Clean Technologies

This study presents an experimental engine map investigation of waste swine oil biodiesel (WSO B100) in a single-cylinder, four-stroke variable compression ratio compression ignition engine, quantifying the coupled effects of compression ratio and load on brake thermal efficiency, brake-specific fuel consumption, torque, brake power, and regulated emissions of NOx, CO, HC, and CO₂. Compression ratios of 12, 14, 16, and 18 were evaluated at dynamometer loads of 25%, 50%, and 75% under steady-state operation. The study’s primary contribution is a structured compression ratio–load mapping framework that produces consistent performance emission response surfaces and, supported by statistical modeling and sensitivity analysis, resolves main and interaction effects to identify operating regions that balance efficiency and emissions. Methodological traceability is strengthened by attaching fuel energy and mass flow calculations to batch-specific fuel properties, including viscosity and density, and by using calorimetry-derived heating value in efficiency calculations. Increasing the compression ratio from 12 to 18 improved brake thermal efficiency by 3–10% at low load and reduced brake-specific fuel consumption, while NOx increased by 20–30% across the load range. Increasing load raised brake thermal efficiency from 29% at 25% load to 42% at 75% load and reduced brake-specific fuel consumption from 309 to 215 g/kWh; NOx peaked at 488 ppm at 75% load and compression ratio 18. CO and HC decreased with both load and compression ratio, reaching minima of 0.15% and 30 ppm, whereas CO₂ increased primarily with load. Relative to diesel, WSO biodiesel showed 8–12% higher brake-specific fuel consumption and 2–4% lower peak brake thermal efficiency, but achieved substantial CO and HC reductions. Generally, WSO biodiesel operates effectively across a wide compression ratio range with broadly comparable performance to diesel. However, increased NOx and reduced low-load efficiency indicate the need for targeted calibration or emission control. Full article

Compared with previous analytical models that mostly neglect air–lining coupled heat transfer, the proposed model innovatively introduces this mechanism and achieves a maximum error reduction of 0.5% against experimental data. The analytical solution of the model is obtained by using the Green’s function method. The reliability and accuracy of this model are confirmed through comparisons with existing experimental data. Research indicates that adjusting the tunnel air temperature improves the ground heat exchanger’s heat exchange efficiency more significantly than modifying the thermal conductivity of the lining. In the tested range, as the flow velocity increases, its influence on the heat transfer effect gradually weakens. The simulation results indicate that under summer operating conditions, only approximately 5–8% of the heat transferred by the ground heat exchanger is dissipated to the tunnel air-side environment, while the vast majority (92–95%) is conducted to the surrounding rock. Full article

Accurate and rapid determination of moisture content in waste sludge is essential for optimizing dewatering processes, reducing disposal costs, and minimizing environmental impact. This study investigates the use of Fourier Transform Near-Infrared (FT-NIR) spectroscopy combined with Partial Least Squares Regression (PLS-R) for predicting the moisture content of dewatered sludge. A total of 96 sludge samples, with dry matter contents ranging from 12.4% to 24.6%, were collected from two treatment plants. FT-NIR spectra were acquired over the 800–2500 nm range, and chemometric models were developed to correlate spectral information with gravimetrically determined moisture content. The optimized PLS-R model demonstrated strong predictive performance, achieving a cross-validated coefficient of determination (R²_CV) of 0.87, a root mean square error of cross-validation (RMSECV) of 0.92%, and a residual predictive deviation (RPD) of 2.73. Independent test set validation confirmed the robustness of the model (R²_Test = 0.88, RMSEP = 0.88%, RPD = 2.92), supported by strong calibration results (R²_CT = 0.95, RMSEE = 0.60%, RPD = 4.46). Principal component analysis indicated that spectral variability observed in sludge samples was primarily associated with wastewater treatment plant (WWTP)-specific characteristics, reflecting moisture–organic matter interactions. These results demonstrate that FT-NIR spectroscopy is a promising tool for sludge moisture prediction. Full article

Domestic wastewater is a chemically complex and highly variable mixture of pollutants generated by everyday household activities, yet its contribution to environmental contamination is still frequently underestimated and only 56% of wastewater worldwide is being treated. This review provides a structured and quantitative assessment of major domestic wastewater pollutant groups, their principal exposure pathways, and current and emerging treatment technologies. Beyond a conventional narrative synthesis, the review derives per capita annual emission estimates from published data and uses these to compare pollutant groups by mass flow and environmental relevance. The analysis shows that high-volume household inputs, particularly sodium chloride from domestic water softening, toilet paper, personal-care products, detergents, and cleaning agents, can contribute substantially to overall pollutant loads, whereas lower-mass contaminants such as pharmaceuticals, antibiotics, PFAS, heavy metals, and microplastics remain critical because of their persistence, biological activity, and incomplete removal during treatment. The review further highlights that conventional wastewater treatment systems are often poorly equipped to remove many of these emerging contaminants effectively, especially under decentralised or only partially advanced treatment conditions. Advanced and hybrid technologies, including membrane bioreactors, nanofiltration, reverse osmosis, adsorption, photocatalysis, and electrochemical processes, offer clear potential, but their broader implementation remains constrained by cost, energy demand, fouling, and concentrate management. Overall, the added value of this review lies in linking mass-based pollutant prioritisation with treatment performance, thereby providing a more systematic basis for identifying dominant household emission pathways and for guiding targeted mitigation and technology selection in future wastewater management. Full article

Chile is widely regarded as a key global player in green hydrogen production due to its exceptional renewable energy potential, which enables low-carbon and competitive production costs. This article provides a comprehensive review of Chile’s green hydrogen sector, evaluating the transition from early strategic goals to the current phase of industrial scaling. It offers an integrated analysis of the regulatory framework, infrastructure deployment, and the techno-economic variables essential for integrating Chilean derivatives into global markets. The country has established a supportive framework through its National Green Hydrogen Strategy (NGHS), which sets out goals of 25 GW of installed electrolyzer capacity and USD 2.5 billion in annual exports by 2030. Despite these ambitious targets, actual deployment remains in the early stages, with only 3.9 GW currently in the implementation phase and a lack of fully operational industrial-scale facilities. Furthermore, initial NGHS projections suggested a levelized cost of hydrogen (LCOH) of USD 1.3–1.4/kg by 2030. However, current calculations point to a more complex reality of approximately USD 3.1/kg due to infrastructure bottlenecks and global supply chain pressures. While Chile’s renewable resources ensure low production-stage emissions, the absence of explicit regulatory carbon targets underscores the need for comprehensive life-cycle assessments encompassing manufacturing and global distribution. Overall, this review concludes that Chile should overcome persistent regulatory and logistical constraints to consolidate a robust and internationally competitive green hydrogen sector, aligned with its 2050 carbon neutrality objectives. Full article

The construction sector is a major consumer of raw materials and a significant source of greenhouse gas emissions, necessitating data-driven approaches to support circular economy implementation and sustainable project management. This study develops an integrated framework combining machine learning-based material stock prediction, carbon footprint assessment, and Environmental, Social, and Governance (ESG) performance evaluation for construction projects. A dataset of 128 residential buildings was compiled from official use-permit documentation. After dimensionality reduction using variance filtering and Spearman correlation analysis, 25 regression algorithms were evaluated to estimate quantities of concrete, reinforcement, and brick products. The K-Nearest Neighbor (KNN) Regressor achieved the best predictive performance, with mean absolute percentage errors of 10.64% for concrete, 10.23% for reinforcement, and 16.05% for brick products. Predicted material quantities were used to calculate CO₂ emissions across materialization, demolition, and disposal phases under linear and circular scenarios. The results indicate that circular economy implementation significantly reduces total emissions, particularly for concrete, with reductions of up to 97% under idealized full-substitution conditions, representing an upper-bound estimate. ESG assessment using the Delphi method identified environmental indicators as the most significant sustainability dimension. The proposed framework enables early-stage emission estimation and supports informed decision-making toward low-carbon and resource-efficient construction practices. Full article

Rapid global urbanization is driving a surge in solid waste generation, while conventional treatment systems face both environmental risks and operational uncertainty. Digital twins, which enable real-time mapping between physical assets and virtual spaces, offer a computable and verifiable route toward low-carbon, resource-efficient, and intelligent waste management when deeply integrated with the Internet of Things, big data, and artificial intelligence. This study develops a comprehensive review tracing the digital twins from static geometric mirroring to dynamic, cognitive co-symbiosis, and summarizes a multidimensional architecture spanning physical, virtual, data, service, and connectivity layers, together with coupling mechanisms involving IoT sensing, federated learning, multimodal big data, and large model agents. The study aims to provide a theoretical framework and methodological references for advancing digital twin-enabled solid waste valorization. Building on this framework, we examine recent progress in three representative application scenarios for solid waste treatment, and identify key technical bottlenecks, including heterogeneous data fusion, model generalization across facilities and contexts, and real-time computation under constrained resources. We highlight the need for standardization, uncertainty quantification, cybersecurity, and lifecycle evaluation to support reliable prediction, optimization, and decision-making in real operations. Finally, we discuss future directions such as edge intelligence and the integration of city-scale material and energy networks. Full article

Eggshell waste generated by the poultry processing industry represents a significant yet underutilized biogenic resource with substantial potential for sustainable agricultural and environmental applications. Globally, several million metric tons of eggshell residues are produced annually, consisting predominantly of calcium carbonate (CaCO₃) in the form of calcite, along with minor quantities of organic matrices and trace minerals. These physicochemical characteristics make eggshells a promising renewable alternative to conventional mineral sources for use as fertilizers, soil amendments, and biomaterials. Recent studies have shown that finely ground eggshell powder (ESP) is an effective liming material that can regulate soil chemical conditions and improve agronomic performance under acidic soil conditions. Furthermore, eggshell-derived materials have been incorporated into composting systems, biochar composites, and nanostructured fertilizers to enhance nutrient dynamics, immobilization of contaminants, and microbial activity. Advances in nanotechnology have facilitated the synthesis of nano-calcium carbonate (NCC) and nanohydroxyapatite (nHAP) fertilizers with improved nutrient supply and controlled-release properties. However, challenges associated with nanosafety evaluation, large-scale processing technologies, regulatory harmonization, and long-term field validation remain. Therefore, this review critically synthesizes the structural, biochemical, and physicochemical properties of eggshells and eggshell membranes, examines their applications in sustainable agriculture and environmental remediation, and identifies the key research priorities required to advance eggshell valorization within circular bioeconomy strategies. Full article

Propyl-paraben (PrP) is a common preservative found in cosmetics and pharmaceutical products. It is classified as a category 1 endocrine-disrupting compound, which highlights the importance of efficiently removing it from water during treatment processes. This study investigates the potential of using Leptolyngbya sp. dominated cyanobacterial biomass residues, in both their raw and hydrothermally treated (hydrochar) forms, for the removal of PrP from aqueous media. Batch and fixed-bed column experiments were carried out under varying conditions to assess adsorption kinetics and equilibrium behavior. Both raw biomass and hydrochar exhibited satisfactory PrP removal, achieving maximum adsorption capacities of 224.58 and 258.55 mg/g respectively, at 10 mg/L initial PrP concentration and 23.33 mg/L adsorbent dosage. Equilibrium data were best described by the Freundlich isotherm model, indicating a heterogeneous surface and multilayer adsorption. The kinetic analysis revealed that the adsorption behavior, for both adsorbents, was best described by the pseudo-second-order model, while the thermodynamic evaluation revealed negative ΔH° and ΔS° values, confirming an exothermic, physisorption-driven process. The adsorption mechanism was further investigated through surface characterization techniques, including Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, N₂ physisorption, and zeta potential analysis. The findings demonstrate the potential of microalgal biomass as a low-cost, sustainable biosorbent, for emerging contaminants, reinforcing its role in advanced water treatment and circular economy strategies. Full article

Emerging compounds in water, ranging from dyes to pharmaceuticals, negatively impact living organisms and challenge the industries responsible for their release. These pollutants exhibit chemical persistence and resistance to conventional treatment processes. Adsorption is considered an effective and accessible approach, particularly when low-cost and renewable materials are employed. The Problem-Intervention-Comparison-Outcome (PICO) framework and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines were followed. A structured search of Scopus was conducted to identify English-language original peer-reviewed articles published between 2016 and 2025 addressing the use of fruit waste (FW)-derived adsorbents for water decontamination. After independent screening, 528 studies were included. Risk of bias was assessed qualitatively. Due to substantial heterogeneity in materials, contaminants, and experimental designs, findings were synthesized narratively. FW-derived adsorbents were evaluated in terms of synthesis routes, physicochemical characteristics, adsorption mechanisms, kinetic and equilibrium behavior, process optimization and regeneration performance. Correlations were observed between surface functionalization, material properties and contaminant-specific removal efficiency, while limitations were noted for multi-component systems, regeneration stability, standardization and scale-up. By integrating material design with process-level considerations, this review outlines priorities for advancing FW valorization toward practical and sustainable water treatment applications. Full article

This study investigates the use of type A zeolite as a filtering material for the removal of toxic and carcinogenic compounds from cigarette smoke, which contains nicotine and other harmful substances produced by tobacco combustion. The aim is to evaluate the effectiveness of zeolite in reducing exposure to secondhand smoke, with particular attention to health and environmental impacts. The zeolite was characterized using SEM-EDS, XRD, DSC, and TGA to determine its morphology, chemical composition, crystalline structure, and thermal stability. An experimental setup was designed to simulate realistic smoking conditions and test filter efficiency based on the active mass. The system allowed identification of harmful substances trapped in the filter and those remaining in the air. Performance was assessed through gravimetric analysis and GC-MS, enabling identification of adsorbed and non-adsorbed compounds. Results demonstrate significant efficiency in selective removal of toxic components. Finally, filter performance was compared with carbon nanotubes, tested under the same experimental protocol. Full article

Maritime transport is energy-efficient but remains heavily dependent on fossil fuels. Renewable electricity-based ammonia (e-NH₃) has emerged as a promising alternative, particularly through small-scale, modular production. Assessing its economic viability is essential for future adoption, and techno-economic analysis offers a structured way to evaluate its feasibility. This study investigates the cost performance of a small-scale offshore e-NH₃ plant of 2.4 tons per day (tpd) at the Port of Santander, Spain, based on nitrogen obtained via membrane separation and hydrogen from electrolysis of pretreated seawater. The results are based on process simulation outcomes obtained using ASPEN v14, and the detailed cost breakdown is derived from modular costing methodologies applied to preliminary process designs and sensitivity analyses of the levelized cost of ammonia (LCOA) with respect to the main variables. A comparative review of LCOA values reported in the literature for offshore and onshore e-NH₃ plants is provided. An estimated CAPEX of 5.99 M EUR (equivalent to 0.53 M EUR/y), OPEX of 1.58 M EUR/y, and an LCOA of 2408 EUR/tNH₃ are obtained, with equipment investment and operating costs identified as the most influential parameters. The results highlight the need for supraregional techno-economic studies considering optimal offshore wind availability within a collaborative interregional framework. Full article

The valorization of agro-industrial by-products through sustainable extraction of bio-compounds is a key challenge within circular economy and clean-processing frameworks, as large volumes of tomato and artichoke residues are generated by the food industry. This study evaluated the impact of non-thermal technologies on the recovery of biocompounds from tomato peels and blanched artichoke bracts using single green solvents instead of solvent mixtures. Ultrasound-assisted extraction (sonication), high-pressure processing (pressurization), and dual processing (pressurization + sonication) were compared with conventional extraction. Ethanol was used for lycopene extraction, while water was employed for inulin-type fructan recovery. Lycopene, total phenolic content, antioxidant activity, and inulin-type fructans were quantified. Non-thermal treatments significantly influenced extraction yields (p < 0.05). The dual processing provided the highest lycopene and inulin-type fructan contents (1440.09 ± 0.71 µg/g DW and 5.17 ± 0.51 g/100 g DW, respectively) and enhanced antioxidant activity in tomato peels and blanched artichoke bracts (25.50 ± 0.20% and 66.11 ± 2.03%), and phenolic co-extraction (1783.2 ± 215.3 μg GAE/g DW and 27.68 ± 1.29 mg GAE/g DW) outperformed individual technologies and conventional extraction. Compared with the conventional process, dual processing improved the extraction yields of lycopene (20.60 ± 0.44%) and inulin (26.40 ± 13.95%). The findings prove that non-thermal processes, particularly when combined, intensify mass transfer and enable efficient extraction using green solvents, offering a sustainable strategy for recovering bioactive compounds from tomato and artichoke by-products. Full article

The continuous increase in atmospheric CO₂ concentration exacerbates global climate change, making carbon reduction an urgent global priority. Carbonic anhydrase (CA), a highly efficient biocatalyst that converts CO₂ into bicarbonate, demonstrates significant potential for carbon capture and resource utilization. However, the stability and catalytic efficiency of native CA in industrial environments are limited, particularly its poor thermal tolerance under flue gas conditions and its sensitivity to impurities, hindering its direct large-scale application. This review systematically summarizes recent advances in modifying microbial CA through protein engineering (e.g., directed evolution, rational design) and immobilization techniques, which have markedly enhanced its thermal stability, adaptability, and reusability. Among these, the integration of machine learning with high-throughput experimentation has emerged as a transformative strategy for CA engineering. Furthermore, we outline CA-driven pathways for CO₂ conversion into high-value chemicals and bioenergy. Finally, future prospects are discussed, including interdisciplinary integration, computational modeling coupled with experimental validation, and comprehensive life-cycle and techno-economic assessments, to facilitate the scaled application of engineered microbial CA in carbon neutrality pathways. Collectively, this review highlights the critical role of engineered CA in bridging biocatalysis with industrial carbon management, offering a viable and sustainable pathway toward carbon neutrality. Full article

The transition toward low-carbon and circular Municipal Solid Waste (MSW) systems requires integrated evaluation approaches that consider environmental performance, technological maturity, and governance capacity. This study presents a structured, systematic review of MSW disposal and treatment practices published between 2018 and 2026, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. A total of 71 studies were included and analyzed. Due to heterogeneity in methodologies, system boundaries, and reported indicators, no formal meta-analysis was conducted. Instead, the review provides a comparative and qualitative synthesis of key environmental indicators and structural determinants. Results indicate a transition from open dumping toward engineered landfills and advanced treatment technologies, including waste-to-energy and biological processes. Open dumping is consistently associated with high greenhouse gas emissions and environmental risks, while engineered systems improve containment and enable partial resource recovery. The findings highlight that environmental performance is not determined solely by technology but by the interaction between infrastructure design, operational quality, governance capacity, and economic conditions. The proposed analytical framework supports context-sensitive waste management strategies aligned with circular economy principles and climate mitigation objectives. Full article

Polyunsaturated fatty acids, particularly γ-linolenic acid, are recognized for their therapeutic and nutritional properties. Zygomycetes, such as Cunninghamellaelegans, represent a promising microbial platform for sustainable gamma-linolenic acid (GLA) production as an alternative to conventional sources. Despite this potential, the immunomodulatory activity of metabolites from C. elegans has not been previously explored. In this study, C. elegans was cultivated on hydrolysates from discarded residues of Pleurotus spp. cultures (DRPC-HL), optimized to release assimilable compounds, promoting valorization of low-value biomass within a circular bioeconomy. Dry mycelial biomass, lipid-free biomass, and intracellular lipids from these cultures, alongside previously reported C. elegans cultures grown under nitrogen-excess (N-Xs) and nitrogen-limited (N-Lim) conditions, were tested on THP-1-derived macrophages, under lipopolysaccharide (LPS)-induced inflammatory conditions. Following in vitro gastrointestinal digestion, dry biomass and lipid-free dry biomass fractions upregulated the anti-inflammatory cytokine IL10 and downregulated IL1B and TNF, particularly from N-Xs and DRPC-HL cultures. Lipids mainly enhanced IL10 expression, especially when derived from N-Xs cultures. No changes were observed in upstream regulators (TLR2, TLR4, NFKB1, RELA), suggesting a feasible post-receptor immunomodulatory action. Overall, these findings highlight the dual value of fungal bioproducts derived from agro-industrial residues, combining sustainable bioprocessing with bioactive compound generation, supporting environmentally friendly microbial platforms for industrial applications. Full article

With the rapid growth of the medicinal cannabis sector, there is a growing concern regarding its environmental impact and sustainability. In recent years, life cycle assessment (LCA) studies on medicinal cannabis cultivation and processing have been conducted since 2021. However, there is a lack of comprehensive LCA studies that include all stages of medicinal cannabis cultivation and processing. In this systematic review, various LCA studies conducted from 2021 to 2025 using the ISO 14040/44 methodology are reviewed and discussed in terms of their goal and scope, life cycle inventory (LCI), life cycle impact assessment (LCIA), and result interpretation. Various environmental impact indicators are considered in this review, such as greenhouse gas emissions, energy demand, water usage, eutrophication, acidification, and resource depletion. All of these impact indicators point to a significant environmental impact of indoor cultivation in terms of greenhouse gas emissions, which vary from 2.3 × 10³ to 5.2 × 10³ kg CO₂ eq kg⁻¹ of dried cannabis product. Nevertheless, it is important to note that this is significantly influenced by regional electricity sources. Low-carbon-based electricity sources, especially hydro-based sources, can reduce emissions to a significant level. Cultivation outdoors presents significantly lower emissions of (60–110 kg CO₂ eq kg⁻¹), but fertilizers and substrates used in cultivation contribute significantly to emissions. Also, outdoor plants use 22.7 L plant⁻¹ d⁻¹ water at peak growth, while indoor plants use 9–11 L plant⁻¹ d⁻¹ water. Improvements in the life cycle of cannabis cultivation can be achieved through renewable energy use, water and fertilizers, substrate use and reuse, and inventories for post-harvesting activities like drying and extraction. Botanical parameters including genotype, planting density, and harvesting frequency are identified as significant but under-characterized determinants of LCA outcomes. Ethical and legal barriers are shown to be structural drivers of the LCA data gap. A SWOT analysis contextualizes the opportunities and constraints of the sector. Future research should focus on cradle-to-grave LCA and incorporate socio-economic factors for sustainability in the medicinal cannabis sector. Full article

Sustainable structural composites can significantly lower vehicle-related emissions. To evaluate the recycling of different composite materials, laboratory-scale pyrolysis was conducted and assessed both technically and environmentally. Two demonstrators were studied: a truck side skirt made from natural flax and hemp fibres with polypropylene (PP), and a car front header composed of glass fibres and PP. Additional materials examined included thermoplastic composites containing polyamide 6 (PA6), bio-based polyamide 11 (PA11) and thermoset polyester. Results showed that material type strongly influenced the pyrolysis outcome, product composition and recycling potential. Glass fibres could be recovered and reused as reinforced fibres, while natural fibres could be recovered as biooil for potential use in biofuel production. Polymers were recovered as pyrolysis products that, depending on their composition, can be used in different applications, from recovering monomers from PA6 to producing hydrocarbons that may replace naphtha (from PP) or aromatics (from polyester) in the petrochemical industry. Life cycle assessment (LCA) findings revealed that the climate impact of composite recycling is primarily driven by the environmental burdens of the recycling process itself and by the ability of recovered materials and chemicals to substitute conventional fossil-based alternatives. Efficient recycling pathways are therefore essential to maximising environmental benefits. Full article

As the world faces the challenge of mitigating climate change, energy- and emissions-intensive industrial processes must be addressed urgently worldwide. The cement production industry accounts for over 8% of global greenhouse gas (GHG) emissions from calcination and fuel use. Mexico, a middle-income economy, has rising cement demand for infrastructure and commercial growth. Thus, this study analysed national cement production, the primary emitting manufacturing industry in the country, under a business-as-usual (BAU) and two alternative scenarios, using a top-down approach to model energy consumption and GHG emissions by 2050. These scenarios follow the projection of national cement production, estimated using socio-economic indicators, which are considered the main drivers of cement demand, reaching 97.3 Mt. A qualitative analysis evaluates the strengths, weaknesses, opportunities, and threats (SWOT) of implementing emission-reduction strategies. The analysis showed that the BAU scenario might reach 66.5 Mt CO_2e by 2050, while the most ambitious scenario reduced direct emissions by 80.1% through carbon capture, clinker-to-cement reduction, thermal energy intensity reduction, and the use of municipal solid waste as an alternative fuel. However, incorporating these strategies in Mexico requires a more active role and investment support from key stakeholders. Full article