Clean Technologies

Microalgae have attracted wide attention due to their extensive application potential. Dewatering is a necessary work for the application of microalgae, especially in biofuel production, where forward osmosis (FO) research is relatively advanced but still faces technical bottlenecks hindering large-scale commercialization. Based on the current research in recent years, the research progress in the causes and control of membrane fouling, the development of membrane materials and optimization of membrane structure, and the energy saving and efficiency of the process are reviewed in this paper. We found that different species of algae have direct effects on membrane fouling. Chlorella vulgaris has a low membrane fouling trend, but the mechanisms of fouling need further investigation. The material development and structure optimization of membranes are the main research methods to reduce membrane fouling, but there are still some defects, such as complicated preparation and low water flux, which are difficult to apply on a large scale. The research progress of reducing costs by using seawater, urine, fertilizer, etc. as new draw solutions (DS) is reviewed. At present, many aspects of FO microalgae dewatering technology are still not well understood, and future research should focus on scaling up the existing technologies. Full article

Heat stress on workers wearing PPE (Personal protective equipment) in hot outdoor environments is of rising concern, especially in cases when rest breaks and clothing changes are impractical. Mist fan evaporative cooling could provide low-energy continuous cooling, even during work activity. The cooling effect of a misting fan was compared to that of a fan alone, as well as natural convection. A thermal mannequin with heat flux sensors at eight body locations was exposed to an outdoor misting fan while being clothed in typical work clothes and PPE. Work clothes were dry or saturated with water to simulate sweat. The distance from the misting fan ranged from 4 m (wetting common) to 7 m (wetting unlikely). On average, the misting fan had a cooling effect of 0.31 met (18.3 W/m²) higher than natural convection when PPE is worn with wet work clothes, and 0.35 met (20.3 W/m²) higher than when PPE is worn with dry work clothes. This equates to reducing the thermal metabolic load from light industrial work to walking about in office work, or from standing to reclining. Under the ISO 7243 international standard for workers in hot environments, this would increase the acceptable WBGT (wet bulb globe temperature) by over 0.6 °C. Full article

Pore-scale remediation investigation of oil-contaminated soil is important in several environmental and industrial applications, such as quick responses to sudden accidents. This work aims to investigate the oil pollutant removal process and optimize the oil-contaminated soil remediation performance at the pore scale to find the underlying mechanisms for oil removal from soil. The conservative forms of the phase-field model and the non-Newtonian power-law fluid model are employed to track the moving interface between two immiscible phases, and oil pollutant flushing removal process from soil pores is investigated. The effects of viscosity, interfacial tension, wettability, and flushing velocity on pore-scale oil pollutant removal regularity are explored. Then, the oil pollutant removal effects of two flushing agents (surfactant system and surfactant–polymer system) are compared using an oil content prediction curve based on UV-Visible transmittance. The results show that the optimal removal efficiency is obtained for a weak water-wetting system with a contact angle of 60° due to the stronger two-phase fluid interaction, deeper penetration, and more effective entrainment flow. On the basis of the dimensionless analysis, a relatively larger flushing velocity, resulting in a higher capillary number (Ca) in a certain range, can achieve rapid and efficient oil removal. In addition, an appropriately low interfacial tension, rather than ultra-low interfacial intension, contributes to strengthening the oil removal behavior. A reasonably high viscosity ratio (M) with a weak water-wetting state plays synergetic roles in the process of oil removal from the contaminated soil. In addition, the flushing agent combined with a surfactant and polymer can remarkably enhance the oil removal efficiency compared to the sole use of the surfactant, achieving a 2.5-fold increase in oil removal efficiency. This work provides new insights into the often-overlooked roles of the pore scale in fluid dynamics behind the remediation of oil-contaminated soil via flushing agent injection, which is of fundamental importance to the development of effective response strategies for soil contamination. Full article

To develop a biomass and power-to-gas (BPtG) process for renewable electricity storage and sustainable synthetic natural gas (SNG) production, this work investigated five BPtG processes integrated with different electricity-driven gasification technologies based on simulation data. These processes were evaluated for SNG composition and yield, life-cycle energy and exergy efficiencies, life-cycle carbon emissions, and the equivalent unit production cost. The results show that the energy and exergy efficiencies of SNG from those processes range between 53.1 and 58.6% and 36.4 and 41.1%, respectively. Based on the energy allocation method, the carbon emissions without and with CO₂ capture ranges from 22.0 to 34.8 and from −43.4 to −17.6, respectively, in gCO₂e/MJ_SNG. These BPtG processes can produce low-carbon SNG and even achieve negative carbon emissions with CO₂ capture. Both feedstock and electricity costs have significant influences on the profitability of the processes. The BPtG process integrated with resistance heating gasification, plasma-assisted gasification, and moderate water electrolysis are recommended for their compromise of multi-perspective performances. This paper provided the orders of the five processes based on these indicators and recommendations for different applicable scenarios. Full article

Cruise ships function as a means of transport while simultaneously accommodating thousands of guests, providing a holiday experience with various entertainment options. This translates to high energy requirements for propulsion and hotel operations, typically covered by the combustion of fossil fuels. The operation of cruise vessels with fossil fuels contributes to carbon dioxide and also local harmful emissions in ports when shore power connections are not available. To enable cleaner and sustainable cruising, alternative technologies and fuels must be adopted. The present study evaluated the applicability of hydrogen fuel in combustion engines in a Meraviglia-class cruise ship. The fuel consumption of the ship was based on a real operation in Europe. This study examined how fuel energy in the form of LH₂ could be stored on the ship for a European cruise route and concludes that 3700 m³ of storage space would be needed to accommodate the liquid hydrogen. The mass of the LH₂ would only be one-third of that of fossil fuels, but the weight of the LH₂ tanks would most likely increase the total weight of the hydrogen storage. Additional new technologies and combined power production could significantly reduce the amount of LH₂ to be stored. Full article

This study assesses supply risks for critical raw materials (CRMs) essential to Europe’s thermoelectric (TE) technology, which transforms heat into electricity. Given the EU’s heavy reliance on imports for key materials like tellurium, antimony, bismuth, and lead, the analysis incorporates market forecasting, scarcity quantification, and Monte Carlo simulations to model demand and supply risks. This study reveals that tellurium poses high risks due to scarcity and potential geopolitical impacts, with antimony and bismuth at moderate risk, and lead presenting notable health hazards. The findings suggest the necessity of circular supply chains and material alternatives to mitigate resource, environmental, and geopolitical challenges for sustainable TE development in Europe. Moreover, there is a pressing need to update and expand data availability for materials like tellurium to enable more robust risk assessments in the immediate future. Full article

This study analyzed the anaerobic co-digestion of inoculum (I), rubber plant effluent (RPE) and Gliricidia leaves slurry (GLS) at different mixing ratios for the simultaneous production of methane and organic fertilizer. The results were analyzed for volatile fatty acids, pH, C/N ratio, and methane production. The organic quality of the substrate mixture before and after anaerobic digestion was analyzed for total organic carbon, total nitrogen, potassium, and phosphorus contents. This study concluded that the inoculum, rubber plant effluent (RPE), and Gliricidia leaves slurry (GLS) mixed at the ratio of 10:2:2 showed higher methane production than other experiments conducted at different mixing ratios. The nitrogen, potassium, and phosphorus contents of the substrates were increased after anaerobic digestion. However, the organic carbon content in the substrate decreased in all experiments. This research recommends the planting of rubber trees and Gliricidia maculata to promote energy sustainability and the socio-economic development of Mauritania. Full article

In this study, vapor–liquid equilibrium (VLE) experimental data were measured for two binary solvents based on 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), which can be used as a new CO₂-binding organic liquids (CO₂-BOLs) solvent. No experimental data are available in the literature and are fundamental to determine whether the considered mixtures are suitable to be possible alternatives to traditional amine solutions for CO₂ removal. The bubble point data of 1,2-propanediol+1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and 1,4-butanediol+DBU mixtures were measured at 30 kPa. The experimental determination was carried out in an all-glass dynamic recirculation still at the Process Thermodynamics laboratory (PT lab) of Politecnico di Milano. The thermodynamic modeling of the VLE behavior of two DBU-based mixtures was performed considering the NRTL, the UNIQUAC, and the Wilson models, and binary interaction parameters of the NRTL activity coefficients model were regressed on the basis of the measured experimental data. Full article

Strontium (⁹⁰Sr) is a typical radionuclide, which can act as a contaminant and poses a big problem for the eco-environment if left untreated. In this study, an original nitrogen-doped calcite (N-CaCO₃) was synthesized using a solvothermal and calcination method and used to remove Sr(II) from simulated water. XRD, SEM, and XPS analyses proved that N was successfully doped into CaCO₃, resulting in porous CaCO₃ with a regular morphology. The specific surface area of N-CaCO₃ (136.53 m²/g) can reach 2.19-fold greater than that of CaCO₃. The results based on the batch adsorption data indicated that the pseudo-second-order kinetic model (R² = 0.9964) and the ion exchange model (R² = 0.9859) fitted the adsorption data well. The as-synthesized N-CaCO₃ exhibited better adsorption performance in regard to low concentrations of Sr(II) (below 64.5 mg/L) compared with commercial CaCO₃. The structural analysis suggested that Ca and N played pivotal roles in the adsorption process and that the adsorption mechanism was dominated by ion exchange and surface complexation. This study successfully fabricated a nitrogen-doped calcite for Sr(II) cleanup, presenting an efficient strategy to modulate the microstructure of CaCO₃, or other materials, to enhance its adsorption performance. Full article

This study investigates the potential of utilizing livestock waste and vineyard residues for sustainable energy production in Portugal. Through the physical and chemical characterization of swine waste, grape seeds and skins, cork powder, sawdust, and biochar, 53 distinct samples, including 11 individual biomasses and their derived mixtures, were analyzed to identify optimal combinations for biofuel pellet production. The best-performing mixture, composed of 50% swine waste, 25% grape seeds and skins, and 25% cork powder, achieved a Lower Heating Value (LHV) of 18.34 MJ/kg and low ash content, qualifying it as a class B pellet. This mixture offers significant energy potential while minimizing environmental impacts. The research also presents three energy valorization scenarios, with the most balanced scenario meeting up to 6% of Portugal’s electricity demand and providing energy savings equivalent to 485,463 tons of oil equivalent (toe) annually. A case study on a “Case Study Farm” in the Douro region, managing 2000 pigs and producing 500 tons of wine grapes annually, demonstrated that implementing the optimal biomass mixture could generate 3854 MWh of heat and 1156 MWh of electricity per year. This could result in annual revenues of EUR 189,258 from pellet sales, covering the initial investment of EUR 283,938 within 6.36 years, with a total surplus of EUR 689,666 over 20 years. These findings highlight the economic viability and environmental benefits of converting agricultural waste into renewable energy, contributing to Portugal’s carbon neutrality and reducing energy dependence. Full article

BAT-based regulations necessitate defining key environmental issues (KEIs) to focus data collection and discussions on the main topics when establishing best available techniques (BATs) at the sector level. However, Article 14 of the Industrial Emissions Directive (IED) suggests that some significant environmental issues may not be covered by BAT conclusions but still require the implementation of BATs at the local level, even in the absence of defined sectoral BAT references. The IED, along with the associated Commission Implementing Decisions and guides, does not offer guidelines for selecting KEIs at the local level, whether by the competent authority or the operator. To ensure full compliance with the IED by installations under its scope, this paper proposes a methodology for determining KEIs locally. Based on the environmental aspects of the installation, the sensitivity of the environment, and the levels of emissions or consumption, this methodology has been tested on a case study at the plant level to demonstrate its effectiveness. The paper then discusses the contributions and limitations of the methodology and suggests areas for future research. The proposed methodology was tested at the factory level, where it effectively identified and prioritized key environmental issues (KEIs) by focusing on site-specific environmental aspects not covered by sectoral BAT conclusions. The results suggested improved alignment with local environmental challenges, indicating the methodology’s effectiveness in capturing key issues that may require immediate action under Article 14 of the IED. This approach provides a practical framework for prioritizing environmental impacts based on local context and regulatory requirements. Full article

This research study addresses the challenges of extended charging times and limited ranges in electric vehicles by conducting a techno-economic analysis of integrating renewable energy technologies—solar modules, wind turbines, and piezoelectric materials—into double-decker electric buses in London, UK. Consequently, the empirical study evaluates the power output of renewable energy technologies through simulation modelling based on vehicle specifications and energy requirements, which is followed by numerical modelling to assess economic viability. Furthermore, CFD (computational fluid dynamics) modelling is undertaken to examine the performance levels of vehicular-mounted wind turbines. The solar modules are placed on the rooftop and sides of the bus, generating 15.9 kWh/day, and the wind turbine in the front bumper of the bus generates 8.3 kWh/day. However, the piezoelectric material generated only 22.6 Wh/day, thereby rendering this technology impractical for further analysis. Therefore, both the solar modules and wind turbines combined generate 24.2 kWh/day, which can increase the driving range by 16.3 km per day, resulting in savings of 19.36 min for charging at the stations. Investing in such projects would have a positive return as the internal rate of return (IRR) and net present value (NPV) are 2.8% and £11,175, respectively. The annual revenue would be £6712, and the greenhouse gas (GHG) reduction would be two metric tons annually. Electricity generation, the electricity generation rate, and the initial investment are identified as key factors influencing power outages in a sensitivity analysis. In conclusion, this numerical modelling study paves the way for experimental validation toward the implementation of renewable energy technologies on electric bus fleets. Full article

Nanofine zero−valent iron (nZVI) is a new, eco−friendly material with strong reducing and adsorbent properties that can be used to clean up heavy metal−affected soils. Herein, nZVI encapsulated with carboxymethyl cellulose (CMC−nZVI) is synthesized via an aqueous−phase reduction technique and subsequently deployed to evaluate its effectiveness in Cr(VI) soil remediation. The characterization analysis used SEM−EDS, XRD, XPS, and LSV to determine the relevant properties of the material. The results show that at an initial Cr(VI) concentration of 169.5 mg·kg⁻¹, 93.2% of Cr(VI) was removed from the soil after 10 h of treatment with CMC−nZVI at pH 3.3. The kinetic analysis showed that CMC−nZVI had the maximum equilibrium adsorption capacity for removing Cr(VI) from soil at 105.3 mg·g⁻¹. This followed a pseudo−second−order kinetic model. The study shows that CMC−nZVI converts Cr(VI) to Cr(III), which forms complexes with Fe(III) ions in the presence of hydroxide ions (OH⁻) to form a highly stable compound that eventually adsorbs into the nanomaterial’s surface for efficient removal. Full article

Alternative options have been studied to mitigate the negative impact of fossil fuel sources, mainly especially when it comes to alternative energy sources. In this work, cannabis residues have been considered as a potential biomass residues for energy recovery due to their energy content, and the increase in the cannabis market in Canada has created an opportunity niche for treating and valorizing these residues as energy. This study thus aims to investigate the potential of energy recovery from cannabis residue pellets via combustion and the impact of steam explosion on the pellets’ properties as well as combustion behavior. Two batches of pellets were produced namely with and without the steam explosion pretreatment. The properties of the pellets were then compared to those of the CANplus certification. Cannabis pellets were then combusted at 290 °C in a fixed-bed reactor using three different air coefficients (α) ranging from 1 to 1.3 (α = 1.0, α = 1.15, and α = 1.3). Flue gas quantification was performed using gas chromatography combined with a NO_x detector. Results showed that the properties of this biomass is comparable to other sources of lignocellulosic biofuels. The steam explosion pretreatment enhanced pellet properties, including higher heating value (HHV), ash content, durability, and fines allowing the product to reach the CANplus requirements. The air coefficients influenced the emission levels, with an optimal value at α = 1.15, that indicated an improved combustion quality. However, steam explosion negatively affected combustion efficiency, resulting in incomplete combustion. Overall, cannabis residues show a strong potential for energy recovery and could offer a sustainable option for bioenergy applications. Full article

While the attempts to find new energy sources have intensified, the interest in the use of biomass as a carbon-rich raw material still is increasing. In this work, we studied iron-, cobalt-, and nickel-based materials in the process of CO₂-assisted gasification of sunflower husk. The materials with and without metal additives were examined by XRD, SEM, EDX, and TEM techniques and were tested in their gasification under the action of CO₂. It was found that the Co-based material demonstrates the best activity among the studied ones (the CO₂ conversion was up to 83%). The possible reason for such superiority may be related to the capability of Ni compounds to the formation of the metallic nickel phase and insufficient activity of iron species. Full article

Enhancing the eco-efficiency of municipal solid waste (MSW) services is pivotal for the shift toward a circular economy. Although the Data Envelopment Analysis (DEA) method is widely used, it is susceptible to overfitting, potentially distorting eco-efficiency assessments. This study applies the efficiency analysis tree (EAT) method, which synergizes machine learning and linear programming, offering a more reliable framework for eco-efficiency evaluation in the MSW sector. This innovative approach provides deeper insights into the optimal levels of operational costs and unsorted waste. The research encompasses a case study of 98 Chilean municipalities from 2015 to 2019, uncovering significant disparities in optimal operational expenses and unsorted waste quantities, which underscores the necessity for customized waste management approaches. The average eco-efficiency scores for 2015–2019 range between 0.561 and 0.566. This means that assessed municipalities can reduce unsorted waste by amounts ranging from 1,632,409 tons/year (2016) to 1,822,663 tons/year (2018). Potential economic savings estimated are 105,973 USD/year (2019), which represents 44% of the total MSW management costs. Additionally, the investigation into the effects of external factors on eco-efficiency furnishes nuanced perspectives that can guide policymakers and municipal authorities in developing effective, context-specific waste management strategies. Beyond refining eco-efficiency evaluations, this study contributes to more informed decision-making processes, aiding the progression toward sustainable waste management practices. Full article

This study addresses the significant environmental challenge of pharmaceutical pollutants by demonstrating the effectiveness of a hybrid electrocoagulation–adsorption (EC-A) technique for removing Montelukast Sodium (MS) from contaminated water. The research was conducted in three stages—adsorption, electrocoagulation, and adsorption using the residual water from the electrocoagulation process. The adsorbent materials were characterised using various analytical techniques: X-ray Diffraction (XRD) for determining the crystalline structure, Energy-Dispersive X-ray Spectroscopy (EDX) for elemental composition, Scanning Electron Microscopy (SEM) for surface morphology, and Fourier Transform Infrared Spectroscopy (FTIR) for identifying functional groups before and after interaction with the pollutants. The adsorption phase achieved optimal results at a pH of 3 and a contact time of 120 min, with a maximum removal efficiency of 99.5% for a starting MS concentration of 50 mg/L using Calcium Ferric Oxide–Silica Sand (CFO-SS) adsorbent. The electrocoagulation phase showed a 97% removal efficiency with a pH of 11, a current density of 20 mA, and a 5 mm electrode distance, achieved in just 20 min. Finally, the combined EC-A process, with the pH of residual water adjusted to 3, further enhanced the removal efficiency to 74%, highlighting the method’s potential for pharmaceutical contaminant removal. These findings underscore the potential of the EC-A technique as a highly effective and adaptable solution for mitigating pharmaceutical contaminants in water. Full article

This study investigates the optimization of aeration rates for the biodrying of market waste using negative-pressure ventilation. Market waste, characterized by a high moisture content (MC) and rapid decomposition, presents challenges in waste management. Over 12 days, three aeration rates (ARs) of 0.2, 0.4, and 0.6 m³/kg/day were examined, and the most effective continuous ventilation configuration was identified in terms of heat generation, moisture reduction, and biodrying efficiency. The results indicate that the most effective AR for heat retention and moisture removal was 0.2 m³/kg/day, achieving a 6.63% MC reduction and a 9.12% low heating value (LHV) increase. Gas analysis showed that, while AR 0.2 supported high microbial activity during the initial 7 days, AR 0.6 sustained higher overall CO₂ production due to its greater aeration rate. The findings also suggest that the biodrying of market waste with a high initial MC can achieve significant weight loss and leachate generation when paired with a high aeration rate of 0.6 m³/kg/day, with a 69.8% weight loss and increased waste compaction being recorded. The study suggests that variable ARs can optimize biodrying, making market waste more suitable for conversion to refuse-derived fuel or landfill pre-treatment and improving waste-to-energy processes and sustainability. Full article

The growing adoption of lithium iron phosphate (LiFePO₄) batteries in electric vehicles (EVs) and renewable energy systems has intensified the need for sustainable management at the end of their life cycle. This study introduces an innovative method for recycling lithium from spent LiFePO₄ batteries and repurposing the recovered lithium carbonate (Li₂CO₃) as a carbon dioxide (CO₂) absorber. The recycling process involves dismantling battery packs, separating active materials, and chemically treating the cathode to extract lithium ions, which produces Li₂CO₃. The efficiency of lithium recovery is influenced by factors such as leaching temperature, acid concentration, and reaction time. Once recovered, Li₂CO₃ can be utilized for CO₂ capture in hydrogen purification processes, reacting with CO₂ to form lithium bicarbonate (LiHCO₃). This reaction, which is highly effective in aqueous solutions, can be applied in industrial settings to mitigate greenhouse gas emissions. The LiHCO₃ can then be thermally decomposed to regenerate Li₂CO₃, creating a cyclic and sustainable use of the material. This dual-purpose process not only addresses the environmental impact of LiFePO₄ battery disposal but also contributes to CO₂ reduction, aligning with global climate goals. Utilizing recycled Li₂CO₃ decreases the demand for virgin lithium extraction, supporting a circular economy. Furthermore, integrating Li₂CO₃-based CO₂ capture systems into existing industrial infrastructure provides a scalable and cost-effective solution for lowering carbon footprints while securing a continuous supply of lithium for future battery production. Future research should focus on optimizing lithium recovery methods, improving the efficiency of CO₂ capture, and exploring synergies with other waste management and carbon capture technologies. This comprehensive strategy underscores the potential of lithium recycling to address both resource conservation and environmental protection challenges. Full article