Microplastics in wastewater treatment plants: Detection, occurrence and removal

Chapter 9 - Microplastics and nanoplastics: Occurrence, fate, and persistence in wastewater treatment plants

A review on the characteristics of microplastics in wastewater treatment plants: A source for toxic chemicals

In last 10 years, the interest about the presence of microplastics (MPs) in the environment has strongly grown. Wastewaters function as a carrier for MPs contamination from source to the aquatic environment, so the knowledge of the fate of this emerging contaminant in wastewater treatment plants (WWTPs) is a priority. This work aims to review the presence of MPs in the influent wastewater (WW) and the effectiveness of the treatments of conventional WWTPs. Moreover, the negative impacts of MPs on the management of the processes have been also discussed. The work also focuses on the possible approaches to tackle MPs contamination enhancing the effectiveness of the WWTPs. Based on literature results, despite WWTPs are not designed for MPs removal from WW, they can effectively remove the MPs (up to 99 % in some references). Nevertheless, they normally act as “hotspots” of MPs contamination considering the remaining concentration of MPs in WWTPs' effluents can be several orders of magnitude higher than receiving waters. Moreover, MPs removed from WW are concentrated in sewage sludge (potentially >65 % of MPs entering the WWTP) posing a concern in case of the potential reuse as a soil improver. This work aims to present a paradigm shift intending WWTPs as key barriers for environmental protection. Approaches for increasing effectiveness against MPs have been discussed in order to define the optimal point(s) of the WWTP in which these technologies should be located. The need of a future legislation about MPs in water and sludge is discussed.

Pollution of the aquatic environment with microplastics has recently been recognised as a new environmental threat considering their negative impact on the ecosystem. Due to the low density and small particle size of microplastics, they are easily discharged into sewage systems and wastewater treatment plants. Thus, wastewater treatment plants are considered major sources of microplastic pollution in aquatic and terrestrial environments. Therefore, there is an urgent need for an in-depth understanding of the occurrence, behaviour, and fate of microplastics in wastewater treatment plants before they are discharged into natural water bodies. This paper comprehensively reviews the current state of knowledge on the characteristics and removal of microplastics in a series of wastewater treatment plants by comparing their removal efficiency in different unit processes, both during pretreatment, biological treatment, and tertiary treatment. The study found varying efficiencies in wastewater treatment technologies, with the first stage of treatment removing between 16.5 and 98.4% of microplastics, while during biological treatment the overall efficiency of microplastics removal ranges from 78.1 to 99.9% (membrane bioreactor). Nevertheless, given the large volumes of wastewater continuously discharged to receiving bodies, even tertiary treatment plants can be a significant source of microplastics in surface waters. The largest fraction of MPs removed in conventional wastewater treatment plants is trapped in the sludge. Among the critical treatment technologies, microplastic quantitative analysis showed that membrane bioreactors and filter-based treatment technologies have the highest microplastic removal efficiency. Based on a review of the existing literature, it was concluded that existing wastewater treatment plants are ineffective in removing microplastics completely, and there is a risk that they could be discharged into surrounding water sources.

Microplastics aging in wastewater treatment plants: Focusing on physicochemical characteristics changes and corresponding environmental risks

Occurrence, characteristics, and removal of microplastics in wastewater treatment plants located on the Moroccan Atlantic: The case of Agadir metropolis

Conversion and removal strategies for microplastics in wastewater treatment plants and landfills

Microplastic (MP) contamination has grown to be a serious environmental issue in recent years. Microplastics are plastic particles, with a size of less than 5 mm, that are either produced specifically for use in a variety of products or emerge through the decomposition of larger plastic items. Data from prior research conducted in wastewater treatment plants (WWTPs) regarding the abundances of microplastics across different treatment stages of WWTPs in different countries were compiled using online scientific databases. This research found that although Turkey only managed to attain a removal rate of 48.0%, Iran and the United States were able to reach removal rates of over 90.0%. It was discovered that two plants in Morocco had relatively high removal efficiencies, with one achieving a remarkable 74.0% removal rate and the other an 87.0% removal rate. The predominance of fibers and fragments in the influent and effluent across all studied locations shows the difficulty in effectively removing them from wastewater. The widespread abundance of microplastic polymers from diverse sources poses a significant challenge for wastewater treatment facilities in efficiently managing and eliminating these pollutants. This research further demonstrated regional differences in the color composition of microplastics, with black, transparent, blue, and red being prominent colors in the influent and effluent of some regions. These color variations can influence the detection and identification processes, which are crucial for developing targeted removal strategies. In conclusion, it is essential to address the pervasiveness of microplastics in wastewater treatment plants. Improving treatment procedures, protecting the ecosystem, and conserving water quality for a sustainable future all depend on addressing the various sources of these contaminants.

Microplastic (MP) water pollution is a major problem that the world is currently facing, and wastewater treatment plants (WWTPs) represent one of the main alternatives to reduce the MP release to the environment. Several studies have analysed punctual samples taken throughout the wastewater treatment line. However, there are few long-term studies on the evolution of MPs over time in WWTPs. This work analyses the performance of a WWTP sited in Southwest Europe in relation with annual occurrence and fate of MPs. Samples were monthly taken at different points of the facility (influent, secondary effluent, final effluent, and sludge) and MPs were quantified and characterised by means of stereomicroscopy and FTIR spectrophotometry. The majority of MPs found in wastewater and sludge samples were fragments and fibres. Regarding to the chemical composition, in the water samples, polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP) stood out, whereas, in the sludge samples, the main polymers were PET, polyamide (PA) and polystyrene (PS). The MPs more easily removed during the wastewater treatment processes were those with sizes greater than 500 µm. Results showed that the MPs removal was very high during all the period analysed with removal efficiencies between 89% and 95%, so no great variations were found between months. MP concentrations in dry sludge samples ranged between 12 and 39 MPs/g, which represented around 79% of the total MPs removed during the wastewater treatment processes. It is noticeable that a trend between temperature and MPs entrapped in sewage sludge was observed, i.e., higher temperatures entailed higher percentage of retention.

Environmental contamination caused by microplastics (MPs) is an issue of grave concern which is pervasive in global water, air, and soil. Wastewater treatment plants (WWTPs) are recognized as the vital source of MPs into the environment. Hence understanding the fate and behavior of MPs in WWTPs is of utmost importance. Studies have also reported the presence of MPs in the treated effluent. Challenges in MPs removal in different treatment units need to be identified, and advancements of existing treatment technologies are to be explored for enhancing the removal of MPs in WWTPs. This chapter presents the occurrence and fate of MPs in different treatment processes such as biodegradation, adsorption, membrane processes, filtration, electrocoagulation, and advanced oxidation processes. The removal efficiency of MPs in different treatment units, the mechanism of removal, and the challenges involved in removing MPs in each treatment unit are discussed in detail. The efficiency of the existing treatment technologies in WWTPs are compared, and the modifications suggested by recent studies to improve the removal of MPs are presented in this chapter.KeywordsMicroplasticsOccurrenceMitigationAdvanced oxidation processesAdsorptionBioreactorElectrocoagulationFiltrationWastewater treatment

This review discusses the most recent research focused on the abundance and removal of microplastics in wastewater treatment plants.

Microplastics in wastewater plants: A review of sources, characteristics, distribution and removal technologies

Microplastics in wastewater treatment plants: Occurrence, fate and identification

The occurrence of microplastics (MPs) in the environment has become an emerging global concern and has been reported to pose consequential risks to organisms, human health and the environment. Due to their small size (ranging from 1 μm to 5 mm in size), eliminating MPs from wastewater poses a significant challenge, which leads to their accumulation in wastewater treatment plants (WWTPs). This review article explores the method of characterizing MPs in WWTPs to understand their environmental impact better. It also discusses various techniques for characterising MPs in WWTPs, drawing on existing scientific literature. The article provides a comprehensive review of the current methodologies used for the characterisation (chemical, morphology, thermal) of MPs in WWTPs. Furthermore, analytical techniques such as scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy are discussed along with their limitations and potential for recognition and differentiation of various kinds of MPs. The article also highlights the need for standardisation of sampling, extraction, and analytical methods to ensure comparability of results from different studies. The review identifies several obstacles in characterising MPs within WWTPs, such as the absence of standardised methods, restricted detection thresholds, and challenges in quantifying MPs within intricate environmental contexts. To overcome these obstacles, the review recommends prioritising research efforts aimed at enhancing current methodologies, emphasising the need to refine techniques for better comprehension and analysis of MPs within WWTPs.

Microplastics (MPs) are ubiquitous emerging pollutants that have been found in the marine, freshwater, air, and soil environments. Wastewater treatment plants (WWTPs) play an important role in releasing MPs to the environment. Therefore, understanding the occurrence, fate, and removal mechanism of MPs in WWTPs is of great importance towards microplastic control. In this review, the occurrence characteristics and removal rates of MPs in 78 WWTPs from 57 studies were discussed based on Meta-analysis. Specifically, the key aspects regarding MPs removal in WWTPs, such as wastewater treatment processes and MPs shapes, sizes, and polymer compositions were analyzed and compared. The results showed that:① the abundances of MPs in the influent and effluent were 1.56×10-2-3.14×104 n·L-1 and 1.70×10-3-3.09×102 n·L-1, respectively. The abundance of MPs in the sludge ranged from 1.80×10-1 to 9.38×103 n·g-1. ② The total removal rate (>90%) of MPs by WWTPs using oxidation ditch, biofilm, and conventional activated sludge treatment processes was higher than that using sequencing batch activated sludge, anaerobic-anoxic-aerobic, and anoxic-aerobic processes. ③ The removal rate of MPs in primary, secondary, and tertiary treatment process were 62.87%, 55.78%, and 58.45%, respectively. The combination process of "grid+ sedimentation tank+primary sedimentation tank" had the highest removal rate towards MPs in primary treatment processes, and the membrane bioreactor had the highest one beyond other secondary treatment processes. Filtration was the best process in tertiary treatment. ④ The film, foam, and fragment MPs were easier to remove (>90%) than fiber and spherical (<90%) MPs by WWTPs. The MPs with particle size larger than 0.5 mm were easier to remove than those with particle size smaller than 0.5 mm. The removal efficiencies of polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP) MPs were higher than 80%.