H₂ productivity. Overall, the study provided a background on the H₂ production using R. sphaeroides KCTC 1434 which might be a good co-culture candidate because of its high SCE on butyrate and propionate.