Horizontal subsurface flow constructed wetlands as tertiary treatment: Can they be an efficient barrier for microplastics pollution?

Distribution of microplastics between ice and water in aquatic systems: The influence of particle properties, salinity and freshwater characteristics

Microplastics (MPs) are an anthropogenic emerging pollutant, with global contamination of both marine and freshwater systems extensively documented. The interplay of MP particle properties and environmental conditions needs to be understood in order to assess the environmental fate and evaluate mitigation measures. In cold climate, ice formation has appeared to significantly affect the distribution of MPs, but so far, limited research is available comparing different aquatic systems, especially freshwater. Experiments often rely on artificial water and specific MP model particles. This study used laboratory tests to investigate the ice-water distribution of a variety of environmentally relevant MP particle types (PP, PE, PS and PVC fragments (25-1000 μm), PET fibers (average length 821 μm, diameter 15 μm)) across different water types, including artificial water of high and low salinity, as well as natural water from a lake and a treatment wetland. Overall, ice entrapment of MPs occurred in almost all tests, but the ice-water distribution of MPs differed across the different water types tested. Among the tests with artificial water, salinity clearly increased MP concentrations in the ice, but it cannot be resolved whether this is caused by increased buoyancy, changes in ice structure, or thermohaline convection during freezing. In the natural freshwater tests, the partition of MPs was shifted towards the ice compared to what was seen in the artificial freshwater. The influence of different types of dissolved and particulate substances in the different waters on MPs fate should be considered important and further explored. In this study, the higher content of suspended solids in the lake water might have enhanced MP settling to the bottom and thereby contributed to the absence of MPs in the ice of the lake test, compared to the wetland test with low suspended solids and considerably more MPs in the ice. Furthermore, the higher negative charge in the lake water possibly stabilized the negatively charged MPs in suspension, and reduced ice entrapment. Regarding particle properties, shape had a distinct effect, with fibers being less likely incorporated into ice than fragments. No fibers were found in freshwater ice. However, it became clear that ice entrapment of MPs depends on factors other than the particles' buoyancy based on density differences and particle size and shape alone.

Microplastic removal and risk assessment framework in a constructed wetland for the treatment of combined sewer overflows

Combined sewer overflows (CSOs) release a significant amount of pollutants, including microplastics (MPs), due to the discharge of untreated water into receiving water bodies. Constructed Wetlands (CWs) offer a promising strategy for CSO treatment and have recently attracted attention as a potential solution for MP mitigation. Nevertheless, limited research on MP dynamics within CSO events and MP removal performance in full-scale CW systems poses a barrier to this frontier of application. This research aims to address both these knowledge gaps, representing the first investigation of a multi-stage CSO-CW for MP removal. The study presents one year of seasonal data from the CSO-CW upstream of the WWTP in Carimate (Italy), evaluating the correlation of MP abundance with different water quality/quantity parameters and associated ecological risks. The results show a clear trend in MP abundance, which increases with rainfall intensity. The strong correlation between MP concentration, flow rate, and total suspended solids (TSS) validates the first flush phenomenon hypothesis and its impact on MP release during CSOs. Chemical characterization identifies acrylonitrile-butadiene-styrene (ABS), polyethylene (PE), and polypropylene (PP) as predominant polymers. The first vertical subsurface flow (VF) stage showed removal rates ranging from 40 % to 77 %. However, the unexpected increase in MP concentrations after the second free water surface (FWS) stage suggests the stochasticity of CSO events and the different hydraulic characteristics of the CW units have diverse effects on MP retention. These data confirm filtration as the main retention mechanism for MP within CW systems. The MP ecological risk assessment indicates a high-risk category for most of the water samples, mainly related to the frequent presence of ABS fragments. The results contribute to the current understanding of MPs released by CSOs and provide insights into the performance of different treatment units within a large-scale CSO-CW system, suggesting the requirement for further attention.

Are micro/nanorobots an effective solution to eliminate micro/nanoplastics in water/wastewater treatment plants?

The extensive production and widespread use of plastic products have resulted in the gradual escalation of plastic pollution. Micro/nano/plastic pollution has become a global issue, and addressing how to "green" remove them is a crucial topic that needs to be tackled at this stage. Recently, micro/nanorobots have offered a promising solution for improving water monitoring and remediation as an environmentally friendly remediation strategy. Micro/nanorobots have been proven to efficiently remove micro/nanoplastics from water bodies. Micro/nanoplastics are captured by micro/nanorobots in water through electrostatic adsorption and electrophoretic interactions, and separation is achieved under the action of an external transverse rotating magnetic field. Their small size enables them to navigate easily in complex environments, while magnetic and optical drives help them move along established routes and reach different areas. With the assistance of these innovative robots, diffusion-limited reactions can be overcome, allowing for active contact with target pollutants. However, research on the removal of micro/nanoplastics by micro/nanorobots is still in its early stages. The dependence on chemical fuels and high costs severely limit the development and application of micro/nanorobots. Micro/nanoplastics are frequently captured by micro/nanorobots, but the degradation efficiency of micro/nanoplastics remains very low. Additionally, the secondary pollution caused by micro/nanorobots is also a key factor limiting their implementation. Although micro/nanorobots are a very promising technology for removing micro/nanoplastics, they still need to be explored in their applications. This paper discusses the opportunities and challenges faced by micro/nanorobots in removing micro/nanoplastics. Development and application of self-driven intelligent micro/nanorobots will help expedite the eco-friendly removal of micro/nanoplastics and other emerging pollutants.

The crucial factor for microplastics removal in large-scale subsurface-flow constructed wetlands

Constructed wetlands (CWs) are an effective method for removing microplastics (MPs). Nevertheless, the understanding of the impact of various parameters on MPs removal within CWs remains incomplete. Through field investigations of large-scale CWs and the application of machine learning methods with an interpretable attribution technique (the Shapley Additive Explanation), we investigated the critical factors influencing MPs removal within CWs. The MPs abundance in the influent and the inlet of Z-CW (400.1 ± 20.8 items/L and 699.6 ± 50.6 items/kg) was significantly higher compared to that in M-CW (138.8 ± 20.5 items/L and 166.5 ± 36.8 items/kg), with no significant difference observed in the effluent. The primary characteristic of MPs is their fibrous and transparent appearance. The MPs removal range from 87.9% to 95.5 %, influenced by the types and characteristics of MPs, physical and chemical parameters, biofilms, and different processes. Among these factors, dissolved organic carbon with high humic content, aromaticity, and carboxyl abundance may serve as a crucial factor in MPs removal. The results of this study highlight the significance of physical and chemical parameters for the MPs removal in CWs, providing the necessary theoretical data for the construction of future large-scale engineering applications.

Microplastic retention in green walls for nature-based and decentralized greywater treatment

In wastewater treatment, two issues have recently received increased attention: nature-based solutions for addressing urban water stress through decentralized treatment and re-use; and emerging pollutants such as microplastics (MPs). At the interface of these, this study investigated living green walls for greywater treatment and their potential for MP removal. A large, pilot-scale green wall was irrigated with greywater (a mix of water collected from laundry, dishwasher, bathroom sinks, and synthetic greywater), and effluent from planted and unplanted sections was compared. MPs >50 μm were analyzed using μRaman spectroscopy and supplementary fluorescence microscopy imaging. The green wall proved efficient for the reduction of chemical oxygen demand (COD) (around 80%), removal of total suspended solids (TSS) (around 90%) and MPs, especially for MPs of the non-polar, hydrophobic polymer type polystyrene and MPs sized 100-500 μm. MP removal was improved in the planted (50-60%) compared to the unplanted section (20%), especially for the size fraction 100-500 μm. Physical filtration by the green wall growing media (a mix of perlite with a grain size of 1-5 mm, and coconut fiber), which was further enhanced by plant roots decreasing the effective pore size, can be considered the most important removal mechanism. Charge-mediated adsorption cannot be expected as MPs and growing media mix were both negatively charged at the prevailing water pH (7-8). Fluorescence imaging for MP analysis, using a merged UV/blue light fluorograph, overestimated MP concentrations in greywater (hundreds of MPs per sample were identified by fluorescence imaging versus tens of MPs by μRaman spectroscopy) and would benefit from further improvement before it can be reliably applied as a cheaper and faster alternative methodology for MP analysis.

Critical role of benthic fauna in enhancing nanoplastics removal in constructed wetland: Performance, fate and mechanism

The presence of nanoplastics (NPs) in wastewater poses a considerable risk to ecosystems. Although constructed wetlands (CWs) have the potential to removal NPs, their efficiency is limited by insufficient consideration of ecosystem integrity. Herein, three typical benthic fauna (Corbicula fluminea, Chironomus riparius and Tubifex tubifex) were added to CWs to improve the ecological integrity of CWs, and further enhance the ecological benefits. Results indicated that the addition of C. fluminea, C. riparius and T. tubifex increased NPs removal by 19.14 %, 17.02 %, and 15.76 % than that without benthic faunas, respectively. Based on fluorescence signal analysis, the presence of benthic fauna could intake NPs, and enhanced the adsorption of NPs by plants. The addition of C. fluminea significantly increased catalase (1541.82 ± 41.35 U/g), glutathione S-transferase (0.34 ± 0.02 U/g), and superoxide dismutase (116.33 ± 6.91 U/g) activities (p < 0.05) as a defense mechanism against NPs-induced oxidative stress. Metagenomic analysis revealed that the abundances of key enzymes involved in glycolysis, the tricarboxylic acid cycle, and polystyrene metabolism pathways were increased when C. fluminea was added, corresponding to the microbial degradation of NPs. Overall, the results of this study implied that the benthic fauna can efficiently remove NPs from wastewater in CWs.

Microplastics in aquatic systems: An in-depth review of current and potential water treatment processes

Plastic products, despite their undeniable utility in modern life, pose significant environmental challenges, particularly when it comes to recycling. A crucial concern is the pervasive introduction of microplastics (MPs) into aquatic ecosystems, with deleterious effects on marine organisms. This review presents a detailed examination of the methodologies developed for MPs removal in water treatment systems. Initially, investigating the most common types of MPs in wastewater, subsequently presenting methodologies for their precise identification and quantification in aquatic environments. Instruments such as scanning electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, Raman spectroscopy, surface-enhanced Raman spectroscopy, and Raman tweezers stand out as powerful tools for studying MPs. The discussion then transitions to the exploration of both existing and emergent techniques for MPs removal in wastewater treatment plants and drinking water treatment plants. This includes a description of the core mechanisms that drive these techniques, with an emphasis on the latest research developments in MPs degradation. Present MPs removal methodologies, ranging from physical separation to chemical and biological adsorption and degradation, offer varied advantages and constraints. Addressing the MPs contamination problem in its entirety remains a significant challenge. In conclusion, the review offers a succinct overview of each technique and forwards recommendations for future research, highlighting the pressing nature of this environmental dilemma.

Occurrence, potential sources, and ecological risk assessment of microplastics in the inland river basins in Northern China

Microplastics (MPs) are the pollutants, found widely across various environmental media. However, studies on the MP pollution in urban rivers and the necessary risk assessments remain limited. In this study, the abundance and characteristics of microplastics in a typical urban river were examined to evaluate their distribution, sources, and ecological risks. It was observed that the abundance of MPs in sediments (220-2840 items·kg-1 dry weight (DW)) was much higher than that in surface water (2.9-10.3 items·L-1), indicating that the sediment is the "sink" of river MPs. Surface water and sediment were dominated by small particle size MPs (< 0.5 mm). Fiber and debris were common shapes of MPs in rivers and sediments. The microplastics in river water and sediments were primarily white and transparent, respectively. Polypropylene (PP) and polyethylene (PE) were the major polymers found.

Advances in the process-based models of constructed wetlands and a way forward for integrating emerging organic contaminants

This research examines advancements in the development of process-based models of constructed wetlands (CWs) tailored for simulating conventional water quality parameters (CWQPs). Despite the promising potential of CWs for emerging organic contaminant (EOC) removal, the available CW models do not yet integrate EOC removal processes. This study explores the need and possibility of integrating EOCs into existing CW models. Nevertheless, a few researchers have developed process-based models of other wastewater treatment systems (e.g., activated sludge systems) to simulate certain EOCs. The EOC removal processes observed in other wastewater treatment systems are analogous to those in CWs. Therefore, the corresponding equations governing these processes can be tailored and integrated into existing CW models, similarly to what was done successfully in the past for CWQPs. This study proposed the next generation of CW models, which outlines 12 areas for future work: integrating EOC removal processes; ensuring data availability for model calibration and validation; considering quantitative and sensitive parameters; quantifying microorganisms in CWs; modifying biofilm dynamics models; including pH, aeration, and redox potential; integrating clogging and plant sub-models; modifying hydraulic sub-model; advancing computer technology and programming; and maintaining a balance between simplicity and complexity. These suggestions provide valuable insights for enhancing the design and operational features of current process-based models of CWs, facilitating improved simulation of CWQPs, and integration of EOCs into the modelling framework.

A review of the influence of environmental pollutants (microplastics, pesticides, antibiotics, air pollutants, viruses, bacteria) on animal viruses

Microorganisms, especially viruses, cause disease in both humans and animals. Environmental chemical pollutants including microplastics, pesticides, antibiotics sand air pollutants arisen from human activities affect both animal and human health. This review assesses the impact of chemical and biological contaminants (virus and bacteria) on viruses including its life cycle, survival, mutations, loads and titers, shedding, transmission, infection, re-assortment, interference, abundance, viral transfer between cells, and the susceptibility of the host to viruses. It summarizes the sources of environmental contaminants, interactions between contaminants and viruses, and methods used to mitigate such interactions. Overall, this review provides a perspective of environmentally co-occurring contaminants on animal viruses that would be useful for future research on virus-animal-human-ecosystem harmony studies to safeguard human and animal health.

A review of microplastic transport in coastal zones

Transport of microplastics (MPs) in coastal zones is influenced not only by their own characteristics, but also by the hydrodynamic conditions and coastal environment. In this article, we first summarized the source, distribution and abundance of MPs in coastal zones around the world through the induction of in-situ observation literature, and then comprehensively reviewed the different transports of MPs in coastal zones, including sedimentation, vertical mixing, resuspension, drift and biofouling. Afterwards, we conducted a comparative analysis of relevant experimental literature, and found that the current experimental research on microplastic transport mainly focused on the settling velocity under static water and the transport distribution under dynamic water. Based on the relevant literature on numerical simulation of microplastic transport in coastal zones, it was also found that the Euler-Lagrange method is the most widely used. The main influencing factor in the Euler method is hydrodynamic, while the Lagrange method and Euler-Lagrange method is hydrodynamic and microplastic particle characteristics. Tides in hydrodynamics are mentioned the most frequently, and the role of turbulence in almost all the literature. The density of MPs is the most influencing factor on transport results, followed by size, while shape is only studied in small-scale models. Some literature has also found that the influence of biofilms is mainly reflected in the changes in the density and size of MPs.

Assessing Contributions of Synthetic Musk Compounds from Wastewater Treatment Plants to Atmospheric and Aquatic Environments

The high environmental concentrations, persistence, and toxicity of synthetic musk compounds (SMCs) necessitate a better grasp of their fate in wastewater treatment plants (WWTPs). To investigate the importance of WWTPs as pathways of SMCs to the environment, air and wastewater samples were collected at four WWTPs in Ontario, Canada. Polycyclic musks (PCMs) were present at higher concentrations than nitro musks (NMs) and macrocyclic musks (MCMs). Three PCMs [galaxolide (HHCB), tonalide (AHTN), and iso-E super (OTNE)] were the most abundant compounds (0.30-680 ng/m3 in air, 0.40-15 μg/L in influent, and 0.007-6.0 μg/L in effluent). Analyses of multiyear data suggest that risk management measures put in place have been effective in reducing the release of many SMCs into the environment. The highest removal efficiency, up to almost 100% of some SMCs, was observed for the plant with the longest solid retention time. A fugacity-based model was established to simulate the transport and fate of SMCs in the WWTP, and good agreement was obtained between the measured and modeled values. These findings indicate that the levels of certain SMCs discharged into the atmospheric and aquatic environments were substantial, potentially resulting in exposure to both humans and wildlife.

Microplastics removal mechanisms in constructed wetlands and their impacts on nutrient (nitrogen, phosphorus and carbon) removal: A critical review

Microplastics (MPs) are now prevalent in aquatic ecosystems, prompting the use of constructed wetlands (CWs) for remediation. However, the interaction between MPs and CWs, including removal efficiency, mechanisms, and impacts, remains a subject requiring significant investigation. This review investigates the removal of MPs in CWs and assesses their impact on the removal of carbon, nitrogen, and phosphorus. The analysis identifies crucial factors influencing the removal of MPs, with substrate particle size and CWs structure playing key roles. The review highlights substrate retention as the primary mechanism for MP removal. MPs hinder plant nitrogen uptake, microbial growth, community composition, and nitrogen-related enzymes, reducing nitrogen removal in CWs. For phosphorus and carbon removal, adverse effects of MPs on phosphorus elimination are observed, while their impact on carbon removal is minimal. Further research is needed to understand their influence fully. In summary, CWs are a promising option for treating MPs-contaminated wastewater, but the intricate relationship between MPs and CWs necessitates ongoing research to comprehend their dynamics and potential consequences.

Optimization of microplastic removal based on the complementarity of constructed wetland and microalgal-based system

As one of the emblematic emerging contaminants, microplastics (MPs) have aroused great public concern. Nevertheless, the global community still insufficiently acknowledges the ecological health risks and resolution strategies of MP pollution. As the nature-based biotechnologies, the constructed wetland (CW) and microalgal-based system (MBS) have been applied in exploring the removal of MPs recently. This review separately presents the removal research (mechanism, interactions, implications, and technical defects) of MPs by a single method of CWs or MBS. But one thing with certitude is that the exclusive usage of these techniques to combat MPs has non-negligible and formidable challenges. The negative impacts of MP accumulation on CWs involve toxicity to macrophytes, substrates blocking, and nitrogen-removing performance inhibition. While MPs restrict MBS practical application by making troubles for separation difficulties of microalgal-based aggregations from effluent. Hence the combined strategy of microalgal-assisted CWs is proposed based on the complementarity of biotechnologies, in an attempt to expand the removing size range of MPs, create more biodegradable conditions and improve the effluent quality. Our work evaluates and forecasts the potential of integrating combination for strengthening micro-polluted wastewater treatment, completing the synergistic removal of MP-based co-pollutants and achieving long-term stability and sustainability, which is expected to provide new insights into MP pollution regulation and control.

Removal of selected sulfonamides and sulfonamide resistance genes from wastewater in full-scale constructed wetlands

Sulfonamides are high-consumption antibiotics that reach the aquatic environment. The threat related to their presence in wastewater and the environment is not only associated with their antibacterial properties, but also with risk of the spread of drug resistance in bacteria. Therefore, the aim of this work was to evaluate the occurrence of eight commonly used sulfonamides, sulfonamide resistance genes (sul1-3) and integrase genes intI1-3 in five full-scale constructed wetlands (CWs) differing in design (including hybrid systems) and in the source of wastewater (agricultural drainage, domestic sewage/surface runoff, and animal runs runoff in a zoo). The CWs were located in low-urbanized areas in Poland and in Czechia. No sulfonamides were detected in the CW treating agricultural tile drainage water. In the other four systems, four sulfonamide compounds were detected. Sulfamethoxazole exhibited the highest concentration in those four CWs and its highest was 12,603.23 ± 1000.66 ng/L in a CW treating a mixture of domestic sewage and surface runoff. Despite the high removal efficiencies of sulfamethoxazole in the tested CWs (86 %-99 %), it was still detected in the treated wastewater. The sul1 genes occurred in all samples of raw and treated wastewater and their abundance did not change significantly after the treatment process and it was, predominantly, at the level 105 gene copies numbers/mL. Noteworthy, sul2 genes were only found in the influents, and sul3 were not detected. The sulfonamides can be removed in CWs, but their elimination is not complete. However, hybrid CWs treating sewage were superior in decreasing the relative abundance of genes and the concentration of SMX. CWs may play a role in the dissemination of sulfonamide resistance genes of the sul1 type and other determinants of drug resistance, such as the intI1 gene, in the environment, however, the magnitude of this phenomenon is a matter of further research.

Retention of microplastics and tyre wear particles in stormwater ponds

Stormwater runoff from urban areas contain a wide variety of pollutants which is typically managed using stormwater retention ponds. However, their performance with regards to emerging pollutants such as microplastics and tyre wear material remains unclear. In this study, samples of effluent water and sediments from four stormwater retention ponds were analysed for their content of microplastics and tyre wear material. Microplastics were analysed using state-of-the-art hyperspectral imaging technique while tyre wear material was analysed using pyrolysis-GC-MS. Microplastics were recovered in all samples and the mass balance revealed that on average 88% of small microplastics (<500 µm) were retain in the ponds while the removal efficiency for large microplastics (>500 µm) was 95%. Tyre wear material was identified in all sediment samples but found below the detection limit in three out of four effluent samples. On average 95% of the tyre wear material was removed by the retention ponds. The results from this study show that stormwater retention ponds are very effective in removing microplastics as well as tyre wear material from stormwater runoff.

Are algae a promising ecofriendly approach to micro/nanoplastic remediation?

How to reduce microplastic pollution in aquatic ecosystem has become the focus of the global attention. The re-removal of microplastics of wastewater treatment plant (WWTP) effluent is gradually being put on the agenda. Recently, algae have been used as an ecofriendly remediation strategy for microplastic removal. Microplastics in sewage can be removed by algae through interception, capture, and entanglement, and can also form heterogeneous aggregates with algae, thereby reducing their free suspensions. Algae can recover nitrogen and carbon from wastewater and can be made into biochar, biofertilizers, and biofuels. However, problematically, this technology has been in the laboratory research stage, and existing research results cannot provide effective basis for its application. Microplastic removal via algae is influenced by wastewater flow rate, microplastic types, and pollutants. Microplastics are only physically fixed by algae, and ensuring that microplastics do not re-enter the environment during resource and capacity recovery is also a key factor limiting the implementation of this technology. The topic of this paper is to discuss the performance of the current tertiary wastewater treatment process - algae process to remove microplastics. Algae can remove nitrogen and phosphorus pollutants in sewage and remove microplastics at the same time, which can realize energy recovery and reduce ecological risks of the effluent. Although algae combined tertiary sewage treatment is a green technology for microplastic removal, its application still needs to be explored. The key challenges that need to be addressed, from single laboratory conditions to complex conditions, from small-scale testing to large-scale simulations, lie ahead of the application of this friendly technology.

The fate of microplastics from municipal wastewater in a surface flow treatment wetland

Microplastics (MPs) are an anthropogenic pollutant of emerging concern prominent in both raw and treated municipal wastewater as well as urban and agricultural run-off. There is a critical need for the mitigation of both point- and diffuse sources, with treatment wetlands a possible sustainable nature-based solution. In this study, the possible retention of MPs in treatment wetlands of the widely used surface flow (SF) type was investigated. In- and outflow water, as well as atmospheric deposition, at a full-scale reed-based SF wetland (operating as a polishing phase of municipal wastewater treatment) was analyzed for MPs in a size range of 25-1000 μm. FPA-based μFT-IR spectroscopic imaging was used in combination with automated data analysis software, allowing for an unbiased assessment of MP numbers, polymer types and size distribution. Inflow water samples (secondary treated wastewater) contained 104 MPs m-3 and 56 MPs m-3 in sampling campaigns 1 and 2, respectively. Passage through the SF wetland increased the MP concentration in the water by 92 % during a rain intense period (campaign 1) and by 43 % during a low precipitation period (campaign 2). The MP particle numbers, size and polymer type distribution varied between the two sampling campaigns, making conclusions around the fate of specific types of MPs in SF wetlands difficult. Atmospheric deposition was measured to be 590 MPs m-2 week-1 during the rain-intense period. Our findings point towards atmospheric deposited MPs as an important factor in the fate of MPs in SF wetlands, causing an increase of MP concentrations, and potentially explaining the variations observed in MP concentrations in wetland effluent and removal efficiency. Furthermore, atmospheric deposition might also be a reason for the considerable inter-study variation regarding MPs removal efficiency in SF wetlands found in the available literature.

Column-based removal of high concentration microplastics in synthetic wastewater using granular activated carbon

Microplastic (MP) is an emerging contaminant of concern due to its abundance in the environment. Wastewater treatment plant (WWTP) can be considered as one of the main sources of microplastics in freshwater due to its inefficiency in the complete removal of small MPs. In this study, a column-based MP removal which could serve as a tertiary treatment in WWTPs is evaluated using granular activated carbon (GAC) as adsorbent/filter media, eliminating clogging problems commonly caused by powder form activated carbon (PAC). The GAC is characterized via N2 adsorption-desorption isotherm, field emission scanning electron microscopy, and contact angle measurement to determine the influence of its properties on MP removal efficiency. MPs (40-48 μm) removal up to 95.5% was observed with 0.2 g/L MP, which is the lowest concentration tested in this work, but still higher than commonly used MP concentration in other studies. The performance is reduced with further increase in MP concentration (up to 1.0 g/L), but increasing the GAC bed length from 7.5 to 17.5 cm could lead to better removal efficiencies. MP particles are immobilized by the GAC predominantly by filtration process by being entangled with small GAC particles/chips or stuck between the GAC particles. MPs are insignificantly removed by adsorption process through entrapment in GAC porous structure or attachment onto the GAC surface.

Constructed wetlands as neglected fixed source of microplastics and antibiotic resistance genes in natural water bodies?

The pollution status and the harm caused by microplastics and antibiotic resistance genes (ARGs) in aquatic ecosystems have been a growing concern. The presence of microplastics could accelerate the transfer and spread of ARGs. Before sewage reaches natural water bodies, microplastics and ARGs need to be eliminated through specific processes. Constructed wetlands are currently an effective and environmentally friendly wastewater treatment process. Research has shown significant effectiveness in removing microplastics and ARGs. Microplastics and ARGs can be removed through processes such as adsorption, capture, adhesion, and biodegradation. However, long-term continuous operation could lead to constructed wetlands becoming significant reservoirs of microplastics and ARGs. Inflow loads and seasonal variations in constructed wetlands may result in the reintroduction of persistent microplastics and ARGs into the receiving water body, establishing the constructed wetland as a continuous source of these pollutants in the receiving water body. The key to the widespread application of constructed wetlands lies in solving this challenging problem. Therefore, although constructed wetlands serve as a green strategy for removing microplastics and ARGs, there are still many gaps in our knowledge. Based on the current accumulation of microplastics and ARGs in constructed wetlands, this paper summarizes the removal of microplastics and ARGs in existing constructed wetlands and explores the interaction between them. Additionally, it proposes suggestions for optimizing the process and improving the reliability of monitoring microplastics and ARGs in sewage.

Removal characteristics of microplastics in sewage flowing through a long-term operation surface flow wetland

Microplastics (MPs) in sewage pose significant threats to aquatic system. Surface flow wetland (SFW) is a common natural wetland type, and is also used as a cheap and easy-to-build sewage treatment system for small and scattered settlements. However, seasonal variation patterns of MPs in sewage removed by SFW are still limited. Therefore, a field investigation was conducted in an SFW that has been operated for 17 years. The concentration of microplastics in the influent of the SFW (CMPs, in) ranged from 56 ± 6 to 250 ± 14 items L-1. The dominant plastic types were fibers and polyethylene terephthalate (PET). CMPs, in were high in summer and winter, significantly related to the seasonal dressing habits. The removal efficiencies of MPs in SFW were 48.03-92.32 % in different seasons, and the mechanisms of MP removal were different with traditional pollutants. Before flowing out occasionally or by heavy precipitation, MPs were primarily trapped in the SFW and underwent certain oxidation. Simulation experiments demonstrated that 47.5-92.9 % of MPs would be trapped in the SFW, and plants would significantly enhance the trapping capacities. This study sheds light on the seasonal variation characteristics and patterns of MPs in actual sewage, and clarifies the fate of MPs in a long-term operation SFW.

A critical review on remediation of microplastics using microalgae from aqueous system

Microplastics (MPs) are deemed to be a global concern due to their harmful negative effects on the aquatic environment and human beings. MPs have a significant impact on both fresh and marine water ecosystems. In many countries, there is concern about the deleterious consequences of MPs on human health due to the presence of MPs in aquatic life for higher intake of marine food (fish and shellfish). Exposure to MPs causes fish to suffer from growth retardation, neurotoxicity, and behavioural abnormalities and it affects human as well. It causes oxidative stress, neurotoxicity, cytotoxicity, and immune system disruption after being ingested to these contaminated fish in human body. Due to these reasons, it has become imperative to find ways to resolve this problem. This review paper represents a pioneering endeavor by consolidating comprehensive information on microplastic-polluted Indian riverine ecosystems and effective MPs removal methods into a single, cohesive document. It meticulously evaluates the principles, removal efficiency, benefits, and drawbacks of various techniques, aiming to identify the most optimal solution. Furthermore, this paper provides a comprehensive exploration of the interesting interactions between MPs and microalgae, delving into the intricate processes of hetero-aggregation. Additionally, it shines a spotlight on the latest advancements in understanding the efficacy of microalgae in removing MPs, showcasing recent breakthroughs in this field of research. Moreover, the work goes beyond conventional assessments by elucidating the characteristics of MPs and exploring diverse influencing parameters that impact MPs removal by microalgae and also addresses the potential future aspects. This thorough investigation uncovers important factors that could significantly contribute to the development of more efficient and sustainable remediation strategies.

Are microplastics in aquaculture an undeniable driver in accelerating the spread of antibiotic resistance genes?

Aquaculture products have been a key source of protein in the human food supply. Contamination by microplastics and antibiotic resistance genes (ARGs) directly affects food quality and safety. Plastic fishing gear and the long-term misuse of antibiotics result in the persistent residue, migration, and spread of microplastics and ARGs in the aquaculture environment, causing in ecological imbalance and endangering human security. Microplastics can act as "petri dishes" for the reproduction, communication, and spread of ARGs, which adds an additional layer of complexity to the global issues surrounding microplastics and ARGs. Aquaculture has become an important source of microplastics and ARGs in natural waters. Accordingly, this paper mainly discusses the contribution of aquaculture to the presence of microplastics and ARGs in aquatic ecosystems. Microplastics and ARGs can (1) affect the production and quality of aquatic products; (2) influence the development and reproduction of aquatic organisms; and (3) accelerate the spread of resistant bacteria. How to eliminate microplastics and ARGs and block their transmission has become a worldwide problem. Actually, further research is required to understand the scale and scope of these effects.

A study on managing plastic waste to tackle the worldwide plastic contamination and environmental remediation

Over the past 50 years, the emergence of plastic waste as one of the most urgent environmental problems in the world has given rise to several proposals to address the rising levels of contaminants associated with plastic debris. Worldwide plastic production has increased significantly over the last 70 years, reaching a record high of 359 million tonnes in 2020. China is currently the world's largest plastic producer, with a share of 17.5%. Of the total marine waste, microplastics account for 75%, while land-based pollution accounts for responsible for 80-90%, and ocean-based pollution 10-20% only in overall pollution problems. Even at small dosages (10 μg/mL), microplastics have been found to cause toxic effects on human and animal health. This review examines the sources of microplastic contamination, the prevalent reaches of microplastics, their impacts, and the remediation methods for microplastic contamination. This review explains the relationship between the community composition and the presence of microplastic particulate matter in aquatic ecosystems. The interaction between microplastics and emerging pollutants, including heavy metals, has been linked to enhanced toxicity. The review article provided a comprehensive overview of microplastic, including its fate, environmental toxicity, and possible remediation strategies. The results of our study are of great value as they illustrate a current perspective and provide an in-depth analysis of the current status of microplastics in development, their test requirements, and remediation technologies suitable for various environments.

Control strategies for microplastic pollution in groundwater

Groundwater is the primary source of water that occurs below the earth's surface. However, the advancement in technology and the increasing population, which lead to the discharge of contaminants such as microplastics (MPs), have an adverse impact on the quality of groundwater. MPs are ubiquitous pollutants that are widely found throughout the world. The maximum abundance of MPs is 4 items/L and 15.2 items/L in groundwater at the specific location of China and USA. Various factors can affect the migration of MPs from soil to groundwater. The occurrence of MPs in water causes serious health issues. Therefore, taking appropriate strategies to control MP contamination in groundwater is urgent and important. This review summarizes the current literature on the migration process of MPs from soil to groundwater along with possible methods for the remediation of MP-polluted groundwater. The main objective of the review is to summarize the technical parameters, process, mechanism, and characteristics of various remediation methods and to analyze strategies for controlling MP pollution in groundwater, providing a reference for future research. Possible control strategies for MP pollution in groundwater include two aspects: i) prevention of MPs from entering groundwater; ii) remediation of polluted groundwater with MPs (ectopic remediation and in-situ remediation). Formulating legislative measures, strengthening public awareness and producing more environment-friendly alternatives can be helpful to reduce the production of MPs from the source. Manage plastic waste reasonably is also a good strategy and the most important part of the management is recycling. The shortcomings of the current study and the direction of future research are also highlighted in the review.

Abundance, characteristics, and removal of microplastics in the Cihu Lake-wetland microcosm system

Sewage treatment plants (STPs) are significant routes through which microplastics (MPs) are released into the aquatic environment. Constructed wetland is an effective facility for deep treatment of tailwater. At present, research on the removal of MPs in the tailwater of STPs by multi-stage constructed wetlands is limited. This work investigated and analyzed the removal characteristics of MPs in the tailwater treatment system of Cihu wetland park in Huangshi, Hubei Province of China. The abundance/removal of MPs in the Cihu Lake-wetland microcosm system was investigated. The results showed that the multi-stage constructed wetlands achieved a total removal rate of 94.7% for MPs with 2.2 particles/L MPs in the effluent. The removal rates of MPs reached 89 and 37.5%, respectively, in the (horizontal/vertical) subsurface flow constructed wetland and surface flow constructed wetland. The abundance of MPs in receiving water of Cihu Lake substantially decreased due to the dilution of wetland effluents. This study partially bridged the knowledge gap hypothesis on the treatment of MPs in tailwater by multi-stage constructed wetlands.

Recent advances towards micro(nano)plastics research in wetland ecosystems: A systematic review on sources, removal, and ecological impacts

In recent years, microplastics/nanoplastics (MPs/NPs) have received substantial attention worldwide owing to their wide applications, persistence, and potential risks. Wetland systems are considered to be an important "sink" for MPs/NPs, which can have potential ecological and environmental effects on the ecosystem. This paper provides a comprehensive and systematic review of the sources and characteristics of MPs/NPs in wetland ecosystems, together with a detailed analysis of MP/NP removal and associated mechanisms in wetland systems. In addition, the eco-toxicological effects of MPs/NPs in wetland ecosystems, including plant, animal, and microbial responses, were reviewed with a focus on changes in the microbial community relevant to pollutant removal. The effects of MPs/NPs exposure on conventional pollutant removal by wetland systems and their greenhouse gas emissions are also discussed. Finally, current knowledge gaps and future recommendations are presented, including the ecological impact of exposure to various MPs/NPs on wetland ecosystems and the ecological risks of MPs/NPs associated with the migration of different contaminants and antibiotic resistance genes. This work will facilitate a better understanding of the sources, characteristics, and environmental and ecological impacts of MPs/NPs in wetland ecosystems, and provide a new perspective to promote development in this field.

Microplastics occurrence and fate in full-scale treatment wetlands

Treatment wetlands (TWs) are an efficient technology for removing microplastics (MPs) from wastewater, according to previous studies. This study investigates the dynamics and fate of MPs in two wastewater treatment plants (WWTPs) using TWs, one with horizontal subsurface flow (HF) and another with a floating plant system (FS). Special attention is paid to the retention produced in the sludge and the role of macrophyte roots. The abundance of MPs in the influent to the WWTPs was on average 20.3 ± 0.85 MP/L and 8.4 ± 1.13 MP/L in HF and FS respectively, while the effluent had 0.58 ± 0.07 MP/L and 0.17 ± 0.06 MP/L, thus giving overall efficiencies of 97.42% and 98.13%, respectively. In the HF wetland, sludge samples near the inlet and the outlet were taken, distinguishing between sludge adhered to gravel and sludge attached to roots. In the floating macrophytes, sludge samples from secondary and tertiary treatments were taken. The results indicate that roots play a significant role in MPs retention. In the HF wetland, the complex formed by roots and gravel attached more MPs than gravel alone in the final zone of the wetland. In the FS, roots retained a significant quantity of MPs, both in the secondary and tertiary treatments, thus giving rise to a sludge less concentrated in MPs. This study aims to improve the knowledge of MPs behavior and fate in full-scale TWs, providing valuable information to enhance retention efficiency.

Using circular economy principles in the optimisation of sludge-based activated carbon production for the removal of perfluoroalkyl substances

Massive sewage sludge (SS) production from municipal wastewater treatment plants and the presence of numerous pollutant types render the process of SS treatment and disposal costly and complex. Here, resource recovery from SS was maximised via the optimisation of sludge-based activated carbon (SBAC) production for the removal of poly- and perfluoroalkyl substances (PFASs), while considering economic factors and minimising environmental impacts. SBAC production optimisation was realised under different operating conditions (different ZnCl₂ impregnation ratios and different pyrolysis activation temperatures and durations). The sorption capacity of the optimised SBAC with respect to the removal of nine commonly detected PFASs, with environmentally relevant concentrations (∽50 μg/L), from simulated wastewater was evaluated. Economic analysis and life-cycle assessment (LCA) were also performed to determine the feasibility of the process and its potential role in the circular economy. Batch adsorption tests confirmed the high efficiency of the optimised SBACs for PFAS removal (93-100 %), highlighting the possibility of converting SS to SBAC. Economically speaking, the optimised SBAC at 1.5 M ZnCl₂, 500 °C, and 0.75 h reduced total production cost by 49 %. Further, the cost could be reduced to as little as 1087 US $/metric-ton compared with that corresponding to the original conditions (2.5 M ZnCl₂, 500 °C, 2 h; 2144 US $/metric-ton). LCA results also showed that freshwater ecotoxicity, marine ecotoxicity, and human non-carcinogenic toxicity were the most affected environmental impact indicators, showing a 49 % decrease when ZnCl₂ impregnation ratio was reduced from 2.5 to 1.5 M. These findings highlighted the optimal conditions for the production of SBAC with high sorption capacity at a reduced cost and with reduced environmental impacts. Thus, they can serve as valuable tools for decision making regarding the selection of the most sustainable and economically feasible process for PFAS removal.

Impact of separate concentrations of polyethylene microplastics on the ability of pollutants removal during the operation of constructed wetland-microbial fuel cell

Microplastics (MPs) in water pose a great threat to the ecological environment, but the impact of MPs on constructed wetland microbial fuel cells (CW-MFCs) has not been studied, so in order to fill the research gap and enrich the research in the field of microplastics, a 360-day experiment was designed to determine the operating status of CW-MFCs at different concentrations (0, 10, 100 and 1000 μg/L) polyethylene microplastics (PE-MPs) at different times, focusing on the changes of the CW-MFCs' ability to handle pollutants, power production performance and microbial composition. The results showed that with the accumulation of PE-MPs, the removal effect of COD and TP did not change significantly, and that the removal rate was maintained at around 90% and 77.9% respectively, within 120 d of operation. What's more, the denitrification efficiency increased (from 4.1% to 19.6%), but with the passage of time, it decreased significantly (from 7.16% to 31.9%) at the end of the experiment, while oxygen mass transfer rate was significantly increased. Further analysis showed that the accumulation of PE-MPs did not affect the current power density significantly with the changes of time and concentration, but the accumulation of PE-MPs would inhibit the exogenous electrical biofilm and increase the internal resistance, thereby affecting the electrochemical performance of the system. In addition, the results of microbial PCA showed that the composition and the activity of the microorganisms were changed under the action of PE-MPs, that the microbial community in CW-MFC showed a dose effect on the input of PE-MPs, and that the relative abundance of nitrifying bacteria with time was significantly affected by PE-MPs concentration. The relative abundance of denitrifying bacteria decreased over time, but PE-MPs promoted the reproduction of denitrifying bacteria, which was consistent with the changes in nitrification and denitrification rates. The removal modes of EP-MPs by CW-MFC include the adsorption and the electrochemical degradation, with two isothermal adsorption models of Langmuir and Freundlich being constructed in the experiment, and the electrochemical degradation process of EP-MPs being simulated. In summary, the results show that the accumulation of PE-MPs can induce a series of changes in substrate, microbial species and activity of CW-MFCs, which in turn affects the pollutant removal efficiency and power generation performance during its operation.

Fibrous microplastics released from textiles: Occurrence, fate, and remediation strategies

Microplastics (MP), i.e., particles measuring less than 5 mm in size, are considered emerging pollutants. The ubiquity of MP is causing great concern among environmental and public health agencies. Anthropogenic activities are responsible for the extensive dispersal of MP in nature. Adverse effects on living organisms, interactions with other contaminants occurring in the environment, and the lack of effective degradation/removal techniques are significant issues related to MP. Most MP found in nature are fibrous (FMP). FMP originate from textile products, mainly synthetic fibers (e.g., polyester). Synthetic fibers are intensively used to produce countless goods due to beneficial characteristics such as high mechanical resistance and economic feasibility. FMP are ubiquitous on the planet and impart lasting adverse effects on biodiversity. Data on the consequences of long-term exposure to these pollutants are scarce in the literature. In addition, few studies address the main types of synthetic microfibers released from textiles, their occurrence, adverse effects on organisms, and remediation strategies. This review discusses the relevant topics about FMP and alerts the dangers to the planet. Furthermore, future perspectives and technological highlights for the FMP mitigation/degradation are presented.

Land use-based characterization and source apportionment of microplastics in urban storm runoffs in a tropical region

Urban stormwater runoff has been suggested as one important land-based pathway of microplastics (MPs) entering the oceans, in which the abundance and characteristics of MPs may be influenced by urban land use types. However, little information has been reported regarding this, especially in the tropical monsoon region. This study first reports the MPs in urban stormwater runoffs in a tropical monsoon region that were collected from four typical urban land use types, including industrial, highways, commercial, and residential areas. The average MP particle count and mass concentration were measured as 4.7 ± 3.5 particles/L and 3.8 ± 2.9 mg/L, respectively. MP abundances showed clear urban land use gradients following the order of industrial > transportation > commercial > residential area. In terms of the seasonal variation in MP abundances, a slightly increasing particle count in the dry season was noted for the residential site. Source apportionment of MPs in stormwater runoffs was demonstrated based on the land use type, particle morphology, and chemical compositions. With the simple apportionment approach, approximately 85% of the MP sources were able to be identified in the industrial, transportation, and residential sites. However, the commercial site showed high variability in terms of the morphology and polymer type of MPs. Furthermore, significantly positive correlations between MP abundance and runoff turbidity, TSS, COD, and rainfall intensity were identified, while, no significant correlation was found between MP characteristics and selected water quality/meteorological parameters.

Distribution and removal mechanism of microplastics in urban wastewater plants systems via different processes

Microplastic pollution threatens water systems worldwide. As one of the most important parts of city wastewater treatment, wastewater treatment plants are not only microplastics interception barriers but also emission sources. Water samples were collected from each sewage treatment plant stage and sludge from the sludge dewatering room. Microplastics were extracted using wet peroxide oxidation and flotation, and the abundance, size, shape, and polymer type of microplastics were detected. Basis on the results, the influence of each process on the removal rate and characteristics of microplastics under the same influent source was analysed. The influent microplastic concentration in this study was 32.5 ± 1.0 n/L, which rapidly decreased after treatment. The removal rates of the sequencing batch reactor activated sludge, cyclic activated sludge, and anaerobic anoxic oxic technologies were 73.0%, 75.6%, and 83.9%, respectively. Most microplastics were transported to the sludge, and the concentration of microplastics in dehydrated sludge was 27.2 ± 3.1 n/g. Microplastics removal occurred primarily during the primary and secondary stages. Disposal processes, settling time, and process design affected wastewater treatment plant microplastic removal rates at each stage. Significant differences in microplastic characteristics were observed at each stage, with the most abundant being fragment shaped, particle sizes of 30-100 μm, and black in colour. Sixteen polymer types were identified using a Raman spectrometer. The predominant polymers are polypropylene, polyethylene, and polyethylene terephthalate. This study demonstrates that optimising the process design of existing wastewater treatment plants is crucial for the prevention and control of microplastic pollution. It is suggested that the process settings of contemporary wastewater treatment plants should be studied in depth to develop a scientific foundation for avoiding and managing microplastic pollution in urban areas.

Removal of microfiber in vertical flow constructed wetlands treating greywater

Nature-based solutions such as constructed wetlands (CW) are considered as a sustainable, green technology for greywater treatment. However, their efficiency to remove microplastics is not well-known even though greywater is considered as a significant source of microfiber pollution. In this study, the removal of fiber microplastics from greywater using a vertical flow constructed wetland (VFCW) was investigated. For the purposes of this study, an experimental wetland was constructed, planted with the flowering plant Zantedeschia aethiopica and filled with a substrate made of sand/gravel of several sizes. The system's performance was monitored for five months during which it received real laundry wastewater. Promising results were obtained showing the significant removal of microfibers from the influent (> 95 %). Moreover, the ability of the system to remove microfibers from laundry wastewater was not significantly affected from the hydraulic loading rate (HLR) applied. The average microfibers concentration decreased from 71 ± 25 microparticles/L in the influent to 1 ± 1 microparticles/L in the effluent of VFCW when an HLR of 63.7 mm/d was applied. High removal efficiencies were also observed for COD and turbidity (93 % and 94 %, respectively). Thus, the results indicate a significant improvement in the overall quality of laundry wastewater due to the use of the VFCW.

Environmental microplastics: Classification, sources, fates, and effects on plants

Microplastic (MP) pollution has become a global concern due to the generation of extensive plastic waste and products (370 million metric tons in 2020) that are difficult to biodegrade. Therefore, MPs have attracted a great deal of research attention, and many new findings regarding MPs (over 9000 papers published in the last 3 years) have been reported. MPs generally exert adverse effects on plants. As MPs accumulate in agricultural ecosystems, many studies have sought to understand the sources and fates of MPs and their effects on various plants. However, there have been few reviews of the properties of MPs, their effects on plants, and their interactions with other factors (e.g., drought, heat, ultraviolet light, plant hormones, heavy metals, and other pollutants) remain poorly understood. In this review, we performed scientometrics analyses of research papers (January 1, 2019, to September 30, 2022) in this field. We focused on the recent progress in the classification of MPs and their sources, circulation, and deposition in agricultural ecosystems. We review MP uptake and transport in plants, as well as factors (size, type, and environmental factors) that affect MP uptake, the positive and negative effects of MPs on plants, and the mechanisms of MP impacts on plants. We discuss current issues and future perspectives concerning research into plant interactions with MPs, along with some promising methods to manage the MP issue.

Adsorptive behavior of micro(nano)plastics through biochar: Co-existence, consequences, and challenges in contaminated ecosystems

The abundance of micro(nano)plastics in natural ecosystems is a crucial global challenge, as these small-sized plastic particles originate from land-based and marine-based activities and are widely present in marine, freshwater, and terrestrial ecosystems. Micro(nano)plastics can significantly be reduced through various methods, such as biological, chemical, and physical techniques. Biochar is a low-cost adsorbent and is considered an efficient material and its application is ecologically effective carbon-negative for remediation of organic and inorganic pollutants. Therefore, this review critically discusses the fate and transport of micro(nano)plastics and their interactions with different biochar in aqueous and column porous media. This review outlines the implications of biochar with the co-existence of micro(nano)plastics in efforts to understand their coupled effects on soil physicochemical properties, microbial communities, and plant growth, along with the removal of heavy metals and other toxic contaminants. In batch experiments, biochar synthesized from various biomasses such as corn straw, hardwood, pine and spruce bark, corncob, and Prosopis juliflora had shown high level of removal efficiency (>90 %) for microplastic adsorption under varying environmental conditions viz., pH, temperature, ionic strength, particle size, and dose due to chemical bonding and electrostatic attractions. Increased temperature of the aqueous solutions encouraged higher adsorption, while higher pH and dissolved organic matter and nutrients may show decreased adsorption capacities for micro(nano)plastics using biochar. Compared to other available physical, chemical, and biological methods, biochar-amended sand filters in column experiments have been very efficient in removing micro(nano)plastics. In saturated column porous media, various microplastics could be inhibited using biochar due to decreased electrostatic repulsion, steric hindrance, and competitive sorption due to humic acid, ionic strength, and cations. Finally, this review provides in-depth insights on further investigations and recommendations for overall micro(nano)plastics removal using biochar-based materials.

Microplastics removal and characteristics of a typical multi-combination and multi-stage constructed wetlands wastewater treatment plant in Changsha, China

Wastewater treatment plants (WWTPs) are an important source of microplastics (MPs) entering the aquatic environment. As environmental awareness increases, WWTPs are gradually using constructed wetlands (CWs) in the depth treatment stage. There were few studies related to MPs removal efficiency of CWs, especially in multi-stage and multi-combinations CWs. Therefore, we studied MPs characteristics and removal in a typical CWs WWTP in Changsha, comparing the MPs removal efficiencies of different processes in a WWTP, focusing on the MPs abundance variation in different stages CWs. Result showed that the MPs removal efficiency of Phase Ⅰ was 87.72% and that of Phase II was 80.65%. Approximate estimates showed that the daily discharge of MPs reached 7.20 * 10⁸ items. The MPs removal efficiency of vertical flow CWs was 25.71%. The MPs removal efficiencies of secondary and tertiary horizontal subsurface flow CWs (HSSFCWs) were 32.00% and 21.43%. The MPs removal efficiencies of secondary and tertiary surface flow CWs were 23.53% and 12.50%. The MPs removal efficiencies of three bio-ponds were -23.08%, -12.90%, and -27.27%. Combined system of bio-pond + CWs reduced the MPs removal efficiency. The most dominant shape of MPs in wastewater was fibers. The most common MPs were polyethylene and polystyrene. The primary treatment in the Changsha WWTP had the highest MPs removal efficiency. Results of this investigation showed the multi-combination and multi-stage CWs WWTP can remove most of MPs in influent, which greatly reduced the amount of MPs discharged into the aquatic environment through WWTP and provided data for analyzing the distribution of MPs in the aquatic environment.

Current status of microplastics and nanoplastics removal methods: Summary, comparison and prospect

In modern society, plastics also play an indispensable role in people's lives due to their various excellent properties. However, when these plastic products are discarded after being used, after being subjected to external influences, they will continue to be worn, damaged and degraded into micro- and nano-scale plastics, which are microplastics and nanoplastics (M/NPs). Although people's attention has been paid to M/NPs at present, the focus is still mainly on the detection and hazard of M/NPs, and how to remove M/NPs is relatively less popular. This review was written in order to draw the attention of more researchers to remove M/NPs. This review first briefly introduces the research background of M/NPs, and also shows the main analytical methods currently used for qualitative and quantitative M/NPs. Then, most of the current literature on the removal of M/NPs was collected, and they were classified, summarized, and introduced according to the classification of physical, physicochemical, and biological methods. The advantages and disadvantages of various methods are summarized, and they are also compared, which can help more researchers choose the appropriate method for research. In addition, the application scenarios of these methods are briefly introduced. Finally, some future research directions are proposed for the current research status of M/NPs removal. It is hoped that this will further promote the development on the method of removing M/NPs.

Global distribution of microplastic contaminants in aquatic environments and their remediation strategies

This review describes the occurrence and distribution of microplastics in freshwater and marine environments in recent years (2017-2022). Use of microplastics often results in contamination of aquatic environments, threatens biodiversity, and creates the need for environmental remediation. Such remediation strategies can involve primary, secondary, and tertiary treatments. Tertiary treatment is a frequent research subject due to its high efficiency and the possibility for advancements and enhancements. This study discusses tertiary treatments with remediation efficiencies of 95% and greater and their advantages, disadvantages, and future perspectives. Biochar-mediated remediation of microplastics is an effective method that may be able to achieve efficiencies approaching 100%. The study concludes by exploring methods of removing microplastics, including constructed wetlands and biochar, which offer high efficiency. PRACTITIONER POINTS: Tertiary treatments are an effective microplastic remediation strategy applicable succeeding secondary or primary treatments or as an individual remediation strategy. Biochar is a highly efficient adsorbent for microplastic remediation from aquatic environment with eco-friendly aspect and reusability. Modifications in tertiary treatments and enhancement in remediation efficiency are still a subject of research for future studies.

Microplastics profile in constructed wetlands: Distribution, retention and implications

Wastewater and stormwater are both considered as critical pathways contributing microplastics (MPs) to the aquatic environment. However, there is little information in the literature about the potential influence of constructed wetlands (CWs), a commonly used wastewater and stormwater treatment system. This study was conducted to investigate the abundance and distribution of MPs in water and sediment at five CWs with different influent sources, namely stormwater and wastewater. The MP abundance in the water samples ranged between 0.4 ± 0.3 and 3.8 ± 2.3 MP/L at the inlet and from 0.1 ± 0.0 to 1.3 ± 1.0 MP/L at the outlet. In the sediment, abundance of MPs was generally higher at the inlet, ranging from 736 ± 335 to 3480 ± 4330 MP/kg dry sediment and decreased to between 19.0 ± 16.4 and 1060 ± 326 MP/kg dry sediment at the outlet. Although no significant differences were observed in sediment cores at different depth across the five CWs, more MPs were recorded in silt compared to sandy sediment which indicated sediment grain size could be an environmental factor contributing to the distribution of MPs. Polyethylene terephthalate (PET) fibres were the dominant polymer type found in the water samples while polyethylene (PE) and polypropylene (PP) fragments were predominantly recorded in the sediment. While the size of MPs in water varied across the studied CWs, between 51% and 64% of MPs in the sediment were smaller than 300 μm, which raises concerns about the bioavailability of MPs to a wider range of wetland biota and their potential ecotoxicological effects. This study shows that CWs can not only retain MPs in the treated water, but also become sinks accumulating MPs over time.

Microplastics in urban runoff: Global occurrence and fate

Public concerns on microplastic (MP) pollution and its prevalence in urban runoff have grown exponentially. Huge amounts of MPs are transported from urban environments via surface runoff to different environment compartments, including rivers, lakes, reservoirs, estuaries, and oceans. The global concentrations of MPs in urban runoff range from 0 to 8580 particles/L. Understanding the sources, abundance, composition and characteristics of MPs in urban runoff on a global scale is a critical challenge because of the existence of multiple sources and spatiotemporal heterogeneity. Additionally, dynamic processes in the mobilization, aging, fragmentation, transport, and retention of MPs in urban runoff have been largely overlooked. Furthermore, the MP flux through urban runoff into rivers, lakes and even oceans is largely unknown, which is very important for better understanding the fate and transport of MPs in urban environments. Here, we provide a critical review of the global occurrence, transport, retention process, and sinks of MPs in urban runoff. Relevant policies, regulations and measures are put forward. Future global investigations and mitigation efforts will require us to address this issue cautiously, cooperating globally, nationally and regionally, and acting locally.

Microplastics in landfill and leachate: Occurrence, environmental behavior and removal strategies

Plastic wastes buried in landfill are gradually broken and decomposed into microplastics under physical, chemical and biological effects, bringing environmental risks to the exploitation of waste resources. Landfill leachate as a potential source of environmental microplastics has not good attention. Microplastics in leachate carry toxic and harmful pollutants and antibiotic resistance genes, and these vectors pose greater risks to human and environmental health without systematic treatment. Recently, the main technologies of landfill leachate treatment process include order batch activated sludge process, membrane biological reaction process, flocculation process, combined filtration process, and constructed wetland process. However, there is still little knowledge about microplastic removal of the existing leachate treatment facilities, and some technologies to alleviate the sources of such microplastics should be timely developed. This paper systematically summarizes the occurrence of plastics, microplastics and nanoplastics in leachate and their interactive pollution with other toxic pollutants. Meanwhile, the prospects of their environmental behaviors in landfill and leachate are put forward. The microplastic removal by existing leachate treatment equipment and the limitations and challenges to upgrading process of development and implementation are also discussed. The paper can provide a scientific basis for studying the fate of microplastics in landfill and leachate.

A review on the remediation of microplastics using constructed wetlands: Bibliometric, co-occurrence, current trends, and future directions

Massive prevalence of microplastics (MPs) in the environment has become one of the world's most serious environmental concerns. Human dependence on plastics has created a constant flow of MPs from different sources into natural environment, which has raised public concern regarding consequences of MPs coming into contact with the natural environment. Deploying constructed wetlands (CWs) to reduce MPs pollution is considered a promising method, however there are still barriers for breakthroughs in this technology, particularly knowledge gaps in the mechanisms affect removal process. Recognising this, we provide a comprehensive summary of current advances and theories regarding the mechanisms of occurrence in this research area. In this work, the bibliometric methods were first used to identify annual publication trends and topical topics of research interest. The selected documents were then statistically analyzed using VOSviewer and the 'bibliometrix' package in R to derive the annual productivity of countries or organizations, the most relevant affiliations, the most relevant authors, the most relevant sources, textual analysis, co-occurrence analysis, and cluster analysis of keywords. Finally, detailed information concerning the removal of MPs by CWs was summarised, covering the most common operational and design parameters (i.e., structure types, wetland plants, substrate materials, and microbial communities), to reveal how these parameters can be adjusted for more efficient MPs removal rate. Challenges and future directions were additionally proposed. It is hoped that the review will help identify current research trends, provide insight into the mechanisms of the removal process, and contribute further to the development of this important area.

An enlarging ecological risk: Review on co-occurrence and migration of microplastics and microplastic-carrying organic pollutants in natural and constructed wetlands

Wetlands are a key hub for the accumulation of microplastics (MPs) and have great load capacity to organic pollutants (OPs), thus, have been a hot research topic. It has shown that OPs adsorbed on MPs could be transported to anywhere and MP-associated biofilms also affects the co-occurrence of MPs and OPs. This would induce the desorption of MP-carrying OPs into environment again, increasing latent migration and convergence of MPs and OPs in wetlands. Considering MPs vector effect and MP-associated biofilms, it is necessary to integrate MPs information on its occurrence characteristics and migration behavior for an improved assessment of ecological risk brought by MPs and MP-carrying OPs to whole wetland ecosystems. In this review, we studied papers published from 2010 to 2020, focused on the interaction of MPs with OPs and the role of their co-occurrence and migration on ecological risk to wetlands. Results suggested the interaction between MPs and OPs dominated by adsorption altered their toxicity and environmental behavior, and the corresponding ecological risk induced by their co-occurrence to wetlands is various and complicated. Especially, constructed wetlands as the special hub for the migration of MPs and MP-carrying OPs might facilitate their convergence between natural and constructed wetlands, posing a potential enlarging ecological risk to whole wetlands. Since the study of MPs in wetlands has still been in a primary stage, we hope to provide a new sight to set forth the potential harm of MPs and MP-carrying OPs to wetlands and useful information for follow-up study.

Microplastic removal from urban stormwater: Current treatments and research gaps

Stormwater is a major contributor to microplastic (MP) pollution in the aquatic environment. Although MPs are associated with many toxicological effects, their levels in stormwater are not regulated. This review compared the effectiveness of different MP removal technologies from stormwater runoff and examined the performance of typical stormwater treatment systems for MP removal to assess possible MP pollution control via stormwater management. Bioretention and filtration systems performed similarly with 84-96% MP removal efficiencies. Despite the limited number of studies that focused on wetlands and retention ponds, preliminary data suggested potential for MP removal with efficiencies of 28-55% and 85-99%, respectively. Despite the higher efficiency of bioretention and filtration systems, their removal efficiency of fibrous MPs was not optimal. Furthermore, wetlands were less effective in removing MPs than retention ponds, although the limited data might lead to an inaccurate representation of typical performances. Therefore, more research is required to arrive at definitive conclusions and to investigate alternative treatment options, such as ballasted sand flocculation, flotation, and biological degradation, and evaluate the effectiveness of bioretention and filtration for MPs <100 μm.

Reduction performance of microplastics and their behavior in a vermi-wetland during the recycling of excess sludge: A quantitative assessment for fluorescent polymethyl methacrylate

Large amounts of microplastics (MPs) that have accumulated in excess sludge may increase the environmental risk for its subsequent treatment. This study aimed to investigate the performance and mechanism of the reduction of MPs in excess sludge in a vermi-wetland. For this, 1 μm, 100 μm, and 500 μm of fluorescent MPs stained with Nile red were added to raw sludge, and their decreased numbers were quantified during the treatment of sludge. The results showed that the removal rates of chemical oxygen demand and total solids from the excess sludge were 63.44%-90.98% and 37.61%-51.56% in the vermi-wetland, respectively. The numbers of 1 μm, 100 μm, and 500 μm MPs could be reduced by 86.62%-95.69%, 95.44%-99.52%, and 100% in the vermi-wetland, respectively. These results indicate that the vermi-wetland is more effective at eliminating MPs. Further insight into the vermi-wetland stratification was obtained, and more than 74.87% of the MPs were intercepted in the vermicompost layer. Moreover, all the particle sizes of MPs were found in the excrement of earthworms. However, only 1 μm MPs were detected in their digestive organs. This study suggests that the interception effect is primarily responsible for elimination of MPs in excess sludge, and the bioturbation of earthworms plays an important role in the mobilization of MPs in vermi-wetlands.

Knowledge Atlas on the Relationship between Water Management and Constructed Wetlands—A Bibliometric Analysis Based on CiteSpace

Water management is a crucial resource conservation challenge that mankind faces, and encouraging the creation of manmade wetlands with the goal of achieving long-term water management is the key to long-term urban development. To summarise and analyse the status of the research on the relationship between water management and constructed wetlands, this paper makes use of the advantages of the bibliometric visualization of CiteSpace to generate country/region maps and author-collaboration maps, and to analyse research hotspots and research dynamics by using keywords and literature co-citations based on 1248 pieces of related literature in the core collection in the Web of Science (WoS) database. The existing research shows that the research content and methods in the field of constructed-wetland and water-management research are constantly being enriched and deepened, including the research methods frequently used in constructed wetlands in water management and in the research content under concern, the functions and roles of constructed wetlands, the relevant measurement indicators of the purification impact of constructed wetlands on water bodies, and the types of water bodies treated by constructed wetlands in water management. We summarise the impact pathways of constructed wetlands on water management, as well as the impact factors of constructed wetlands under water-management objectives, by analysing the future concerns in the research field to provide references for research.

Urban natural wetland as a sink for microplastics: A case from Lalu Wetland in Tibet, China

Microplastics have been reported in a wide range of aquatic habitats. The wetlands are considered to be important roles in microplastic migration in water bodies. Nevertheless, knowledge about the occurrence and fate of microplastics in urban natural wetland is still limited for us to better understand how they become a sink of microplastics. In this study, the distribution and characteristics of microplastics in surface water, surface sediments, and sediment cores of the Lalu Wetland watershed, China's highest urban wetland, were investigated in August 2020 and January 2021. The abundances of microplastics in the surface water were 0.06-3.05 MPs/L. Microplastic abundance in the surface sediment and sediment core was 0.01-1.10 MPs/g and 0-16.23 MPs/g, respectively. The abundance of microplastics in the water was significantly lower in the wetland than that in the channel in the watershed. Comparing the wetland inlet and outlet water, the microplastic interception rates were 53% in January and 95% in August. The characteristics and seasonal variation of microplastics in the Lalu Wetland implied that urban natural wetlands were good at intercepting microplastics, and vegetation growth might play an important role on the interception of microplastics by the wetland. The increasing of microplastics from bottom to top in the sediment cores of Lalu Wetland also indicated that the ecological risks of microplastics accumulation in sediments of urban natural wetland required further attention.

Impact of microplastics on the treatment performance of constructed wetlands: Based on substrate characteristics and microbial activities

Presence of microplastics (MPs) in wastewater has posed a huge ecosystem risk. Constructed wetlands (CWs) can effectively intercept MPs, while with MPs accumulation the response of CWs' performance is still unclear. In order to evaluate those effects, we conducted a 370-day experiment using CW microcosms fed with different levels (0, 10, 100, and 1000 μg/L) of polystyrene (PS) MPs (diameter: 50-100 μm). Results showed that nitrogen removal efficiency was increased (by 3.9%-24.7%) during the first 60 days and then decreased (by 7.1%-41.3%) with MPs accumulating, but no obvious change in COD and TP removal was observed. From further analysis, MPs accumulation changed the biofilm composition (TOC content increased from 41.4% to 52.7%), substrate porosity (electrical resistivity increased by 1.2-2.4 folds), and oxygen mass transfer (|K_La,O2| increased from 3.5% to 18.6%). Moreover, the microbial dynamics presented a higher abundance of nitrifiers (Nitrospira and Nitrosomonas) during the 60-day experiment and a lower abundance in the last days, while denitrifiers (Thauera, Thiobacillus, and Anaerolinea) had a high relative abundance throughout the experiment, being consistent with the variation of nitrification and denitrification rates. Finally, structural equation model analysis proved that due to the changes of substrate characteristics and microbial compositions and activities, the obvious decrease in nitrification efficiency was a direct reason for the decline of nitrogen removal during 370-day MPs accumulation. Overall, our study first prove that MPs accumulation can cause a series of changes in physicochemical and microbial characteristics of substrate, and ultimately affect the nitrogen-transforming process in CWs. Although our conclusions were based on the lab-scale CWs being different from the real wetlands, we hope that the conclusions can provide the effective regulatory strategies to guide the control of MPs in the actual wetlands.

Generation of environmental persistent free radicals (EPFRs) enhances ecotoxicological effects of the disposable face mask waste with the COVID-19 pandemic

A large amount of disposable plastic face masks (DPFs) is produced and used during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, which results in an inevitable consequence of the dramatic increase of DPFs waste. However, the impact of DPFs exposure to the environment on their toxicity is rarely considered. In this study, a range of 76-276 items/L microplastics (MPs) was detected in the DPFs leachates, and fibrous (> 80.3%) and polypropylene (PP, > 89.2%) MPs were dominant. Co, Cu, Ni, Sr, Ti and Zn, were commonly detected in all leachates of the tested DPFs. Organics, such as acetophenone, 2,4-Di-tert-butylphenol, benzothiazole, bisphenol-A and phthalide, were found in the DPFs leachate, which were including organic solvents and plasticizer. Besides, we first found an emerging environmental risk substance, namely environmentally persistent free radicals (EPFRs), was generated in the DPFs leachates. The characteristic g-factors of the EPFRs was in a range of 2.003-2.004, identified as mixture of carbon- and oxygen-centered radicals. By means of in vitro toxicity assay, the DPFs leachate were confirmed to cause cytotoxicity and oxidative stress. Significantly, it is found that the formed EPFRs could contribute more toxic effects. Furthermore, when compared to N95 respirators, the tested surgical masks tend to release more MPs, leach more metals and organics, and generate more EPFRs. Surgical masks were thus showed higher risk than N95 respirators after exposure to water. This work highlights the importance of understanding the chemical complexity and possible toxicity of DPFs for their risk assessment.