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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Environmental Sciences".

Deadline for manuscript submissions: closed (30 January 2026) | Viewed by 15138

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Special Issue Editors

Dr. Carlos Morales-Polo

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Guest Editor

ICAI School of Engineering, Comillas Pontificial University, Alberto Aguilera 25, 28015 Madrid, Spain
Interests: the characterization and monitoring of the anaerobic digestion of wastewater and wastes; the integration of waste and wastewater into the circular economy; waste valorization; environmental pollution analysis; the determination of microplastics
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Francisco Jesús Fernández Morales

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Guest Editor

Chemical Engineering Department, Chemical and Environmental Technologies Institute (ITQUIMA), University of Castilla-La Mancha, 13071 Ciudad Real, Spain
Interests: anaerobic digestion; biogas; anaerobic fermentation; bio-hydrogen; microbial fuel cell; bio-electro systems; bioelectrochemistry; energetic valorisation of wastes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The increasing demand for sustainable waste management solutions has intensified interest in the valorization of waste and by-products, as well as the development of innovative treatment technologies. This Special Issue aims to collect original research and comprehensive reviews on novel strategies for the treatment, recovery, and reuse of a wide range of waste streams and secondary materials—whether originating from industrial processes, agricultural activities, or from waste treatment operations themselves.

Special attention will be given to by-products that are not always at the center of valorization strategies, such as digestates, leachates, and other residual outputs generated during processes like anaerobic digestion, composting, and wastewater treatment. Emphasis will be placed on technologies that enhance the value of these materials, including biological, physicochemical, and integrated treatment systems. Contributions related to circular economy approaches, process optimization, resource recovery, and environmental impact assessments are particularly welcome.

This Special Issue encourages submissions that explore the technical, environmental, and economic dimensions of waste and by-product management, aiming to foster sustainable, efficient, and low-impact practices. By showcasing recent scientific advances and practical case studies, it seeks to contribute to the transition from waste disposal to resource recovery and reuse within a circular economy and industrial ecology framework.

Dr. Carlos Morales-Polo
Prof. Dr. Francisco Jesús Fernández Morales
Guest Editors

Manuscript Submission Information

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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. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

industrial by-products
waste-derived streams
digestate valorization
waste valorization
anaerobic digestion
circular economy
resource recovery
waste-to-resource strategies
environmental biotechnology
sustainable waste management

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Published Papers (5 papers)

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Research

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22 pages, 1678 KB

Open AccessArticle

Reduction of Anisakis Allergenicity in Gilthead Seabream (Sparus aurata) Fed with Fish Viscera Silage-Based Diets

by Guzman Diez, Maria Lavilla, Bruno Iñarra, Urtzi Izagirre, Xabier Lekube, Manuel Soto, Mikel Azkargorta, Félix Elortza and Carlos Bald

Appl. Sci. 2026, 16(9), 4188; https://doi.org/10.3390/app16094188 - 24 Apr 2026

Viewed by 545

Abstract

Anisakis simplex allergens are highly resistant to conventional processing, posing a health risk that limits the use of infested fish both for human consumption and for animal feed. To assess the safety and nutritional value of viscera silage, hake (Merluccius merluccius) viscera were processed with formic acid and stored for four months. Two experimental diets were prepared—one containing silage and another with untreated viscera—alongside a commercial control feed. Juvenile gilthead seabreams (Sparus aurata) were fed these diets for 86 days, and growth performance, muscle composition, and allergenicity were analysed. All groups achieved more than 20% weight gain, and the silage-fed fish showed the lowest residual allergenicity (15.3%), compared to the fish fed untreated viscera (24%) and commercial feed (21.9%). Silage processing caused extensive protein hydrolysis, reducing high-molecular-weight proteins, though some IgE-reactive fragments remained. Proteomic analysis detected only seabream structural and metabolic proteins, with no confirmed Anisakis allergens. These findings indicate that silage produced from Anisakis-infested viscera should not pose a higher risk to consumers than the fishmeal used in aquaculture feeds and could support the valorisation of currently discarded fish viscera. Full article

(This article belongs to the Special Issue Novel Research on By-Products and Treatment of Waste)

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26 pages, 2109 KB

Open AccessArticle

Integrated Assessment of Odour Emissions from a Municipal Wastewater Pumping Station Using Field Olfactometry and Chemometric Modelling

by Mirosław Szyłak-Szydłowski, Andrzej Kulig and Wojciech Kos

Appl. Sci. 2026, 16(1), 468; https://doi.org/10.3390/app16010468 - 1 Jan 2026

Viewed by 753

Abstract

Odour emissions from wastewater infrastructure represent a significant environmental and social challenge in urban areas. This study evaluates the odour impact of a municipal wastewater pumping station using an integrated field-based approach that combines sensory observations, chemical measurements and meteorological data. Field olfactometry and on-site gas monitoring were applied over a two-year campaign covering different operational and seasonal conditions. The results indicate that odour perception is strongly influenced by hydrogen sulphide concentration, air temperature and wind speed, with short-term high-intensity episodes playing a disproportionate role in odour nuisance. To support integrated interpretation, a Synthetic Odour Index (SOI) was developed to consolidate chemical, sensory and microclimatic information into a single numerical indicator, extending existing odour indices by explicitly integrating field-based sensory and meteorological data. The SOI showed a moderate but statistically significant association with odour intensity (r ≈ 0.3) and effectively differentiated low- and high-nuisance conditions. The proposed methodology demonstrates the value of combining field measurements with integrated data analysis for assessing and managing odour emissions from urban wastewater pumping stations and provides a practical basis for operational monitoring and odour mitigation strategies. Full article

(This article belongs to the Special Issue Novel Research on By-Products and Treatment of Waste)

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14 pages, 1798 KB

Open AccessArticle

Risk Assessment for Reducing Thermoset Waste: Predictive Modelling of Water Ageing in Epoxy Infrastructure

by Marcela Elisabeth Penoff, Guillermina Capiel, Pablo E. Montemartini and Luis A. Miccio

Appl. Sci. 2025, 15(22), 11857; https://doi.org/10.3390/app152211857 - 7 Nov 2025

Viewed by 734

Abstract

Thermoset composites are a fast-growing waste stream that resists conventional reusing routes. Water is the principal ageing agent for epoxy-based thermoset materials that bind high-pressure piping, wind-turbine blades and aircraft skins, yet its action is deceptively complex: a rapid, reversible plasticisation is often followed by a far slower, irreversible chemical hydrolysis. Here we bridge that gap to access a reliable diagnosis inspection. Gravimetric immersion tests (from 8 to 93 °C, up to more than a year) and in situ FTIR spectroscopy were performed on four industrial DGEBA networks (two amine-cured matrices and two anhydride-cured matrices that hydrolyse). This 2 + 2 design isolates reversible from irreversible changes and exposes the individual signatures of diffusion, specific sorption and bond scission. The data are rationalised with a compact three-contribution model that superposes Fickian diffusion through nano-voids, adsorption site saturation through hydrogen bonds and a power-law hydrolysis term sharing global Arrhenius parameters. Since the parameters retain clear physical meaning, the approach can be extrapolated to service temperatures, providing a fast, transparent tool for lifetime prediction and for separating recoverable plasticisation from permanent chemical degradation in critical epoxy infrastructure. Full article

(This article belongs to the Special Issue Novel Research on By-Products and Treatment of Waste)

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19 pages, 5147 KB

Open AccessArticle

Valorization of Fine Recycled Concrete Aggregate By-Products from Construction Waste as a Sustainable Material for Granular Subbases: Mechanical and Environmental Assessments

by José Eduardo Salcedo Fontalvo, Daniela L. Vega A., Rodrigo Polo-Mendoza, Felipe Ángeles Puc Hernandez, Luisa Navarro Ortiz and Grey Meneses Vides

Appl. Sci. 2025, 15(20), 11184; https://doi.org/10.3390/app152011184 - 18 Oct 2025

Viewed by 1369

Abstract

The valorization of by-products from construction waste offers significant potential for developing sustainable materials in road infrastructure. Accordingly, this study investigates the incorporation of Fine Recycled Concrete Aggregate (FRCA) as a partial replacement of virgin aggregates in Granular Subbases (GSB), considering both mechanical performance and environmental impacts. Replacement levels of 10% and 15% FRCA are examined and benchmarked against standard specifications for GSB within the Colombian context. The experimental campaign is composed of grain size distribution, Atterberg limits, Proctor compaction, Los Angeles abrasion, and California bearing ratio tests. Furthermore, a cradle-to-gate life-cycle assessment was conducted to evaluate the potential environmental benefits of diverting FRCA by-products from disposal and valorizing them as construction materials. Overall, the mechanical and environmental assessments reveal that if the Los Angeles abrasion criterion is set aside (because any FRCA content surpasses the allowable limits), the optimal mixture is the one formed by 85% GSB38 and 15% FRCA. This combination satisfies the standards for high-traffic roads while providing approximately 22.5–25% relative environmental savings. Full article

(This article belongs to the Special Issue Novel Research on By-Products and Treatment of Waste)

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Review

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32 pages, 1939 KB

Open AccessReview

A Review on Anaerobic Digestate as a Biofertilizer: Characteristics, Production, and Environmental Impacts from a Life Cycle Assessment Perspective

by Carmen Martín-Sanz-Garrido, Marta Revuelta-Aramburu, Ana María Santos-Montes and Carlos Morales-Polo

Appl. Sci. 2025, 15(15), 8635; https://doi.org/10.3390/app15158635 - 4 Aug 2025

Cited by 35 | Viewed by 11217

Abstract

Digestate valorization is essential for sustainable waste management and circular economy strategies, yet large-scale adoption faces technical, economic, and environmental challenges. Beyond waste-to-energy conversion, digestate is a valuable soil amendment, enhancing soil structure and reducing reliance on synthetic fertilizers. However, its agronomic benefits depend on feedstock characteristics, treatment processes, and application methods. This study reviews digestate composition, treatment technologies, regulatory frameworks, and environmental impact assessment through Life Cycle Assessment. It analyzes the influence of functional unit selection and system boundary definitions on Life Cycle Assessment outcomes and the effects of feedstock selection, pretreatment, and post-processing on its environmental footprint and fertilization efficiency. A review of 28 JCR-indexed articles (2018–present) analyzed LCA studies on digestate, focusing on methodologies, system boundaries, and impact categories. The findings indicate that Life Cycle Assessment methodologies vary widely, complicating direct comparisons. Transportation distances, nutrient stability, and post-processing strategies significantly impact greenhouse gas emissions and nutrient retention efficiency. Techniques like solid–liquid separation and composting enhance digestate stability and agronomic performance. Digestate remains a promising alternative to synthetic fertilizers despite market uncertainty and regulatory inconsistencies. Standardized Life Cycle Assessment methodologies and policy incentives are needed to promote its adoption as a sustainable soil amendment within circular economy frameworks. Full article

(This article belongs to the Special Issue Novel Research on By-Products and Treatment of Waste)

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