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A topical collection in Clean Technologies (ISSN 2571-8797).

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Dr. Sabino De Gisi

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Department of Civil, Environmental, Land, Building Engineering and Chemistry (DICATECh), Polytechnic University of Bari, Via E. Orabona n. 4, 70125 Bari, Italy
Interests: environmental impact assessment; industrial and municipal wastewater treatment and reuse technologies; innovative materials for environmental applications; multidisciplinary approaches for complex problems; remediation of contaminated sites; thermal treatments; waste management
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Dear Colleagues,

Recent reports by the Intergovernmental Panel on Climate Change (IPCC) show that, during the 20th century, the world increased its use of fossil fuels tenfold, as well as the extraction of material resources. This era of abundant and cheap resources is coming to an end. Raw materials, water, air, biodiversity, and marine, terrestrial, and aquatic ecosystems are all under pressure. Many of the world's major ecosystems are in a state of degradation and the services they provide are being used unsustainably.

The increasing impact of climate change and related environmental problems—including ocean acidification, changes in ocean circulation, rising sea water temperatures, melting Arctic ice, decreasing seawater salinity, land degradation, land use loss of soil fertility, water scarcity, droughts and floods, seismic and volcanic hazards, changes in the spatial distribution of species, chemical pollution, the overexploitation of resources, and the loss of biodiversity—indicate that the planet is approaching the limits of its sustainability.

Sustainable supply together with a resource-efficient management of raw materials, including exploration, extraction, processing, reuse, recycling, and substitution, are essential for the functioning of modern societies and their economies. The ability of the economy to adapt, become more resilient to climate change, and become more resource efficient—while maintaining competitiveness—depends on high levels of economic, social, organizational, and technological eco-innovation.

This is the context for the collection Review Papers in Clean Technologies, where the published articles consist of literature reviews, i.e., studies that summarize or reinterpret high-level scientific findings in a new way. The scope of the topics covered is very broad, relates to the fields covered by the journal, and is consistent with the Sustainable Development Goals (SDGs) of the UN 2030 Agenda.

Dr. Sabino De Gisi
Collection Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the collection website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Clean Technologies is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (9 papers)

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2023

Open AccessReview

Toward Efficient Recycling of Vanadium Phosphate-Based Sodium-Ion Batteries: A Review

Aleksandr Sh. Samarin

Alexey V. Ivanov

and

Stanislav S. Fedotov

Clean Technol. 2023, 5(3), 881-900; https://doi.org/10.3390/cleantechnol5030044 - 06 Jul 2023

Viewed by 931

Abstract

Sodium-ion batteries (SIBs) have demonstrated noticeable development since the 2010s, being complementary to the lithium-ion technology in predominantly large-scale application niches. The projected SIB market growth will inevitably lead to the generation of tons of spent cells, posing a notorious issue for proper battery lifecycle management, which requires both the establishment of a regulatory framework and development of technologies for recovery of valuable elements from battery waste. While lithium-ion batteries are mainly based on layered oxides and lithium iron phosphate chemistries, the variety of sodium-ion batteries is much more diverse, extended by a number of other polyanionic families (crystal types), such as NASICON (Na₃V₂(PO₄)₃), Na₃V₂(PO₄)₂F_3−yO_y, (0 ≤ y ≤ 2), KTiOPO₄-type AVPO₄X (A—alkali metal cation, X = O, F) and β-NaVP₂O₇, with all of them relying on vanadium and phosphorous—critical elements in a myriad of industrial processes and technologies. Overall, the greater chemical complexity of these vanadium-containing phosphate materials highlights the need for designing specific recycling approaches based on distinctive features of vanadium and phosphorus solution chemistry, fine-tuned for the particular electrodes used. In this paper, an overview of recycling methods is presented with a focus on emerging chemistries for SIBs. Full article

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Open AccessReview

Offshore Electrical Grid Layout Optimization for Floating Wind—A Review

Magnus Daniel Kallinger

José Ignacio Rapha

Pau Trubat Casal

and

José Luis Domínguez-García

Clean Technol. 2023, 5(3), 791-827; https://doi.org/10.3390/cleantechnol5030039 - 26 Jun 2023

Viewed by 747

Abstract

Electrical grid layout optimization should consider the placements of turbines and substations and include effects such as wake losses, power losses in cables, availability of different cable types, reliability-based power losses and operational/decommissioning cost besides the initial investment cost. Hence, optimizing the levelized cost of energy is beneficial capturing long-term effects. The main contribution of this review paper is to identify the current works and trends on electrical layout optimization for offshore wind farms as well as to analyze the applicability of the found optimization approaches to commercial-scale floating wind farms which have hardly been investigated so far. Considering multiple subproblems (i.e., micrositing and cabling), simultaneous or nested approaches are advantageous as they avoid sequential optimization of the individual problems. To cope with this combinatorial problem, metaheuristics seems to offer optimal or at least close-to-optimal results while being computationally much less expensive than deterministic methods. It is found that floating wind brings new challenges which have not (or only insufficiently) been considered in present optimization works. This will also be reflected in a higher complexity and thus influence the suitability of applicable optimization techniques. New aspects include the mobility of structures, the configurations and interactions of dynamic cables and station-keeping systems, the increased likelihood of prevailing heterogeneous seabeds introducing priority zones regarding anchor and riser installation, the increased importance of reliability and maintainability due to stricter weather limits, and new floating specific wind farm control methods to reduce power losses. All these facets are crucial to consider when thoroughly optimizing the levelized cost of energy of commercial-scale floating offshore wind farms. Full article

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Open AccessReview

Moving towards Greener Road Transportation: A Review

and

Clean Technol. 2023, 5(2), 766-790; https://doi.org/10.3390/cleantechnol5020038 - 07 Jun 2023

Viewed by 1177

Abstract

Road transportation accounts for about 20% of the total GHG emissions in the EU. Nowadays, the substitution of conventional fossil fuel-based ICEs with electric engines, or their hybridization, operating along with Energy Storage Systems, seems to be the most appropriate measure to achieve reductions in both fuel consumption and GHGs. However, EVs encounter crucial challenges, such as long charging time and limited driving range. Hence, the transition to the mass adoption of EVs requires considerable effort and time. However, significant steps have been taken in the hybridization of road vehicles, with the aid of renewables and energy recovery/saving systems. In this context, this paper presents a comprehensive literature review of modern green technologies for GHG reduction that are applicable to road transportation, such as on-vehicle energy harvesting and recovery (e.g., thermal, kinetic, etc.) systems and the incorporation of RES into EV charging stations. The impact of road vehicles on the environment is discussed in detail, along with the EU roadmap towards the decarbonization of transportation. Next, methods and techniques for fuel consumption and GHG reduction are systematically presented and categorized into on-vehicle and off-vehicle ones. Finally, a future outlook on more environmentally friendly road transportation is presented. Full article

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Open AccessReview

Carbon Capture, Utilization, and Storage in Saline Aquifers: Subsurface Policies, Development Plans, Well Control Strategies and Optimization Approaches—A Review

Ismail Ismail

and

Vassilis Gaganis

Clean Technol. 2023, 5(2), 609-637; https://doi.org/10.3390/cleantechnol5020031 - 15 May 2023

Viewed by 1499

Abstract

To mitigate dangerous climate change effects, the 195 countries that signed the 2015 Paris Agreement agreed to “keep the increase in average global surface temperature below 2 °C and limit the increase to 1.5 °C” by reducing carbon emissions. One promising option for reducing carbon emissions is the deployment of carbon capture, utilization, and storage technologies (CCUS) to achieve climate goals. However, for large-scale deployment of underground carbon storage, it is essential to develop technically sound, safe, and cost-effective CO₂ injection and well control strategies. This involves sophisticated balancing of various factors such as subsurface engineering policies, technical constraints, and economic trade-offs. Optimization techniques are the best tools to manage this complexity and ensure that CCUS projects are economically viable while maintaining safety and environmental standards. This work reviews thoroughly and critically carbon storage studies, along with the optimization of CO₂ injection and well control strategies in saline aquifers. The result of this review provides the foundation for carbon storage by outlining the key subsurface policies and the application of these policies in carbon storage development plans. It also focusses on examining applied optimization techniques to develop CO₂ injection and well control strategies in saline aquifers, providing insights for future work and commercial CCUS applications. Full article

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Open AccessReview

Vapor Compression Cycle: A State-of-the-Art Review on Cycle Improvements, Water and Other Natural Refrigerants

and

Clean Technol. 2023, 5(2), 584-608; https://doi.org/10.3390/cleantechnol5020030 - 05 May 2023

Viewed by 2875

Abstract

Air conditioning and refrigeration have become necessary in modern life, accounting for more than 7.8% of greenhouse gases (GHG) emitted globally. Reducing the environmental impact of these systems is crucial for meeting the global GHG emission targets. Two principal directions must be considered to reduce the environmental impact of air conditioning systems. Firstly, reducing the direct effect by looking at less harmful refrigerants and secondly, reducing the indirect effect by searching for options to improve the system efficiency. This study presents the latest developments in the vapor compression cycle and natural refrigerants, focusing on water as a refrigerant. Natural refrigerants, and especially water, could be the ultimate solution for the environmental problems associated with the operation of vapor compression cycle (VCC) cooling systems, including ozone depletion (OD) and global warming (GW). Reducing the environmental impact of building cooling systems is essential, and the recent system improvements made to enhance the system coefficient of performance (COP) are thoroughly discussed in this paper. Though the cycle improvements discussed in this work are essential and could increase the system efficiency, they still need to solve the direct environmental impact of refrigerants. Accordingly, this paper suggests that natural refrigerants, including water, are the most suitable strategic choice to replace the current refrigerants in the refrigeration and air conditioning industry. Finally, this study reviews the latest VCC system improvements and natural refrigerants in order to guide interested researchers with solutions that may reduce the environmental impact of VCC systems and suggest future research areas. Full article

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Open AccessReview

Investigation of Hydrogen Production System-Based PEM EL: PEM EL Modeling, DC/DC Power Converter, and Controller Design Approaches

and

Clean Technol. 2023, 5(2), 531-568; https://doi.org/10.3390/cleantechnol5020028 - 23 Apr 2023

Viewed by 1939

Abstract

The main component of the hydrogen production system is the electrolyzer (EL), which is used to convert electrical energy and water into hydrogen and oxygen. The power converter supplies the EL, and the controller is used to ensure the global stability and safety of the overall system. This review aims to investigate and analyze each one of these components: Proton Exchange Membrane Electrolyzer (PEM EL) electrical modeling, DC/DC power converters, and control approaches. To achieve this desired result, a review of the literature survey and an investigation of the PEM EL electrical modeling of the empirical and semi-empirical, including the static and dynamic models, are carried out. In addition, other sub-models used to predict the temperature, gas flow rates (H₂ and O₂), hydrogen pressure, and energy efficiency for PEM EL are covered. DC/DC power converters suitable for PEM EL are discussed in terms of efficiency, current ripple, voltage ratio, and their ability to operate in the case of power switch failure. This review involves analysis and investigation of PEM EL control strategies and approaches previously used to achieve control objectives, robustness, and reliability in studying the DC/DC converter-PEM electrolyzer system. The paper also highlights the online parameter identification of the PEM electrolyzer model and adaptive control issues. Finally, a discussion of the results is developed to emphasize the strengths, weaknesses, and imperfections of the literature on this subject as well as proposing ideas and challenges for future work. Full article

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Open AccessSystematic Review

Machine Learning Applications in Renewable Energy (MLARE) Research: A Publication Trend and Bibliometric Analysis Study (2012–2021)

Samuel-Soma M. Ajibade

Festus Victor Bekun

Festus Fatai Adedoyin

Bright Akwasi Gyamfi

and

Anthonia Oluwatosin Adediran

Clean Technol. 2023, 5(2), 497-517; https://doi.org/10.3390/cleantechnol5020026 - 19 Apr 2023

Cited by 1 | Viewed by 1285

Abstract

This study examines the research climate on machine learning applications in renewable energy (MLARE). Therefore, the publication trends (PT) and bibliometric analysis (BA) on MLARE research published and indexed in the Elsevier Scopus database between 2012 and 2021 were examined. The PT was adopted to deduce the major stakeholders, top-cited publications, and funding organizations on MLARE, whereas BA elucidated critical insights into the research landscape, scientific developments, and technological growth. The PT revealed 1218 published documents comprising 46.9% articles, 39.7% conference papers, and 6.0% reviews on the topic. Subject area analysis revealed MLARE research spans the areas of science, technology, engineering, and mathematics among others, which indicates it is a broad, multidisciplinary, and impactful research topic. The most prolific researcher, affiliations, country, and funder are Ravinesh C. Deo, National Renewable Energy Laboratory, United States, and the National Natural Science Foundation of China, respectively. The most prominent journals on the top are Applied Energy and Energies, which indicates that journal reputation and open access are critical considerations for the author’s choice of publication outlet. The high productivity of the major stakeholders in MLARE is due to collaborations and research funding support. The keyword co-occurrence analysis identified four (4) clusters or thematic areas on MLARE, which broadly describe the systems, technologies, tools/technologies, and socio-technical dynamics of MLARE research. Overall, the study showed that ML is critical to the prediction, operation, and optimization of renewable energy technologies (RET) along with the design and development of RE-related materials. Full article

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Open AccessReview

Membranes and Integrated Membrane Operations as Clean Technologies in the Leather Industry

Enrico Drioli

and

Alfredo Cassano

Clean Technol. 2023, 5(1), 274-296; https://doi.org/10.3390/cleantechnol5010016 - 16 Feb 2023

Cited by 2 | Viewed by 1713

Abstract

The leather industry is characterized by the production of a huge amount of wastewater with a high organic/inorganic charge, causing widespread water and soil pollution. Pressure-driven membrane operations and membrane bioreactors have long been proven to be a valid approach for the treatment of tanning wastewaters aimed at the recovery of raw materials as well as for the removal of toxic and environmentally harmful substances. Such processes, opportunely integrated among themselves and/or with conventional physical-chemical and biological treatments, also provide useful protocols for the treatment of global wastewaters with significant advantages in terms of environmental protection, decrease of disposal costs, simplification of cleaning-up processes and saving of water and chemicals. This paper, as the state of the art, attempts to revise the potential and perspectives of membrane-based technologies in the leather industry with related applications in beamhouse, tanning and post-tanning operations as well as in the treatment of global wastewaters. Full article

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Open AccessSystematic Review

A Literature Review on Existing Methods and Indicators for Evaluating the Efficiency of Power-to-X Processes

and

Clean Technol. 2023, 5(1), 167-189; https://doi.org/10.3390/cleantechnol5010010 - 31 Jan 2023

Viewed by 1585

Abstract

The challenges posed by climate change have prompted significant growth in efficiency evaluation and optimization research, especially in recent years. This has spawned a variety of heterogeneous methods and approaches to the assessment of technical processes. These methods and approaches are rarely comparable and are usually only applicable to specific sectors. This paper provides an overview of the literature on efficiency assessment methods and KPIs, leading to a more manageable selection of an appropriate method with special regard to energy system integration technologies. In addition to reviewing the literature systematically, this paper examines existing methods and indicators’ applicability to and significance for efficiency optimization. In this context, a holistic approach to process design, evaluation, and improvement is given with particular regard to power-to-X systems. Within the framework of the study, three overarching goals could be defined as levels of efficiency evaluation of power-to-X systems: 1. identification of the process (steps) with the most significant optimization potential, 2. identification of the process phases with the greatest optimization potential (timewise considered), and 3. derivation of specific recommendations for action for the improvement of a process. For each of these levels, the most suitable evaluation methods were identified. While various methods, such as life cycle assessment and physical optimum, are particularly suitable for Level 1 and Level 2, for Level 3, even the best-identified methods have to be extended on a case-by-case basis. To address this challenge, a new approach to a holistic evaluation of power-to-X systems was developed based on the study’s findings. Full article

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Published Papers (9 papers)

2023

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