Dosage and pH dependence of coagulation with polytitanium salts for the treatment of Microcystis aeruginosa-laden and Microcystis wesenbergii-laden surface water: The influence of basicity

Polytitanium coagulants have been recently developed and have received wide attention due to both strong coagulation capability and sludge recycling to produce valuable by-products, titanium dioxide (TiO2). This study reports the performance of coagulation with emerging polytitanium salts, polytitanium chloride (PTC) and polytitanium sulfate (PTS), for the treatment of two common cyanobacteria (Microcystis aeruginosa, MA and Microcystis wesenbergii, MW)-laden surface water, which has been barely reported. Of particular concern is the coagulant dosage and solution pH dependence of polytitanium coagulation, which are the main parameters influencing coagulation efficiency. The influence of basicity (B) of PTC and PTS on coagulation performance was simultaneously included. Results show the optimized B value of 1.5 with coagulant dosage of 30 mg/L and initial solution pH between 7-9 for both PTC and PTS coagulation, wherein obvious advantage of PTC was observed over PTS regardless of MA- or MW-laden surface water treatment. The PTC coagulation could achieve almost complete removal of algae (about 99.0 %) with synergic removal of organic matter with high-efficiency. Both PTC and PTS were more capable at alkaline solution pH conditions for turbidity and algae removal through sweep flocculation, while satisfied removal of the humic acid-representative organic matters was observed at acidic to neutral pH conditions by charge neutralization. Satisfied flocculation zones were determined according to synergic removal of algae, turbidity and organic matters, with most of the satisfied points distributed at solution pH 7-9 conditions. This study will provide theoretical basis and facilitate wide application of the polytitanium coagulation for algae-loaded surface water treatment.