Flocculation of sewage sludge with FeCl3 modifies the bioavailability of potentially toxic elements when added to different soils

The chemical flocculation treatment of waste water with FeCl3 and addition to soils reduces PTE availability in neutral soils amended with SS, but markedly increases their solubility and bio-availability in acid soils. Therefore, the application of SS obtained from flocculation with FeCl3 should be restricted to neutral or calcareous soils.