The application of freeze-thaw cycle treatment on landfill sludge: Impact on physicochemical properties and physical-mechanical characteristics

The physical-mechanical properties of dewatered sludge are important for the stability of landfills and their resource utilization. In this study, the physical-mechanical properties of sludge were comprehensively investigated by considering its various properties (e.g., particle morphology and size, compression and consolidation characteristics, shear strength, dewatering capacity, and microstructure) under different freeze-thaw cycles. The results indicated that extracellular polymers (EPS) will be destroyed during freeze-thaw cycles, and bound and interstitial water are converted to free water, which also enhances the sludge's dewatering efficiency and strength. Furthermore, multiple freeze-thaw cycles significantly enhanced the consolidation efficiency, leading to a denser sludge cake under pressure. A dense sludge structure enhances particle interlocking, improving internal friction angle and shear strength. The highest treatment efficiency was observed after 1–3 freeze-thaw cycles. Sludge properties tend to be stable when the freeze-thaw cycles are over 6. The research results will provide a reference for sludge dewatering reduction and its resource utilization.