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Applied Sciences
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Waste Valorization, Green Technologies and Circular Economy
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Waste Valorization, Green Technologies and Circular Economy

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

Deadline for manuscript submissions: 20 December 2024 | Viewed by 4442

Special Issue Editors

Dr. Amanda Laca Pérez

E-Mail Website
Guest Editor
Department of Chemical and Environmental Engineering, University of Oviedo, 33006 Oviedo, Spain
Interests: enzymatic hydrolysis; fungi; biological treatment; lignocellulosic biomass; cellulose; hemicellulose; lignin
Special Issues, Collections and Topics in MDPI journals
Dr. Yolanda Patiño

E-Mail Website
Guest Editor
Catalysis, Reactors and Control Research Group (CRC), Department of Chemical and Environmental Engineering, University of Oviedo, 33006 Oviedo, Spain
Interests: emerging pollutants; adsorption process; electrochemical degradation; sludge valorization
Special Issues, Collections and Topics in MDPI journals
Dr. Daniel Sol

E-Mail Website
Guest Editor
Department of Chemical and Environmental Engineering, University of Oviedo, C/Julián Clavería s/n, 33006 Oviedo, Spain
Interests: environmental technologies; material science; waste management; water quality

Special Issue Information

Dear Colleagues,

Global waste generation is continuing to grow today, which entails the need to develop new strategies to convert residues into valuable materials. This affects various different sectors; for example, it is well known that one third of the world’s food produced for human consumption becomes waste every year, whereas sewage sludge management requires important costs, both in economic and environmental terms. In this context, waste valorization is an excellent option to embrace the strategy of the circular economy and sustainable development.

In view of the current situation, this Special Issue aims to compile the latest research on waste valorization topics, including but not limited to the following:

  • Development of green technologies to waste management;
  • Sludge valorization;
  • Wastewater reuse;
  • Obtention of bioactive compounds from food industry residues;
  • Environmental assessment of waste management;
  • Physical, chemical, and biological treatments for waste valorization.

Dr. Amanda Laca Pérez
Dr. Yolanda Patiño
Dr. Daniel Sol
Guest Editors

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 special issue 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. Applied Sciences is an international peer-reviewed open access semimonthly 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 2400 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 valorization
  • life cycle assessment
  • circular economy
  • recycling
  • sustainable development

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Published Papers (4 papers)

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Research

12 pages, 763 KiB  
Article
Solid-State Fermentation Initiated by Pleurotus ostreatus of a Cottonseed Cake and Lathyrus clymenum Pericarp Mixture: Impact on Nutritional Profile and Gossypol Content
by Christos Eliopoulos, Ioanna Langousi, Eleni Kougia, Georgia Saxami, Giorgos Markou, Serkos A. Haroutounian and Dimitrios Arapoglou
Appl. Sci. 2024, 14(12), 5066; https://doi.org/10.3390/app14125066 - 11 Jun 2024
Cited by 1 | Viewed by 698
Abstract
Solid-State fermentation (SSF) is a valuable process used for the enhancement of the nutritional profile of agro-industrial by-products. The main objective of the present study concerns the exploitation of a mixture consisting of Cottonseed Cake (CSC) and Lathyrus clymenum pericarp (LCP) at a [...] Read more.
Solid-State fermentation (SSF) is a valuable process used for the enhancement of the nutritional profile of agro-industrial by-products. The main objective of the present study concerns the exploitation of a mixture consisting of Cottonseed Cake (CSC) and Lathyrus clymenum pericarp (LCP) at a ratio of 80–20% w/w, which was utilized as substrate for the initiated by Pleurotus ostreatus SSF process. The final goal is the improvement of their nutritional value and the parallel reduction in their gossypol content. The obtained results revealed a statistically significant increase (p < 0.05) in protein content by 34.91%, while 1,3-1,6 β-glucans exceeded a 5-fold statistically significant increment (p < 0.05) at Day 11. Furthermore, lignin was reduced significantly (−26.71%) at Day 11. Free gossypol’s presence was lowered by 12.45%, while SSF presented a profound effect concerning the total gossypol level since the latter underwent a statistically significant reduction (p < 0.05) that exceeded 9-fold at Day 11. The study herein highlights SSF’s efficiency as a potential means to reduce free and total gossypol content with a parallel upgrade of its nutritional value. The fermentation outcome reveals its potential as a feed supplement and contributes to the reduction in the environmental footprint within the framework of a circular economy. Full article
(This article belongs to the Special Issue Waste Valorization, Green Technologies and Circular Economy)
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11 pages, 4545 KiB  
Article
Energy Recovery from Municipal Sewage Sludge: An Environmentally Friendly Source for the Production of Biochemicals
by Luigi di Bitonto, Antonella Angelini and Carlo Pastore
Appl. Sci. 2024, 14(12), 4974; https://doi.org/10.3390/app14124974 - 7 Jun 2024
Viewed by 615
Abstract
In this work, a detailed analysis of the lipid component in primary sludge and sewage scum up-taken from several wastewater treatment plants located in southern Italy was carried out. Lipids in the primary sludge accounted for 200–250 mg/g of the total solids (TS), [...] Read more.
In this work, a detailed analysis of the lipid component in primary sludge and sewage scum up-taken from several wastewater treatment plants located in southern Italy was carried out. Lipids in the primary sludge accounted for 200–250 mg/g of the total solids (TS), with calcium soaps as a main component (70–82%), while total lipids made up about 350–500 mg/gTS in the sewage scum and consisted mainly of FFAs (45–60%) and calcium soaps (27–35%). In addition, estolides and 10-hydroxystearic acid were also quantified. A specific valorization process was then developed and tested for either primary sludge or sewage scum. In detail, lipids were first recovered, chemically activated by the addition of acids (calcium soaps were converted to free fatty acids) and finally reacted with methanol to obtain methyl esters. The lipid recovery from primary sludge and sewage scum was particularly efficient (recoverability of 92–99%). The conversion of the starting acids into FAMEs (yield > 98%) was achieved under very mild conditions (70 °C, 2 h) with AlCl3·6H2O as a catalyst. Biodiesel (according to EN14214), methyl 10-hydroxystearate and methyl estolides were efficiently isolated by distillation under vacuum. Finally, a feasibility study of the proposed processes was carried out to evaluate their possible integration into a wastewater treatment plant, critically analyzing both the positive aspects and the relative limitations. Full article
(This article belongs to the Special Issue Waste Valorization, Green Technologies and Circular Economy)
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13 pages, 479 KiB  
Article
Combined Pre-Treatment Technologies for Cleaning Biogas before Its Upgrading to Biomethane: An Italian Full-Scale Anaerobic Digester Case Study
by Adolfo Le Pera, Miriam Sellaro, Crescenzo Pellegrino, Carlo Limonti and Alessio Siciliano
Appl. Sci. 2024, 14(5), 2053; https://doi.org/10.3390/app14052053 - 29 Feb 2024
Cited by 2 | Viewed by 872
Abstract
Biogas produced by anaerobic digestion contains different types of contaminants, and it is preferable to eliminate those contaminants before biogas’ energetic valorization or upgrading to biomethane as they are harmful to human health and detrimental to combustion engines. This study presents the biogas [...] Read more.
Biogas produced by anaerobic digestion contains different types of contaminants, and it is preferable to eliminate those contaminants before biogas’ energetic valorization or upgrading to biomethane as they are harmful to human health and detrimental to combustion engines. This study presents the biogas cleanup system optimized by an Italian full-scale anaerobic digester treating food waste (FW) and represented by micro-oxygenation, chemical scrubber, cooling, and activated carbon sections. The cleaned biogas is upgraded to biomethane using a membrane-based upgrading unit and injected into the natural gas network for transport sector use. H2S and volatile organic compound (VOC) concentration in raw biogas was reduced from an annual average value of 1207 ppmv and 895 mg/Nm3, respectively, to below 0.1 mg/Nm3 in the final biomethane. In the summer, the H2S average content in raw biogas was 833 ppmv due to a greater presence of low-sulfur-containing vegetables in FW, while in the winter it was an average of 1581 ppmv due to a larger portion of protein-containing FW. On the other hand, raw biogas VOC content in the winter was an average of 1149 mg/Nm3, with respect to 661 mg/Nm3 in the summer, due to the greater consumption of citrus fruits containing high amount of terpene compounds. The concentration of other trace contaminants, such as HCl, NH3, and siloxanes, was lowered from 17, 36, and 0.6 mg/Nm3 in raw biogas, respectively, to below 0.1 mg/Nm3 in the final biomethane. All the considerations and evaluations underlying the technological and plant engineering choices together with the individuation of the best operating conditions are discussed. Full article
(This article belongs to the Special Issue Waste Valorization, Green Technologies and Circular Economy)
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21 pages, 1662 KiB  
Article
A Green Technology Approach Using Enzymatic Hydrolysis to Valorize Meat Waste as a Way to Achieve a Circular Economy
by Miguel Angulo and Mª Carmen Márquez
Appl. Sci. 2023, 13(15), 8763; https://doi.org/10.3390/app13158763 - 29 Jul 2023
Cited by 3 | Viewed by 1549
Abstract
The retail meat industry produces a significant amount of waste, containing proteins, lipids, and other elements that could serve as the basis for other products. This work presents the results of research on the enzymatic hydrolysis of meat waste as a green technology [...] Read more.
The retail meat industry produces a significant amount of waste, containing proteins, lipids, and other elements that could serve as the basis for other products. This work presents the results of research on the enzymatic hydrolysis of meat waste as a green technology to obtain products with added value as a substitute for other raw materials. pH, temperature, the protease/proteinic substrate ratio (Eo/So), and the lipolase/lipidic substrate ratio (Eo’/So’) were studied as process variables for hydrolysis of proteins and lipids, respectively. Hydrolysis for the recovery of proteins (as protein hydrolysates or collagen) was carried out with the protease Alcalase; pH around 8.0, temperature around 50 °C, and Eo/So around 0.16 AU/g were the optimum process variables’ values for obtaining high amounts of recovered proteins and peptides that are easily digestible and have a pleasant taste. The lipase Resinase was used to hydrolyze the lipids; a clear relationship was observed between Eo’/So’ and the amounts of recovered fatty acids. The optimum process variables’ values were found to be Eo’/So’ around 0.83 kLU/g, pH around 8.0 and temperature around 50 °C. Unsaturated fatty acids prevailed in the final product. For the simultaneous recovery of protein hydrolysates, collagen, and fatty acids, a combination of Alcalase and Resinase was used; the process variables examined included the optimal range of values for Eo/So and Eo’/So’, as well as pH and temperature that were suggested in research for both Alcalase and Resinase, separately. The results showed that the simultaneous process was mainly influenced by the Eo/So and Eo’/So’ ratios, instead of being influenced by the pH and temperature values which were less influential. For Eo/So = 0.16 AU/g, Eo’/So’ = 1.11 kLU/g, pH = 7.5, T = 50 °C, the maximum amounts of products (0.8 kg by kg of dry meat waste) were obtained more economically, where the whole of the proteins and lipids in meat waste were practically recovered. Therefore, in order to preserve a circular economy for retail meat waste, enzymatic hydrolysis is appealing and environmentally friendly. Full article
(This article belongs to the Special Issue Waste Valorization, Green Technologies and Circular Economy)
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