Clean Technol., Volume 7, Issue 1 (March 2025) – 11 articles

Plastic products are used in agriculture to increase crop yield and improve crop quality to face a double challenge: a growing world population and a depletion and scarcity of natural resources. In this framework, the European Commission is working on establishing biodegradation criteria under natural conditions for certain plastic products. Such criteria are particularly important for products where biodegradation is key once reaching the end of their shelf life, considering an end-of-life scenario where their waste management is either unfeasible or highly complex. Under this scope, this work aims to provide a comprehensive assessment of the current status of European regulations in terms of plasticulture product biodegradability, highlighting the specific tests and standards regarding the biodegradability assessment. Biodegradation of plasticulture products in soil and water has been considered for biodegradability criteria, establishing a threshold of at least 90% of the organic carbon converted into CO₂. These regulations have followed a tool-based study of a mathematical prediction model for the main existing families of biodegradable polymers in soil. These regulations will help the fertilizer industry to develop new formulations that are more sustainable and effective in the agriculture field. Full article

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