The role of lime in dredged mud dewatered by a plate and frame filter press and potential substitutes

Dredged mud is a kind of construction material that can be reused as waste. It needs to be dehydrated before it is used. At present, plate and frame pressure filtration (hereafter referred to as PFP) using lime for conditioning after flocculation is widely employed. The addition of lime causes the mud cake to exhibit a high pH, and reduces its subsequent use. In response to this problem, this study examines the mechanism of lime in the PFP and identifies neutral alternative materials according to this principle. British kaolin-modified mud and dredged Taihu mud were treated with lime and various conditioners, and the size and specific resistance (hereafter referred to as SRF) of the floc were measured to evaluate the mud’s properties, the compressibility index of the mud layer, the dewatering effect of the PFP, and the properties of the cake. The results showed that lime ensures the filtration speed in the pumping-filtering phase by increasing floc stiffness and reducing the compressibility of the layer, so that continuous drainage can achieve a high-pressure filtration efficiency. SAC can basically achieve the same pressure filtration principle and dewatering effect as lime under conditions in which the pH of the mud cake is close to neutral.