Return unit (240), wherein the return unit (240) is arranged in an aerobic basin (200) and the return unit (240) comprises a feed section (241), a treatment section (242) and a
discharge section (243) which are connected sequentially; wherein the feed section (241) is configured to feed a
reflux substance; the treatment section (242) is configured for the deoxidation of the
reflux substance supplied through the feed section (241); and the
discharge section (243) is configured to
discharge the deoxidized
reflux substance; wherein the treatment section (242) is positioned at least partially above a ventilation opening (251) of a ventilation device (250); or the treatment section (242) is attached to a surface of the
aeration device (250) such that vibration deoxidation of the reflux substance in the treatment section (242) is carried out by using the vibration generated by the
aeration device (250) during operation, or the treatment section (242) is driven to vibrate by an
impact force from a position below, generated by bubble conveying the
aeration device (250), wherein the reflux unit (240) further includes a filter plate (244), the filter plate (244) being arranged in an inner cavity of the treatment section (242), the treatment section (242) being provided with a gas outlet (2421) and a water outlet (320), the gas outlet (2421) being configured to discharge
oxygen generated by deoxidation, and the water outlet (320) being configured to discharge a filtrate passing through the filter plate (244), and the gas outlet (2421) being provided with a one-way drain valve, and the one-way drain valve being configured to discharge the
oxygen generated by deoxidation unidirectionally to an outside of the treatment section (242), wherein a maximum height of a first connecting opening (2411) formed by the feed section (241) and the treatment section (242) does not exceed 2 / 3 of a maximum height of the treatment section (242), and the first connecting opening (2411) is arranged in an upper position, and a maximum height of a second connecting opening (2431) formed by the discharge section (243) and the treatment section (242) does not exceed 2 / 3 of the maximum height of the treatment section (242), and the second connecting opening (2431) is arranged in a lower position.