Enhanced coagulation of Microcystis aeruginosa using titanium xerogel coagulant.

Abstract

Cyanobacterial blooms are prevalent globally and present a significant threat to water security. Titanium salt coagulants have garnered considerable attention due to their superior coagulation properties and the absence of metal residue risks. This paper explored the influencing factors in the coagulation process of titanium xerogel coagulant (TXC), the alterations in cell activity during floc storage, and the release of cyanobacterial organic matters, thereby determining the application scope of TXC for cyanobacterial water treatment. The findings indicated that at a TXC dosage of 8 mg Ti/L, the removal rate of Microcystis aeruginosa (M. aeruginosa) exceeded 86% across a pH range of 5-9. The coagulation performance with anions HCO₃^-, CO₃^2- and H₂PO₄^-/HPO₄^2- was unsatisfactory at concentrations of 10, 20, and 50 mg/L, with corresponding chlorophyll a (Chl-a) levels of 168, 129, and 196 μg/L, respectively. While the presence of Cl^-, NO₃^-, SO₄^2-, K⁺, NH₄⁺, Ca²⁺ and Mg²⁺ had little influence on the removal efficiency. At sodium alginate (SA) concentration of 6 mg/L, the Chl-a content was 116 μg/L, with humic acid (HA) not affecting M. aeruginosa removal but hindering turbidity reduction, leaving a residual turbidity of 11 NTU. Following TXC treatment, a floc storage study with cyanobacteria-laden surface water showed a decrease in microcystins (MCs) content. The low residual titanium concentration post-TXC coagulation (<0.06 mg/L) and MCs reduction contributed to reduced effluent toxicity, indicating TXC's versatile applicability for treating cyanobacterial-contaminated waters.