Continuous production of biohydrogen from oil palm empty fruit bunch hydrolysate in tubular photobioreactors

Production of hydrogen by the photosynthetic bacterium Rhodobacter sphaeroides was compared in continuously operated tubular photobioreactors illuminated by natural outdoor sunlight (0.15-66 klux; diurnal cycle) and constant indoor artificial light (10 klux; tungsten lamps). In both cases the operating temperature was 35 °C and the organic carbon source was an acid hydrolysate of oil palm empty fruit bunch (EFB), an agroindustrial waste. In the outdoor photobioreactor, under the best production conditions, the daytime feeding rate of the mixed carbon substrate was 48 mL h−1 and the average pseudo-steady state hydrogen production rate was 36 mL H2 L−1 medium h−1. The cumulative hydrogen production was 430 mL H2 L−1 medium. For the indoor photobioreactor fed at the same rate as the outdoor system, the steady state average hydrogen production rate was 43 mL H2 L−1 h−1 and the cumulative hydrogen production was 517 mL H2 L−1 medium. Reducing the feed rate to less than 48 mL h−1, enhanced the biomass concentration, but reduced hydrogen production in both bioreactors. The sunlight-based cumulative hydrogen production was only about 17% less compared to the artificially lit system, but required only 22% of the electrical energy.