Performance of Coagulation-Assisted Dissolved Air Flotation Process for Microplastics Removal from Synthetic Wastewater Containing Fat, Oil and Grease

Microplastics (MPs) are emerging contaminants of growing concern due to their ubiquity and negative environmental impacts. Owing to their small size, hydrophobicity, and large surface area, MPs adsorb toxic chemicals and bypass conventional wastewater treatment processes. Fat, oil and grease (FOG) from domestic and industrial discharges interferes with wastewater treatment plant (WWTP) operations and serves as a carrier for MPs, facilitating their release in aquatic environments. This study investigates the performance of dissolved air flotation (DAF) process, coupled with coagulation, for polyethylene (PE) and polystyrene (PS) removal from synthetic wastewater. Key operational parameters, including air pressure, coagulant dosage, water flow rate, and pH, were optimized. DAF alone achieved limited MP removal efficiencies (27–28%). However, the addition of coagulants (150 mg/L alum and 15 mg/L polyacrylamide) substantially improved efficiencies to 88.4% for PE and 90.2% for PS. Hydrophobic interactions and charge neutralization were identified as the dominant removal mechanisms. Furthermore, the presence of FOG enhanced MP removal to 95%, suggesting that hydrophobic interactions facilitate the aggregation of MPs and their association with FOG. These findings demonstrate that an optimized coagulation-assisted DAF at the primary treatment stage provides a sustainable and effective method to remove MPs and FOG, reducing their environmental release.