Clean Technol., Volume 7, Issue 4 (December 2025) – 18 articles

CO₂ emissions from various anthropogenic activities have led to serious global concerns (climate change and global warming), and, therefore, CO₂ capture by sustainable methods is a priority research topic. One of the most widely used and cost-effective technologies for post-combustion CO₂ capture (PCC) is the chemical absorption method, where potassium carbonate solution is proposed as a solvent (with or without the addition of promoters, such as amines). An ecological alternative, presented in this study, is the use of amino acids instead of amines as promoters—alanine (Ala), glycine (Gly) and sarcosine (Sar)—in concentrations of 25% by weight of K₂CO₃ + 5 or 10% by weight of amino acid salt, thus resulting in the so-called green solvents, which do not show high toxicity and inertness to biodegradability. The studies had as a first objective the characterization of the proposed green solvents, in terms of density and viscosity, and then the comparative testing of their efficiency for CO₂ retention from gaseous fluxes containing high CO₂ concentrations. The experiments were performed at temperatures of 298 K, 313 K, and 333 K at atmospheric pressure. The best performance was observed with K₂CO₃ + 5% Sar salt at 313 K, reaching an absorption capacity of 2.58 mol CO₂/L solvent, which is a promising improvement over the reference solution based on K₂CO₃. Increasing the amino acid concentration to 10% generally led to a reduced performance, especially for sarcosine, probably due to an increase in solution viscosity or a possible kinetic inhibition. This study provides valuable experimental data supporting the ecological potential of amino acid-promoted potassium carbonate systems, paving the way for further development of chemisorption processes and their implementation on an industrial scale. Full article

In recent years, industrial symbiosis (IS) has gained attention as a strategy to enhance circularity and to reduce the environmental impacts of solid waste management through resource reuse and recovery. Life Cycle Assessment (LCA) is increasingly used to evaluate the environmental performance of such inter-industry collaborations. Given the growing diversity of IS practices and LCA models, this updated review serves as a methodological reference, mapping existing approaches and identifying gaps to guide future research on the systematic assessment of circular strategies. Moreover, it investigates the environmental performance of IS approaches in the field, based on the LCA results of the analyzed case studies. We analyzed 48 peer-reviewed studies to examine how LCA has been applied to model and assess the environmental impacts and benefits of IS in the context of waste management. The literature revealed wide methodological variability, including differences in system boundaries, functional units, and impact categories, affecting comparability and consistency. Case studies confirm that IS can contribute to reducing environmental burdens, particularly with regard to climate change and resource depletion, though challenges remain in modelling the complex inter-organizational exchanges and accessing reliable data. Socio-economic aspects are increasingly considered but remain underrepresented. Future research should focus on methodological improvements, such as greater standardization and the better integration of indirect effects, to strengthen LCA in decision-making and to explore a wider range of scenarios reflecting different stakeholders, analytical perspectives, and the evolution of symbiotic systems over time. Full article

The reaction between polyols and diisocyanates forms polyurethane (PU) adhesives. However, these materials are derived from petroleum-based chemicals, whose availability is declining. As an environmentally friendly, renewable, and formaldehyde-free alternative, tannins offer a promising solution. This study aimed to characterize tannin-based polyurethane (TPU) adhesives modified with bio-polyol, analyze their performance, and determine optimal tannin extract formulation for use as a plywood adhesive, as the first step toward developing eco-friendly TPU adhesives. TPU adhesives were made using modified polyvinyl alcohol (PVOH) and tannins at concentration levels of 0%, 10%, 20%, 30%, 40%, and 50%. The analysis is carried out on raw materials, adhesives, and plywood. The results showed that adding tannin extracts had a significant effect on viscosity, tannin solids content, density, delamination, and dry and wet adhesion strength, but not for moisture content. Functional group analysis (FTIR) confirmed that both liquid and solid TPU adhesives contained urethane, hydroxyl, and isocyanate functional groups. The lowest DMA loss modulus was observed in TPU with tannin 20%. Additionally, the highest adhesion strength was achieved with 20% TPU, which correlated with increased wood failure. Based on these findings, PVOH/tannin 20% was considered an effective formula for TPU adhesives. Full article

The rapid expansion of global aquaculture has led to wastewater enriched with nitrogen, phosphorus, organic matter, antibiotics, and heavy metals, posing serious risks such as eutrophication, ecological imbalance, and public health threats. Conventional physical, chemical, and biological treatments face limitations including high cost, secondary pollution, and insufficient efficiency, limiting sustainable wastewater management. Algal–bacterial symbiotic systems (ABSS) provide a sustainable alternative, coupling the metabolic complementarity of microalgae and bacteria for effective pollutant mitigation and concurrent biomass valorization. Immobilizing microbial consortia within carrier materials enhances system stability, tolerance to environmental changes, and scalability. This review systematically summarizes the pollution characteristics and ecological risks of aquaculture effluents, highlighting the limitations of conventional treatment methods. It focuses on the metabolic cooperation within ABSS, including nutrient cycling and pollutant degradation, the impact of environmental factors, and the role of immobilization carriers in enhancing system performance and biomass resource valorization. Despite their potential, ABSS still face challenges related to mass transfer limitations, complex microbial interactions, and difficulties in scale-up. Future research should focus on improving environmental adaptability, regulating microbial dynamics, designing intelligent and cost-effective carriers, and developing modular engineering systems to enable robust and scalable solutions for sustainable aquaculture wastewater treatment. Full article

Energy transition is crucial for climate change mitigation and Sustainable Development Goals (SDGs), and has been a key government focus in Colombia since 2022, which must carefully consider its energy roadmap. This study evaluates three potential scenarios for achieving nearly 100% renewable energy by 2035: replacing fossil fuels with biofuels, using hydrogen for transport and industrial heat, and relying entirely on renewable electricity. This paper discusses these scenarios’ technical, economic, and social challenges, including the need for substantial investments in renewable energy technologies and energy storage systems to replace fossil fuels. The discussion highlights the importance of balancing energy security, environmental concerns, and economic growth while addressing social priorities such as poverty eradication and access to healthcare and education. The results show that while the Colombian government’s energy transition goals are commendable, a rapid energy transition requires 4 to 8 times the government’s projected 34 billion USD investment, making it economically unfeasible. Notably, focusing on wind, photovoltaic, and green hydrogen systems, which need storage, is too costly. Furthermore, replacing fossil fuels in transport is impractical, though increasing biofuel production could partially substitute fossil fuels. Less energy-intensive alternatives like trains and waterway transport should be considered to reduce energy demand and carbon footprint. Full article

The fashion and textile industry (FTI) is a significant contributor to greenhouse gas emissions, resource consumption, and waste generation, necessitating sustainable alternatives. Chitosan, a biodegradable and renewable biopolymer, has shown potential in reducing environmental impact throughout the textile lifecycle. However, existing studies often focus on isolated applications rather than its broader role in industrial sustainability. This review synthesises findings from 142 academic studies to assess chitosan’s applications in textile production, dyeing, finishing, and waste management, emphasising its impact on energy efficiency, carbon reduction, and resource circularity. Chitosan’s biodegradability, antimicrobial properties, and affinity for sustainable dyeing offer a viable alternative to synthetic materials while also enhancing wastewater treatment and eco-friendly finishing techniques. By evaluating its contributions to sustainable manufacturing, this review highlights its potential in supporting decarbonisation and circular economy transitions within the textile sector, while also identifying challenges for future research. Full article

Fuel cells are highly efficient electrochemical devices that convert the chemical energy of fuel directly into electrical energy, while generating minimal pollutant emissions. In recent decades, they have established themselves as a key technology for sustainable energy supply in the transport sector, stationary systems, and portable applications. In order to assess their real contribution to environmental protection and energy efficiency, a comprehensive analysis of their life cycle, Life Cycle Assessment (LCA) is necessary, covering all stages, from the extraction of raw materials and the production of components, through operation and maintenance, to decommissioning and recycling. Particular attention is paid to the environmental challenges associated with the extraction of platinum catalysts, the production of membranes, and waste management. Economic aspects, such as capital costs, the price of hydrogen, and maintenance costs, also have a significant impact on their widespread implementation. This manuscript presents detailed mathematical models that describe the electrochemical characteristics, energy and mass balances, degradation dynamics, and cost structures over the life cycle of fuel cells. The models focus on proton exchange membrane fuel cells (PEMFCs), with possible extensions to other types. LCA is applied to quantify environmental impacts, such as global warming potential (GWP), while the levelized cost of electricity (LCOE) is used to assess economic viability. Particular attention is paid to the sustainability challenges of platinum catalyst extraction, membrane production, and end-of-life material recovery. By integrating technical, environmental, and economic modeling, the paper provides a systematic perspective for optimizing fuel cell deployment within a circular economy. Full article

The Allam power cycle is a groundbreaking elevated-pressure power generation unit that utilizes oxygen and fossil fuels to generate low-cost electricity while capturing carbon dioxide (CO₂) inherently. In this project, we utilize the CO₂ generated from the Allam cycle as feedstock for a newly envisioned industrial complex dedicated to producing renewable hydrocarbons. The industrial complex (FAAR) comprises four subsystems: (i) a Fischer–Tropsch synthesis plant (FTSP), (ii) an alkaline water electrolysis plant (AWEP), (iii) an Allam power cycle plant (APCP), and (iv) a reverse water-gas shift plant (RWGSP). Through effective material, heat, and power integration, the FAAR complex, utilizing 57.1% renewable energy for its electricity needs, can poly-generate sustainable hydrocarbons (C₁–C₃₀), pure hydrogen, and oxygen with near-zero emissions from natural gas and water. Economic analysis indicates strong financial performance of the development, with an internal rate of return (IRR) of 18%, a discounted payback period of 8.7 years, and a profitability index of 2.39. The complex has been validated through rigorous modeling and simulation using Aspen Plus version 14, including sensitivity analysis. Full article

Coal is commonly used as both fuel and reducing agent in producing synthetic rutile from ilmenite (FeTiO₃) via the Becher process, which upgrades ilmenite to high-purity TiO₂ (>88%). However, coal-based reduction generates significant carbon waste. This study investigated the effect of adding 1–5% w/w potassium hydroxide (KOH), sodium hydroxide (NaOH), and sodium tetraborate (borax) to coal during ilmenite reduction to improve metallisation and reduce carbon burn-off. Results showed that 1% w/w additives significantly increased metallisation to 96% (KOH), 95% (NaOH), and 93% (borax), compared to 80% without additives, while higher concentrations (3–5% w/w) decreased metallisation. Scanning electron microscopy (SEM)analysis showed cleaner particle surfaces and optimal metallisation at 1% w/w, whereas higher additive levels caused agglomeration or sintering due to elevated silica and alumina activity. Additive type also influenced TiO₂ quality, with KOH enhancing TiO₂ at low concentrations but causing negative effects at higher levels, while NaOH and borax reduced TiO₂ quality via sodium-based compound formation. All additives reduced carbon burn-off, with KOH producing the greatest reduction. The iodine number of the carbon residue increased with higher additive concentrations, with KOH achieving 710 mg/g at 1% w/w and 900 mg/g at 5% w/w, making the residue suitable for water treatment. Overall, KOH is the most effective additive for producing high-quality synthetic rutile while minimising carbon waste. Full article

Agro-industrial activities require adaptations of technological energy systems to align with the European Sustainable Development Goals, and their highly seasonal and intermittent consumption profiles necessitate precise environmental assessment. This study aims at investigating the photovoltaic (PV) energy in various existing olive mills to assess the reduction in olive oil carbon footprint (CF) when it is supplied by either a rooftop PV system or by PV combined with a battery energy storage system (BESS) to promote the self-consumption of the renewable energy produced, compared to the case when electricity is supplied by the national grid (NG). To this end, an algorithm was developed to optimise a decision-making tool for low-carbon energy systems in agro-industrial activities. An economic assessment was performed to complement the decision-making process. The potential energy self-consumed by the mill ranged between 11% and 18.1%. The renewable energy produced covered between 11% and 84.7% of the mill’s energy consumption. CF reduction resulted between 22% and 119%, depending on the system boundaries considered. The proposed methodology allows for replicability to other industrial activities, having different energy consumption profiles, with seasonal and discontinued consumption paths, since it is based on an hourly energy consumption evaluation. Full article

Sewage sludge, as a by-product of wastewater treatment, represents a significant cost factor in the operation of wastewater treatment plants and accounts for up to 50% of total costs. As sewage sludge still contains a high proportion of water after the basic treatment processes (thickening, stabilization and dewatering), sludge drying helps to reduce further treatment and disposal costs. Conventional drying methods are associated with high energy consumption, making solar drying a more cost-effective alternative. This paper analyzes the economic aspects of constructing a sewage sludge solar drying facility with the help of an expert system based on neural networks. The system considers a range of parameters (plant capacity, transport distance, transport and treatment costs, etc.) to assess the values of the investment as well as the operation and maintenance costs. The analysis was carried out using NeuralTools (Lumivero). Two main options for sludge disposal were investigated: treatment at a regional center (with the sub-options of own or outsourced transport) and handing over of sludge to another legal entity. In total, five neural network models were developed based on the input load (from 75 to 10,000 t/year and from 10,000 to 20,000 t/year) and transport method (own or outsourced transport), resulting in an analysis of over 670,000 scenarios. The key output variable was the net present value of costs over a 30-year period. The results demonstrated high model accuracy (error < 5%) and allowed a comparison of the profitability of constructing a sewage sludge solar drying facility with alternative methods of sludge disposal, in particular with the transport and disposal of the dewatered sludge. Full article

In Abidjan, the treatment of pig waste is becoming a priority given the continued growth of pig farms, which readily reuse manure as organic fertilizer. This study evaluated the effectiveness of anaerobic digestion for simultaneous biogas production and pathogen reduction from pig farm residues. Two 1600 L biodigesters were installed at pig farms in Port Bouët (PBk) and Abobo (Ab). They were fed with pig manure and water (1:4 ratio) and monitored over 56 days. The total biogas production was 22.63 m³ and 16.31 m³ for the PBk and Ab digesters, respectively, with peak production occurring between days 14 and 28. Following biofilter treatment, the methane content increased to 80–82%, yielding potential energy outputs of 2.32–3.29 kWh/d, with optimal production occurring at a pH of 7.28–7.76. The COD, BOD₅, organic acid, and total nitrogen levels decreased progressively in the biodigesters, while the mineral element content remained almost unchanged. Complete elimination was achieved for most of the bacteria tested (E. coli, Enterococcus, Salmonella, etc.). However, Bacillus and Clostridium were able to persist, albeit with significant reductions of between 3.11 and 5.79 log₁₀. Anaerobic digestion is an effective method of combining waste treatment and energy recovery. It eliminates major pathogens while producing valuable biogas. This makes it a sustainable waste management solution for urban agricultural systems. Full article

In this work a multi-criteria analysis and an optimization tool were developed, which allows the substitution of fossil-based solvents with bio-based alternatives based on Hansen solubility parameters and various physical parameters, such as the boiling point, evaporation rate, viscosity or wetting behavior. The proof of concept was achieved by formulating two different paints used in coil coatings using the bio-based solvents, and they performed equally as well as their fossil-based counterparts. A potential decrease in CO₂ emissions was determined by a life cycle assessment and cradle-to-grave analysis of bio- and fossil-based solvents, which showed a large sustainability bonus when using solvents based on biomass. The introduced methodology provides initial insights into substituting currently used solvents systematically. Overall, implementing bio-based solvents is a viable drop-in method to decrease the environmental impact of paints and coatings, while maintaining the same performance. Full article

The hydrogen economy stands at the forefront of the global energy transition, and additive manufacturing (AM) is increasingly recognized as a critical enabler of this transformation. AM offers unique capabilities for improving the performance and durability of hydrogen energy components through rapid prototyping, topology optimization, functional integration of cooling channels, and the fabrication of intricate, hierarchical, structured pores with precisely controlled connectivity. These features facilitate efficient heat and mass transfer, thereby improving hydrogen production, storage, and utilization efficiency. Furthermore, AM’s multi-material and functionally graded printing capability holds promise for producing components with tailored properties to mitigate hydrogen embrittlement, significantly extending operational lifespan. Collectively, these advances suggest that AM could lower manufacturing costs for hydrogen-related systems while improving performance and reliability. However, the current literature provides limited evidence on the integrated techno-economic advantages of AM in hydrogen applications, posing a significant barrier to large-scale industrial adoption. At present, the technological readiness level (TRL) of AM-based hydrogen components is estimated to be 4–5, reflecting laboratory-scale progress but underscoring the need for further development, validation and industrial-scale demonstration before commercialization can be realized. Full article

Hydrogen is increasingly recognized as a clean energy vector and storage medium, yet its viability and strategic role in the Western Balkans remain underexplored. This study provides the first comprehensive techno-economic, environmental, and strategic evaluation of hydrogen production pathways in Albania. Results show clear trade-offs across options. The levelized cost of hydrogen (LCOH) is estimated at 8.76 €/kg H₂ for grid-connected, 7.75 €/kg H₂ for solar, and 7.66 €/kg H₂ for wind electrolysis—values above EU averages and reliant on lower electricity costs and efficiency gains. In contrast, fossil-based hydrogen via steam methane reforming (SMR) is cheaper at 3.45 €/kg H₂, rising to 4.74 €/kg H₂ with carbon capture and storage (CCS). Environmentally, Life Cycle Assessment (LCA) results show much lower Global Warming Potential (<1 kg CO₂-eq/kg H₂) for renewables compared with ~10.39 kg CO₂-eq/kg H₂ for SMR, reduced to 3.19 kg CO₂-eq/kg H₂ with CCS. However, grid electrolysis dominated by hydropower entails high water-scarcity impacts, highlighting resource trade-offs. Strategically, Albania’s growing solar and wind projects (electricity prices of 24.89–44.88 €/MWh), coupled with existing gas infrastructure and EU integration, provide strong potential. While regulatory gaps and limited expertise remain challenges, competition from solar-plus-storage, regional rivals, and dependence on external financing pose additional risks. In the near term, a transitional phase using SMR + CCS could leverage Albania’s gas assets to scale hydrogen production while renewables mature. Overall, Albania’s hydrogen future hinges on targeted investments, supportive policies, and capacity building aligned with EU Green Deal objectives, with solar-powered electrolysis offering the potential to deliver environmentally sustainable green hydrogen at costs below 5.7 €/kg H₂. Full article

The cement industry accounts for approximately 7–8% of global CO₂ emissions, primarily due to energy-intensive clinker production and limestone calcination. With cement demand continuing to rise, particularly in emerging economies, decarbonization has become an urgent global challenge. The objective of this study is to systematically map and synthesize existing evidence on technological pathways, policy measures, and economic barriers to four core decarbonization strategies: clinker substitution, energy efficiency, alternative fuels, as well as carbon capture, utilization, and storage (CCUS) in the cement sector, with the goal of identifying practical strategies that can align industry practice with long-term climate goals. A scoping review methodology was adopted, drawing on peer-reviewed journal articles, technical reports, and policy documents to ensure a comprehensive perspective. The results demonstrate that each mitigation pathway is technically feasible but faces substantial real-world constraints. Clinker substitution delivers immediate reduction but is limited by SCM availability/quality, durability qualification, and conservative codes; LC₃ is promising where clay logistics allow. Energy-efficiency measures like waste-heat recovery and advanced controls reduce fuel use but face high capital expenditure, downtime, and diminishing returns in modern plants. Alternative fuels can reduce combustion-related emissions but face challenges of supply chains, technical integration challenges, quality, weak waste-management systems, and regulatory acceptance. CCUS, the most considerable long-term potential, addresses process CO₂ and enables deep reductions, but remains commercially unviable due to current economics, high costs, limited policy support, lack of large-scale deployment, and access to transport and storage. Cross-cutting economic challenges, regulatory gaps, skill shortages, and social resistance including NIMBYism further slow adoption, particularly in low-income regions. This study concludes that a single pathway is insufficient. An integrated portfolio supported by modernized standards, targeted policy incentives, expanded access to SCMs and waste fuels, scaled CCUS investment, and international collaboration is essential to bridge the gap between climate ambition and industrial implementation. Key recommendations include modernizing cement standards to support higher clinker replacement, providing incentives for energy-efficient upgrades, scaling CCUS through joint investment and carbon pricing and expanding access to biomass and waste-derived fuels. Full article

This study presents a comprehensive assessment of the energy systems in eight Eastern European countries—Bulgaria, Croatia, the Czech Republic, Hungary, Poland, Romania, Slovakia, and Slovenia—focusing on their energy transition, security of supply, decarbonisation, and energy efficiency. Using principal component analysis (PCA) and clustering techniques, we identify three different energy profiles: countries dependent on fossil fuels (e.g., Poland, Bulgaria), countries with a balanced mix of nuclear and fossil fuels (e.g., the Czech Republic, Slovakia, Hungary), and countries focusing mainly on renewables (e.g., Slovenia, Croatia). The sectoral analysis shows that industry and transport are the main drivers of energy consumption and CO₂ emissions, and the challenges and policy priorities of decarbonisation are determined. Regression modelling shows that dependence on fossil fuels strongly influences the use of renewable energy and electricity consumption patterns, while national differences in per capita electricity consumption are influenced by socio-economic and political factors that go beyond the energy structure. The Decarbonisation Level Index (DLI) indicator shows that Bulgaria and the Czech Republic achieve a high degree of self-sufficiency in domestic energy, while Hungary and Slovakia are the most dependent on imports. A typology based on energy intensity and import dependency categorises Romania as resilient, several countries as balanced, and Hungary, Slovakia, and Croatia as vulnerable. The projected investments up to 2030 indicate an annual increase in clean energy production of around 123–138 TWh through the expansion of nuclear energy, the development of renewable energy, the phasing out of coal, and the improvement of energy efficiency, which could reduce CO₂ emissions across the region by around 119–143 million tons per year. The policy recommendations emphasise the accelerated phase-out of coal, supported by just transition measures, the use of nuclear energy as a stable backbone, the expansion of renewables and energy storage, and a focus on the electrification of transport and industry. The study emphasises the significant influence of European Union (EU) policies—such as the “Clean Energy for All Europeans” and “Fit for 55” packages—on the design of national strategies through regulatory frameworks, financing, and market mechanisms. This analysis provides important insights into the heterogeneity of Eastern European energy systems and supports the design of customised, coordinated policy measures to achieve a sustainable, secure, and climate-resilient energy transition in the region. Full article

This research investigated how detergent type and concentration, solution temperature, and flow rate affect ultrasonic cleaning efficiency in jewelry manufacturing. A silver bracelet without gemstones served as the test sample, and the study combined harmonic response analysis to assess acoustic pressure distribution with computational fluid dynamics to examine fluid flow patterns inside an ultrasonic cleaning machine. Cleaning tests were performed under real factory conditions to verify the simulations. Results showed that cleaning efficiency depends on the combined chemical and ultrasonic effects. Adding detergent lowered surface tension, encouraging cavitation bubble formation; higher temperatures (up to 60 °C) softened dirt, making removal easier; and moderate solution flow improved the cleaning, helping to carry dirt away from jewelry surfaces. Too much flow, however, decreased cavitation activity. The highest cleaning efficiency (93.890%) was achieved with 3% U-type detergent at 60 °C and a flow rate of 5 L/min, while pure water at room temperature (30 °C) without flow had the lowest efficiency (0.815%), confirmed by weighing and scanning electron microscope measurements. Interestingly, maximum ultrasonic power concentration did not always match the highest cleaning efficiency. The study supports sustainable practices by limiting detergent use to 3%, in line with Sustainable Development Goal (SDG) 9 (Industry, Innovation, and Infrastructure). Full article