Determination of microplastics in municipal wastewater treatment plant effluents and sludge using micro-Raman spectroscopy

Abstract

Microplastics (MPs) increase global awareness due to their ubiquity, high concentration levels, and devastating effects on the aquatic environment. Wastewater treatment plants (WWTPs) are recognized as a significant source of microplastics in aquatic and terrestrial environments, particularly for plastics used in personal care products and textile fibers from the clothing industry. The focus of the present study was the determination of MP in wastewater and sewage sludge samples of WWTP of Ioannina city, according to their shape, size, concentration, and polymer type. A wet peroxide oxidation (WPO) method using 30% H₂O₂ and 0.05 M ferrous (II) solution was applied to the water effluent, while an enzymatic digestion method combined with WPO was employed to eliminate the organic matter and extract MPs from sludge samples. Micro-Raman spectroscopy coupled with appropriate software was applied to detect and quantify the microplastic particles. The outcomes from this study showed that the most representative shape of MP in effluent wastewater and sludge was fragments (66.7% and 75%, respectively), followed by fibers, spheres, and films. Polyamide (PA), p-acrylic acid (PAA), and p-acrylamide-co-p-acrylic acid (PAM-co-PAA) were the most abundant polymers (100% frequency of detection), followed by p-vinyl chloride (PVC), p-butyl methacrylate (PBMA), p-ethylene (PE), p-styrene (PS), p-propylene (PP), p-vinyl alcohol (PVA), and p-vinyl butyral (PVB) (20%-80% frequency of detection). The mean concentration of MPs in five sampling campaigns was 5.8 ± 0.6 particles/L in secondary WWTP effluents and 33.3 ± 8 particles/g in sludge. This study focused on monitoring campaign, in order to better understand the occurrence, impact, and risks associated with MPs on WWTPs.

Keywords

Microplastics / wastewater effluents / sewage sludge / micro-Raman spectroscopy / risk assessment

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