Laminarin-assisted PAC coagulation for polystyrene microplastic removal from aqueous solutions: Response surface optimization and an evidence-based flocculation mechanism

PS MPs are persistent contaminants in aquatic systems, and their efficient removal requires treatment processes that combine high separation efficiency with reduced dependence on conventional metal coagulants. This study evaluates a PAC–LA coagulation–flocculation system for PS MP removal from aqueous solutions and examines the role of LA as a biodegradable coagulant aid. RSM based on a BBD was used to examine the effects of PS concentration, PAC dosage, and pH on removal efficiency. Under the optimized PAC-only condition, PS removal reached 82.3%, whereas the PAC–LA system increased removal to 97.23% at 50 mg/L PAC and 80–100 mg/L LA. FTIR, FESEM, EDX, elemental mapping, and XRD analyses suggest that the improved removal was associated with the combined effects of charge neutralization, sweep flocculation, adsorption, hydrogen bonding, and LA-assisted polymer bridging. The system-maintained removal efficiencies above 90% in the presence of common coexisting ions, indicating preliminary tolerance to simple inorganic matrices. The main contribution of this work is the application of LA to enhance PAC-assisted removal of PS MPs, a polymer type less specifically examined in previous PAC–LA studies, while linking process optimization with floc-level characterization. However, the findings should be interpreted as laboratory-scale evidence, and further validation using real water matrices, residual aluminum measurements, sludge characterization, and continuous-flow operation is required before practical implementation.