Variable-volume improved A /O deep nitrogen and phosphorus removal process for sewage

The invention discloses a variable-volume improved A /O deep nitrogen and phosphorus removal process for sewage, belongs to the field of urban sewage and industrial waste water treatment, and particularly relates to a deep nitrogen and phosphorus removal process for the sewage. Specific to the problem concerned with synchronous removal of organic matters and the problem of poor nitrogen and phosphorus removal effect in a conventional A /O process, the process is characterized in that firstly, a pre-anoxic pool is arranged in front of an anaerobic pool to lower the influences of dissolved oxygen and nitric oxygen carried in returned sludge on the phosphorus removal effect, wherein 5-25 percent of sewage enters the pre-anoxic pool, and 75-95 percent of the sewage enters the anaerobic pool; and secondly, movable clapboards are arranged among the pre-anoxic pool, the anaerobic pool, an anoxic pool and an aerobic pool, and the volume ratio of each water pool can be adjusted flexibly according to the ratio of C:N:P in the sewage in order to change the hydraulic retention time of the sewage in each water pool. Meanwhile, the aim of deep nitrogen and phosphorus removal of the sewage is fulfilled under the condition that the inner reflux ratio is 100-200 percent and the sludge reflux ratio is 50-150 percent; and output water is stable, and reaches the national grade-A discharge standard.