Filtration and adsorption of low concentration phosphate by dolomite-biochar composite membrane

Abstract

With the development of industry and agriculture, a large amount of phosphorus is discharged into natural water bodies, leading to eutrophication in water bodies. Traditional chemical and biological methods cannot effectively remove low concentration of phosphate from water. Combining adsorbent with ultrafiltration membrane is expected to capture and adsorb low concentration of phosphate by cross-flow filtration. Dolomite modified biochar adsorbent(DO/BB) was loaded into polyvinylidene difluoride(PVDF) ultrafiltration membrane(PVDF-DO/BB). The microstructure, mechanical property and phosphate adsorption/separation performance of PVDF-DO/BB were investigated. The results showed that compared with pure PVDF membrane, the surface roughness of PVDF-DO/BB composite membrane increased and its hydrophilicity deteriorated. The tensile strength of PVDF-DO/BB was increased by about 23%, and the flexibility was also improved. When the initial phosphate concentration was 1.0 mg/L, it could be reduced to 0.16 mg/L after PVDF-DO/BB treatment, and the removal rate remained >75% after five adsorption-desorption cycles. Through the models fitting of adsorption kinetic and isotherm data, it was found that the adsorption process was mainly controlled by monolayer chemical reaction. The distribution of active sites was uniform. Combined with the XPS analysis of PVDF-DO/BB before and after phosphate adsorption, it was clarified that the adsorption mechanism mainly consisted of electrostatic attraction, inner sphere monodentate complex formation, inner sphere bidentate complex formation and hydroxyapatite precipitation. Moreover, PVDF-DO/BB could efficiently reject macromolecular pollutants, with the dual function of adsorption-ultrafiltration.

Keywords

• low concentration phosphate
• dolomite-biochar
• separation membrane based on adsorption
• dual functions