PURPOSE: To provide a method which efficiently and effectively utilizes the sludge digestion gas generated from a treatment plant without generating secondary pollution.

CONSTITUTION: The sludge digestion gas generated when sludge digestion gas is anaerobically digested is brought into gas-liquid contact with the alkaline treated water obtd. from a stage for a tertiary treatment of sewage, etc., in desulfurizing column 6 to execute desulfurizing and is then supplied to a fuel battery 7, by which power generation is executed. Honeycomb-shaped structural bodies are preferably used for the gas-liquid contact.