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Clean Technol., Volume 4, Issue 3 (September 2022) – 11 articles

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Review
Floating Photovoltaics: A Review
Clean Technol. 2022, 4(3), 752-769; https://doi.org/10.3390/cleantechnol4030046 (registering DOI) - 08 Aug 2022
Abstract
The world is transitioning towards a net zero emissions future and solar energy is at the forefront of the transition. The land use requirements to install solar farms present a barrier for the industry as population density increases and land prices rise. Floating [...] Read more.
The world is transitioning towards a net zero emissions future and solar energy is at the forefront of the transition. The land use requirements to install solar farms present a barrier for the industry as population density increases and land prices rise. Floating photovoltaics (FPV) addresses this issue by installing solar photovoltaics (PV) on bodies of water. Globally, installed FPV is increasing and becoming a viable option for many countries. A 1% coverage of global reservoirs with FPV would have a potential capacity of 404GWp benign power production. There are numerous advantages to FPV compared to ground mounted PV (GPV), which are discussed in this review. The major gap in research is the impact FPV has on water quality and living organisms in the bodies of water. This review paper examines the most recent research around FPV, analyzing the benefits, downfalls, and future. The review provides more insight into FPV in terms of varying water bodies that can be used, system efficiency, global potential, and potential for coupling FPV with other technologies. Full article
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Article
Effect of Various Growth Medium on the Physiology and De Novo Lipogenesis of a Freshwater Microalga Scenedesmus rotundus-MG910488 under Autotrophic Condition
Clean Technol. 2022, 4(3), 733-751; https://doi.org/10.3390/cleantechnol4030045 - 01 Aug 2022
Viewed by 319
Abstract
The microalga Scenedesmus rotundus, isolated from Jabalpur, Madhya Pradesh, India was designated as Scenedesmus rotundus-MG910488 after morphological and molecular identification. In this study, the effects of various autotrophic growth media on the physiology and lipid accumulation of this microalga were investigated. The [...] Read more.
The microalga Scenedesmus rotundus, isolated from Jabalpur, Madhya Pradesh, India was designated as Scenedesmus rotundus-MG910488 after morphological and molecular identification. In this study, the effects of various autotrophic growth media on the physiology and lipid accumulation of this microalga were investigated. The cell density, amount of photosynthetic pigments, the productivity of biomass and lipid content and the cell morphology of the microalga were shown to be significantly affected by the variation in growth media. The highest biomass of 754.56 ± 14.80 mg L−1 with biomass productivity of 37.73 ± 0.74 mg L−1 day−1 was achieved when this microalgae was cultivated in the Zarrouk’s medium, whereas the highest lipid content of 33.30 ± 1.21% was observed in the BG-11 medium. The results confirm that the BG-11 is a cost-effective and efficient growth medium for this microalga. It also shows that the ingredients of the growth medium and its concentration influence the growth and synthesis of biomolecules produced by microalga. The biodiesel produced from obtained lipids was qualitatively estimated by Gas Chromatography-Mass Spectroscopy (GC-MS), Nuclear Magnetic Resonance (1H, 13C NMR) and Fourier Transform-Infrared Spectroscopy (FT-IR), which indicate the presence of oleic acid methyl ester, linoleic acid methyl ester and palmitic acid methyl ester as the leading fatty acid methyl esters (FAME) in the samples, which make this strain an ideal feedstock for biodiesel production. Full article
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Article
Enhancement of Chiller Performance by Water Distribution on the Adiabatic Cooling Pad’s Mesh Surface
Clean Technol. 2022, 4(3), 714-732; https://doi.org/10.3390/cleantechnol4030044 - 26 Jul 2022
Viewed by 303
Abstract
Evaporative cooling is widely recognized as an energy efficient and environmentally-friendly air conditioning solution, and it has drawn a lot of market interest in recent years. However, this technology is accompanied by several challenges. For instance, insufficient evaporation due to poor and non-homogenous [...] Read more.
Evaporative cooling is widely recognized as an energy efficient and environmentally-friendly air conditioning solution, and it has drawn a lot of market interest in recent years. However, this technology is accompanied by several challenges. For instance, insufficient evaporation due to poor and non-homogenous water distribution of the pre-cooling pad significantly reduces the cooling performance. The aim of the study is to develop a technique for numerical simulation of the distribution of a droplet liquid (water) on the mesh surface of an adiabatic cooler to improve the performance of air conditioning equipment. Modern computer-aided design (CAD)/computational fluid dynamics (CFD) programs were used to solve the issue. For the mathematical modelling of the medium motion, non-stationary Navier–Stokes equations were used. Parameters such as heat, mass transfer, and the efficiency of liquid droplet spraying were determined. The current study presents CAD modelling, conducted in SolidWorks platform, of water distribution on the adiabatic cooling pad’s mesh surface for improving air conditioning equipment performance. This study provides the methodology for computer modeling and numerical calculation of the parameters of adiabatic cooling, such as modelling of water atomization process. The results show that the use of additional metal mesh intended as cooling pads increases the mass transfer coefficient by Sh ≈ 15–40%; heat transfer coefficient Nu increases by ≈20–40%; and the atomization efficiency increases by ≈30–40%. The installation of metal pad mesh allows for equalized uniformity of the water distribution. The results imply that there are more opportunities to optimize the parameters of adiabatic cooling, which should be evaluated in further research on the subject. Full article
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Article
A Simplified Model for Estimating Household Air Pollution in Challenging Contexts: A Case Study from Ghana
Clean Technol. 2022, 4(3), 703-713; https://doi.org/10.3390/cleantechnol4030043 - 25 Jul 2022
Viewed by 320
Abstract
Almost three billion people rely primarily on inefficient and polluting cooking systems worldwide. Household air pollution is a direct consequence of this practice, and it is annually associated with millions of premature deaths and diseases, mainly in low- and lower-middle-income countries. The use [...] Read more.
Almost three billion people rely primarily on inefficient and polluting cooking systems worldwide. Household air pollution is a direct consequence of this practice, and it is annually associated with millions of premature deaths and diseases, mainly in low- and lower-middle-income countries. The use of improved cookstoves often represents an appropriate solution to reduce such health risks. However, in the distribution of such units, it can be necessary to prioritize the beneficiaries. Thus, in this study, we conducted field research involving five rural villages in the Northern part of Ghana, where using three-stone fires or rural stoves was common. Concentrations of PM2.5, PM10, and carbon monoxide (CO) were measured indoors and outdoors. Considering each field mission lasted less than 24 h, assumptions were made so as to calculate the average pollutant concentrations in 24 h through a new, simplified equation that combined efficiency and cost-savings by shortening field assessments. The obtained values were compared with international guidelines. The results showed that PM2.5 and PM10 limits were overstepped in two villages, which should thus be prioritized. However, further research will be necessary to strengthen and validate our proposed equation, which must be seen as a starting point. Full article
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Article
Iron and Magnesium Impregnation of Avocado Seed Biochar for Aqueous Phosphate Removal
Clean Technol. 2022, 4(3), 690-702; https://doi.org/10.3390/cleantechnol4030042 - 22 Jul 2022
Viewed by 393
Abstract
There has been increasing interest in using biochar for nutrient removal from water, and its application for anionic nutrient removal such as in phosphate (PO43−) necessitates surface modifications of raw biochar. This study produced avocado seed biochar (AB), impregnated Fe- [...] Read more.
There has been increasing interest in using biochar for nutrient removal from water, and its application for anionic nutrient removal such as in phosphate (PO43−) necessitates surface modifications of raw biochar. This study produced avocado seed biochar (AB), impregnated Fe- or Mg-(hydr)oxide onto biochar (post-pyrolysis), and tested their performance for aqueous phosphate removal. The Fe- or Mg-loaded biochar was prepared in either high (1:8 of biochar to metal salt in terms of mass ratio) or low (1:2) loading rates via the co-precipitation method. A total of 5 biochar materials (unmodified AB, AB + High Fe, AB + Low Fe, AB + High Mg, and AB + Low Mg) were characterized according to their selected physicochemical properties, and their phosphate adsorption performance was tested through pH effect and adsorption isotherm experiments. Fe-loaded AB contained Fe3O4, while Mg-loaded AB contained Mg(OH)2. The metal (hydr)oxide inclusion was higher in Fe-loaded AB. Mg-loaded AB showed a unique free O–H functional group, while Fe-loaded AB showed an increase in its specific surface area more than 10-times compared to unmodified AB (1.8 m2 g−1). The effect of the initial pH on phosphate adsorption was not consistent between Fe-(anion adsorption envelope) vs. Mg-loaded AB. The phosphate adsorption capacity was higher with Fe-loaded AB in low concentration ranges (≤50 mg L−1), while Mg-loaded AB outperformed Fe-loaded AB in high concentration ranges (75–500 mg L−1). The phosphate adsorption isotherm by Fe-loaded AB fit well with the Langmuir model (R2 = 0.91–0.96), indicating the adsorptive surfaces were relatively homogeneous. Mg-loaded biochar, however, fit much better with Freundlich model (R2 = 0.94–0.96), indicating the presence of heterogenous adsorptive surfaces. No substantial benefit of high loading rates in metal impregnation was found for phosphate adsorption. The enhanced phosphate removal by Mg-loaded biochar in high concentration ranges highlights the important role of the chemical precipitation of phosphate associated with dissolved Mg2+. Full article
(This article belongs to the Special Issue Biochar Technology for Waste Reclamation)
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Article
Drying Kinetics of Macroalgae as a Function of Drying Gas Velocity and Material Bulk Density, Including Shrinkage
Clean Technol. 2022, 4(3), 669-689; https://doi.org/10.3390/cleantechnol4030041 - 22 Jul 2022
Viewed by 351
Abstract
Macroalgae have many potential applications and can make important contributions to sustainability and circular economy objectives. Macroalgae are degradable high-moisture biomaterials and drying is a necessary step, but drying is an energy and capital-intensive part of their production process. This study presents convective [...] Read more.
Macroalgae have many potential applications and can make important contributions to sustainability and circular economy objectives. Macroalgae are degradable high-moisture biomaterials and drying is a necessary step, but drying is an energy and capital-intensive part of their production process. This study presents convective drying curves for commercially promising fresh and saltwater species (U. ohnoi and O. intermedium), obtained over a range of industry-relevant drying gas velocities (0.3–2 m/s) and material bulk densities (33–100 kg/m3). Pragmatic diffusion-based drying models that account for the influence of drying gas velocity, material bulk density, and material shrinkage are presented. Results provide critical insights into the validity of diffusion model assumptions for compressible biomaterials and new mechanisms describing gas penetration into such materials are proposed. The drying models provided in this work demonstrate a high degree of accuracy for both species. Full article
(This article belongs to the Special Issue Feature Papers for Clean Technologies 2021)
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Article
Thermochemical Conversion Processes as a Path for Sustainability of the Tire Industry: Carbon Black Recovery Potential in a Circular Economy Approach
Clean Technol. 2022, 4(3), 653-668; https://doi.org/10.3390/cleantechnol4030040 - 12 Jul 2022
Viewed by 442
Abstract
The common use of tires is responsible for the production of large quantities of waste worldwide, which are landfilled or energetically recovered, with higher economical cost and known environmentally harmful consequences. This type of problem must be studied, and all efforts must be [...] Read more.
The common use of tires is responsible for the production of large quantities of waste worldwide, which are landfilled or energetically recovered, with higher economical cost and known environmentally harmful consequences. This type of problem must be studied, and all efforts must be conducted to eliminate, or at least mitigate, such high costs. The use of thermochemical conversion processes, such as pyrolysis, can allow the recycling and the reuse of raw materials for the tire industry, namely, in the production of carbon black, usually produced using the controlled combustion of fossil fuels. This article reports the production of torrefied and carbonized waste tire samples using a laboratorial procedure, and their subsequent laboratory characterization, specifically the elemental and proximate analysis. This preliminary approach found that carbon concentration in the produced rubber char reached values higher than 75%, indicating the possibility of its reuse in the production of carbon black to in turn be used in the production of new tires or other industrial rubber materials. The possibility of using this rubber char for other uses, such as energy recovery, is still depending on further studies, namely, the evaluation of the amount of sulfur present in the final product. Full article
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Review
Adsorption of Lead from Aqueous Solution by Biochar: A Review
Clean Technol. 2022, 4(3), 629-652; https://doi.org/10.3390/cleantechnol4030039 - 08 Jul 2022
Viewed by 456
Abstract
Industrialization has resulted in the discharge of a certain amount of lead (Pb) from industrial sources causing damage risk to water quality and human health. Adsorption is an effective technique to remove Pb, and biochar has been widely studied owing to its advantages [...] Read more.
Industrialization has resulted in the discharge of a certain amount of lead (Pb) from industrial sources causing damage risk to water quality and human health. Adsorption is an effective technique to remove Pb, and biochar has been widely studied owing to its advantages of low cost and high adsorption capacity. This review summarizes the influence of raw materials and modification methods on the adsorption capability of biochar. The adsorption isotherms and kinetics of biochar were summarized, and the main Pb removal mechanisms were studied systematically. In addition, the challenges and future perspectives were discussed comprehensively. It is expected that the review could provide insightful fundamentals for the experimental research and practical applications of biochar. Full article
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Article
Defect Properties of Li2NiGe3O8
Clean Technol. 2022, 4(3), 619-628; https://doi.org/10.3390/cleantechnol4030038 - 01 Jul 2022
Viewed by 461
Abstract
There is a growing interest in finding a suitable electrolyte material for the construction of rechargeable Li-ion batteries. Li2NiGe3O8 is a material of interest with modest Li-ionic conductivity. The atomistic simulation technique was applied to understand the defect [...] Read more.
There is a growing interest in finding a suitable electrolyte material for the construction of rechargeable Li-ion batteries. Li2NiGe3O8 is a material of interest with modest Li-ionic conductivity. The atomistic simulation technique was applied to understand the defect processes and Li-ion diffusion pathways, together with the activation energies and promising dopants on the Li, Ni, and Ge sites. The Li-Ni anti-site defect cluster was found to be the dominant defect in this material, showing the presence of cation mixing, which can influence the properties of this material. Li-ion diffusion pathways were constructed, and it was found that the activation energy for a three-dimensional Li-ion migration pathway is 0.57 eV, which is in good agreement with the values reported in the experiment. The low activation energy indicated that Li-ion conductivity in Li2NiGe3O8 is fast. The isovalent doping of Na, Fe and Si on the Li, Ni and Ge sites is energetically favorable. Both Al and Ga are candidate dopants for the formation of Li-interstitials and oxygen vacancies on the Ge site. While Li-interstitials can improve the capacity of batteries, oxygen vacancies can promote Li-ion diffusion. Full article
(This article belongs to the Special Issue Advances in Lithium Ion Batteries)
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Article
State of Charge and Capacity Tracking in Vanadium Redox Flow Battery Systems
Clean Technol. 2022, 4(3), 607-618; https://doi.org/10.3390/cleantechnol4030037 - 28 Jun 2022
Viewed by 513
Abstract
The vanadium redox flow battery electrolyte is prone to several capacity loss mechanisms, which must be mitigated to preserve electrolyte health and battery performance. This study investigates a simple and effective technique for the recovery of capacity loss arising from symmetrical mechanisms via [...] Read more.
The vanadium redox flow battery electrolyte is prone to several capacity loss mechanisms, which must be mitigated to preserve electrolyte health and battery performance. This study investigates a simple and effective technique for the recovery of capacity loss arising from symmetrical mechanisms via automatic electrolyte rebalancing. However, chemical or electrochemical techniques must be used to mitigate capacity loss from asymmetrical mechanisms (e.g., air oxidation of V2+), which requires knowledge of the oxidation states present in the electrolytes. As such, this study assesses the suitability of SOC tracking via electrolyte absorption for independent monitoring of the anolyte and catholyte within an existing VRFB system. Testing is performed over cycling of a 40 cell, 2.5 kW with 40 L of electrolyte. Optical monitoring is performed using a custom-made flow cell with optical paths (interior cavity thicknesses) ranging from 1/4 to 1/16. Light transmitted through the cell by a 550 lumen white light source is monitored by a simple photodiode. The electrolyte rebalancing mechanism displayed success in recovering symmetrical capacity losses, while optical monitoring was unsuccessful due to the high absorbance of the electrolyte. Potential improvements to the monitoring system are presented to mitigate this issue. Full article
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Article
Cleaner Technology and Natural Resource Management: An Environmental Sustainability Perspective from China
Clean Technol. 2022, 4(3), 584-606; https://doi.org/10.3390/cleantechnol4030036 - 28 Jun 2022
Viewed by 596
Abstract
In economies, cleaner technology, increased demand for renewable energy, and more efficient use of natural resources contribute to meeting environmental sustainability targets. The Chinese economy is no exception in its attempts to conserve economic and natural resources via collaborative efforts to embrace cleaner [...] Read more.
In economies, cleaner technology, increased demand for renewable energy, and more efficient use of natural resources contribute to meeting environmental sustainability targets. The Chinese economy is no exception in its attempts to conserve economic and natural resources via collaborative efforts to embrace cleaner technology, green energy sources, and resource conservation management to preserve resources for future generations. This research examines the influence of cleaner technologies, green energy sources, and natural resource management on reducing greenhouse gas emissions using quarterly data for the Chinese economy from 2000Q1 to 2020Q4. The findings demonstrate that increasing demand for green energy reduces greenhouse gas emissions, hence substantiating the premise of ‘green is clean’ energy development. Additionally, optimum resource usage enhances environmental quality, corroborating the ‘resource cleaner blessing’ hypothesis. The positive link between inward foreign direct investment and greenhouse gas emissions substantiates the ‘pollution haven’ concept, according to which inward foreign direct investment uses unsustainable technology in manufacturing processes, hence degrading air quality indicators. Inadequate access to clean cooking technology and increased population density has a detrimental effect on the country’s environmental sustainability agenda, which must be corrected via sustainable regulations. The causality estimates show the feedback relationship between renewable energy demand (and economic growth) and cleaner technology, between economic growth and green energy (and inbound foreign direct investment), and between population density and economic growth (and green energy). The Impulse Response function estimates suggested that economic growth and population density would likely increase GHG emissions. In contrast, cleaner technology, green energy demand, natural resource management, and inbound foreign direct investment would likely decrease greenhouse gas emissions for the next ten-year time period. The sustainability of the environment and natural resources in China is bolstered by developing cleaner technologies, a greater reliance on renewable energy sources, and better management of natural resources. Full article
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