Removal of calcium ions from aqueous solution by bovine serum albumin (BSA)-modified nanofiber membrane: Dynamic adsorption performance and breakthrough analysis

The presence of calcium ion (Ca²⁺) in process streams has always been a challenge because of its impact to the heat transfer efficiency of process equipment. Polyacrylonitrile (PAN) nanofiber membrane was selected as the basic matrix in this study owing to its strong mechanical strength and chemical stability. Cation-exchange nanofiber membranes with different properties, namely weak ion exchanger (P−COOH), strong ion exchanger (P-SO₃H) and amphoteric ion exchanger (P−COOH-BSA; coupled with bovine serum albumin) were synthesized via hydrolysis and coupling reactions. The physicochemical characteristics of these nanofiber membranes were investigated by Fourier-transform infrared spectroscopy, scanning electron microscope, and thermogravimetric analysis. Dynamic adsorption performance and breakthrough analysis of these nanofiber membranes were evaluated at different Ca²⁺ influent concentrations, flow rate, and configuration of membrane stacking. The maximal removal efficiency of Ca²⁺ (∼62 %, corresponding to dynamic binding capacity = ∼122 mg/g) was achieved by P−COOH-BSA at 500 mg/L of Ca²⁺ influent concentration, 2 mL/min of flow rate, and one-layer membrane configuration. Two commonly used mathematical models (Thomas and bed depth service time) were applied in the data fitting for the prediction of breakthrough curve and the determination of optimum operating parameters. The results indicate that the removal of Ca²⁺ by these nanofiber membranes was very effective due to the high interface mass transfer. In this work, Thomas model was found to be more suitable in elucidating the experimental result trends observed from the dynamic adsorption system.