Enhanced removal of polystyrene microplastics from water using γ-Al₂O₃: process optimization and predictive modeling

PS MPs have emerged as pervasive pollutants in aquatic environments, raising environmental and public health concerns because of their persistence, widespread distribution, and potential for bioaccumulation. In this study, PS MP removal from aqueous solutions was investigated using γ-Al₂O₃ as an inorganic coagulant. The effects of key operational parameters, including γ-Al₂O₃ dosage (200–1000 mg/L), initial PS concentration (100–600 mg/L), and pH ( [4] , [5] , [6] , [7] , [8] , [9] , [10] ), were evaluated using BBD within the RSM framework. The highest experimentally observed removal efficiency among the BBD runs was 80.45%, which was obtained at 600 mg/L γ-Al₂O₃, 350 mg/L initial PS concentration, and pH 7. The quadratic model predicted a removal efficiency of 77.20% at the center point of the experimental design. Confirmatory experiments performed in triplicate under these conditions yielded an average removal efficiency of 78.1 ± 1.2%, indicating acceptable agreement with the model prediction within the tested experimental domain. Moreover, the findings confirmed the adequacy of the quadratic model and showed that nonlinear effects, particularly those related to PS concentration, played a significant role in the removal process. Characterization analyses suggested that PS removal was governed by a combination of electrostatic interactions and aggregation mechanisms. Although electrostatic attraction contributed to particle destabilization, the occurrence of maximum removal at pH values above the PZC of γ-Al₂O₃ (pHₚzc = 5.95) indicates that aggregation-driven processes, including sweep flocculation and particle enmeshment, were key factors in floc formation and stabilization. Overall, the findings indicate that γ-Al₂O₃ has potential as a candidate coagulant for MP removal under controlled experimental conditions. However, validation in realistic water matrices, direct comparison with conventional coagulants under identical conditions, and assessment at larger scales are required before practical application can be recommended. This study provides a basis for the design and optimization of coagulation-based treatment processes for MP-contaminated water.