PURPOSE: To enable to use an inexpensive apparatus having small pressure and corrosion resistance, by carrying out the heat treatment of excess sludge separated in the final precipitating pool at a treating temperature lowered to 100W120°C while aerating it with air.
CONSTITUTION: Organic filthy water 1 is successively treated by using a primary precipitating pool 2, an aerating tank 4 and a final precipitating pool 5. Excess sludge 6 separated in the final precipitating pool 5 is heat-treated in a heat- treating means 7 and mixed with crude sludge 3 separated in the primary precipitating pool 2, and the mixture is methane-fermented in an anaerobic digesting tank 8 to form methane-contg. gas. In this sludge-treating method, said heat- treating step is carried out under the condition of 100W120°C at gauge pressure below about 1kg/cm2 which aerating the sludge with air. That is, an inexpensive apparatus having small pressure corrosion resistance can be used, although a decomposing ratio is slidhtly sacrified. Consequently, the abrasion or breakdown of a valve for discharging air from high to normal pressure and other troubles derived from high pressure are eliminated.
FUJIWARA GOROU
KANAZAWA MASARU
