## 5 Influence of Pressure Filtration Parameters on Mud Cake Deformation
### Effect of Initial Cake Thickness and Dewatering Time on Cake Deformation  
Figure 9 illustrates the variation in the calculated compression deformation of the mud cake with the dewatering time for different initial cake thicknesses at filtration pressures of 0.8 MPa and 1.2 MPa. Comparing Figure 9a,b, it can be seen that the deformation pattern of a mud cake with the dewatering time under different filtration pressures is basically the same, only differing in values; therefore, only working conditions with filtration pressures of 0.8 MPa and 1.2 MPa are shown here.  
As can be seen from Figure 9, the compression deformation of the mud cake at the beginning of pressure filtration is very similar under different initial cake thicknesses, and the rate of compression deformation gradually slows down over time. When the compression deformation of the mud cake changes less with the dewatering time, in other words, when the deformation-time curve tends to flatten, the filtration can be considered to have been completed completely. According to the trend of the curves in Figure 9, the time needed to complete the pressure filtration process is shorter when the initial mud cake thickness is smaller, and a longer time is needed as the initial mud cake thickness increases. Obviously, the increase in the mud cake thickness increases the drainage path of the pore water, resulting in a longer time being required to complete pressure filtration.  
According to Equation (6) mentioned above, the void ratio \(e\) of the mud cake can be calculated using the compression deformation of the mud cake, and then the water content of the mud cake after pressure filtration can be obtained by substituting \(e\) into Equation (5), which is one of the important indexes that needs to be considered in the process of mud slurry dewatering using pressure filtration. In this paper, the water content of the mud cake after pressure filtration is also used as the basis for evaluating the effect of pressure filtration. Combined with the previous laboratory tests, the lowest water content of a mud cake obtained after the pressure filtration process in a coastal landfill in Wenzhou, China, is about 70%, which is used as a control index in this paper, and the relationship between the  
Figure 9: Variation in mud cake compression deformation over time: (**a**) variation in deformation over time under 0.8 MPa and (**b**) variation in deformation over time under 1.2 MPa.  
initial mud cake thickness and the dewatering time when the water content is reduced to 70% under different filtration pressures is shown in Figure 10.  
As shown in Figure 10, the dewatering time increases nonlinearly with an increase in the initial mud cake thickness, and referring to the linear trend line, such a nonlinear characteristic is more obvious with a smaller filtration pressure. In terms of the processing efficiency, an increase in the initial cake thickness leads to a multiplied increase in the dewatering time and the reduction in the processing efficiency. Meanwhile, in terms of the pressure filtration processing time, most of the working conditions are below 40 min, and the shortest can be up to 10 min or less. When the initial cake thickness is 420 mm, the dewatering time is below 40 min only when the pressure reaches 1.4 MPa. Therefore, in order to shorten the processing time, one should consider reducing the initial cake thickness appropriately.