Anchored adsorption and in-situ coagulation of cyanobacteria via Ce(III)-based salt: Enhanced removal efficiency and reduced toxicity

This study compared the coagulation performance, floc characteristics, and algal cell integrity between cerium-based coagulants and polyaluminum chloride (PAC). Under optimal dosage (6 mg Ce/L), both CAN (Ce(IV)-based) and CCl (Ce(III)-based) exhibited comparable algal removal efficiency to PAC (>90%), while generating larger flocs (>1200 µm) that settled rapidly (90% within 5 min). However, CAN caused significant algal cell lysis during floc aging, whereas CCl exhibited minimal cell damage. Analysis of CCl flocs revealed a distinct increase in the Ce(IV) concentration post-coagulation, accompanied by pronounced phosphate and carboxyl peaks on the floc surface. Further investigation into the extracellular polymeric substances (EPS) during algal coagulation proved that the coagulation mechanism of CCl proceeded in two steps: 1) Anchoring of the coagulant onto the algal surface via strong adsorption of phosphate and carboxyl groups; 2) Synergistic interactions between algae and EPS, which induced partial oxidation of Ce(III) to Ce(IV), triggering in-situ hydrolysis of Ce(IV). This process generated large floc structures and the subsequent coagulation targeted to algae. This study highlights CCl as an eco-friendly and effective alternative with high algal removal and low toxicity (attributed to reduced Ce(IV) dosage), offering practical advantages for water treatment applications.