The seaweed is crushed, then made into slurry by adding dilution water, and then fermented using microorganisms to produce methane.
Seaweed is great stuff in sushi or miso soup, but too much of a good thing, rotting on the beach, can get a bit smelly; disposal is a big expense for Japanese coastal communities. Tokyo Gas Company is now collecting it, fermenting it in vats and generating methane gas, which then is used to produce electricity. Seaweed also absorbs a lot of CO2 while it grows, so using it as a biomass fuel produces energy without a net gain in greenhouse gases. This gives new meaning to the phrase "power plant", the first of which will open next year. ::Trends in Japan