The membrane type diffuser "AEREVO." is for an oxygen diffusion to an aeration tank in a sewage treatment. AEREVO. has the ability of generating fine air bubbles and supplying them effectively into an aeration tank. A large reduction of air flow rate will be expected by using AEREVO. because of the high oxygen transfer efficiency. According to the test results in water tank and sewage treatment plant, it is proved that the oxygen transfer efficiency of AEREVO. is nearly two times of conventional one for the circular flow aeration tank. Actually, AEREVO. has been applied to several practical sewage plants. As a result, 24〜54％ of reduction of air flow rate compared with existing diffuser has been achieved. On the occasion of replace of existing facilities of sewage treatment plant, a large reduction of power consumption for aeration will be expected by applying of AEREVO. instead of a conventional type diffuser.