Decreasing Settlement in the Aerator in ASP

We have a problem with settlement in an aerator in a vegetable oil manufacturing company.

We have a conventional activated sludge process (ASP) treatment plant with 3 surface aerators of different capacity.

The ASP is designed so that the water from the primary clarifier goes to aerator 1, water from aerator 1 to aerator 2, and from aerator 2 to aerator 3.

The problem is that the settleability test shows the settlement of:

How to reduce the settlement in aerator 3?