NOVELTY - Method for treating wastewater involves (a) carrying out facultative anaerobic-aerobic process which involves discharging sludge including microorganism with degraded activity into water tank or aeration tank, (b) carrying out chemical coagulation process, (c) carrying out solid-liquid separation process and transferring the precipitated sludge to dewatering facility, (d) carrying out culturing and proliferation of microorganism, (e) carrying out precipitate separation process, and (f) carrying out sludge processing.    USE - The method is useful for treating wastewater.    ADVANTAGE - The method has improved wastewater treatment processing efficiency.    DETAILED DESCRIPTION - Method for treating wastewater involves (a) carrying out facultative anaerobic-aerobic process which involves discharging sludge including microorganism with degraded activity into water tank or aeration tank, where the wastewater flows into the tank, (b) carrying out chemical coagulation process which involves reacting wastewater with chemicals in a cohesion reaction tank, (c) carrying out solid-liquid separation process which involves separating solid and liquid, and transferring the precipitated sludge to dewatering facility, (d) carrying out culturing and proliferation of microorganism in a bioreactor, (e) carrying out precipitate separation process which involves precipitating and removing contaminants adsorbed onto activated sludge, and (f) carrying out sludge processing step which involves processing and discharging sludge generated from the solid-liquid separation process and precipitate separation process, and filtering supernatant to allow reprocessing of the filtrate generated in sludge processing process. The facultative anaerobic-aerobic process further involves high quality water separating process which involves installing one or more precipitation baffles by using microorganism carrier used for adhesion and growth of microorganism, temporarily dividing into aeration portion and precipitation portion, precipitating through precipitation baffle, and separating the water, and the microorganism culturing and proliferation step further involves culturing microorganism through microorganism cultivator, supplying the microorganism to water collection tank or aeration tank.