Experimental Study on Treating Landfill Sludge by Freeze-Thaw Combined with Vacuum Preloading Using Prefabricated Horizontal Drains

The traditional chemical vacuum preloading method for landfill sludge (LS) often has problems of pollution, deformation, and blockage of the drainage plate. Consequently, we proposed a freeze-thaw process with vacuum preloading via prefabricated horizontal drains (PHDs). First, the LS was pretreated by freeze-thaw. Then, a comparative model test of prefabricated vertical drains (PVDs) and PHDs was carried out to investigate the anticlogging mechanism and vacuum consolidation effect of PHDs from macro- and microaspects. The results showed that the water discharge of PHD was 13.4% higher than that of PVD, the settlement of PHD was 16% higher than that of PVD, the volume reduction ratio of PVD was 58.2%, and that of PHD was 67.5%. The initial water content of LS was 86%, the minimum for PVD was 61%, and the minimum for PHD was 56%. The particles of PVD were mainly transported in the radial direction, PHD was transported primarily in the vertical direction, and there were more small particles in the center of the PVD. PHD had a high degree of consolidation, mainly with micropores and mesoporous distribution, and the PVD consolidation degree was low, primarily the distribution of small pores. The study found that freezing, thawing, and vacuum preloading with PHDs may efficiently minimize the amount of LS.

Automated summary

This study proposed a freeze-thaw process with vacuum preloading via prefabricated horizontal drains (PHDs) to address the problems of pollution, deformation, and blockage commonly associated with the traditional chemical vacuum preloading method for landfill sludge (LS). Experiment results showed that the water discharge and settlement of PHDs were higher than those of prefabricated vertical drains (PVDs), and PHDs achieved a greater volume reduction ratio. The study also revealed that PHDs had a high consolidation degree, mainly with micropores and mesoporous distribution.