The urgent need to mitigate carbon dioxide (CO₂) emissions and address climate change has propelled the exploration of innovative approaches for carbon capture and storage (CCS). Among these, the carbonation of Industrial Alkaline Wastes (IAW) emerges as a promising avenue. In the design of a carbonation process, the primary challenges revolve around enhancing the CO₂ absorption rate while minimizing energy consumption and water demand. This holds true irrespective of the nature of the gas stream—whether it be flue gas, pure CO₂, or even air. Beyond the storage of CO₂, the main co-benefit of IAW carbonation lies in the value added through waste stabilization, facilitating its reutilization.

The study seeks to contribute to the optimization of carbonation reactors by providing a comprehensive understanding of the relevant factors influencing both the CO₂ absorption rate and the waste stabilization during MSWIA aqueous carbonation in open systems. The investigation considers Ca(OH)₂, Mg(OH)₂, and MSWIA carbonation individually, with a focus on free Ca and Mg oxides/hydroxides as the main phases providing cations for carbonation to occur. The detailed exploration of operational parameters aims to guide the design of efficient strategies, addressing the critical question of "How can an IAW carbonation reactor be optimized to achieve maximum CO₂ absorption, high yields, and stable byproducts?". The investigated operational parameters include:

• Ca(OH)₂, Mg(OH)₂, MSWIA initial concentrations;
• CO₂ flow rate;
• CO₂ concentration in the gas stream;
• Temperature;
• NaCl concentration (salinity);
• NaSO₄ concentration as accumulating impurities;
• MSWIFA concentration as accumulating impurities;
• Mixing system, with a comparison of bubbling (pipe), sparger and porous stone diffusor;
• Ball-milling of MSWIFA for particle size reduction;
• One-step vs two-step process (mineral extraction through pH-swing).

An experimental dataset, based on batch experiments, was collected using high-precision gas flow sensors to measure the percentage of flowing CO₂ absorbed by the reactor under a wide range of operational conditions. Leaching tests were carried out according to the EN 12457-2 standard on solid waste. Solid-liquid phases characterisation was conducted using XRPD with Rietveld refinement, SEM-EDS and ICP-MS. A computational set comprising equilibrium and dissolution kinetic models was developed using Phreeqc to interpret CO₂ absorption vs. time patterns as well as the pH dependence of the MSWIA leaching.

We acquired numerous relevant findings:

• Ca/Mg (hydr-)oxides dissolution is widely considered as the main rate-controlling step for IAW carbonation over CO₂. Using a CO₂ diffusion systems, we have shown that increasing the CO₂-water interfacial surface area by reducing the size of the bubbles causes a cascade of kinetic acceleration of dissolution.
• The average NaCl seawater concentration, 3.5 wt.%, optimizes the CO₂ absorption rate.
• By employing CO₂ sparger/porous stone diffusion alongside a 3.5 wt.% NaCl concentration, it becomes feasible to achieve an absorption rate exceeding 90 % for 2 L/min of CO₂ when using a solution with 7.5 wt.% Ca(OH)₂ in just 1 kilogram of water.

These insights pave the way for more energy-efficient and environmentally sustainable IAW reactor designs with the potential for widespread application in carbon capture and storage efforts. 

How to cite: Wehrung, Q., Pastero, L., Destefanis, E., Caviglia, C., Cavagna, S., Cotellucci, A., and Pavese, A.: Industrial Alkaline Waste Carbonation: Challenges and Opportunities. The case of Municipal Solid Waste Incineration Ashes (MSWIA), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-631, https://doi.org/10.5194/egusphere-egu24-631, 2024.

As a bulk by-product of the chemical phosphoric acid industry, phosphogypsum (PG) has not been effectively utilised because of the large number of impurities, and the large amount of stockpiled on the surface of the ground poses a potential risk of environmental pollution due to the leaching of its harmful elements. Therefore, the current consideration is to combine the bulk consumption of PG with the management of the underground mining area by cementing paste backfilling technology (CPB), so as to realise the harmless disposal of PG in the management of the mining area at the same time. However, there are several scientific problems as follows:

• PG has a large amount of phosphoric acid residue in the output process, which makes the pH of phosphogypsum around 2~3, and it is difficult to meet the alkaline environment requirements for cement hydration.
• The poor cementing properties of PG and silicate cement lead to limited development of the strength of the PG backfilling body, and increasing the proportion of cementitious materials is bound to increase the cost of backfilling.
• Although PG cemented backfiller can fix/stabilise most of the harmful elements leaching pollution, according to the preliminary experimental research, the fluorine leaching amount in the backfiller is still far more than the original groundwater quality grade standard (>2.0mg/L).

Therefore, on the basis of CaO neutralisation and modification of PG, we choose diversified active solid wastes such as steel slag and slag as backfilling cementitious materials, and use PAC or biochar as targeted fluorine fixation materials. Afterwards, we can obtain the parameters of PG backfilling ratios in line with the requirements of strength and environmental protection through a large number of experiments. The hydration and fluorine leaching mechanisms were explained by XRD, EPMA-WDS, heat of hydration test, compressive strength test and fluorine leaching test.

How to cite: Wang, D., Zhang, Q., and Tao, Y.: Research on the transformation and immobilization mechanism of fluorine-containing phase in phosphogypsum low-carbon gel backfilling system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6954, https://doi.org/10.5194/egusphere-egu24-6954, 2024.

An effective magnetic polymeric composite was produced from steelmaking waste in this work. For the elimination of methyl orange MO and methylene blue MB from synthetic solutions, steel slag was treated with an acrylamide acrylic acid (SSAA) copolymer. TGA thermogravimetric analysis, SEM scanning electron microscope, XRD X-ray diffraction, BET Brunauer-Emmett-Teller surface area, and FTIR Fourier transform infrared were used to analyze the SSAA composite. The SSAA adsorption behavior for MO and MB was studied, and the impact of various factors was analyzed using one factor at a time (OFAT) and the RSM-BBD response surface method-Box Behnken Design. The second-order kinetic model accurately described the kinetic data of MO and MB, and the primary rate-limiting phase is film diffusion. The Dubinin-Raudshkevish (D-R) and Freundlich isotherms accurately characterized the MB and MO experimental outcomes, respectively. MO and MB had maximal absorption efficiencies of 97% and 94%, respectively, and capacities of 47 and 463 mg/g. The thermodynamic studies revealed that MO and MB adsorption on the SSAA was favorable and spontaneous. Physical adsorption was discovered to be the dominant mechanism for MB, whereas chemisorption was identified for MO. The regeneration investigation verified these mechanisms, in which SSAA was regenerated for MB and a negligible decline in adsorption capacity was seen after five cycles. However, for MO ions, a minor renewal of the SSAA was achieved, confirming the chemisorption mechanism. According to the thermodynamic study, the SSAA composite might be employed for the removal of cationic and anionic dyes from wastewater spontaneously and feasibly.

How to cite: Basaleh, A., Al-Malack, M., Saleh, T., and Tawabini, B.: Utilization of steelmaking waste as a sustainable low-cost adsorbent for cationic and anionic dyes removal , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1777, https://doi.org/10.5194/egusphere-egu24-1777, 2024.

The hydration of alkali-activated slag (AAS) is highly sensitive to the curing temperature, especially at early ages. In low temperature environment, cemented paste backfill made of AAS (AAS-CPB) exhibits notably reduced early-age uniaxial compressive strength (UCS), attributable to the inhibitory effect of low temperature on slag hydration. This study aims to improve the performance of AAS-CPB at low temperatures by incorporating chemical additives. The results shows that calcium salts, specifically CaCl2, CaSO4, and Ca(COOCH3)2, can increase the early-age UCS of AAS-CPB by up to 1050%, depending on the specific anion involved. Overall, CaCl2 provides the greatest enhancement in the UCS. However, the presence of these salts result in strength degradation at later ages. A pronounced exponential relationship is evident between UCS and ultrasonic pulse velocity. The change of conductivity and moisture content are valuable indicators of hydration process at low temperatures. C(N)-A-S-H, hydrotalcite and portlandite are the primary hydration products. Anions play a decisive role in the morphology, precipitation and quantity of C(N)-A-S-H. The slag hydration degree and UCS basically exhibit a consistent trend. 

How to cite: Wang, Z., Gu, X., and Jiang, H.: Improving early-age performance of alkali-activated slag paste backfill with calcium salts at low temperature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5156, https://doi.org/10.5194/egusphere-egu24-5156, 2024.

Through this study, a novel method for producing magnetic biochar from waste wood sourced from Acacia auriculiformis is achieved. Slow pyrolysis method of biochar was used for the conversion of waste wood which in turn proved to be more efficient than other procedures. Nanoparticles which were successfully deposited onto the surface of biochar were derived from iron powder transformed into iron-oxide. High specific surface area of 266.564 m²g^-1 was achieved through Brunauer–Emmett–Teller (BET) analysis. Scanning Electron Microscopy (SEM) images demonstrate the formation of triangular pyramid-shaped nanoparticles in the adsorbent's inner and outer wall pores. Fe₃O₄ was coated on the surface of the adsorbent in a crystalline, carbonaceous form, as indicated by XRD peaks. A number of hydroxyl and aliphatic stretching bonds of carbon serve as functional groups in the impregnation and anionic targeted pollutants adsorption process, according to FTIR research. The establishment of the best-fit model for several anionic pollutants followed the method of multi-layer heterogeneous adsorption. Removal efficiencies of 95%, 85%, and 80% of arsenic, chromium, and fluoride are attained, respectively. Kinetic models were used to determine the adsorption process. Surface mechanism involved electrostatic attraction followed by pseudo first, second order, Bangham equation and Weber Morris intra-particle diffusion and complexation helping in adsorption of the anionic ions. Whereas, chromium and fluoride followed Temkin and Dubinin-Radushkevich adsorption isotherms. The maximum capacity of the manufactured biochar for arsenic, chromium and fluoride is estimated to be 294.1176, 204.22 and 102.36 mgg^-1 respectively. Regeneration studies showed that upto 80-90% of ions can be recovered from the magnetic biochar.

How to cite: Das, S. and Mondal, S.: Separation and recovery of anions from aqueous solution through iron oxide nanoparticle impregnated biochar derived from waste wood, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-515, https://doi.org/10.5194/egusphere-egu24-515, 2024.

Ordinary Portland Cement (OPC) is the most widely used cementitious material in cemented paste backfill at present. However, OPC production consumes massive energy and is one of the main contributors to greenhouse gas emissions. Hybrid alkali-activated cement (HAAC) is a promising alternative to Ordinary Portland Cement (OPC), mainly consisting of supplementary cementitious materials (SCMs), OPC, and alkali activators. This innovative solution not only reduces energy consumption but also mitigates carbon footprint compared to OPC production. Moreover, it is worth noting that the production process of widely used commercial alkali activators, including sodium hydroxide and sodium silicate, is associated with notable energy consumption and environmental pollution. Therefore, addressing these concerns is essential for enhancing the sustainability of HAAC and making it an environmentally friendly choice in cemented paste backfill.

Red mud (RM) is a by-product generated by the Bayer process during the production of alumina from bauxite, which is a potential alternative to commercial alkali activators due to its high alkalinity. The experimental results show that the cemented paste backfill with RM-NaOH activated slag cement exhibits higher compressive strength than that with OPC or NaOH activated slag cement as binders in different curing ages. By comparing the Life Cycle Assessment (LCA) results, the RM-NaOH activated slag cement shows reductions mainly in the environmental impact categories of terrestrial acidification potential (TAP), fossil depletion potential (FDP), ozone depletion potential (ODP), and global warming potential (GWP). The total environmental impact of RM-NaOH activated slag cement is reduced by 13.67% compared to OPC, indicating that the production of HAAC with RM as the primary activator would significantly decrease the environmental effect of OPC manufacturing.

How to cite: Feng, Y., Zhao, C., Zhang, Q., and Wang, D.: Using Bayer red mud as an alternative activator in hybrid alkali-activated cement for cemented paste backfill: Experimental investigation and life cycle assessments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3326, https://doi.org/10.5194/egusphere-egu24-3326, 2024.

In the quest for achieving the principles of a circular economy, our Helios Lab seeks to optimize the e-waste recycling industry with its innovative Ramses-4-CE project (KIC RM 19262). Ramses focuses on the development of a smart network comprising multimodal optical non-invasive sensors mimicking industrial scenarios with a conveyor belt that can attain speeds of several meters per second. The primary objective is to facilitate the comprehensive identification and characterization of e-waste materials, particularly printed circuit boards (PCBs), plastics, and rare earth elements (REE).

The sensor ensemble encompasses a laser profiler generating height maps, an RGB camera capturing surface spatial features, hyperspectral cameras capturing the spectral features, and chemical characteristics obtained with a Raman spectroscopy sensor affixed to a robotic arm. Each sensor type offers unique advantages and inherent challenges. RGB cameras with their data facilitate fast, highly accurate, and smart data processing e.g., using machine learning (ML) and deep learning (DL) object detection and segmentation techniques in shredded plastics, while hyperspectral imaging (HSI) aids in polymer identification based on spectral fingerprint libraries. Nonetheless, HSI poses challenges such as large data size due to its abundant information, noise interference, and overlong processing times.

To optimize the data processing pipeline, meticulous preprocessing and processing methods have been devised. Upon data acquisition of different objects and materials, data co-registration is executed on the resulting RGB images and hyperspectral cubes, followed by object detection and segmentation of valuable objects on both data types. For objects eluding identification via RGB and hyperspectral imagery, a Raman spectroscopy-based validation is involved for detailed chemical analysis.

Yet, exerting high accuracy in HSI pixel-wise classification on multi-unseen data cubes necessitates HSI classification models with robust generalization capabilities. Towards this aim, smart automated masking of undesired objects in the hyperspectral scene is developed. HS cube contains abundant data causing their large volume size. This abundance highlights the useful information, while concurrently amplifying noises and artifacts, detrimentally affecting both data processing speed and model generalization. Masking undesired objects in the HSI reduces the number of pixel vectors skewing calculations in preprocessing steps and DL models training routines, leading to enhanced segmentation models, i.e., masking unwanted data vectors from HSI allows exclusive processing for desired targets elevating processing speed without compromising accuracy. 

How to cite: Arbash, E., Fuchs, M., Rasti, B., Lorenz, S., Ghamisi, P., and Gloaguen, R.: Ramses-4-CE: Towards Enhanced Generalization of RGB/Hyperspectral Imaging Data Processing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13218, https://doi.org/10.5194/egusphere-egu24-13218, 2024.

The implementation of efficient municipal waste management systems is crucial to address current environmental challenges. These systems allow for the minimization of waste generation, promotion of reuse and recycling, and proper management of remaining waste. By reducing the amount of waste sent to landfills, soil, water, and air pollution decreases, and the emission of greenhouse gases is limited. Moreover, efficient municipal waste management fosters the circular economy by recovering valuable resources from waste, thereby contributing to the conservation of raw materials and long-term sustainability.

This work presents a methodology for urban waste management tailored to medium-sized municipalities (approximately 10,000 inhabitants). It highlights the resources and tools available at the municipal level to achieve the objectives set by European Directives on waste management. These resources encompass environmental communication and information, economic, fiscal, and regulatory instruments, as well as a proposal for a model of urban solid waste collection.

The proposed methodology is applied to the municipality of l'Alcora (Castellón, Spain), whose current management model relies on anonymous municipal waste collection, where citizens voluntarily decide where to dispose of their waste based on their environmental awareness, without any form of reward or penalty for their actions. This voluntariness and limited promotion of environmental awareness have led to a general lack of interest among the population in waste management. This situation has, in general, caused Spain to lag behind other EU member states in achieving the goals of waste prevention, valorization, and recycling set by the European Union.

How to cite: Pérez, E., Rodrigo-Ilarri, J., and Rodrigo-Clavero, M.-E.: Implementing a new model of urban solid waste management at a local scale: application to the municipality of l'alcora (castellón, spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15399, https://doi.org/10.5194/egusphere-egu24-15399, 2024.

KEU (Kraftanlagen Energie und Umwelttechnick) is a by-product of a pyrolyzed waste of sewage sludge produced by wastewater treatment from tannery industries. KEU is regarded as an industrial non-hazardous waste after inertization to obtain a sintering granulate and usually mixed with demolition-construction or industrial mud products to produce EoW (End of Waste) material. However, the resulting materials are apparently responsible of the anomalous concentrations of Cr and CrVI and other PTEs (Potentially Toxic Elements), recovered in several domestic wells distributed along the Siena-Empoli motorway (Tuscany, central Italy) since KEU was used as roadbed. Similar concerns were also evidenced in other areas, as in the local groundwater system, where the KEU industrial by-product is stored, anomalous contents of heavy metals were determined.

In this work, an extensive analytical work was conducted to characterize the mineralogical and chemical bulk composition of eight KEU-bearing samples collected from different cumulus stored in an aggregate crushing plant and one pyrolysis char (the KEU) sample. It is remarkable the presence of high Rare Earth Elements (REEs) concentrations. While pure KEU has total REEs of 14 mg/kg, the KEU-bearing materials are up 4300 mg/kg.

To verify whether the KEU-bearing samples were able to release PTEs, three leaching tests (after 1-hour, 1-day and 7-days) were performed by shaking 20 g in 200 mL of MilliQ and 20 g in 200 mL of CO₂-saturated MilliQ water, the latter simulating the interaction between meteoric waters and KEU-bearing materials. The resulting suspensions of all the aliquots were centrifuged and the surnatant was analyzed for pH, electrical conductivity, main composition, CrVI and trace elements. The 1-day post-centrifugation residue was leached and shaken for 7 days to evidence whether the PTEs were still released after a relatively long-term leaching. The analytical results showed that the MilliQ water leachates have high pH values (up to 11.75) whereas those obtained by CO₂-saturated MilliQ partly buffer the pH although moderately alkaline pH values were measured. Our study indicates that, as expected, in most cases the CO₂-saturated MilliQ water is able to more efficiently scavenge PTEs than those solubilized by MilliQ water. Moreover, the 1-day leachates resulted to be enriched in many PTEs with concentrations, in most cases, from hundreds to thousands microg/L. Despite a general decrease, in the 7-days leachates, high contents of some heavy metals were still measured, suggesting that prolonged interaction between meteoric waters and the KEU-bearing materials is able to transfer PTEs to the groundwater systems. The 1-hour and 1-day leachates showed relatively high concentrations of CrVI (from 20 to 1370 microg/L) while REEs were always approaching the detection limit or below it. Another important aspect is that the investigated samples are chemically heterogeneous, indicating that the inertization process was not performed by using the same amount of demolition and construction materials although the main composition was mostly Ca-SO₄. Notwithstanding such an inertization, aimed at stabilizing unwanted toxic elements, its efficiency is rather scarce and, consequently, its use as by-product is strongly discouraged unless a more adequate inertization process is applied.

How to cite: Vaselli, O., Meloni, F., Nisi, B., Panarese, M., Cabassi, J., Montegrossi, G., and Fagiolino, I.: When environmentally friendly solutions are worse than the contaminated product: the KEU case study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15407, https://doi.org/10.5194/egusphere-egu24-15407, 2024.

The organic fraction of municipal solid waste (OFMSW) represents between 40% and 50% of the solid waste of a megacity and despite its great potential for use, continues to generate environmental problems, which highlights the need to continue the search for sustainable and efficient solutions [1].  Current research processes have been geared towards anaerobic digestion (AD) as a promising technology to treat this waste. To this end, this study focuses on examining variables and mathematical models to precisely implement AD processes in a megacity, while exploring its technical and economic feasibility to address the increased amounts of these wastes, in order to optimize current technological developments.  

In megacities such as Bogotá, the case study area for this research paper, addressing the environmental, social and public health impacts generated by OFMSW is of the utmost importance. Anaerobic digestion is projected as an innovative and sustainable alternative, which not only contributes to treating waste, but also as a source of renewable energy, in addition to generating valuable by-products for agriculture. However, successfully applying AD in a megacity requires an in-depth analysis of the processes involved and the examination of multiple variables for its integration into models that become essential decision-making tools.

The following are among the technical variables of analysis for these processes and their subsequent modeling: OFMSW composition, temperature, carbon-to-nitrogen ratio, pH, volatile fatty acids and the presence of inhibitors as critical factors that impact AD performance. Given this scenario, having an adaptive approach that ensures predictive and consistent results over time is indispensable. In addition to these variables, aspects associated with economic, environmental, and social viability should be included, such as population size and projections, climate variability and seasonality, costs associated with the comprehensive service, correct separation at the source, policies and governance models, and land use plans established within the development plans of the cities[2]. Thus, the results obtained from this research study will provide a comprehensive understanding of the factors, processes and variables that influence the efficiency of AD of OFMSW in a megacity. These findings will not only contribute to the design of more efficient systems, but also support decision-making processes, as well as the formulation of waste management strategies, policies and practices at the city level.

[1]      L. M. Ulloa-Murillo, L. M. Villegas, A. R. Rodríguez-Ortiz, M. Duque-Acevedo, and F. J. Cortés-García, "Management of the Organic Fraction of Municipal Solid Waste in the Context of a Sustainable and Circular Model: Analysis of Trends in Latin America and the Caribbean," Int J Environ Res Public Health, vol. 19, no. 10, 2022, doi: 10.3390/ijerph19106041.

[2]       L. Mu, L. Zhang, K. Zhu, J. Ma, and A. Li, "Semi-continuous anaerobic digestion of extruded OFMSW: Process performance and energetics evaluation," Bioresour Technol, vol. 247, pp. 103-115, 2018, doi: 10.1016/j.biortech.2017.09.085.

How to cite: Becerra Quiroz, A. P., Solano Meza, J. K., Rodrigo-Clavero, M. E., and Rodrigo-Ilarri, J.: Modeling Anaerobic Digestion Processes to Treat the Organic Fraction of Municipal SolidWaste in a Megacity: A Comprehensive Approach to Sustainable Waste Management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19079, https://doi.org/10.5194/egusphere-egu24-19079, 2024.