Separation Techniques and Circular Economy

Topic Information

Dear Colleagues,

Efficient separation techniques play an important role in the process of resource recovery, such as physical, chemical, physico-chemical, and/or biological methods, which are selected due to being low-cost, low-energy, and free of secondary pollution. Additionally, the highest possible value added of the separated products is obtained to enhance the economy. For example, to address concerns regarding the contamination of water resources, various separation techniques, such as membrane separation, adsorption, ion exchange, solvent extraction, magnetic separation, filtration, flocculation, sedimentation, and centrifugal separation with physico-chemical processes, have been developed for wastewater treatment to effectively recycle various substances such as phosphates, humic substances, biological plastics, cellulose, polysaccharides, proteins, lipids, extracellular polymer substances, organics, and precious metals. Furthermore, parallel developments in biorefinery technologies further enable the transformation of biomass into renewable chemicals and biofuels, reducing the dependence on petrochemical feedstocks. This Topic, entitled “Separation Techniques and Circular Economy”, aims to address novel separation technologies involving resource recovery in various fields. It seeks to include, but is not limited to, recent progress in separation technologies, both at the industrial and scientific levels, as well as studies relating to value-added products and economic assessments.

We look forward to receiving your contributions.

Yours faithfully,

Dr. Da-Qi Cao
Prof. Dr. Qunhui Wang
Dr. Yuanyuan Ren
Dr. Yangmo Zhu
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
ChemEngineering ChemEngineering	3.7	6.0	2017	32.8 Days	CHF 1800	Submit
Fermentation fermentation	4.1	7.7	2015	19.5 Days	CHF 2100	Submit
Membranes membranes	4.2	9.4	2011	15.3 Days	CHF 2200	Submit
Recycling recycling	5.2	7.5	2016	18.9 Days	CHF 1800	Submit
Separations separations	3.5	6.4	2014	16 Days	CHF 2600	Submit
Sustainability sustainability	4.1	8.9	2009	17.9 Days	CHF 2400	Submit

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Published Papers (9 papers)

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All Fermentation Membranes Recycling Sustainability Separations ChemEngineering

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18 pages, 4299 KB  

Open AccessArticle

Breaking Recovery Bottlenecks in Long-Chain Dicarboxylic Acid Extraction: Effect of pH and Solvents

by Priyanka Mondal, Iris Cornet, Inge Noëlle Adrienne Van Bogaert, Anita Buekenhoudt and Kristien De Sitter

Separations 2026, 13(6), 176; https://doi.org/10.3390/separations13060176 - 13 Jun 2026

Viewed by 203

Abstract

Efficient recovery of long-chain dicarboxylic acids (LCDAs) from aqueous fermentation broths is a key challenge for the industrial development of bio-based LCDA production. This study evaluates liquid–liquid extraction (LLE) as a downstream recovery strategy, comparing physical extraction (PE) and reactive extraction (RE) for [...] Read more.

Efficient recovery of long-chain dicarboxylic acids (LCDAs) from aqueous fermentation broths is a key challenge for the industrial development of bio-based LCDA production. This study evaluates liquid–liquid extraction (LLE) as a downstream recovery strategy, comparing physical extraction (PE) and reactive extraction (RE) for DCA 12, DCA 16, and DCA 18. The novelty of this work lies in demonstrating that LCDA extraction is governed by mechanisms fundamentally different from those of short- and medium-chain dicarboxylic acids. Whereas shorter chain dicarboxylic acids are mainly controlled by dissociation degree, LCDA recovery is strongly influenced by carbon-chain apolarity, low aqueous solubility, and compound losses through agglomeration, precipitation, and/or micellization. PEs enabled the selective recovery of the more hydrophobic DCA 16 and DCA 18 over DCA 12, confirming the dominant role of chain length in LCDA separation. In contrast, RE with Aliquat^®336 maximized total LCDA recovery, achieving extraction efficiencies above 85%, but with reduced selectivity. Validation in autoclaved fermentation broth from UCO feedstock confirmed the potential of Aliquat^®336 in octanol for high LCDA recovery, while revealing lower extraction efficiencies than in model mixtures due to broth matrix complexity. Overall, this study establishes LLE as a promising platform for LCDA recovery and highlights that future downstream process design must balance total recovery, chain-length selectivity, and broth-specific matrix effects. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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17 pages, 2823 KB  

Open AccessArticle

Extracellular Polymeric Substance-Intercalated MXene Membranes Toward Removal of Emerging Contaminants

by Da-Qi Cao, Wen-Yu Qu, Yi-Xuan Song, Bi-Xiao Xu, Wen-Yu Zhang and Rongling Wu

Membranes 2026, 16(6), 200; https://doi.org/10.3390/membranes16060200 - 8 Jun 2026

Viewed by 401

Abstract

Resource recovery from excess sludge, specifically the extraction of extracellular polymeric substances (EPSs), has become a frontier issue; yet achieving high-value utilization of this recovered resource remains a key bottleneck. Two-dimensional MXene membranes show great potential for emerging contaminants (ECs) separation owing to [...] Read more.

Resource recovery from excess sludge, specifically the extraction of extracellular polymeric substances (EPSs), has become a frontier issue; yet achieving high-value utilization of this recovered resource remains a key bottleneck. Two-dimensional MXene membranes show great potential for emerging contaminants (ECs) separation owing to their lamellar structure and tunable surface chemistry. In this study, biological macromolecule (BM)-intercalated MXene (BM-M) composite membranes were fabricated using practical EPSs and model EPSs such as sodium alginate (SA), bovine serum albumin (BSA), and silk fibroin (SF) as sustainable intercalators. The interlayer spacing, surface charge, hydrophilicity, mechanical strength, functional group of BM-M membranes and their EC removal behaviors were systematically investigated. The practical EPS performed better than the model EPS, highlighting the importance of molecular complexity in interlayer design. The practical EPS-intercalated MXene (EPS-M) membrane achieved the removal efficiencies of 64.0%, 90.2% and 67.5% for diethyl phthalate (DEP), erythromycin (ERY) and sulfamethoxazole (SMX), respectively. The separation mechanism of ECs mainly included electrostatic, sieving, hydrophobic, and hydrogen bonding. This work highlights the effectiveness of EPS intercalation in tailoring MXene membrane structure for the removal of diverse ECs. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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20 pages, 4136 KB  

Open AccessArticle

Flotation of Spodumene Against Quartz by Punicines

by Stéphanie Mireille Tsanang, Atzin Moran Mendoza, Ali Zgheib, Maximilian Hans Fischer, Annett Wollmann, Ursula E. A. Fittschen, Thomas Schirmer and Andreas Schmidt

Separations 2026, 13(6), 168; https://doi.org/10.3390/separations13060168 - 6 Jun 2026

Viewed by 164

Abstract

Five pH- and light-switchable punicine derivatives were investigated as collectors in the flotation of spodumene and quartz. At the natural pH of the minerals, the punicine substituted with a C17 alkyl residue showed the best recovery under daylight (>5000 lux), with values up [...] Read more.

Five pH- and light-switchable punicine derivatives were investigated as collectors in the flotation of spodumene and quartz. At the natural pH of the minerals, the punicine substituted with a C17 alkyl residue showed the best recovery under daylight (>5000 lux), with values up to 65.0% and 97.8%, and also the highest absolute recovery difference between the two minerals. For pH values of 2 and 12, the punicine collector with a viologen moiety and a C9 alkyl residue shows the best absolute recovery difference, with values of 32.45% and 32.88%, respectively. Studies on the influence of pH, particle size distribution, UV light and darkness, ζ-potential measurements, and IR spectroscopic measurements were carried out to gain insight into the mechanisms. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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26 pages, 1718 KB  

Open AccessArticle

Influence of Ethanol on Ultrasound-Assisted Extraction of Bioactive Compounds from Cocoa Pod Husk and Their Antioxidant, Antihypertensive, and Antihyperglycemic Activity

by Fanny Adabel González-Alejo, Areli Carrera-Lanestosa, Mario Moscosa-Santillán, Ricardo García-Alamilla, Jesús Alfredo Araujo-León, Diakaridia Sangaré, Juan José Acevedo-Fernández and Pedro García-Alamilla

ChemEngineering 2026, 10(4), 43; https://doi.org/10.3390/chemengineering10040043 - 27 Mar 2026

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Abstract

Cocoa pod husk (CPH), a major agro-industrial residue, contains valuable bioactive compounds whose recovery can support sustainable waste valorization. This study evaluated the influence of increasing ethanol concentrations on the ultrasound-assisted extraction (UAE) of bioactive compounds from CPH and their antioxidant, antihypertensive, and [...] Read more.

Cocoa pod husk (CPH), a major agro-industrial residue, contains valuable bioactive compounds whose recovery can support sustainable waste valorization. This study evaluated the influence of increasing ethanol concentrations on the ultrasound-assisted extraction (UAE) of bioactive compounds from CPH and their antioxidant, antihypertensive, and antihyperglycemic activity. Dried and milled CPH was extracted using ethanol–water mixtures (0–100% ethanol) under fixed ultrasonic conditions. Cocoa pod husk powder characterization and the resulting extracts were analyzed in terms of chemical composition (lignocellulosic compounds, proximate and elemental composition, and bromatological composition), antioxidant capacity, and in vivo antihypertensive and antihyperglycemic effects in Wistar rats. The results showed that solvent polarity strongly modulated extraction efficiency: absolute ethanol yielded the highest phenolic (171.43 mg GAE/g) and flavonoid (132.05 mg QE/g) content, whereas hydroalcoholic mixtures, particularly 50:50, enhanced overall antioxidant performance, especially in FRAP. The chemical analysis results showed the selective recovery of compounds such as quercetin, hesperidin, and theobromine, and FTIR-PCA results revealed distinct solvent-dependent chemical profiles. In vivo assays indicated modest blood pressure stabilization and a more pronounced antihyperglycemic effect after chronic administration. Overall, UAE proved an effective, rapid, and solvent-efficient method for CPH valorization, highlighting its potential for producing natural antioxidants applicable to food, nutraceutical, and cosmetic formulations. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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16 pages, 2191 KB  

Open AccessArticle

A Co-Fermentation Strategy from Corncob Hydrolysate to Enhance Simultaneous Co-Production of Lactic Acid and Ethanol

by Xiaona Wang, Yongsheng Li, Yuanchun Zhang, Yuanyuan Ren, Hongzhi Ma, Jianguo Liu and Qunhui Wang

Fermentation 2026, 12(2), 95; https://doi.org/10.3390/fermentation12020095 - 7 Feb 2026

Cited by 2 | Viewed by 844

Abstract

Efficient co-utilization of mixed sugars from lignocellulosic hydrolysates is often hindered by carbon catabolite repression and pretreatment-derived inhibitors. In this study, a co-fermentation strategy using Saccharomyces cerevisiae (S. cerevisiae) and Enterococcus mundtii (E. mundtii) was developed to simultaneously produce [...] Read more.

Efficient co-utilization of mixed sugars from lignocellulosic hydrolysates is often hindered by carbon catabolite repression and pretreatment-derived inhibitors. In this study, a co-fermentation strategy using Saccharomyces cerevisiae (S. cerevisiae) and Enterococcus mundtii (E. mundtii) was developed to simultaneously produce ethanol and lactic acid from non-detoxified corncob hydrolysate. Co-fermentation performed at 39 °C significantly improved substrate utilization compared with monoculture systems, achieving pentose and total sugar utilization percentages of 67.1% and 83.7%, respectively. S. cerevisiae preferentially consumed glucose and effectively detoxified furfural and 5-hydroxymethylfurfural (5-HMF), thereby alleviating inhibitory stress and carbon catabolite repression on E. mundtii. By optimizing the inoculation sequence, a 3 h delayed inoculation of E. mundtii significantly enhanced pentose utilization from 68.6% to 80.2% and increased total sugar utilization to 90.4%. This synergistic co-fermentation strategy provides an effective approach for improving mixed-sugar utilization and multi-product bioconversion efficiency in lignocellulosic biorefineries. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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20 pages, 1277 KB  

Open AccessArticle

Ammonia Recovery from Animal Manure via Hollow Fibre Membrane Contactors: Impact of Filtration Pre-Treatment and Organic Foulants on Mass Transfer and Performance

by Niloufar Azizi, Shaun Connolly, Dominika Krol and Eoin Syron

Membranes 2026, 16(1), 15; https://doi.org/10.3390/membranes16010015 - 31 Dec 2025

Viewed by 1092

Abstract

Ammonia (NH₃) recovery from animal manure offers both environmental and economic benefits by reducing nitrogen emissions and producing valuable fertilisers. Hollow fibre membrane contactors (HFMCs) are a promising technology for this purpose, yet their performance is strongly influenced by the complex [...] Read more.

Ammonia (NH₃) recovery from animal manure offers both environmental and economic benefits by reducing nitrogen emissions and producing valuable fertilisers. Hollow fibre membrane contactors (HFMCs) are a promising technology for this purpose, yet their performance is strongly influenced by the complex composition of manure. In this study, the effects of solids concentration and organic foulants concentration on the mass transfer coefficients governing NH₃ recovery were systematically investigated. Total suspended solids (TSS) were reduced through graded filtration, and protein concentrations in the ammonium solutions were quantified to assess their role in limiting mass transfer. Results showed that TSS concentration primarily affected the shell-side film resistance. After extensive filtration, residual proteins attached to the membrane surface induced partial wetting, thereby reducing the effective membrane mass transfer coefficient. Using a penalty function approach, it was possible to separately describe TSS- and protein-related resistances, enabling improved prediction of effective model coefficients under real world conditions. These findings highlight the dual importance of solid–liquid separation and protein management in optimising HFMC operation for NH₃ recovery and provide a framework for up-scaling the technology in agricultural nutrient management systems. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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31 pages, 4884 KB  

Open AccessReview

A Paradigm Shift in End-of-Life Membrane Recycling: From Conventional to Emerging Techniques

by Noman Khalid Khanzada, Yazan Ibrahim, Muzamil Khatri, Mohamed Khayet and Nidal Hilal

Membranes 2025, 15(12), 350; https://doi.org/10.3390/membranes15120350 - 23 Nov 2025

Cited by 2 | Viewed by 2100

Abstract

The conventional linear life cycle of membrane materials, spanning fabrication, use, and disposal through landfilling or incineration poses serious sustainability challenges. The environmental burden associated with both the production of new membranes and the disposal of end-of-life (EoL) modules is considerable, further intensified [...] Read more.

The conventional linear life cycle of membrane materials, spanning fabrication, use, and disposal through landfilling or incineration poses serious sustainability challenges. The environmental burden associated with both the production of new membranes and the disposal of end-of-life (EoL) modules is considerable, further intensified by the reliance on fossil fuel-derived polymers, toxic solvents, and resource-intensive manufacturing processes. These challenges underscore the urgent need to integrate sustainability principles across the entire membrane life cycle, from raw material selection to reuse and regeneration. Emerging approaches such as membrane regeneration using recyclable polymers based on covalent adaptable networks (CANs) have introduced a new paradigm of closed-loop design, enabling complete depolymerization and reformation. In parallel, more conventional strategies, including the valorization of recycled plastic waste and the upcycling or downcycling of EoL membranes, offer practical routes toward a circular membrane economy. In this review, we consolidate current advances in membrane recycling, critically evaluate their practical constraints, and delineate the technical and environmental challenges that must be addressed for broader implementation. The insights presented here aim to guide the development of next-generation circular membrane technologies that harmonize sustainability with performance. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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21 pages, 8458 KB  

Open AccessArticle

Chemo-Ultrasonication Rehabilitation of Thin-Film Composite Ultrapure Water Membrane for Spent Dialysate Recovery

by Nuhu Dalhat Mu’azu, Mukarram Zubair, Mohammad Saood Manzar, Aesha H. Alamri, Ishraq H. Alhamed, Asaad Al Alawi and Muhammad Nawaz

Membranes 2025, 15(11), 340; https://doi.org/10.3390/membranes15110340 - 14 Nov 2025

Viewed by 1040

Abstract

The ever-increasing number of discarded end-of-life dialysate polyamide thin-film composite membranes (DEoLMs) from presents both environmental and economic challenges for health centers. Traditional thermo-chemical cleaning techniques have been deployed for the rehabilitation of DEoLMs. This study further investigated the application of chemo-ultrasonication rehabilitation [...] Read more.

The ever-increasing number of discarded end-of-life dialysate polyamide thin-film composite membranes (DEoLMs) from presents both environmental and economic challenges for health centers. Traditional thermo-chemical cleaning techniques have been deployed for the rehabilitation of DEoLMs. This study further investigated the application of chemo-ultrasonication rehabilitation of dialysate-production-related DEoLM for potential reuse in spent dialysate recovery considering salt and creatinine—a typical uremic toxin-removal from water. The DEoLM was rehabilitated using low-concentration citric acid (CA) and sodium lauryl sulfate (SLS) under ultrasonic waves (45 kHz, 30 min agitation). Considering different rehabilitation protocols, the synergistic effects of heating (HT) and the chemical agents, with and without and ultrasonic waves (SC) were evaluated through FTIR, SEM, and EDX analyses, and the performance of the rehabilitated DEoLM was assessed via water flux and permeance, and efficiencies for conductivity and creatinine rejection. The fully integrated protocol chemo-ultrasonication (HT + SC + chemical agents) yielded the highest performance, achieving 93.56% conductivity and 96.83% creatinine removal, with water flux of 113.48 L m⁻² h⁻¹ and permeances of 6.31 L m⁻² h⁻¹ bar⁻¹, at markedly reduced pressures. The chemo-sonic-rehabilitated-DEoLM removed the organic–inorganic foulants beyond thermo-chemical cleaning. This suggests that the sonication waves had a great impact regarding rejuvenating the fouled DEoL dialysate membrane, offering a sustainable, cost-effective pathway for extending membrane life, and supporting sustainable water management to achieve circular economy goals within healthcare centers. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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33 pages, 1525 KB  

Open AccessArticle

Mineral Extraction from Mixed Brine Solutions

by M. A. Salman, M. Ahmed, H. Al-Sairfi and Y. Al-Foudari

Separations 2025, 12(10), 266; https://doi.org/10.3390/separations12100266 - 1 Oct 2025

Cited by 2 | Viewed by 1722

Abstract

Sulfate minerals (SMs), such as BaSO₄, SrSO₄, and CaSO₄, precipitate when incompatible solutions from the oil industry, such as seawater (SW) and high-salinity brine solutions (HSBSs), are mixed during the oil production process. To investigate the potentiality [...] Read more.

Sulfate minerals (SMs), such as BaSO₄, SrSO₄, and CaSO₄, precipitate when incompatible solutions from the oil industry, such as seawater (SW) and high-salinity brine solutions (HSBSs), are mixed during the oil production process. To investigate the potentiality to extract SM by mixing three different brine solutions, such as HSBS-1, -2, and -3, with SW, at different temperatures and pressures, a practical simple model was used to predict the saturation index (SI), the quantity of precipitated minerals (Y), and the induction time (t_ind) required for precipitation. From the results, it was found that CaSO₄ hemihydrate and SrSO₄ yield lower amounts of precipitate. BaSO₄ precipitation ranges from 20 to 60 mg/L and 1500 mg/L of CaSO₄ anhydrous under ambient conditions. These findings suggest that recovering low-solubility minerals is technically feasible and environmentally preferable to direct disposal. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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