Insights into the dewatering of excavated landfill sludge conditioned by polyferric silicate sulfate

Large quantities of landfill sludge (LS) with higher water content (WC) were stored underground, and excavation and re-dewatering of LS is a sustainable and economic strategy to save landfill space and reduce the leaching of contaminants. In this study, polyferric silicate sulfate (PFSS) was first applied in the conditioning of excavated LS, and the effects of the Si/Fe mass ratio and PFSS dosage on physicochemical properties, dewaterability and rheological properties were investigated. At the best Si/Fe of 0.18, PFSS conditioning obtained compact aggregates with the strongest internal structure, thus achieving the lowest WC. Large sludge flocs were formed, and slime and loosely-bound extracellular polymeric substances were effectively removed with the PFSS dosage above 100 mg/g dried solids, which made the WC to be lower than 51.4%. The whole mechanical compression process of conditioned LS can be described by the modified Terzaghi-Voigt model, and increasing the PFSS dosage induced the release of bound water and migration of the consolidation stage from ternary to secondary. PFSS is an economically sustainable conditioner for LS, integrating multiple functions such as charge neutralization, particle aggregation, interparticle bridging and skeleton building in one chemical.