Biohydrogen production by Rhodobacter capsulatus in solar tubular photobioreactor on thick juice dark fermenter effluent

The purpose of this study was to operate a pilot scale solar tubular photobioreactor (90 L) for photofermentative hydrogen production from thick juice dark fermenter effluent (DFE) by photosynthetic purple-non-sulfur bacterium, Rhodobacter capsulatus. The tubular photobioreactor was equipped with internal cooling tubes for effective temperature control, which is essential for stable, long-term operation. The photobioreactor was operated in fed-batch mode throughout September 2009 in Ankara, Turkey. R. capsulatus had a rapid growth with a specific growth rate of 0.025 h−1 in the exponential phase. The growth was modeled and the parameters were compared with the results obtained in artificial medium. An exponential relationship was found between daily specific growth rates during fed-batch operation and daily total light energy received. The average molar productivity calculated according to daylight time was 0.15 mol H2/(m3 h). The yield obtained was 0.4 mol H2/mol acetic acid consumed. The hydrogen yield factor was related to the daily total light energy received. Acetic acid utilization for different metabolic pathways was investigated. Maximum COD removal efficiency throughout the operation was calculated as 68%. This study showed that sequential operation of dark and photofermentation is a promising route to produce biological hydrogen from thick juice.