Abstract
While the presence of microplastics has been reported in aquatic habitats across the globe, the pathways through which they enter the environment are still poorly understood. Studies investigating the fate of microplastics in wastewater are gaining attention but are still scarce, despite the urgent need to understand the role of wastewater treatment plants (WWTP) as point sources of aquatic microplastic pollution. A likely reason for the limited number of WWTP-associated studies is that working with a biogenic organic matter (BOM)-rich sample matrix like wastewater is challenging. Here, we investigated the presence of microplastics (MP) throughout several stages of a wastewater treatment plant (WWTP) at multiple depths, employing Fenton’s reagent and focal plane array-based reflectance micro-Fourier-transform infrared spectroscopic (FPA-based reflectance micro-FTIR) imaging, a protocol that allows the automated detection and identification of microplastics in complex samples with high organic matter content, without the need for previous visual sorting, or reducing considerably the thickness of the sample, or the use of IR-transparent transmission windows. It was found that the number of microplastic fragments detected at downstream stages of the WWTP notably decreased following the primary settlement stage, with primary settlement stage samples responsible for 76.9% of total microplastics detected. Despite the marked reduction in the number of microplastic particles following the primary settlement stage, an average total of 1.5 MP L-1 were identified in the final effluent of the WWTP.
Highlights
While microplastic (MP) pollution is an important environmental concern and its presence has been extensively studied globally (Browne et al, 2011; Cole et al, 2011), the pathways by which microplastics enter aquatic environments remain understudied
Murphy et al (2016) investigated microplastic abundances in various wastewater treatment stages and found that the majority of microplastics were removed during the grease removal, yet 0.25 (±0.04) MP L−1 were found in later stages including final effluent, where extrapolation of this data suggested 65 million microplastics could be released into natural waters every day from the wastewater treatment plants (WWTP) studied
This study demonstrates the effectiveness of focal plane array (FPA)-based reflectance micro-FTIR imaging for detecting microplastic present throughout key stages of wastewater treatment, by imaging the entire membrane filters directly, with no need for a visual pre-selection step or requirement of very thin samples and IR-transparent transmission windows
Summary
While microplastic (MP) pollution is an important environmental concern and its presence has been extensively studied globally (Browne et al, 2011; Cole et al, 2011), the pathways by which microplastics enter aquatic environments remain understudied. Microplastics Monitoring Using Reflectance Micro-FTIR organic matter (BOM)-rich sample matrix like wastewater is very challenging. Despite the difficulty of detecting microplastics in BOM-rich matrices, there is a growing trend to investigate the fate of these pollutants in wastewater to help build a better picture of how wastewater treatment plants (WWTPs) cope with microplastic load and to what extent microplastics enter river systems through WWTPs (Lares et al, 2018; Sun et al, 2019). Murphy et al (2016) collected bulk samples before a sieving step (65 μm mesh size), Carr et al (2016) fixed stacked sieves (400–445 μm) in a wastewater stream directly without taking bulk samples, Mintenig et al (2017) applied enzymatic-oxidative purification in combination with focal plane array (FPA)-based transmission micro-FTIR, and Simon et al (2018) used sieve meshes to eliminate particles and fibers larger than 500 μm in the raw and treated wastewater only. As the studies were conducted in areas with differing climate, rainfall and other geographical factors, it is perhaps unsurprising that the results show disparity
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