Identification of Microplastics in Biosolids Using Ftir and Vis-Nir Spectroscopy Enhanced by Chemometric Methods

Abstract

This study aims to characterize the microplastics (MPs) present in biosolids from Wastewater Resource Recovery Facilities (WRRFs) located in a city in northeastern United States. MP particles were extracted by two procedures: wet sieving for plastic particles greater than 2 mm, and density separation after oxidative treatment for MPs smaller than 2 mm. The amount of visually identifiable MPs extracted from biosolids ranged from 0.01 to 0.04%. MPs were investigated by two different infrared spectroscopy techniques, visible near-infrared (Vis-NIR) and Fourier-transform infrared (FTIR) spectroscopy, in combination with the chemometric approach. The resulting spectra were preprocessed by Savitzky-Golay (SG), standard normal variate (SNV) and first derivative (FD) transformations. This was followed by multivariate principal component analysis (PCA). PCA provided an interpretable overview of the main information contained in the Vis-NIR and FTIR spectra datasets and was able to differentiate MPs when the spectra were compared with those for reference plastic materials. Our results show that MPs in the biosolids are mainly composed of polyethylene terephthalate (PET), low and high-density polyethylene (LDPE, HDPE), polystyrene (PS), and polypropylene (PP) with polyamide (PA) fibers. The primary sources of MPs in the biosolids are likely discarded consumer packaging (containers, bags, bottles) and fibers from laundry.

Keywords: microplastics, Biosolids, FTIR spectroscopy, Vis-NIR spectroscopy, Chemometrics