Investigating the impact of PVC microplastics on membrane fouling behavior in MBR for enhanced wastewater treatment efficiency

Studies show membrane bioreactor (MBRs) remove microplastics (MPs) effectively, yet their impacts on fouling, sludge, and microbes remain unclear. Findings vary, few investigations exist, and simplified conditions restrict applicability, highlighting the need for more robust, realistic research on wastewater treatment systems. In this study, the effect of MPs on MBR treating simulated urban wastewater was investigated by evaluating chemical oxygen demand (COD) removal and membrane fouling by adding polyvinyl chloride microparticles (PVC-MPs) into synthetic feed wastewater. The average particle size of MPs was 6.69 ± 4.2 µm. At steady state, the COD removal was 84.76 ± 4.27% and 92.48 ± 5.62% for MBR and MPs-MBR, respectively. The presence of MPs in the MBR led to a ca. 16 and 35% reduction in extracellular polymeric substances (EPS) and soluble microbial products (SMP) content of the sludge cake layer, respectively. Furthermore, the average permeate flux of the MPs-MBR was 48% higher, which was attributed to the properties of the sludge. The presence of MPs had no adverse effect on sludge settleability. The total membrane fouling resistance in the MPs-MBR was lower (1.85 × 1012 1/m) than MBR (3.21 × 1012 1/m). Scanning electron microscope (SEM) micro images confirmed the presence of fewer fouling agents on the fouling layer of the MPs-MBR. Fourier transform infrared spectroscopy (FTIR) and excitation-emission matrix (EEM) fluorescence spectroscopy analyses confirmed the lower intensity of proteins/carbohydrates functional groups in the cake layer of MPs-MBR, and no functional groups related to PVC-MPs were detected in the effluent from the MPs-MBR. Overall, it can be concluded that MPs were effectively retained by the membrane without adverse effect on membrane fouling behaviour.