Microplastics present a significant environmental threat due to their longevity in both terrestrial and aquatic systems. Once in the environment, microplastics degrade via biotic and abiotic pathways, resulting in changes to their morphology, functionality, and size. Thus, the overall impact of microplastics is highly dependent on the physicochemical changes that microplastics undergo upon exposure to environmentally relevant conditions. The wastewater treatment process presents an understudied and societally relevant process through which microplastics are transported. Herein, we examine the impact of the wastewater treatment process on the surface chemistry and crystallinity of two common polymers – polylactic acid (PLA) and polyethylene (PE).<br/>Wastewater treatment plants (WWTPs) are not specifically designed to remove microplastics; however, it has been estimated that 88-94% of microplastics are removed throughout the wastewater treatment process. This means that most microplastics that enter WWTPs accumulate in sludge (i.e., the solid, semi-solid, or liquid waste generated from a WWTP). Many countries have started using this sludge byproduct as a fertilizer. As a result, the land application of sludge represents one of the largest sources of microplastics entering the environment. Previous research in this area has focused on quantification of microplastics in sludge samples or microplastic exposure to isolated WWTP processes such as sulfidation or biological treatment. However, little work has been done to characterize changes in the properties of microplastics resulting from accumulation in sludge. In this work, we characterize the degradation of PLA and PE films after exposure to sludge with the use of attenuated total reflection Fourier-transform infrared spectroscopy and X-ray diffraction. From this, we demonstrate the ability to quantify (1) changes in oxygen-containing functional groups and (2) the percent crystallinity of microplastic films that have been exposed to sludge for up to 12 days. Herein, we directly compare the degradation of the emerging biodegradable thermoplastic PLA to the more conventionally studied, non-biodegradable PE. This work expands on the growing body of research assessing physicochemical changes to microplastics.

Changes in surface chemistry and crystallinity of polylactic acid and polyethylene films with exposure to sludge from a wastewater treatment plant

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ACS Fall 2022

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