Theoretical and analytical solution on vacuum preloading consolidation of landfill sludge treated by freeze-thaw and chemical preconditioning

At present, the treatment method for urban sludge is mainly sludge landfill, which requires the water content of sludge to be less than 60%. Therefore, many researchers have proposed different methods to reduce sludge water content. Freeze-thaw (F/T) and chemical conditioning of sludge, combined with vacuum pressure and vertically inserted drainage board, has been proven to be an effective method to reduce the moisture content of landfill sludge (LS). Based on the consolidation theory of radial drainage, the characteristics of LS in the process of vacuum preloading were studied. A method of instantaneous multistage loading was proposed. The concept of free drainage stage before consolidation drainage is proposed, and the correction of the consolidation coefficient is introduced. Finally, the rationality of the theory was verified by experimental data. The results showed that the consolidation theory is rational for deep dewatering of LS in the vacuum preloading method. The difference between sludge dewatering after F/T pretreatment and chemical pretreatment was mainly reflected in the consolidation coefficient and the free drainage stage. The sludge after F/T pretreatment has higher permeability, more water precipitation, and low moisture content after vacuum preloading.