Effects of lime and polymer flocculants on consolidation behaviours of high-water content sludge

Vacuum preloading combined with flocculation has shown great potential for improving the dredged sludge's dewatering and consolidation. To identify a suitable flocculant combined with vacuum preloading method, this study investigated the effects of various common flocculants on the sludge's filtration properties and consolidation behaviors. The results indicated that dual-use of polymeric aluminium chloride (PAC) and polyacrylamide (PAM) had the most significant improvement on sludge's filtration performance, as reflected by capillary suction time. In addition, a single dose of PAM had the most substantial improvement on the sludge's compressibility. While, lime improved the sludge's permeability the most. To predict the consolidation settlement of flocculated sludge during vacuum preloading, a method was proposed based on a small homemade vacuum preloading apparatus and the Taylor method. The influence of different flocculants on sludge properties was also analyzed based on their flocculation mechanisms and microstructure. Finally, an appropriate flocculant for the sludge in vacuum preloading projects was suggested in accordance with different project goals.