Coagulation removal and recycling strategy of TiO2 nanoparticles based on Enteromorpha prolifera polysaccharide application

Abstract

Owing to electrostatic adsorption, ligand exchange, and surface complexation between TiO2 nanoparticles (NPs) and humic acid (HA), TiO2 NPs-HA complex pollutants in sewage are difficult to remove using traditional coagulation process. This study optimized TiO2 NPs-HA removal efficiency by combined application of Enteromorpha prolifera polysaccharide (Ep) and poly aluminum chloride (PACl), and recycled the TiO2 NPs from the resultant flocs. Under different hydraulic conditions, rapid stirring (90 s, 200 rpm), slow stirring (10 min, 60 rpm), and 45-min sedimentation yielded the highest TiO2-HA removal efficiency. The optimum reaction temperature and solution pH were 25 °C–35 °C and 6–7, respectively. Secondary dosing of PACl exhibited better coagulation effects than one-time and continuous dosing methods. The highest TiO2 NPs-HA removal efficiencies (95.68 % and 87.12 %) were achieved with 10 mg·L−1 of PACl dosing followed by 1.0 mg/L of Ep dosing. Additionally, Ep application resulted in faster growing, larger, and stronger flocs, which is beneficial for the recovery of TiO2 NPs. Photocatalytic results showed that the TiO2 NPs recovered from flocs exhibited photocatalytic activity, characteristic diffraction angles, and crystal plane indices that were highly correlated with those of anatase TiO2 NPs (P25).