Electrospun Nanofiber Membranes for Microplastic Removal from Wastewater: Performance and Mechanism Analysis

Microplastic pollution in aquatic environments is one of the most pressing global issues that adversely affects the environment. Besides, conventional wastewater treatment facilities have very limited removal efficiency for particles smaller than 100 µm. Hence, the research reported herein describes the fabrication and the optimization process of the electrospun polyvinylidene fluoride (PVDF) nanofiber membranes functionalized with titanium dioxide (TiO₂) nanoparticles to improve microplastic removal from synthetic and real wastewater matrices. Electron microscopy and surface topology assessments of the membranes also suggested a homogeneous fiber diameter in the range of 150-300 nm with a very high porosity (>85%) of the membrane. Adsorption by removal experiments showed that under the optimizations of the conditions the maximum removal efficiency reached was 98.7% in case of polystyrene microspheres (10-50 µm) at: pH 6.5, contact time 120 min, and membrane dosage 0.5 g/L. The Langmuir isotherm model (R² = 0.993) was more appropriate than Freundlich and Temkin models, signifying monolayer adsorption with the maximum capacity being 156.8 mg/g. Experimental kinetic data fitted the pseudo-second-order model the best (R² = 0.997), which implies chemisorption as the main mechanism. The thermodynamic variables (ΔG° = -18.4 kJ/mol, ΔH° = +12.6 kJ/mol, ΔS° = +98.3 J/(mol·K)) reflect a spontaneous and endothermic adsorption process. Analyses of the used membranes by field emission electron microscopy (FE-SEM) and Fourier-transform infrared spectroscopy (FTIR) revealed that the microplastics adhered to the membranes via hydrogen bonding and hydrophobic interactions.Testing under continuous flow conditions at a municipal wastewater treatment plant showed that the membrane removal performance was stable beyond 94% for 30 consecutive days of continuous operation with intermittent backwashing. Moreover, the analysis of energy consumption pointed out that the operational costs are $0.38 per m³, which makes it competitive with the already existing tertiary treatment technologies. This membrane technology, therefore, provides a very promising and sustainable solution for microplastic pollution in wastewater treatment infrastructures.