No. 11: Increase the generation amount of biogas by mixing food scraps and sewage sludge (October 24, 2011)

A sewage treatment plant in Osaka will start the experiment to increase the amount of biogas by treating sewage sludge and food scraps together coming November for an investment of about 28 million yen. This plant currently generates electricity using biogas produced by sewage sludge for operation, and plants to add food scraps to the sewage sludge for increased efficiency of biogas generation and decreased amount of food scraps. Osaka plans to put the technology into practical application by 2020. The method to utilize food scraps for biogas generation can be found in small local cities, but Osaka may be the first major city to work seriously on this method in Japan.  

The plant produces about 8,000 cubic meters biogas daily from 400 tons of sewage sludge. Because organic substances in food scraps are not resolved as much as in sewage sludge, Osaka presumes that 120-130 cubic meters biogas can be generated from 1 ton of food scraps. Hence, it thinks that the generation efficiency will increase by treating them together. In the experiment, a research team will collect food scraps from hotels and department stores, liquefied them, and put them into the digester chamber. The will verify the optimal method for the operation because it is necessary to eliminate chopsticks and other products unsuitable for the process beforehand. Osaka treats about 1,200,000 tons of trash annually, about 30% of which are food scraps. Osaka is promoting the concept “Building a recycling-oriented community of resources and energy,” and the investment on the experiment is part of this approach.