Influences of typical inorganic flocculants on flocculation effects of dredging materials and quality of effluent water

In view of the problems such as slow siltation and solidification of natural bottom sludge in the landfill disposal of sludge yards, the chemical agents are often added in the project to speed up the process of sludge-water separation. The influences of five typical inorganic flocculants on the flocculation sedimentation effects of dredged materials with high water content and the quality of overlying water (turbidity) are studied through the measuring cylinder sedimentation tests. Among the five typical inorganic flocculants, CaCl₂ and PAS (polyaluminum sulfate) have relatively good flocculation effects. On this basis, the influences of these two flocculants on the sedimentation laws of dredged sludge under different dosages are investigated. The test results show that with different contents of CaCl₂ and PAS, the settlement amount, rate and stabilization time of the sludge after self-weight sedimentation and consolidation are different. The optimum contents of CaCl₂ and PAS obtained in this study are 0.8% and 0.2%, respectively. Under the optimal dosage, the turbidity removal rate of the overlying water can reach about 84%. CaCl₂ plays a role of flocculation through Ca²⁺ exchange and electrical neutralization; and PAS mainly plays a role of flocculation through electrical neutralization on the surface of soil particles. The results may provide a referencees for the research and design of rapid flocculation and residual water discharge of large-scale dredged materials.