US Patent 7850851 Biological phosphorus removal

A process for treating waste water to remove phosphorous and nitrogen in a treatment system including an anaerobic zone (5) containing an anaerobic mixed liquor having organisms which release phosphorous into the anaerobic mixed liquor; an anoxic zone (7) containing an anoxic mixed liquor having organisms which uptake phosphorous and denitrify the anoxic mixed liquor and an aerobic zone (9) containing an aerobic mixed liquor having organisms which uptake phosphorous and nitrify the aerobic mixed liquor; the process including the steps of providing wastewater to be treated into the anaerobic zone (5) and communicating anaerobic mixed liquor from the anaerobic zone (5) to the anoxic zone (7). The anoxic mixed liquor is then communicated from the anoxic zone (7) to the anaerobic zone (5) and the anoxic mixed liquor from the anoxic zone (7) to the amble zone (9). The aerobic mixed liquor is applied to a feed side of a membrane filter (10) to produce a treated effluent from a filtrate side of the membrane filter (10). Oxygen-containing gas bubbles is flowed past the feed side of the membrane filter (10) to remove accumulated solids. At least some of the material rejected by the membrane filter (10) is communicated to a degassing device (20) to remove some or all of any dissolved oxygen contained in the rejected material and the degassed material is communicated to the anoxic zone (7).