Understanding the mechanism of enhanced anaerobic biodegradation of biodegradable plastics after alkaline pretreatment

Effect of alkaline-thermal pretreatment on biodegradable plastics degradation and dissemination of antibiotic resistance genes in co-compost system

Biodegradable plastics (BDPs) are an eco-friendly alternative to traditional plastics in organic waste, but their microbial degradation and impact on antibiotic resistance genes (ARGs) transmission during co-composting remain poorly understood. This study examines how alkaline-thermal pretreatment enhances BDPs degradation and influences the fate of ARGs and mobile genetic elements (MGEs) in co-composting. Pretreatment with 0.1 mol/L NaOH at 100℃ for 40 minutes increased the surface roughness and hydrophilicity of BDPs while reducing their molecular weight and thermal stability. Incorporating pretreated BDPs film (8 g/kg-TS) into the compost reduced the molecular weight of the BDPs by 59.70 % during the maturation stage, facilitating compost heating and prolonging the thermophilic stage. However, incomplete degradation of BDPs releases numerous smaller-sized microplastics, which can act as carriers for microorganisms, facilitating the dissemination of ARGs across environments and posing significant ecological and public health risks. Metagenomic analysis revealed that pretreatment enriched plastic-degrading bacteria, such as Thermobifida fusca, on BDPs surfaces and accelerated microbial plastic degradation during the thermophilic stage, but also increased ARGs abundance. Although pretreatment significantly reduced MGEs abundance (tnpA, IS19), the risk of ARGs dissemination remained. Three plastic-degrading bacteria (Pigmentiphaga sp002188465, Bacillus clausii, and Bacillus altitudinis) were identified as ARGs hosts, underscoring the need to address the risk of horizontal gene transfer of ARGs associated with pretreatment in organic waste management.

The strategic role of a mild hydrothermal pretreatment in enhancing anaerobic degradation of commercial bio-based compostable plastics associated to food waste

The expansion of Anaerobic Digestion (AD) technology to turn food waste (FW) into biogas will influence the management of the associated compostable bio-based plastics disposed of in the organic fraction of municipal waste collection. Waste processing aspects and bio-based plastic biodegradation profile in anaerobic conditions need research. The fate of some commercially available compostable items made of thermoplastic starch or PLA-based blends was investigated, by performing lab-scale disposal phase and thermophilic AD, with the integration of a mild hydrothermal pretreatment. For comprehensive understanding of bio-based plastics degradation, the biomethane production, structural (visual inspection, weight, dimension) and composition changes (solids, organics and carbohydrates content) were analyzed. Thermal pretreatment promoted thermoplastic starch-based product disintegration (40 ± 2 %) and the extraction of carbohydrates into the liquid eluate, with the potential to be transformed into high-value-added products through fermentative upgrading processes. A significant biodegradation of pretreated bio-based plastics up to 27.5 % and 40 %, respectively for thermoplastic starch- and polylactic acid (PLA)-based material, was observed. These preliminary results evidence the strategic role of the hydrothermal pretreatment in enhancing anaerobic degradation and the possibility to treat the bio-based plastics as FW co-substrate, avoiding the time and cost-consuming sorting phase in waste management plants.

Microbial strategies for effective microplastics biodegradation: Insights and innovations in environmental remediation

Microplastics (MPs), diminutive yet ubiquitous fragments arising from the degradation of plastic waste, pervade environmental matrices, posing substantial risks to ecological systems and trophic dynamics. This review meticulously examines the origins, distribution, and biological impacts of MPs, with an incisive focus on elucidating the molecular and cellular mechanisms underpinning their toxicity. We highlight the indispensable role of microbial consortia and enzymatic pathways in the oxidative degradation of MPs, offering insights into enhanced biodegradation processes facilitated by innovative pretreatment methodologies. Central to our discourse is the interplay between MPs and biota, emphasizing the detoxification capabilities of microbial metabolisms and enzymatic functions in ameliorating MPs' deleterious effects. Additionally, we address the practical implementations of MP biodegradation in environmental remediation, advocating for intensified research to unravel the complex biodegradation pathways and to forge effective strategies for the expeditious elimination of MPs from diverse ecosystems. This review not only articulates the pervasive challenges posed by MPs but also positions microbial strategies at the forefront of remedial interventions, thereby paving the way for groundbreaking advancements in environmental conservation.

Rapid start-up and excellent performance of anaerobic membrane bioreactor for treating poly (butylene adipate-co-terephthalate) wastewater by using one-step feeding mode

The traditional anaerobic treatment process for highly concentrated, toxic, and acidic poly (butylene adipate-co-terephthalate) (PBAT) wastewater faces challenges. In contrast, the anaerobic membrane bioreactor (AnMBR) offers the advantage of robust performance, but the influence of start-up modes has not been explored. This study investigated the impact of one-step and stepwise startup (gradual dilution of wastewater) strategies in AnMBR treating PBAT wastewater. The results indicated that the one-step startup group achieved COD removal efficiency of 91.2% ± 2.7% and methane conversion rate of 234.7 ± 8.5 mLCH4/gCOD, which were 21.7% and 81.8 mL CH4/gCOD respectively higher than those achieved by the stepwise start-up group. Furthermore, the one-step startup led to the reduction of startup time by 10 days and the decrease in the average membrane fouling cycle by 6.6 days. Compared to the stepwise start-up group, the one-step startup group exhibited a lower abundance of Bacteroidota (11.3%), and a higher abundance of Proteobacteria (27.1%), Chloroflexi (10.5%), and Actinobacteria (11.8%). The one-step startup strategy facilitated the rapid development of a toxicity-tolerant hydrogenotrophic methanogenic pathway. Consequently, the one-step startup method provided a promising approach for the rapid start-up and excellent performance of AnMBR in PBAT wastewater treatment.

Advances in plastic mycoremediation: Focus on the isoenzymes of the lignin degradation complex

This study investigates P. ostreatus and A. bisporus biodegradation capacity of low density polyethylene (LDPE) oxidised to simulate environmental weathering. Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were used to analyse the degradation of LDPE treated with fungal cultures. Molecular implications of LDPE degradation by P. ostreatus and A. bisporus were evaluated by Reverse transcription followed by quantitative PCR (qRT-PCR) of lac, mnp and lip genes expression. After 90 days of incubation, FT-IR analysis showed, for both fungal treatments, an increasing in the intensity of peaks related to the asymmetric C-C-O stretching (1160 to 1000 cm-1) and the -OH stretching (3700 to 3200 cm-1) due to the formation of alcohols and carboxylic acid, indicating depolymerisation of LDPE. This was confirmed by the SEM analysis, where a widespread alteration of the surface morphology was observed for treated LDPE fragments. Results revealed that the exposure of P. ostreatus to oxidised LDPE treatment led to a significant increase in the expression of the lac6, lac7, lac9, lac10 and mnp2 genes, while A. bisporus showed an over-expression in lac2 and lac12 genes. The obtained results offer new perspectives for a biotechnological use of P. ostreatus and A. bisporus for plastic bioremediation.

Poly(Propylene Carbonate)-Based Biodegradable and Environment-Friendly Materials for Biomedical Applications

Poly(propylene carbonate) (PPC) is an emerging "carbon fixation" polymer that holds the potential to become a "biomaterial of choice" in healthcare owing to its good biocompatibility, tunable biodegradability and safe degradation products. However, the commercialization and wide application of PPC as a biomedical material are still hindered by its narrow processing temperature range, poor mechanical properties and hydrophobic nature. Over recent decades, several physical, chemical and biological modifications of PPC have been achieved by introducing biocompatible polymers, inorganic ions or small molecules, which can endow PPC with better cytocompatibility and desirable biodegradability, and thus enable various applications. Indeed, a variety of PPC-based degradable materials have been used in medical applications including medical masks, surgical gowns, drug carriers, wound dressings, implants and scaffolds. In this review, the molecular structure, catalysts for synthesis, properties and modifications of PPC are discussed. Recent biomedical applications of PPC-based biomaterials are highlighted and summarized.

Effects of particle size on the pretreatment efficiency and subsequent biogas potential of polylactic acid

The fragmentation of bioplastics (BPs) before pretreatment and anaerobic digestion is conducted for higher efficiency; however, based on the literature, the size reduction varies widely. In this study, initially, various combinations of thermal-alkaline pretreatments were applied at different strengths to the polylactic acid (PLA) in three groups (<0.5, 0.5 < size < 1.0, and 1.0 < size < 2.0 mm). After pretreatment, the solubilization of PLA was increased to 11.5-40.0 % using alkaline dosage and temperature ranging from 50 to 200 g OH-/kg BP, 60-100 °C, respectively, in a 1-10 h timeframe. The results were statistically proved using a 3D response surface graph, where the pretreatment was more effective for smaller particle sizes. The reduction in particle size also increased the CH4 production, which was more pronounced at the strong pretreatment (24 % increment vs. 10-15 %). Computed results indicated 44-86 % conversion of pretreated PLA particles to CH4, supported by Fourier transform infrared spectroscopy analysis, especially focusing on the intensity of -OH bands.

Biodegradation of microplastics: Advancement in the strategic approaches towards prevention of its accumulation and harmful effects

Microplastics (MPs) are plastic particles in a size ranging from 1 mm to 5 mm in diameter, and are formed by the breakdown of plastics from different sources. They are emerging environmental pollutants, and pose a great threat to living organisms. Improper disposal, inadequate recycling, and excessive use of plastic led to the accumulation of MP in the environment. The degradation of MP can be done either biotically or abiotically. In view of that, this article discusses the molecular mechanisms that involve bacteria, fungi, and enzymes to degrade the MP polymers as the primary objective. As per as abiotic degradation is concerned, two different modes of MP degradation were discussed in order to justify the effectiveness of biotic degradation. Finally, this review is concluded with the challenges and future perspectives of MP biodegradation based on the existing research gaps. The main objective of this article is to provide the readers with clear insight, and ideas about the recent advancements in MP biodegradation.

The impact of esterified nanofibrillated cellulose content on the properties of thermoplastic starch/PBAT biocomposite films through ball-milling

To enhance the mechanical properties and interfacial compatibility of thermoplastic starch (TPS) highly filled poly(butylene adipate co-terephthalate) (PBAT) composite films, esterified NFC was innovatively fabricated and introduced into the composite system. The influences of NFC content and ball-milling treatment were thoroughly investigated. Interestingly, the amphiphilic esterified NFC provided a "bridge-like" effect between TPS and PBAT interfaces, which significantly improved the interfacial compatibility and mechanical properties. Notably, the tensile properties of the composite films reached their maximums at a 7 wt% NFC content, displaying a tensile strength of 6.2 MPa and an elastic modulus of 263 MPa. These values corresponded to a 59 % and 180 % increase, respectively, compared to the composition without NFC. More importantly, ball-milling contributed to uniform dispersion and surface activation of NFC, preventing starch retrogradation, and enhancing the tensile strength and elastic modulus by 30.3 % and 56.6 %, respectively. Additionally, the film exhibited excellent UV-blocking, foldable, writable, and transparent performance. These findings provide valuable data supporting the expanded applications of starch-based composite films.

Microbial community acclimatization enhances bioplastics biodegradation and biogas production under thermophilic anaerobic digestion

This paper reports the results of a novel study of microbial acclimatization for bioplastics anaerobic degradation and conversion into biogas. Three sequential anaerobic digestion (AD) runs were carried out to favour microbial acclimatization to two different bioplastics, starch-based (SBS) and polyactic-acid (PLA). AD of SBS and PLA bioplastics was favoured by the acclimatization of the inoculum to the substrate after each run of AD. SBS conversion into biogas increased by 52 % (from 94 to 143 NL kgVS-1) and it was correlated with the enhanced growth of starch degrading bacteria such as Hydrogenispora, Halocella and Haloplasma. PLA anaerobic degradation increased by 97 % (from 395 to 779 NLbiogas kgVS-1) and it was related to the acclimatization of known PLA-degraders such as Tepidimicrobium, Methanothermobacter and Tepidanaerobacter. Microbial acclimatization appears a suitable and low-cost strategy to enhance bioplastics circularity by promoting their anaerobic biodegradation and conversion into biogas.

Biodegradation of plastics by white-rot fungi: A review

Plastic pollution is one of the most environmental problems in the last two centuries, because of their excessive usage and their rapidly increasing production, which overcome the ability of natural degradation. Moreover, this problem become an escalating environmental issue caused by inadequate disposal, ineffective or nonexistent waste collection methods, and a lack of appropriate measures to deal with the problem, such as incineration and landfilling. Consequently, plastic wastes have become so ubiquitous and have accumulated in the environment impacting ecosystems and wildlife. The above, enhances the urgent need to explore alternative approaches that can effectively reduce waste without causing harsh environmental consequences. For example, white-rot fungi are a promising alternative to deal with the problem. These fungi produce ligninolytic enzymes able to break down the molecular structures of plastics, making them more bioavailable and allowing their degradation process, thereby mitigating waste accumulation. Over the years, several research studies have focused on the utilization of white-rot fungi to degrade plastics. This review presents a summary of plastic degradation biochemistry by white-rot fungi and the function of their ligninolytic enzymes. It also includes a collection of different research studies involving white-rot fungi to degrade plastic, their enzymes, the techniques used and the obtained results. Also, this highlights the significance of pre-treatments and the study of plastic blends with natural fibers or metallic ions, which have shown higher levels of degradation. Finally, it raises the limitations of the biotechnological processes and the prospects for future studies.

Biodegradable mulch films improve yield of winter potatoes through effects on soil properties and nutrients

Biodegradable mulch films are recognized as a promising substitute of polyethylene (PE) films to alleviate the "white pollution". Biodegradable mulch films with optimum degradation rates increase crop yield even compared to PE films. However, the mechanisms underlying this yield-increasing effect remains elusive. In this study, three biodegradable film treatments (BFM1, BFM2 and BFM3) and one PE film treatment (PFM) were used to evaluate their effects on soil and winter potatoes, and a partial least squares path model (PLS-PM) was constructed to investigate their relationships. The degradation rates of films under different treatments were ranked as BFM3 > BFM2 >BFM1 > PFM, and presented distinctive effects on soil properties and nutrients, structure of soil bacterial community, and yield traits of winter potatoes. The PLS-PM showed that mulch treatments affected potato yield through effects on soil properties (soil water and temperature) and soil nutrients (TOC, DOC, TN and NO3--N). The disintegration of the biodegradable films decreased soil water content and temperature, and reduced the loss of soil nutrients in the topsoil at the later growth stage of winter potatoes compared to PE films. Additionally, the elevated content of soil TN and NO3--N under treatment BFM1 may play a key role in its yield-increasing effect on potatoes compared to treatments PFM and BFM2. Thus, biodegradable mulch films with proper degradation rates regulate soil TN and NO3--N through their effects on soil water and temperature, and subsequently improve the yield of winter potatoes compared to PE mulch films.