Waste Disposal & Sustainable Energy最新文献

Abstract

Microbial fuel cells (MFCs) are innovative devices that combine microbial processes with electrochemical reactions to convert organic matter in wastewater into electricity while simultaneously treating the wastewater. One such application is the treatment of spent wash, a highly polluting effluent generated from the distillery industry after crude mesh is separated into ethanol and spent wash. Spent wash, also known as distillery effluent or stillage, is a highly challenging wastewater treatment method due to its high chemical oxygen demand (COD), biological oxygen demand (BOD), and total dissolved solids (TDS). These characteristics make it a complex and polluting industrial effluent that requires specialized treatment processes to reduce its environmental impact effectively. However, MFCs have shown promise in treating spent wash, as they can utilize the organic matter in wastewater as a fuel source for microbial growth as well as for electricity generation. For the treatment of spent wash, Saccharomyces cerevisiae sp. was used as a biocatalyst along with 340 mol/L potassium ferricyanide in the cathode chamber and 170 mol/L methylene blue in the anode as a mediator. All tests were conducted by balancing a one-liter volume for power production from spent wash in MFC with the optimal conditions of 10% agarose, pH 8.5, 300 mL/min of aeration in the cathode chamber, and 40% (in weight) substrate concentration. At an ideal concentration, the maximum current and power density are roughly 53.41 mA/m² and 72.22 mW/m², respectively. For each litre of processed spent wash, a maximum voltage of 850 mV (4.5 mA) was obtained. Amazingly, 91% of COD and BOD were removed from the effluent MFC. These findings show that MFCs are capable of producing electricity and efficiently removing COD from wasted wash at the same time.

This study explores the potential of valorizing sewage sludge as a carbon source for the co-production of biochar and carbon nanomaterial via a two-stage thermal-catalytic process. In the first stage, sewage sludge underwent slow pyrolysis, resulting in a biochar yield of 66% (in weight) at 550 °C. The resulting pyrolysis vapor was then introduced into a second reactor, where catalytic chemical vapor deposition (CCVD) took place in the presence of a cobalt catalyst, leading to the production of carbon nanotubes (CNTs). It was found that CNTs with an inner diameter of ~ 3.2 nm and an outer diameter of 20–40 nm can be formed in the second stage reactor at temperatures between 650 °C and 950 °C with a maximum yield of 30% (in weight) under the employed experimental conditions. The obtained CNTs displayed a multiwall structure, exhibited a lack of crystallinity, and demonstrated a high level of disorder. The research findings also indicate that temperature exerts a significant influence on both the yield and properties of the CNTs synthesized.

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Abstract

MXene nanomaterials have attracted great interest as the electrode of supercapacitors. However, its energy storage mechanisms in organic electrolytes are still unclear. This work investigated the size effect of cations (i.e., Li⁺, Na⁺, K⁺, and EMIM⁺) on the capacitive behaviors of MXene-based supercapacitors. The experimental results demonstrate that the specific capacitance increases obviously with decreasing cation size (i.e., from 43 F g⁻¹ (EMIM⁺) to 129 F g⁻¹ (Li⁺) at 2 mV s⁻¹). Density-functional theory calculation reveals a correlation between cation size and ion–electrode surface interaction, supporting experimental observations of the capacitive-dominant behavior. Molecular dynamics simulations reveal that the ionic solvation structure and desolvation degree of intercalated cations as a function of solvation size, providing dynamic insights into the experimentally observed specific capacitance trends. Our comprehensive experimental and computational study provides valuable insights into the intricate solvation effects governing the charge storage mechanisms. This finding of ion dynamics, solvation structure, and desolvation may contribute to guide the design and optimization of appropriate ions/electrolytes combinations for MXene-based supercapacitors.

The widespread use of disposable batteries to power common electronic devices is a major source of e-waste. There are growing environmental and health concerns due to the expansion of e-waste around the world. Hence, developing a reliable system for recycling old batteries has reached the top of the recycling priority list. The current study presents a novel approach to synthesis carbon nanoparticles (CNPs) from spent batteries via an eco-friendly method that offers economical, environment-friendly, and nontoxic approaches in comparison to conventional chemical methods. The synthesized nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX), powder X-ray diffractometry (XRD), UV–VIS absorption analysis (UV), Fourier transform infrared spectroscopy (FT-IR), Atomic force microscope (AFM), and thermo-gravimetric analysis (TGA). The average diameter of the synthesized particles was 40.16 nm, and the particles tended to be aspherical in shape. EDX analysis also predicted the presence of pure carbon, with some contamination arrived at 15% (in weight). This is a novel study in which nanocarbons were synthesized in a brine (7600×10⁻⁶) from a target (CNPs>75 nm), which paves the way for future use of CNPs derived from spent batteries and helps the environment by decreasing the amount of electronic waste dumped in landfills.

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Abstract

Anaerobic digestion (AD) as a waste management method has the potential to reduce greenhouse gas emissions while producing renewable energy, making it a viable option for managing the organic fraction of municipal solid waste (OFMSW). OFMSW characteristics can vary depending on factors such as waste source, composition and separation units. The characteristics of OFMSW are critical for analyzing and monitoring the AD process to optimize biogas production. In this study, the waste composition and physicochemical characteristics of the mechanically separated OFMSW (ms-OFMSW) were determined at a full-scale AD plant in Türkiye. The ms-OFMSW samples were collected monthly after mechanical separation and were subsequently sent to the anaerobic digester. The composition and physicochemical characteristics of the samples were determined by manual sorting. The results showed that the majority of the ms-OFMSW (76.45%±1.71%) was organic, while 8.99%±1.56% was recyclable and 14.56%±1.69% was non-recyclable. Loss of environmental benefits for the recyclable materials was determined using a free online tool provided by Environmental Protection Agency. Metals (399.7 GJ) and plastics (403.7 GJ) both saved nearly the same amount of energy while metals saved the most water (421.8 m³), with the greatest positive impact. Greenhouse benefits ranged from 3 tons to 40 tons of carbon dioxide equivalent for each waste stream. These findings suggest that efficient pre-separation units can improve the anaerobic digestibility of OFMSW, while also providing greater environmental benefits by preventing recyclable waste from the anaerobic digester. In addition to encouraging source separation applications, this study demonstrates the need for improved technologies to separate OFMSW from mixed MSW.

Heavy metal pollution in landfill humus can cause serious environmental problems and may endanger soil ecosystems and human health. The biological toxicity of heavy metals is not only related to their total amount but also influenced to a greater extent by the distribution of their chemical speciation. Exploring the different chemical speciation and proportions of heavy metals can provide a more comprehensive and accurate understanding of the pollution characteristics and biological toxicity of heavy metals in landfill soil. Based on a review of the relevant literature, this paper systematically summarizes the recent research status of typical heavy metal chemical speciation in landfill humus. This chemical speciation is diverse and complex. For instance, heavy metals in residual states and organically bound states have little impact on organisms, while heavy metals in exchangeable states and Fe–Mn oxide states can easily migrate and transform. The chemical speciation of heavy metals is affected by many factors, among which the soil pH and organic matter content are some of the most important factors. Finally, the existing gaps in the current research on the chemical speciation of heavy metals in landfills are described and future research directions are proposed. This work provides a theoretical reference for researching the restoration of heavy metal-contaminated humus soil and the resource utilization of humus soil.

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Mercury pollution is created by coal combustion processes in multi-component systems. Adsorbent injection was identified as a potential strategy for capturing Hg⁰ from waste gases, with adsorbents serving as the primary component. The hydrothermal approach was used to synthesize a series of MnO_x–CeO_x nanorod adsorbents with varying Mn/Ce molar ratios to maximize the Hg⁰ capture capabilities. Virgin CeO_x had weak Hg⁰ elimination activity; <8% Hg⁰ removal efficiency was obtained from 150 °C to 250 °C. With the addition of MnO_x, the amount of surface acid sites and the relative concentration of Mn⁴⁺ increased. This ensured the sufficient adsorption and oxidation of Hg⁰ while overcoming the limitations of restricted adsorbate-adsorbent interactions caused by the lower surface area, endowing MnO_x–CeO_x with increased Hg⁰ removal capacity. When the molar ratio of Mn/Ce reached 6/4, the adsorbent’s Hg⁰ removal efficiency remained over 92% at 150 °C and 200 °C. As the molar ratio of Mn/Ce grew, the adsorbent’s Hg⁰ elimination capacity declined due to decreased surface area, weakened acidity, and decreased activity of Mn⁴⁺; <75% Hg⁰ removal efficiency was reached between 150 °C and 250 °C for virgin MnO_x. Throughout the overall Hg⁰ elimination reactions, Mn⁴⁺ and O_α were in charge of oxidizing Hg⁰ to HgO, with Ce⁴⁺ acting as a promoter to aid in the regeneration of Mn⁴⁺. Because of its limited adaptability to flue gas components, further optimization of the MnO_x–CeO_x nanorod adsorbent is required.

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Sub-Saharan Africa is witnessing a proliferation of photovoltaic (PV) waste due to the increasing number of solar PV power plants. PV waste (panels, batteries, electrical cables, mounting structures, and inverters) consists of elements such as mercury, cadmium, chromium, lead, copper, aluminum, fluorinated compounds, and plastics that are toxic to human health and the environment if a proper management system is not available. Although many studies worldwide have focused on PV waste management, very few have been conducted in sub-Saharan Africa. This study aims to investigate the current PV waste management system in Burkina Faso, determine stakeholder profiles, and propose strategies to enhance the existing system. Documentary research, interviews, questionnaires, and field visits were used in the methodology. The survey showed that young people, mainly under 30 years of age and with a primary education, dominate (70%) in terms of PV waste collection and repair activities, while the more technical recycling and export activities are carried out mainly (88%) by stakeholders older than 40 years and with a secondary education (60%). Among the older stakeholders, 100% are aware of the hazardous nature of PV waste, whereas 36% are young people. From an environmental perspective, the main source of contamination observed is the release of lead-rich sulfuric acids into water and soil during the collection and repair phases. During the recycling of batteries and electrical cables, toxic fumes are emitted into the air, and recycling residues rich in toxic substances are landfilled. To reduce risks to human health and the environment when managing PV waste, the introduction of legislation, the multiplication of collection points and appropriate infrastructures, the training and awareness-raising of stakeholders, and the extended responsibility of manufacturers are recommended. Studies on the economic feasibility of setting up formal management structures are needed to complete this work.

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The moisture content (MC) of municipal sludge is the key factor affecting sludge treatment and disposal technologies, while the vast majority of existing measurement methods are off-line and time-consuming. To realize rapid online detection for the MC of sludge, a detection method based on the microwave reflection principle is proposed: experiments are carried out and the MC computation model of the sludge is derived using the resonant frequency and the permittivity ((varepsilon^{prime})). The results reveal that the detection accuracy of granular sludge with a thickness of 10 mm is higher. The theoretical model between the MC and the real part of (varepsilon^{prime}) is developed, and the relationship between the resonant frequency and (varepsilon^{prime}) is expressed by a cubic polynomial. The average error and the root mean square error (RMSE) of sludge are 2.06% and 2.49%, respectively. The prediction model for the MC of sludge is also given, and the determination coefficient and RMSE are 0.981 and 2.06%, respectively.

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This article has the general objective of estimating the efficiency of urban solid waste management in 940 Brazilian municipalities through Data Envelopment Analysis (DEA) technique and has specific objectives: (i) to estimate efficiency scores; (ii) to compare the performance between different groups of municipalities; and (iii) to analyze the profile of efficient municipalities from the perspective of the guidelines of Law 12,305/2010 and socio-economic and environmental indicators. The technique used was DEA with output-oriented and variable scale to return modeling. The results showed higher efficiency scores in the municipalities with populations above 500,000 inhabitants. The score variation ranged from 0.5 (municipalities with populations <10,000 inhabitants) to 0.9 (municipalities with more than 500,000 inhabitants). Of the sample set, only 12.34% of the municipalities were considered efficient, and when analyzing the efficient group, it was found that adherence to legislation was not a major factor in achieving efficiency.

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