I think the sludge pumped ...

I think the sludge pumped into the holding tank needs to be dosed with a polymer to aid its thickening, and the supernatant can be decanted and pumped back to the head of the works at 10% of the plant flow rate. The thickened sludge can be spread over drying beds and the subnatant recycled together with the supernatant as well. A jar test can be carried out to determine a suitable polymer for the thickening process. This is a common industry practice. Hope this helps. Good Luck