延長Rhodopseudomonas palustris WP3-5光合產氫操作策略及LED燈對光合產氫與PHB累積之影響

Abstract

Hydrogen is considered as an environmentally friendly fuel due to its carbon-neutral characteristic that only produces water and energy (121 kJ/g) after combustion. Using purple non-sulfur bacteria is a promising method to produce hydrogen biologically because this kind of bacteria can produce hydrogen gas under photo-heterotrophic condition. However, some problems associated with purple non-sulfur bacteria to produce hydrogen are still necessary to be solved, e.g., low cell growth rate, low conversion efficiency of light, and decreased hydrogen production rate and hydrogen content caused by heterotrophs which have high growth rate in photo-bioreactors. In this study, several strategies, including immobilized cell, diurnal-cycle operation, co-culture system and fed-batch mode operation, were tried to solve those problems which have been mentioned before and to enhance their hydrogen production. On the other hand, lots of studies used tungsten lamp as their light source for photo-hydrogen production, and it would waste high amount of energy when lighting on. Thus, second part of this study was to investigate the effect of LED light as a light source on photo-hydrogen production and PHB accumulation by Rhodopseudomoans palustris WP3-5. From the results, it can be concluded that (i) Rps. palustris strain WP3-5 can not successfully produce hydrogen in immobilized cells because of the limitation in light penetration, substrate transportation and waste exclusion; (ii) strain WP3-5 generated less hydrogen and lower biomass under a diurnal cycle operation than continuous illumination with a hydrogen consumption by uptake hydrogenase; (iii) batch experiments of co-culture hydrogen production by Rps. palustris WP3-5/Anabaena sp. CH3 under mixed ratio of 1/1 exhibited a maximum hydrogen volume of 45.8 and 43.1 ml when co-culture medium contained 50 and 100 mg/L glutamate, respectively; (iv) fed-batch mode photo-bioreactor using acetate and lactate as electron donor can continuously produce hydrogen until 823 and 871 hours, respectively, even if heterotrophs existed in the reactor. In addition, Rps. palustris WP3-5 had the highest cell growth rate, substrate consumption rate and hydrogen production rate when using tungsten lamp as a light source. Among various kinds of LED lamp for the other source, green-LED lamp had a higher hydrogen production rate than the other LED lamps. On the other hand, influence of light source on the PHB accumulation by strain WP3-5 was not observed. Otherwise, the energy demand to produce one mole of hydrogen gas by Rps. palustris WP3-5 was compared between the green-LED and tungsten lamps. The result showed that using green-LED lamp is of benefit to energy effiency by saving 95% of electric demand.