Evaluation of Microplastic Removal Efficiency at the Wastewater Treatment Plant of a Kraft Paper Factory in Vietnam

Wastewater treatment plants (WWTPs) are one of the critical sinks and sources of microplastics in the environment. Previous studies in Vietnam mainly examined combined treatment plants and centralized plants at industrial zones and lacked data on microplastics in industrial wastewater or sludge. Recycled paper industry wastewater has lots of plastic waste, possibly including microplastics. Therefore, this study aims to evaluate the microplastic pollution load and microplastic removal efficiency of the paper mill wastewater treatment plant. WWTP of the Kraft paper factory A, using primary treatment facilities, level I (Dissolved Air Flotation-DAF), level II (Upflow Anaerobic Sludge Banket-UASB and Conventional Activated Sludge-CAS), and level III (DAF and Fenton), with a capacity of 24,000 m3 day−1 was selected for the survey. The results show that the microplastic load of this factory was 288,000 items day−1, although the removal efficiency was 99.8% and the concentration of microplastics in treated wastewater was 12 items m−3. The primary and secondary treatment processes removed microplastics with the highest efficiency, 75.8–97.9%, especially DAF had a microplastic removal efficiency of  >95%. Microplastic concentration in the sludge sample was 22,772 items kg−1 of dry weight. For morphologies, microplastics in the wastewater and sludge samples existed solely in the form of fragments (55% and 91%) and fibers (44% and 9%), respectively, and blue and white microplastics accounted for 37% and 30% of the total.