Effects of polymer flocculant on dredged sediment by plate and frame filter press dewatering technology and its influence mechanism

The plate and frame filter press dewatering technology has been gradually popularized and applied in treatment projects of dredged sediment, but there are problems such as poor applicability of flocculant selection and unclear mechanism. In response to the phenomenon, two typical polymer flocculants are selected. One is the synthetic polyacrylamide flocculant with more applications in engineering, and the other is the natural environment-friendly flocculant chitosan. Through the measuring cylinder settling column experiment, the variation rules of settlement and dewatering of the dredged sediment are studied under two flocculants of anionic polyacrylamide (APAM) and chitosan with different dosages and the optimal dosage of flocculants is obtained. The settling volume of dredged sediment (after 7 days) under the optimal dosage is reduced by 25.9% and 32.4% respectively compared with the original sediment. On this basis, the combined flocculation and plate and frame filter press dewatering tests are carried out. The results show that the addition of APAM has a greater impact on the dewatering of the dredged sediment at the filtration stage. The dewatering effects of the chitosan-added sediment are better at the pressing stage. During the process of plate and frame filter press, the filtrate of the mud cake with APAM and chitosan flocculants increase by 17.23% and 24.5%, respectively, compared with those of the original sediment. The influence mechanism of APAM and chitosan on the dewatering effects of the dredged sediment by the plate and frame filter press is further investigated by using the particle size analysis, XRD and SEM tests. The particle analysis tests show that after the addition of 0.6‰ APAM and 1.8‰ chitosan, the small particles in the dredged sediment are bridged into large particle flocs by flocculation, and the lengths of d₉₀ increase from 10.97 μm to 29.48 and 29.63 μm, respectively.