Challenges in biodegradation of non-degradable thermoplastic waste: From environmental impact to operational readiness

Biodegradation of low-density polyethylene LDPE by marine bacterial strains Gordonia alkanivorans PBM1 and PSW1 isolated from Mediterranean Sea, Alexandria, Egypt

Plastic has become an essential part of daily human activity. Nonetheless, its over-utilization has resulted in environmental accumulation, leading to marine contamination. Biodegradation is the most effective approach for managing synthetic plastic waste. It encompasses various biological processes that depolymerize polymeric compounds into oligomers or monomers that can enter the biogeochemical cycle. Although research on microplastic biodegradation is abundant and increasing, studies on the biodegradation of low-density polyethylene (LDPE) by marine microorganisms remain scarce and underexplored. In the present study, a total of 17 bacterial isolates were isolated from plastic-contaminated sites in Abu Qir Bay, Alexandria, Egypt. Two bacterial strains demonstrated the highest LDPE biodegradation potential and were identified using 16 S rRNA sequencing, exhibiting 100% and 99.87% sequence identity to Gordonia alkanivorans. Biodegradation of LDPE was confirmed through dry weight loss, with G. alkanivorans strains PSW1 and PBM1 achieving reductions of 0.88 ± 0.658% and 0.66 ± 0.508%, respectively. Biodegradation was further confirmed through the formation of cracks and cavities observed through scanning electron microscopy (SEM). Infrared analysis indicated significant changes in LDPE functional groups and a decrease in the carbonyl index. Biodegradation of LDPE films was also demonstrated through gas chromatography-mass spectrometry (GC/MS) via the release of metabolites, correlating with LDPE utilization. The findings highlight the ability of marine bacteria G. alkanivorans strains PSW1 and PBM1 to biodegrade LDPE.

From plankton to fish: The multifaceted threat of microplastics in freshwater environments

The detrimental impact of emerging pollutants, specifically microplastics (MPs), on the ecological environment are receiving increasing attention. Freshwater ecosystems serve as both repositories for terrestrial microplastic (MP) sources and conduits for their subsequent entry into marine environments. Consequently, it is imperative to rigorously investigate the toxicological effects of MPs on freshwater ecosystems. This article provides a comprehensive analysis of the ecological toxicity effects of MP pollution, both in isolation and in combination with other pollutants, on freshwater aquatic organisms, including plankton, benthic organisms, and fish. The review elucidates potential mechanisms underlying these effects, which encompass oxidative stress, metabolic disorders, immune and inflammatory responses, dysbiosis of the gut microbiota, DNA damage, and cell apoptosis. This paper advocates for the integrated application of multi-omics technologies to investigate the molecular mechanisms underlying the toxicity of MPs to freshwater aquatic organisms from interdisciplinary and multifaceted perspectives. Additionally, it emphasizes the importance of enhancing research on the compounded pollution effects arising from various pollution modes, particularly in conjunction with other pollutants. This study aims to establish a foundation for assessing the ecological risks posed by MPs in freshwater ecosystem and offers valuable insights for the protection of aquatic biodiversity and ecosystem stability.

High-barrier, flexible, hydrophobic, and biodegradable cellulose-based films prepared by ascorbic acid regeneration and low temperature plasma technologies

Regenerated cellulose (RC) films are considered a sustainable packaging material that can replace non-degradable petroleum-based plastics. However, their susceptibility to water vapor and oxygen can limit their effectiveness in protecting products. This study introduces a novel approach for enhancing RC films to create durable, flexible, hydrophobic, high-barrier, and biodegradable packaging materials. By exploring the impact of ascorbic acid coagulation bath treatment and plasma-enhanced chemical vapor deposition (PECVD) on the properties of RC films, we found that the coagulation bath treatment facilitated the organized reconfiguration of cellulose chains, while PECVD applied a dense SiOx coating on the film surface. The results demonstrated a significant enhancement in water vapor and oxygen barrier properties of the composite film, almost reaching the level of commercial barrier films. Moreover, the composite film displayed exceptional biodegradability, fully degrading in soil within 35 days. Additionally, it showcased impressive mechanical strength, hydrophobic characteristics, and freshness preservation, positioning it as a valuable option for bio-based high-barrier packaging applications.

Review of the Synthesis and Degradation Mechanisms of Some Biodegradable Polymers in Natural Environments

The escalating demand for sustainable materials has been fueling the rapid proliferation of the biopolymer market. Biodegradable polymers within natural habitats predominantly undergo degradation mediated by microorganisms. These microorganisms secrete enzymes that cleave long-chain polymers into smaller fragments for metabolic assimilation. This review is centered around dissecting the degradation mechanisms of specific biodegradable polymers, namely PLA, starch-based polymers, and plant fiber-based polymers. Recent investigations have unveiled that PLA exhibits augmented biocompatibility when combined with HA, and its degradation is subject to the influence of enzymatic and abiotic determinants. In the case of starch-based polymers, chemical or physical modifications can modulate their degradation kinetics, as evidenced by Wang et al.'s superhydrophobic starch-based nanocomposite cryogel. For plant fiber-based polymers, the effects of temperature, humidity, and cellulose degradation on their properties, along with the implications of various treatments and additives, are probed, as exemplified by Liu et al.'s study on jute/SiO2/PP composites. Specifically, with respect to PLA, the polymerization process and the role of catalysts such as SnCl2 in governing the structure and biodegradability are expounded in detail. The degradation of PLA in SBF and its interaction with β-TCP particles constitute crucial aspects. For starch-based polymers, the enzymatic degradation catalyzed by amylase and glucosidase and the environmental impacts of temperature and humidity, in addition to the structural ramifications of amylose and amylopectin, are further elucidated. In plant fiber-based polymers, the biodegradation of cellulose and the effects of plasma treatment, electron beam irradiation, nanoparticles, and crosslinking agents on water resistance and stability are explicated with experimental substantiation. This manuscript also delineates technological accomplishments. PLA incorporated with HA demonstrates enhanced biocompatibility and finds utility in drug delivery systems. Starch-based polymers can be engineered for tailored degradation. Plant fiber-based polymers acquire water resistance and durability through specific treatments or the addition of nanoparticles, thereby widening their application spectrum. Synthetic and surface modification methodologies can be harnessed to optimize these materials. This paper also consolidates reaction conditions, research techniques, their merits, and demerits and delves into the biodegradation reaction mechanisms of these polymers. A comprehensive understanding of these degradation mechanisms is conducive to their application and progression in the context of sustainable development and environmental conservation.

Single-use commercial bio-based plastics under environmental degradation conditions: Is their biodegradability and compostability a fact?

Evaluating compostability is increasingly essential for proving commercial bio-based cutlery or packaging since these materials must biodegrade under controlled conditions quickly. Utensils for eating represent Mexico's most popular consumer single-use materials, and Mexican regulations based on biodegradation or compostability are still vague and lack scientific evaluations. This study analyzed three bio-based polymeric materials (bags, dishes, and forks) from commercial brands following Mexican regulations and using various analytical techniques to verify their biodegradability and compostability. First, weight loss measurements, stress-strain tests, and topographic imaging were applied for preliminary observations at the macro scale up to 90 days of compostability. Besides, spectroscopy, microscopy, and thermal techniques indicate changes and behavior of the bio-based materials depending on the composition. The results suggest that bags exhibited the highest decomposition rate (80 %) compared to dishes and forks. Similarly, mechanical resistance indicates a reduction of 62 % for bags, 30 % for dishes, and almost none for forks. Texture image analysis revealed that the complexity and roughness of the materials increased over time, correlating with the physical changes observed. These results indicate minimal surface topography changes and higher stiffness for dishes and forks, indicating low biodegradability. SEM images supported these findings, showing surface degradation in bags and dishes but not in forks. FTIR and XRD analyses confirmed the presence of polyamide (bags) and polypropylene (dishes and forks). These results reduce biodegradation and differ from the claims made by manufacturers. The thermal analysis found similar results, indicating that the materials' thermal stability decreased after degradation, which is related to lower biodegradability and compostability. Overall, the study concluded only bags meet the criteria for compostability in national regulations. However, dishes and forks made of petroleum-derived polymers have higher resistance to natural and microbial degradation.

Review of key issues and potential strategies in bio-degradation of polyolefins

Polyolefins are the most widely used plastic product and a major contributor to white pollution. Currently, studies on polyolefin degradation systems are mainly focused on microorganisms and some redox enzymes, and there is a serious black-box phenomenon. The use of polyolefin-degrading enzymes is limited because of the small number of enzymes; in addition, the catalytic efficiency of these enzymes is poor and their catalytic mechanism is unclear, which leads to the incomplete degradation of polyolefins to produce microplastics. In this review, three questions are addressed: the generation and degradation of action targets that promote the degradation of polyolefins, the different modes by which enzymes bind substrates and their application scenarios, and possible multienzyme systems in a unified system. This review will be valuable for mining or modifying polyolefin degradation enzymes and constructing polyolefins degradation systems and may provide novel ideas and opportunities for polyolefin degradation.

A biodegradable multifunctional pectin-montmorillonite fertilizer coating: Controlled-release, water-retention and soil-cementation

Coated fertilizers have been widely used to improve fertility in barren land. However, improving soil structure and water-retention capacity is also essential for arid and semi-arid areas with sandy soils to promote crop growth. Most currently available coated fertilizers rarely meet these requirements, limiting their application scope. Therefore, this study "tailored" pectin-montmorillonite (PM) multifunctional coatings for arid areas, featuring intercalation reactions and nanoscale entanglement between pectin and montmorillonite via hydrogen bonding and electrostatic and van der Waals forces. Notably, PM coatings have demonstrated an effective "relay" model of action. First, the PM-50 coating could act as a "shield" to protect urea pills, increasing the mechanical strength (82.12 %). Second, this coating prolonged the release longevity of urea (<0.5 h to 15 days). Further, the remaining coating performed a water-retention function. Subsequently, the degraded coating improved the soil properties. Thus, this coating facilitated the growth of wheat seedlings in a simulated arid environment. Moreover, the cytotoxicity test, life cycle assessment, and soil biodegradation experiment showed that the PM coating exhibited minimal environmental impact. Overall, the "relay" model of PM coating overcomes the application limitations of traditional coated fertilizers and provides a sustainable strategy for developing coating materials in soil degradation areas.

Characterization of HDPE microparticles in sludge aerobic digestion and their influence on the process

The occurrence of microplastics (MPs) in wastewater has been studied in the last years. The high efficiency of their removal from wastewater is linked to their transfer to the sludge. In this work, the effect of high-density polyethylene (HDPE) on aerobic digestion was evaluated and these MPs were monitored, characterizing them by three different techniques. Two parallel batch digesters were monitored. AD-Control (meaning Aerobic Digester) operated as a reference, with no external HDPE particles, whereas these polymeric fragments were introduced to the second aerobic digester (AD-HDPE) using ring pulls as microplastic support. FTIR, Raman spectroscopies and fluorescence analysis of these microparticles showed some relevant results that should be highlighted. Higher fluorescence appeared after 7 days in the digester. It coincided with an increase of active volatile suspended solids (AVSS) in the AD-HDPE, which means that an increase of the microbial activity took place. Despite the presence of HDPE particles in the sludge, the digester performance was not compromised. Besides, the HDPE particles did not affect the microbial diversity (Shannon index) of the bacterial community at the end of the experiment compared to the bacterial community of the aerobic digester control tank. Based on the analysis of the relative abundances of microbial taxa, it was concluded that HDPE had selective effects on sludge microbial community, increasing the relative abundance of Bacteroridota phylum.

Unravelling biosynthesis and biodegradation potentials of microbial dark matters in hypersaline lakes

Biosynthesis and biodegradation of microorganisms critically underpin the development of biotechnology, new drugs and therapies, and environmental remediation. However, most uncultured microbial species along with their metabolic capacities in extreme environments, remain obscured. Here we unravel the metabolic potential of microbial dark matters (MDMs) in four deep-inland hypersaline lakes in Xinjiang, China. Utilizing metagenomic binning, we uncovered a rich diversity of 3030 metagenome-assembled genomes (MAGs) across 82 phyla, revealing a substantial portion, 2363 MAGs, as previously unclassified at the genus level. These unknown MAGs displayed unique distribution patterns across different lakes, indicating a strong correlation with varied physicochemical conditions. Our analysis revealed an extensive array of 9635 biosynthesis gene clusters (BGCs), with a remarkable 9403 being novel, suggesting untapped biotechnological potential. Notably, some MAGs from potentially new phyla exhibited a high density of these BGCs. Beyond biosynthesis, our study also identified novel biodegradation pathways, including dehalogenation, anaerobic ammonium oxidation (Anammox), and degradation of polycyclic aromatic hydrocarbons (PAHs) and plastics, in previously unknown microbial clades. These findings significantly enrich our understanding of biosynthesis and biodegradation processes and open new avenues for biotechnological innovation, emphasizing the untapped potential of microbial diversity in hypersaline environments.

Microplastics Biodegradation by Estuarine and Landfill Microbiomes

Plastic pollution poses a worldwide environmental challenge, affecting wildlife and human health. Assessing the biodegradation capabilities of natural microbiomes in environments contaminated with microplastics is crucial for mitigating the effects of plastic pollution. In this work, we evaluated the potential of landfill leachate (LL) and estuarine sediments (ES) to biodegrade polyethylene (PE), polyethylene terephthalate (PET), and polycaprolactone (PCL), under aerobic, anaerobic, thermophilic, and mesophilic conditions. PCL underwent extensive aerobic biodegradation with LL (99 ± 7%) and ES (78 ± 3%) within 50-60 days. Under anaerobic conditions, LL degraded 87 ± 19% of PCL in 60 days, whereas ES showed minimal biodegradation (3 ± 0.3%). PE and PET showed no notable degradation. Metataxonomics results (16S rRNA sequencing) revealed the presence of highly abundant thermophilic microorganisms assigned to Coprothermobacter sp. (6.8% and 28% relative abundance in anaerobic and aerobic incubations, respectively). Coprothermobacter spp. contain genes encoding two enzymes, an esterase and a thermostable monoacylglycerol lipase, that can potentially catalyze PCL hydrolysis. These results suggest that Coprothermobacter sp. may be pivotal in landfill leachate microbiomes for thermophilic PCL biodegradation across varying conditions. The anaerobic microbial community was dominated by hydrogenotrophic methanogens assigned to Methanothermobacter sp. (21%), pointing at possible syntrophic interactions with Coprothermobacter sp. (a H2-producer) during PCL biodegradation. In the aerobic experiments, fungi dominated the eukaryotic microbial community (e.g., Exophiala (41%), Penicillium (17%), and Mucor (18%)), suggesting that aerobic PCL biodegradation by LL involves collaboration between fungi and bacteria. Our findings bring insights on the microbial communities and microbial interactions mediating plastic biodegradation, offering valuable perspectives for plastic pollution mitigation.

Influence of waste polyethylene/WCO composite on physical and chemical properties of asphalt

The use of waste polyethylene (WPE) in modified asphalt is frequently employed to reduce environmental pollution and improve asphalt properties. However, research has shown that using WPE alone as a modifier does not effectively enhance the low-temperature flexibility of asphalt. This study aims to investigate the potential of utilizing WPE and waste cooking oil (WCO) as composite modifiers to enhance the properties of virgin asphalt under both high and low-temperature conditions. The contents of WPE and WCO were used, and the preparation process for the modified asphalt was optimized through an orthogonal experiment. The experimental results indicate that the optimal formulation for the WPE/WCO composite modified asphalt (WPE/WCO-A) is obtained with an additive dosage of 8% and 1% by mass of virgin asphalt for WPE and WCO, respectively, as well as the maintenance process at a temperature of 140 °C and a duration of 2 h. Dynamic shear rheometer (DSR) results reveal that WPE/WCO composite modifier can greatly improve the high-temperature deformation resistance of asphalt. Bending beam rheometer (BBR) tests confirm that WPE adversely affects the low-temperature flexibility of asphalt, while the addition of WCO can improve it. WPE/WCO-A has even better low-temperature properties than virgin asphalt (VA). The Fourier transform infrared spectroscopy (FT-IR) results suggest that the composite modification of asphalt by WPE/WCO modifiers is dominated by physical action. Furthermore, the fluorescence microscopy test results demonstrate that WCO can promote WPE swelling in asphalt. This study offers a novel approach to improve the comprehensive properties of asphalt through composite modification using WPE and WCO.

Dual-channel fluorescence dye: Fluorescent color-dependent visual detection of microplastics and selective polyurethane

In this study, we developed a dual-channel fluorescent dye ((E)-N'-(4-(diphenylamino)benzylidene)pyrazine-2-carbohydrazide) DPC for visual detection of 8 types of microplastics (MPs; HDPE, MDPE, LDPE, PET, PU, PVC, PS, and PP) and selective PU. The intramolecular charge transfer (ICT) and aggregation-induced emission (AIE) properties of DPC were demonstrated by the spectroscopic analysis, DFT calculations, and Tyndall effect. MPs and nonplastics (cellulose, chitin, sand, shell, and wood) were stained with DPC in water and their respective fluorescence signals in the blue and green channels were analyzed. The staining procedure using DPC was optimized with the concentration of DPC and staining time as parameters. DPC was able to effectively stain 8 types of MPs and only PU in blue and green fluorescence signals, respectively. Furthermore, false positive detections of DPC were minimized through additional ethanol treatment after staining. Moreover, the effects of temperature, pH, and salinity on the staining ability of DPC were investigated. Surprisingly, DPC was able to selectively detect PU through the green fluorescence signal even in a single environment where various MPs existed. Most importantly, DPC is the first fluorescent dye capable of selectively monitoring PU in the green channel as well as staining 8 types of MPs in the blue channel. DPC showed promising potential to be used for MP monitoring on real environmental samples.

A comprehensive review on enzymatic biodegradation of polyethylene terephthalate

Polyethylene terephthalate (PET) is a polymer synthesized via the dehydration and condensation reaction between ethylene glycol and terephthalic acid. PET has emerged as one of the most extensively employed plastic materials due to its exceptional plasticity and durability. Nevertheless, PET has a complex structure and is extremely difficult to degrade in nature, causing severe pollution to the global ecological environment and posing a threat to human health. Currently, the methods for PET processing mainly include physical, chemical, and biological methods. Biological enzyme degradation is considered the most promising PET degradation method. In recent years, an increasing number of enzymes that can degrade PET have been identified, and they primarily target the ester bond of PET. This review comprehensively introduced the latest research progress in PET enzymatic degradation from the aspects of PET-degrading enzymes, PET biodegradation pathways, the catalytic mechanism of PET-degrading enzymes, and biotechnological strategies for enhancing PET-degrading enzymes. On this basis, the current challenges within the enzymatic PET degradation process were summarized, and the directions that need to be worked on in the future were pointed out. This review provides a reference and basis for the subsequent effective research on PET biodegradation.

A multi-objective optimization approach for the production of polyhydroxybutyrate via Chlorogloea fritschii under diurnal light with single-stage cultivation

The present study aims to optimize the nutrients for maximization of cyanobacterial biomass with high content of polyhydroxybutyrate (PHB), a bioplastic, and recovery of biomass by auto-sedimentation under diurnal light mimic to sunlight. The multi-objective optimization with desirability approach was used to improve dry cell weight (DCW), PHB content (% w/w), and auto-sedimentation concentration factor (SCF) of biomass. Initially, NaNO3, K2HPO4, TRACE (micronutrient solution), Na2EDTA, and MgSO4.7H2O were screened as important media compositions. Screening was followed by the application of response surface methodology for the development of a model used in multi-objective optimization. The optimized media selected from many optimal solutions, a set of Pareto solutions generated by multi-objective optimization was validated in a flat panel photobioreactor. Using a single-stage cultivation strategy under diurnal light, Chlorogloea fritschii TISTR 8527 has shown capability to produce DCW of 1.23 g/l with PHB content of 31.78 % and SCF of 93.63 with optimal media. This leads to the enhancement of both PHB content (2.72 fold) and SCF (1.64 fold) were observed when compared to the non-optimal medium. This is the first multi-objective optimization study for media optimization using cyanobacteria reported till now under diurnal light mimic to sunlight for bioplastic production.

Advancing Plastic Recycling: Challenges and Opportunities in the Integration of 3D Printing and Distributed Recycling for a Circular Economy

The concept of the circular economy has emerged as a promising solution to address the mounting concerns surrounding plastic waste and the urgent need for sustainable resource management. While conventional centralized recycling remains a common practice for plastic waste, centralized facilities may prove inadequate in handling the ever-increasing volumes of plastic waste generated globally. Consequently, exploring alternative recycling methods, such as distributed recycling by additive manufacturing, becomes paramount. This innovative approach encompasses actively involving communities in recycling practices and promotes a circular economy. This comprehensive review paper aims to explore the critical aspects necessary to realize the potential of distributed recycling by additive manufacturing. In this paper, our focus lies on proposing schemes that leverage existing literature to harness the potential of distributed recycling by additive manufacturing as an effective approach to plastic waste management. We explore the intricacies of the recycling process, optimize 3D printing parameters, address potential challenges, and evaluate the mechanical properties of recycled materials. Our investigation draws heavily from the literature of the last five years, as we conduct a thorough critical assessment of DRAM implementation and its influence on the properties of 3D printing structures. Through comprehensive analysis, we reveal the potential of recycled materials in delivering functional components, with insights into their performance, strengths, and weaknesses. This review serves as a comprehensive guide for those interested in embracing distributed recycling by additive manufacturing as a transformative approach to plastic recycling. By fostering community engagement, optimizing 3D printing processes, and incorporating suitable additives, it is possible to collectively contribute to a more sustainable future while combatting the plastic waste crisis. As progress is made, it becomes essential to further delve into the complexities of material behavior, recycling techniques, and the long-term durability of recycled 3D printed components. By addressing these challenges head-on, it is feasible to refine and advance distributed recycling by additive manufacturing as a viable pathway to minimize plastic waste, fostering a circular economy and cultivating a cleaner planet for generations to come.

Enhancing Structural and Thermal Properties of Poly(lactic acid) Using Graphene Oxide Filler and Anionic Surfactant Treatment

Graphene has attracted extensive attention in various fields due to its intriguing properties. In this work, nanocomposite films based on poly(lactic acid) (PLA and PLLA) polymers filled with graphene oxide (GO) were developed. The impact of treating GO with the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) on the properties of the resulting nanocomposites was investigated. To determine the morphological, optical, and structural properties of the obtained materials, physicochemical analyses were performed, including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. Additionally, the thermal properties and wettability of neat polymers and nanocomposites were thoroughly investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and contact angle analysis. It was observed that GO was well dispersed throughout the PLA and PLLA matrix, leading to stronger interface bonding. The results demonstrate that the untreated and treated GO improved the crystallinity and thermal stability properties of the PLA and PLLA. However, the AOT-treated GO has significantly higher performance compared to the untreated GO in terms of crystallinity, melting temperature (increased by ~15 °C), and wettability (the contact angle decreased by ~30°). These findings reveal the high performance of the developed novel composite, which could be applied in tissue engineering as a scaffold.

A critical review and future perspective of plastic waste recycling

Plastic waste is increasing rapidly due to urbanisation and globalization. In recent decades, plastic usage increased, and the upward trend is expected to continue. Only 9% of the 7 billion tonnes of plastic produced were recycled in India until 2022. India generates 1.5 million tonnes of plastic waste (PW) every year and ranks among top ten plastic producer countries. Large amount of waste plastics could harm environment and human health. The current manuscript provides a comprehensive approach for mechanical and chemical recycling methods. The technical facets of mechanical recycling relating to collection, sorting, grading, and general management to create plastic products with additional value have been elaborated in this study. Another sustainable methods aligned with the chemical recycling using pyrolysis, gasification, hydrocracking, IH2 (Integrated Hydropyrolysis 2), and KDV (Katalytische Drucklose Verolung) techniques have also been highlighted with the critical process parameters for the sustainable conversion of plastic waste to valuable products. The review also adheres to less carbon-intensive plastic degrading strategies that take a biomimetic approach using the microorganism based biodegradation. The informative aspects covering the limitations and effectiveness of all PW technologies and its applications towards plastic waste management (PWM) are also emphasized. The existing practices in PW policy guidelines along with its economic and ecological aspects have also been discussed.

Utilization of Bacillus cereus strain CGK5 associated with cow feces in the degradation of commercially available high-density polyethylene (HDPE)

The accumulation and mismanagement of high-density polyethylene (HDPE) waste in the environment is a complex problem in the present scenario. Biodegradation of this thermoplastic polymer is a promising environmentally sustainable method that offers a significant opportunity to address plastic waste management with minimal negative repercussion on the environment. In this framework, HDPE-degrading bacterium strain CGK5 was isolated from the fecal matter of cow. The biodegradation efficiency of strain was assessed, including percentage reduction in HDPE weight, cell surface hydrophobicity, extracellular biosurfactant production, viability of surface adhered cells, as well as biomass in terms of protein content. Through molecular techniques, strain CGK5 was identified as Bacillus cereus. Significant weight loss of 1.83% was observed in the HDPE film treated with strain CGK5 for 90 days. The FE-SEM analysis revealed the profused bacterial growth which ultimately caused the distortions in HDPE films. Furthermore, EDX study indicated a significant decrease in percentage carbon content at atomic level, whereas FTIR analysis confirmed chemical groups' transformation as well as an increment in the carbonyl index supposedly caused by bacterial biofilm biodegradation. Our findings shed light on the ability of our strain B. cereus CGK5 to colonize and use HDPE as a sole carbon source, demonstrating its applicability for future eco-friendly biodegradation processes.

Methine initiated polypropylene-based disposable face masks aging validated by micromechanical properties loss of atomic force microscopy

The contagious coronavirus disease-2019 pandemic has led to an increasing number of disposable face masks (DFMs) abandoned in the environment, when they are exposed to the air condition, the broken of chemical bond induced aging is inevitably occurred which meantime would cause a drastic decrease of the mechanical flexibility. However, the understanding of between chemical bond change related to aging and its micromechanical loss is limited due to the lack of refined techniques. Herein, the atomic force microscopy (AFM) technique was firstly used to observe the aging process induced by methine of the polypropylene-based DFMs. By comparing the micromechanical properties loss, the influences of humidity and light density on the DFM aging were systematically studied in the early 72 h, and it revealed that the increasing scissions number of the easiest attacked methine (C^t-H) can gradually decrease the micromechanical properties of the polypropylene (PP)-based DFM. Furthermore, the results are also validated by the in- situ FTIR and XPS analysis. This work discloses that an aging process can be initially estimated with the micromechanical changes observed by AFM, which offers fundamental data to manage this important emerging plastic pollution during COVID-19 pandemic.

Assembly strategies for polyethylene-degrading microbial consortia based on the combination of omics tools and the "Plastisphere"

Numerous microorganisms and other invertebrates that are able to degrade polyethylene (PE) have been reported. However, studies on PE biodegradation are still limited due to its extreme stability and the lack of explicit insights into the mechanisms and efficient enzymes involved in its metabolism by microorganisms. In this review, current studies of PE biodegradation, including the fundamental stages, important microorganisms and enzymes, and functional microbial consortia, were examined. Considering the bottlenecks in the construction of PE-degrading consortia, a combination of top-down and bottom-up approaches is proposed to identify the mechanisms and metabolites of PE degradation, related enzymes, and efficient synthetic microbial consortia. In addition, the exploration of the plastisphere based on omics tools is proposed as a future principal research direction for the construction of synthetic microbial consortia for PE degradation. Combining chemical and biological upcycling processes for PE waste could be widely applied in various fields to promote a sustainable environment.

Influence of Polymer Size on Polystyrene Biodegradation in Mealworms (Tenebrio molitor): Responses of Depolymerization Pattern, Gut Microbiome, and Metabolome to Polymers with Low to Ultrahigh Molecular Weight

Biodegradation of polystyrene (PS) in mealworms (Tenebrio molitor lavae) has been identified with commercial PS foams. However, there is currently limited understanding of the influence of molecular weight (MW) on insect-mediated plastic biodegradation and the corresponding responses of mealworms. In this study, we provided the results of PS biodegradation, gut microbiome, and metabolome by feeding mealworms with high-purity PS microplastics with a wide variety of MW. Over 24 days, mealworms (50 individuals) fed with 0.20 g of PS showed decreasing removal of 74.1 ± 1.7, 64.1 ± 1.6, 64.4 ± 4.0, 73.5 ± 0.9, 60.6 ± 2.6, and 39.7 ± 4.3% for PS polymers with respective weight-average molecular weights (M_w) of 6.70, 29.17, 88.63, 192.9, 612.2, and 1346 kDa. The mealworms degraded most PS polymers via broad depolymerization but ultrahigh-MW PS via limited-extent depolymerization. The gut microbiome was strongly associated with biodegradation, but that with low- and medium-MW PS was significantly distinct from that with ultrahigh-MW PS. Metabolomic analysis indicated that PS biodegradation reprogrammed the metabolome and caused intestinal dysbiosis depending on MW. Our findings demonstrate that mealworms alter their gut microbiome and intestinal metabolic pathways in response to in vivo biodegradation of PS polymers of various MWs.

Oxidative degradation of UV-irradiated polyethylene by laccase-mediator system

Polyethylene (PE) is one of the most widely used plastics. However, the chemical inertness, inefficient recycling, and random landfilling of PE waste have caused serious pollution to the natural environment. In this study, a series of laccase-mediator systems (LMS) were constructed by combination of two laccases from Botrytis aclada (BaLac) and Bacillus subtilis (BsLac) with three synthetic mediators (ABTS, HBT, and TEMPO) to oxidize LDPE films (UVPE) pretreated with high-temperature UV irradiation. Scanning electron microscopy showed aging phenomena such as etching, fragmentation, and cracking on the surface of the UVPE films after LMS incubation. The FTIR results showed that LMS-UVPE added new oxygen-containing functional groups such as -OH, -CO, and CC. High-temperature gel chromatography confirmed that the average reduction in weight-average molecular weight (Mw) was approximately 40% for the BaLac experimental group. GC-MS analysis showed the presence of oxygen-containing products, such as aldehydes, ketones, and alcohols, in the reaction mixture. To verify the oxidation process UVPE degradation by LMS, we inferred three possible pathways by combined analysis of the oxidation products of LMS on UVPE and model substrates oleic acid and squalene.

Oxidative degradation of pre-oxidated polystyrene plastics by dye decolorizing peroxidases from Thermomonospora curvata and Nostocaceae

Biodegradation of PS has attracted lots of public attentions due to its environmental friendliness. However, no specific PS degrading enzyme has been identified yet. Dye decolorizing peroxidases (DyPs) are heme-containing peroxidases named for the ability to degrade a variety of organic dyes. Herein, the abilities of two DyPs from Thermomonospora curvata (TcDyP) and Nostocaceae (AnaPX) to degrade PS were evaluated. Preoxidation methods by ultraviolet (UV) irradiation and chemical oxidants were developed to initially activate C-C bonds in the PS skeleton. DyPs degradation caused obvious etching and enhanced hydrophilicity of UV-PS films, and also generated new CO and C-OH groups. The cleavage of activated C-C bonds by DyPs was experimentally proven by analyzing the degradation products of UV-PS and model substrates. Furthermore, better pre-oxidation was obtained by using chemical oxidants KMnO₄/H₂SO₄ and ^mCPBA to oxidize PS materials in dissolved state. And AnaPX exhibited stronger degradation effects on KMnO₄/H₂SO₄-PS and ^mCPBA-PS by causing greater changes in functional groups CO, C-O, -OH groups and substituted benzenes and higher molecular weight reductions of 19.7% and 31.0%, respectively. To our knowledge, this is the first report on the identification of PS-degrading enzymes that provides experimental evidence.

An NMR look at an engineered PET depolymerase

Plastic environmental pollution is a major issue that our generation must face to protect our planet. Plastic recycling has the potential not only to reduce the pollution but also to limit the need for fossil-fuel-based production of new plastics. Enzymes capable of breaking down plastic could thereby support such a circular economy. Polyethylene terephthalate (PET) degrading enzymes have recently attracted considerable interest and have been subjected to intensive enzyme engineering to improve their characteristics. A quadruple mutant of Leaf-branch Compost Cutinase (LCC) was identified as a most efficient and promising enzyme. Here, we use NMR to follow the initial LCC enzyme through its different mutations that lead to its improved performance. We experimentally define the two calcium-binding sites and show their importance on the all-or-nothing thermal unfolding process, which occurs at a temperature of 72°C close to the PET glass transition temperature. Using various NMR probes such as backbone amide, methyl group, and histidine side-chain resonances, we probe the interaction of the enzymes with mono-(2-hydroxyethyl)terephthalic acid. The latter experiments are interpreted in terms of accessibility of the active site to the polymer chain.

A pandemic-induced environmental dilemma of disposable masks: solutions from the perspective of the life cycle

The coronavirus disease 2019 (COVID-19) has swept the world and still afflicts humans. As an effective means of protection, wearing masks has been widely adopted by the general public. The massive use of disposable masks has raised some emerging environmental and bio-safety concerns: improper handling of used masks may transfer the attached pathogens to environmental media; disposable masks mainly consist of polypropylene (PP) fibers which may aggravate the global plastic pollution; and the risks of long-term wearing of masks are elusive. To maximize the utilization and minimize the risks, efforts have been made to improve the performance of masks (e.g., antivirus properties and filtration efficiency), extend their functions (e.g., respiration monitoring and acting as a sampling device), develop new disinfection methods, and recycle masks. Despite that, from the perspective of the life cycle (from production, usage, and discard to disposal), comprehensive solutions are urgently needed to solve the environmental dilemma of disposable masks in both technologies (e.g., efficient use of raw materials, prolonging the service life, and enabling biodegradation) and policies (e.g., stricter industry criteria and garbage sorting).

Production and waste treatment of polyesters: application of bioresources and biotechniques

Chemical resources and techniques have long been used in the history of bulk polyester production and still dominate today's chemical industry. The sustainable development of the polyester industry demands more renewable resources and environmentally benign polyester products. Accordingly, the rapid development of biotechnology has enabled the production of an extensive range of aliphatic and aromatic polyesters from renewable bio-feedstocks. This review addresses the production of representative commercial polyesters (polyhydroxyalkanoates, polylactic acid, poly ε-caprolactone, polybutylene succinate, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene furandicarboxylate, polypropylene furandicarboxylate, and polybutylene furandicarboxylate) or their monomers (lactic acid, succinic acid, 1,4-butanediol, ethylene glycol, terephthalic acid, 1,3-propanediol, and 2,5-furandicarboxylic acid) from renewable bioresources. In addition, this review summarizes advanced biotechniques in the treatment of polyester wastes, representing the near-term trends and future opportunities for waste-to-value recycling and the remediation of polyester wastes under sustainable models. For future prospects, it is essential to further expand: non-food bioresources, optimize bioprocesses and biotechniques in the preparation of bioderived or biodegradable polyesters with promising: material performance, biodegradability, and low production cost.

On the degradation of (micro)plastics: Degradation methods, influencing factors, environmental impacts

Plastics and microplastics are difficult to degrade in the natural environment due to their hydrophobicity, the presence of stable covalent bonds and functional groups that are not susceptible to attack. In nature, microplastics are more likely to attract other substances due to their large specific surface area, which further prevents degradation from occurring. Some of these substances are toxic and harmful, and can be spread to various organisms through the food chain along with the microplastics to cause harm to them. Degradation is an effective way to eliminate plastic pollution, and a comprehensive understanding of the methods and mechanisms of plastic degradation is necessary, because it is the result of synergistic effects of several degradation methods, both in nature and in consideration of future engineering applications. The authors firstly summarize the degradation methods of (micro)plastics; secondly, review the influence of intrinsic properties and environmental factors during the degradation process; finally, discuss the environmental impact of the degradation products of (micro)plastics. It is evident that the degradation of (micro)plastics still has many challenges to overcome, and there are no mature and effective methods that can be applied in engineering practice or widely used in nature. Therefore, there is an urgent need for research on the degradation of (micro)plastics.

Recent Advancements in Plastic Packaging Recycling: A Mini-Review

Today, the scientific community is facing crucial challenges in delivering a healthier world for future generations. Among these, the quest for circular and sustainable approaches for plastic recycling is one of the most demanding for several reasons. Indeed, the massive use of plastic materials over the last century has generated large amounts of long-lasting waste, which, for much time, has not been object of adequate recovery and disposal politics. Most of this waste is generated by packaging materials. Nevertheless, in the last decade, a new trend imposed by environmental concerns brought this topic under the magnifying glass, as testified by the increasing number of related publications. Several methods have been proposed for the recycling of polymeric plastic materials based on chemical or mechanical methods. A panorama of the most promising studies related to the recycling of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS) is given within this review.