Clean Technologies

18 pages, 2203 KB

Open AccessArticle

Assessing the Feasibility of Geothermal-to-X for Sustainable Maritime Refueling in Alaska

by Emily Cook and Magnus de Witt

Clean Technol. 2025, 7(4), 115; https://doi.org/10.3390/cleantechnol7040115 - 18 Dec 2025

The Arctic is warming three to four times faster than the global average. This is transforming global maritime routes, thereby increasing shipping and resource extraction in Alaska. This surge requires sustainable energy solutions as policy trends towards stricter emissions standards. This article assesses [...] Read more.

The Arctic is warming three to four times faster than the global average. This is transforming global maritime routes, thereby increasing shipping and resource extraction in Alaska. This surge requires sustainable energy solutions as policy trends towards stricter emissions standards. This article assesses the potential of Geothermal-to-X (GtX) technologies in establishing clean refueling infrastructure across Alaska, using its untapped geothermal resources. GtX uses electrolysis to split water into hydrogen and oxygen, a process powered by geothermal energy. Hydrogen and its X products, such as green methane or green ammonia, can be stored as fuels and are largely recognized as the key to a carbon-free future to address the growing energy demand. This study assesses the technical, economic, strategic, and geological feasibility of GtX refueling hubs in Alaska. Five locations were denoted as potential candidates and beckon future research. This study concludes that Unalaska is the most viable initial GtX hub given the highest Multi Criteria Decision Analysis (MCDA) score from its combination of a high-quality geothermal resource, an existing and accessible deepwater port, and a sizable local energy demand. The goal of this study is to provide an accessible and comprehensive resource for stakeholders and policymakers, outlining an energy future with sustainable maritime development, powered by affordable and secure energy. Full article

(This article belongs to the Topic Sustainable Energy: Efficient Technological Solutions Combining Environmental, Economic, Political and Social Aspects, 2nd Edition)

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16 pages, 543 KB

Open AccessArticle

Use of Liquid Industrial By-Products as Biostimulants in the Remediation of Hydrocarbon-Contaminated Soils

by Emilio Ritoré, Carmen Arnaiz, José Morillo, Agata Egea-Corbacho and José Usero

Clean Technol. 2025, 7(4), 114; https://doi.org/10.3390/cleantechnol7040114 - 11 Dec 2025

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Abstract

Soil contamination by petroleum hydrocarbons represents a significant environmental challenge, especially in industrial and urban areas. This study evaluates the use of three industrial liquid by-products—sludge dewatering sidestream (SD), leftover yeast (LY), and secondary clarifier effluent (SC)—as biostimulant agents for the bioremediation of [...] Read more.

Soil contamination by petroleum hydrocarbons represents a significant environmental challenge, especially in industrial and urban areas. This study evaluates the use of three industrial liquid by-products—sludge dewatering sidestream (SD), leftover yeast (LY), and secondary clarifier effluent (SC)—as biostimulant agents for the bioremediation of soils contaminated with gasoline and diesel mixtures. The novelty lies in applying these waste streams within a circular economy framework, with the added advantage that they can be injected directly into the subsurface. Microcosm tests were conducted over 20 weeks, analyzing the degradation of total petroleum hydrocarbons (TPHs) and their aliphatic and aromatic fractions using gas chromatography. The results show that all by-products improved biodegradation compared to natural attenuation. LY was the most effective, achieving 73.2% TPH removal, followed by SD (70.6%) and SC (65.4%). The greatest degradation was observed in short-chain hydrocarbons (C6–C16), while compounds with higher molecular weight (C21–C35) were more recalcitrant. In addition, aliphatic hydrocarbons showed greater degradability than aromatics in heavy fractions. Kinetic analysis revealed that the second-order model best fitted the experimental data, with higher correlation coefficients (R²) and more representative half-lives. Catalase enzyme activity also increased in soils treated with LY and SD, indicating higher microbial activity. Full article

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21 pages, 6534 KB

Open AccessArticle

The Potential of Barista Coffee Waste to Adsorb Copper and Zinc from Aqueous Solutions

by Basmah Bushra, Paul J. Wood and Diganta B. Das

Clean Technol. 2025, 7(4), 113; https://doi.org/10.3390/cleantechnol7040113 - 5 Dec 2025

Viewed by 286

Abstract

This study investigates the removal of copper and zinc at environmentally relevant concentrations from aqueous solutions using barista coffee waste in both standalone and blended forms (with rice husk biochar). A fixed-bed horizontal column adsorption study was conducted to determine the effects of [...] Read more.

This study investigates the removal of copper and zinc at environmentally relevant concentrations from aqueous solutions using barista coffee waste in both standalone and blended forms (with rice husk biochar). A fixed-bed horizontal column adsorption study was conducted to determine the effects of contact time, adsorbent type, and initial metal concentration on the removal efficiency. As far as we are aware, this study is the first to focus on eliminating low concentrations in accordance with World Health Organization (WHO) guideline levels, employing a horizontal fixed-bed column setup. Adsorption equilibrium was achieved around six hours after initiation and resulted in a high percentage of metal removal (up to 96.71%). Ground coffee waste performed better for lower initial metal concentrations (2.5 ppm copper and 10 ppm zinc), although a mixture of coffee waste and biochar performed better at concentrations greater than 5 ppm for copper and 25 ppm for zinc. Experimental results were applied to the Thomas model to determine the efficiency of the adsorbents. Results indicated it was linear with a good correlation coefficient (R² = 0.94). The experimental data also fitted the pseudo-first-order reaction kinetic with a higher correlation coefficient (R² = 0.93) than the second-order reaction kinetics. The experimental and calculated values were very similar for the first-order reaction kinetic. The metal adsorption was affected by both external mass transfer and intra-particle diffusion mechanisms. This study developed an engineered solution to remove heavy metals from wastewater using widely available ground coffee waste as an effective adsorbent. Full article

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19 pages, 828 KB

Open AccessArticle

Green Extraction of Orange Peel Using Deep Eutectic Solvents Assisted by Ultrasound: Bioactivity Assessment and Compound Quantification

by Alejandro Delgado-Cortez, Carlos Castillo-Zacarias, Isaías Juárez-Ramírez, Sergio Arturo Galindo-Rodríguez, Catalina Rivas-Morales, Catalina Leos-Rivas and Ezequiel Viveros-Valdez

Clean Technol. 2025, 7(4), 112; https://doi.org/10.3390/cleantechnol7040112 - 5 Dec 2025

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Abstract

Oranges are widely consumed worldwide and are highly valued both for their nutritional properties and their economic importance. In Mexico, particularly in the northeastern citrus-producing region, large amounts of peel are generated during industrial processing, representing a significant source of agro-industrial waste. This [...] Read more.

Oranges are widely consumed worldwide and are highly valued both for their nutritional properties and their economic importance. In Mexico, particularly in the northeastern citrus-producing region, large amounts of peel are generated during industrial processing, representing a significant source of agro-industrial waste. This byproduct is naturally rich in compounds of interest, including flavonoids, polyphenols, and pectin, which motivates the development of sustainable recovery strategies. In this work, orange peel biomass was valorized using ultrasound-assisted extraction in combination with deep eutectic solvents (DESs). Among the evaluated formulations, the choline chloride–lactic acid DES at a 1:10 molar ratio produced the highest overall extraction yield (43.88% by dry weight/mass). The 2:1 formulation, however, was the most efficient for the recovery of phenolic compounds, reaching 4.12 mg GAE/g, and exhibited the greatest antioxidant activity (2.55 mmol Trolox/g) and the strongest antimicrobial response against clinically relevant microorganisms. This same DES ratio enabled the highest quantification of key phenolics such as naringin (1150.29 µg/g), caffeic acid (139.41 µg/g), and ferulic acid (379.96 µg/g). For polysaccharide extraction, the 1:1 DES ratio was the most effective, achieving a pectin yield of 48.24%. Overall, the findings demonstrate that DES, particularly when combined with ultrasound, offers a green and efficient approach for the integrated recovery of pectin, phenolic antioxidants, and antimicrobial compounds from citrus byproducts, contributing to environmentally sustainable biorefinery strategies. Full article

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11 pages, 726 KB

Open AccessTechnical Note

Toward Expanding the Utilisation of Deep Eutectic Solvents: Rare Earth Recovery from Primary Ores and Process Tailings

by K. Yamini, Laurence G. Dyer, Bogale Tadesse and Richard D. Alorro

Clean Technol. 2025, 7(4), 111; https://doi.org/10.3390/cleantechnol7040111 - 5 Dec 2025

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Abstract

The increasing emphasis on green chemistry has led numerous researchers to focus on environmentally friendly solvents for mineral extraction. Among them, deep eutectic solvents (DESs) have garnered significant attention due to their eco-friendly, non-toxic, and biodegradable properties. These solvents possess comparable physicochemical properties [...] Read more.

The increasing emphasis on green chemistry has led numerous researchers to focus on environmentally friendly solvents for mineral extraction. Among them, deep eutectic solvents (DESs) have garnered significant attention due to their eco-friendly, non-toxic, and biodegradable properties. These solvents possess comparable physicochemical properties to conventional ionic liquids but are more cost-effective and environmentally friendly. While DESs have been widely studied for extracting metals from synthetic minerals and end-of-life products, its use with primary ores and associated wastes remains relatively unexplored. This study aims to bridge that gap by assessing the effectiveness of choline chloride- and ethylene glycol-based DESs in extracting rare earth elements from primary feedstocks with varied grades and mineralogy, including sub-economic ores, monazite flotation tailings, and acid-crack and leach residue. The study also examines the practical challenges in preparing DES and assesses the applicability of the solvents for primary materials. By examining both solvent preparation challenges and the variable responses of different feed materials, this work provides a high-level scoping analysis to better understand the suitability and limitations of DES for primary resource extraction. This study highlights the challenges with physical properties and mineral breakdown in using DES. Full article

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21 pages, 1766 KB

Open AccessArticle

Floating Offshore Wind Farm Inter-Array Cabling Topology Optimisation with Metaheuristic Particle Swarm Optimisation

by Sergi Vilajuana Llorente, José Ignacio Rapha, Magnus Daniel Kallinger and José Luis Domínguez-García

Clean Technol. 2025, 7(4), 110; https://doi.org/10.3390/cleantechnol7040110 - 4 Dec 2025

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Abstract

Floating offshore wind is now receiving much attention as an expansion to bottom-fixed, especially in deep waters with large wind resources. In this regard, improving the performance and efficiency of floating offshore wind farms (FOWFs) is currently a highly addressed topic. The inter-array [...] Read more.

Floating offshore wind is now receiving much attention as an expansion to bottom-fixed, especially in deep waters with large wind resources. In this regard, improving the performance and efficiency of floating offshore wind farms (FOWFs) is currently a highly addressed topic. The inter-array (IA) cable connection is a key aspect to be optimised. Due to floating offshore wind (FOW) particularities such as dynamic cable designs, higher power capacities, and challenging installation, IA cabling is expected to be a primary cost driver for commercial-scale FOWFs. Therefore, IA cabling optimisation can lead to large cost reductions. In this work, an optimisation with an adaptive particle swarm optimisation (PSO) algorithm for such wind farms is proposed, considering the floating substructures’ horizontal translations and its impact on the dynamic cable length. The method provides an optimised IA connection, reducing acquisition costs and power losses by using a clustered minimum spanning tree (MST) as an initial solution and improving it with the PSO algorithm. The PSO achieves a reduction in the levelised cost of energy (LCOE) between 0.018% (0.022 EUR/MWh) and 0.10% (0.12 EUR/MWh) and a reduction in cable acquisition costs between 0.18% (0.3 M EUR) and 1.34% (3.8 M EUR) compared to the initial solution, showing great potential for future commercial-sized FOWFs. Full article

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36 pages, 2395 KB

Open AccessReview

Advancements in Carbon Capture, Utilization, and Storage (CCUS): A Comprehensive Review of Technologies and Prospects

by Nisreen Salem, Kamalpreet Kaur Brar, Ali Asgarian, Kulwinder Kaur, Sara Magdouli and Nancy N. Perreault

Clean Technol. 2025, 7(4), 109; https://doi.org/10.3390/cleantechnol7040109 - 4 Dec 2025

Viewed by 989

Abstract

Carbon dioxide (CO₂) is the most significant anthropogenic greenhouse gas (GHG), accounting for approximately 81% of total emissions, with methane (CH₄), nitrous oxide (N₂O), and fluorinated gases contributing the remainder. Rising atmospheric CO₂ concentrations, driven primarily [...] Read more.

Carbon dioxide (CO₂) is the most significant anthropogenic greenhouse gas (GHG), accounting for approximately 81% of total emissions, with methane (CH₄), nitrous oxide (N₂O), and fluorinated gases contributing the remainder. Rising atmospheric CO₂ concentrations, driven primarily by fossil fuel combustion, industrial processes, and transportation, have surpassed the Earth’s natural sequestration capacity, intensifying climate change impacts. Carbon Capture, Utilization, and Storage (CCUS) offers a portfolio of solutions to mitigate these emissions, encompassing pre-combustion, post-combustion, oxy-fuel combustion, and direct air capture (DAC) technologies. This review synthesizes advancements in CO₂ capture materials including liquid absorbents (amines, amino acids, ionic liquids, hydroxides/carbonates), solid adsorbents (metal–organic frameworks, zeolites, carbon-based materials, metal oxides), hybrid sorbents, and emerging hydrogel-based systems and their integration with utilization and storage routes. Special emphasis is given to CO₂ mineralization using mine tailings, steel slag, fly ash, and bauxite residue, as well as biological mineralization employing carbonic anhydrase (CA) immobilized in hydrogels. The techno-economic performance of these pathways is compared, highlighting that while high-capacity sorbents offer scalability, hydrogels and biomineralization excel in low-temperature regeneration and integration with waste valorization. Challenges remain in cost reduction, material stability under industrial flue gas conditions, and integration with renewable energy systems. The review concludes that hybrid, cross-technology CCUS configurations combining complementary capture, utilization, and storage strategies will be essential to meeting 2030 and 2050 climate targets. Full article

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21 pages, 3522 KB

Open AccessArticle

An Experimental Analysis of the Influence of Pyrolytic Oil on the Spray Breakup Process

by Tilen Jernejc, Gorazd Bombek, Ignacijo Biluš, Luka Kevorkijan and Luka Lešnik

Clean Technol. 2025, 7(4), 108; https://doi.org/10.3390/cleantechnol7040108 - 3 Dec 2025

Viewed by 264

Abstract

Solid waste presents a very large problem in the developed world. Waste plastics, which make up a large part of solid waste, have high energy value, which is discarded if they are not treated properly. Most of the plastic found in solid waste [...] Read more.

Solid waste presents a very large problem in the developed world. Waste plastics, which make up a large part of solid waste, have high energy value, which is discarded if they are not treated properly. Most of the plastic found in solid waste is produced from petrochemical material, so it can be used in resource recovery processes to produce various materials. One promising resource recovery process is the pyrolysis process, from which pyrolytic oil, gas, and solid residue are obtained. Pyrolytic oils have properties that are similar to conventional fossil fuels, and are promising fuels for use in heat engines or heating applications. In the present work, HDPE plastic in the form of plastic bottles caps was collected from solid waste and used in a thermal pyrolysis process for the production of pyrolytic oil. The obtained oil was characterised, and the obtained results were compared to conventional fuels. The obtained oil was used further in an oil burner fuel injection application, in which the spray breakup characteristics were monitored and analysed using VisiSize particle characterisation systems. The obtained results were compared to those of conventional fuel. The results indicate that the difference in fuel properties influences the spray breakup process slightly, but the differences are rather small. This indicates that from a spray development perspective, pyrolytic oil can be used as a substitute for conventional fuels in oil burners. Full article

(This article belongs to the Special Issue Innovative Approaches to Sustainable Design, Recovery, and Circular Management of Solid Waste)

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19 pages, 2045 KB

Open AccessArticle

Evaluation of Emission Reduction Systems in Underground Mining Trucks: A Case Study at an Underground Mine

by Hector Garcia-Gonzalez and Pablo Menendez-Cabo

Clean Technol. 2025, 7(4), 107; https://doi.org/10.3390/cleantechnol7040107 - 1 Dec 2025

Viewed by 283

Abstract

Underground mining environments present elevated occupational health risks, primarily due to substantial exposure to diesel exhaust emissions within confined and poorly ventilated spaces. This study assesses the real-world performance of two advanced retrofit emission control systems—Proventia NOxBuster and Purifilter—installed on underground mining trucks [...] Read more.

Underground mining environments present elevated occupational health risks, primarily due to substantial exposure to diesel exhaust emissions within confined and poorly ventilated spaces. This study assesses the real-world performance of two advanced retrofit emission control systems—Proventia NOxBuster and Purifilter—installed on underground mining trucks operating in a Spanish mine. Emissions of carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxide (NO₂) were quantified using a Testo 350 multigas analyser, while ultrafine particle (UFP) concentrations were measured with an Engine Exhaust Particle Sizer (EEPS-3090) equipped with a thermodiluter. Controlled tests under both idling and acceleration conditions revealed substantial reductions in pollutant emissions: CO decreased by 60–98%, NO by 51–92%, and NO₂ by 20–87%, depending on the system and operational phase. UFP concentrations during idling dropped by approximately 90%, from 542,000 particles/cm³ in untreated trucks to below 50,000 particles/cm³ in retrofitted vehicles. Under acceleration, the Proventia NOxBuster achieved reductions exceeding 95%. Conversely, Purifilter-equipped trucks exhibited a counterintuitive increase in UFPs within the 5.6–40 nm range, potentially due to ammonia slip events during selective catalytic reduction (SCR). Despite these discrepancies, both systems demonstrated considerable mitigation potential, albeit highly dependent on exhaust temperature (optimal: 200–450 °C), urea dosing precision, and maintenance protocols. This work underscores the necessity of in situ performance verification, regulatory vigilance, and targeted intervention strategies to protect underground workers effectively. Further investigation is warranted into the long-term health benefits, system durability, and nanoparticle emission dynamics under variable load conditions. Full article

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21 pages, 2428 KB

Open AccessArticle

A Performance and Environmental Impact Study on a Combined Cycle Power Plant with a Bottoming ORC Unit

by Dan-Teodor Bălănescu, Vlad-Mario Homutescu and Marius-Vasile Atanasiu

Clean Technol. 2025, 7(4), 106; https://doi.org/10.3390/cleantechnol7040106 - 1 Dec 2025

Viewed by 359

Abstract

The depletion of fossil fuel reserves and the pollution produced by fuel combustion are major concerns in the energy generation sector. Due to this, waste heat recovery has become a stringent objective in this domain. The current study pursues this objective with regard [...] Read more.

The depletion of fossil fuel reserves and the pollution produced by fuel combustion are major concerns in the energy generation sector. Due to this, waste heat recovery has become a stringent objective in this domain. The current study pursues this objective with regard to gas–steam combined cycle power plants, which are currently viewed as the most advanced technology in fossil fuel power generation. The proposed solution for waste heat recovery is to add an organic Rankine cycle (ORC) power system to the gas–steam combined cycle power plant with a Solar Centaur 40 gas turbine, produced by Solar Turbines, a Caterpillar Company (San Diego, CA, USA). The ORC power system is placed along the path of the flue gas, downstream of the heat recovery steam generator of the combined cycle power plant. R1336mzz (Z), R1233zd (E), and R601a were investigated as working fluids. The performance of the ORC system was analyzed as a function of the degree of superheat. The superheating process was proven to be disadvantageous since it led to performance deterioration. The numerical study showed that the overall efficiency of the combined cycle power plant increased up to 0.014 (1.4%) as a consequence of adding the ORC system, which itself achieves a maximum efficiency of 0.133 (13.3%). The annual fuel (natural gas) savings achievable under these conditions were roughly estimated at 398,185 Nm³/year, equating to annual fuel cost savings of approximately 269,000 EUR/year and an 810 t/year reduction in CO₂ emissions. Full article

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17 pages, 4351 KB

Open AccessArticle

Sequential Treatment of Domestic Wastewater in Rural Zones Applying Aloe Vera Extract as Coagulant (Preliminar), E. crassipes in a Horizontal Biofilter (Secondary), and Activated Carbon from Soursop Seeds (Tertiary)

by Franco Hernan Gomez, Maria Cristina Collivignarelli, Stefano Bellazzi, Kelly Cristina Torres, Alessandro Abbà and Sabrina Sorlini

Clean Technol. 2025, 7(4), 105; https://doi.org/10.3390/cleantechnol7040105 - 24 Nov 2025

Viewed by 444

Abstract

The absence of domestic wastewater (DWW) treatment in impoverished rural communities of the global south remains a pressing challenge for both public health and environmental sustainability. This study presents a simplified and decentralized treatment chain at laboratory-scale designed under the principles of nature-based [...] Read more.

The absence of domestic wastewater (DWW) treatment in impoverished rural communities of the global south remains a pressing challenge for both public health and environmental sustainability. This study presents a simplified and decentralized treatment chain at laboratory-scale designed under the principles of nature-based solutions (NBS) and the circular economy (CE), emphasizing the integration of the macrophyte Eichhornia crassipes (EC) and bioproducts derived from aloe vera waste (AVW) and soursop seed waste (SSW). The system comprises three sequential stages: (1) coagulation using AVW, which achieved up to 39.9% turbidity reduction; (2) a horizontal flow biofilter system (HFB) employing the aquatic macrophyte EC, which removed 97.9% of fecal coliforms, 82.4% of Escherichia coli, and 99.9% of heterotrophic bacteria; and (3) a tertiary treatment step employing adsorbent derived from SSW, which attained 99.7% methylene blue removal in preliminary tests and an average 97.5% turbidity reduction in DWW. The integrated configuration demonstrates a practical, effective, and replicable approach for decentralized domestic wastewater treatment, fostering local waste valorization, reducing reliance on commercial chemicals, and enhancing water quality in resource-limited rural areas, with potential for scaling to pilot applications in rural communities. Full article

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18 pages, 873 KB

Open AccessArticle

Assessment of Diesel Engine Exhaust Levels in an Underground Mine Before and After Implementing Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) Systems

by Pablo Menendez-Cabo and Hector Garcia-Gonzalez

Clean Technol. 2025, 7(4), 104; https://doi.org/10.3390/cleantechnol7040104 - 19 Nov 2025

Viewed by 626

Abstract

Diesel-powered machinery is the primary energy source in underground mining, exposing workers to hazardous diesel exhaust emissions. This study evaluates occupational exposure to diesel particulate matter (DPM) and gaseous pollutants (NO, NO₂) at an underground mine before and after implementing Diesel [...] Read more.

Diesel-powered machinery is the primary energy source in underground mining, exposing workers to hazardous diesel exhaust emissions. This study evaluates occupational exposure to diesel particulate matter (DPM) and gaseous pollutants (NO, NO₂) at an underground mine before and after implementing Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) in mining equipment. A comprehensive monitoring campaign was conducted, employing elemental carbon (EC) as a tracer for diesel particulate emissions and electrochemical sensors for gas measurements. Results show a substantial reduction in EC concentrations following the implementation of DPFs, with median EC exposure decreasing from 0.145 mg/m³ in 2021 to 0.034 mg/m³ in 2023, and the proportion of samples exceeding the occupational exposure limit (OEL) falling from 90% to 28%. Similarly, SCR implementation led to a 72% reduction in NO₂ levels and a 77.5% decrease in NO concentrations in certain equipment; however, NO levels remained persistently high near loaders, suggesting that additional mitigation measures are required. These findings underscore the efficacy of DPF and SCR technologies in improving air quality and reducing occupational exposure in underground mining environments. Nevertheless, persistent NO concentrations and maintenance-related challenges highlight the need for a holistic emission control approach, integrating ventilation improvements, expanded DPF adoption, alternative propulsion systems, and enhanced maintenance protocols. This study provides critical insights into the effectiveness of advanced emission reduction strategies and informs future regulatory compliance efforts in the mining industry. Full article

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26 pages, 362 KB

Open AccessArticle

Exploratory Survey—The Role of Traceability Systems in Quality Assurance and Advancement of the Circular Economy for Recycled Plastics in Australia

by Benjamin Gazeau, Atiq Zaman, Roberto Minnuno and Faiz Uddin Ahmed Shaikh

Clean Technol. 2025, 7(4), 103; https://doi.org/10.3390/cleantechnol7040103 - 12 Nov 2025

Viewed by 897

Abstract

Plastic recycling is critical to transitioning toward a circular economy (CE), yet traceability systems for recycled plastics remain unevenly adopted. While effective traceability supports transparency, compliance, and supply chain accountability, its implementation is shaped not only by technological readiness but also by organisational [...] Read more.

Plastic recycling is critical to transitioning toward a circular economy (CE), yet traceability systems for recycled plastics remain unevenly adopted. While effective traceability supports transparency, compliance, and supply chain accountability, its implementation is shaped not only by technological readiness but also by organisational behaviours and strategic priorities. This study explores how traceability adoption is influenced by company size, internal CE strategy, and perceptions of cost, risk, and regulatory demand. A survey of 65 Australian industry stakeholders reveals that 76% of companies with a CE strategy have implemented traceability systems, compared to 42% without. Larger firms report higher adoption rates than small and medium enterprises, largely due to resource advantages and differing interpretations of traceability’s value. Key barriers include high perceived costs, lack of standardised frameworks, and scepticism toward digital tools. Conversely, motivations such as reputational benefits, regulatory alignment, and inter-organisational trust were identified as enablers, alongside emerging technologies like blockchain and chemical tracers. The findings underscore the role of organisational context in shaping traceability practices and highlight the need for tailored interventions. Recommendations include financial incentives, harmonised standards, and sector-specific guidance that address not only technical gaps but behavioural and structural factors limiting uptake. Positioning traceability as an integrated organisational strategy may accelerate its adoption and support broader circular economy outcomes across the plastics value chain. Full article

17 pages, 3812 KB

Open AccessArticle

MnO₂-Supported Pd Nanocatalyst for Efficient Electrochemical Reduction of 2,4-Dichlorobenzoic Acid

by Yaxuan Peng and Meiyan Wang

Clean Technol. 2025, 7(4), 102; https://doi.org/10.3390/cleantechnol7040102 - 11 Nov 2025

Viewed by 800

Abstract

Chlorobenzoic acids (CBAs) are a group of chlorinated persistent environmental pollutants with hard biodegradability, high water solubility, and well-documented carcinogenic and endocrine-disrupting properties. Electrocatalytic hydrodechlorination (ECH) is a highly efficient method under mild conditions without harmful by-products, but the ECH process commonly requires [...] Read more.

Chlorobenzoic acids (CBAs) are a group of chlorinated persistent environmental pollutants with hard biodegradability, high water solubility, and well-documented carcinogenic and endocrine-disrupting properties. Electrocatalytic hydrodechlorination (ECH) is a highly efficient method under mild conditions without harmful by-products, but the ECH process commonly requires adding precious metal catalysts such as palladium (Pd). To address the economic constraints and more effective utilization of Pd, a palladium/manganese dioxide (Pd/MnO₂) composite catalyst was developed in this study by chemical deposition. This method utilized the excellent electrochemical activity of MnO₂ as a carrier as well as the hydrogen storage and activation capacity of Pd. The test showed the optimal Pd loading was 7.5%, and the removal percent of 2,4-dichlorobenzoic acid (2,4-DCBA), a typical CBA, reached 97.3% using 0.5 g/L of Pd/MnO₂ after 120 min of electrochemical reaction. Under these conditions, the dechlorination percent can also be as high as 89.6%. A higher current density enhanced the dechlorination efficiency but showed the lower current utilization efficiency. In practical applications, current density should be minimized on the premise of compliance with the water treatment requirement. Mechanistic studies showed that MnO₂ synergistically promoted hydrolysis dissociation and hydrogen spillover and facilitated Pd-mediated adsorption of atomic hydrogen (H*) for dehydrogenation of 2,4-DCBA. The presence of MnO₂ can effectively disperse the loaded Pd and reduce the amount of Pd via the above process. The catalyst exhibited excellent stability over multiple cycles, and the 2,4-DCBA removal could still reach more than 80% after the five cycles. This work establishes electrocatalytic strategies for effectively reducing Pd usage and maintaining high removal of typical CBAs to support CBA-related water treatment. Full article

(This article belongs to the Collection Water and Wastewater Treatment Technologies)

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20 pages, 1524 KB

Open AccessPerspective

Biomethanol as a Marine Fuel Within Land Use Sustainability Boundaries

by Homa Esfandiari, Helene Muri and Diogo Kramel

Clean Technol. 2025, 7(4), 101; https://doi.org/10.3390/cleantechnol7040101 - 7 Nov 2025

Viewed by 923

Abstract

Global shipping is an essential, energy-efficient enabler of trade, yet it remains a hard-to-abate sector. With shipping demand projected to continue to rise in the coming decades, identifying scalable and sustainable fuel alternatives is critical. Biofuels, and particularly biomethanol, offer a promising option [...] Read more.

Global shipping is an essential, energy-efficient enabler of trade, yet it remains a hard-to-abate sector. With shipping demand projected to continue to rise in the coming decades, identifying scalable and sustainable fuel alternatives is critical. Biofuels, and particularly biomethanol, offer a promising option due to their compatibility with existing infrastructure. However, their sustainability critically hinges on land use impacts. From this Perspective, we argue that biomethanol derived from a dedicated crop could contribute to maritime decarbonisation, with ~71–77% well-to-wake greenhouse gases (GHG) reductions under cropland-only constraints. We further point to the fact that a wider adoption faces challenges such as higher costs, limited availability, and lower energy density relative to fossil fuels. Continued research and monitoring are essential to ensure that biofuel production does not inadvertently contribute to deforestation or biodiversity loss. We underscore the need for spatially sensitive biofuel deployment strategies that align maritime decarbonisation with land-system sustainability and climate objectives. Full article

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18 pages, 3830 KB

Open AccessArticle

Green CO₂ Capture from Flue Gas Using Potassium Carbonate Solutions Promoted with Amino Acid Salts

by Ramona Elena Tataru-Farmus, María Harja, Lucia Tonucci, Francesca Coccia, Michele Ciulla, Liliana Lazar, Gabriela Soreanu and Igor Cretescu

Clean Technol. 2025, 7(4), 99; https://doi.org/10.3390/cleantechnol7040099 - 5 Nov 2025

Viewed by 887

Abstract

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 CO [...] Read more.

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

(This article belongs to the Special Issue Green Solvents and Materials for CO₂ Capture)

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31 pages, 2524 KB

Open AccessReview

Life Cycle Assessment of Industrial Symbiosis for Circular Solid Waste Management: A Literature Review

by Reza Vahidzadeh, Marta Domini and Giorgio Bertanza

Clean Technol. 2025, 7(4), 100; https://doi.org/10.3390/cleantechnol7040100 - 5 Nov 2025

Viewed by 959

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Innovative Approaches to Sustainable Design, Recovery, and Circular Management of Solid Waste)

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18 pages, 2737 KB

Open AccessArticle

Greener Polyurethane Adhesive Derived from Polyvinyl Alcohol/Tannin-Based Polyol for Plywood

by Dhimas Pramadhani, Rita Kartika Sari, Mahdi Mubarok, Apri Heri Iswanto, Antonios Papadopoulos, Ioanna A. Papadopoulou, Dimitrios I. Raptis, Tati Karliati and Muhammad Adly Rahandi Lubis

Clean Technol. 2025, 7(4), 98; https://doi.org/10.3390/cleantechnol7040098 - 4 Nov 2025

Viewed by 638

Abstract

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) [...] Read more.

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

(This article belongs to the Special Issue Environmental Engineering Perspectives on Waste Management, Nature-Based Solutions (NbS) and Green/Blue Infrastructure)

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35 pages, 4852 KB

Open AccessReview

From Waste to Resource: Algal–Bacterial Systems and Immobilization Techniques in Aquaculture Effluent Treatment

by Jiangqi Qu, Ruijun Ren, Zhanhui Wu, Jie Huang and Qingjing Zhang

Clean Technol. 2025, 7(4), 97; https://doi.org/10.3390/cleantechnol7040097 - 4 Nov 2025

Viewed by 1784

Abstract

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, [...] Read more.

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

(This article belongs to the Special Issue Pollutant Removal from Wastewater by Microalgae-Based Processes)

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30 pages, 2719 KB

Open AccessArticle

The Energy Transition in Colombia: Government Projections and Realistic Scenarios

by Alexis Sagastume Gutiérrez, Juan José Cabello Eras and Daniel David Otero Meza

Clean Technol. 2025, 7(4), 96; https://doi.org/10.3390/cleantechnol7040096 - 4 Nov 2025

Viewed by 2078

Abstract

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 [...] Read more.

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

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23 pages, 3112 KB

Open AccessReview

Chitosan-Based Composites for Sustainable Textile Production: Applications Across the Lifecycle

by An Liu, Buer Qi and Lisbeth Ku

Clean Technol. 2025, 7(4), 95; https://doi.org/10.3390/cleantechnol7040095 - 3 Nov 2025

Viewed by 1237

Abstract

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 [...] Read more.

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

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26 pages, 4685 KB

Open AccessArticle

Life Cycle of Fuel Cells: From Raw Materials to End-of-Life Management

by Plamen Stanchev and Nikolay Hinov

Clean Technol. 2025, 7(4), 94; https://doi.org/10.3390/cleantechnol7040094 - 3 Nov 2025

Viewed by 966

Abstract

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 [...] Read more.

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

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20 pages, 1797 KB

Open AccessArticle

An Innovative Industrial Complex for Sustainable Hydrocarbon Production with Near-Zero Emissions

by Viral Ajay Modi, Qiang Xu and Sujing Wang

Clean Technol. 2025, 7(4), 93; https://doi.org/10.3390/cleantechnol7040093 - 23 Oct 2025

Viewed by 803

Abstract

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 [...] Read more.

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

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25 pages, 11863 KB

Open AccessArticle

Effect of Borax-, KOH-, and NaOH-Treated Coal on Reducing Carbon Waste and Activated Carbon Production in Synthetic Rutile Production from Ilmenite

by William Spencer, Don Ibana, Pritam Singh and Aleksandar N. Nikoloski

Clean Technol. 2025, 7(4), 92; https://doi.org/10.3390/cleantechnol7040092 - 20 Oct 2025

Viewed by 731

Abstract

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 [...] Read more.

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

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32 pages, 4717 KB

Open AccessArticle

Integrating Rooftop Grid-Connected Photovoltaic and Battery Systems to Reduce Environmental Impacts in Agro-Industrial Activities with a Focus on Extra Virgin Olive Oil Production

by Grazia Cinardi, Provvidenza Rita D'Urso and Claudia Arcidiacono

Clean Technol. 2025, 7(4), 91; https://doi.org/10.3390/cleantechnol7040091 - 16 Oct 2025

Viewed by 806

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Multidisciplinary Applications of Life Cycle Assessment (LCA) in the Development, Optimization, and Validation of Sustainable Solutions)

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33 pages, 4214 KB

Open AccessArticle

Expert Support System for Calculating the Cost-Effectiveness of Constructing a Sewage Sludge Solar Drying Facility

by Emir Zekić, Dražen Vouk and Domagoj Nakić

Clean Technol. 2025, 7(4), 90; https://doi.org/10.3390/cleantechnol7040090 - 13 Oct 2025

Viewed by 975

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Innovative Approaches to Sustainable Design, Recovery, and Circular Management of Solid Waste)

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19 pages, 2224 KB

Open AccessArticle

Enhanced Biogas Production and Pathogen Reduction from Pig Manure Through Anaerobic Digestion: A Sustainable Approach for Urban Waste Management in Abidjan, Côte d’Ivoire

by Alane Romaric N’guessan, Youan Charles Tra Bi, Edi Guy-Alain Serges Yapo, Akeyt Richmond Hervé Koffi, Franck Orlando Yebouet, Alessio Campitelli, Boko Aka and N’Dédé Théodore Djeni

Clean Technol. 2025, 7(4), 89; https://doi.org/10.3390/cleantechnol7040089 - 11 Oct 2025

Viewed by 2276

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Biomass Valorization and Sustainable Biorefineries)

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12 pages, 503 KB

Open AccessArticle

Substitution of Fossil-Based Solvents in Organic Coatings

by Elias Rippatha, Hector Rolando Mendez Rossal, Bernhard Strauß and Clemens Schwarzinger

Clean Technol. 2025, 7(4), 88; https://doi.org/10.3390/cleantechnol7040088 - 10 Oct 2025

Viewed by 754

Abstract

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 [...] Read more.

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

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26 pages, 2204 KB

Open AccessReview

Hydrogen Economy and Climate Change: Additive Manufacturing in Perspective

by Isaac Kwesi Nooni and Thywill Cephas Dzogbewu

Clean Technol. 2025, 7(4), 87; https://doi.org/10.3390/cleantechnol7040087 - 9 Oct 2025

Viewed by 882

Abstract

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, [...] Read more.

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

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25 pages, 1344 KB

Open AccessArticle

Is Green Hydrogen a Strategic Opportunity for Albania? A Techno-Economic, Environmental, and SWOT Analysis

by Andi Mehmeti, Endrit Elezi, Armila Xhebraj, Mira Andoni and Ylber Bezo

Clean Technol. 2025, 7(4), 86; https://doi.org/10.3390/cleantechnol7040086 - 9 Oct 2025

Viewed by 1590

Abstract

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 [...] Read more.

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

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