Influence of composite flocculant FeCl3–APAM on vacuum drainage of river-dredged sludge

Sludge is an inevitable product of river dredging and is characterized by a high water content, high fluidity, and high heavy metal content. Its treatment requires consideration of the economic and environmental implications. In this study, a composite flocculant comprising anionic polyacrylamide (APAM) and FeCl 3 was used in combination with vacuum preloading to conduct indoor tests on the treatment of dredged sludge. The monitored parameters included the water drainage rate and sludge settlement, and the water content and shear strength after testing. The addition of the composite flocculant was found to effectively enhance the flocculation of the soil and increase the soil particle size, resulting in accelerated water drainage, thus improving the treatment effect and the solidification of the contained heavy metals. The treatment was found to be optimized by an APAM:FeCl 3 ratio of 1:5 in the composite flocculant, under which the moisture content of the sludge was reduced from 140% to 50%, and the solidification rate of the heavy metals exceeded 88%.