Performance of activated carbon for polypropylene microplastic removal in wastewater

Nowadays, microplastics (MPs) are ubiquitous contaminants in aquatic ecosystems, raising global concern regarding these micropollutants. The main challenge with MPs lies in the difficulty of removing these particles during wastewater and drinking water treatment processes. Adsorption could be an efficient and environmentally friendly alternative for the removal of microplastics from water. In this work, the capacity of granular activated carbon (GAC) to retain standard polypropylene (PP) microplastics has been evaluated. Batch experiments were carried out under different conditions with the aim of analysing the adsorption performance. The results showed that the adsorption kinetics followed a pseudo-first order model, indicating that the retention of MPs is driven by physical processes. This observation was further supported by FTIR, as the surface functional groups of the GAC did not undergo any modifications after the adsorption process. In addition, only the Freundlich isotherm provided a good fit, suggesting that the adsorption takes place in a cooperative manner. When MPs obtained from wastewater samples were employed in the experiments using 0.5 g/L of GAC, the removal percentage achieved after 7 hours was approximately 30 %, a lower value than that obtained with the PP MP standards (43 %), which can be attributed to the nature of the MPs. This value increased to 90 % when a concentration of 1.5 g GAC/L was used. This study reveals that GAC can be considered a moderate adsorbent for the removal of PP microplastics in water treatment plants, with MPs attaching to the GAC surface through weak bonds such as Van der Waals forces.