A critical review and future perspective of plastic waste recycling

Microplastic pollution in the glaciers, lakes, and rivers of the Hindu Kush Himalayas: Knowledge gaps and future perspectives

The Hindu Kush Himalayas (HKH), often referred to as the Third Pole and the Water Tower of Asia, represents a vital geo-ecological asset, providing essential services to millions of people. However, this once-pristine environment is increasingly threatened by the influx of microplastics. This study provides a comprehensive overview of the current state of microplastic pollution in the HKH region, identifies key research gaps, and highlights areas for future research. A review of existing literature reveals the lack of standardized protocols for microplastics analysis, which hinders cross-study comparisons. The reported microplastic abundances vary widely across environmental matrices including 0.14-31,200 MPs m-3 in river water, 0.072-26,000 MPs kg-1 in river sediments, 180-5500 MPs kg-1 in lake sediments, 55-2380 MPs kg-1 in lake shoreline sediments, 30-871.34 MPs L-1 in glaciers, and 2.23-130 MPs L-1 in lake surface water. Polymer characterization using spectroscopic techniques has identified 54 polymer types across different environmental matrices in the HKH region with polypropylene (PP) being the most dominant, followed by polyethylene (PE), and polystyrene (PS). The sources of microplastics in the HKH region include both local activities and long-range atmospheric transport. Although research on microplastics in the region has gained momentum in recent years, significant knowledge gaps remain regarding their fate, degradation mechanisms, and environmental impacts. Further studies are essential to investigate the role of microplastics as light-absorbing impurities that may accelerate glacier melting, as well as their implications for biodiversity and human health in the region.

Unveiling the duality of cement and concrete addressing microplastic pollution: a review

Microplastic pollution has emerged as a global environmental concern, with diverse consequences for ecosystems and human health. While the focus has primarily been on the sources and impacts of microplastics, this review paper explores the roles of cement and concrete in potentially mitigating microplastic pollution and addressing their negative impacts with the focus of 165 relevant publications. Cementitious materials, widely used in construction, have unique properties that greatly increase the formation and transport of microplastics in the environment, and affect circular economy practice. This paper gathers all the information we already know about how cement, concrete, and microplastics interact with each other. It also presents the potential opportunities and challenges of using these materials to deal with microplastic pollution, entailing the advancement of porous concrete as a filtering system, exploration of concrete wetting phenomena based on concrete's surface chemistry and characteristics, proper urban water management systems for concrete green spaces, assessment of innovative technologies with concrete for microplastic mitigation, and the formation of standards and guidelines such as precise Life Cycle Assessment (LCA) tools, environmental product declaration (EPD), policy for urban planning, and green finance paradigms.

Enhanced production of jet fuel precursors via furfural/cyclopentanone aldol condensation by synergistic pairing TiO2 with nano-ZSM-5 zeolite

Aldol condensation of biomass-derived compounds offers a sustainable route to jet fuel precursors. This study explores catalysts based on nanocrystalline ZSM-5 zeolite (n-ZSM-5) modified with various metals (Ca, Mg, Sn, Ti, Zr) for the aldol condensation of furfural (FFL) and cyclopentanone (CPO). While both reactants can enter the ZSM-5 micropores, the resulting C10 (FC) and C15 (F2C) adducts are too large to be formed within or to exit the microporosity, being instead produced over the external acid sites. Metal modification significantly impacts catalytic activity: Ca and Mg reduce conversion, Sn is neutral, whereas Zr and Ti leads to enhanced performance. The TiO2/n-ZSM-5 catalyst shows by far the best behavior, doubling FFL conversion and sharply increasing the FC + F2C yield, which is attributed to a synergistic effect arising from the generation of accessible weak Lewis acid sites by highly dispersed TiO2 that complement the external Brønsted acidity of ZSM-5.

Reflecting the aging behavior of polystyrene nanoplastics in the seawater through Young's modulus by atomic force microscope

Nanoplastics (NPs), with different physicochemical properties at various aging stages, have severe impacts on human health and the ecological environment. Restricted by the traditional technique, such as time-consuming, sample concentration, and the destructive of the sample, it is hard to precisely determine their aging behavior. Interestingly, we found that the nano-mechanical properties of the NPs were largely influenced by the oxidation and the cross-linking, however, their deep relationship remains lacking. Herein, this study investigates the aging behaviors of commodity plastics, microplastics and NPs in seawater via testing the changes of the physicochemical properties by combination of atomic force microscope. The results indicated that the changing behavior of Young's modulus (YM) for NPs exhibited distinctly with a rapid to a slow growth trend, an initial slow increase followed by an acceleration for microplastics, while there was almost no significant change for commodity plastics. And it was further validated by the changing trend of hydroxyl index and degree of cross-linking of the aged plastics with different sizes, which undoubtedly showed a consistent trend with the YM changes. These findings provide a new perspective for measuring the degree of cross-linking of aged NPs.

An appropriate artificial intelligence technique for plastic materials recycling using bipolar dual hesitant fuzzy set

Plastic recycling has become more important than ever as the globe struggles with growing environmental issues. This research explores the significant environmental impact of recycling plastic and its growing relevance. The pervasive material known as plastic presents a complex risk to both human health and ecosystems in contemporary life. It exacerbates problems including marine pollution, habitat damage, and wildlife entanglement because of its persistence in landfills and seas, which leads to serious ecological deterioration. In addition, producing plastic uses a lot of energy and produces a lot of greenhouse gas emissions, which exacerbate climate change. Through the use of multi-criteria decision making (MCDM), this study emphasizes how vital it is to support recycling activities in order to protect the environment and promote a sustainable future. The elimination and choice ex-pressing reality (ELECTRE) approach is used to rank the alternatives in this proposed research study that employs bipolar dual hesitant fuzzy sets (BDHFs). The most efficient and versatile outranking method for making decisions is the BDHF-ELECTRE approach. The weights of environment, economic, social, technical, and finally safety is computed using the entropy distance metric. The economic factor received the highest score of 0.2945 among the other factors since economic considerations are crucial in choosing the most efficient plastic recycling method, as they ensure sustainability, cost-effectiveness, resource allocation, and overall feasibility in managing plastic waste. The decision-makers determined that the mechanical recycling approach ought to be prioritized over all others for the efficient recycling of plastic waste. The robustness of the system is examined in the sensitive and comparative analyses. The proposed MCDM technique thus presents a viable solution, mitigating the adverse effects of plastic waste by conserving resources, reducing energy consumption, and curbing pollution.

Integrated approaches for plastic waste management

Plastic pollution is the challenging problem of the world due to usage of plastic in daily life. Plastic is essential for packaging food and other goods and utensils to avoid the risk of microbial attack. Due to its hydrophobic nature, it is used for wrapping as laminates or packaging liquid substances in pouches and sachets. The tensile strength of the plastic is more therefore it is used for manufacturing carrying bags that can bear heavy loads. Plastic is available in various forms as per the requirements in our daily life. Annually millions to trillions of polyethene carry bags are being manufactured and utilized throughout the world. The plastic requires millions of years for natural degradation. The physical and chemical processes are able to degrade plastic material at the meager level by 200 to 500 years in natural conditions. Many industries focus on recycling of plastic. Biodegradation is a comparatively slow and cheaper process that involves microbes. To dispose of plastic completely there is a need of an integrated process in which all the possible methods of disposal are involved and used sustainably so that minimum depletion occurs to the livestock and the environment. In the current review, we could try to emphasize the intricate nature of plastic polymers, pollution caused by it and possible mitigation strategies for plastic waste management.

Effects of Contamination with Selected Polymers on the Mechanical Properties of Post-Industrial Recycled Polypropylene

The effect of contamination of polypropylene (PP) with selected polymers is studied to simulate the effect of mis-sorting in recycling streams. Polystyrene (PS), polyethylene terephthalate (PET), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and polylactic acid (PLA) were compounded with PP at different concentrations varying between 3 and 10%. Infrared spectroscopy proved the absence of chemical bonds between the constituents. Generally, melt flowability, except for the PP/PLA blend, and crystallinity were only slightly affected by the incorporation of the contaminating polymers. Samples of the polymer blends were injection moulded and further tested for their tensile and impact properties. Critical behaviour was induced by the introduction of a weld line as a result of the application of multiple gating points during injection moulding. Results generally show the applicability of PP mixtures within the investigated range of contamination, without much sacrifice in mechanical performance. However, in the case of ABS and PLA, more care should be taken when designing complex parts with weld lines, due to reduced toughness.

Temperature fluctuation in soil alters the nanoplastic sensitivity in wheat

Despite the wide acknowledgment that plastic pollution and global warming have become serious agricultural concerns, their combined impact on crop growth remains poorly understood. Given the unabated megatrend, a simulated soil warming (SWT, +4 °C) microcosm experiment was carried out to provide a better understanding of the effects of temperature fluctuations on wheat seedlings exposed to nanoplastics (NPs, 1 g L-1 61.71 ± 0.31 nm polystyrene). It was documented that SWT induced oxidative stress in wheat seedlings grown in NPs-contaminated soil, with an 85.56 % increase in root activity, while decreasing plant height, fresh weight, and leaf area by 8.72 %, 47.68 %, and 15.04 % respectively. The SWT also resulted in reduced photosynthetic electron-transfer reaction and Calvin-Benson cycle in NPs-treated plants. Under NPs, SWT stimulated the tricarboxylic acid (TCA) metabolism and bio-oxidation process. The decrease in photosynthesis and the increase in respiration resulted in an 11.94 % decrease in net photosynthetic rate (Pn). These results indicated the complicated interplay between climate change and nanoplastic pollution in crop growth and underscored the potential risk of nanoplastic pollution on crop production in the future climate.

The role of Geographic Information Systems in mitigating plastics pollution in the Global South-A spatial analysis of recycling facilities in Costa Rica

Costa Rica is at the forefront of environmental conservation in Central America, with its focus on sustainability and green practices. Building on this foundation, the country joins a cohort of middle-income developing countries that have set forth ambitious goals to eliminate plastic pollution and become plastics-free. Recycling remains one of the most effective ways of removing plastic waste from the environment. Although GIS has been utilized in environmental research, its use is still expanding in developing countries of the Global South. These countries are experiencing unprecedented adverse climate and ecological impacts while also pursuing fundamental socioeconomic growth. The application of more cost-effective and strategic technological solutions, as well as data-driven decision-making, could fast-track the achievement of their urgent environmental goals. Using Geographic Information Systems (GIS) analysis, this study applies hot spot, location-allocation, and time-distance measures to examine Costa Rica's capacity to recycle plastic waste. Focusing specifically on availability and the public's access to recycling facilities, this article offers insights into the resource constraints and evolution of plastics governance in developing countries with environmentally-focused priorities. The findings of this study suggest that while Costa Rica is implementing progressive plastics regulatory policies, the ability to achieve plastics-free status is hampered by shortfalls in the number and distribution of recycling facilities and the public's access to recycling services. Expanding recycling infrastructure, including transportation, and adopting a less canton-centric waste administration system could contribute to resolving these challenges. This study contributes to discourses on global plastics governance and environmental change management in the Global South.

Application of starch-rich mango by-product as filler for the development of an additive manufacturing filament compound

The surge in global polymeric waste underscores the imperative for biodegradable materials to substitute traditional polymers. Crucially, advancements are needed for emerging technologies like Materials Extrusion (ME) in additive manufacturing, where current biodegradable materials exhibit limitations. This work was based on the development of a biodegradable composite filament. The inner of the mango seed (kernel) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were used as raw materials. The properties of PHBV and mango by-product mixture were first evaluated by direct-extrusion printing. Then, the feasibility of manufacturing the filaments was studied. Initially, the kernel seed mango was characterized thermally, chemically, and morphologically by DSC, FTIR, and SEM, respectively. It was observed that the addition of mango by-product contributed to the decrease of PHBV crystallinity, resulting in the reduction of printed parts retraction and increases the Tg, as shown by the DMA. The structure of the native starch was preserved due to non-gelatinization, even after processing steps, as indicated by thermal, chemical, and morphological analyses. Finally, PHBV filaments containing mango by-products were fabricated, and prototypes were manufactured by ME to demonstrate the potential for market acceptance and commercialization of the studied filament.

Waste to energy: Trending key challenges and current technologies in waste plastic management

Due to the 'forever' degrading nature of plastic waste, plastic waste management is often complicated. The applications of plastic are ubiquitous and inevitable in many scenarios. Current global waste plastics production is ca. 3.5 MMT per year, and with the current trend, plastic waste production will reach 25,000 MMT by 2040. However, the rapid growth in plastic manufacture and the material's inherent nature resulted in the accumulation of a vast amount of plastic garbage. The current recycling rate is <10 %, while the large volumes of discarded plastic waste cause environmental and ecological problems. Recycling rates for plastic vary widely by region and type of plastic. In some developed countries, the recycling rate for plastics is around 20-30 %, while in many developing nations, it is much lower. These statistics highlight the magnitude of the plastic waste problem and the urgent need for comprehensive strategies to manage plastic waste more effectively and reduce its impact on the environment. This review critically analyses past studies on the essential and efficient techniques for turning plastic trash into treasure. Additionally, an attempt has been made to provide a comprehensive understanding of the plastic upcycling process, the 3Rs policy, and the life-cycle assessment (LCA) of plastic conversion. The review advocates pyrolysis as one of the most promising methods of turning plastic trash into valuable chemicals. In addition, plastic waste management can be severely impacted due to uncontrollable events, such as Covid 19 pandemic. Recycling and chemical upcycling can certainly bring value to the end-of-life plastic. However, the LCA analysis indicated there is still a huge scope for innovation in chemical upcycling area compared to mechanical recycling. The formulation of policies and heightened public participation could play a pivotal role in reducing the environmental repercussions of plastic waste and facilitating a shift towards a more sustainable future.

Driving sustainable circular economy in electronics: A comprehensive review on environmental life cycle assessment of e-waste recycling

E-waste, encompassing discarded materials from outdated electronic equipment, often ends up intermixed with municipal solid waste, leading to improper disposal through burial and incineration. This improper handling releases hazardous substances into water, soil, and air, posing significant risks to ecosystems and human health, ultimately entering the food chain and water supply. Formal e-waste recycling, guided by circular economy models and zero-discharge principles, offers potential solutions to this critical challenge. However, implementing a circular economy for e-waste management due to chemical and energy consumption may cause environmental impacts. Consequently, advanced sustainability assessment tools, such as Life Cycle Assessment (LCA), have been applied to investigate e-waste management strategies. While LCA is a standardized methodology, researchers have employed various routes for environmental assessment of different e-waste management methods. However, to the authors' knowledge, there lacks a comprehensive study focusing on LCA studies to discern the opportunities and limitations of this method in formal e-waste management strategies. Hence, this review aims to survey the existing literature on the LCA of e-waste management under a circular economy, shedding light on the current state of research, identifying research gaps, and proposing future research directions. It first explains various methods of managing e-waste in the circular economy. This review then evaluates and scrutinizes the LCA approach in implementing the circular bioeconomy for e-waste management. Finally, it proposes frameworks and procedures to enhance the applicability of the LCA method to future e-waste management research. The literature on the LCA of e-waste management reveals a wide variation in implementing LCA in formal e-waste management, resulting in diverse results and findings in this field. This paper underscores that LCA can pinpoint the environmental hotspots for various pathways of formal e-waste recycling, particularly focusing on metals. It can help address these concerns and achieve greater sustainability in e-waste recycling, especially in pyrometallurgical and hydrometallurgical pathways. The recovery of high-value metals is more environmentally justified compared to other metals. However, biometallurgical pathways remain limited in terms of environmental studies. Despite the potential for recycling e-waste into plastic or glass, there is a dearth of robust background in LCA studies within this sector. This review concludes that LCA can offer valuable insights for decision-making and policy processes on e-waste management, promoting environmentally sound e-waste recycling practices. However, the accuracy of LCA results in e-waste recycling, owing to data requirements, subjectivity, impact category weighting, and other factors, remains debatable, emphasizing the need for more uncertainty analysis in this field.

Recent advances in the biological depolymerization and upcycling of polyethylene terephthalate

Polyethylene terephthalate (PET) is favored for its exceptional properties and widespread daily use. This review highlights recent advancements that enable the development of biological tools for PET decomposition, transforming PET into valuable platform chemicals and materials in upcycling processes. Enhancing PET hydrolases' catalytic activity and efficiency through protein engineering strategies is a priority, facilitating more effective PET waste management. Efforts to create novel PET hydrolases for large-scale PET depolymerization continue, but cost-effectiveness remains challenging. Hydrolyzed monomers must add additional value to make PET recycling economically attractive. Valorization of hydrolysis products through the upcycling process is expected to produce new compounds with different values and qualities from the initial polymer, making the decomposed monomers more appealing. Advances in synthetic biology and enzyme engineering hold promise for PET upcycling. While biological depolymerization offers environmental benefits, further research is needed to make PET upcycling sustainable and economically feasible.

Micromotors of MnO2 for the Recovery of Microplastics

Plastics, primarily microplastics, are among the greatest pollutants in aquatic environments. Their removal and/or degradation in these environments are crucial to ensure an optimal future of these ecosystems. In this work, MnO2 particles were synthesized and characterized for the removal of polystyrene microplastics as a model. MnO2 catalyzes the peroxide reaction, resulting in the formation of oxygen bubbles that propel the pollutants to the surface, achieving removal efficiencies of up to 80%. To achieve this, hydrothermal synthesis was employed using various methods. Parameters such as MnO2, pH, microplastics, and H2O2 concentrations were varied to determine the optimal conditions for microplastics recovering. The ideal conditions for a low microplastic concentrations (10 mg L-1) are 0.2 g L-1 MnO2, 1.6% of H2O2 and 0.01 triton as a surfactant. In these conditions, the micromotors can recover approximately 80% of 300 nm sized polystyrene microplastic within 40 min.

Chemical recycling of plastic wastes with alkaline earth metal oxides: A review

Plastics have been widely used in daily life and industries due to their low cost and high durability, leading to huge production of plastics and tens of millions of plastic wastes every year. Chemical recycling can recycle contaminated and degraded plastics (that mechanical recycling cannot deal with) to obtain value-added products, which potentially solves the environmental problems caused by plastics and realizes a circular economy. Alkaline earth metal oxides, as a category of cost-effective and multi-functional materials, have been widely used in chemical recycling of common plastics, acting as three roles: catalyst, template, and absorbent. Among five commercial plastics, polyethylene terephthalate is suitable for pyrolysis and solvolysis. Polyethylene and polypropylene, which are ideal precursors for synthesis of carbon nanotubes, could be combined with biomass for co-pyrolysis. Polyvinyl chloride needs to be pretreated to reduce chloride content prior to pyrolysis. Depolymerization of polystyrene into monomers is attractive. This review summarized the chemical recycling approaches of commercial plastics and the strategies with alkaline earth metal oxides for the development of efficient recycling processes. It will aid understanding of the advances and challenges in the field and promote the future research.

Removal of most frequent microplastic types and sizes in secondary effluent using Al2(SO4)3: choosing variables by a fuzzy Delphi method

Microplastics (MPs) as an emerging pollutant can affect aquatic organisms through physical ingestion, chemical problems and possible creation of biological layers on their surfaces in the environment. One of the significant ways for MPs to enter the aquatic environment is through the effluent discharge of wastewater treatment plants (WWTPs). In this study, first, the concentration and characteristics of MPs in secondary wastewater effluent, and the influential variables related to the coagulation process, for MPs removal were identified using systematic reviews of previous studies. Then, the most proper MPs characterization and coagulation variables were chosen by experts' opinions using a fuzzy Delphi method. Therefore, the experiment tested in conditions close to the full-scale wastewater treatments. Finally, in the laboratory removal of MPs by coagulation of polyamide (PA), polystyrene (PS), and polyethylene (PE), < 125 and 300-600 μm in size, was tested by a jar test applying Al2(SO4)3 in doses of 5 to 100 mg/L plus 15 mg/L polyacrylamide as a coagulant aid. Using R and Excel software, the results were analyzed statistically. It was concluded that the maximum and minimum removal efficiency was 74.7 and 1.39% for small PA and large PE, respectively. Smaller MPs were found to have higher removal efficiency. The MPs type PA achieved greater removal efficiency than PS, while PE had the least removal efficiency.

Waste plastics derived nickel-palladium alloy filled carbon nanotubes for hydrogen evolution reaction

Carbon nanotubes (CNTs) composed of bimetallic nickel-palladium (NiPd) nanoparticles encapsulated in graphitic carbon shells (NdPd@CNT) are prepared by the chemical vapour deposition method using waste polyethylene terephthalate (PET) plastic carbon sources and NiPd-decorated carbon sheets (NiPd@C) catalyst. The characterization results reveal that the face-centered cubic crystalline (fcc)-structured NiPd bimetallic alloy nanoparticles are encased by thin carbon nanotubes. The bimetallic synergism of NiPd nanoparticles actuates the outer CNT layers and accelerates the electrical conductivity, stimulating the electrochemical activity toward an effective hydrogen evolution reaction (HER). By virtue of the collective individualities of highly conductive aligned carbon walls and bimetallic active sites, the NiPd@CNT-equipped HER delivers a minimum overpotential of 87 mV and a Tafel slope value of 95 mV dec-1. The existing intact contact between NiPd and CNT facilitates continuous electron and ion transportation and firm stability toward long-term hydrogen production in HER. Notably, the NiPd@CNT reported here produces excellent electrochemical activity with minimal charge transference resistance, substantiating the efficacy of NiPd@CNT for futuristic green hydrogen production.

Novel and Accessible Physical Recycling for Expanded Polystyrene Waste with the Use of Acetone as a Solvent and Additive Manufacturing (Direct Ink-Write 3D Printing)

The current high production of plastics has prompted the exploration of alternative pathways to facilitate recycling, aiming for a progressively sustainable society. This paper presents an alternative and affordable technology for treating waste expanded polystyrene (EPS) mixed with acetone in a 100:1 volume ratio to be used as 3D printing ink for Direct Ink Write technology. In order to optimize the printing parameters, a comprehensive study was conducted, evaluating different needle diameters, printing speeds, and bed temperature values to achieve homogenous pieces and a highly repeatable 3D printing process. Results showed that the main optimum printing parameters were using needles with diameters of 14 to 16 G and printing speeds ranging from 2 to 12 mm/s, which were found to yield the most uniform ribbons. Increasing the bed temperature, despite favoring acetone evaporation, led to the generation of more heterogeneous structures due to void growth inside the printed ribbons. Thus, employing room temperature for the bed proved to be the optimal value. Lastly, a comparative study between the starting material and the EPS after the printing process was conducted using FTIR-ATR and GPC analyses, ensuring the preservation of the original polymer's integrity during physical recycling.