It has been conducted to develop a microwave converter for producing high-quality gas fuel by carbon-CO2 gasifying using the carbon in biomass carbide and the CO2 in combustion exhaust gas, and obtained the following results. When gasification gas was applied as a simulated combustion gas, CO2 conversion, lower heating value, and H2/CO ratio all increased as the concentrations of each component such as the amount of CO2, O2, and water vapor was increased. The same trend was also observed when the Ni-SiC portion among biochar and gasification gas temperature were high. It was found that there is a good fuel value with CO2 conversion of 56% and lower heating value of 2.6 MJ/Nm3 when the percentage of CO2: N2: O2 is 20:70:10 and the amount of water vapor is 15 mL/min by simulating gasification gas as the combustion gas, and biomass carbide is used as the percentage of Ni-SiC among biochar of 70:30 in order to increase microwave receptive energy.

Plastic waste management is of global concern while construction industry keeps searching for innovations to become more sustainable. In this scenario, recycling plastic waste as fibers for reinforcement of concrete stands out as a promising alternative to address both problems. In the last decade, many reviews have focused on how plastic fibers affect concrete properties and how waste can be used to produce these fibers. This paper presents an umbrella review of 47 previous reviews published from 2008 to 2021, covering papers from 1949 to 2021. As a result, bases were set to clarify the full life cycle of recycled plastic fiber-reinforced concrete (RP-FRC), including circularity strategies, to strengthen consistent contributions to the area in the future. The review compares and discusses the types of plastic waste suitable for producing plastic fibers, the effects of recycled plastic fibers on concrete properties and the sustainability of this recycling alternative. Finally, recommendations and unanswered questions for further research were formulated.Graphical abstract

The process of disposing discarded tyre is considered as a significant environmental and economic concern. As a result, many recycling technologies have been investigated to account for their re–use. Pyrolysis is considered to be most hopeful of all these methods. Pyrolysis is the process of a waste tyre being thermally degraded at a high temperature. The value–added products of the pyrolysis process include tyre pyrolysis oil (TPO), pyrochar, and pyrogas etc. TPO corresponds to an alternative fuel for engines as well as a starting material for producing of benzene, toluene, xylene, and limonene. In process of producing carbon nanotubes (CNTs), TPO is used as a precursor. Transformation of porous carbon structure from pyrochar is utilized for absorption and energy storage in batteries and supercapacitors. Pyrogas acts as a source of hydrogen and also may be utilized as an industrial fuel. Pyrolysis may be used to turn the waste tyre into useful materials in this fashion. In this review, we collectively addressed the recent developments of the waste tyre disposal and their by–products.

Phosphorus (P) recovery and recycling play a crucial role in improving resource efficiency, sustainable nutrient management and moving toward circular economy. Increasing demand for fertilizers, signs of geopolitical constraints, and high discharge of P to waterbodies are the other reasons to pursue the circularity of P. Various research have been carrying out and several processes have been developed for P-recovery from different resources. However, there is still a huge unexplored potential for P-recovery specially in the regional framework from the four main P-rich waste resources: food waste, manure, mining waste, and sewage sludge. This study reviews recovery methods of P from these secondary resources comprehensively. Additionally, it analyzes the Nordic viewpoint of P-cycle by evaluating Nordic reserves, demands, and secondary resources to gain a systematic assessment of how Nordic countries could move toward circular economy of P. Results of this study show that secondary resources of P in Nordic countries have the potential of replacing mineral fertilizer in these countries to a considerable extent. However, to overcome the challenges of P-recovery from studied resources, policymakers and researchers need to take decisions and make innovation along each other to open the new possibilities for Nordic economy.

Plastic waste is a growing environmental concern. This study compared plastic waste management between India and Japan using SWOT analysis and a comparison of the five landscapes of the plastic value chain. A t test and multiple linear regression analyzed the differences. The comparison revealed that the status of plastic waste generation and raw material production is different in the two countries. Notably Japan’s per capita plastic waste is 67.4 kg annually, significantly higher than India’s 6.9 kg. However, India’s amount is rapidly increasing, while Japan’s amount has not increased. Additionally, plastic raw material production has significantly impacted on plastic waste generation in both countries. The SWOT analysis showed that India and Japan have different trends in plastic waste management. The study found that India should create an enabling environment that considers the cost of separate collection, the local government’s willingness to participate, and the availability of a market for recycled products, in addition to the formulation of regulations. Japan can leverage India’s initiatives, like prioritizing material recycling and creating swift campaigns. By considering the successes and challenges of plastic waste management in both, a way for leapfrogging can be paved.

Municipal solid waste (MSW) management is a challenging task due to waste that is not separated at the source. This study believes the importance of promoting MSW separation at the source (SAS). Numerous articles reveal the role of knowledge and attitude in motivating the households’ pro-environmental behavior. Thus, this study examined the knowledge, attitudes, and practices (KAP) concerning waste SAS program in Lao Cai city, Vietnam. The results showed that the households in the city of Vietnam had a positive knowledge and attitude towards MSW SAS. Despite it, the public has inadequate knowledge about some aspects of MSW SAS program. While the results from the ordinary least square regression model had strongly indicated the positive effect of attitude and knowledge toward MSW SAS program, this study still recommends for the enhancement of the information and education campaigns for the program with the help of potential role models in the city. In addition, this article also investigated the relationship between households’ KAP and the perception of households about the new waste collection and treatment fee option under Vietnam’s Law on Environmental Protection 2020, which needs special attention and strategies to gain support among the city’s populace.

The supplanting of fine aggregate was encapsulated in this study to reduce the usage of non-renewable materials in concrete. Initially, nano–micro cementitious material (NMCM) such as metakaolin (MK) and nano silica (NS) was incorporated with Portland cement to make referral concrete (RC). An alternate for virgin river sand is crushed gravel sand (Csand) which is mostly in use. The objective of this research is to effectively supplant Csand by means of ferrochrome slag (FS). Precisely, the optimum level of MK (10%) and NS (1%) was used in place of cement. In addition, the FS was incorporated in place of Csand by 10, 20, 30, 40, 50 and 100%. A significant rise in the compressive strength of about 3.18% was achieved by replacing FS4 at 28 days than RC. Ultrasonic pulse velocity (UPV) and water permeability (WP) results of FS4 were better than those of RC. F4 was 12.5% higher in the RCPT result than for the RC specimen. The SEM image of FS4 indicates the densest calcium silicate hydrate (CSH(H)) and rigidified interfacial transition zone (ITZ). TG/DTG predicts that the FS4 mix has a minimal Portlandite (CH-3.92%) compared to RC. The strength, durability, microstructure and TG results of the FS4 matrix imply that FS can be substituted for fine aggregate.Graphical Abstract

The culture substrate of Auricularia auricula contains lots of wood residues, which is not easy to compost or be used to produce feed. In this study, the spent culture substrate of Auricularia auricula (SSA) was used as raw material to prepare cellulose nanocrystals (CNCs). The CNCs were prepared by hydrolysis of the cellulose extracted from SSA (SSAC) with H2SO4 aqueous solution. The effect of concentration of H2SO4, acid hydrolysis temperature and hydrolysis time on the properties of CNCs and the reaction mechanism were studied. When the cellulose extracted from SSA (SSAC) was treated with 45 wt% H2SO4 at 45 °C for 120 min, the obtained CNCs was slender needle-like and the yield was 67.25 wt% (based on the mass of cellulose from pretreated SSA). The obtained CNCs in this condition have a crystallinity of 73.15% and the diameter distribute between 4 and 16 nm. The results show that the residual wood in SSA could prepare CNCs with higher crystallinity and smaller particle size under a more moderate condition. This study provides a new approach for the reuse of spent culture substrate of Auricularia auricula as well as a new cheap raw material for preparation of CNCs.Graphical abstract

Anaerobic digestion of the organic fraction of municipal solid wastes is a well-established process for biogas production and various forms of pre-treating the biomass have been evaluated to increase the methane yield. The present study evaluated the pre-treatment of 14 fruits and vegetables wastes (FVW) samples from a central food distribution market, using sodium hydroxide (NaOH), varying the concentration (3 and 6%) and exposure time (24 and 48 h) to the alkali reagent. The biochemical methane potential (BMP) assays of the pretreated and untreated wastes were carried out under mesophilic conditions (37 ºC). Biogas generation by the residues treated with 3% NaOH generated an average of 65% more methane (≈127 NmLCH4.gVS−1) as compared to the untreated waste (77 NmLCH4.gVS−1) and 25% more than that treated with 6% NaOH (102 NmLCH4.gVS−1). Thus, we observed that doubling the pretreatment time and concentration of the chemical reagent did not result in greater methane production. This behavior could have been associated with the presence of some compounds (sodium, pesticides, etc.) that have an inhibitory effect in the aqueous solution. Finally, this study confirmed that the optimal conditions for the pretreatment and biodigestion phases must be reevaluated according to the nature of the substrate evaluated.Graphical abstract

Herein, fluorine fixation, nitrogen removal, and the alkaline solution recovery of alumina were studied using calcium-based high-temperature soda roasting. In addition, the effects of roasting conditions, dissolution conditions, and additives (carbon alkali and calcium salt) on fluorine fixation and alumina recovery were studied. The results show that when the roasting temperature was 1100 ℃ and the roasting time was 2 h, the dissolution temperature was 80 °C, while the dissolution time was 20 min. The ratio of soda to dross was 1.0, and 30 wt% CaCO3 had been added as a fluorine fixing agent. The Al extraction rate from aluminum dross (AD) reached 86.21%, the denitrification rate reached 99.54%, the concentration of soluble fluoride ion was reduced to 0.111 g·L−1, and the fluoride fixation rate was 75.04 wt%. CaF2 is the main component of the leaching residue, which can be added as an insulation material for electrolysis. Alkaline oxidation roasting and calcium-based fluoride fixation are effective methods to separate aluminum, fluoride, and nitrogen. This study provides a new method for the safe and efficient utilization of AD.

Si, Al, Cu, and Ag particles’ mixture which mainly composes pulverized silicon-based waste solar cells were individually separated by the batch flotation experiments with high recovery and content, and then a general flow chart of the sequential flotation procedure of n-component was postulated including 2-, 3-, and 4-components. The n-component mixture was separated to 1: n-1 or i: j (i + j = n) by a flotation procedure and n-1 times operation was necessary to divide into the individual component. The first flotation process to separate Al into the froth layer was carried out with a collector of SDS solution after dipping Si, Al, Cu, and Ag mixture into the SDS solution. Si was separated in the froth by the second flotation with a collector of a commercial neutral detergent after Al etching by HCl, and Si, Cu and Ag mixture dipped in the detergent. The Cu and Ag mixture was calcinated at 673 or 773 K and dipped into the detergent, and the third flotation with the collector of the detergent led to Cu in the froth and Ag in the sediment. The 4-component mixture was successfully separated into each component by the 3-consecutive flotation processes.

The treatment and utilization of coal gangue, one of the main solid wastes produced during coal mining, are of great significance in environmental protection and resource development. In the contemporary context of the carbon neutralization strategy, due to the property of the carbon in coal gangue, it is necessary to be cautious of the carbon effect during its treatment and utilization process. To grasp the concept of the carbon effect of coal gangue more comprehensively and systematically and provide more economic and reasonable technical strategies for the treatment and utilization of coal gangue against the background of carbon neutralization, this study systematically summarizes the research results from three aspects: the carbon emission risk of coal gangue itself, the carbon emission risk during its treatment and utilization process, and the potential effect of the application carbon sequestration. There are many types of carbon emission risks when considering coal gangue itself, such as direct carbon emissions resulting from spontaneous combustion and extended carbon emissions due to its negative pollution impacts on soil and vegetation. At present, the main utilization modes of coal gangue include fuel, building materials, filling materials, and ecological materials. Most of them have certain carbon emission risks, while some of them also have certain carbon fixation effects. Against the background of the carbon neutralization strategy, the treatment and utilization of coal gangue should focus on three aspects: its own carbon-free emissions; its carbon absorption effect and low-carbon emission in the treatment process; and taking comprehensive technical measures, such as the oxidation inhibition of coal gangue, enhancement of the ecological carbon sink function, excavation of the carbon absorption function, and nearby utilization and pollution prevention and control, to achieve high value and low-carbon release in the treatment and utilization of coal gangue.

Millions of tonnes of green waste are produced annually in the UK. Composting usually extends to more than two months as well as producing greenhouse gases that can affect the environment if not optimised. We proposed a potential approach to use the algal extract from Ascophyllum nodosum as a compost accelerator. Seaweed-based treatments offer an economical and effective biological solution that activates and stabilises organic matter decomposition, promoting better carbon sequestration. Reducing both the cost and time associated with widely used composting approaches. The seaweed was collected from the Scottish coastline, extracted, and formulated to enhance application. Its effects on the timeline of the composting process were systematically investigated through physical, biological, and observational quantification. The emission of gases, the pH, temperature, humidity, consistency, and microbial growth of the compost were studied. Interestingly, the results showed that the compost reached a stable state within six weeks, with lower ammonia and carbon dioxide production. The use of this formulation can minimise expense, reduce resources used, and also lower the levels of harmful volatile organics. This approach is economically beneficial and environmentally crucial in compost formation, controlling contamination, and carbon sequestration optimisation.

In this study, the effects of different contents of Nano-SiO2 (NS) on a slump, compressive strength, splitting tensile strength, flexural strength, hydration products, and microstructure of recycled fine aggregate concrete (RFAC) were investigated. The results show that the addition of recycled fine aggregate (RFA) has a significant negative impact on the mechanical properties of concrete, but with the addition of NS, the mechanical properties of RFAC are improved. When the content of NS is 3%, the compressive strength, splitting tensile strength and flexural strength at 28 d of RFAC increased by 30.7%, 35.1%, and 18.7% respectively, and the durability was also improved significantly. Meanwhile, Thermogravimetric differential scanning calorimeter (TG-DSC), and X-Ray diffraction analysis (XRD) demonstrated that the addition of NS reduced the content of calcium hydroxide (CH) crystal in RFAC samples. Scanning electron microscopy (SEM) results show that NS doping can refine CH crystal, adsorb hydration products and improve the compactness of RFAC microstructure. The maximum efficiency is obtained when the content of NS is 3%. This study aims to research the possibility of using 100% recycled fine aggregate (RFA) in concrete and helps to maintain the better mechanical properties and durability of RFAC for a longer time.

The purpose of this study is to clarify how material flow cost accounting (MFCA) can contribute to the SDGs and indicate how to introduce it into a company. First, we undertake a literature review to examine which SDGs MFCA can potentially contribute to. We then analyse the interplay between MFCA and management decision-making on the SDGs using an MFCA-LCA integrated model. Finally, we discuss how to introduce MFCA into a company to integrate the SDGs into management decision-making with reference to the SDG Compass. The main contributions are as follows: First, we revealed that MFCA could potentially contribute to multiple goals in the SDGs. Second, we clarified that MFCA could integrate the SDGs into actual management decision-making. Third, we suggested appropriate steps for implementation, regarding how managers should introduce MFCA into the management process on the condition that it does not prioritise economic benefit over social and environmental benefits in contributing to the SDGs. Therefore, this study provides evidence that MFCA can contribute to the SDGs by integrating them into management decision-making, and suggests appropriate implementation steps for promoting the pursuance of SDGs in any company.

E-waste is becoming a concern due to its toxic content and serious pollution effect. Many studies have focused on the detrimental impacts of hazardous e-waste and extended producer responsibility for e-waste recycling. There is, however, a lack of case studies from the perspectives of consumers’ awareness of e-waste, and willingness to pay (WTP) for e-waste recycling. An e-waste management system cannot be efficient when consumers are not actively involved in. Based on a survey of 544 respondents in Ho Chi Minh City, this paper investigates the respondents’ WTP for e-waste recycling and factors affecting their WTP by integrating the theory of planned behaviour and the norm activation model. The Contingent Valuation Method and Tobit model were applied to estimate and explain consumers’ WTP for e-waste recycling. The model showed that subjective/social norms, moral/personal norms, inconvenience of recycling, perception of e-waste pollution, age, home ownership, and income significantly affected WTP for e-waste recycling. The estimated mean WTP from the Tobit model was 1.588% (Televisions), 1.644% (Computers) and 1.656% (Mobile phones) of the purchasing bills. The findings are useful for policy-makers in developing more effective environmental management policies for e-waste.

Isothermal pyrolysis of waste polystyrene over CuO/kaolin was investigated and optimized for maximum oil yield using Box-Behnken response surface design. The results revealed that the reaction variables affect the yields of the gaseous, liquid and char, respectively. Optimization of the reaction variables predicted an optimal yield of 96.07% at a residence time, heating rate, and catalyst loading of 45 min, 10 °C/min and 30%, respectively in agreement with the validation results of 95.56 ± 1.90%. The physicochemical properties of the oil conformed with petrodiesel properties and could be used as its substitute. The oil has a 84% dominance of benzene,1,1-(1-butenylidene)bis, and the mechanism through which it was formed has been proposed.

Implementing retorts in artisanal and small-scale gold mining (ASGM) to mitigate mercury emissions is a positive development. However, it creates a new challenge: the need for proper management of retorted mercury waste. This study aimed to estimate the global waste management cost for retorted mercury using stringent guidelines for mercury waste management. The results showed that the estimated cost could reach a maximum of 16.6 million USD by 2050, which is 44.7 times higher than the global retort purchase cost. Thus, securing waste management costs for retorted mercury is essential when implementing retorts for mercury mitigation. However, this may be challenging in many artisanal and small-scale gold mining countries due to low governance levels and underestimated short-term 5-year National Action Plan budgets. To address this issue, an additional 33.2% long-term budget in comparison with cumulative global environment facility ASGM funding so far will be required globally during 2015–2050 for proper waste management of retorted mercury. This study proposes a strategy for proper mercury waste management from a financial viewpoint by examining the context of mercury waste management in national action plans and estimating the global environment facility ASGM funding contribution by gold-consuming countries.

Mercury (Hg) is a naturally occurring chemical found in rock and coal deposits that can exist in various forms, including elemental Hg, inorganic Hg compounds, methylmercury, and other organic compounds. Exposure to Hg, primarily inorganic Hg, can have severe environmental and occupational hazards and harm human health. Therefore, it is crucial to understand the complex natural transformations and cyclic environmental processes of Hg and its impact on human health and the ecosystem. Both natural and human activities are mainly responsible for the Hg cycles in the environment. Combustion of fossil fuel and subsequent smelting activities are the primary sources from nature for the Hg cycles, while human activities like industrial processes and the use of products containing mercury also contribute to Hg in the environment. These sources ultimately release elemental Hg into the environment, and this Hg vapor can stay in the atmosphere for years and spread throughout the environment via various media. Besides, the whole process repeats and completes the Hg cycle. This review provides detailed knowledge of Hg cycles in the environment, proper end-of-life management of mercury-contained products, and the most up-to-date compilation of Hg recycling technologies, emphasizing the importance of proper Hg waste management. The study also emphasizes the need for a clear understanding of the relationship between local conditions and Hg levels in the environment to forecast Hg concentrations and their ability to be absorbed by living matter. The study also highlights the significance of suitable collection and recovery of Hg waste to prevent its improper disposal, which may lead to contamination of the air, rivers, lakes, and drinking water, thus increasing the risk to the environment and human health.

Pakistan is among the few countries generating and receiving enormous e-waste, which posits a threat to its future generations. A systematic literature review also suggests exploring e-waste awareness in Asia to understand awareness and behavior. Therefore, the present study explored university students’ awareness of e-waste and the factors hindering the disposal of laptops, personal computers, and cellphones and suggested a conceptual framework. The study used the qualitative research approach and non-probability sampling. We collected data through four focus group discussions (FGDs) with students at a Pakistani university. After data saturation, we developed themes from FGDs and found computer sciences and engineering students with better awareness than others. The factors hindering e-waste disposal were lower monetary benefits for disposal, breach of sensitive information, nostalgic association with devices, and non-availability of disposal facilities. Other variables like lower resale value and high family sharing increased the storage of e-devices and reduced e-waste disposal. The research is among a few initial attempts to explore e-waste awareness and factors hindering disposal behavior in e-waste-receiving countries (e.g., Pakistan) and provides evidence from students who are the primary users. Our findings are crucial for policymakers to take corrective actions, introduce monetary benefits, and secure disposal to reduce e-waste.