Integrated nanofiltration and photocatalytic processes for the removal of polystyrene nanoplastics waste in water

The rising amount of plastic waste in aquatic environments highlights the need for innovative solutions. In response, this study introduces an integrated approach that combines membrane separation with a photocatalytic process to tackle the removal of nanoplastics from water. Membrane processes effectively concentrated polystyrene nanoplastics (PS NPs), thereby decreasing the volume of wastewater requiring photocatalytic treatment. The nanofiltration process achieved a 100 % rejection of the nanoplastics, increasing their concentration from 2 mg/L to 100 mg/L and reducing the wastewater volume with a volume reduction factor (VRF) of 44.25. In addition, a low impact on membrane fouling was observed, with an almost complete restoration of the initial membrane performance (98 %) after a washing with water. This indicates the formation of reversible fouling, identified by Hermia’s models as a mechanism of cake layer formation. Photocatalytic degradation of concentrated wastewater using semiconductor photocatalysts titanium dioxide (TiO2) was conducted to evaluate the performance of the integrated system under varying operating conditions, including NPs concentration and photocatalyst dosage. The results showed the mineralization of 10 mg/L of PS NPs after 24 h, using 1 g/L of TiO2 under UV light in water as solvent under atmospheric air, confirmed by total organic carbon (TOC) and py-GC/MS analyses. In addition, experimental results at shorter reaction time demonstrate the capability of the photocatalytic system to chemically transform PS into valuable intermediates. This highlights the potential of photocatalysis as a sustainable approach for addressing plastic pollution while creating opportunities for recycling plastic waste into useful products. This study demonstrates a promising system that combines recovery and degradation into a single, optimized step, paving the way for application in the tertiary treatment stage of wastewater treatment plants (WWTPs).