Municipal solid waste recycling by burning it as part of composite fuel with energy generation

Modeling risk assessment of soil heavy metal pollution using partial least squares and fuzzy logic: A case study of a gully type coal-based solid waste dumpsite

Continuous release and migration of heavy metals from coal-based solid waste (CSW) dumpsites often results in significant encroachment on ecological lands and pollution of natural environments. As a result, there is an urgent need for long-term and rapid monitoring, analysis, and assessment to control environmental risks associated with large CSW dumpsites. We constructed a new composite model (PLS-FL) that uses partial least squares regression (PLSR) and fuzzy logic inference (FLI) to accurately predict heavy metal concentrations in soils and assess pollution risk levels. The potential application of the PLS-FL was tested through a gully type CSW case study. We compared 20 modeling strategies using the PLS-FL: five types heavy metals (Cd, Zn, Pb, Cr and As) * four spectral transformation methods (first derivative (FD), second derivative (SD), reverse logarithm (RL), and continuum removal (CR)) * one variable selection method (competitive adaptive reweighted sampling (CARS)). The results showed that the combination of derivative transformation and CARS was recommended for estimation, with R2C > 0.80 and R2P > 0.50. When comparing the PLSR model with four traditional machine learning methods (Support Vector Machines (SVM), Random Forests (RF), Extreme Learning Machines (ELM), and KNN), the PLSR model demonstrated the highest average prediction accuracy. Additionally, the FLI process no longer relies on human perception and expert opinion, enhancing the model's objectivity and reliability. The evaluation results revealed that the heavy metal contamination areas of the CSW dumpsite are concentrated at the bottom of the gully, with more severe contamination in the north. Furthermore, a high-risk zone exists in the interim storage area for CSW to the east of the dump. These findings align with the initial detections at the sampling sites and highlight the need for targeted monitoring and control in these areas. The application of the model will empower regulators to quickly assess the overall situation of large-scale heavy metal pollution and provide scientific program and data support for continuous large-scale pollution risk monitoring and sustainable risk management.

Eco-Friendly Coal Gangue and/or Metakaolin-Based Lightweight Geopolymer with the Addition of Waste Glass

Massive amounts of deposited coal gangue derived from the mining industry constitute a crucial problem that must be solved. On the other hand, common knowledge about the recycling of glass products and the reuse of waste glass is still insufficient, which in turn causes economic and environmental problems. Therefore, this work investigated lightweight geopolymer foams manufactured based on coal gangue, metakaolin, and a mix of them to evaluate the influence of such waste on the geopolymer matrix. In addition, the effect of 20% (wt.) of waste glass on the foams was determined. Mineralogical and chemical composition, thermal behaviour, thermal conductivity, compressive strength, morphology, and density of foams were investigated. Furthermore, the structure of the geopolymers was examined in detail, including pore and structure thickness, homogeneity, degree of anisotropy, porosity with division for closed and open pores, as well as distribution of additives and pores using micro-computed tomography (microCT). The results show that the incorporation of waste glass increased compressive strength by approximately 54% and 9% in the case of coal-gangue-based and metakaolin-based samples, respectively. The porosity of samples ranged from 67.3% to 58.7%, in which closed pores constituted 0.3-1.8%. Samples had homogeneous distributions of pores and additions. Furthermore, the thermal conductivity ranged from 0.080 W/(m·K) to 0.117 W/(m·K), whereas the degree of anisotropy was 0.126-0.187, indicating that the structure of foams was approximate to isotropic.

Ball milling transformed electroplating sludges with different components to spinels for stable electrocatalytic ammonia production under ambient conditions

Electroplating sludge is classified as hazardous waste, but it is also a potential raw resource since it contains plenty of transition metals. However, the component of electroplating sludge is unstable, which hinders recycling. This work investigates the possibility to synthesize spinels with stable catalytic performances by different electroplating sludges. The obtained catalysts are used in electrocatalytic N₂ reduction to produce ammonia. As a result, CuCr₂O₄, ZnCr₂O₄, and NiCr₂O₄ spinels are successfully synthesized by a ball-milling and calcination method. These spinels result in ammonia yields of 7.30-8.86 μg h^-1 mg^-1_cat. Among the three spinels, CuCr₂O₄ shows the highest yield of 8.86 μg h^-1 mg^-1_cat at -0.9 V. Its faradaic efficiency reaches 0.57%. In addition, no by-product N₂H₄ is detected, indicating a high selectivity. The catalytic process is carried out by both distal and alternating pathways, in which metal doping and oxygen vacancy function as binding sites for N₂ adsorption and reduction. Above results indicate that electroplating sludges with unstable components are feasible to produce spinels for stable electrocatalytic ammonia production under ambient temperature. This is in favor of high-value-added utilization of hazardous waste, and devotes to circular economy.

BASIC: A Comprehensive Model for SO x Formation Mechanism and Optimization in Municipal Solid Waste (MSW) Combustion

Municipal solid waste (MSW) incineration is one of the main techniques currently used for waste to energy (WTE) conversion in China. Although the sulfur content in MSW is lower than that in coal, its emission cannot be neglected due to environmental pollution, malodor, health problems, and global climate change. Therefore, it is particularly important to effectively predict and control the sulfur pollutants. In this study, a comprehensive model was developed and coupled with the full combustion process bed model bulk accumulated solids incineration code (BASIC) to investigate the formation and transformation processes of sulfur in MSW incineration. The submodels of the four stages in the MSW combustion processes; governing equations of mass, momentum, and energy conservation; and various chemical reactions were included in the model. Based on this model, the effects of different parameters on the formation of sulfur pollutants during the incineration process were studied under different operating conditions. The study finds that for SO _X formation, initial temperature, primary air volume, and material particle size have significant impacts, whereas pressure shows a less significant effect. This article also considers H₂S, COS, and CS₂ formation under different conditions. An optimization study was performed to reduce SO _X pollutants.

Anthropogenic emissions from the combustion of composite coal-based fuels

Composite fuels made of waste from coal, petroleum and wood processing industries have a high environmental and economic potential. In this research, we experimentally studied the concentrations of the most hazardous gaseous anthropogenic emissions (CO₂, SO₂, NO) from waste-based fuel combustion. Using two techniques operating in complementary temperature ranges, we obtained data on SO₂ and NO emissions in the temperature range from 300 °C to 1000°C, including all the stages of thermochemical conversion of fuels. A quasi-stationary technique was used, based on a setup of thermogravimetric analysis with mass spectrometry, to obtain information in a low-temperature range (300-600°C). This technique allows the conversion at a low controlled rate of heating a sample together with the furnace. To obtain data in a high-temperature range (700-1000°C), a non-stationary technique was used, where the sample was introduced into a pre-heated furnace. The conditions were established in which it was possible to reduce the concentration of flue gases from the combustion of the compositions under study (replacement of the coal part with water, injection of water vapor, addition of biomass, selection of the temperature range). The impact of water vapors was determined when they were injected into the chemical reaction zone together with air and when they were formed naturally by evaporation from the fuel sample. Unlike biomass that reduces the emissions of sulfur oxides from composite fuels due to the mechanical dilution of the mixture, water vapor present in the heterogeneous reaction zone decreases the gaseous anthropogenic emissions through chemical reactions and conversion of a part of fuel sulfur and nitrogen to an inactive form (neutral to the environment).

Energy Treatment of Solid Municipal Waste in Combination with Biomass by Decentralized Method with the Respect to the Negative Effects on the Environment

Waste is a product of society and one of the biggest challenges for future generations is to understand how to sustainably dispose of large amounts of waste. The main objective of this study was to determine the possibility and conditions of the decentralized combustion of non-hazardous municipal waste. The analysis of the combustion properties of a mixture of wood chips and 20–30% of municipal solid waste showed an improvement in the operating parameters of the combustion process. Analysis also confirmed that the co-combustion of dirty fuels and biomass reduced the risk of releasing minerals and heavy metals from fuel into the natural environment. Approximately 55% of the heavy metals passed into the ash. The analysis of municipal solid waste and fuel mixtures containing municipal solid waste for polycyclic aromatic hydrocarbons showed the risk of increasing polycyclic aromatic hydrocarbon concentrations in flue gases.

Technical indicators to improve municipal solid waste management in developing countries: A case in Mexico

Nowadays, increasingly complex sets of indicators are used to compare and diagnose municipal solid waste management (MSWM). These sets incorporate new priorities regarding sustainability and focus on measuring the progress to zero waste. Nevertheless, in developing countries, where MSWM is still striving to protect health from the potential impacts of waste, the MSWM information available is scarce and of low quality. This work proposes a basic set of indicators for analyzing technical aspects of street cleaning, waste collection and disposal in such contexts. Based on the assessment of 66 Mexican municipalities, ten indicators were identified that can be calculated with the information available. For each indicator, reference values were established, and their performance was evaluated by means of a traffic light system. In addition, a method that allows the quality of the information to be classified into four levels according to the data source, its uncertainty, the temporal coverage, and its spatial coverage was applied. The results obtained revealed an incipient implementation of MSWM and highlighted the need to increase the coverage of the collection services and to improve the conditions of the disposal sites in most of the municipalities that were studied. The proposed set of indicators can be used as a starting point to systematize the monitoring and detection of areas of improvement in the MSWM of the municipalities studied, as well as in other systems in similar contexts.

Switching Coal-Fired Thermal Power Plant to Composite Fuel for Recovering Industrial and Municipal Waste: Combustion Characteristics, Emissions, and Economic Effect

Combustion characteristics were studied experimentally for single droplets of fuel slurries based on wet coal processing waste with municipal solid waste components (cardboard, plastic, rubber, and wood) and used turbine oil. We established the ignition delay time for three various groups of fuel compositions in motionless air at 600–1000 °C. The minimum values are 3 s, and the maximum ones are 25 s. The maximum temperatures in the droplet vicinity reach 1300 °C during fuel combustion for compositions with 10% of used oil. The combustion temperatures of fuel compositions without oil are 200–300 °C lower. The concentrations of anthropogenic emissions in flue gases do not exceed those from dry coal combustion. Adding used oils to composite fuels reduces the concentrations of dioxins and furans in flue gases when municipal solid waste in the fuel burns out due to high combustion temperatures. Based on the experimental research findings, we have elaborated a strategy of combined industrial and municipal waste recovery by burning it as part of composite fuels, as illustrated by three neighboring regions of the Russian Federation with different industrial structures and levels of social development. This strategy suggests switching three typical coal-fired thermal power plants (one in each of the regions) to composite liquid fuel. It will reduce the hazard of waste to the environment and decrease the consumption of high-quality coals for power generation. Implementing the developed strategy for 25 years will save 145 Mt of coal and recover 190–260 Mt of waste. The positive economic effect, considering the modernization of fuel handling systems at thermal power plants and the construction of a fuel preparation plant, will make up 5.7 to 6.9 billion dollars, or 65–78%, respectively, of the main costs of three thermal power plants operating on coal within the identical period.

Reutilization of high COD leachate via recirculation strategy for methane production in anaerobic digestion of municipal solid waste: Performance and dynamic of methanogen community

The influences of reutilization of high COD leachate via recirculation strategy on methane production and dynamic of methanogen community in anaerobic digestion of Municipal Solid Waste (MSW) were revealed. With a COD concentration of 6000 mg·L^-1 recirculation, the efficiency of hydrolytic acidification process was improved and alleviated the pH reduction during acidification, while the highest COD removal efficiency was achieved. The maximum methane production rate and accumulated CH₄ production by the 6000 mg·L^-1 group increased by 90.7% and 156.0%, respectively. Whereas the performance of the 9000 mg·L^-1 group was actually below the control group. According to high-throughput sequencing, the superiority of acetotrophic Methanothrix was replaced by hydrogenotrophic Methanobacterium in the 3000- and 6000-mg·L^-1 systems. Methanoculleus predominated in the 9000-mg·L^-1 system, while Methanoregula, Methanolinea, and Methanospirillum suffered intensive inhibition effects. Canonical correspondence analysis verified a positive correlation between the dominant methanogens Methanobacterium and CH₄ production, and a negative correlation with Methanoculleus.