Energy Production from Marine Biomass: Fuel Cell Power Generation Driven by Methane Produced from Seaweed

Global warming has become one of the most serious environmental problems. To cope with the problem, it is necessary to substitute renewable energy for nonrenewable fossil fuel. Biomass, which is one of the renewable energies, is considered to be carbon-neutral, meaning that the net CO{sub 2} concentration in the atmosphere remains unchanged provided the CO{sub 2} emitted by biomass combustion and that fixed by photosynthesis are balanced. Biomass is also unique because it is the only organic matter among renewable energies. In other words, fuels and chemicals can be produced from biomass in addition to electricity and heat. Marine biomass has attracted less attention than terrestrial biomass for energy utilization so far, but is work considering especially for a country like Japan which has long available coastlines. This paper discusses the utilization of marine biomass as an energy resource in Japan. A marine biomass energy system in Japan was proposed consisting of seaweed cultivation (Laminaria japonica) at offshore marine farms, biogas production via methane fermentation of the seaweeds, and fuel cell power generation driven by the generated biogas. The authors estimated energy output, energy supply potential, and CO{sub 2} mitigation in Japan on the basis of the proposed system. As a result, annual energy production was estimated to be 1.02 x 10{sup 9} kWh/yr at nine available sites. Total CO{sub 2} mitigation was estimated to be 1.04 x 10{sup 6} tonnes per annum at the nine sites. However, the CO{sub 2} emission for the construction of relevant facilities is not taken into account in this paper. The estimated CO{sub 2} mitigation is equivalent to about 0.9% of the required CO{sub 2} mitigation for Japan per annum under the Kyoto Protocol framework.