PROBLEM TO BE SOLVED: To produce usable energy from the conventionally wasted residual air of a volume of air that supplies dissolved oxygen into water rather than releasing the residual air into the atmosphere above the water surface.SOLUTION: In an air-water separation measurement downflow means disposed in a low head position around 1-5 m above the liquid surface or water surface in an aeration tank or natural water area containing aeration tank mixed liquid or water, liquid or water is pumped by an air lift pump or water pump, and the aeration mixed liquid or water flows down to the intake of a low head water wheel having an intake means. The low head water wheel is driven rotatably and electricity is generated by a generator as a result. In addition, an overflow diversion means is connected to a rising flow pipe and a falling flow pipe, and a normal aeration tank in which a shallow layer diffused air supply means is disposed and a deep layer aeration tank or ultra-deep layer aeration tank are formed. The air lift pump and a circulation pump provide the motive force for generating the downflow in the aeration tanks, and further, the undissolved air from the diffused air for aeration is collected by a collecting means and used as an air source for the diffused air for the air lift pump to form an energy efficient means for air diffusion.【課題】水中へ溶存酸素を供給する空気量の内で、従来では無駄に廃棄されていた残存空気量を単に水面上大気へ開放することなく、有効エネルギーとすることが課題である。【解決手段】曝気槽混合液又は水を内容した曝気槽又は自然水域における水面上方１～５m前後の低落差位置に配設した気水分離軽量流下手段に、液又は水を気泡ポンプ又は揚水ポンプで揚水し、該曝気槽混合液又は水を低落差水車に取水流下して、前記低落差水車を回転駆動し、連結した発電機で発電する。又、上昇流管及び下降流管と越流移流手段を連結して、浅層散気空気供給手段を配設した通常曝気槽、深層曝気槽又は超深層曝気槽を構成し、気泡ポンプ及び循環ポンプで前記各曝気槽の下降流生成動力源とし、さらに、曝気用散気における未溶解空気を捕集手段で捕集し、気泡ポンプの散気空気源とし、省エネルギー散気手段とする。【選択図】図３
