High-efficiency lake sediment treatment: integrating biobased polymers with pipe flow mixing

Sediment dredging can be used for lake restauration by removing accumulated phosphorus from lakes but flocculation is often necessary to facilitate easy dewatering and to retain phosphorus within sediment. Flocculation of lake sediment has been investigated using biobased polymers (chitosan) and synthetic polymer (polyacrylamide, PAM), both individually and in combination. A pipe flow mixing system was used. Chitosan allowed for rapid charge neutralization and forming small compact flocs. However, its flocs are fragile due to the dominance of patching mechanisms. PAM form stronger flocs via bridging mechanisms but required either prolonged low-shear mixing or short-duration high-shear mixing to achieve optimal performance. Dual flocculants resulted in larger and more robust flocs while reducing the requiring dosage (0.56 mg/g of chitosan and 0.28 mg/g of PAM). In contrast, the use of single flocculants needed higher doses, i.e. 0.84 mg/g of chitosan or 1.12 mg/g of PAM. Further, dual flocculants reduced residual turbidity and improved sediment dewatering. The pipe flow mixing method minimized floc breakage, enhanced flocculation efficiency, and facilitated subsequent liquid-solid separation processes. Combining biobased- and synthetic polymers reduce flocculant dosage and energy consumption compared to single flocculant approaches. • Dual flocculation with both biobased and synthetic polymers gave the best result • Dual flocculation forms stronger, larger flocs at lower doses • Dual flocculation enhanced efficiency of lower turbidity and increased dry matter • Pipe flow mixing minimizes floc breakage and enhances liquid-solid separation