Carbon sequestration in unmineable coal seams has been proposed as one of the most attractive technologies to mitigate carbon dioxide (CO₂) emissions in which CO₂is stored in the microporous structure of the coal matrix in an adsorbed state. The CO₂adsorption process is hence considered one of the more effective methodologies in environmental sciences. Thus, adsorption isotherm measurements and modelling are key important scientific measures required in understanding the adsorption system, mechanism, and process optimization in coalbeds. In this paper, three renowned and reliable adsorption isotherm models were employed including Langmuir, Freundlich, and Temkin for pure CO₂adsorption data, and the extended-Langmuir model for multicomponent, such as flue gas mixture-adsorption data as investigated in this research work. Also, significant thermodynamics properties including the standard enthalpy change ( $$\Delta H^\circ$$ΔH∘ ), entropy change ( $$\Delta S^\circ$$ΔS∘ ), and Gibbs free energy ( $$\Delta G^\circ$$ΔG∘ ) were assessed using the van’t Hoff equation. The statistical evaluation of the goodness-of-fit was done using three (3) statistical data analysis methods including correlation coefficient (R²), standard deviation (σ), and standard error (SE). The Langmuir isotherm model accurately represent the pure CO₂adsorption on the coals than Freundlich and Temkin. The extended Langmuir gives best experimental data fit for the flue gas. The thermodynamic evaluations revealed that CO₂adsorption on the South African coals is feasible, spontaneous, and exothermic; and the adsorption mechanism is a combined physical and chemical interaction between the adsorbate and the adsorbent.

Carbon dioxide (CO₂) injection into geologic formations has gained global traction, including in South Africa, to mitigate anthropogenic emissions through carbon capture, utilisation, and storage technology. These technological and technical developments require a comprehensive and reliable study of CO₂ sorption equilibria under in situ unmineable coal reservoir conditions. This paper presents novel findings on the study of the equilibrium adsorption of CO₂ on two South African coals measured at four temperatures between 30 and 60 °C and pressures up to 9.0 MPa using the volumetric technique. Additionally, the sorption mechanism and thermodynamic nature of the process were studied by fitting the experimental data into Langmuir–Freundlich (Sips), Tóth, and Dubinin–Astakhov (DA) isotherm models, and the Clausius–Clapeyron equation. The findings indicate that the sorption process is highly exothermic, as presented by a negative temperature effect, with the maximum working capacity estimated to range between 3.46 and 4.16 mmol/g, which is also rank- and maceral composition-dependent, with high-rank vitrinite-rich coal yielding more sorption capacity than low-rank inertinite-rich coal. The experimental data fit well in Sips and Tóth models, confirming their applicability in describing the CO₂ sorption behaviour of the coals under the considered conditions. The isosteric heat of adsorption varied from 7.518 to 37.408 kJ/mol for adsorbate loading ranging from 0.4 to 3.6 mmol/g. Overall, the coals studied demonstrate well-developed sorption properties that characteristically make them viable candidates for CO₂ sequestration applications for environmental sustainability.

The modern world has brought extensive socioeconomic and ecological changes. Urbanization in developing nations has significantly increased municipal solid waste, necessitating in-depth understanding of waste composition particularly in developing nations for sustainable management practices. This study aimed to classify and characterize waste while evaluating potential waste management methods. Mixed methods were used to examine landfilled waste from Soshanguve and Hatherley sites in Tshwane Metropolitan, South Africa, using techniques such as Fourier transform infrared spectroscopy, X-ray fluorescence, proximate, and ultimate analysis. Seasonal variations in waste components were analysed over two seasons. The study identified that both sites are predominantly composed of organic waste, accounting for over 42 wt.%, with moisture content of ~50 wt.%, and minimal recyclables (<5 wt.%). Seasonal variations in MSW were significant for glass (<4% increase), organic waste (50%) and oxygen (>40%) levels, low ash content (<18%), and calorific values of 15–19 MJ/kg. Biodegradables mainly contained oxides of calcium, silicon, iron (III), and potassium with chemical composition indicating functional groups that emphasize composting and energy recovery benefits. The research provides insights into sustainable waste management, revealing waste composition at Tshwane landfills, aiding informed decision-making for resource usage and environmental conservation.

Landfilling is one of the primary techniques utilized globally to manage municipal solid waste (MSW), particularly in developing nations. Unlike existing conventional methods, hybrid bioreactor landfilling technology is a promising sustainable approach for maximizing biogas production from MSW. This study aimed to evaluate the application of hybrid bioreactor technology to enhance biogas production from the organic fraction of MSW. Over a 7-month period, two columns were utilized to simulate typical (Br-1) and hybrid (Br-2) landfill bioreactors while monitoring the quality of leachate and biogas generated. Results showed contaminant reduction in leachate with the pH increasing to 8 in Br-2, while Br-1 remained acidic below 7. Physicochemical parameter reductions ranged from 33 to 98%, while total organic carbon and carbon oxygen demand (TOC/COD) ratio varied between 0.04 and 0.61. Analyzed heavy metals reductions ranged from 3 to 88%. Biogas generated was 8.75 L with methane (CH₄) below 50% in Br-1, while Br-2 produced 21.5 L with CH₄ exceeding 60%. The final CH₄ concentration reached 67% in Br-2 and 52% in Br-1. Partial aeration and diluted leachate recirculation enhanced biodegradation in Br-2 while the leachate was treated in situ. The high CH₄ content and 41-fold greater biogas yield in Br-2 showed the economic and ecological viability of this method for biogas-to-energy projects.

Greenhouse gases (GHGs) have sharply increased over the past four decades due to intensifying industrial activities; as a result, the earth has been faced with global warming in which the major contributor is the anthropogenic carbon dioxide (CO 2 ) emissions. Carbon sequestration in unmineable coal seams has been proposed as one of the most attractive technologies to mitigate CO 2 emissions in which CO 2 is stored in the microporous structure of the coal matrix in an adsorbed state. The CO 2 adsorption process is hence considered one of the more effective methodologies in environmental sciences. Thus, adsorption isotherm measurements and modelling are key important scientific measures required in understanding the adsorption system, mechanism, and process optimization in coalbeds. In this paper, three renowned adsorption isotherm models were employed including Langmuir, Freundlich, and Temkin for pure CO 2 adsorption data, and the Extended-Langmuir model for multicomponent, such as flue gas mixture-adsorption data as investigated in this research work. The adsorption data was acquired from a high-pressure volumetric sorption system (HPVSS) experiment involving two South African coal samples from Ermelo and Somkhele coalfields with pure CO 2 and synthetic industrial flue gas to simulate emissions that are representative of a typical coal-fired power plant (12% CO 2 , 5.5% O 2 , 82% N 2 , 0.38% SO 2 , and 0.12% NO 2 ). The adsorption data was measured on 10 g samples with a mean size of 2 mm at temperatures ranging from 30 ºC to 60 ºC and pressure up to 9.0 MPa using the HPVSS. The statistical evaluation of the goodness-of-fit was done using three (3) statistical data analysis methods including correlation coefficient (R 2 ), standard deviation ( σ ), and standard error (SE). The Langmuir isotherm model conventionally fits the pure CO 2 gas experimental data better than Freundlich and Temkin. The Extended Langmuir gives best experimental data fit for the flue gas.