Hydrogen production by indigenous photosynthetic bacterium Rhodopseudomonas palustris WP3–5 using optical fiber-illuminating photobioreactors

A novel optical fiber-based photobioreactor was utilized to produce H2 by indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3–5 using acetate as the sole carbon source. Plastic cladding of conventional end-light optical fibers was removed to obtain side-light optical fibers (SLOF), which was inserted into photobioreactors as the internal light source. External irradiation by conventional lamps may also be provided for the bioreactor as supplemental light sources. The H2 production performance and light conversion efficiency of the photobioreactor were assessed when various illumination systems were used. The light sources examined included SLOF excited by halogen lamp (OF-HL), SLOF excited by metal–halide lamp (OF-MH), tungsten filament lamp (TL), halogen lamp (HL), and binary combinations of the above. Compared with bioreactors illuminated by external lamps, the OF-HL system produced more H2 (625 ml), had higher light conversion efficiency (1.80%), and achieved higher H2 yield (1.19 mol H2/mol acetic acid). However, among the single light sources examined, HL gave the highest overall (νH2νH2) and specific (νs,H2νs,H2) H2 production rate of 8.68 ml/l h and 3.01 ml/h g cell, respectively, primarily due to enabling better cell growth. Using OF-MH system resulted in poor H2 production, indicating that emission spectrum of light sources was critical to photo-H2 production. Combination of two different light sources appeared to further enhance photo-H2 production, especially when optical fibers and external lamps were combined. Combination of OF-HL and TL exhibited the highest H2 yield, νH2νH2, and νs,H2νs,H2 of 2.64 mol H2/mol acetic acid, 17.06 ml/h l, and 9.47 ml/h g cell, respectively. However, the highest total H2 production (944 ml) and light conversion efficiency (1.42%) were attained when two types of optical fibers were incorporated (i.e., the OF-HL/OF-MH system).