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Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A4: Bio-Energy".

Deadline for manuscript submissions: closed (17 February 2023) | Viewed by 22785

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Prof. Dr. Margarida Gonçalves

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Mechanical Engineering and Resource Sustainability Center, Faculty of Science and Technology, NOVA University of Lisbon, 2829-516 Caparica, Portugal
Interests: biofuels; biomass; thermochemical processes; waste valorization; microalgae; biorefineries
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Cândida Vilarinho

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Mechanical Engineering and Resource Sustainability Center; Department of Mechanical Engineering, University of Minho, 4710-057 Braga, Portugal
Interests: waste management and treatment; biomass; thermochemical processes; life cycle analysis; circular economy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Wastes are produced by most essential activities necessitated by modern society, and their adequate disposal or valorization poses a significant sustainable development challenge. Waste-to-energy systems may contribute to waste valorization due to their diverse nature as well as their capacity to process large amounts of materials. Innovations in catalysts, reactor design, genetic engineering of microorganisms, and downstream processing techniques have driven technological progress in waste conversion.

This Special Issue invites original research papers to address new applications of thermochemical, biological, or integrated technologies for the conversion of organic, lignocellulosic, or polymeric wastes to energy or fuels. Additionally, authors are encouraged to submit papers addressing the state of the art and recent advancements in these areas to provide useful guidelines for future research.

Biorefinery approaches combining material and energy valorization may be used to achieve waste valorization solutions that are both economically viable and environmentally friendly.

Finally, emerging technologies for carbon dioxide capture, storage, and conversion to gas or liquid fuels exhibit great potential in lowering greenhouse gas emissions and valorizing this gaseous waste.

Efficient waste-to-energy solutions are necessary to reduce our consumption of essential raw materials as well as preserve the quality of air, water, and soils that constitute ecosystems.

Thermochemical processes, such as combustion, carbonization, pyrolysis, and gasification, have been mainly applied to lignocellulosic or polymeric wastes, while biological processes such as anaerobic digestion or fermentation have been used to convert organic and lignocellulosic materials.

Potential topics include, but are not limited to, the following:

Conversion of wastes to solid biofuels;
Production of liquid biofuels from lipidic wastes, lignocellulosic wastes, or polymeric wastes;
Production of gaseous biofuels through thermochemical or biological processes;
Production of alcohols from organic or lignocellulosic wastes;
Production of hydrogen from wastes;
Catalytic upgrading of waste-derived fuels;
Waste biorefineries;
Microalgae-based biorefineries;
Carbon dioxide capture, storage, and conversion to gas or liquid fuels;
Life cycle analysis of waste-to-energy systems.

Dr. Margarida Gonçalves
Dr. Cândida Vilarinho
Guest Editors

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 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.

Keywords

waste-to-energy systems
thermochemical processes
biological processes
biorefineries
microalgae
carbon dioxide conversion
life cycle analysis

Published Papers (12 papers)

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Research

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14 pages, 2059 KiB

Open AccessArticle

Influence of Temperature in the Thermo-Chemical Decomposition of Below-Stoichiometric RDF Char—A Macro TGA Study

by Carlos Castro, Margarida Gonçalves, Andrei Longo, Cândida Vilarinho, Manuel Ferreira, André Ribeiro, Nuno Pacheco and José C. Teixeira

Energies 2023, 16(7), 3064; https://doi.org/10.3390/en16073064 - 28 Mar 2023

Viewed by 1072

Abstract

Due to the energy crisis that some countries are facing nowadays, the gasification process appears to be a good alternative to produce some energy from solid materials. Increasingly, gasification involves using wastes as a solid fuel, making the process green and reusing some materials that otherwise could end up in a landfill. However, the process of finding the best gasification parameters of a sample can be very expensive and time-consuming. In this sense, a refuse-derived fuel (RDF) char produced from an original RDF under 30 min at 400 °C was tested on a small-scale reactor using macro thermogravimetric analysis (TGA), as presented in this paper. The goal was to study and evaluate the devolatilization and residual carbon rate of the sample under several conditions and, at the same time, quantify and analyze the released gas. In the first round of tests, 5, 10, and 20 g of samples were tested at 750 °C with an excess of air coefficient (λ) = 0 and 0.2. It was possible to conclude that the lower the mass, the higher the devolatilization rate. The λ only had an influence on the devolatilization rate with a 20 g sample. Regarding the gas, CO, CO₂, and H₂ had no variation in the sample mass in contrast to CH₄, which increased with the increase in the sample mass. The second round of tests was performed with samples of 10 g of mass at temperatures of 700, 800, and 900 °C and λ values of 0.15, 0.2, and 0.25. The tests indicated that the temperature influenced the devolatilization rate but not the residual carbon combustion rate. Regarding the gas composition, CH₄, CO₂, and CO followed the same trend, decreasing the concentration with the increase in temperature; in contrast, H₂ increased in concentration with an increase in temperature. The heating value of the gas followed the same behavior as CH₄. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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27 pages, 7691 KiB

Open AccessArticle

Chemically and Physically Pretreated Straw in Moderate Conditions: Poor Correlation between Biogas Production and Commonly Used Biomass Characterization

by Shruthi Meenakshisundaram, Vincenzo Calcagno, Claire Ceballos, Antoine Fayeulle, Estelle Léonard, Virginie Herledan, Jean-Marc Krafft, Yannick Millot, Xiaojun Liu, Claude Jolivalt and André Pauss

Energies 2023, 16(3), 1146; https://doi.org/10.3390/en16031146 - 20 Jan 2023

Cited by 1 | Viewed by 1634

Abstract

Straw is a substantial agricultural by-product for biogas production. Hydrolysis of straw is found to be a rate-limiting step during its anaerobic digestion and could be enhanced by pretreatment. In this paper, the effect of various combinations of particle size reduction, autoclaving, and low-level Fenton reaction was studied on straw for biogas production. Grinding of straw contributed to the maximum increase in the biomethane potential. Only Fenton or only the autoclave process improves the kinetics slightly but does not considerably improve the biomethane potential. Combining autoclaving and low-concentration Fenton pretreatment considerably improves the BMP values. Lignin content, CHNSO elemental analysis, Scanning Electronic Microscopy (SEM), Simon’s staining, infrared spectroscopy (DRIFT and ATR), Nuclear magnetic resonance spectroscopy, and wide-angle X-ray diffraction analysis (WAXD) were used to characterize the physical and chemical changes of straw due to pretreatment. Results show a poor correlation between biogas production and the different physical and chemical biomass characteristics. It makes it difficult to explain the outcome of various pretreatment methods applied to biomass. Without further improvement and development of analytical techniques, the prediction of the biomethane potential of a feedstock with the aid of pretreatment can only be considered in case-by-case studies. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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25 pages, 2393 KiB

Open AccessArticle

Common Reed and Maize Silage Co-Digestion as a Pathway towards Sustainable Biogas Production

by Robert Czubaszek, Agnieszka Wysocka-Czubaszek, Wendelin Wichtmann, Grzegorz Zając and Piotr Banaszuk

Energies 2023, 16(2), 695; https://doi.org/10.3390/en16020695 - 06 Jan 2023

Cited by 3 | Viewed by 1403

Abstract

The key factor in sustainable biogas production is a feedstock whose production has no adverse impact on the environment. Since maize cultivation harms the environment, biogas plant operators seek a more sustainable feedstock. Common reed is an invasive species mown as part of wetland conservation measures, or it can be harvested from paludiculture. This study aimed to investigate wet co-digestion of maize silage with 10%, 30%, and 50% content of common reed silage using the biochemical methane potential (BMP) test. In addition, the potential energy generated and avoided greenhouse gas (GHG) emissions were calculated. The substitution of maize silage with 10%, 30%, and 50% content of reed silage reduced the methane (CH₄) yield by 13%, 28%, and 35%, respectively. A disadvantage of reed silage addition was increased ammonia (NH₃) and hydrogen sulfide (H₂S) concentrations in biogas. Although substituting maize silage with reed silage decreases the CH₄ yield, the co-digestion of maize and reed biomass from conservation or paludiculture may positively affect environmental aspects of energy generation. The substitution of maize with reed in biogas plants decreases the area used for maize cultivation and reduces GHG emissions. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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16 pages, 5660 KiB

Open AccessArticle

Biomass and Coal Ash Sintering—Thermodynamic Equilibrium Modeling versus Pressure Drop Test and Mechanical Test

by Karol Król, Wojciech Moroń and Dorota Nowak-Woźny

Energies 2023, 16(1), 362; https://doi.org/10.3390/en16010362 - 28 Dec 2022

Cited by 2 | Viewed by 1109

Abstract

The problem of biomass combustion and co-combustion is a particularly important aspect of many district heating systems, where the use of biomass makes it possible to reduce CO₂ emissions. The present article is a continuation of previous studies of the behavior of the mineral matter of selected fuels during the sintering processes. Three biomasses were studied: wheat straw, barley straw and rye straw, as well as two coals from Polish mines: bituminous coal and lignite. The study included ultimate and proximate analyses and oxide analysis. On the basis of the oxide analysis and using FactSage 8.0. software, the sintering process of ash from selected fuels was simulated. In particular, the content of the slag phase as well as the values of the specific heat c_p and density were determined without considering the gas phase. The obtained results were compared with the results of measurements of fracture stress (mechanical method) and pressure drop (pressure drop test) determined during the sintering process of the ash samples. The study showed that there is a fairly pronounced correlation between the sintering temperatures determined by the mechanical and pressure drop test and the physical properties of the ashes, such as density and heat capacity, and chemical properties, i.e., the content of the slag phase. The completed research work indicates and confirms that nonstandard methods of studying ash sintering temperatures (mechanical and pressure drop test) are very promising because they directly reflect the behavior of coals and biofuels in combustion systems. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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13 pages, 2499 KiB

Open AccessArticle

Anaerobic Digestion as a Component of Circular Bioeconomy—Case Study Approach

by Przemysław Seruga, Małgorzata Krzywonos, Emilia den Boer, Łukasz Niedźwiecki, Agnieszka Urbanowska and Halina Pawlak-Kruczek

Energies 2023, 16(1), 140; https://doi.org/10.3390/en16010140 - 23 Dec 2022

Cited by 7 | Viewed by 2111

Abstract

Current and future trends in the world population lead to the continuous growth of municipal waste volumes. Only in the EU-28 approx. 86 million tons of biowaste is produced yearly. On the other hand, the recent energy crisis calls for a fast transition towards more local and renewable energy sources. Most of this stream could be recycled through anaerobic digestion (AD) to produce energy and high-quality fertilizers. This paper presents a balance of dry anaerobic digestion of municipal biowaste based on three years of system monitoring in an industrial-scale AD plant. The results indicate that the average biogas production rate of 120 Nm³/ton of fresh waste can be achieved. Biogas utilization in combined heat and power (CHP) units leads to an overall positive energy balance at significantly reduced CO₂ emissions. The overall CO₂ emission reduction of 25.3–26.6% was achieved, considering that biogas utilization is environmentally neutral. Moreover, biowaste conversion allows digestate production to substitute mineral fertilizers in agriculture and other applications. It is beneficial for soil protection and a broader environmental perspective. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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26 pages, 17355 KiB

Open AccessArticle

Preliminary Studies of Slag and Ash from Incinerated Municipal Waste for Prospective Applications

by Katarzyna Godyń and Barbara Dutka

Energies 2023, 16(1), 117; https://doi.org/10.3390/en16010117 - 22 Dec 2022

Cited by 2 | Viewed by 1478

Abstract

The assessment of the possibility of using incinerated municipal waste, which is classified as non-hazardous, is a priority of the European zero waste strategy. The aim of this work was to identify the properties of slag and ash to develop a simple, targeted way of using post-process waste. The material was analyzed by microscopic methods in terms of composition and internal structure. Gas and water permeability tests were carried out. Slag and ash texture was obtained using densimetric methods. BCR sequential extraction was carried out to assess the impacts of the waste on the water and soil environment. It was shown that individual fractions were characterized by different compositions and pore contents. The increase in the waste layer density resulted in porosity reduction of the slag and post-process ash, which had a significant impact on permeability. The increase in density index from 0.92 to 0.98 resulted in reduction of the filtration coefficient by two orders of magnitude. The obtained results showed that the division into fractions is important for prospective applications of incinerated municipal waste. With very low permeability and negligible leachability of heavy metals, the characteristics of slag and ash predispose them to support the needs of specialized hydrotechnical construction. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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19 pages, 1669 KiB

Open AccessArticle

Gasification of Solid Recovered Fuels with Variable Fractions of Polymeric Materials

by Octávio Alves, Luís Calado, Roberta M. Panizio, Catarina Nobre, Eliseu Monteiro, Paulo Brito and Margarida Gonçalves

Energies 2022, 15(21), 8139; https://doi.org/10.3390/en15218139 - 01 Nov 2022

Cited by 1 | Viewed by 1514

Abstract

Gasification is a promising thermochemical technology used to convert waste materials into energy with the introduction of low amounts of an oxidant agent, therefore producing an environmental impact that is lower when compared to incineration and landfilling. Moreover, gasification allows a sustainable management of wastes and reduces the use of fossil fuels responsible for the increment of greenhouse gases. This work aimed to perform gasification tests with solid recovered fuels (SRF) containing organic fractions mainly retrieved from construction and demolition wastes to assess the potential for energy conversion. Tests were conducted in a pilot-scale downdraft gasifier (maximum feedstock input of 22 kg/h) at c.a. 800 °C, using SRF samples containing different proportions of polymeric wastes ranging between 0 and 20 wt %. Gas and chars obtained as by-products were analysed to evaluate their properties and to establish valid pathways for their valorisation. The addition of polymeric wastes reduced char production but rose both tar and HCl concentrations in the gas. The SRF with 10 wt % of polymeric wastes generated the best results, producing the highest calorific value for the gas (3.5 MJ/Nm³) and the highest cold-gas efficiency (45%). Possible char applications include their use as catalysts for tar decomposition, or as an additive in construction materials. Gasification can therefore be considered a valid solution for the energetic valorisation of these SRFs. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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19 pages, 2829 KiB

Open AccessArticle

Importance of Feedstock in a Small-Scale Agricultural Biogas Plant

by Robert Czubaszek, Agnieszka Wysocka-Czubaszek and Piotr Banaszuk

Energies 2022, 15(20), 7749; https://doi.org/10.3390/en15207749 - 20 Oct 2022

Cited by 5 | Viewed by 2025

Abstract

Although no legal sustainability criteria have been formulated for electricity and heat production from biogas, the sustainability and profitability of large-scale biogas plants which use mainly energy crops is now questioned. Small (farm-size) biogas plants characterized by CHP electrical output in the range between 15 kW_el and 99 kW_el, operating on agricultural wastes and by-products, seem more suitable; however, the variety of feedstock may be crucial in the proper design and operation of such family biogas plants. This paper aims to present the problems that occurred in small agricultural biogas plants fed with sheep manure (SM), horse manure (HM), and grass-clover silage (GCS). This paper also focuses on analyzing the energy balance and carbon dioxide (CO₂) emissions related to four technological solutions (Scenarios 1–4) based on various feedstocks, grinding and feeding systems, and wet/dry fermentation. The biogas plant was originally based on dry fermentation with an organic loading rate ~10.4 kg_VS·m⁻³·d⁻¹, a hydraulic retention time of 16 days, and temperature of 45 °C in the fermentation chamber. The material was shredded and mixed in a mixing device, then the mixture of manures and silage was introduced to the horizontal fermentation chamber through a system of screw feeders. The biogas and the digestate were collected in a reinforced concrete tank. The biogas was sent to the CHP unit of an installed electrical power of 37 kW_el, used to produce electricity and recover the heat generated in this process. Scenario 1 is based on the design assumptions used for the biogas plant construction and start-up phase. Scenario 2 includes a new feeding and grinding system, in Scenario 3 the feedstock is limited to SM and HM and wet fermentation is introduced. In Scenario 4, a dry fermentation of SM, HM, and maize silage (MS) is assumed. Avoided CO₂ emissions through electricity and heat production from biogas were the highest in the case of Scenarios 1 and 4 (262,764 kg CO₂·y⁻¹ and 240,992 kg CO₂·y⁻¹) due to high biogas production, and were the lowest in Scenario 3 (7,481,977 kg CO₂·y⁻¹) because of the low specific methane yield (SMY) of SM and HM. Nevertheless, in all scenarios, except Scenario 3, CO₂ emissions from feedstock preparation and biogas plant operation are much lower than that which can be avoided by replacing the fossil fuel energy for the electricity and heat produced from biogas. Our observations show that a small agricultural biogas plant can be an effective energy source, and can contribute to reducing CO₂ emissions only if the appropriate technological assumptions are adopted, and the entire installation is designed correctly. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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Review

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31 pages, 2206 KiB

Open AccessReview

Overview of Numerical Simulation of Solid-State Anaerobic Digestion Considering Hydrodynamic Behaviors, Phenomena of Transfer, Biochemical Kinetics and Statistical Approaches

by Xiaojun Liu, Arnaud Coutu, Stéphane Mottelet, André Pauss and Thierry Ribeiro

Energies 2023, 16(3), 1108; https://doi.org/10.3390/en16031108 - 19 Jan 2023

Cited by 5 | Viewed by 1739

Abstract

Anaerobic digestion (AD) is a promising way to produce renewable energy. The solid-state anaerobic digestion (SSAD) with a dry matter content more than 15% in the reactors is seeing its increasing potential in biogas plant deployment. The relevant processes involve multiple of evolving chemical and physical phenomena that are not crucial to conventional liquid-state anaerobic digestion processes (LSAD). A good simulation of SSAD is of great importance to better control and operate the reactors. The modeling of SSAD reactors could be realized either by theoretical or statistical approaches. Both have been studied to a certain extent but are still not sound. This paper introduces the existing mathematical tools for SSAD simulation using theoretical, empirical and advanced statistical approaches and gives a critical review on each type of model. The issues of parameter identifiability, preference of modeling approaches, multiscale simulations, sensibility analysis, particularity of SSAD operations and global lack of knowledge in SSAD media evolution were discussed. The authors call for a stronger collaboration of multidisciplinary research in order to further developing the numeric simulation tools for SSAD. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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17 pages, 1035 KiB

Open AccessReview

Biogas Production Depending on the Substrate Used: A Review and Evaluation Study—European Examples

by Katarzyna Ignatowicz, Gabriel Filipczak, Barbara Dybek and Grzegorz Wałowski

Energies 2023, 16(2), 798; https://doi.org/10.3390/en16020798 - 11 Jan 2023

Cited by 8 | Viewed by 4101

Abstract

Biogas production is the most important and promising alternative for replacing fossil fuels in an environmentally friendly manner. Along with the many renewable energy sources available, biogas production occupies an irreplaceable position due to the undeniable availability of biomass and the need to manage agro-commercial waste. The article reviews the current state of technology used in the production of biogas for selected European examples in terms of methane fermentation efficiency and actual energy production. The novelty of the article is its description of innovative trends that have great potential to play an important role in this field in the near future. The development of the biogas industry in Europe is evident, although the dynamics vary from country to country. Different models are presented, which are based on the different types of feedstock used for biogas production and the proportion of substrates used in co-digesters. Of course, Germany is the undisputed pioneer in the use of this renewable energy source. Nevertheless, the efforts to improve energy self-reliance and environmental impacts are reflected in the growing number of operational biogas plants in other European countries, which provides hope for rapid progress toward the complete abolition of the conventional exploitation of fossil fuels. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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13 pages, 294 KiB

Open AccessReview

Occurrence, Fate, and Implications of Heavy Metals during Anaerobic Digestion: A Review

by Rahul Kadam, Kamonwan Khanthong, Heewon Jang, Jonghwa Lee and Jungyu Park

Energies 2022, 15(22), 8618; https://doi.org/10.3390/en15228618 - 17 Nov 2022

Cited by 9 | Viewed by 1299

Abstract

Over the years, anaerobic digestion (AD) has evolved as a competent technology to retrieve energy potential from various organic substrates, including wastewater. However, the energy metabolisms of anaerobic microorganisms, biochemical reactions, and biogas production are affected by various parameters, including heavy metals. It is important to understand the interaction of heavy metals with anaerobes and their potential influence on the process to enhance energy potential. This review methodically outlines the occurrence and role of heavy metals in the AD process. Additionally, the repercussions of the most common heavy metals (i.e., Cu, Zn, Cd, Fe, and Ni) on each stage of AD (i.e., hydrolysis, acidogenesis, and methanogenesis) have been discussed. We found that traces of heavy metals can endorse anaerobic digestion, but inhibition increases with increasing concentration. Methanogenic archaea are more susceptible to heavy metal inhibition than hydrolytic and acidogenic archaea. An improved understanding and relevant intuition will help to promote biogas production along with heavy metal management. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

Other

Jump to: Research, Review

14 pages, 664 KiB

Open AccessPerspective

Research and Innovation Needs for the Waste-To-Energy Sector towards a Net-Zero Circular Economy

by Alessandro Dal Pozzo, Mathieu Lucquiaud and Johan De Greef

Energies 2023, 16(4), 1909; https://doi.org/10.3390/en16041909 - 15 Feb 2023

Cited by 4 | Viewed by 2369

Abstract

This perspective article aims to identify key research priorities to make the waste-to-energy sector compatible with the societal goals of circularity and carbon neutrality. These priorities range from fundamental research to process engineering innovations and socio-economic challenges. Three focus areas are highlighted: (i) the optimization of flue gas cleaning processes to minimize gaseous emissions and cross-media, (ii) the expansion of process control intelligence to meet targets for both material recovery and energy recovery, and (iii) climate neutrality, with the potential for negative emissions via the removal of atmospheric carbon dioxide across the full cycle of the waste resource. For each area, recent research trends and key aspects that are yet to be addressed are discussed. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes 2022)

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