The state of microplastic removal processes in liquid effluents and domestic water

Synthesis

Disclaimer: The content of this publication is based on the state of knowledge and the regulatory framework in force at the time of publication of the documents

Study context

Plastics are ubiquitous in our environment due to their low production cost and physical properties, which make them suitable for many applications. In 2023, 413.8 megatonnes of plastics were produced worldwide according to the Plastics Europe study published in 2024 (Plastics Europe 2024), and this production continues to increase. Micro- and nanoplastics, mainly originating from the degradation of macroplastics, tend to accumulate in the environment, leading to persistent pollution that is therefore harmful to the environment and to health. The growing number of scientific publications on nano- and microplastics reflects the magnitude of this concerning pollution.

Study objectives

This study aims to identify methods for removing nano- and microplastics present in wastewater. To address the different aspects of the topic, a definition of the terms nano- and microplastics is proposed. A focus is provided on current global, European and French regulations. The study reviews analytical techniques for the characterization and quantification of N MPs in clean waters as well as in more complex matrices. This part highlights current bottlenecks in research aimed at implementing nano- and microplastic treatments. Finally, one of the main objectives of the study is to describe the treatments currently implemented or under development in wastewater treatment plants. The project concludes with a review of treatments aimed at removing this pollution from sludge.

Definition of N MPs

Nanoplastics (NPs) and microplastics (MPs) are very small plastic particles. They may be intentionally produced, in which case they are referred to as primary. They may also result from the wear of an item or from the degradation of macroplastics under the effect of environmental processes; in that case they are referred to as secondary, within the scope of this study.

The size range of these particles is debated within the scientific community. To facilitate reading, this study considers NPs to range from 1 nm to 1,000 nm and MPs from 1 µm to 5 mm. N MPs can take various shapes, grouped here into five categories: fragment, fibre, bead, pellet and foam.

Plastic polymers are distinguished by the monomer used to synthesize them. A plastic made from the same monomer can have different characteristics depending on polymer chain length, the manufacturing method and the additives used. In 2023, the five most-produced plastics worldwide were high- and low-density polyethylene (HDPE and LDPE, 26.2%), polypropylene (PP, 19%), polyethylene terephthalate (PET, 6.2%), polyurethane (PUR, 5.3%) and polystyrene (PS, 5.2%) (Plastics Europe 2024).

Plastic degradation is a slow process that occurs under the effect of abiotic and biotic environmental factors. Several parameters can influence it, in addition to chemical composition. In particular, additives can play an important role by modifying physico-chemical characteristics (antioxidants, dyes, surfactants, etc.). These additives can account for more than 50% of the material’s mass, and some are known to be hazardous and toxic to organisms. 

Conversely, UV radiation from sunlight induces the formation of hydrophilic chemical groups on the surface of N MPs, thereby accelerating their deterioration.

Seven major sources of microplastics have been identified by the International Union for Conservation of Nature (IUCN): synthetic textiles, car tyres, urban dust, road markings, marine paints, personal care products, and plastic pellets. Between 1.8 and 5 million tonnes of microplastics would be released into the environment every year worldwide when considering only these seven sources of N MPs.

Overall, there is a lack of data on N MP pollution, and some sources are emphasized more because they are easier to quantify. In addition, nanoplastics are not accounted for in many studies, as their quantification remains particularly difficult to date.

N MPs, resulting from the degradation of, or direct use of, various products (textiles, tyres, cosmetics, paints, etc.), can follow multiple transfer pathways before reaching natural environments. These pathways include wastewater effluents (urban and industrial), runoff waters, and sewer overflows.

The toxicity of N MPs in the environment and for human health depends on many factors, including their size, shape, surface charge, chemical composition and the presence of additives, whose so called “cocktail effects” are still insufficiently studied.

Current data are insufficient to determine whether exposure to N MPs is associated with chronic diseases.

Regulations have been implemented in many countries over the past decade. These regulations mainly target the reduction of primary microplastics in personal care products as well as single use plastics.

Characterization and quantification of micro- and nanoplastics

Characterizing and quantifying micro- and nanoplastics is a real challenge. Figure 1 helps to understand the different choices for sample preparation

Figure 1: summary diagram of the preliminary steps prior to analysis (RECORD, 2025)

As noted, several standardized methods are referenced; Figure 2 provides an overview of these methods.

Figure 2: Standardized analytical techniques for N MP characterization (RECORD,2025)

Several points have been highlighted to better understand the challenges of analyses. Vigilance against cross-contamination and strict adherence to protocols are essential to ensure the reliability of results. Indeed, each step, from sampling to sample treatment, then filtration and analysis, can influence the data obtained, even when methods are standardized. Comparisons between laboratories therefore remain difficult. Finally, as the various analytical techniques do not provide the same information, they should be considered complementary.

In addition, recovering and identifying nanoparticles (NPs) remains challenging. Research is mostly conducted on clean matrices rather than complex ones, which limits the representativeness of the results. Moreover, the NPs recovered represent only a fraction of the NPs initially present in the sample.

Finally, the cost of the analyses, which currently ranges from €500 to €3,000, depends on the treatment applied,  which in turn depends on the organic and inorganic content of the samples, as well as on the analytical technique used, depending on the information required.

Removal of N MPs present in wastewater

Wastewater treatment plants are currently neither designed nor sized to efficiently treat this type of micropollutant. Several studies have therefore been carried out to assess their performance. This is notably the case for the MEDIPLAST study which, after evaluating four wastewater treatment plants in the Toulon area, reported removal efficiencies between 90% and 99%.

Many difficulties were encountered in the study. Several articles do not report the lower size limit of detected microplastics, but only the filter size used. In addition, as seen in the previous section, microplastic analysis involves many uncertainties, whether related to sampling, sample preparation or the analytical technique used. Therefore, the reported removal percentages should be considered orders of magnitude.

Wastewater treatment plants implement different processes, each with a specific function. Each treatment step is therefore able to remove some of the microplastics present in the effluents.

The following table (Table 1) compares the different preliminary and primary treatment processes. Primary treatment is mainly a physicochemical process that makes it possible to treat colloidal suspensions.

Table 1: Summary of preliminary and primary treatments and their MP removal efficiency (compilation RECORD, 2025) (Asadi et al. 2025) (Mebarki et al. 2025; Peydayesh et al. 2021) (Shen et al. 2022) (Esfandiari & Mowla, 2021; Pramanik et al., 2021; Swart et al., 2022)

Secondary treatment, in turn, is a biological treatment based on biomass. It aims to remove organic matter (COD and BOD), as well as nitrogen and phosphorus. The following table (Table 2) helps to understand the differences between the technologies.

Table 2: Summary of secondary treatments and their MP removal efficiency (compilation RECORD, 2025) (Asadi et al. 2025; Shen et al. 2022) (Bayo et al., 2020) (F. Liu et al., 2020)

Finally, tertiary treatment aims to further improve water quality by removing residual pollutants. Table 3 helps to better understand the different categories of processes and their effectiveness in removing microplastics.

Table 3: Summary of tertiary treatments and their MP removal efficiency (compilation RECORD, 2025) (Bayo et al. 2023; Sembiring et al. 2021) (Simon et al. 2019) (Akarsu et al. 2021; Pizzichetti et al. 2021)( Enfrin et al. 2020; Luogo et al. 2022) (Kara et al. 2023; Lin et al. 2025; Sawma et al. 2024)( Cai et al. 2022) (Easton et al. 2023) (Topkaya et al. 2025) (Bitter et al. 2022)

The following table (Table 4) presents various microplastic treatment techniques corresponding to technology readiness levels ranging from TRL 4 to TRL 7. These methods, still under development, have been described in scientific reviews and tested at laboratory scale. However, few have been evaluated on complex matrices, and scaling up to full scale remains one of their main limitations.

Table 4: Summary of technologies under development aimed at removing MPs (compilation RECORD, 2025) (Thacharodi et al. 2024) (Tang et al. 2021) (Ahmad et al. 2023; Ganie et al. 2025) (Lee et al. 2020) (Zhao et al. 2022)

These tables make it possible to compare the different treatments. As indicated above, the reported removal percentage depends on the cut off threshold used during sampling, on the analysis itself, and on the type of effluent to which the techniques are applied. The study showed that combining several processes makes it possible to remove microplastics more effectively in the most complex effluents.

Removal of N MPs present in sludge

The techniques presented above can separate and/or degrade N MPs present in an aqueous solution. However, during preliminary, primary and secondary treatments, for example, N MPs are transferred into sludge. In wastewater treatment plants, more than 80% of the microplastics present in wastewater end up in sludge. In France, around 60% of sludge from wastewater treatment plants is recycled in agriculture (20–25% is landfilled and 10–15% is incinerated). It is therefore necessary to identify a way to remove these N MPs before spreading sludge on land.

Dewatering, anaerobic digestion, aerobic composting and thermal treatments are processes already applied to wastewater treatment sludge. They can reduce sludge volume by 50% to 80%, leading to a significant decrease in transport and management costs. Some processes, such as anaerobic digestion, also enable the production of biogas that can be used as an energy source. Lastly, sludge stabilization helps limit health risks linked to the presence of pathogens and the release of toxins.

Although these treatments are not designed to remove N MPs present in sludge, they may nevertheless have an effect on them.

Thermal treatments enable total or near-total destruction of microplastics. Their main drawback is the energy consumption required for implementation.

The issue of microplastics in agricultural soils is gaining increasing attention. As a result, some technologies have been developed to address this problem. This is the case for wet air oxidation, which treats sludge using oxygen as the oxidizing agent. This treatment has proven effective at full scale and has enabled mineralization of a large share of the microplastics present in sludge. One limitation of this process may be the cost of oxygen and electricity required to heat the sludge. Other techniques studied in this project have already been described in the previous section, such as flotation or high gradient magnetic separation.

As with microplastic removal in complex liquid matrices, studies have shown that a preferred approach would be to combine several treatments in order, on the one hand, to fully mineralize microplastics through processes that enable their degradation, and on the other hand, to limit costs and treatment times.

Several studies also show that a separation treatment, such as electrocoagulation, could concentrate microplastics in a smaller volume so that they can then be treated more effectively, for example via a biological treatment such as biodegradation.

Conclusion and discussion of results

This study provides an overall view of the treatment processes implemented in wastewater treatment plants to remove microplastics, as well as technologies currently under development. In light of these results, several questions were raised.

• First, a general observation must be made regarding the lack of standards governing microplastic, and even more so nanoplastic, analysis, as well as the high cost of these analyses. These limitations hinder innovation and the implementation of effective strategies to address microplastic pollution.
• Nevertheless, this study shows that the wastewater treatment plants implemented in France and Europe already achieve a significant removal of microplastics. This raises the question of whether it is necessary to impose treatments specifically dedicated to microplastics, whose primary objective would be targeted removalgiven other forms of pollution that may be just as dangerous, and the financial investments this would entail.
• Finally, the issue of sludge remains significant. However, analytical bottlenecks are still too substantial at this stage to identify concrete, fully operational solutions.