NOVELTY - Organic material particles in sludge is changed into soluble organic material by heat-treating. The eluted organic material with microorganism is subjected to hydroxyl-radical contact oxidation, and the microorganism cell wall is oxidized in high active ionized gas generating device (30). A high voltage aqueous discharging process is carried out by deriving plasma discharging in discharge tube, and discharging waste activated sludge in liquid phase. Thus, the method of decreasing waste activated sludge and improving anaerobic digestion efficiency is carried out.    USE - Method of decreasing waste activated sludge and improving anaerobic digestion efficiency.    ADVANTAGE - The method enables improved anaerobic digestion efficiency, and efficiently improves generation rate of methane gas.    DETAILED DESCRIPTION - Organic material particles in sludge is changed into soluble organic material by heat-treating the sludge through sludge transfer pipe (22) in double pipe-type steam jacket (23) using warm water at temperature more than 60 degrees C for specific time. The eluted organic material with microorganism is subjected to hydroxyl-radical contact oxidation, and the cell wall of microorganism in sludge is oxidized by producing hydroxyl radical using high active ionized gas generating device. A high voltage aqueous discharging process is carried out by deriving plasma discharging in discharge tube, and discharging waste activated sludge in liquid phase. Thus, the method of decreasing waste activated sludge and improving anaerobic digestion efficiency is carried out. An INDEPENDENT CLAIM is included for processing apparatus for decreasing waste activated sludge and improving anaerobic digestion efficiency.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of processing apparatus. (Drawing includes non-English language text)    Settling tank (10)    Sludge transfer pipe (22)    Steam jacket (23)    High active ionized gas generating device (30)    Biological processing bath (50)    Digestion tank (70)    Desulfurization tub (80)    Boiler (110)