Activated sludge plant for purificn. of waste water - uses suction of aeration impeller to recycle sludge from settlement tank

摘要

The liq. for treatment first enters an aeration tank provided with a rotary impeller to aerate the surface. From the aeration tank liq. passes to a final settlement tank from which activated sludge is recycled to the aeration tank. The means for recycling sludge comprises of the settlement tank into the suction zone of the surface aerating impeller. Transfer of liq. from the aeration tank to the settlement tank is pref. by overflow. The aeration tank can be comparatively shallow, without a circulation chimney leading up to the impeller; the top of the sludge recycling pipe then delivers just below the impeller. Alternatively, the aeration tank can be deep, with a circulation chimney rising towards the impeller; in this case the sludge recycling pipe delivers into the chimney.