Comparison of solid-liquid separation technologies for dewatering of lake sediment flocculated with biobased flocculants

Dredging and dewatering lake sediment effectively reduce internal phosphorus loads, providing an opportunity to recycle phosphorus as fertilizer. However, lake sediments generally have high water content, which limits the efficiency of handling and transport. This study evaluates the effectiveness of bio-based and synthetic flocculants for dewatering lake sediment, comparing four separation technologies: Geotube, plate and frame filter press, decanter centrifuge, and vacuum drum filter. The study tested three flocculants: a synthetic polymer, chitosan, and starch, chosen for their distinct charge, molecular weight, and chemical structure.

Flocculation prior to dewatering in a Geotube or decanter centrifuge use improved filtrate clarity. Additionally, flocculation was essential for the effective operation of the plate and frame filter press and vacuum drum filter. The plate and frame filter press produced the lowest total phosphorus (TP) content (6–23 µg/L) and turbidity (0.87 NTU) in the filtrate, indicating superior quality, especially with biobased polymeric flocculants. Decanter centrifuges achieved the highest dry matter (DM) content (22.5 %) but required starch as a flocculant to improve filtrate quality. Conversely, the drum filter performed less effectively, likely due to elevated TP levels in the filtrate caused by its coarser mesh size.

This study demonstrates the potential of bio-based flocculants for enhancing sediment dewatering and phosphorus removal. The findings underscore the value of bioflocculants, particularly in low-shear processes, as a sustainable solution for lake restoration. Further research should explore scale-up possibilities and optimize conditions to maximize bio-based flocculant performance in practical applications.