Effect of freeze–thaw–vacuum pretreatment modes on the performance of sludge reduction

To reduce the volume of landfill sludge, a more environmentally friendly technology is used to study the effects of different freeze–thaw–vacuum pretreatment modes. In addition to the cumulative effect of cooling time within different temperature bands, we analyse the temperature difference loss rate of shallow sludge over the period of cooling. During the annular freezing process, the mechanism of ice front formation is revealed by exploring the energy transfer process of landfill sludge. When repeated freeze–thaw–vacuums are performed, the pretreatment modes of a single pre-freeze–thaw and two consecutive pre-freeze–thaws are compared. The superiority of two modes is discussed in the light of local differences in dewatering performance and overall settlement trend characteristics. Furthermore, the final micromorphological structure indicates that the repeated freeze–thaw–vacuum pretreatment mode of sludge is affected by its depth to a certain extent. It is found that factors such as sludge depth and radial water migration have a significant impact on the time accumulative effect and energy transfer of frozen sludge. The sludge treatment mode of two consecutive pre-freeze–thaws has a better effect on the overall dewatering and reduction.