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Exploring the influence of sludge dewatering agents on Microplastic aging under hydrothermal treatment: Insights from Polylactic Acid microplastics
Summary
This study examined how industrial wastewater sludge treatment chemicals (dewatering agents) interact with hydrothermal processing to alter the physical and chemical properties of polylactic acid (PLA) microplastics in sludge. The findings matter because different treatment chemistries transform microplastic surfaces in distinct ways — affecting their porosity, reactivity, and persistence — which has implications for how microplastics behave after leaving wastewater treatment facilities.
In this research, we examined the combined effects of hydrothermal treatment and different dewatering agents on the morphological, molecular, and functional properties of Polylactic Acid Microplastics (PLA-MPs). Under hydrothermal treatments, the presence of dewatering agents leads to pronounced alterations in PLA-MPs as evidenced by SEM, showing the compound effects of both treatments. In detail, PFS (polyferric sulfate) results in an enhanced porosity on the surface, PAC (polyaluminum chloride) imparts a distinct roughness, while Fe/PMS (iron/peroxymonosulfate) leads to surface deterioration with the emergence of larger pores. Fe/PMS exhibits the most significant difference in its impact on microplastics in both water and sludge, significantly reducing molecular weight in water, while its effect becomes minimal in sludge. The carbonyl index (CI) predominantly increases across agents in water treatments, with PAC standing out with a CI of 17.50. Conversely, in sludge environments, the CI displays a decreasing trend, especially with Fe/PMS which shows a CI of 15.00. Additionally, employing FTIR and XPS analyses, this study validates the rise in oxygen-centric functional groups on PLA-MPs post hydrothermal treatments, particularly a marked enhancement in C=O and C-O groups due to Fe/PMS. Two-dimensional correlation spectroscopy revealed a distinct sequence of spectral changes in PLA-MPs. The hydrothermal samples in water showed the earliest structural alterations, whereas the presence of iron and persulfate in sludge led to the most pronounced molecular transitions, emphasizing the intricate interactions of the microplastics with different chemicals. This study highlights the impact of hydrothermal treatment and dewatering agents on the properties of the microplastics.
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