Generation of Biogas by Use of Food Wastes -Development of a Small-Scale System of Methane Fermentation-

摘要

The research on generation of biogas was carried out as one of subjects in a project which has been promoted to make pig feeds using food recyclable resources. The aim of the research was to recycle all of leftover foods collected except those used as the pig feeds. A 1m^3 digestion tank and some small 18ℓ tanks were provided. The former was placed in a vinyl house to examine the effect of heating by the sun, and the latter ones were kept at a temperature of about 38℃ so as to be appropriate for methane fermentation to find the biogas generation rate. It was found that the biogas generation rate for the leftover foods of 1 kg was 70ℓ/kg a day and a proper amount of leftover foods for the tank volume of 1 m^3 was appropriately 11 kg/m^3 a day. This means that, for instance, a digestion tank with the volume of 20 m^3 and leftover foods of 220 kg per day were needed if you require biogas of 16 m^3 per day which is equivalent to kerosene of 10 ℓ as the calorific value.It is effective in heating the digestion tank to place it in a vinyl house. Although the heating is necessary in wintertime or nighttime, the subtropical climate at Okinawa is advantageous to methane fermentation. Therefore it is considered that the electricity consumption for the heating could be saved much more by use of renewable energies such as solar water heaters, solar batteries or small-sized wind power generators.