Microplastic Removal in Urban Wastewater: A Systematic Review of Treatment Technologies, Efficiency Determinants, and Environmental Fate

Abstract

Microplastics have emerged as pervasive contaminants in aquatic environments, with urban wastewater treatment plants acting as major pathways for their entry into receiving water bodies. Although conventional wastewater treatment processes remove a substantial proportion of microplastics, complete elimination remains challenging, and the mechanisms underlying removal variability are not fully understood. This study presents a structured review of microplastic removal technologies in urban wastewater, synthesizing evidence on treatment approaches, reported removal efficiencies, and emerging research trends. A systemic literature search across major academic databases identified approximately 250 records, of which 19 studies met the inclusion criteria following staged screening and focused full-text assessment. The findings indicate that conventional wastewater treatment systems achieve median removal efficiencies of approximately 85–90%, primarily through sedimentation and sludge partitioning, yet residual microplastics persist in treated effluents. In contrast, advanced and hybrid treatment technologies consistently exceed 90% removal efficiency, with some studies reporting near-complete removal under optimized conditions. However, removal performance is strongly influenced by particle characteristics, including size, morphology, and polymer type, rather than treatment technology alone. Importantly, a significant proportion of microplastics is transferred from the aqueous phase into sludge, suggesting that current systems function as redistribution pathways rather than definitive removal solutions. This review provides a system-level perspective on microplastic removal and highlights the need for full-scale validation of emerging technologies, methodological standardization, and comprehensive assessment of microplastic fate to support effective wastewater management strategies.