Effective removal of algae and phosphate by CaO2-modified carbon nanotube-polyvinylidene fluoride pellets: Performance investigation and mechanistic insights

Abstract

Simultaneous removal of toxic algae and phosphate nutrient is crucial to remediate algae-contaminated waters. Herein, we report the approach for synthesis of CaO2-modified carbon nanotube-polyvinylidene fluoride (CaO2-CNT-PVDF) pellets for the remediation. The pellets were prepared by an in-situ co-precipitation approach and optimized for the best performance through such key parameters as content of CNT, concentrations of CaCl2 and H2O2 and times. The pellet prepared by 1% of CNT, 0.25-M of H2O2 and CaCl2 with an incubation time of 8-h (termed as CHAT-1228) exhibited the best performance in terms of inhibition of cyanobacteria growth at least for 40-d and uptake of phosphate of 3.6 mg/g CHAT-1228 (270.7 mg-phosphate per gram-CaO2). Our mechanistic studies showed that the cyanobacteria are inactivated by the slow and long-lasting H2O2 release and phosphate is removed via its chemical reactions with calcium species (mainly CaO2). Furthermore, CHAT-1228 can easily collected from water and reused. It works well in the removal of phosphate with a wider pH range (from 3.4 to 10.9) and in the presence of chloride, fluoride, nitrate, bicarbonate, and sulphate ions. This study demonstrates that the optimized CaO2-CNT-PVDF pellet has a great potential for industrial applications in algae-laden water treatment.