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Conversion of Solid Waste into Green Materials: Innovations in Synthesis...
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Conversion of Solid Waste into Green Materials: Innovations in Synthesis Processes and Valorization Options

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Environmental and Green Processes".

Deadline for manuscript submissions: 31 May 2026 | Viewed by 796

Special Issue Editors

Dr. Salah Jellali

E-Mail Website
Guest Editor
Centre for Environmental Studies and Research, Sultan Qaboos University, 123, Al-khoudh, Muscat, Oman
Interests: wastewater and solid wastes sustainable management; biochar synthesis; biochar valorization for wastewater treatment; biochar valorization for nutrients recovery; biochar valorization in agriculture; sustainability; circular economy
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Mejdi Jeguirim

E-Mail Website
Guest Editor
Institut de Sciences des Matériaux de Mulhouse, 3 Rue Alfred Werner, 68093 Mulhouse, France
Interests: biomass; pyrolysis; gasification; combustion; biochars; hydrochars; wastewater treatment; gaseous effluents treatment; nutrients recovery; agronomic valorization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The conversion of solid waste into green materials has been identified as a promising method for preserving the environment, boosting circular economy, and promoting sustainability. Several technologies are currently used for this purpose, including direct physico-chemical treatment, pyrolysis, gasification, incineration, and hydrothermal carbonization. These synthesized green materials can be used in various domains, including removal and/or recovery of pollutants from wastewater, soil remediation, boosting sustainable agriculture, and energy recovery. However, recent works have shown that the effectiveness of applying these green materials is highly dependent on the nature of the solid waste, the selected modification method and conditions, and the valorization conditions. Therefore, innovations in both synthesis processes and the experimental conditions for valorization are of great importance to guarantee the effectiveness of these green materials at both laboratory and industrial scales.

This Special Issue, “Conversion of Solid Waste into Green Materials: Innovations in Synthesis and Valorization”, seeks experimental/numerical studies of high scientific quality on optimizing the conversion of solid waste into green materials, as well as their tailored application in the domains of the environment, agriculture, and energy. Topics of interest include, but are not limited to, the following:

  • Synthesis of green materials from mineral or organic wastes (i.e., biochar, hydrochar, ash, etc.);
  • In-depth characterization of green materials;
  • Valorization of green materials for removal of pollutants from aqueous and gaseous effluents;
  • Valorization of green materials for recovering nutrients from wastewater;
  • Application of nutrient-loaded green materials in agriculture;
  • Application of green materials for energy recovery.

Dr. Salah Jellali
Prof. Dr. Mejdi Jeguirim
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 250 words) can be sent to the Editorial Office for assessment.

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. Processes 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

  • synthesis processes
  • biochar
  • hydrochar
  • ash
  • detailed characterization
  • pollutant adsorption and oxidation
  • nutrient recovery
  • bioremediation
  • reuse in agriculture
  • reuse for energy recovery

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Published Papers (2 papers)

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Research

28 pages, 1136 KB  
Article
Preliminary Evaluation of Bioactive Compound Profiles and Antioxidant Properties of Selected Agri-Food Wastes
by Jelena Vukosavljević, Sara Hourani, Uroš Gašić, Jan Turan, Boris M. Popović and Branimir Pavlić
Processes 2026, 14(10), 1561; https://doi.org/10.3390/pr14101561 - 12 May 2026
Abstract
The increasing generation of agri-food waste represents a significant environmental challenge, but also a valuable source of bioactive compounds with potential industrial applications. In this study, selected minimally processed agri-food wastes from the food processing industry were evaluated as potential sources of bioactive [...] Read more.
The increasing generation of agri-food waste represents a significant environmental challenge, but also a valuable source of bioactive compounds with potential industrial applications. In this study, selected minimally processed agri-food wastes from the food processing industry were evaluated as potential sources of bioactive compounds and antioxidants. Seven types of agri-food waste were investigated: green bean cutting waste, yellow bean cutting waste, sweet corn waste from the air selector, edamame pods, pepper seed by-products, potato peels, and potato waste from the air selector. Solid–liquid extraction was performed using ethanol at different concentrations (20, 40, 60, 80, and 96%, w/w) as a green solvent. Total polyphenol content (TPC) and antioxidant activity (DPPH, FRAP, and ABTS assays) were determined. The results demonstrated significant differences among the investigated raw materials, with the highest antioxidant activity observed in the potato peel extracts. Specifically, the strongest activity was recorded using 40% ethanol, yielding values of 3.9596 mg TE/g DW for DPPH and 11.4555 mg TE/g DW for ABTS assays. In contrast, the highest FRAP value (2.3970 mg Fe2+/g DW) was obtained with 60% ethanol. The highest TPC was detected in pepper seed by-products, reaching 6.7829 mg GAE/g DW when extracted with 20% ethanol. Furthermore, selected extracts were subjected to LC-MS analysis to obtain a preliminary characterization of their chemical profiles. Untargeted LC-MS analysis identified 115 metabolites belonging to different chemical classes, highlighting agri-food waste as a rich source of bioactive compounds, particularly flavonoids and phenolic acids. These findings demonstrate agri-food wastes as sustainable sources of bioactive compounds and support their valorization within circular economy and green processing frameworks. Full article
(This article belongs to the Special Issue Conversion of Solid Waste into Green Materials: Innovations in Synthesis Processes and Valorization Options)
21 pages, 1912 KB  
Article
Porous Activated Carbons from Olive Stone-Derived Biochar and Hydrochar: Production, Characterization and Application for Amoxicillin Removal
by Ahmed Bourafa, Meriem Belhachemi, Emna Berrich Kilani, Salah Jellali and Mejdi Jeguirim
Processes 2026, 14(7), 1064; https://doi.org/10.3390/pr14071064 - 26 Mar 2026
Viewed by 448
Abstract
The sustainable management of olive wastes represents an important environmental challenge. Biochars and hydrochars derived from biomass are promising adsorbents for removing emerging pollutants from water. In the present work, olive stone wastes were converted into biochar and hydrochar by using pyrolysis (500 [...] Read more.
The sustainable management of olive wastes represents an important environmental challenge. Biochars and hydrochars derived from biomass are promising adsorbents for removing emerging pollutants from water. In the present work, olive stone wastes were converted into biochar and hydrochar by using pyrolysis (500 °C for 30 min) and hydrothermal carbonization (HTC) processes (220 °C for 10 h). Then, the obtained materials were physically activated by using CO2 gas (750 °C for 30, 60 and 180 min). Various analytical techniques were applied for the chemical, textural and structural characterization of these carbonaceous materials (i.e., ultimate and proximate analysis, scanning electron microscopy (SEM), BET surface area, Raman spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy). Afterwards, the selected activated biochar and hydrochar were applied for the removal of amoxicillin from aqueous solutions. The experimental results show that the generated hydrochar has many microspheres on its surface and inside, while the produced biochar exhibits a porous structure with irregular forms. CO2 physical activation has induced an important improvement of the biochar and hydrochar’s structural, textural, and surface chemistry properties. For instance, the activated biochar samples show a highly porous structure, with large specific surface areas that increase with the burn-off, reaching 1349.3 m2 g−1 following 3 h of activation. Regarding the activated hydrochar samples, they exhibit a spherical morphological structure with an important specific surface area, which increased to 846.7 m2 g−1 after 3 h of activation. Moreover, both activated materials have an amorphous structure with low oxygen surface groups. The selected novel CO2-activated biochar and hydrochar efficiently remove amoxicillin from aqueous solutions under wide experimental conditions, with adsorption capacities of 386.4 and 215.9 mg g−1, respectively. These efficiencies are higher than those reported for various activated biochars derived from lignocellulosic biomass, from sewage sludge, and from animal manure. Future research works are required to assess these materials’ effectiveness in treating real pharmaceutical effluents, to optimize the regeneration of the amoxicillin-loaded materials, and to design full-scale devices for a real application. Full article
(This article belongs to the Special Issue Conversion of Solid Waste into Green Materials: Innovations in Synthesis Processes and Valorization Options)
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