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Hybrid Wastewater Treatment: Efficiency and Challenges in Microplastic Removal
Summary
Researchers reviewed laboratory, pilot, and full-scale evidence for hybrid wastewater treatment configurations — combining membrane bioreactors, coagulation-flocculation, electrocoagulation, ozonation, and advanced filtration — finding near-complete microplastic removal is achievable, though fibers and particles below 100 µm remain the most persistent fraction across all treatment combinations.
Hybrid treatment trains, integrating complementary physical, biological, and chemical barriers, deliver more robust control of microplastics (MPs) in wastewater treatment plants than conventional single-unit operations. However, fibers and small fragments (<50–100 μm) often persist. Across laboratory, pilot, and full-scale evidence, conventional baselines are size- and site-dependent: rapid sand filtration achieves ∼75% removal at full scale for coarse classes; dissolved air flotation ∼95% for >20 μm; disc filtration ∼98%; and conventional activated sludge ∼64–98%. These removals are reported on a count basis above study-specific lower size cutoffs (typically ≥ 20 μm). However, hybrid treatments report removals ∼100%, though values vary with detection limits and MP size classes analyzed. Membrane-centric trains (e.g., membrane bioreactor with ultrafiltration) reach nearly complete removal. Chemical–physical hybrid treatments (coagulation–flocculation with membranes; electrocoagulation–electroflotation plus ultrafiltration) can reach ∼100% removal. Ozonation coupled with granular activated carbon sustains ∼92% removal at pilot scale and up to 98% at full scale. Bubble-enhanced flotation exceeds 98% removal for 20–100 μm. Adsorbent-assisted hybrids capture ∼99% of smaller MPs. Despite these gains, fibers and <100 μm MPs remain the dominant challenge. This review consolidates laboratory, pilot, and full-scale evidence to guide influent-tuned hybrid designs that deliver robust MP removal approaching complete removal.