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Unveiling the hidden roles of microplastic-derived dissolved organic matter in membrane fouling using fluorescence and stable carbon isotope tracers
Summary
Researchers investigated the role of microplastic-derived dissolved organic matter (MP-DOM) in membrane fouling during water and wastewater treatment, using fluorescence and stable carbon isotope tracers to distinguish MP-DOM from coexisting effluent organic matter. They found MP-DOM acts as a significant foulant, and stable carbon isotopes proved effective as a quantitative tracer for separating its contribution to fouling dynamics.
Microplastic-derived dissolved organic matter (MP-DOM), released during the weathering and aging of microplastics (MPs), has emerged as a poorly constrained class of organic foulants in water and wastewater treatment systems. However, its mechanistic role in membrane fouling and its quantitative separation from coexisting effluent organic matter (EfOM) remain largely unexplored. This study systematically investigated the role of MP-DOM in fouling dynamics and identified optimal tracers for quantifying its contribution relative to effluent organic matter (EfOM) during ultrafiltration (UF). Mixtures of δC-labeled EfOM and three representative MP-DOMs, including polyethylene (PE), polystyrene (PS), and polylactic acid (PLA), were examined across a 3-50 % MP-DOM gradient. Several optical indices, including humification index and fluorescence index, and stable carbon isotope ratios (δC) were compared for their ability to trace MP-DOM in reversible (RF) and irreversible foulants (IF). Among all tested parameters, δC consistently met the evaluation criteria, outperforming optical tracers in accuracy, sensitivity, and cross-polymer applicability. δC-based source apportionment revealed that even at 3 % MP-DOM, its contribution to IF (9.5-13.5 %) was significant and exceeded ideal mixing predictions. With increasing MP-DOM content, the synergistic effect remained strongly positive for irreversible fouling while shifted from positive to negative for reversible fouling, indicating a mechanistic shift from EfOM-dominated reversible to MP-DOM-driven irreversible fouling. The enhancement was most pronounced for petroleum-based MP-DOMs (PE- and PS-DOM), driven by their humic-like and hydrophobic fractions that enhance adsorption and pore blocking, compared to PLA-DOM. Overall, the δC tracer proved to be a robust, source-specific indicator for quantifying MP-DOM in fouling layers, offering new mechanistic insights into how MP-DOM alters fouling behaviour and degrades membrane performance in wastewater treatment systems.