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4 pages, 475 KiB

Open AccessProceeding Paper

A Ceramic Foam Structure Design with the Valorization of Fly Ash Cenospheres: A Promising Avenue for Sustainable Bioscaffolds

by Dimitrios Flegkas, Nikolaos Pagonis, Konstantinos Kountouras, Petros Samaras, Constantinos Tsanaktsidis and Vayos Karayannis

Proceedings 2025, 121(1), 1; https://doi.org/10.3390/proceedings2025121001 - 15 Jul 2025

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Abstract

Nowadays, there is wide advocacy for a transition to circular economic models. Fly Ash (FA) in particular is a major by-product of coal combustion and its annual waste has reached one million tonnes. Cenospheres (CSs) are considered as possibly the most valuable element [...] Read more.

Nowadays, there is wide advocacy for a transition to circular economic models. Fly Ash (FA) in particular is a major by-product of coal combustion and its annual waste has reached one million tonnes. Cenospheres (CSs) are considered as possibly the most valuable element within FA. Thus, in this research, polymeric foam replication was employed to fabricate ceramic foams based on a CS matrix, for potential biomedical applications. For the fabrication of foams, four types of natural marine sponges were used as templates along with a binder agent. The specimens were sintered at 1200 °C for 1 h. The results were encouraging as the specimens obtained retained the given shape and geometry. Further research will enhance the potential of such materials for future use in biomedical engineering. Full article

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4 pages, 872 KiB

Open AccessProceeding Paper

Metal Coatings for Electrocatalytic Applications: Towards a Safe and Sustainable by Design Approach

by Konstantina-Roxani Chatzipanagiotou, Foteini Petrakli, Joséphine Steck and Elias P. Koumoulos

Proceedings 2025, 121(1), 2; https://doi.org/10.3390/proceedings2025121002 - 15 Jul 2025

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Abstract

Several attempts have been made to replace the critical raw material platinum (Pt) with other metals, mainly focusing on its functional performance, while safety and sustainability criteria are often overlooked. Here, the substitution of Pt by nickel-based coatings is addressed for water electrolysis [...] Read more.

Several attempts have been made to replace the critical raw material platinum (Pt) with other metals, mainly focusing on its functional performance, while safety and sustainability criteria are often overlooked. Here, the substitution of Pt by nickel-based coatings is addressed for water electrolysis applications. Risk assessment and life cycle assessment are iteratively performed at the laboratory scale and after upscaling metal coating protocols. The challenges for the transition towards an integrated safe and sustainable by design (SSbD) approach are identified, and strategies are proposed to resolve them. Valuable insights emerge from the individual assessments (e.g., hotspots, trade-offs, and recommendations for sustainability and safety), as well as regarding the transition towards an integrated SSbD (e.g., dealing with data gaps and uncertainties). Full article

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4 pages, 412 KiB

Open AccessProceeding Paper

Application of Machine Learning Algorithms to Predict Composting Process Performance

by Vassilis Lyberatos and Gerasimos Lyberatos

Proceedings 2025, 121(1), 3; https://doi.org/10.3390/proceedings2025121003 - 16 Jul 2025

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Abstract

Four machine learning models (Decision Tree Regressor, Linear Regression, XGBoost Regression, K-Neighbors Regressor) were developed to predict the outcomes of a composting process based on key input parameters, including Ambient Temperature, mixture composition, and initial feedstock volume. The models were trained on data [...] Read more.

Four machine learning models (Decision Tree Regressor, Linear Regression, XGBoost Regression, K-Neighbors Regressor) were developed to predict the outcomes of a composting process based on key input parameters, including Ambient Temperature, mixture composition, and initial feedstock volume. The models were trained on data from 88 composting batches, monitoring temperature evolution, and compost yield. Performance evaluation demonstrated high accuracy in predicting compost maturity, process duration, and final product quantity. These predictive models could optimize composting operations by enabling real-time adjustments, improving efficiency, and enhancing resource management in sustainable waste processing. Full article

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5 pages, 488 KiB

Open AccessProceeding Paper

Digital Twins for Circular Economy Optimization: A Framework for Sustainable Engineering Systems

by Shubham Gupta

Proceedings 2025, 121(1), 4; https://doi.org/10.3390/proceedings2025121004 - 16 Jul 2025

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Abstract

This paper introduces sustainable engineering systems built using digital twin technology and circular economy principles. This research presents a framework for monitoring, modeling, and making decisions in real timusing virtual replicas of physical products, processes, and systems in product lifecycles. A digital twin [...] Read more.

This paper introduces sustainable engineering systems built using digital twin technology and circular economy principles. This research presents a framework for monitoring, modeling, and making decisions in real timusing virtual replicas of physical products, processes, and systems in product lifecycles. A digital twin was used to show that through a digital twin, waste was reduced by 27%, energy consumption was reduced by 32%, and the resource recovery rate increased to 45%. The proposed approach under the framework employs various machine learning algorithms, IoT sensor networks, and advanced data analytics to support closed-loop flows of materials. The results show how digital twins can enhance progress toward the goals the circular economy sets to identify inefficiencies, predict maintenance needs, and optimize the use of resources. This integration is a promising industry approach that will introduce more sustainable operations and maintain economic viability. Full article

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4 pages, 429 KiB

Open AccessProceeding Paper

Overview of the Use of Anaerobic Digestion on Swine Farms and the Potential for Bioenergy Production in Minas Gerais, Brazil

by Marcela de Souza Silva, Sibele Augusta Ferreira Leite and Brenno Santos Leite

Proceedings 2025, 121(1), 5; https://doi.org/10.3390/proceedings2025121005 - 17 Jul 2025

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Abstract

This study provides a comprehensive panorama of wastewater treatment on swine farms in Pará de Minas, MG, focusing on the performance of the anaerobic digester technologies adopted. Considering the economic and environmental importance of swine production, wastewater treatment is critical for mitigating environmental [...] Read more.

This study provides a comprehensive panorama of wastewater treatment on swine farms in Pará de Minas, MG, focusing on the performance of the anaerobic digester technologies adopted. Considering the economic and environmental importance of swine production, wastewater treatment is critical for mitigating environmental impacts while providing renewable energy opportunities. Data compilation from the Minas Gerais Institute of Agriculture (IMA), technical visits, and physicochemical analyses were conducted. Our results indicate that the region has significant potential to increase biogas production by expanding the number of plants and improving the efficiency of existing systems. Investments in scalable technological solutions tailored for small-scale operations are essential to enhance both wastewater treatment and biogas generation. This study demonstrates the potential for new business opportunities within the biogas value chain in Brazilian agribusiness. Full article

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5 pages, 958 KiB

Open AccessProceeding Paper

Modification of Ornamental Stone Wastes with Terephthalic Acid for Use as an Additive in Drilling Fluids

by Kelly C. C. S. R. Moreira, Cleocir J. Dalmaschio and Andreas Nascimento

Proceedings 2025, 121(1), 6; https://doi.org/10.3390/proceedings2025121006 - 16 Jul 2025

Viewed by 164

Abstract

This study explores the reuse of Ornamental Stone Waste (OSW) in water-based drilling fluids, investigating its potential as a substitute for bentonite. To enhance stability and rheology, OSW particles were functionalized with terephthalic acid (TPA) and combined with xanthan gum (XG). Characterization confirmed [...] Read more.

This study explores the reuse of Ornamental Stone Waste (OSW) in water-based drilling fluids, investigating its potential as a substitute for bentonite. To enhance stability and rheology, OSW particles were functionalized with terephthalic acid (TPA) and combined with xanthan gum (XG). Characterization confirmed successful surface modification, with increased stability at a basic pH. However, rheological analysis showed that the physical mixing of OSW-TPA with XG resulted in low viscosity and poor yield stress, indicating weak interactions. All formulations exhibited shear-thinning behavior. Future work will focus on promoting chemical interactions to form nanocomposite structures and improve fluid performance. Full article

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5 pages, 665 KiB

Open AccessProceeding Paper

Opportunities of Coupling Hydrothermal Liquefaction with Wet Oxidation: Significance of Appropriate Thermodynamic Model Selection in Process Modeling

by Arif Hussain, Bertram Thoning Hvass Søgaard and Konstantinos Anastasakis

Proceedings 2025, 121(1), 7; https://doi.org/10.3390/proceedings2025121007 - 17 Jul 2025

Viewed by 202

Abstract

This study examines the significance of thermodynamic model selection to improve predictions when modeling a wet oxidation (WO) process. WO is a promising technology for treating the highly concentrated process water stream from hydrothermal liquefaction (HTL) while generating heat, due to the exothermic [...] Read more.

This study examines the significance of thermodynamic model selection to improve predictions when modeling a wet oxidation (WO) process. WO is a promising technology for treating the highly concentrated process water stream from hydrothermal liquefaction (HTL) while generating heat, due to the exothermic oxidation reactions, leading to a potential integrated HTL-WO autothermal process. However, the harsh process conditions employed fail to describe oxygen solubility accurately, leading to major deviations in predicted COD reduction, heat generation, vapor fraction, and final design. To accurately capture oxygen solubility at elevated temperatures and pressures, experimental oxygen solubility data were regressed using activity coefficient models. This yielded improved oxygen solubility predictions at 280–350 °C, more realistic vapor fractions and heat outputs, and COD reduction close to experimental values. Full article

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4 pages, 531 KiB

Open AccessProceeding Paper

Waste Collection Vehicle Route Optimization: A Case Study at the Hellenic Military Academy

by Nicholas J. Daras, Paraskevi C. Divari, Constantinos C. Karamatsoukis, Konstantinos G. Kolovos, Theodore Liolios, Georgia Melagraki, Christos Michalopoulos and Dionysios E. Mouzakis

Proceedings 2025, 121(1), 8; https://doi.org/10.3390/proceedings2025121008 - 18 Jul 2025

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Abstract

In this article, we present a case study of the waste collection problem at the Hellenic Military Academy. The waste is sorted by type and collected by a garbage truck. To minimize the travel cost of the waste collection vehicle, we apply the [...] Read more.

In this article, we present a case study of the waste collection problem at the Hellenic Military Academy. The waste is sorted by type and collected by a garbage truck. To minimize the travel cost of the waste collection vehicle, we apply the Markov Decision Process methodology. This approach enables the development of more efficient algorithms. Full article

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5 pages, 1506 KiB

Open AccessProceeding Paper

Electrocoagulation as a Revived Method for Industrial Wastewater Pre-Treatment

by Dimitris V. Vayenas, Christina Vasiliki Lazaratou, Maria Gourniezaki, Maria Kakkou, Stavros Koutroupis, Michael Mageiras, Athanasios Iliopoulos and Alexandros Zolotas

Proceedings 2025, 121(1), 9; https://doi.org/10.3390/proceedings2025121009 - 23 Jul 2025

Viewed by 238

Abstract

This study investigates the efficiency of electrocoagulation–flotation (EC) as a pre-treatment method for industrial wastewater with a high chemical oxygen demand (COD), high levels of suspended solids (TSS), and different colors. Real wastewater from a brewery, dairy, winery, and marine oil processing industry [...] Read more.

This study investigates the efficiency of electrocoagulation–flotation (EC) as a pre-treatment method for industrial wastewater with a high chemical oxygen demand (COD), high levels of suspended solids (TSS), and different colors. Real wastewater from a brewery, dairy, winery, and marine oil processing industry was treated using aluminum electrodes under various current densities. Laboratory-scale experiments demonstrated significant COD, TSS, and color removal, with marine oils and dairy wastewater showing the highest COD removal efficiencies (up to 88.6%), while for all the examined wastewater samples, the TSSs removal exceeded 95%. The results confirm EC’s effectiveness and adaptability across diverse wastewater types, supporting its potential as a sustainable, low-cost alternative as a industrial wastewater pre-treatment process. Full article

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5 pages, 270 KiB

Open AccessProceeding Paper

Building a Circular Economy Option Through Wastewater Treatment and a Resource Recovery Approach

by Anastasios Zouboulis and Effrosyni Peleka

Proceedings 2025, 121(1), 10; https://doi.org/10.3390/proceedings2025121010 - 24 Jul 2025

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Abstract

This work studies and analyzes the transition from a linear to a circular economy through wastewater treatment and resource recovery. As wastewater volumes grow, sustainable management becomes critical. This study highlights the reuse of treated effluent, beneficial sludge utilization, and energy generation via [...] Read more.

This work studies and analyzes the transition from a linear to a circular economy through wastewater treatment and resource recovery. As wastewater volumes grow, sustainable management becomes critical. This study highlights the reuse of treated effluent, beneficial sludge utilization, and energy generation via anaerobic digestion. Wastewater treatment plants should be envisioned as hubs for recovering water, materials, and energy, rather than disposal facilities. Emphasizing resource efficiency, the circular economy approach offers viable solutions to challenges related to resource scarcity, climate change, and ecological impact. Full article

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5 pages, 569 KiB

Open AccessProceeding Paper

Hybrid Modelling Framework for Reactor Model Discovery Using Artificial Neural Networks Classifiers

by Emmanuel Agunloye, Asterios Gavriilidis and Federico Galvanin

Proceedings 2025, 121(1), 11; https://doi.org/10.3390/proceedings2025121011 - 25 Jul 2025

Viewed by 300

Abstract

Developing and identifying the correct reactor model for a reaction system characterized by a high number of reaction pathways and flow regimes can be challenging. In this work, artificial neural networks (ANNs), used in deep learning, are used to develop a hybrid modelling [...] Read more.

Developing and identifying the correct reactor model for a reaction system characterized by a high number of reaction pathways and flow regimes can be challenging. In this work, artificial neural networks (ANNs), used in deep learning, are used to develop a hybrid modelling framework for physics-based model discovery in reactions systems. The model discovery accuracy of the framework is investigated considering kinetic model parametric uncertainty, noise level, features in the data structure and experimental design optimization via a differential evolution algorithm (DEA). The hydrodynamic behaviours of both a continuously stirred tank reactor and a plug flow reactor and rival chemical kinetics models are combined to generate candidate physics-based models to describe a benzoic acid esterification synthesis in a rotating cylindrical reactor. ANNs are trained and validated from in silico data simulated by sampling the parameter space of the physics-based models. Results show that, when monitored using test data classification accuracy, ANN performance improved when the kinetic parameters uncertainty decreased. The performance improved further by increasing the number of features in the data set, optimizing the experimental design and decreasing the measurements error (low noise level). Full article

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5 pages, 175 KiB

Open AccessProceeding Paper

General Concepts from the Risk Assessment and Hazard Identification of HTL-Derived Bio-Oil: A Case Study of the MARINES Project

by Nicholas J. Daras, Paraskevi C. Divari, Constantinos C. Karamatsoukis, Konstantinos G. Kolovos, Theodore Liolios, Georgia Melagraki, Christos Michalopoulos and Dionysios E. Mouzakis

Proceedings 2025, 121(1), 12; https://doi.org/10.3390/proceedings2025121012 - 25 Jul 2025

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Abstract

This study evaluates the risk assessment and hazard identification of hydrothermal liquefaction (HTL)-derived bio-oil from the MARINES project, which converts military organic waste into fuel. The high oxygen content (35–50 wt%), acidic pH (2–4), and viscosity (10–1000 cP) of bio-oils pose unique challenges, [...] Read more.

This study evaluates the risk assessment and hazard identification of hydrothermal liquefaction (HTL)-derived bio-oil from the MARINES project, which converts military organic waste into fuel. The high oxygen content (35–50 wt%), acidic pH (2–4), and viscosity (10–1000 cP) of bio-oils pose unique challenges, including oxidative polymerization, corrosion, and micro-explosions during combustion. Key hazards include storage instability, particulate emissions (20–30% higher than diesel), and aquatic toxicity (LC50 < 10 mg/L for phenolics). Mitigation strategies such as inert gas blanketing, preheating, and spill containment are proposed. While offering renewable fuel potential, HTL bio-oil demands rigorous safety protocols for military/industrial deployment, warranting further experimental validation. Full article

5 pages, 1385 KiB

Open AccessProceeding Paper

Economic Evaluation of Novel C-Zero Processes for the Efficient Production of Energy, Chemicals, and Fuels

by Dimitris Ipsakis, Georgios Varvoutis, Athanasios Lampropoulos, Costas Athanasiou, Maria Lykaki, Evridiki Mandela, Theodoros Damartzis, Spiros Papaefthimiou, Michalis Konsolakis and George E. Marnellos

Proceedings 2025, 121(1), 13; https://doi.org/10.3390/proceedings2025121013 - 29 Jul 2025

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Abstract

The aim of this study is to provide a comprehensive analysis of the outcome of two separate techno-economic studies that were conducted for the scaled-up and industrially relevant processes of a) synthetic natural gas (SNG) production from captured (cement-based) CO₂ and green-H [...] Read more.

The aim of this study is to provide a comprehensive analysis of the outcome of two separate techno-economic studies that were conducted for the scaled-up and industrially relevant processes of a) synthetic natural gas (SNG) production from captured (cement-based) CO₂ and green-H₂ (via renewable-assisted electrolysis) and b) combined electricity and crude biofuel production through the integration of biomass pyrolysis, gasification, and solid oxide fuel cells. As was found, the SNG production process seems more feasible from an economic perspective as it can be comparable to current market values. Full article

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5 pages, 814 KiB

Open AccessProceeding Paper

Numerical Investigation of Low-Reynolds-Number Flow in Double Schwarz-D TPMS Structure

by Kasimhussen Vhora, Dominique Thévenin, Gábor Janiga and Kai Sundmacher

Proceedings 2025, 121(1), 14; https://doi.org/10.3390/proceedings2025121014 - 7 Aug 2025

Viewed by 85

Abstract

This study presents a comprehensive computational fluid dynamics (CFD) analysis of airflow in double Schwarz-D Triply Periodic Minimal Surface (TPMS) structures under laminar steady-flow conditions. The pressure drop characteristics of these structures are investigated using representative elementary volume (REV)-scale CFD simulations. Two porosities, [...] Read more.

This study presents a comprehensive computational fluid dynamics (CFD) analysis of airflow in double Schwarz-D Triply Periodic Minimal Surface (TPMS) structures under laminar steady-flow conditions. The pressure drop characteristics of these structures are investigated using representative elementary volume (REV)-scale CFD simulations. Two porosities, 58% and 80%, are analyzed to evaluate the influence of porosity on the flow characteristics and pressure drop. The results reveal that an increase in porosity significantly affects the hydraulic Reynolds number. For the 58% porosity structure, laminar flow is observed at hydraulic Reynolds numbers of 50 or lower, whereas the 80% porosity structure maintains laminar flow at Reynolds numbers up to 180. These findings provide valuable insights into the design and optimization of double Schwarz-D TPMS structures for engineering applications, particularly in scenarios requiring efficient fluid transport with controlled pressure drops. Full article

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