Optimization of flow dynamics in single-pass and recirculating systems for enhanced Escherichia coli removal efficiency using polyhexamethylene biguanide (PHMB) modified PAN-based nanofiber membranes

This study explores the effectiveness of polyhexamethylene biguanide (PHMB) modified PAN (polyacrylonitrile)-based nanofiber membranes in treating Escherichia coli (E. coli) in biological wastewater. Initially, PAN nanofiber membranes were fabricated via electrospinning and subsequently modified into AEA-COOH-PHMB membranes by incorporating carboxylic acid groups and coupling with the antibacterial agent PHMB. The killing rate was evaluated using unidirectional upward flow and recirculating liquid flow filtration processes under varying operating conditions with newly designed nanofiber membranes (effective membrane area: 3.7 cm²). The assessment included different flow rates (1–3 mL/min), E. coli concentrations (2 × 10⁴–2 × 10⁶ CFU/mL), varying numbers of stacked membrane layers, and multiple cycles of repeated use (1–3). Various kinetic models were applied to fit the results for each parameter across the different flow systems. In the unidirectional up-flow system, with a 1.0 mL/min flow rate and an E. coli concentration of 2.0 × 10⁶ exceed CFU/mL, the killing rate initially reached around 50 %. However, it was increased to approximately 90 % when 3–5 membrane layers were stacked. Backflow filtration achieved up to 100 % killing rate under various conditions. Notably, AEA-COOH-PHMB membranes reduced E. coli concentration by 100 % in just 0.2 min in a recirculating flow system featuring 3 − 5 stacked membrane layers. The rapid and efficient reduction in E. coli concentration underscores the practical utility of AEA-COOH-PHMB nanofiber membranes for addressing microbial contamination challenges in wastewater treatment applications. These results emphasize the biocompatibility of the modified nanofiber membrane and demonstrate the potential of the AEA-COOH-PHMB nanofiber membrane for treating biological wastewater.