In an apparatus for the biological removal of phosphorus, use is made of the luxury uptake phenomenon such that return sludge is introduced into an anaerobic tank into which the raw water is introduced and phosphorus is released from the sludge, and the raw water which contains the phosphorus-deficient sludge is subjected to an aerobic treatment and the phosphorus is taken up in excess by the sludge and phosphorus is removed.
In an apparatus for the biological removal of phosphorus of this type, the phosphorus is taken up in the sludge and separated from the water along with the excess sludge, but there is a disadvantage in that a large amount of sludge is formed.