Long-term impacts of polyethylene terephthalate (PET) microplastics in membrane bioreactor

Effects of co-exposure to microplastics and perfluorooctanoic acid on the Caco-2 cells

As plastics are produced and used, humans are inevitably exposed to microplastics (MPs) on a daily basis. The pollution of MPs has aroused widespread human concern. Perfluorooctanoic acid (PFOA), a persistent organic pollutant (POP), can be adsorbed by microplastics and may exacerbate human health hazards. In this study, we investigated the effects of co-exposure of PET MPs and PFOA on the human intestinal tract in terms of both cytotoxicity and intestinal barrier through in vitro experiments. The results showed that PFOA induced cellular oxidative stress, mitochondrial dysfunction exerted cytotoxic effects, and inhibited tight junction (TJ) protein expression causing intestinal barrier damage. PET MPs can synergize with PFOA to exacerbate the deleterious effects on the intestinal tract by decreasing cell membrane permeability to increase PFOA accumulation in the cell and enhancing the ability of PFOA to inhibit zonula occludens-1 (ZO-1) proteins.

Effects of microplastics accumulation and antibiotics contamination in anaerobic membrane bioreactors for municipal wastewater treatment

Municipal wastewater treatment plants are the main collection points for plastics and antibiotics. Anaerobic membrane bioreactor (AnMBR) is one the most potential municipal wastewater treatment technologies. This study evaluated the impact of microplastic (aged polyvinyl chloride, aged PVC, 1.5 g/L), antibiotics (ciprofloxacin, CIP, 100 μg/L) and their interaction effect on AnMBR treatment performance and membrane fouling. Results showed that the inhibition of CIP on AnMBR organic removal and methane production was intensified, owing to the CIP adsorption on aged PVC. The enzyme activities of electron transport (ETS), adenosine triphosphate (ATP) and F420 were also significantly restrained by 47-52 % with combined exposure. The combined effects also significantly aggravated the membrane fouling of AnMBR, which shorted the membrane operational period by half due to more soluble microbial products (SMP) secretion. The microbial diversity analyses indicated that aged PVC and CIP addition can accumulate some main anaerobic fermentation bacteria but inhibit the archaea. The abundance of related enzyme in the acetoclastic and hydrogenotrophic methanogenesis decreased with the sole aged PVC and CIP addition and severely inhibited with their combine effect. The absolute abundance mcrA significantly reduced by 92 % with combined exposure, validating the negative impact on methanogenic activity. These findings provide valuable insight into the AnMBR implementation in complex wastewater treatment.

Effect of polypropylene microplastics on the performance of membrane bioreactors in wastewater treatment

Membrane bioreactors (MBRs) can effectively remove microplastics (MPs) because of their good rejection performance. However, the influence of MP concentration and particle size on the short-term and long-term operation efficiency of MBRs remains unclear. To address this issue, this study investigated the effects of short-term stress and long-term accumulation of polypropylene microplastics (PP-MPs) with different particle sizes on the operational efficiency of MBRs by running three MBR systems at four concentration stages. Variations in pollutant removal, biological activity, composition of extracellular polymeric substances (EPS), membrane fouling, and microbial communities in the MBRs were systematically investigated. The results showed that low concentrations (0.02 g/L) of PP-MPs stimulated the biological activity in the MBRs in the short term, and small particle size PP-MPs exhibited higher biological toxicity while accelerating membrane fouling. With an increase in time and concentration (0.2-2.0 g/L), PP-MPs showed significant toxic inhibition effects, increasing EPS secretion and accelerating membrane fouling. This effect was more significant for small particle size PP-MPs. In addition, at 0.02 g/L of PP-MPs, the richness and diversity of microbial communities in activated sludge tend to increase, such as the relative abundance of Bacteroidota, while the growth of Proteobacteria is inhibited. The results of this study provide a reference for understanding the effects of short-term stress and long-term accumulation of MPs on MBR efficiency. It provides reference for exploring the influence of MPs with different particle sizes on MBR reactor and the future research direction.

Effect of long-term exposure to non-biodegradable and biodegradable microplastics in continuous anoxic/aerobic bioreactors: Nitrogen removal performance, microbial communities and functional gene responses

The environmental hazards caused by microplastics (MPs) have received widespread attention, but the effects of non-biodegradable and biodegradable MPs of long-term presence on continuously operating sewage treatment bioreactors are not well known. In this study, we investigated the effect of a representative non-biodegradable MP, polyethylene terephthalate (PET), and a biodegradable MP, polylactic acid (PLA), on the nitrogen removal performance of conventional anoxic/aerobic (A/O) process. The NH4+-N removal efficiencies were suppressed to 91.7 ± 5.5% and 80.8 ± 4.1% at concentrations of 10 and 100 mg/L PLA, significantly (p < 0.05) lower than 96.3 ± 1.0% and 95.0 ± 1.5% with the presence of PET. PLA resulted in a significant (p < 0.05) decrease in adenosine triphosphate of living cells (cATP) and dehydrogenase activities. PLA enhanced redox stress and induced a series of oxidative stress reactions that were detrimental to the normal growth and metabolism of microorganisms. The relative abundance of several functional microorganisms (Nitrosomonas,Nitrospira and Ellin6067) and genes (amoA, amoB and amoC) associated with NH4+-N conversion were reduced. The potential risk of biodegradable MPs to the long-term wastewater treatment process cannot be ignored and needs to be emphasized.

Sustainable control of microplastics in wastewater using the electrochemically enhanced living membrane bioreactor

Wastewater treatment plant (WWTP) discharges are major contributors to the release of microplastics (MPs) into the environment. This research work aimed to assess the performance of the novel living membrane bioreactor (LMBR), which utilizes a biological layer as a membrane filter for the removal of polyethylene (PE) MPs from wastewater. The impact of an intermittently applied low current density (0.5 mA/cm2) on the reduction of MPs in the electrochemically enhanced LMBR (e-LMBR) has also been examined. The reactors were also compared to a conventional membrane bioreactor (MBR) and an electro-MBR (e-MBR). 1H nuclear magnetic resonance spectroscopy (1H NMR) was implemented for the MPs detection and quantification in terms of mass per volume of sample. The LMBR and MBR achieved comparable mean PE MPs reduction at 95% and 96%, respectively. The MPs mass reduction in the e-LMBR slightly decreased by 2% compared to that achieved in the LMBR. This potentially indicated the partial breakdown of the MPs due to electrochemical processes. Decreasing and inconsistent NH4-N and PO4-P removal efficiencies were observed over time due to the addition of PE MPs in the MBR and LMBR. In contrast, the integration of electric field in the e-MBR and e-LMBR resulted in consistently high values of conventional contaminant removals of COD (99.72-99.77 %), NH4-N (97.96-98.67%), and PO4-P (98.44-100.00%), despite the MPs accumulation. Integrating electrochemical processes in the e-LMBR led to the development of a stable living membrane (LM) layer, as manifested in the consistently low effluent turbidity 0.49 ± 0.33 NTU. Despite the increasing MPs concentration in the mixed liquor, applying electrochemical processes reduced the fouling rates in the e-LMBR. The e-LMBR achieved comparable efficiencies in contaminant reductions as those observed in the e-MBR, while using a low-cost membrane material.

Detection of Microplastics in Human Breast Milk and Its Association with Changes in Human Milk Bacterial Microbiota

Background: Presently, there is increasing public consciousness regarding the contamination and detection of microplastics (MPs) within the human body, and studies on the detection and characterization of MPs in human breast milk are limited. Objectives: This study aims to investigate the prevalence and characteristics of MPs found in human breast milk and examine the relationship between maternal hygiene practices, complications that may arise during breastfeeding, and the composition of the bacterial microbiota. Methods: Postpartum breast milk was analyzed for MPs using Raman micro-spectroscopy. The relationship between MP detection, maternal hygiene, breastfeeding complications, and bacterial microbiota was examined. In order to identify correlations and differences between groups that had detected and non-detected MPs, statistical analyses were performed, which involved demographic comparisons and correlation network analysis. Results: The mean age of the 59 postpartum women was 28.13 years. We found MPs in 38.98% of breast milk samples (23 of 59), exhibiting diverse morphological and chemical characteristics. Most MP polymers were polypropylene, polyethylene, polystyrene, and polyvinyl chloride. Maternal hygiene and breastfeeding complications differed between the MPs-detected and non-detected groups. Maternal behaviors may influence the presence of microplastics in breast milk, which were associated with these differences. Bacterial microbiota analysis revealed significant taxonomic differences between the MPs-detected and non-detected groups. Staphylococcus and Streptococcus dominated the MPs-detected group, while Enterobacter, Escherichia, Pseudomonas, and Acinetobacter dominated the non-detected group. The MPs-detected group had a more even bacterial distribution, especially Bacteroides. Conclusions: This study found MPs in 38.98% of breast milk samples using Raman micro-spectrometry, with PP, PE, and PVC being the most common. Significant differences in maternal hygiene and breastfeeding complications were found between the groups with and without MPs. Breast milk microbiota may be linked to MP detection. Further study should be conducted to identify the possible maternal-child health.

Effects of microplastics on microbial community structure and wheatgrass traits in Pb-contaminated riparian sediments under flood-drainage-planting conditions

The coexistence of microplastics (MPs) and heavy metals in sediments has caused a potential threat to sediment biota. However, differences in the effects of MPs and heavy metals on microbes and plants in sediments under different sediment conditions remain unclear. Hence, we investigated the influence of polyethylene (PE) and polylactic acid (PLA) MPs on microbial community structure, Pb bioavailability, and wheatgrass traits under sequential incubation of sediments (i.e., flood, drainage, and planting stages). Results showed that the sediment enzyme activities presented a dose-dependent effect of MPs. Besides, 10 % PLA MPs significantly increased the F1 fractions in three stages by 11.13 %, 30.10 %, and 17.26 %, respectively, thus resulting in higher Pb mobility and biotoxicity. MPs altered sediment bacterial composition and structures, and bacterial community differences were evident in different incubation stages. Moreover, the co-exposure of PLA MPs and Pb significantly decreased the shoot length and total biomass of wheatgrass and correspondingly activated the antioxidant enzyme activity. Further correlation analysis demonstrated that community structure induced by MPs was mainly driven by sediment enzyme activity. This study contributes to elucidating the combined effects of MPs and heavy metals on sediment ecosystems under different sediment conditions.

Leachate from municipal solid waste landfills: A neglected source of microplastics in the environment

Over the past decade or so, microplastics (MPs) have received increasing attention due to their ubiquity and potential risk to the environment. Waste plastics usually end up in landfills. These plastics in landfills undergo physical compression, chemical oxidation, and biological decomposition, breaking down into MPs. As a result, landfill leachate stores large amounts of MPs, which can negatively impact the surrounding soil and water environment. However, not enough attention has been given to the occurrence and removal of MPs in landfill leachate. This lack of knowledge has led to landfills being an underestimated source of microplastics. In order to fill this knowledge gap, this paper collects relevant literature on MPs in landfill leachate from domestic and international sources, systematically summarizes their presence within Asia and Europe, assesses the impacts of landfill leachate on MPs in the adjacent environment, and particularly discusses the possible ecotoxicological effects of MPs in leachate. We found high levels of MPs in the soil and water around informal landfills, and the MPs themselves and the toxic substances they carry can have toxic effects on organisms. In addition, this paper summarizes the potential impact of MPs on the biochemical treatment stage of leachate, finds that the effects of MPs on the biochemical treatment stage and membrane filtration are more significant, and proposes some novel processes for MPs removal from leachate. This analysis contributes to the removal of MPs from leachate. This study is the first comprehensive review of the occurrence, environmental impact, and removal of MPs in leachate from landfills in Asia and Europe. It offers a comprehensive theoretical reference for the field, providing invaluable insights.

Microplastics' toxic effects and influencing factors on microorganisms in biological wastewater treatment units

Prior to entering the water body, microplastics (MPs) are mostly collected at the sewage treatment plant and the biological treatment unit is the sewage treatment facility's central processing unit. This review aims to present a comprehensive analysis of the detrimental impacts of MPs on the biological treatment unit of a sewage treatment plant and it covers how MPs harm the effluent quality of biological treatment processes. The structure of microbial communities is altered by MPs presence and additive release, which reduces functional microbial activity. Extracellular polymers, oxidative stress, and enzyme activity are explored as micro views on the harmful mechanism of MPs on microorganisms, examining the toxicity of additives released by MPs and the harm caused to microorganisms by harmful compounds that have been adsorbed in the aqueous environment. This article offers a theoretical framework for a thorough understanding of the potential problems posed by MPs in sewage treatment plants and suggests countermeasures to mitigate those risks to the aquatic environment.

Long-term presence of microplastics in aerobic and anaerobic sequential batch reactors: Effect on treatment, microbial diversity, and microplastics morphology

Sewage treatment plants (STPs) are identified as the significant sink and source of microplastics (MPs) in aquatic bodies and terrestrial systems. A major fraction of MPs gets retained in STPs for a longer duration, and their potentiality for secondary MPs generation and additives leaching remain under investigated. Therefore, this study focussed on the effect of long-term exposure of aerobic and anaerobic biological sewage treatment units on MPs, along with the effect of MPs on treatment efficiency and microbial consortium. A mixture of polyvinyl chloride, polystyrene, and nylon MPs at 262 MPs/L was spiked in the aerobic and anaerobic sequential batch reactors (SBRs) for 120 days at the start of study. The study revealed a release of noteworthy fraction of secondary MPs into the reactors from spiked MPs. At the end of 120th day, the presence of secondary generated MPs was estimated as 1000 ± 71 MPs/L and 650±141 MPs/L in aerobic and anaerobic SBRs respectively. Most of the observed secondary MPs were of size < 300 µm. Leaching of additives, i.e. cyclohexylamine, cyclotetradecane, octadecanol, pipericine etc., into the SBR effluents were also observed. The depuration capacities of the reactors were not affected with the presence of MPs during the study. While the microbial diversity and abundance were negatively impacted in aerobic SBRs, no such impacts were observed in anaerobic SBRs due to MPs. These results do suggest such exposures to potentially cause secondary MPs and chemical pollution in receiving matrices for the treated effluent, as well as effect on the native microbial community.

Interactions between MPs and PFASs in aquatic environments: A dual-character situation

Microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs) have drawn great attention as emerging threats to aquatic ecosystems. Although the literature to study the MPs and PFASs alone has grown significantly, our knowledge of the overlap and interactions between the two contaminations is scarce due to the unawareness of it. Actually, numerous human activities can simultaneously release MPs and PFASs, and the co-sources of the two are common, meaning that they have a greater potential for interactions. The direct interaction lies in the PFASs adsorption by MPs in water with integrated mechanisms including electrostatic and hydrophobic interactions, plus many influence factors. In addition, the existence and transportation of MPs and PFASs in the aquatic environment have been identified. MPs and PFASs can be ingested by aquatic organisms and cause more serious combined toxicity than exposure alone. Finally, curbing strategies of MPs and PFASs are overviewed. Wastewater treatment plants (WWTPs) can be an effective place to remove MPs from wastewater, while they are also an important point source of MPs pollution in water bodies. Although adsorption has proven to be a successful curbing method for PFASs, more technological advancements are required for field application. It is expected that this review can help revealing the unheeded relationship and interaction between MPs and PFASs in aquatic environments, thus assisting the further investigations of both MPs and PFASs as a whole.

Pyrolysis Kinetic Behavior and Thermodynamic Analysis of PET Nonwoven Fabric

This research aims to maximize polyethylene terephthalate (PET) nonwoven fabric waste and make it as a new source for benzoic acid extraction using a pyrolysis process. The treatment was performed using a thermogravimetric analyzer (TGA) and released products were characterized using FTIR spectroscopy and gas chromatography-mass spectrometry (GC-MS). The pyrolysis kinetic and thermodynamic behavior of PET fabric was also studied and simulated using different linear and nonlinear models. The results show that the PET fabric is very rich in volatile matter (80 wt.%) and can completely degrade under 490 °C with a weight loss of 84%. Meanwhile, the generated vapor was rich in the carbonylic C=O functional group (FTIR), and the GC-MS analysis concluded that benzoic acid was the major compound with an abundance of 75% that was achieved at the lowest heating rate (5 °C/min). The linear kinetic results showed that PET samples had an activation energy in the ranges of 193-256 kJ/mol (linear models) and ~161 kJ/mol (nonlinear models). The thermodynamic parameters, including enthalpy, Gibbs free energy, and entropy, were estimated in the ranges of 149-250 kJ/mol, 153-232 kJ/mol, and 256-356 J/mol K, respectively. Accordingly, pyrolysis treatment can be used to extract benzoic acid from PET fabric waste with a 134% increase in the benzoic acid abundance that can be recovered from PET bottle plastic waste.

Improvement of MBBR-MBR Performance by the Addition of Commercial and 3D-Printed Biocarriers

Moving bed biofilm reactor combined with membrane bioreactor (MBBR-MBR) constitute a highly effective wastewater treatment technology. The aim of this research work was to study the effect of commercial K1 biocarriers (MBBR-MBR K1 unit) and 3D-printed biocarriers fabricated from 13X and Halloysite (MBBR-MBR 13X-H unit), on the efficiency and the fouling rate of an MBBR-MBR unit during wastewater treatment. Various physicochemical parameters and trans-membrane pressure were measured. It was observed that in the MBBR-MBR K1 unit, membrane filtration improved reaching total membrane fouling at 43d, while in the MBBR-MBR 13X-H and in the control MBBR-MBR total fouling took place at about 32d. This is attributed to the large production of soluble microbial products (SMP) in the MBBR-MBR 13X-H, which resulted from a large amount of biofilm created in the 13X-H biocarriers. An optimal biodegradation of the organic load was concluded, and nitrification and denitrification processes were improved at the MBBR-MBR K1 and MBBR-MBR 13X-H units. The dry mass produced on the 13X-H biocarriers ranged at 4980-5711 mg, three orders of magnitude larger than that produced on the K1, which ranged at 2.9-4.6 mg. Finally, it was observed that mostly extracellular polymeric substances were produced in the biofilm of K1 biocarriers while in 13X-H mostly SMP.

Enhancing quorum quenching media with 3D robust electrospinning coating: A novel biofouling control strategy for membrane bioreactors

Bacterial quorum quenching (QQ) is an effective strategy for controlling biofouling in membrane bioreactor (MBR) by interfering the releasing and degradation of signal molecules during quorum sensing (QS) process. However, due to the framework feature of QQ media, the maintenance of QQ activity and the restriction of mass transfer threshold, it has been difficult to design a more stable and better performing structure in a long period of time. In this research, electrospun fiber coated hydrogel QQ beads (QQ-ECHB) were fabricated by using electrospun nanofiber coated hydrogel to strengthen layers of QQ carriers for the first time. The robust porous PVDF 3D nanofiber membrane was coated on the surface of millimeter-scale QQ hydrogel beads. Biocompatible hydrogel entrapping quorum quenching bacteria (sp.BH4) was employed as the core of the QQ-ECHB. In MBR with the addition of QQ-ECHB, the time to reach transmembrane pressure (TMP) of 40 kPa was 4 times longer than conventional MBR. The robust coating and porous microstructure of QQ-ECHB contributed to keeping a lasting QQ activity and stable physical washing effect at a very low dosage (10g beads/5L MBR). Physical stability and environmental-tolerance tests also verified that the carrier can maintain the structural strength and keep the core bacteria stable when suffering long-term cyclic compression and great fluctuations in sewage quality.

Impact of microplastics on lead-contaminated riverine sediments: Based on the enzyme activities, DOM fractions, and bacterial community structure

Microplastics (MPs) are able to interact with diverse contaminants in sediments. However, the impacts of MPs on sediment properties and bacterial community structure in heavy metal-contaminated sediments remain unclear. In this study, we investigated the adsorption of Pb(II) by sediment-MPs mixtures and the effects of different concentration MPs on sediment enzyme activities, DOM fractions, and Pb bioavailability in riverine sediments, and further explored the response of sediment microbial community to Pb in the presence of MPs. The results indicated that the addition of MPs significantly decreased the adsorption amount of Pb(II) by sediments, especially decreased by 12.6% at 10% MPs treatment. Besides, the changes in enzyme activities, DOM fractions exhibited dose-dependent effects of MPs. The higher level of MPs (5% and 10%) tends to transform Pb into more bioavailable fractions in sediments. Also, MPs amendment was observed to alter sediment bacterial community structures, and community differences were evident in the uncontaminated and lead-contaminated sediments. Therein, significant increase of Bacteroidota, Proteobacteria and decrease of Firmicutes abundance in Pb-contaminated sediment at the phylum level were observed. These findings are expected to provide comprehensive information for assessing the combined ecological risks of heavy metals and MPs in riverine sediments.