A review on technological options of waste to energy for effective management of municipal solid waste

Incidental iron oxide nanoclusters drive confined Fenton-like detoxification of solid wastes towards sustainable resource recovery

The unique properties of nanomaterials offer vast opportunities to advance sustainable processes. Incidental nanoparticles (INPs) represent a significant part of nanomaterials, yet their potential for sustainable applications remains largely untapped. Herein, we developed a simple strategy to harness INPs to upgrade the waste-to-resource paradigm, significantly reducing the energy consumption and greenhouse gas emissions. Using the recycling of fly ash from municipal solid waste incineration (MSWI) as a proof of concept, we reveal that incidental iron oxide nanoclusters confined inside the residual carbon trigger Fenton-like catalysis by contacting H2O2 at circumneutral pH (5.0-7.0). This approach efficiently detoxifies the adsorbed dioxins under ambient conditions, which otherwise relies on energy-intensive thermal methods in the developed recovery paradigms. Collective evidence underlines that the uniform distribution of iron oxide nanoclusters within dioxin-enriched nanopores enhances the collision between the generated active oxidants and dioxins, resulting in a substantially higher detoxification efficiency than the Fe(II)-induced bulk Fenton reaction. Efficient and cost-effective detoxification of MSWI fly ash at 278‒288 K at pilot scale, combined with the satisfactory removal of adsorbed chemicals in other solid wastes unlocks the great potential of incidental nanoparticles in upgrading the process of solid waste utilization and other sustainable applications.

Social cost--benefit analysis of solid waste management options with application to Mumbai, India

Managing solid waste continues to be an environmental, technical and economic challenge, especially for developing countries. Though these countries' urban local bodies (ULBs) are moving up the waste management hierarchy, most waste is still openly dumped. One key reason for this choice is the non-accounting of (a) social costs associated with open dumping (OD) and (b) direct/indirect benefits of other options. The current study conducts a complete social cost-benefit analysis (SCBA) comparing OD to sanitary landfilling, composting, bio-methanation, incineration and gasification alternatives. The study finds that when only private costs/benefits are considered, a mix of OD and sanitary landfills is preferred; however, when external costs/benefits are factored in, the mix shifts towards alternatives like incineration and gasification. These learnings from the SCBA are then applied to Mumbai, which generates 9000 tonnes of waste daily. To determine the optimal mix for Mumbai ULB, a constrained optimization exercise is carried out considering the technical feasibility of the alternatives and the ULB's capital budget. The study finds that with the current practice of OD, the net present value (NPV) of the social costs over a 30-year horizon will be over US$ 6-9 billion. However, even if one-fifth of the ULB's capital budget is allocated towards other waste management alternatives, the mix would shift towards sophisticated technologies and the NPV of social costs would reduce to around half that amount.

Biochemical conversion of municipal solid waste to biofuels and bioproducts: a review

The disposal of municipal solid waste (MSW) in urban areas is a big issue nowadays in most of the countries. Developing countries like India are struggling with the continuous indiscriminate disposal of MSW due to rapid increase in the urbanization, industrialization, and human population growth. The mismanagement of MSW causes adverse environmental impacts, public health risks, and other socio-economic problems. India, the second most populated country in the world, faces the problem of MSW and simultaneously grave the crisis of energy as management problems of MSW provide a platform to utilize it as a promising renewable energy source, thus resolving the related issues. The pressing need for the development of alternatives gave several different technological solutions; among them, Waste-to-Energy is being recognized as a renewable option for energy generation and waste remediation. The associated challenges of managing regularly generated MSW make it difficult to adopt the suitable technique/process to treat it. However, detailed information and discussion are needed to decide which strategy is to be adopted. Considering the large availability and potential of MSW, this article has been reviewed to collect and represent different strategies of using MSW for different products based on the requirements of society. The article reviews the up-to-date biochemical conversion strategies being employed to treat the MSW and simultaneously harness the energy, and other value-added products. Besides, the life cycle assessment highlights the futuristic scope for industrial growth to determine the environmental impact of using MSW as a renewable energy source and substrate for biopolymers.

Towards responsible resource utilization: A review of sustainable vs. unsustainable reuse of wood waste

Abundant wood waste is generated globally, but the literature lacks a framework distinguishing sustainable versus unsustainable reuse practices. This gap hinders policy makers and stakeholders from effectively supporting responsible resource utilization. As such, this scoping review aimed to address this gap by evaluating wood waste reuse practices through ecological, financial, and social sustainability lenses. A comprehensive database search yielded 1,150 records, narrowed to 106 included studies through eligibility screening. Data on study details and sustainability factors was extracted without a formal quality appraisal. The protocol ensures a rigorous evidence-mapping approach. The findings revealed that sustainable uses included renewable energy, adsorbents, construction materials, and composting applications. However, toxic preservatives, uncontrolled emissions from burning, intensive harvesting impacts, and contamination risks from uncontrolled mulching perpetuate ecological, social, and financial challenges. Preventing contamination and managing sustainability trade-offs are key priorities. Research innovations, stringent quality control, and supportive policies are imperative to distinguish practices aligned with sustainability principles from those inadvertently causing harm. This review provides a comprehensive framework for making informed decisions to progress wood waste systems toward responsible resource utilization.

Development of an integrated online deposition and corrosion monitoring system in a full-scale solid waste CFB boiler

Solid waste incineration is a clean and sustainable approach for solid waste management. However, ash deposition and corrosion remain a critical issue due to fuel's inherent enrichment of alkali chlorine. This study develops an integrated online deposition and corrosion monitoring system to enhance the operational safety and efficiency of solid waste incineration boilers. This system combines linear polarization resistance (LPR) for corrosion rate estimation with heat flux measurements for ash deposition analysis. It can offer a novel approach for real-time monitoring of heat exchangers' safety during solid waste combustion. It was deployed in a full-scale circulating fluidized bed (CFB) boiler that purely combust solid wastes. Key findings demonstrate the system's capability to deliver continuous, real-time data, crucial for the dynamic control of combustion processes and the maintenance of heat transfer surfaces. Its robust diagnostic capabilities were evident across various scenarios. Specially, initial corrosion rates sharply increase with deposition rates due to the enrichment of alkali chlorine on inner deposit layer, in which chlorine serves as a catalyst, facilitating the rapid penetration and aggravation of corrosion by other agents. As deposit further buildup, the corrosion rate steadily decreases along with surface temperature, highlighting a dynamic interaction. Moreover, measured corrosion rates can quickly response to temperature variations. Such multi-process online monitoring system provide more possibilities to investigate the inherent interaction between deposition and corrosion. Therefore, this work offers insights that could significantly influence operational strategies, maintenance protocols, and the overall reliability of waste-to-energy technologies.

Towards planetary boundary sustainability of food processing wastewater, by resource recovery & emission reduction: A process system engineering perspective

Meeting the needs of a growing population calls for a change from linear production systems that exacerbate the depletion of finite natural resources and the emission of environmental pollutants. These linear production systems have resulted in the human-driven perturbation of the Earth's natural biogeochemical cycles and the transgression of environmentally safe operating limits. One solution that can help alleviate the environmental issues associated both with resource stress and harmful emissions is resource recovery from waste. In this review, we address the recovery of resources from food and beverage processing wastewater (FPWW), which offers a synergistic solution to some of the environmental issues with traditional food production. Research on resource recovery from FPWW typically focuses on technologies to recover specific resources without considering integrative process systems to recover multiple resources while simultaneously satisfying regulations on final effluent quality. Process Systems Engineering (PSE) offers methodologies able to address this holistic process design problem, including modelling the trade-offs between competing objectives. Optimisation of FPWW treatment and resource recovery has significant scope to reduce the environmental impacts of food production systems. There is significant potential to recover carbon, nitrogen, and phosphorus resources while respecting effluent quality limits, even when the significant uncertainties inherent to wastewater systems are considered. This review article gives an overview of the environmental challenges we face, discussed within the framework of the planetary boundary, and highlights the impacts caused by the agri-food sector. This paper also presents a comprehensive review of the characteristics of FPWW and available technologies to recover carbon and nutrient resources from wastewater streams with a particular focus on bioprocesses. PSE research and modelling advances are discussed in this review. Based on this discussion, we conclude the article with future research directions.

Unveiling dioxin dynamics: A whole-process simulation study of municipal solid waste incineration

Theoretical research has explained the process of dioxin (DXN) formation in the municipal solid waste incineration (MSWI). This process includes the generation, adsorption, and emission of DXN. Actual DXN concentrations often significantly deviate from theoretical models. This discrepancy is influenced by several key factors: the type of integrated municipal solid waste (MSW) treatment process, the characteristics of the waste, and the operational controls. The progression of DXN generation, adsorption, and emission concentrations within the MSWI process remains unclear. This lack of clarity is especially pronounced when examining the accounting for the specific components of the MSW. To unravel the evolution of DXN, this article proposes a comprehensive numerical simulation model for the entire process of DXN concentration in an MSWI plant. The model is designed based on existing knowledge of MSW combustion and DXN mechanisms, leveraging FLIC and ASPEN simulation software. It incorporates six key stages to facilitate the DXN simulation: precipitation and formation, high-temperature pyrolysis, high-temperature gas-phase synthesis, low-temperature catalytic synthesis, adsorption on activated carbon, and emission to the atmosphere. Under both benchmark and multiple operating conditions, the simulated experiments confirm the effective representation of the evolution of DXN concentrations throughout the process. Consequently, this study presents a model designed to enhance the development of strategies aimed at reducing DXN emissions and to foster innovation in intelligent control technologies.

Conversion of waste polystyrene into valuable aromatic hydrocarbons via microwave-assisted pyrolysis

The prime objective of the current research work was to understand the role of microwave-assisted pyrolysis for the upgradation of expanded polystyrene (EPS) waste into valuable aromatic hydrocarbons. Ethyl acetate solvent was used to dissolve the EPS to enhance the homogeneous dispersion of EPS with susceptor particles. Biochar obtained from the pyrolysis was used as a susceptor. The design of experiments method was used to understand the role of microwave power (300 W, 450 W, and 600 W) and susceptor quantity (5 g, 10 g, and 15 g) in the pyrolysis process. The pyrolysis was conducted till the temperature reached up to 600 °C, and this temperature was achieved in the time interval of 14-38 min based on the experimental conditions. The obtained average heating rates varied in the range of 15 to 41 °C/min to attain the pyrolysis temperature. The EPS feed was converted into char (~ 2.5 wt.%), oil (51 to 60 wt.%), and gaseous (37 to 47 wt.%) products. The specific microwave energy (J/g) was calculated to know the energy requirement; it increased with an increase in susceptor quantity and microwave power, whereas specific microwave power (W/g) was a function of microwave power and increased from 15 to 30 W/g. The predicted values calculated using the model equations closely matched the actual values showing that the developed model equations via optimization had a good fit. The obtained pyrolysis oil physicochemical properties including viscosity (1 to 1.4 cP), density (990 to 1030 kg/m3), heating value (39 to 42 MJ/kg), and flash point (98 to 101 °C) were thoroughly analyzed. The pyrolysis oil was rich in aromatic hydrocarbons and it was predominantly composed of styrene, cyclopropyl methylbenzene, and alkylbenzene derivates.

A mini-review for identifying future directions in modelling heating values for sustainable waste management

Global estimations suggest energy content within municipal solid waste (MSW) is underutilized, compromising efforts to reduce fossil CO2 emissions and missing the opportunities for pursuing circular economy in energy consumption. The energy content of the MSW, represented by heating values (HVs), is a major determinant for the suitability of incinerating the waste for energy and managing waste flows. Literature reveals limitations in traditional statistical HV modelling approaches, which assume a linear and additive relationship between physiochemical properties of MSW samples and their HVs, as well as overlook the impact of non-combustible substances in MSW mixtures on energy harvest. Artificial intelligence (AI)-based models show promise but pose challenges in interpretation based on established combustion theories. From the variable selection perspectives, using MSW physical composition categories as explanatory variables neglects intra-category variations in energy contents while applying environmental or socio-economic factors emerges to address waste composition changes as society develops. The article contributes by showing to professionals and modellers that leveraging AI technology and incorporating societal and environmental factors are meaningful directions for advancing HV prediction in waste management. These approaches promise more precise evaluations of incinerating waste for energy and enhancing sustainable waste management practices.

Recent evolution in thermochemical transformation of municipal solid wastes to alternate fuels

The management of solid waste poses a worldwide obstacle in the pursuit of a sustainable society. This issue has intensified with the increase in waste production caused by rapid population expansion, industrialization, and urbanization. The continuously growing volume of municipal solid waste, particularly the substantial volume of organic waste, along with improper disposal practices, results in the release of greenhouse gases and other harmful airborne substances which simultaneously causes health risks and socioeconomic concerns. This article examines various waste-to-energy (energy production in the form of heat and electricity) concepts as well as waste-to-materials (various value-added materials including biofuel, biochemical, char, bio-oil, soil fertilizer, etc.) methods of converting municipal solid waste into environmentally friendly fuels, which appear to be economically feasible and attractive. It starts with a thorough analysis of the characteristics of municipal solid waste followed by the generation procedure. The study provides an overview of different thermochemical conversion methods including incineration, pyrolysis, co-pyrolysis, liquefaction, hydrothermal carbonization, gasification, combustion for transformation of municipal solid waste, and their recent advancement. The review comprehensively discussed the pros and cons of each method highlighting their strength, weakness, opportunities, and threats to transforming MSW. The current state of municipal solid waste management, including effective dumping and deviation, is comprehensively assessed, along with the prospects and challenges involved. Energy justice concepts and fuzzy logic tool is used to address the selection criteria for choosing the best waste treatment techniques. Moreover, several recommendations are offered to enhance the existing solid waste management system. This review could assist scholars, researchers, authorities, and stakeholders in making informed decisions regarding MSW management.

A New Paradigm on Waste-to-Energy Applying Hydrovoltaic Energy Harvesting Technology to Face Masks

The widespread use of single-use face masks during the recent epidemic has led to significant environmental challenges due to waste pollution. This study explores an innovative approach to address this issue by repurposing discarded face masks for hydrovoltaic energy harvesting. By coating the face masks with carbon black (CB) to enhance their hydrophilic properties, we developed mask-based hydrovoltaic power generators (MHPGs). These MHPGs were evaluated for their hydrovoltaic performance, revealing that different mask configurations and sizes affect their efficiency. The study found that MHPGs with smaller, more structured areas exhibited better energy output, with maximum open-circuit voltages (VOC) reaching up to 0.39 V and short-circuit currents (ISC) up to 65.6 μA. The integration of CB improved water absorption and transport, enhancing the hydrovoltaic performance. More specifically, MHPG-1 to MHPG-4, which represented different sizes and features, presented mean VOC values of 0.32, 0.17, 0.19 and 0.05 V, as well as mean ISC values of 16.57, 15.59, 47.43 and 3.02 μA, respectively. The findings highlight the feasibility of utilizing discarded masks in energy harvesting systems, offering both environmental benefits and a novel method for renewable energy generation. Therefore, this work provides a new paradigm for waste-to-energy (WTE) technologies and inspires further research into the use of unconventional waste materials for energy production.

First-principles study on the heterogeneous formation of environmentally persistent free radicals (EPFRs) over α-Fe2O3(0001) surface: Effect of oxygen vacancy

Metal oxides with oxygen vacancies have a significant impact on catalytic activity for the transformation of organic pollutants in waste-to-energy (WtE) incineration processes. This study aims to investigate the influence of hematite surface oxygen point defects on the formation of environmentally persistent free radicals (EPFRs) from phenolic compounds based on the first-principles calculations. Two oxygen-deficient conditions were considered: oxygen vacancies at the top surface and on the subsurface. Our simulations indicate that the adsorption strength of phenol on the α-Fe2O3(0001) surface is enhanced by the presence of oxygen vacancies. However, the presence of oxygen vacancies has a negative impact on the dissociation of the phenol molecule, particularly for the surface with a defective point at the top layer. Thermo-kinetic parameters were established over a temperature range of 300-1000 K, and lower reaction rate constants were observed for the scission of phenolic O-H bonds over the oxygen-deficient surfaces compared to the pristine surface. The negative effects caused by the oxygen-deficient conditions could be attributed to the local reduction of FeIII to FeII, which lower the oxidizing ability of surface reaction sites. The findings of this study provide us a promising approach to regulate the formation of EPFRs.

Techno-economic and environmental analysis of organic municipal solid waste for energy production

Addressing the critical conundrum of escalating municipal solid waste (MSW) and shrinking landfill spaces in urban areas, this research pioneers a sustainable approach for Bangladesh by exploring the potential of biogas production from MSW. Distinctly, it fills the research gap by providing a detailed techno-economic and environmental analysis of decentralized fixed-dome anaerobic digestion facilities in the urban context of Chittagong, Bangladesh, a domain previously underexplored. Our findings demonstrate the feasibility of converting MSW into a renewable energy source, offering an innovative solution that simultaneously tackles waste management and energy generation challenges. Each proposed plant showcases the capability to generate 536 m³ of biogas daily, sufficient to power a 50 kW gas engine and supply 44 households, thereby contributing significantly to urban waste reduction and CO2 emissions mitigation by approximately 500 tons monthly. The economic analysis reveals an attractive investment payback period of two years, underscoring the model's viability and its potential as a replicable framework for similar urban settings grappling with waste management crises. This study not only bridges a critical knowledge gap but also introduces a novel, sustainable waste-to-energy model, marking a pivotal step towards achieving energy security and environmental sustainability in developing nations.

Landfill leachate treatment using fungi and fungal enzymes: a review

Landfill leachate raises a huge risk to human health and the environment as it contains a high concentration of organic and inorganic contaminants, heavy metals, ammonia, and refractory substances. Among leachate treatment techniques, the biological methods are more environmentally benign and less expensive than the physical-chemical treatment methods. Over the last few years, fungal-based treatment processes have become popular due to their ability to produce powerful oxidative enzymes like peroxidases and laccases. Fungi have shown better removal efficiency in terms of color, ammonia, and COD. However, their use in the treatment of leachate is relatively recent and still needs to be investigated. This review article assesses the potential of fungi and fungal-derived enzymes in treating landfill leachate. The review also compares different enzymes involved in the fungal catabolism of organic pollutants and the enzyme degradation mechanisms. The effect of parameters like pH, temperature, contact time, dosage variation, heavy metals and ammonia are discussed. The paper also explores the reactor configuration used in the fungal treatment and the techniques used to improve leachate treatment efficacy, like pretreatment and fungi immobilisation. Finally, the review summarises the limitations and the future direction of work required to adapt the fungal application for leachate treatment on a large scale.

Waste-to-energy barriers and solutions for developing countries with limited water and energy resources

The environmental risks of conventional waste disposal methods, along with the resource and energy value of waste, have formed the foundation for waste-to-energy (WtE) technology. WtE systems that work on recovering energy present a suitable solution to generate energy and sustainably manage waste. This type of waste management system in the Middle East and North Africa (MENA) region is still considered underutilized as WtE technology is rarely used due to a lack of experience in their specific local conditions, lack of qualified competencies, and the absence of an appropriate regulatory and legislative structure. This study reviews the existing WtE policies and regulations, and it investigates the potential of WtE techniques in the MENA region. Moreover, sustainability in water consumption is critical; therefore, various water-conservation techniques were reviewed and considered when selecting regulatory actions. The radiative sky cooling technique was recommended to reduce water consumption. Barriers to implementing WtE and solutions for developing countries were presented to enable proper WtE implementation.

Electricity out of electronic trash: Triboelectric nanogenerators from discarded smartphone displays for biomechanical energy harvesting

In the context of escalating electronic waste (e-waste) generated by the rapid evolution of electronic devices, particularly smartphones/mobiles, the imperative for effective e-waste management to mitigate adverse environmental and health consequences has become increasingly apparent. Herein, novel mobile phone-based triboelectric nanogenerators (M-TENGs) are fabricated from discarded smartphone displays of eight different brands (B1-B8) for harvesting electrical energy. Analytical characterization techniques such as SEM and EDS are employed for morphological investigation. The tribopositivity and tribonegativity of the smartphone display layers are confirmed using the FTIR technique and test materials. The percentage tensile strength of the selected triboactive layers is measured to assess the mechanical durability. The electrical measurements are performed for all eight M-TENG devices, notably the device constructed from B8 smartphone display layers outperforms other brands by generating about three and five times higher voltage and current than the M-TENG device composed of B1 layers. Further, the optimized device is subjected to frequency, force, and stability tests, and also the impact of fluctuating humidity on the device performance is analyzed. Moreover, the M-TENG demonstrates its versatility by efficiently charging commercial electrolytic capacitors, powering LEDs, and effectively harvesting biomechanical energy. Thus, the present study represents a significant step towards mitigating the challenges posed by electronic smartphone waste disposal while simultaneously offering a viable pathway to harvest electricity and power a variety of applications.

In-depth analysis to develop a social marketing model to promote women's participation in waste segregation behaviour: A qualitative study

Waste separation is one of the key factors in managing solid waste and creating a healthy environment. Waste separation at source has always been associated with challenges. Therefore, this study was conducted to determine the perceptions of housewives and related parties regarding the factors that influence waste separation behaviour and to identify approaches to improve behaviour based on the social marketing framework. This study was conducted as a qualitative content analysis in Amol City in 2022. The data was collected through semi-structured individual interviews. A total of 25 housewives were selected as main participants and 5 stakeholders through purposive selection. The results of the study included lack of awareness of recyclable materials (product), personal, family and environmental barriers (price), lack of doorstep collection of dry waste (place), and lack of use of appropriate technology (promotion). The lack of financial resources, inappropriate political measures and the coronavirus pandemic were also the causes of this challenge. Most participants cited environmental and educational deficits as the main reason for not separating waste. It is possible to improve waste sorting behaviour at source through appropriate behavioural interventions at the individual, social and environmental levels. Researchers can use the results of this study to design, implement and evaluate waste segregation intervention programmes for housewives.

Sustainable waste management and waste-to-energy in the context of a circular economy through various waste management technologies

Inappropriate waste management is a considerable ecological risk, leading to detrimental effects on the soil, air, and water quality. It is imperative to address these concerns promptly to minimize the repercussions of solid waste on public health and the ecosystem. It is evident that the level of economic growth directly impacts waste generation. This study intends to use the life cycle assessment (LCA) technique to evaluate the environmental impacts of four alternative municipal solid waste (MSW) management scenarios in Peshawar City, Pakistan. The goal is to discover an option that is both sustainable and minimizes environmental damage. The study examined the system boundaries encompassing the collection and transportation of MSW, along with its processing and final disposal, employing composting, anaerobic digestion (AD), material recovery facilities (MRF), and landfill methods. Comprehensive field studies and an in-depth literature review provided the data regarding Peshawar's existing MSW management system and the proposed scenarios, all of which was inventoried in the OpenLCA 1.10.3 database. Following data collection, the CML-IA technique was employed to analyze the data, measuring the environmental footprint in terms of climate change potential, human toxicity, acidification potential, photochemical oxidation, and eutrophication. A sensitivity analysis was also performed to identify the influence of varying recycling rates on the environmental strain correlated with the proposed scenarios. The analysis results indicated that scenario S2, which combined composting, landfilling, and MRF, exhibited the least environmental impact compared to the other considered scenarios. Furthermore, the sensitivity analysis reflected an inverse correlation between alterations in the recycling rate and the total environmental impact. To counter the environmental problems arising from waste generation, it is essential to incorporate principles of the circular economy into the MSW management approach.

Sustainability assessment of biofuel and value-added product from organic fraction of municipal solid waste

The current study aims to examine the techno-economic and environmental assessment of biorefinery development within a circular bioeconomy context by using an organic fraction of municipal solid waste (OFMSW) by extraction of lipids, carbohydrates, and proteins with 98, 51 and 62 % by mass of conversion efficiency and yield recovery, and value-added fractions production as well. Fatty acid methyl ester (biodiesel) and glycerol (biofuel) were produced by applying transesterification process, and the remaining biomass was converted into biocrude oil by thermal liquefication. The biorefinery using 613 kg of OFMSW produced biodiesel, glycerol, and bioethanol with 126 litter, 14.3 kg, and 172 litter respectively, as well as value-added fractions, such as biocrude oil with 78 kg. The environmental impact was assessed using the life cycle assessment (LCA) framework, ReCiPe2016 Mid-point (H) approach, through 18 different environmental categories. The key findings elucidate that Terrestrial ecotoxicity, Climate change, Fossil depletion and Human toxicity were the main impact categories which are potentially contributed 9.81E+02 kg 1,4-DB eq., 1.43E+03 kg CO2 eq., 2.04E+02 kg oil eq., and 8.08E+01 kg 1,4-DB eq. The normalization (person per equivalent) analysis revealed that only categories of resource reduction (fossil and metal depletion) are the key contributors to environmental degradation. The biorefinery system's total revenue was estimated at USD 6.817,509 million annually. The calculated revenue was USD 0.026 million daily in a shift of 8 h. The Net present worth (NPW) was calculated at USD 499.97 million by assuming a discount factor of 10 % and inflation rate of 5 % for 15 years. The project is considered feasible by demonstrating 7.15 payback year. This research showcased the efficient portrayal of the biorefinery system and succinctly conveyed the significant circular bioeconomy for a greener future. Thus, it could be helpful to the stakeholder's context towards techno-economic and environmental evaluation.

Global perspective of municipal solid waste and landfill leachate: generation, composition, eco-toxicity, and sustainable management strategies

Globally, more than 2 billion tonnes of municipal solid waste (MSW) are generated each year, with that amount anticipated to reach around 3.5 billion tonnes by 2050. On a worldwide scale, food and green waste contribute the major proportion of MSW, which accounts for 44% of global waste, followed by recycling waste (38%), which includes plastic, glass, cardboard, and paper, and 18% of other materials. Population growth, urbanization, and industrial expansion are the principal drivers of the ever-increasing production of MSW across the world. Among the different practices employed for the management of waste, landfill disposal has been the most popular and easiest method across the world. Waste management practices differ significantly depending on the income level. In high-income nations, only 2% of waste is dumped, whereas in low-income nations, approximately 93% of waste is burned or dumped. However, the unscientific disposal of waste in landfills causes the generation of gases, heat, and leachate and results in a variety of ecotoxicological problems, including global warming, water pollution, fire hazards, and health effects that are hazardous to both the environment and public health. Therefore, sustainable management of MSW and landfill leachate is critical, necessitating the use of more advanced techniques to lessen waste production and maximize recycling to assure environmental sustainability. The present review provides an updated overview of the global perspective of municipal waste generation, composition, landfill heat and leachate formation, and ecotoxicological effects, and also discusses integrated-waste management approaches for the sustainable management of municipal waste and landfill leachate.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Municipal solid waste management instruments that influence the use of the refuse as fuel in developing countries: A critical review

Landfills are the destination of most of the refuse generated whereas composting, material recycling, and Waste-to-Energy (WtE) technologies are not commonly employed in developing countries. However, the destination for energy purposes could be supplied with this refuse, improving the viability of energy use. Thus, this article raises some questions to identify aspects that could encourage its use as refuse-derived fuel (RDF) in these countries. Among them, does environmental education affect the municipal solid waste (MSW) source separation with emphasis on a destination? Can selective collection and extended producer responsibility (EPR) affect the MSW for energy recovery? Is there competition between the recycling market and the energy market for RDF? A systematic review of the literature was conducted to gather data and provide answers to such questions. This enabled to observe that EPR, selective collect expansion and source separation influence the quantity and quality of waste sent for energy use. Both internal and external factors impact on source separation. Additionally, there is evidence to support that despite several studies showing their technical, economic, environmental and social viability, the methods of energy usage of the refuse still need to improve their deployment in developing countries. In addition to identifying the main research gaps to be filled in future studies, the article also identified the instruments of MSW management that are to be applied in developing countries to divert recyclable and organic waste from landfill.

Evaluating the impact of China's MSW sorting pilot policy on urban sustainable development: Empirical evidence from 95 cities

The escalating challenge of municipal solid waste (MSW) critically tests the sustainable development capacities of urban centers. In response, China initiated pilot policies in 2017 aimed at bolstering MSW management. The effectiveness of these initiatives, however, necessitates empirical scrutiny. This study leverages panel data spanning 95 cities at the prefectural level or higher, covering the period from 2006 to 2020, to assess the impact of the MSW sorting pilot policy on urban sustainable development using a difference-in-differences approach. The research found that the MSW sorting pilot policy has significantly increased the processing volume of MSW, thereby enhancing the sustainable development capabilities of cities. Further, the study identifies augmented fixed asset investments as a key mechanism through which pilot cities have enhanced their MSW management capabilities. Notably, the policy's stimulative effects are more pronounced in less densely populated and economically lagging regions. These findings provide critical insights for developing nations in shaping MSW sorting strategies and advancing urban sustainability.

Strategies of managing solid waste and energy recovery for a developing country - A review

Solid waste is considered one of the major pollutants of both water and surface worldwide. The growing global population, urban expansion, and industrial growth are the main reasons for solid waste generation. This has become a major challenge with both regional and worldwide consequences. The yearly generation of municipal solid wastes around the world is 2.01 BT (billion tons) among which about 33 % are not ecologically handled. To address this, proper solid waste management, especially recycling waste products, is crucial to achieving sustainability. High-income countries are able to recycle 51 % of their waste, while low-income countries only recycle 16 % of their waste. Inadequate solid waste management practices can only compound environmental and social problems. To handle these issues thermochemical and biochemical methods are used to convert solid waste to energy. Thermochemical method is suitable for developing countries though it is energy extensive. This review provides a detailed analysis of developing countries' solid waste management and energy recovery. It explores energy recovery technologies, including thermochemical and biochemical waste conversion processes.

Culture-based and culture-independent approach for the study of the methanogens and obligate anaerobes from different landfill sites

The landfill is a cheap way of solid waste management in developing countries. The majority of landfills are non-sanitary and work as open garbage dumping sites and pose threats to public and environmental health. Therefore, an in-depth understanding of the chemistry and microbiology of landfills is imperative to develop the right policies for landfill management. In the current study, we investigated the chemistry and microbiology of three Indian landfill sites using culture-based and culture-independent molecular approaches. Our data indicate that the nature of landfills varies from site to site in terms of chemistry, pollutants, and pathogens. We also enriched and cultivated three methanogens using an optimized medium and constructed two high-quality draft genomes from enriched microbiomes using metagenome-assembled genome approaches. The phylogenomic study of one draft genome showed the highest 93% sequence similarity with members of Methanomassiliicoccaceae and was always enriched with Acholoplasma and Anaerohalosphaera lusitana. Despite all the efforts, we did not isolate it in pure culture and hypothesized that for the cultivation of some not-yet-cultured methanogen, the presence of other organisms plays an important role, and their syntrophic interaction must be discerned for its successful cultivation in the future. Co-cultivation of amino acid-degrading organisms indicates that their co-culture can assist in boosting the growth of methanogens. In addition, our data indicated that landfill leachate contains a heavy load of pollutants and treatment is a must before discharge in nature or use in irrigation or biofertilizer.

Global trends of waste-to-energy (WtE) technologies in carbon neutral perspective: Bibliometric analysis

Waste-to-energy (WtE) technology is at the forefront of low-carbon municipal solid waste (MSW) treatment. MSW has been favoured by researchers in recent years due to its high potential to dispose of resources with WtE technology, which contributes to the carbon neutrality goal. However, there is a lack of research that integrates MSW WtE treatment from a global perspective and explores its future direction. Bibliometric methods are widely used because of their advantages in qualitative and quantitative literature information analysis. A comprehensive search was conducted in the Web of Science (WOS) Core Collection database, covering the period from 1990-2022, resulting in the collection of 702 articles. Subsequently, bibliometric software such as CiteSpace, VOSviewer, and Bibliometrix, were jointly employed for co-occurrence, co-citation, and cluster analyses, providing an in-depth qualitative and quantitative analysis of the research hotspots and development trends of WtE technology for MSW treatment. The research findings indicate a rapid growth in studies on carbon emission reduction through WtE technology for MSW treatment since 2015, with these related articles accounting for 50% of articles. Globally, China, the United States, Italy, and other countries were active research regions, with Chinese research institutions making the largest contributions. However, contributions from developing countries are limited. Furthermore, this study systematically elaborates on the research hotspots in this field. Finally, this study identified some frontier research hotspots and directions. Research on WtE technology primarily focuses on technological methods and policy management, particularly from the carbon neutrality perspective, emphasis WtE technology sustainability in reducing carbon emissions and achieving carbon neutrality goals. Promoting the use of assisted decision-making models in the MSW management process, and focusing on the conversion of food waste into valuable energy. It is hoped that these research directions will provide new ideas for the balanced and rapid development of WtE technology.

Implementation of anaerobic digestion for valorizing the organic fraction of municipal solid waste in developing countries: Technical insights from a systematic review

Anaerobic digestion (AD) as a waste management strategy for the organic fraction of municipal waste (OFMSW) has received attention in developed countries for several decades, leading to the development of large-scale plants. In contrast, AD of OFMSW has only recently drawn attention in developing countries. This systematic review was carried out to investigate the implementation of AD to treat the OFMSW in developing countries, focusing on assessing pilot and full-scale AD plants reported in the last ten years. Studies that met the selection criteria were analyzed and data regarding operating parameters, feedstock characteristics, and biogas, digestate, and energy production were extracted. As outlined in this systematic review, AD plants located in developing countries are mostly one-stage mesophilic systems that treat OFMSW via mono-digestion, almost exclusively with the aim of producing electrical energy. Based on the analysis done throughout this systematic review, it was noted that there is a large difference in the maturity level of AD systems between developing and developed countries, mainly due to the economic capacity of developed countries to invest in sustainable waste management systems. However, the number of AD plants reported in scientific papers is significantly lower than the number of installed AD systems. Research articles regarding large-scale implementation of AD to treat OFMSW in developed countries were analyzed and compared with developing countries. This comparison identified practices used in plants in developed countries that could be utilized in the large-scale implementation and success of AD in developing countries. These practices include exploiting potential products with high market-values, forming partnerships with local industries to use industrial wastes as co-substrates, and exploring different biological and physical pretreatment technologies. Additionally, the analysis of capital and operational costs of AD plants showed that costs tend to be higher for developing countries due to their need to import of materials and equipment from developed countries. Technical, economical, and political challenges for the implementation of AD at a large-scale in developing countries are highlighted.

Unlocking integrated waste biorefinery approach by predicting calorific value of waste biomass

The current study analyzed the high heating values (HHVs) of various waste biomass materials intending to the effective management and more sustainable consumption of waste as clean energy source. Various biomass waste samples including date leaves, date branches, coconut leaves, grass, cooked macaroni, salad, fruit and vegetable peels, vegetable scraps, cooked food waste, paper waste, tea waste, and cardboard were characterized for proximate analysis. The results revealed that all the waste biomass were rich in organic matter (OM). The total OM for all waste biomass ranged from 79.39% to 98.17%. Likewise, the results showed that all the waste biomass resulted in lower ash content and high fixed carbon content associated with high fuel quality. Based on proximate analysis, various empirical equations (HHV=28.296-0.2887(A)-656.2/VM, HHV=18.297-0.4128(A)+35.8/FC and HHV=22.3418-0.1136(FC)-0.3983(A)) have been tested to predict HHVs. It was observed that the heterogeneous nature of various biomass waste considerably affects the HHVs and hence has different fuel characteristics. Similarly, the HHVs of waste biomass were also determined experimentally using the bomb calorimeter, and it was observed that among all the selected waste biomass, the highest HHVs (21.19 MJ kg-1) resulted in cooked food waste followed by cooked macaroni (20.25 MJ kg-1). The comparison revealed that experimental HHVs for the selected waste biomass were slightly deviated from the predicted HHVs. Based on HHVs, various thermochemical and biochemical technologies were critically overviewed to assess the suitability of waste biomass to energy products. It has been emphasized that valorizing waste-to-energy technologies provides the dual benefits of sustainable management and production of cleaner energy to reduce fossil fuels dependency. However, the key bottleneck in commercializing waste-to-energy systems requires proper waste collection, sorting, and continuous feedstock supply. Moreover, related stakeholders should be involved in designing and executing the decision-making process to facilitate the global recognition of waste biorefinery concept.

Restructuring Co-CoOx Interface with Titration Rate in Co/Nb-CeO2 Catalysts for Higher Water-Gas Shift Performance

H2 production via water-gas shift reaction (WGS) is an important process and applied widely. Cobalt-modified CeO2 are promising catalysts for WGS reaction. Herein, a series of Co/Nb-CeO2 catalysts were prepared by varying the rate of precipitant addition during the coprecipitation method and examined for hydrogen generation through WGS reaction. The rates of precipitant addition were 1, 5, 15, and 25 mL/min. We obtained ceria supported cobalt catalysts with different sizes and morphology such as 3, 8 nm nanoclusters, 30 nm cubic nanoparticles, and 50 nm hexagonal nanoparticles. The well dispersed small cobalt particles in Co/Nb-CeO2 that was prepared at 5 mL/min titration rate exhibit strong interaction between cobalt oxide and CeO2 that retards the reduction of CoOx producing Co-CoOx pairs. In contrast, 1-Co/Nb-CeO2 and 25-Co/Nb-CeO2 result in bigger and aggregated Co particles, resulting in fewer interfaces with CeO2. The Co0, Coδ+, Ce3+, and Ov species are responsible for improved reducibility in Co/Nb-CeO2 catalysts and were quantitively measured using XPS, XAS, and Raman spectroscopy. The Co-CoOx interface assists dissociation of the H2O molecule; CO oxidation requires low activation energy and realizes a high turnover frequency of 9.8 s-1. The 5-Co/Nb-CeO2 catalyst achieved thermodynamic equilibrium equivalent CO conversion with efficient H2 production during WGS reaction at a gas hourly space velocity of 315,282 h-1. Successively, the 5-Co/Nb-CeO2 catalyst exhibited stable performance for straight 168 h attributed to stable CO-Coδ+ intermediate formation, achieving efficient inhibition of typical CO chemistry over the Co metal, suitable for hydrogen generation from waste derived synthesis gas.

Upgrading of solid recovered fuel (SRF) by dechlorination and catalytic pyrolysis over nanocrystalline ZSM-5 zeolite

Globally increasing concern related to municipal solid waste generation is encouraging research efforts on developing alternative routes to valorize mixed refused wastes. In this way, catalytic pyrolysis is emerging as an interesting and efficient technology due to its great flexibility in terms of feedstock. In the current work, upgrading of a Solid Recovered Fuel (SRF) has been investigated by catalytic pyrolysis over nanocrystalline ZSM-5 zeolite (n-ZSM-5), paying special attention to dechlorination effects due to the high Cl content of the raw waste. Thus, pretreatment of the SRF by water washing and mild thermal processing allows for a significant reduction of the Cl concentration. Regarding the catalytic pyrolysis step, the best conditions correspond with a temperature of 400 °C in the catalyst bed and 0.50 catalyst/SRF mass ratio, which lead to ca. 30 wt% oil yield (rich in aromatic hydrocarbons) together with about 40 wt% gas yield (rich in C3-C4 olefins). Accordingly, these products could find use as raw chemicals or for the production of advanced fuels. In addition, zeolite reutilization has been tested for several cycles, denoting a progressive modification of the products distribution because of coke deposition. However, an almost total recovery of the n-ZSM-5 zeolite catalytic performance is achieved after regeneration by air calcination, affording the production of an oil fraction with a Cl content as low as 40 ppm.

Multi-objective optimization and parametric study of a hybrid waste gasification system integrated with reverse osmosis desalination

The increasing population has created two fundamental issues on the islands (in this case, Kish Island): an expansion in waste production and handling and a rise in the need for freshwater for daily consumption. Waste gasification can be used to reduce waste and generate energy. Sea salt water can be converted into drinkable freshwater using energy. This article describes a computational code using a combination of EES (Engineering Equation Solver) and MATLAB software for a hybrid cycle that includes waste gasification and reverse osmosis to generate freshwater and power. Kish Island waste data was carefully collected onsite. An exergy evaluation has been conducted to verify the cycle's irreversibility. Lastly, optimization has been performed to identify the best operation mode. In terms of irreversibility, a gasifier is far more irreversible than any other type of plant equipment. Based on the parametric analysis, salt water and waste flow significantly impact freshwater production. Approximately 20,000 m3/day are consumed on Kish Island each day, so if the entire production power of the steam turbine is used in the reverse osmosis high-pressure pump, 2860 m3/day can be obtained each day (14% of the required amount).

A mini review on the main challenges of implementing mechanical biological treatment plants for municipal solid waste in the Latin America region: Learning from the experiences of developed countries

Most of the municipal solid waste (MSW) generated in the Latin America (LATAM) region is currently disposed of in landfills and dumpsites, which results in many negative environmental impacts. Mechanical biological treatment (MBT) is a strategy that combines the mechanical separation of recoverable materials with the biological stabilization of organic matter. MBT plants have proven to be a good alternative for the management of MSW and have been successfully implemented in developed countries for more than 30 years. However, the efficient introduction of these facilities in developing countries, such as those in the LATAM region, requires further feasibility studies. Therefore, this mini review seeks to offer significant insights into the main challenges that must be overcome to facilitate the implementation and operation of MBT plants, considering the unique technological, sociocultural, economic and political context of the LATAM region, through a comparison of the reported experiences of MBT plants in more developed countries with those in the LATAM region. The analysis herein indicates that key actions for the successful operation of MBT plants in the LATAM region include both the implementation of source separation as well as selective collection practices. Moreover, this work shows that other factors, like the establishment of valorization markets with safe working conditions for informal collectors, the development of intermunicipal cooperation schemes and the enforcement of strong regulatory frameworks for waste disposal specifications, are important contextual factors that have allowed the efficient operation of MBT plants in developed countries. Although the implementation of many of these practices will be challenging, such measures are necessary to increase the sustainability of MSW treatment practices in the LATAM region.

Mapping and visualizing of research output on waste management and green technology: A bibliometric review of literature

The transition to a circular economy (CE) and environmental protection highly depends on waste management (WM) and green technology (GT). The purpose of this study is to examine the past two decades of WM and GT research to identify the most significant advancements and potential future research areas. Bibliometrics content analysis and text mining were utilized to resolve the subsequent issues: Has WM and GT research developed over time in the CE industry? Does WM and GT research have a clearly defined purpose? How do you foresee the future of WM and GT research in the context of CE evolving? Consequently, 1149 journal articles from the Scopus database were used to create and evaluate bibliometric networks. Therefore, five significant CE-related issues requiring additional research were identified: The first category is bio-based WM, followed by CE transition, GT, ecological impacts, municipal solid WM and lifecycle assessment, and finally, bio-based WM. Future research topics and a tool for the CE transition may be impacted by the investigation of inclusive WM systems, GT practices and their defining highlight patterns (which aim to minimalize waste generation). Future research goals include reducing waste and implementing WM into the CE framework.

Perspectives on Thermochemical Recycling of End-of-Life Plastic Wastes to Alternative Fuels

Due to its resistance to natural degradation and decomposition, plastic debris perseveres in the environment for centuries. As a lucrative material for packing industries and consumer products, plastics have become one of the major components of municipal solid waste today. The recycling of plastics is becoming difficult due to a lack of resource recovery facilities and a lack of efficient technologies to separate plastics from mixed solid waste streams. This has made oceans the hotspot for the dispersion and accumulation of plastic residues beyond landfills. This article reviews the sources, geographical occurrence, characteristics and recyclability of different types of plastic waste. This article presents a comprehensive summary of promising thermochemical technologies, such as pyrolysis, liquefaction and gasification, for the conversion of single-use plastic wastes to clean fuels. The operating principles, drivers and barriers for plastic-to-fuel technologies via pyrolysis (non-catalytic, catalytic, microwave and plasma), as well as liquefaction and gasification, are thoroughly discussed. Thermochemical co-processing of plastics with other organic waste biomass to produce high-quality fuel and energy products is also elaborated upon. Through this state-of-the-art review, it is suggested that, by investing in the research and development of thermochemical recycling technologies, one of the most pragmatic issues today, i.e., plastics waste management, can be sustainably addressed with a greater worldwide impact.

Efficient conversion of waste-to-SNG via hybrid renewable energy systems for circular economy: Process design, energy, and environmental analysis

Developing an efficient and environment-friendly route for waste valorization is extremely significant in accelerating the transition toward a circular economy. A novel waste-to-synthetic natural gas (SNG) conversion process comprising hybrid renewable energy systems is proposed for this purpose. This includes thermochemical waste conversion and power-to-gas technologies for simultaneous waste utilization and renewable energy storage applications. The energy and environmental performances of the proposed waste-to-SNG plant are assessed and optimized. Results indicated that the implementation of a thermal pretreatment unit prior to the plasma gasification (two-step) is beneficial to improve the yield of hydrogen in the syngas, thereby leading to less renewable energy requirement for green hydrogen production used in the methanation process. This also enhances SNG yield by a factor of 30% as compared to the case without thermal pretreatment (one-step). The overall energy efficiency (OE) of the proposed waste-to-SNG plant is in the range of 61.36-77.73%, while the energy return on investment (EROI) ranges between 2.66 and 6.11. Most environmental impacts are mainly contributed by the indirect carbon emissions as a consequence of the power requirement for thermal pretreatment, plasma gasifier, and auxiliary equipment. The value of specific electricity consumption for SNG production of the treated RDF exhibits 1.70-9.25 % less than that of raw RDF when the pretreatment temperature is less than 300 °C. The OE of the system declines by 4.52% when 50 wt% of biomass is mixed in the fuel, whereas an enhancement of 18.33% in EROI and a reduction of 16.19% in specific CO₂ emissions are obtained.

Municipal solid waste treatment for bioenergy and resource production: Potential technologies, techno-economic-environmental aspects and implications of membrane-based recovery

World estimated municipal solid waste generating at an alarming rate and its disposal is a severe concern of today's world. It is equivalent to 0.79 kg/d per person footprint and causing climate change; health hazards and other environmental issues which need attention on an urgent basis. Waste to energy (WTE) considers as an alternative renewable energy potential to recover energy from waste and reduce the global waste problems. WTE reduced the burden on fossil fuels for energy generation, waste volumes, environmental, and greenhouse gases emissions. This critical review aims to evaluate the source of solid waste generation and the possible routes of waste management such as biological landfill and thermal treatment (Incineration, pyrolysis, and gasification). Moreover, a comparative evaluation of different technologies was reviewed in terms of economic and environmental aspects along with their limitations and advantages. Critical literature revealed that gasification seemed to be the efficient route and environmentally sustainable. In addition, a framework for the gasification process, gasifier types, and selection of gasifiers for MSW was presented. The country-wise solutions recommendation was proposed for solid waste management with the least impact on the environment. Furthermore, key issues and potential perspectives that require urgent attention to facilitate global penetration are highlighted. Finally, practical implications of membrane and comparison membrane-based separation technology with other conventional technologies to recover bioenergy and resources were discussed. It is expected that this study will lead towards practical solution for future advancement in terms of economic and environmental concerns, and also provide economic feasibility and practical implications for global penetration.

Characterization of dumpsite waste of different ages in Ghana

Open dumping of municipal solid waste is a common practice in developing countries including Ghana and it creates major problems in many municipalities and towns in the countries, and therefore, the dumpsites need to be reclaimed or decommissioned after years of dumping. However, it becomes challenging to infer from the results of studies from other part of the world for dumpsites in Ghana since they may have different waste characteristics. Therefore, this study sought to characterize the dumpsite waste with different age groups from urban city and small town to ascertain the impacts of aging of deposited waste on waste fractions, it also assessed the waste components at different depths within the same and different age groups in both small-town and urban dumpsites; for waste deposited more than 5 years (Zone A), 2-4 years (Zone B), and less than 6 months (Zone C) in Bono region, Ghana. Waste (100 kg) was taken at surface, 0.5 m, 1.0 m and 1.5 m and reduced to 50 kg using coning and quartering method; dried, segregated and analyzed. Plastics waste (24.5-28.1%) increased with age at urban, and increased (5.4-8.5%) with depth at small town dumpsite. Plastic waste was second to Decomposed organic matter (DOM) at both dumpsites. The metal (<1.0%) at all depths in all age groups for both sites. DOM fine particle sizes (FPS) decreased with depth, 26.8% (surface waste) and 14.4% (1.5 m depth), at both dumpsites. Statistically significant effects of age on plastics, metal, DOM-CPS, DOM-FPS (p < 0.05) at urban dumpsite. However, at small town dumpsite, effect of age was statistically significant on only DOM-CPS and DOM-FPS (p < 0.05). The pH, EC, and TDS for both dumpsites decreased with increasing age, and increased with depth. The study provides relevant scientific findings for stakeholders to develop policy framework for dumpsite decommissioning or reclamation.

Microwave-assisted pyrolysis of pine sawdust: Process modelling, performance optimization and economic evaluation for bioenergy recovery

This study aims at optimizing the process conditions to extract maximum yields of bio-oil from pine sawdust using microwave-assisted pyrolysis (MAP). Aspen Plus® V11 was used to model the thermochemical conversion of pine sawdust to pyrolysis products, and response surface methodology (RSM) based on a central composite design (CCD) was employed in the optimization of the process parameters. The mutual effects of pyrolysis temperature and reactor pressure on the product distribution were investigated. The findings have shown that the optimal operating conditions for producing the highest amount of bio-oil (65.8 wt%) were achieved at 550 °C and 1 atm. The product distribution of the simulated model was more significantly influenced by linear and quadratic terms of the reaction temperature. In addition, a high determination coefficient (R² = 0.9883) was obtained for the developed quadratic model. A set of three published experimental results acquired under circumstances comparable to the simulations' operating limitations were used to further validate the simulation results. The process’s economic viability was assessed in order to establish the bio-oil minimum selling price (MSP). A MSP of $1.14/L of liquid bio-oil was evaluated. An economic sensitivity analysis has shown that the annual fuel yield, required rate of return, annual income tax, annual operating costs and initial capital investment have a substantial impact on the MSP of bio-oil. It was inferred that using the optimized process parameters may improve the process' competitiveness on an industrial scale due to its better product yields and improved sustainability in biorefineries, as well as assure waste reduction.

Microbial Enrichment Techniques on Syngas and CO2 Targeting Production of Higher Acids and Alcohols

(1) Background: Microbial conversion of gaseous molecules, such as CO2, CO and H2, to valuable compounds, has come to the forefront since the beginning of the 21st century due to increasing environmental concerns and the necessity to develop alternative technologies that contribute to a fast transition to a more sustainable era. Research efforts so far have focused on C1–C2 molecules, i.e., ethanol and methane, while interest in molecules with higher carbon atoms has also started to emerge. Research efforts have already started to pay off, and industrial installments on ethanol production from steel-mill off-gases as well as methane production from the CO2 generated in biogas plants are a reality. (2) Methodology: The present study addresses C4–C6 acids and butanol as target molecules and responds to how the inherent metabolic potential of mixed microbial consortia could be revealed and exploited based on the application of different enrichment methods (3) Results and Conclusions: In most of the enrichment series, the yield of C4–C6 acids was enhanced with supplementation of acetic acid and ethanol together with the gas substrates, resulting in a maximum of 43 and 68% (e-mol basis) for butyric and caproic acid, respectively. Butanol formation was also enhanced, to a lesser degree though and up to 9% (e-mol basis). Furthermore, the microbial community exhibited significant shifts depending on the enrichment conditions applied, implying that a more profound microbial analysis on the species level taxonomy combined with the development of minimal co-cultures could set the basis for discovering new microbial co-cultures and/or co-culturing schemes.

Effects of perceived stress on public acceptance of waste incineration projects: evidence from three cities in China

Public acceptance is important for the provision of potentially hazardous facilities and may be affected by many factors such as perceived risk/benefit/stress/fairness and public trust. In this study, the underlying mechanism behind the influence of perceived stress on public acceptance of waste-to-energy (WTE) incinerators was explored by structural equation modeling of a face-to-face questionnaire survey of 1066 urban residents in three regional central cities in China. The results indicate that, firstly, the perceived stress of the laypeople has an impact on their acceptance by influencing risk/fairness they perceived and public trust. Secondly, the paths of influence of individual perceptions on acceptance differ between cities with different economic, cultural, and social characteristics. Perceived stress mainly affects public acceptance through perceived risk in the eastern residents while perceived stress mainly affects public acceptance through public trust in the western residents. The findings clarify the theoretical role of perceived stress in shaping laypeople's acceptance of potentially hazardous facilities which are of value for both governments and owners in siting potentially hazardous facilities.

Evaluation of methane generation rate and energy recovery potential of municipal solid waste using anaerobic digestion and landfilling: A case study of Dhanbad, India

In this study, two most common biological waste to energy conversion techniques have been analysed and compared on the basis of methane generation and energy recovery potential. The biogas generation potential has been estimated using anaerobic co-digestion experiment. The main substrate used for this study was food waste, while cow dung and anaerobic digester sludge were used as co-digestion substrates. Food waste was used because of its maximum composition (36% of total wastes) in the study area (Dhanbad city, India) with high biogas generation potential. Cow dung acted as a natural buffer, while anaerobic digester sludge was a source of active inoculum. Based on the maximum biogas yield of 402 mL g^-1 VS and annual food waste generation rate in the study area, the energy recovery potential using anaerobic digestion was estimated to be 6.59 × 10⁶ kWh year^-1. Presently, the wastes in the mixed form are being dumped on a large abandoned land with an approximate area of 93 ha in the outskirts of Dhanbad city in an uncontrolled manner. The annual landfill gas generation from the existing landfill has been estimated using Landfill Gas Emissions Model (LandGEM) based on the waste characteristics, anticipated landfill life and other region-specific parameters of the present study area. The maximum electrical energy recovery potential of 44.62 × 10⁵ kWh from landfill gas has been estimated for the year 2041. Although, the results are based on the waste generation and characteristics of Dhanbad city, the comparison methodology can be applied to other cities.

To dream or not to dream in Havana: multi-criteria decision-making for material and energy recovery from municipal solid wastes

Currently, solid waste management strategies in Havana are outdated. This paper aimed to select the most suitable alternative for integrating material recovery facilities (MRF) with waste-to-energy technologies in the city of Havana, Cuba. Seven scenarios were considered: combustion, gasification, and hydrothermal carbonization (HTC) with and without carbon capture, and anaerobic digestion (AD). The selection was based on environmental, techno-economic, and social parameters using an analytic hierarchy process (AHP) as a multi-criteria decision-making tool (MCDM). The MCDM-AHP accounted for qualitative criteria (based on experts' judgments) and quantitative (based on Aspen Plus simulation models). From the MRF, 63% of the input recyclable materials were recovered, representing an energy saving of 256 kW-h/t_MSW. The AHP results showed that environmental criteria had the highest priority, resulting in ~63% and ~73% higher than social and techno-economic criteria, respectively. Likewise, from the techno-economic, environmental, and social sub-criteria analysis, investment risk, pollution, and work safety had the major concern compared with the other sub-criteria levels. Overall, MRF+AD was the most suitable scenario (21% preference) for treating Havana's municipal solid waste (MSW), followed by combustion and gasification with carbon capture, respectively. This study confirms that AD is a preference option for emerging economies like Cuba, mainly due to low environmental pollution, high social acceptance, and financial stability in the long term.

Sulfur-Resistant CeO2-Supported Pt Catalyst for Waste-to-Hydrogen: Effect of Catalyst Synthesis Method

To improve the sulfur tolerance of CeO2-supported Pt catalysts for water gas shift (WGS) using waste-derived synthesis gas, we investigated the effect of synthesis methods on the physicochemical properties of the catalysts. The Pt catalysts using CeO2 as a support were synthesized in various pathways (i.e., incipient wetness impregnation, sol-gel, hydrothermal, and co-precipitation methods). The prepared samples were then evaluated in the WGS reaction with 500 ppm H2S. Among the prepared catalysts, the Pt-based catalyst prepared by incipient wetness impregnation showed the highest catalytic activity and sulfur tolerance due to the standout factors such as a high oxygen-storage capacity and active metal dispersion. The active metal dispersion and oxygen-storage capacity of the catalyst showed a correlation with the catalytic performance and the sulfur tolerance.

Emerging innovations for sustainable production of bioethanol and other mercantile products from circular economy perspective

Biogenic municipal solid waste (BMSW) and food waste (FW) with high energy density are ready to tap renewable resources for industrial scale ethanol refinery foreseen for establishing bio-based society. Circular economy has occupied limelight in the domain of renewable energy and sustainable chemicals production. The present review highlights the importance of BMSW/FW as newer feed reserves that can cater as parent molecules for an array of high-visibility industrial products along with bioethanol upon implementing a judicious closed-cascade mass-flow mechanism enabling ultimate feed and waste stream valorisation. Though these organics are attractive resources their true potential for energy production has not been quantified yet owing to their heterogeneous composition and associated technical challenges thus pushing waste refinery and industrial symbiosis concepts to backseat. To accelerate this industrial vision, the novel bioprocessing strategies for enhanced and low-cost production of bioethanol from BMSW/FW along with other commercially imperative product portfolio have been discussed.

The face behind the Covid-19 mask - A comprehensive review

The threat of epidemic outbreaks like SARS-CoV-2 is growing owing to the exponential growth of the global population and the continual increase in human mobility. Personal protection against viral infections was enforced using ambient air filters, face masks, and other respiratory protective equipment. Available facemasks feature considerable variation in efficacy, materials usage and characteristic properties. Despite their widespread use and importance, face masks pose major potential threats due to the uncontrolled manufacture and disposal techniques. Improper solid waste management enables viral propagation and increases the volume of associated biomedical waste at an alarming rate. Polymers used in single-use face masks include a spectrum of chemical constituents: plasticisers and flame retardants leading to health-related issues over time. Despite ample research in this field, the efficacy of personal protective equipment and its impact post-disposal is yet to be explored satisfactorily. The following review assimilates information on the different forms of personal protective equipment currently in use. Proper waste management techniques pertaining to such special wastes have also been discussed. The study features a holistic overview of innovations made in face masks and their corresponding impact on human health and environment. Strategies with SDG3 and SDG12, outlining safe and proper disposal of solid waste, have also been discussed. Furthermore, employing the CFD paradigm, a 3D model of a face mask was created based on fluid flow during breathing techniques. Lastly, the review concludes with possible future advancements and promising research avenues in personal protective equipment.

Waste management and green technology: future trends in circular economy leading towards environmental sustainability

The effective treatment of waste to be used as a resource in future has a major role in achieving environmental sustainability and moving towards circular economy. The current research is aimed to provide in-depth detail regarding prominent trends and research themes, evolution, future research orientation, main characteristics, and mapping of research publications on waste management, technological innovation in circular economy domain from the year 2000 to 2021. Different analyses including text mining and bibliometric and content analyses were applied to answer the research question and provide the details on aforementioned variables. From the bibliometric analyses, a total of 1118 articles were drawn out from the Scopus database to conceptualize the core body of research. As a result, the following themes were identified: electronic waste, circular economy transition, plastic waste, bio-based waste management, lifecycle assessment, and ecological impacts, and construction and demolition waste management. The highlighted features, future research orientation, and prominent research perspective can provide guideline for future research to enrich the literature through conducting studies on provided research directions and help lead waste management and technological innovation policymakers, professionals, and practitioners in moving towards circular transition.

An Overview into Polyethylene Terephthalate (PET) Hydrolases and Efforts in Tailoring Enzymes for Improved Plastic Degradation

Plastic or microplastic pollution is a global threat affecting ecosystems, with the current generation reaching as much as 400 metric tons per/year. Soil ecosystems comprising agricultural lands act as microplastics sinks, though the impact could be unexpectedly more far-reaching. This is troubling as most plastic forms, such as polyethylene terephthalate (PET), formed from polymerized terephthalic acid (TPA) and ethylene glycol (EG) monomers, are non-biodegradable environmental pollutants. The current approach to use mechanical, thermal, and chemical-based treatments to reduce PET waste remains cost-prohibitive and could potentially produce toxic secondary pollutants. Thus, better remediation methods must be developed to deal with plastic pollutants in marine and terrestrial environments. Enzymatic treatments could be a plausible avenue to overcome plastic pollutants, given the near-ambient conditions under which enzymes function without the need for chemicals. The discovery of several PET hydrolases, along with further modification of the enzymes, has considerably aided efforts to improve their ability to degrade the ester bond of PET. Hence, this review emphasizes PET-degrading microbial hydrolases and their contribution to alleviating environmental microplastics. Information on the molecular and degradation mechanisms of PET is also highlighted in this review, which might be useful in the future rational engineering of PET-hydrolyzing enzymes.

Site Selection of Urban Parks Based on Fuzzy-Analytic Hierarchy Process (F-AHP): A Case Study of Nanjing, China

The scientific siting of urban parks is critical for sustainable urban environment development, and this study aimed to identify suitable areas for future urban parks in Nanjing, China. This study has integrated geographic information systems (GIS) and fuzzy hierarchical analysis (F-AHP) in order to evaluate the suitability of the site selection of urban parks in Nanjing, China. Different physical, natural, environmental, accessibility, and human activity factors were evaluated in order to assess the suitability of a park site. The results revealed that 5% were highly suitable for urban park site selection, 36% were more suitable, 32% were moderately suitable, 19% were less suitable, and 8% were unsuitable for urban park site selection. The findings suggest that the areas that are highly suitable for urban park placement are located in the western and eastern parts of Nanjing. Carbon storage was the most important factor in the suitability of urban park site selection, followed by the normalized difference vegetation index (NDVI) and the heat-island effect. The methodology that has been adopted in this study helps to improve the methodological framework of combining F-AHP and GIS; in addition, generating urban park site selection maps assists planners and decision-makers in making scientific site selection decisions.