Microplastics In Wastewater Treatment Plants Research Articles

To what extent are wastewater treatment systems a gateway for microplastic particles in the aquatic and terrestrial environments?

Sewage treatment plants are designed to handle wastes that include several types of pollutants, including microplastics (MPs), which are synthetic polymer materials fragmented to sizes < 5 mm. Investigating the abundance and removal efficiency rates of MPs in wastewater treatment plants is important because the water body to which plant effluents are discharged may be adversely affected by the released MPs. Therefore, the abundance, characteristics, and removal of MPs at two sewage treatment plants located on the southwest coast of Norway are studied. Twenty-four samples were collected across two sampling sessions by using an ad hoc-designed plastic-free water sampling device, which was improved by applying a cascade of certified stainless-steel sieves. A combined sequence of enzymatic and strong oxidative incubations was performed for sample preparation. The obtained samples were chemically characterized and quantified using thermoanalytical techniques. The overall amounts of polymers in the inlet wastewater and outlet water were 366-616 μg/L and 34-57 μg/L, respectively, indicating an approximate MPs removal efficiency of 78%-85%. Polyethylene (≈ 36%-68%), polypropylene (≈ 7%-48%), polystyrene (≈ 5%-6%), polyvinyl chloride (≈ 15%-26%), polyamide (≈ 2%), polymethacrylate (≈ 3%-4%), polycarbonate (≈ 2%), and polyethylene terephthalate (≈ 9%-32%) were detected in the investigated samples. In biosolids, the overall quantity of MPs was 3.8-5.5 mg/g dry weight across the two investigated sewage treatment plants. Polyethylene (≈ 24%-44%), followed by polyvinyl chloride (PVC) (≈ 11%-16%), and polyamide (≈ 2%-22%) were the most commonly recurring polymer types. The outcomes of this study indicate that MPs are removed efficiently from wastewaters. However, large amounts of MPs accumulate in biosolids. Therefore, sludge dumping management procedures need to be improved to lower the amount of MPs released into the environment through effluents and biosolids.

Extraction and analytical methods of microplastics in wastewater treatment plants: isolation patterns, quantification, and size characterization techniques

Extraction and analytical methods of microplastics in wastewater treatment plants: isolation patterns, quantification, and size characterization techniques

Research progress on the origin, fate, impacts and harm of microplastics and antibiotic resistance genes in wastewater treatment plants

Previous studies reported microplastics (MPs), antibiotics, and antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). There is still a lack of research progress on the origin, fate, impact and hazards of MPs and ARGs in WWTPs. This paper fills a gap in this regard. In our search, we used “microplastics”, “antibiotic resistance genes”, and “wastewater treatment plant” as topic terms in Web of Science, checking the returned results for relevance by examining paper titles and abstracts. This study mainly explores the following points: (1) the origins and fate of MPs, antibiotics and ARGs in WWTPs; (2) the mechanisms of action of MPs, antibiotics and ARGs in sludge biochemical pools; (3) the impacts of MPs in WWTPs and the spread of ARGs; (4) and the harm inflicted by MPs and ARGs on the environment and human body. Contaminants in sewage sludge such as MPs, ARGs, and antibiotic-resistant bacteria enter the soil and water. Contaminants can travel through the food chain and thus reach humans, leading to increased illness, hospitalization, and even mortality. This study will enhance our understanding of the mechanisms of action among MPs, antibiotics, ARGs, and the harm they inflict on the human body.

Understanding microplastic presence in different wastewater treatment processes: Removal efficiency and source identification

Municipal effluents discharged from wastewater treatment plants (WWTPs) are a considerable source of microplastics in the environment. The dynamic profiles of microplastics in treatment units in WWTPs with different treatment processes remain unclear. This study quantitatively analyzed microplastics in wastewater samples collected from different treatment units in two tertiary treatment plants with distinct processes. The influents contained an average of 15.5 ± 3.5 particles/L and 38.5 ± 2.5 particles/L in the two WWTPs with in the oxidation ditch process and the integrated fixed-film activated sludge process, respectively. Interestingly, microplastic concentrations in the influent were more influenced by the population density in the served area than sewage volume or served population equivalent. Throughout the treatment process, concentrations were reduced to 1.5 ± 0.5 particles/L and 1.0 ± 1.0 particles/L in the final effluents, representing an overall decrease of 90% and 97%, in WWTPs with the oxidation ditch process and integrated fixed-film activated sludge process, respectively. A significant proportion of the microplastics were removed during the primary treatment stage in both WWTPs, with better performance for foam, film, line-shaped and large-sized microplastics. Most microplastics were accumulated in activated sludge, indicating its key role as the primary sink in WWTPs. The multiple correspondence analysis identified laundry washing and daily necessities such as packaging and containers as the major contributors to microplastics in WWTPs. The study proposed recommendations for upgrading WWTPs, modifying designs, and implementing strategies to reduce microplastic sources, aiming to minimize the release of microplastics into the environment. These findings can shed lights on the sources of microplastics in WWTPs, and advance our understanding of the mechanisms for more effective microplastic removals in wastewater treatment technologies in future applications.

Framework to Quantify Uncertainty in Microplastic Concentrations in Wastewaters and Sludges Incorporating Analytical Recovery Information into Data Analysis.

Wastewater treatment plants (WWTPs) serve a pivotal role in transferring microplastics (MPs) from wastewater to sludge streams, thereby exerting a significant influence on their release into the environment and establishing wastewater and biosolids as vectors for MP transport and delivery. Hence, an accurate understanding of the fate and transport of MPs in WWTPs is vital. Enumeration is commonly used to estimate concentrations of MPs in performance evaluations of treatment processes, and risk assessment also typically involves MP enumeration. However, achieving high accuracy in concentration estimates is challenging due to inherent uncertainty in the analytical workflow to collect and process samples and count MPs. Here, sources of random error in MP enumeration in wastewater and other matrices were investigated using a modeling approach that addresses the sources of error associated with each step of the analysis. In particular, losses are reflected in data analysis rather than merely being measured as a validation step for MP extraction methods. A model for addressing uncertainty in the enumeration of microorganisms in water was adapted to include key assumptions relevant to the enumeration of MPs in wastewater. Critically, analytical recovery, the capacity to successfully enumerate particles considering losses and counting error, may be variable among MPs due to differences in size, shape, and type (differential analytical recovery) in addition to random variability between samples (nonconstant analytical recovery). Accordingly, differential analytical recovery among the categories of MPs was added to the existing model. This model was illustratively applied to estimate MP concentrations from simulated data and quantify uncertainty in the resulting estimates. Increasing the number of replicates, counting categories of MPs separately, and accounting for both differential and nonconstant analytical recovery improved the accuracy of MP enumeration. This work contributes to developing guidelines for analytical procedures quantifying MPs in diverse types of samples and provides a framework for enhanced interpretation of enumeration data, thereby facilitating the collection of more accurate and reliable MP data in environmental studies.

A review of microplastics in wastewater treatment plants in Türkiye: Characteristics, removal efficiency, mitigation strategies for microplastic pollution and future perspective

ABSTRACT The effluent of WWTPs is an important source of microplastics (MP) for the aquatic environment. In this review study, MPs in wastewater treatment plants (WWTP) in Türkiye and their removal from WWTPs are reviewed for the first time. First, MP characteristics in the influent and effluent of WWTPs in Türkiye are discussed. In the next section, the abundance of MPs in the influent and effluent of WWTPs in Türkiye and the MP removal efficiency of WWTPs in Türkiye are evaluated. Then, the results of studies on MP abundance and characteristics in Türkiye's aquatic environments are presented and suggestions are made to reduce MPs released from WWTPs into the receiving environments. Strategies for reducing MPs released to the receiving environment from WWTPs of Türkiye are summarized. In the last section, research gaps regarding MPs in WWTPs in Türkiye are identified and suggestions are made for future studies. This review paper provides a comprehensive assessment of the abundance, dominant characteristics, and removal of MPs in WWTPs in Türkiye, as well as the current status and deficiencies in Türkiye. Therefore, this review can serve as a scientific guide to improve the MP removal efficiency of WWTPs in Türkiye.

Characteristics and removal efficiency of microplastics at secondary wastewater treatment plant in Lithuania.

Wastewater treatment plants (WWTPs) are the most significant barrier between anthropogenic microplastics and environmental ecosystems. The distribution and characteristics of microplastics in WWTPs remain uncertain and incompletely understood, particularly in northeastern Europe (Baltic States), where there is a lack of data on microplastic pollution and distribution. This study presents the removal efficiency and variation in characteristics of microplastics in different stages of the secondary WWTP during a 3-month sampling campaign in Lithuania. The abundance, size, shape, color, and chemical composition of microplastics in the wastewater at different treatment stages were thoroughly examined, in a size range from 20 to 1000 μm. On average, 2962 ± 25 particles/L of microplastic enter the studied WWTP. The obtained microplastic removal efficiency was 55.4% ± 3.9%, highlighting the necessity to enhance wastewater treatment strategies focusing on microplastic removal. Fragment-type microplastics smaller than 100 μm were removed from wastewater samples with the highest removal efficiency. Furthermore, our study includes recommendations to improve microplastic removal efficiency and contribute to mitigating microplastic pollution. PRACTITIONER POINTS: A large number of MPs in the size range of 20-1000 μm enter Lithuanian WWTP. Small-sized MPs within a range of 20-50 μm and 50-100 μm were removed with the highest efficiency of 54.07 ± 1.68% and 56.4 ± 2.43%, respectively. The shape and size of MPs have a major impact on the efficiency of their removal. Future research should prioritize the development of economical and energy-efficient systems, specifically designed for the removal of MPs in WWTPs.

Identification and quantification of microplastics in wastewater treatment plants by spectroscopic and microscopic techniques in Johannesburg East, South Africa

Abstract The occurrence of microplastics in water, their chemistry, physical characteristics, and the efficiency of public wastewater treatment work (WWTW) processes in the removal of microplastics are investigated. Samples were collected from the period 2021 December to 2022 September from two WWTWs in Johannesburg East using 24-h autosamplers. The microplastics were imaged using polarised optical microscopy (POM) and the images were processed using image J 1.53 K to determine the particle counts. The total concentration of microplastics at WWTW A was 3,098 MP/L while WWTW B had 3,561 MP/L. The microplastics identified across the seasons were dominated by angular, fibres, fragments, and films. Fourier transforms infrared (FTIR) spectroscopy identified the polymers such as polyethylene, acrylic, polyethylene terephthalate, and polystyrene in WWTW A and B influent while identifying the polymers such as polystyrene, polyacrylamide, polypropylene, polycarbonate, acrylonitrile butadiene styrene, poly(ethyl cyanoacrylate), carboxyl, poly(ethylene terephthalate), polyethylene, poly(methyl methacrylate), and cellulose in the final effluent. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) identified Cr, Ca, Fe, Al, Na, Mg, Zn, Cl, P, S, and silicon as additives to microplastics with high-intensity peaks of oxygen and carbon. It is recommended to monitor and regulate microplastics in discharged effluents from WWTWs to minimise environmental pollution.

Microplastics shape microbial interactions and affect the dissemination of antibiotic resistance genes in different full-scale wastewater treatment plants

Wastewater treatment plants (WWTPs) pose a potential threat to the environment because of the accumulation of antibiotic resistance genes (ARGs) and microplastics (MPs). However, the interactions between ARGs and MPs, which have both indirect and direct effects on ARG dissemination in WWTPs, remain unclear. In this study, spatiotemporal variations in different types of MPs, ten ARGs (sul1, sul2, tetA, tetO, tetM, tetX, tetW, qnrS, ermB, and ermC), class 1 integron integrase (intI1) and transposon Tn916/1545 in three typical WWTPs were characterized. Sul1, tetO, and sul2 were the predominant ARGs in the targeted WWTPs, whereas the intI1 and transposon Tn916/1545 were positively correlated with most of the targeted ARGs. Saccharimonadales (4.15 %), Trichococcus (2.60 %), Nitrospira (1.96 %), Candidatus amarolinea (1.79 %), and SC-I-84 (belonging to phylum Proteobacteria) (1.78 %) were the dominant genera. Network and redundancy analyses showed that Trichococcus, Faecalibacterium, Arcobacter, and Prevotella copri were potential hosts of ARGs, whereas Candidatus campbellbacteria and Candidatus kaiserbacteria were negatively correlated with ARGs. The potential hosts of ARGs had a strong positive correlation with polyethylene terephthalate, silicone resin, and fluor rubber and a negative correlation with polyurethane. Candidatus campbellbacteria and Candidatus kaiserbacteria were positively correlated with polyurethane, whereas potential hosts of ARGs were positively correlated with polypropylene and fluor rubber. Structural equation modeling highlighted that intI1, transposon Tn916/1545 and microbial communities, particularly microbial diversity, dominated the dissemination of ARGs, whereas MPs had a significant positive correlation with microbial abundance. Our study deepens the understanding of the relationships between ARGs and MPs in WWTPs, which will be helpful in designing strategies for inhibiting ARG hosts in WWTPs.

Microplastic removal and management strategies for wastewater treatment plants

Discharging microplastics into the environment with treated wastewater is becoming a major concern around the world. Wastewater treatment plants (WWTPs) release microplastics into terrestrial and aquatic habitats, mostly from textile, laundry, and cosmetic industries. Despite extensive research on microplastics in the environment, their removal, and WWTP management strategies, highlighting their environmental effects, little is known about microplastics' fate and behaviour during various treatment processes. Microplastics interact with treatment technologies differently due to their diverse physical and chemical characteristics, resulting in varying removal efficiency. Microplastics removed from WWTPs may accumulate in soil and harm terrestrial ecosystems. Few studies have examined the cost, energy use, and trade-offs of large-scale implementation of modern treatment methods for the removal of microplastics. To safeguard aquatic and terrestrial habitats from microplastics' contamination, focused and efficient management techniques must bridge these knowledge gaps. This review summarizes microplastic detection, collection, removal and management strategies. A compilation of treatment process studies on microplastics’ removal efficiency and their destiny and transit paths shows recent improvement. Bioremediation, membrane bioreactor (MBR), electrocoagulation, sol-gel technique, flotation, enhanced filtering, and AOPs are evaluated for microplastic removal. The fate and behaviour of microplastics in WWTPs suggest they may be secondary suppliers of microplastics to receiving ecosystems. Innovative microplastic removal strategies and technologies such as nanoparticles, microorganism-based remediation, and tertiary treatment raise issues. These new WWTP technologies are examined for feasibility, limitations, and implementation issues. Pretreatment modifies microplastic size, adsorption potential, and surface morphology to remove microplastics from WWTPs. Membrane bioreactors (MBR) can remove 99.9% of microplastics more efficiently than other approaches. MBR systems require membrane cleaning and fouling control, which raises operational and capital costs. To reduce MPs, plastic alternatives and strict controls, including microplastic waste transformation, should be prioritized. Microplastics must be controlled through monitoring policy execution and awareness.

Comparative analysis of five convolutional neural networks and transfer learning classification approach for microplastics in wastewater treatment plants

Wastewater treatment plants offer an important pathway for microplastics (MPs) to enter natural aquatic systems. Traditional MP analysis often involves manual sorting of MPs, which can be time-consuming and labor-intensive and is susceptible to human errors, particularly when handling large sample sizes. Herein, five convolutional neural networks—EfficientNet_b7, Inception_v3, Resnet_v2_50, Resnet_v2_101, and Mobilenet_v3—were employed using transfer learning (TL) methods to categorize MPs extracted from municipal wastewater treatment plants into four morphologies: fibers, films, fragments, and pellets. A Samsung Galaxy S22 Android smartphone was used to capture pictures of the MPs using a stereomicroscope, which were then used to train the neural networks. First, TL methods were employed using an 80:20 split of training and validation datasets and testing sets, and the effectiveness of the methods was evaluated via five-fold cross validation. Second, the effect of the sizes of the training and validation sets on the performances of different neural networks was estimated through augmentation of these sets to 300% and their combination with the original dataset, yielding 5104 images. The overall performances of the considered neural networks were evaluated in terms of accuracy, precision, recall, F1 score, and training time. The proposed approach achieved accuracies of 92%–96% and 94%–98% in classifying the original and augmented datasets, respectively, based on MP morphologies. Notably, EfficientNet_b7, Inception_v3, and Mobilenet_v3 achieved the highest classification accuracy of 98% when trained on the augmented dataset. Mobilenet_v3 achieved a competitive accuracy on our datasets while being considerably smaller and more computationally efficient, leading to its selection for deployment in Android mobile and web applications. Overall, Mobilenet_v3 can promptly classify MPs in real time, offering an efficient, effective solution for MP image classification on a smartphone.

Microplastics as hazardous pollutants: Occurrence, effects, removal and mitigation by using plastic waste as adsorbents and supports for photocatalysts

Most sectors in our society use plastic-based materials from different polymer sources due to their different properties and wide range of applications. Combined with population growth, this has caused a vertiginous increase in plastic waste. In the last eight decades, plastic production has resulted in over 8.3 billion metric tons, and unfortunately, around 80% of these plastics have been discarded into the environment, causing harmful effects. The lack of management and control of plastic waste results in the presence of microplastics (MPs) in the environment. This affects food chains and causes problems for biodiversity, the environment and human health. In this review, the classification, environmental occurrence, hazardous effects and management of MPs in wastewater treatment plants are discussed in detail. Other issues associated with the presence of MPs are also addressed; for example, the role played by MPs as vehicles for a range of hazardous chemical contaminants, such as pharmaceuticals, hormones and pesticides, “accidentally” contaminating aquatic organisms that feed on these materials. This review also highlights the technologies that have had satisfactory results in recent years in the removal and/or degradation of MPs, such as heterogeneous photocatalysis, adsorption, and electrochemical processes. We also point out that, in order to mitigate the problem, plastic waste can be transformed into high value-added products, such as adsorbents (adsorption capacity: 0.2–1753 mg g-1) and/or supports for photocatalytic materials used in heterogeneous photocatalysis for the degradation of organic contaminants, a subject that is still little discussed in the literature. Finally, during the review, the challenges of this line of investigation are also presented. These insights will offer possibilities and strategies for the development of multifunctional materials based on plastic waste, applied in processes such as adsorption and heterogeneous photocatalysis, as well as for understanding the importance of monitoring MPs in aqueous media, due to the various problems associated with their presence as waste, as vehicles for emerging contaminants, and as possible releasers of organic contaminants arising from additives or their photoinduced weathering.

Microplastics in wastewater treatment plants and their contributions to surface water and farmland pollution in China

Wastewater treatment plants (WWTPs) are usually considered gateways for microplastics (MPs) to enter the environment because large amounts of sewage are produced and MPs are incompletely removed during treatment processes. However, the contribution of effluent MPs to aquatic environmental pollution and that of sludge application to MPs in agricultural soil are still unknown. This study examines the presence of MPs in sewage and sludge in Shenzhen WWTPs and estimates the annual mass loading of MPs from WWTPs to surface water and farmland soil in China. According to our results, for Shenzhen, the annual contribution of MPs from WWTPs (which was obtained by multiplying the annual treated sewage volume by the estimated MP density in the treated sewage) to surface water could be 70.6−302 tons. With a normalized extrapolation model of population density, the contribution of national urban WWTPs to MPs in surface water was estimated to be 734 −3.10 × 103 tons/year, of which 220−950 tons/year entered the marine environment. Furthermore, the riverine flux of MPs from WWTPs to the ocean amounts to at least 7.0%–30% based on the maximum value of WWTP contribution to MPs in surface water. For sludge, the potential contribution of MPs to agricultural soil from Shenzhen WWTPs is (1.00−2.80) × 103 tons/year. With the above calculation procedure, it was estimated that the contribution of MPs to farmland from sludge application in China is (1.30−3.90) × 104 tons/year. The source appointment results for MPs in China's agricultural soil suggested that the contributions of the main four sources, namely, atmospheric deposition, agricultural mulch film, sludge application, and organic fertilizers, are 52%, 30%, 11%, and 7.0%, respectively.

Sludge drying and dewatering processes influence the abundance and characteristics of microplastics in wastewater treatment plants

Wastewater treatment plants (WWTPs) have been identified as high-load receptors of microplastics (MPs) from different sources. However, the influence of specific treatment stanges requires further research. The main objective of this research was to evaluate the abundance and chemical characteristics of MPs in the sludge of two major wastewater treatment plants in the Agadir metropolis (Central Atlantic of Morocco). The Aourir plant receives urban influents and the inputs of the M'zar facility were urban and industrial. Samples were collected from the sludge matrices after primary settling, clarifying, dewatering, and drying systems. In addition, the effect of seasonality on MP load was assessed. The results showed that a higher abundance was noticed in raw sludge than in dewatered one in Aourir WWTP, while in M'zar WWTP, a very low decrease is noticed in dried sludge compared to raw sludge. The concentration of MPs in the summer season was significantly higher compared to other seasons for Aourir WWTP, while the winter season was higher for M'zar WWTP. Moreover, the most abundant shapes were fibers and the fraction 100–500 μm was the most preponderant. Eleven polymers were identified by ATR-FTIR, being polyester, polyethylene, polypropylene, and polystyrene the most abundant ones. Scanning Electron Microscopy coupled with Energy Dispersive X-ray revealed the visible degradation and fragmentation of MPs from sewage sludge and their ability to adsorb inorganic elements. It was estimated that between 2.2 × 107 and 7.4 × 108 MPs were evacuated with the sludge per day. The obtained findings confirmed that WWTP sludge acts as a vector of MPs with a high level of hazard to various matrices, such as landfills, agricultural soils, and groundwater. Overall, consideration must be given to the regulatory system managing the fate of sewage sludge to mitigate the collateral effects and provide solutions.

Are wastewater treatment plants as the source of microplastics in surface water and soil?

Microplastics (MPs) are widely detected in wastewater treatment plants (WWTPs) and natural environment, while the relationship of MPs pollution in both media is not fully understood. In this study, the occurrence of MPs in WWTPs and in surface water and soil was investigated, and their relationship was critically formulated. Results showed although wastewater treatment could effectively remove MPs (58.2%), the effluent was still the important source of MPs in the river, while sludge was not as important as the effluent of MPs in the soil. Specifically, the dominant size ranges of MPs were 0–200 µm, with main type of PE in all wastewater, sludge, river and soil. The dominant shape of MPs in wastewater and river was film. However, the shapes were different between sludge (52.1% of fibers) and soil (40.6% of fragment). Overall, WWTP input and surface runoff were the main source of MPs pollution in surface water, and the abrasion of agricultural films accounted for the MPs pollution in soil. The findings revealed the distribution and interconnection of MPs in WWTPs and environmental media, which could help to trace the sources of MPs pollution and assess the ecological risks in the environment.

Effects of Wastewater Treatment Processes on the Removal Efficiency of Microplastics Based on Meta-analysis

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%.

Microplastic contamination in sewage sludge: Abundance, characteristics, and impacts on the environment and human health

This literature review addresses the presence of plastic in domestic wastewater, an increasingly important facet of the widespread use of plastic and its detrimental effects on the environment, with a focus on microplastics (MPs) in sewage sludge and their implications for a circular economy. Extensive research has been conducted on the occurrence of MPs in wastewater treatment plants. Sewage sludge is a byproduct of such plants that are widely used in the agricultural and other sectors but may contain emerging contaminants, including MPs, that can pose a significant risk to the environment. The review highlights the high concentrations of MPs in sewage sludge and underscores the need for appropriate disposal methods to prevent soil contamination. MPs can also detrimentally interact with other emerging contaminants, such as heavy metals and organophosphate esters. While extraction technologies exist to remove MPs from wastewater, their implementation is subject to technical and economic considerations. Future research should focus on the optimization and efficacy of these technologies to ensure safe sludge management. Given the high levels of MPs and other emerging contaminants found in sewage sludge, it is crucial to implement technologies that enable sustainable sludge disposal. By acknowledging these challenges and developing appropriate solutions, we can mitigate the environmental impacts of plastic and promote sustainable waste management practices.

Microplastics exhibit accumulation and horizontal transfer of antibiotic resistance genes

Although the fates of microplastics (0.1–5 mm) in marine environments and freshwater are increasingly studied, little is known about their vector effect in wastewater treatment plants (WWTPs). Previous studies have evaluated the accumulation of antibiotic resistance genes (ARGs) on microplastics, but there is no direct evidence for the selection and horizontal transfer of ARGs on different microplastics in WWTPs. Here, we show biofilm formation as well as bacterial community and ARGs in these biofilms grown on four kinds of microplastics via incubation in the aerobic and anaerobic tanks of a WWTP. Microplastics showed differential capacities for bacteria and ARGs enrichment, differing from those of the culture environment. Furthermore, ARGs in microplastic biofilms were horizontally transferred at frequencies higher than those in water samples in both tanks. Therefore, microplastics in WWTPs can act as substrates for horizontal transfer of ARGs, potentially causing a great harm to the ecological environment and adversely affecting human health.

Microplastics profile in sludge from a university wastewater treatment plant and the influence of chemical digestions on Nile red stained microplastics

Many of the microplastics (MPs) entering wastewater treatment plants (WWTPs) become entrained in the waste sludge. Here, we assessed the effects of five common digestion methods on the degradation and fluorescence intensity of Nile-red stained MPs. Crumb rubber (CR), cellulose acetate (CA) and polyamide (PA) dissolved in an acid-based digestion; Polyethylene terephthalate (PET), polylactic acid (PLA) and CA degraded in alkali solutions; and CR was destroyed by 30 % H2O2. Fenton’s reagent resulted in little to no damage to the polymers and removed > 95 % of the organic matter, making it the best choice for MP analyses. We then applied Fenton’s reagent to extract MPs in the primary sludge and dewatered sludge from a modern WWTP at the University of Mississippi. There is limited research on MPs in university WWTPs, where the wastewater inflows and composition vary greatly depending on activities and populations on campus. Abundances of putative MPs ranged from 13.2 ± 3.8–380.0 ± 46.4 particles/g (dry weight), with higher levels in the primary sludge and dewatered sludge with students on campus. The majority of MPs were fibers < 500 µm. Over 20 polymers were identified by using µ-FTIR, with polyester (26.4 %), nylon (14.9 %), and polyethylene (12.2 %) most abundant. There was little change in the composition of polymers in the sludge over time. Overall, we found that Fenton’s reagent coupled with µ-FTIR is an effective approach to characterize MPs in WWTP sludge, and that sludge could serve as a source of MPs to the environment depending on its disposal.

Occurrence and removal of microplastics in a municipal wastewater treatment plant with conventional activated sludge process: A case study in Isfahan, Iran

Background: Microplastics (MPs) are nowadays found in the air and in various terrestrial and aquatic environments and have become emerging pollutants. These particles can absorb other chemicals and microbial contaminants and release them into the environment and food chain. Despite the high efficiency of wastewater treatment plants (WWTPs) in removing MPs, WWTPs are still one of the major sources of MPs discharge to the environment. This study was conducted to evaluate the efficiency of MPs removal in a municipal WWTP with conventional activated sludge in Iran. Methods: MPs particles were counted using a stereomicroscope after the initial preparation steps (sieving, chemical digestion with the catalytic wet peroxidation-oxidation and density separation with NaCl) and then analyzed for particle composition using a Raman micro-spectrometer. Results: MPs concentration in the influent, grit chamber, primary sedimentation tank, and effluent were 843.2±147.5, 315.5±54.7, 80.2±19.1, and 11.13±3.14 items/L, respectively. The overall MPs removal efficiency of the WWTP was 98.7%, with the grit chamber, primary sedimentation tank, and secondary sedimentation tank removed 62.6%, 27.9%, and 8.2% of the total MPs, respectively. The most abundant polymers were polypropylene (PP) and polyethylene (PE). Conclusion: Despite the effective removal of MPs in WWTP, on average 4.47×1011±1.03×1011 MPs are discharged into the receiving waters through the effluent of this WWTP annually. This means that WWTPs can be one of the major sources of MPs in the environment and efforts should be made to increase the efficiency of WWTPs and equip them with advanced technologies.