UC Berkeley

Biological systems offer a variety of ways to generate renewable energy. Among them, unicellular green algae have the ability of capturing the visible portion of sunlight and storing the energy as hydrogen (H2). They hold promise in generating a renewable fuel from nature's most plentiful resources, sunlight and water. Anoxygenic photosynthetic bacteria have the ability of capturing the near infrared emission of sunlight and producing H2 and ammonia (NH3), while consuming small organic acids. Dark anaerobic fermentative bacteria consume carbohydrates, thus generating H2, and possibly NH3, while converting sugars into small organic acids. The work addresses the development of an integrated biological H2 and biomass production process based on unicellular green algae, which are driven by the visible portion of the solar spectrum, coupled with purple photosynthetic bacteria, which are driven by the near infrared portion of the spectrum. Thus, a two-dimensional integration of photosynthetic H2 production can be achieved, resulting in better solar irradiance utilization (visible plus infrared) and integration of nutrient utilization for the cost-effective production of substantial amounts of H2 gas. The possibility to improve efficiency even further is discussed, with dark anaerobic fermentations of the photosynthetic biomass, enhancing the yield of H2 production and providing a recursive link in the system to regenerate some of the original nutrients. Cost analysis and design of tubular modular photobioreactors for the scale-up of cultures and H2-production will be presented.