Microplastic sampling from wastewater treatment plant effluents: Best-practices and synergies between thermoanalytical and spectroscopic analysis

Insight into microplastics in the aquatic ecosystem: Properties, sources, threats and mitigation strategies

Globally recognized as emergent contaminants, microplastics (MPs) are prevalent in aquaculture habitats and subject to intense management. Aquaculture systems are at risk of microplastic contamination due to various channels, which worsens the worldwide microplastic pollution problem. Organic contaminants in the environment can be absorbed by and interact with microplastic, increasing their toxicity and making treatment more challenging. There are two primary sources of microplastics: (1) the direct release of primary microplastics and (2) the fragmentation of plastic materials resulting in secondary microplastics. Freshwater, atmospheric and marine environments are also responsible for the successful migration of microplastics. Until now, microplastic pollution and its effects on aquaculture habitats remain insufficient. This article aims to provide a comprehensive review of the impact of microplastics on aquatic ecosystems. It highlights the sources and distribution of microplastics, their physical and chemical properties, and the potential ecological consequences they pose to marine and freshwater environments. The paper also examines the current scientific knowledge on the mechanisms by which microplastics affect aquatic organisms and ecosystems. By synthesizing existing research, this review underscores the urgent need for effective mitigation strategies and further investigation to safeguard the health and sustainability of aquatic ecosystems.

Detection of microplastic traces in four different types of municipal wastewater treatment plants through FT-IR and TED-GC-MS

Large amounts of microplastics are discharged into wastewater treatment plants (WWTPs), from where some of them are released into natural waterbodies on account of their not being fully eliminated by WWTPs. To investigate the behavior and emission of microplastics from WWTPs, we selected four WWTPs with different treatment technologies, including anaerobic-anoxic-aerobic (A2O), sequence batch reactor (SBR), media, and membrane bioreactor (MBR). The number of microplastics detected using Fourier transform infrared (FT-IR) spectroscopy ranged from 520 to 1820 particles/L in influent and from 0.56 to 2.34 particles/L in effluent. The microplastic removal efficiencies of four WWTPs were over 99%, indicating that the type of treatment technologies did not significantly affect the removal rate of microplastics. In the unit process for each WWTP, the major stages relating to microplastic removal were the secondary clarifier and tertiary treatment processes. Most microplastics detected were categorized as fragments and fibers, while other types were hardly detected. The size of more than 80% of microplastic particles detected in WWTPs ranged between 20 and 300 μm, indicating that they were significantly smaller than the size threshold defined for microplastics. Therefore, we used thermal extraction-desorption coupled with gas chromatography-mass spectroscopy (TED-GC-MS) to evaluate the microplastic mass content in all four WWTPs, and the results were compared with those of the FT-IR analysis. In this method, only four components, namely polyethylene, polypropylene, polystyrene, and polyethylene terephthalate, were analyzed because of the analysis limitation, and the total microplastic concentration represented the sum of four components concentrations. The influent and effluent microplastic concentrations estimated by TED-GC-MS ranged from not detectable to 160 μg/L and 0.04-1.07 μg/L, respectively, indicating a correlation coefficient of 0.861 (p < 0.05) between the TED-GC-MS and FT-IR results, when compared to the combined abundance of the four microplastic components by FT-IR analysis.

Recent advances on micro/nanoplastic pollution and membrane fouling during water treatment: A review

Effluent from sewage treatment plant, as an important source of microplastics (MPs) in receiving water, has attracted extensive attention. Membrane separation process shows good microplastic removal performance in the existing tertiary water treatment process. Problematically, membrane fouling and insufficient removal of small organic molecules are still the key obstacles to its further extensive application. Dissolved organics, extracellular polymers and suspended particles in the influent are deposited on the membrane surface and internal structure, reducing the number and pore diameter of effective membrane aperture, and increasing the resistance of membrane filtration. Exploring the mechanism and approach of membrane fouling caused by micro/nanoplastics is the key to alleviate fouling and allow membranes to operate longer. In this paper, removal performance of micro/nanoplastics by current membrane filtration and the contribution to membrane fouling during water treatment are thoroughly reviewed. The coupling mechanisms between micro/nanoplastics and other pollutants and mechanism of membrane fouling caused by composite micro/nanoplastics are discussed. Additionally, on this basis, the prospect of combined process for micro/nanoplastic removal and membrane fouling prevention is also proposed and discussed, which provides a valuable reference for the preferential removal of micro/nanoplastics and development of antifouling membrane.

TUM-ParticleTyper 2: automated quantitative analysis of (microplastic) particles and fibers down to 1 [Formula: see text]m by Raman microspectroscopy

Accurate quantification of small microplastics in environmental and food samples is a prerequisite for studying their potential hazard. Knowledge of numbers, size distributions and polymer type for particles and fibers is particularly relevant in this respect. Raman microspectroscopy can identify particles down to 1 [Formula: see text]m in diameter. Here, a fully automated procedure for quantifying microplastics across the entire defined size range is presented as the core of the new software TUM-ParticleTyper 2. This software implements the theoretical approaches of random window sampling and on-the-fly confidence interval estimation during ongoing measurements. It also includes improvements to image processing and fiber recognition (when compared to the previous software TUM-ParticleTyper for analysis of particles/fibers [Formula: see text] [Formula: see text]m), and a new approach to adaptive de-agglomeration. Repeated measurements of internally produced secondary reference microplastics were evaluated to assess the precision of the whole procedure.

Digest, stain and bleach: Three steps to achieving rapid microplastic fluorescence analysis in wastewater samples

Efforts associated with common analytical techniques for microplastics including spectroscopic and thermo-analytical techniques are limiting the ability to perform large-scale monitoring of microplastics in the aquatic environment, because the analytical equipment required is costly and the analysis itself time consuming. Thus, there is a need to develop low cost, rapid alternative monitoring approaches. One possible alternative is the use of selective fluorescence staining of microplastic particles directly applied to environmental samples. However, to the best of our knowledge this has not yet been successfully implemented for wastewater samples. In this study, sludge samples are used as surrogates for wastewater alongside six different polymers to develop a combined sample preparation and staining protocol that could selectively stain microplastics without significant interference from the natural constituents of the sludge. Results confirmed that using Fenton's reagent to remove the organic matter before staining the sample with Nile red (NR) and subsequently bleaching it by sodium hypochlorite resulted in the best workflow to selectively stain microplastics and then analyze them in wastewater samples using fluorescence microscopy.

Underestimating microplastics? Quantification of the recovery rate of microplastic particles including sampling, sample preparation, subsampling, and detection using µ-Ramanspectroscopy

This study is one of the first to investigate the recovery rate of high- and low-density microplastic particles (polyvinyl chloride and polypropylene) from wastewater treatment plant effluents or comparable technical facilities under nearly realistic experimental conditions. For this purpose, a method of continuous dosing of microplastic particles into an experimental flume for open-channel flow was developed. Subsequently, 12 samples were taken using volume-reduced sampling and the entire sample purification process including oxidative treatment (with hydrogen peroxide and sodium hypochlorite), density separation (with sodium polytungstate), and subsampling was carried out. Detection was conducted using automatic particle recognition and µ-Ramanspectroscopy. An average recovery rate of 27 ± 10% was determined for polypropylene microplastic particles (d = 53 ± 29 µm), decreasing with the particle size, and 78 ± 14% for polyvinyl chloride microplastic particles (d = 151 ± 37 µm). The results suggest that microplastic emissions from wastewater treatment plants are underestimated, particularly because the recovery rate of small microplastic particles < 50 µm is only 9%.