Methane fermentation method

A methane fermentation method comprising the steps of:

• a pulverization step of finely pulverizing an organic substance in which a moisture content is adjusted such that a solid content of the organic substance is equal to or less than 10% in a wet bead mill;
• a methane fermentation step of supplying the organic substance which is finely pulverized in the pulverization step to a methane fermentation chamber and decomposing the organic substance with an anaerobic microorganism to cause methane fermentation so as to generate methane gas;
• a separation step of separating, with an ultrafiltration (UF) membrane, a digestive fluid after the methane fermentation in the methane fermentation step into a concentrated liquid and a permeation liquid;
• a return step of returning the concentrated liquid separated in the separation step to the methane fermentation chamber;
• and
• an agitation step of agitating contents of the methane fermentation chamber with a water flow produced by the return of the concentrated liquid in the return step.