Enhanced algae removal by Ti-based coagulant: comparison with conventional Al- and Fe-based coagulants

Abstract

The water eutrophication caused by cyanobacteria seasonally proliferates, which is a hot potato to be resolved for water treatment plants. This study firstly investigated coagulation performance of titanium tetrachloride (TiCl₄) for Microcystis aeruginosa synthetic water treatment. Results show complete algal cell removal by TiCl₄ coagulation without damage to cell membrane integrity even under harsh conditions; 60 mg/L TiCl₄ was effective in removing the microcystins up to 85%. Furthermore, besides having stronger UV₂₅₄ removal capability and the higher removal of fluorescent substances over Al- and Fe-based coagulants, TiCl₄ coagulant required more compact coagulation and sedimentation tanks due to its significantly improved floc growth and sedimentation speed. Meanwhile, its' short hydraulic retention time avoided algal cell breakage and subsequent algal organic matter release. Microcystin concentrations were kept at a low level during sludge storage period, indicating that the TiCl₄ flocs could prevent algal cells from natural lysis. To facilitate water recycling without secondary contamination, the algae-containing sludge after TiCl₄ coagulation ought to be disposed within 12 days at 20 °C and 8 days at 35 °C.