Method of improving SVI of mixed liquor in aeration tank

A method for improving the SVI of the mixed liquor residing in an aeration tank in an activated sludge treatment system which also includes a sedimentation tank, said method comprising the following steps:

• (A) feeding a concentration system other than said activated sludge treatment system with at least one of the mixed liquor in the aeration tank, the mixed liquor withdrawn from a line connecting the aeration tank and the sedimentation tank, and the settled sludge leaving said sedimentation tank;
• (B) introducing the concentrated sludge from said concentration system into a first mixing zone where said concentrated sludge is mixed with a polyacrylic acid resin which is able to absorb from 50 to 1000 times its own weight of water;
• (C) introducing a gel-like sludge-resin mixture from said first mixing zone into a second mixing zone where calcium chloride is added to said mixture thereby causing the gel to contract;
• and
• (D) returning to said aeration tank a contracted gel-sludge mixture leaving said second mixing zone.