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Recycling
Special Issues
Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization
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Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization

A Special Issue of Recycling (ISSN 2313-4321).

Deadline for manuscript submissions: 31 December 2026 | Viewed by 6582

Editors

Prof. Dr. Miguel Angel Sandoval

E-Mail Website
Guest Editor
Instituto Tecnológico Superior de Guanajuato (ITESG), Tecnológico Nacional de México, Carretera Estatal Guanajuato–Puentecillas km 10.5, Guanajuato 36262, Mexico
Interests: EAOPs; electrocoagulation; circular economy and resource recovery; environmental remediation
Special Issues, Collections and Topics in MDPI journals
Dr. Martín Oscar Armando Pacheco-Álvarez

E-Mail Website
Guest Editor
Instituto Tecnológico Superior de Guanajuato, Tecnológico Nacional de México, Carretera Estatal Guanajuato-Puentecillas Km. 10.5, Guanajuato 36262, Mexico
Interests: electrochemical advanced oxidation processes; photocatalysis; environmental remediation; green hydrogen
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue aims to highlight recent advances in wastewater treatment technologies and the recovery of valuable resources within a circular economy framework. The focus is on innovative strategies that integrate contaminant removal with resource valorization, promoting sustainable reuse of water, nutrients, energy, and materials. The scope includes but is not limited to electrochemical, biological, physicochemical, and hybrid processes that enable both efficient treatment and circular recovery pathways. The purpose of this Special Issue is to provide a platform for multidisciplinary contributions that bridge laboratory research, pilot-scale studies, and practical applications, offering readers a comprehensive overview of the state of the art.

This Special Issue will complement the existing literature by emphasizing the dual goals of treatment and recovery, which are often addressed separately. By integrating these aspects, the collection will contribute to advancing practical, scalable, and sustainable solutions for wastewater management and valorization.

Prof. Dr. Miguel Angel Sandoval
Dr. Martín Oscar Armando Pacheco-Álvarez
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-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Recycling is an international peer-reviewed open access monthly 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 1800 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

  • wastewater treatment
  • resource recovery
  • circular economy
  • electrochemical processes
  • advanced oxidation processes
  • water reuse
  • sustainable technologies
  • valorization pathways

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Published Papers (5 papers)

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Research

24 pages, 17632 KB  
Article
TiO2-Fly Ash Composites for Photocatalytic Degradation of Organic Loading from Real Municipal Wastewater
by Mirela Alina Constantin, Ioana Alexandra Ionescu, Florenta Daniela Constantinov, Cristina Mihaela Nicolescu, Marius Bumbac, Anca Irina Gheboianu and Lucian Alexandru Constantin
Recycling 2026, 11(8), 154; https://doi.org/10.3390/recycling11080154 - 20 Aug 2026
Viewed by 319
Abstract
Fly ash-TiO2 composites were obtained by sol–gel, and their catalytic performance was evaluated on removal of organic loading and expressed as Chemical Oxygen Demand (COD) from real wastewater samples. SEM, X-ray fluorescence, XRD, IR, Raman analysis and determination of PZC characterized the [...] Read more.
Fly ash-TiO2 composites were obtained by sol–gel, and their catalytic performance was evaluated on removal of organic loading and expressed as Chemical Oxygen Demand (COD) from real wastewater samples. SEM, X-ray fluorescence, XRD, IR, Raman analysis and determination of PZC characterized the catalysts. The photocatalytic tests were carried out in a laboratory reactor under UV-VIS irradiation and influence of fly ash (FA) content, and irradiation time was investigated. The catalysts with FA content of 10%, 20% and 30% showed COD removal efficiencies higher than 50% after 5 h of irradiation. The COD degradation followed a pseudo-first order kinetic model. Obtained results proved that FA-TiO2 composites could represent a suitable alternative for removal of organic loading from real wastewater. Full article
(This article belongs to the Special Issue Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization)
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13 pages, 1430 KB  
Article
Integration of Floating Constructed Wetlands and Microbial Fuel Cells for Sustainable Wastewater Treatment and Bioelectricity Generation
by Eduardo Guevara Hernández, Alba Jocelyne Aldabalde Hernández, Fernando Andrés Rojas Aguilar, Efraín Martínez Prior, Luis A. Godínez, Víctor A. Ramírez and Francisco J. Rodríguez-Valadez
Recycling 2026, 11(7), 112; https://doi.org/10.3390/recycling11070112 - 24 Jun 2026
Viewed by 413
Abstract
Floating wetlands have emerged as a sustainable alternative for improving water quality, and although some studies have investigated their performance, there is still much to be understood regarding their integration with energy-generating technologies. This study evaluated a combined system of floating wetlands and [...] Read more.
Floating wetlands have emerged as a sustainable alternative for improving water quality, and although some studies have investigated their performance, there is still much to be understood regarding their integration with energy-generating technologies. This study evaluated a combined system of floating wetlands and microbial fuel cells (MFCs) for treating real wastewater and generating bioelectricity. Experiments were conducted in batch mode to simulate application in natural water bodies, using real wastewater collected on different dates. As a result of the natural variability of the influent, initial chemical oxygen demand (COD) concentrations of 405 and 289 mg/L were observed. Performance was assessed in terms of organic matter and nitrogen removal, as well as voltage generation. COD removal efficiencies reached 50% and 69% for the higher and lower organic loads, respectively, indicating improved treatment at reduced concentrations. Maximum removals of 56% for ammoniacal nitrogen (NH3-N) and 40% for total nitrogen (TN) were achieved, reflecting moderate nutrient removal capacity. Voltage generation was sustained for approximately 21 days, confirming stable bioelectrochemical activity, and power output was found to depend on the organic load serving as substrate for electrogenic microorganisms. Overall, the system represents a viable approach for wastewater treatment with the added benefit of energy recovery, although its performance is influenced by influent characteristics and operation conditions. Full article
(This article belongs to the Special Issue Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization)
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18 pages, 1764 KB  
Article
Valorisation of Rockmelon Skin Through NaOH Modification for Crystal Violet Adsorption
by Chin Mei Chan, Amal Asheeba Romzi, Linda Lim Biaw Leng and Muhammad Raziq Rahimi Kooh
Recycling 2026, 11(5), 80; https://doi.org/10.3390/recycling11050080 - 27 Apr 2026
Viewed by 744
Abstract
Developing practical low-cost adsorbents for dye-contaminated wastewater remains a critical challenge, especially for persistent cationic dyes such as crystal violet (CV). Here, raw rockmelon skin (RMS), an abundant fruit-processing residue, and its NaOH-modified derivative (NaOH-RMS) were investigated as adsorbents for CV adsorption. Alkaline [...] Read more.
Developing practical low-cost adsorbents for dye-contaminated wastewater remains a critical challenge, especially for persistent cationic dyes such as crystal violet (CV). Here, raw rockmelon skin (RMS), an abundant fruit-processing residue, and its NaOH-modified derivative (NaOH-RMS) were investigated as adsorbents for CV adsorption. Alkaline treatment altered the biomass’s characteristics and affected its adsorption behaviour. Equilibrium was reached within 120 min, and the kinetic data were best fit by the pseudo-second-order model. Equilibrium analysis showed that the Freundlich model best described RMS. In contrast, NaOH-RMS was better represented by the Langmuir model, indicating that alkaline treatment altered the adsorption behaviour of the biomass surface. The Langmuir-derived maximum adsorption capacities were 343.7 mg g−1 for RMS and 295.2 mg g−1 for NaOH-RMS, indicating that NaOH modification did not increase the maximum adsorption capacity. Adsorption was spontaneous across 298–343 K, and both materials retained satisfactory removal performance over five regeneration cycles, particularly under basic desorption conditions. Overall, NaOH treatment altered the adsorption behaviour from heterogeneous adsorption on RMS to a more Langmuir-type adsorption pattern on NaOH-RMS, despite not increasing the maximum adsorption capacity. These findings support the valorisation of fruit-processing residues as practical adsorbents for dye-contaminated wastewater. Full article
(This article belongs to the Special Issue Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization)
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20 pages, 3146 KB  
Article
Dewatering of Short-Fibre Digestates from Paper Recycling Mills: Liquid Fraction and Mass Distribution Profiles
by Dheeraja Winter, Svea Ziegner, Simone Krafft, Markus Grömping and Silvio Beier
Recycling 2026, 11(4), 78; https://doi.org/10.3390/recycling11040078 - 15 Apr 2026
Viewed by 1078
Abstract
The paper sector is characterised by high freshwater consumption and a strong need for improved resource efficiency. In this context, industrial digestates derived from short-fibre residues in paper recycling mills represent a promising substrate for water recovery within a circular economy framework. This [...] Read more.
The paper sector is characterised by high freshwater consumption and a strong need for improved resource efficiency. In this context, industrial digestates derived from short-fibre residues in paper recycling mills represent a promising substrate for water recovery within a circular economy framework. This study investigated the dewatering of short-fibre digestates as a pre-treatment for downstream membrane processes, aiming to maximise the liquid fraction (LF) recovery while minimising dry matter (DM) content. Seven scenarios were studied: sedimentation (S0); pre-sedimentation with chemical addition using iron(III) chloride (FeCl3) + polydiallyldimethylammonium chloride (polyDADMAC) (S1), FeCl3 + starch (S2), Nanofloc® (S3), and polyDADMAC (S4); and direct dewatering without pre-sedimentation using polyDADMAC with cloth filtration (S5) and centrifugation (S6). With reference to the sedimentation supernatant, S4 achieved the highest DM separation efficiency of 76%, followed by S1 (64%), whereas S2 and S3 were below 40%. However, LF recovery relative to the initial digestate was limited in scenarios S1–S4 to 17% (170 g/kgdigestate), with DM concentrations of 2.0–4.8 g/kgLF. In contrast, direct dewatering increased LF recovery substantially, with centrifugation (S6) achieving up to 690 gLF/kgdigestate and cloth filtration (S5) 420 g/kgdigestate, while maintaining a low DM (1.7 g/kgLF). Chemical oxygen demand (COD) and phosphorus (Ptot) were largely separated from the liquid fractions in all the scenarios. Nitrogen (Ntot) and ammonium (NH4-N) in the LF remained more variable, ranging from 22 to 153 and 5 to 22 mg/kgdigestate, respectively. These results indicate that centrifugation with polyDADMAC is the most effective approach, suggesting that mechanical force with a chemical additive can be used for the efficient dewatering of short-fibre digestates. Full article
(This article belongs to the Special Issue Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization)
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16 pages, 3259 KB  
Article
Demulsification of Oily Sludge Using Ozone Micro–Nanobubbles in Aqueous Media
by Lingli Wang, Xiaoqi Hu, Tianzhi Wang, Fawei Lin, Yuehua Li, Xiangqi Meng and Manuel Fiallos
Recycling 2026, 11(2), 24; https://doi.org/10.3390/recycling11020024 - 1 Feb 2026
Viewed by 2452
Abstract
Oily sludge is a complex emulsified waste consisting of water, oil, and solid particles. Conventional treatments are often inefficient, energy-intensive, and prone to causing secondary pollution. This study proposes a green demulsification technology based on ozone micro–nanobubbles (O3MNBs) by constructing an [...] Read more.
Oily sludge is a complex emulsified waste consisting of water, oil, and solid particles. Conventional treatments are often inefficient, energy-intensive, and prone to causing secondary pollution. This study proposes a green demulsification technology based on ozone micro–nanobubbles (O3MNBs) by constructing an experimental system to analyze its effects and mechanisms of action on oily sludge treatment. The O3MNBs exhibited a mean particle size of 831 nm and generated a substantial amount of hydroxyl radicals (·OH, 250.4 μmol·L−1) in situ. Compared with conventional aeration, the dissolved ozone concentration and residence time in water of O3MNBs increased by 192% and 213%, respectively. During bubble collapse, intense pressure waves and high-speed microjets were generated to disrupt sludge aggregates, promoting the dispersion of sludge particles while simultaneously stripping oil films. Thus, the oil removal rate reached 41.5%, demonstrating the high demulsification efficiency of O3MNBs. Furthermore, ozone and ·OH attacked alkane C-H bonds in the oil phase, oxidizing hydrophobic films into hydrophilic products and decomposing surfactants that stabilize emulsions. This process promoted oil droplet coalescence and degradation into small organic molecules. After O3MNB treatment, the absorption peak of alkane C-H bonds gradually reduced, while a new C=O absorption peak appeared. This study provides a theoretical foundation and technical support for environmentally sustainable treatment of oily sludge by O3MNB application, offering an effective alternative to chemical demulsification without secondary pollution. Full article
(This article belongs to the Special Issue Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization)
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