Effects of freeze-thaw and chemical preconditioning on the consolidation properties and microstructure of landfill sludge

At present, a large amount of landfill sludge(LS) has been accumulated all over the world. For environmental and engineering purposes, there is an urgent need for deep dewatering and volume reduction of LS. The deep dewatering of LS mainly uses the method of chemical preconditioning and mechanical dewatering, which is easy to cause environmental pollution and is not conducive to the subsequent resource treatment of LS. To find a more environmentally friendly and efficient method for deep dewatering of LS, an in-situ treatment method combining freeze-thaw and vacuum preloading was proposed. In this paper, based on the existing research, through compression consolidation test and MIP, SEM micro test, the consolidation properties and microstructure of LS after freeze-thaw and chemical preconditioning were studied, and the vacuum consolidation principle of different preconditioning was explored. The results show that: Both FeCl3 and freeze-thaw preconditioning can increase the permeability coefficient and consolidation coefficient by one to two orders of magnitude; After freeze-thaw preconditioning, the void ratio of sludge decreases and the permeability coefficient increases; Under low consolidation pressure, the mechanical properties of the two kinds of pretreated sludge changed significantly; The original sludge is mainly composed of small pores. After FeCl3 conditioning, the large pores and mesopores increased significantly, while the small pores decreased. After freeze-thaw, the large pores and mesopores increase greatly, while the small pores decrease greatly; The original sludge is in the form of a dispersive flocculent structure with many impurities. After freeze-thaw, the intercluster pores increase, showing a honeycomb structure. After FeCl3 conditioning, the sludge structure is more compact and uniform. The change of microstructure and consolidation characteristics of sludge after conditioning reflects the difference of two different preconditioning mechanisms. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

A large amount of landfill sludge (LS) has accumulated worldwide, requiring deep dewatering and volume reduction. An in-situ treatment method combining freeze-thaw and vacuum preloading was proposed to address this issue. By studying the consolidation properties and microstructure of LS after different preconditioning methods, the vacuum consolidation principle was explored, showing significant changes in permeability, consolidation coefficient, and microstructure of LS after conditioning.