Microbial and physicochemical responses of anaerobic hydrogen-producing granular sludge to polyethylene micro(nano)plastics

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2-25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

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.

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.

Effects of microplastics on the properties of different types of sewage sludge and strategies to overcome the inhibition: A review

Microplastics have been identified as an emerging pollutant. When microplastics enter wastewater treatment plants, the plant traps most of the microplastics in the sludge during sewage treatment. Therefore, the effects of microplastics on sludge removal performance, and on the physical and chemical properties and microbial communities in sludge, have attracted extensive attention. This review mainly describes the presence of microplastics in wastewater treatment plants, and the effects of microplastics on the decontamination efficiency and physicochemical properties of activated sludge, aerobic granular sludge, anaerobic granular sludge and anaerobic ammonium oxidation sludge. Further, the review summarizes the effects of microplastics on microbial activity and microbial community dynamics in various sludges in terms of type, concentration, and contact time. The mechanisms used to strengthen the reduction of microplastics, such as biochar and hydrochar, are also discussed. This review summarizes the mechanism by which microplastics influence the performance of different types of sludge, and proposes effective strategies to mitigate the inhibitive effect of microplastics on sludge and discusses removal technologies of microplastics in sewage. Biochar and hydrochar are one of the effective measures to overcome the inhibition of microplastics on sludge. Meanwhile, constructed wetland may be one of the important choice for the future removal of microplastics from sewage. The goal is to provide theoretical support and insights for ensuring the stable operation of wastewater treatment plants and reducing the impact of microplastics on the environment.

Pretreatment of free nitrous acid combined with calcium hypochlorite for enhancement of hydrogen production in waste activated sludge

A variety of variables limit the recovery of resources from anaerobic fermentation of waste activated sludge (WAS), hence pretreatment strategies are necessary to be investigated to increase its efficiency. A combination of free nitrous acid (FNA) and calcium hypochlorite [Ca(ClO)2] was employed in this investigation to significantly improve sludge fermentation performance. The yields of cumulative hydrogen for the blank and FNA treatment group were 1.09 ± 0.16 and 7.36 ± 0.21 mL/g VSS, respectively, and 6.59 ± 0.24 [0.03 g Ca(ClO)2/g TSS], 7.75 ± 0.20 (0.06), and 8.58 ± 0.22 (0.09) mL/g VSS for the Ca(ClO)2 groups. The co-treatment greatly boosted hydrogen generation, ranging from 39.97 ± 2.26 to 76.20 ± 4.78 % as compared to the solo treatment. Mechanism analysis demonstrated that the combined treatment disturbed sludge structure and cell membrane permeability even more, which released more organic substrates and enhanced biodegradability of fermentation broth. This paper describes a unique strategy to sludge pretreatment that expands the use of Ca(ClO)2 and FNA in anaerobic fermentation, with implications for sludge disposal and energy recovery.

Mechanistic insights into the response of electroactive biofilms to Cd2+ shock: bacterial viability and electron transfer behavior at the cellular and community levels

Electroactive biofilms (EABs) play a crucial role in environmental bioremediation due to their excellent extracellular electron transfer (EET) capabilities. However, Cd2+ can have toxic effects on the electrochemical performance of EABs, and the comprehensive inhibition mechanism of EABs in response to Cd2+ shock remains elusive. This study indicated that Cd2+ shock significantly reduced biomass and increased oxidative stress in EABs at the cellular level. The bacterial viability of EABs in phase III under 0.5 mM Cd2+ shock (EABCd2+-III0.5) decreased by 16.31% compared to EABCK-III. Moreover, intracellular NADH, c-Cyts, and the abundance of electroactive species were essential indicators to evaluate EET behavior of EABs. In EABCd2+-III0.5, these indicators decreased by 26.32%, 33.40%, and 20.65%, respectively. Structural equation modeling analysis established quantitative correlations between core components and electrochemical activity at cellular and community levels. The correlation analysis revealed that the growth and electron transfer functions of EABs were predictive indicators for their electrochemical performance, with standardized path coefficients of 0.407 and 0.358, respectively. These findings enhance our understanding of EABs' response to Cd2+ shock and provide insights for improving their performance in heavy metal wastewater.

Laboratory tidal microcosm deciphers responses of sediment archaeal and bacterial communities to microplastic exposure

Microplastics (MPs) are 1-5 mm plastic particles that are serious global contaminants distributed throughout marine ecosystems. However, their impact on intertidal sediment microbial communities is poorly understood. In this study, we conducted a 30-day laboratory tidal microcosm experiment to investigate the effects of MPs on microbial communities. Specifically, we used the biodegradable polymers polylactic acid (PLA) and polybutylene succinate (PBS), as well as the conventional polymers polyethylene terephthalate (PET), polycarbonate (PC), and polyethylene (PE). Treatments with different concentrations (1-5%, w/w) of PLA- and PE-MPs were also included. We analyzed taxonomic variations in archaeal and bacterial communities using 16S rRNA high-throughput sequencing. PLA-MPs at concentrations of 1% (w/w) rapidly altered microbiome composition. Total organic carbon and nitrite nitrogen were the key physicochemical factors and urease was the major enzyme shaping MP-exposed sediment microbial communities. Stochastic processes predominated in microbial assembly and the addition of biodegradable MPs enhanced the contribution of ecological selections. The major keystone taxa of archaea and bacteria were Nitrososphaeria and Alphaproteobacteria, respectively. MPs exposure had less effect on archaeal functions while nitrogen cycling decreased in PLA-MPs treatments. These findings expanded the current understanding of the mechanism and pattern that MPs affect sediment microbial communities.

Effects of macrophytes on micro - And nanoplastic retention and cycling in constructed wetlands

Macrophytes play the important roles in purifying pollutants of constructed wetlands (CWs), while their effects on CWs exposed to micro/nano plastics are not clear. Therefore, planted and unplanted CWs were established to reveal the impacts of macrophytes (Iris pseudacorus) on the overall performance of CWs under polystyrene micro/nano plastics (PS MPs/NPs) exposure. Results showed that macrophytes effectively enhanced the interception capacities of CWs to PS NPs, and significantly promoted the removal of nitrogen and phosphorus after exposed to PS MPs/NPs. Meanwhile, macrophytes improved the activities of dehydrogenase, urease, and phosphatase. Sequencing analysis showed that macrophytes optimized the composition of microbial communities in CWs and stimulated the growth of functional bacteria involved in nitrogen and phosphorus transformation. Moreover, macrophytes further altered the absolute abundance of nitrogen transformation functional genes (amoA, nxrA, narG and nirS). Functional annotation analysis revealed that macrophytes promoted metabolic functions such as Xenobiotics, Amino acids, Lipids metabolism and Signal transduction, ensuring the metabolic balance and homeostasis of microbes under PS MPs/NPs stress. These results exhibited profound implications for the comprehensive evaluation on the roles of macrophytes in CWs for treating wastewater containing PS MPs/NPs.

Biodegradation of low-density polyethylene plastic waste by a constructed tri-culture yeast consortium from wood-feeding termite: Degradation mechanism and pathway

Polyethylene (PE) is one of the most common synthetic polymers, and PE waste pollution has been an environmental and health concern for decades. Biodegradation is the most eco-friendly and effective approach for plastic waste management. Recently, an emphasis has been placed on novel symbiotic yeasts isolated from termite guts as promising microbiomes for multiple biotechnological applications. This study might be the first to explore the potential of a constructed tri-culture yeast consortium, designated as DYC, isolated from termites for the degradation of low-density polyethylene (LDPE). The yeast consortium DYC stands for the molecularly identified species Sterigmatomyces halophilus, Meyerozyma guilliermondii, and Meyerozyma caribbica. The LDPE-DYC consortium showed a high growth rate on UV-sterilized LDPE as a sole carbon source, resulting in a reduction in tensile strength (TS) of 63.4% and a net LDPE mass reduction of 33.2% compared to the individual yeasts. All yeasts, individually and in consortium, showed a high production rate for LDPE-degrading enzymes. The hypothetical LDPE biodegradation pathway that was proposed revealed the formation of several metabolites, including alkanes, aldehydes, ethanol, and fatty acids. This study emphasizes a novel concept for using LDPE-degrading yeasts from wood-feeding termites for plastic waste biodegradation.

Biodegradability of polyethylene by efficient bacteria from the guts of plastic-eating waxworms and investigation of its degradation mechanism

Polyethylene (PE) has been regarded as non-biodegradable for decades, and the evidence for its degradation by bacteria remains unclear in the literature. Waxworms have recently gained attention for their ability to degrade natural long-chain polymers and synthetic plastic. This study aims to explore the potential of low-density polyethylene (LDPE)-degrading bacteria from the gut symbionts of lesser waxworm (Achroia grisella) larvae for the effective biodegradation of LEDP. Two bacterial isolates (LDPE-DB1 and LDPE-DB2) exhibited the greatest reduction in tensile strength among all isolates (P < 0.0001), reaching 51.3% and 58.3%, respectively. The bacterial strains LDPE-DB1 and LDPE-DB2 stand for molecularly identified species, Citrobacter freundii and Bacillus sp., respectively. After 5 days of incubation, the cell density of LDPE-DB1 and LDPE-DB2 reached 2.20 × 10⁸ and 1.8 × 10⁸ CFU/mL, respectively. However, after 30 days of incubation, the cell density reached 7.3 × 10⁸ and 5.9 × 10⁸, respectively. The formed cavities indicate the high activity of the isolated bacteria from Achroia grisella larvae where the cavities reach a depth of up to 1.2 µm. The findings of this study demonstrated the presence of LDPE-degrading bacteria in Achroia grisella and provide promising evidence for the biodegradation of plastic waste management in the environment.

The fate of microplastic in sludge management systems

Sewage sludge (SS) from wastewater treatment plants (WWTPs) is commonly used as a soil amendment on agricultural land; however, this sludge contains microplastics (MPs) which harm soil ecosystems and can leach into aquatic environments. This review aims to assess the fate of MPs in SS systems and, in the context of a changing agricultural scene, present alternatives for sustainable SS disposal that are consistent with the practices of a clean, circular economy. Anaerobic digestion and composting, which are commonly used to stabilize SS before land application, were not reported to substantially affect MP removal, although process efficiency and the microbiome were affected by MPs. Alternatively, MPs can be destroyed or removed by mono-incineration or combustion, but unfortunately, some MPs may remain in the ash after these processes. Therefore, the most desirable solutions would prevent MPs from entering the environment and remove them before they enter the biological part of a WWTP, where they build up in SS. Additionally, the management of MP-containing sludge must be adapted to the geographical context and the local economy, and it should begin with legislation addressing MPs in SS. The information presented here will help to develop good practices in waste management for preventing or decreasing the transfer of MPs into the environment.