Hydrogen photoproduction by Rhodopseudomonas palustris 42OL cultured at high irradiance under a semicontinuous regime

The main goal of this study was to increase the hydrogen production rate improving the culture technique and the photobioreactor performances. Experiments were carried out at a constant culture temperature of 30oC and at an average irradiance of 480Wm-2 using a cylindrical photobioreactor (4.0 cm, internal diameter). The culture technique, namely, the semicontinuous regime for growing Rhodopseudomonas palustris 42OL made it possible to achieve a very high daily hydrogen production rate of 594 ± 61mL (H2) L-1 d-1. This value, never reported for this strain, corresponds to about 25mL (H2) L-1 h-1, and it was obtained when the hydraulic retention time (HRT) was of 225 hours. Under the same growth conditions, a very high biomass production rate (496 ± 45 mg (dw) L-1 d-1) was also achieved. Higher or lower HRTs caused a reduction in both the hydrogen and the biomass production rates. The malic-acid removal efficiency (MAre) was always higher than 90%. The maximal hydrogen yield was 3.03 mol H2 mol MA-1 at the HRT of 360 hours. The highest total energy conversion efficiency was achieved at the HRT of 225 hours.