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A special issue of Membranes (ISSN 2077-0375). This special issue belongs to the section "Membrane Processing and Engineering".

Deadline for manuscript submissions: closed (15 May 2023) | Viewed by 15996

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Dr. Daqi Cao

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Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies, Key Laboratory of Urban Stormwater System and Water Environment, Beijing University of Civil Engineering and Architecture, No. 1 Zhanlanguan Rd, Xicheng District, Beijing 100044, China
Interests: membrane separation; preparation of membranes; 2D materials; nanofiber; recovery of resources from wastewater; removal of trace contaminants in wastewater; sludge dewatering; micro–nano energy

Special Issue 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 selected for 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.

This Special Issue of Membranes, entitled “Separation Techniques and Circular Economy”, aims to address novel separation technologies involving resource recovery in wastewater treatment or other 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 related to value-added products and economic assessments.

We look forward to receiving your contributions.

Dr. Daqi Cao
Guest Editor

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. Membranes 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 2700 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

separation techniques
membrane separation
liquid–solid separation
clean separation
extraction
resource recovery
value-added product
economic assessment

Published Papers (10 papers)

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Editorial

Jump to: Research

4 pages, 200 KiB

Open AccessEditorial

Separation Techniques and Circular Economy

by Da-Qi Cao

Membranes 2023, 13(9), 778; https://doi.org/10.3390/membranes13090778 - 04 Sep 2023

Viewed by 1190

Abstract

Efficient separation techniques play an important role in the process of resource recovery, and these techniques include physical, chemical, physicochemical, and/or biological methods that are selected for their low cost and low energy consumption and for being free of secondary pollution [...] Full article

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

Research

Jump to: Editorial

14 pages, 3818 KiB

Open AccessArticle

Effective Removal of Acetaldehyde Using Piperazine/Nitric Acid Co-Impregnated Bead-Type Activated Carbon

by Yu-Jin Kang, Yu-Jin Kim, Seong-Jin Yoon, Dong-Jin Seo, Hye-Ryeong Cho, Kyeongseok Oh, Seong-Ho Yoon and Joo-Il Park

Membranes 2023, 13(6), 595; https://doi.org/10.3390/membranes13060595 - 12 Jun 2023

Cited by 1 | Viewed by 1057

Abstract

Acetaldehyde (CH₃CHO) in the atmosphere is associated with adverse health effects. Among the various options for use in removing CH₃CHO, adsorption is often employed because of its convenient application and economical processes, particularly when using activated carbon. In previous studies, the surface of activated carbon has been modified with amines to remove CH₃CHO from the atmosphere via adsorption. However, these materials are toxic and can have harmful effects on humans when the modified activated carbon is used in air-purifier filters. Therefore, in this study, a customized bead-type activated carbon (BAC) with surface modification options via amination was evaluated for removing CH₃CHO. Various amounts of non-toxic piperazine or piperazine/nitric acid were used in amination. Chemical and physical analyses of the surface-modified BAC samples were performed using Brunauer–Emmett–Teller measurements, elemental analyses, and Fourier transform infrared and X-ray photoelectron spectroscopy. The chemical structures on the surfaces of the modified BACs were analyzed in detail using X-ray absorption spectroscopy. The amine and carboxylic acid groups on the surfaces of the modified BACs are critical in CH₃CHO adsorption. Notably, piperazine amination decreased the pore size and volume of the modified BAC, but piperazine/nitric acid impregnation maintained the pore size and volume of the modified BAC. In terms of CH₃CHO adsorption, piperazine/nitric acid impregnation resulted in a superior performance, with greater chemical adsorption. The linkages between the amine and carboxylic acid groups may function differently in piperazine amination and piperazine/nitric acid treatment. Full article

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

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14 pages, 2376 KiB

Open AccessArticle

Evaluation of Efficiently Removing Secondary Effluent Organic Matters (EfOM) by Al-Based Coagulant for Wastewater Recycling: A Case Study with an Industrial-Scale Food-Processing Wastewater Treatment Plant

by Yu Cheng, Qiangqiang Cheng, Chengjin Zhao, Xianghao Ren, Yu Wang, Yingying Kou, Kangmin Chon, Myung-Han Ko and Moon-Hyun Hwang

Membranes 2023, 13(5), 510; https://doi.org/10.3390/membranes13050510 - 12 May 2023

Cited by 2 | Viewed by 1279

Abstract

The reuse of wastewater has been identified as an important initiative for the sustainable development of the environment; thus, the removal of secondary effluent organic matter (EfOM) to ensure the safety of reused wastewater is the key step and a subject of extensive research. In this study, Al₂(SO₄)₃ and anionic polyacrylamide were selected as coagulant and flocculant, respectively, for the treatment of secondary effluent from a food-processing industry wastewater treatment plant to meet the standard regulatory specifications for water reuse. In this process, the removal efficiencies of chemical oxygen demand (COD), components with UV₂₅₄, and specific ultraviolet absorbance (SUVA) were 44.61%, 25.13%, and 9.13%, respectively, with an associated reduction in chroma and turbidity. The fluorescence intensities (Fmax) of two humic-like components were reduced during coagulation, and microbial humic-like components of EfOM had a better removal efficiency because of a higher Log Km value of 4.12. Fourier transform infrared spectroscopy showed that Al₂(SO₄)₃ could remove the protein fraction of the soluble microbial products (SMP) of EfOM by forming a loose SMP protein complex with enhanced hydrophobicity. Furthermore, flocculation reduced the aromaticity of secondary effluent. The cost of the proposed secondary effluent treatment was 0.034 CNY t⁻¹ %COD⁻¹. These results demonstrate that the process is efficient and economically viable for EfOM removal to realize food-processing wastewater reuse. Full article

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

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18 pages, 2517 KiB

Open AccessArticle

Phenylalanine Losses in Neutralization Dialysis: Modeling and Experiment

by Anton Kozmai, Mikhail Porozhnyy, Violetta Gil and Lasaad Dammak

Membranes 2023, 13(5), 506; https://doi.org/10.3390/membranes13050506 - 11 May 2023

Cited by 2 | Viewed by 939

Abstract

A non-steady state mathematical model of an amino acid (phenylalanine (Phe)) and mineral salt (NaCl) solution separation by neutralization dialysis (ND) carried out in a batch mode is proposed. The model takes into account the characteristics of membranes (thickness, ion-exchange capacity, and conductivity) and solutions (concentration, composition). As compared to previously developed models, the new one considers the local equilibrium of Phe protolysis reactions in solutions and membranes and the transport of all the phenylalanine forms (zwitterionic, positively and negatively charged) through membranes. A series of experiments on ND demineralization of the NaCl and Phe mixed solution was carried out. In order to minimize Phe losses, the solution pH in the desalination compartment was controlled by changing the concentrations of the solutions in the acid and alkali compartments of the ND cell. The validity of the model was verified by comparison of simulated and experimental time dependencies of solution electrical conductivity and pH, as well as the concentration of Na⁺, Cl⁻ ions, and Phe species in the desalination compartment. Based on the simulation results, the role of Phe transport mechanisms in the losses of this amino acid during ND was discussed. In the experiments carried out, the demineralization rate reached 90%, accompanied by minimal Phe losses of about 16%. Modeling predicts a steep increase in Phe losses when the demineralization rate is higher than 95%. Nevertheless, simulations show that it is possible to achieve a highly demineralized solution (by 99.9%) with Phe losses amounting to 42%. Full article

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

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15 pages, 3124 KiB

Open AccessArticle

The Performance of Ultrafiltration Process to Further Refine Lactic Acid from the Pre-Microfiltered Broth of Kitchen Waste Fermentation

by Yan Guo, Chenglong Li, Hongjun Zhao, Xiaona Wang, Ming Gao, Xiaohong Sun and Qunhui Wang

Membranes 2023, 13(3), 330; https://doi.org/10.3390/membranes13030330 - 13 Mar 2023

Cited by 1 | Viewed by 1206

Abstract

Lactic acid (LA) is an important chemical material facing rapid demand in recent years. The oriented fermentation of kitchen waste is a promising route for economic LA production. However, the refinement of LA from fermentation broth is a spiny issue. In this study, the performance of ultrafiltration (UF) process for the refinement of LA from the pre-microfiltered broth of kitchen waste fermentation was first investigated. The results showed that with 50 KDa polyethersulfone membrane, under the optimum pressure of 120 KPa, the pH of 6.0, and the backflushing mode with the deionized water for 3 min, the best performance was achieved with the chroma removal efficiency, turbidity removal efficiency, protein removal efficiency and total sugar removal efficiency of 54.3%, 89.8%, 71.7% and 58.5%, respectively, and LA recovery efficiency was 93.6%. The results indicated that the UF process could further effectively refine the pre-microfiltered broth of kitchen waste fermentation, and the combination of microfiltration and UF process is ideal for achieving desirable LA refinement performance. This study verified the feasibility of UF process in LA refinement from pre-microfiltered broth of kitchen waste fermentation, and based on the results, the further exploration of proper post-process to treat UF filtrate for obtaining LA product with higher quality should be explored in the future. Full article

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

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15 pages, 3674 KiB

Open AccessArticle

The Performance of Microfiltration Process for Purifying Lactic Acid in the Fermented Broth of Kitchen Waste

by Yan Guo, Chenglong Li, Hongjun Zhao, Ming Gao and Qunhui Wang

Membranes 2023, 13(3), 280; https://doi.org/10.3390/membranes13030280 - 27 Feb 2023

Cited by 1 | Viewed by 2127

Abstract

Fermentation broth is plentiful with lactic acid, an important chemical applied in many fields, such as food processing, the chemical industry, and cosmetics. However, the purification of the lactic acid from the broth is still troublesome, when considering the economy. This study first investigated the purification performance of microfiltration (MF) membrane technology for a fermentation broth from kitchen waste. The effect of operation pressure, broth pH, and membrane flushing mode on the membrane filtration performance were investigated. In addition, the change in filtration performance over the increase in cycle time was also investigated. The results showed that under the optimum pressure of 100 KPa, pH of 6.0, and a backflushing mode with deionized water for 3 min, the best performance was achieved, with chroma removal, turbidity removal, protein removal and total sugar removal efficiencies of 60, 92.8, 57.64 and 32.93%, respectively. The results indicated that the MF process could be a desirable broth purification process to some extent, and it is promising in actual application. The MF process combined with other post-purification processes will form the ideal process system, which should be explored in future research. Full article

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

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15 pages, 1794 KiB

Open AccessArticle

Calcium Alginate Production through Forward Osmosis with Reverse Solute Diffusion and Mechanism Analysis

by Da-Qi Cao, Kai Tang, Wen-Yu Zhang, Cheng Chang, Jia-Lin Han, Feng Tian and Xiao-Di Hao

Membranes 2023, 13(2), 207; https://doi.org/10.3390/membranes13020207 - 08 Feb 2023

Cited by 4 | Viewed by 1739

Abstract

Calcium alginate (Ca-Alg) is a novel target product for recovering alginate from aerobic granular sludge. A novel Ca-Alg production method was proposed herein where Ca-Alg was formed in a sodium alginate (SA) feed solution (FS) and concentrated via forward osmosis (FO) with Ca²⁺ reverse osmosis using a draw solution of CaCl₂. An abnormal reverse solute diffusion was observed, with the average reverse solute flux (RSF) decreasing with increasing CaCl₂ concentrations, while the average RSF increased with increasing alginate concentrations. The RSF of Ca²⁺ in FS decreased continuously as the FO progressed, using 1.0 g/L SA as the FS, while it increased initially and later decreased using 2.0 and 3.0 g/L SA as the FS. These results were attributed to the Ca-Alg recovery production (CARP) formed on the FO membrane surface on the feed side, and the percentage of Ca²⁺ in CARP to total Ca²⁺ reverse osmosis reached 36.28%. Scanning electron microscopy and energy dispersive spectroscopy also verified CARP existence and its Ca²⁺ content. The thin film composite FO membrane with a supporting polysulfone electrospinning nanofiber membrane layer showed high water flux and RSF of Ca²⁺, which was proposed as a novel FO membrane for Ca-Alg production via the FO process with Ca²⁺ reverse diffusion. Four mechanisms including molecular sieve role, electrification of colloids, osmotic pressure of ions in CARP, and FO membrane structure were proposed to control the Ca-Alg production. Thus, the results provide further insights into Ca-Alg production via FO along with Ca²⁺ reverse osmosis. Full article

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

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23 pages, 3863 KiB

Open AccessArticle

Screening and Scale-up of Nanofiltration Membranes for Concentration of Lactose and Real Whey Permeate

by Katrin Hofmann and Christof Hamel

Membranes 2023, 13(2), 173; https://doi.org/10.3390/membranes13020173 - 31 Jan 2023

Cited by 2 | Viewed by 1818

Abstract

In dairy industry huge quantities of whey accumulate as a by-product. In particular the containing lactose was not produced profitably in the past. Thus, the trend goes towards modification and sustainable use of lactose for which a concentration step is required. Nanofiltration (NF) has shown to be a good choice since partial demineralization can be realized in parallel. Therefore, in this study, 10 commercial polymer NF membranes were studied in detail and systematically for their suitability to concentrate lactose, with the proviso of high flux and high to complete rejection. Preliminary trials were conducted with flat-sheet membranes and a lactose model solution and the influence of transmembrane pressure (TMP), temperature and lactose concentration was studied. Finally, results were evaluated by using spiral wound modules and real industrial whey permeate. The results offered that a membrane screening is essentially since no correlation between molecular weight cut-off (MWCO) and permeate flow could be found. The conclusions found for the lactose model solution were in good agreement with the whey permeate, but as the ions contribute to the osmotic pressure of the feed the deviations increase in the course of concentration since ions are also partly retained. Full article

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

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11 pages, 2255 KiB

Open AccessArticle

Separation Properties of Plasmid DNA Using a Two-Stage Particle Adsorption-Microfiltration Process

by Nobuyuki Katagiri, Daisuke Shimokawa, Takayuki Suzuki, Masahito Kousai and Eiji Iritani

Membranes 2023, 13(2), 168; https://doi.org/10.3390/membranes13020168 - 29 Jan 2023

Cited by 1 | Viewed by 1842

Abstract

Plasmid DNA is used as a vector for gene therapy and DNA vaccination; therefore, the establishment of a mass production method is required. Membrane filtration is widely employed as a separation method suitable for the mass production of plasmid DNA. Furthermore, the separation of plasmid DNA using microfiltration and ultrafiltration membranes is being investigated. Because plasmid DNA has a circular structure, it undergoes significant deformation during filtration and easily permeates the membrane, hindering the selection of separation membranes based on molecular weight. In this study, we applied affinity microfiltration to plasmid DNA purification. α-Fe₂O₃ with an isoelectric point of approximately 8 and a particle size of 0.5 μm was selected as the ligand for two-stage affinity microfiltration of plasmid DNA. In the first stage of microfiltration, the experiment was conducted at a pH of 5, and a cake of α-Fe₂O₃ with bound plasmid DNA was obtained. Next, liquid permeation (pH 9 and 10) through the cake was performed to elute the bound plasmid DNA. Plasmid DNA was eluted during the early phase of liquid permeation at pH 10. Furthermore, agarose gel analysis confirmed the usefulness of the two-stage affinity microfiltration method with adsorption and desorption for plasmid DNA purification. Full article

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

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20 pages, 4774 KiB

Open AccessArticle

Recovery of Extracellular Polymeric Substances from Excess Sludge Using High-Flux Electrospun Nanofiber Membranes

by Da-Qi Cao, Xiao-Dan Liu, Jia-Lin Han, Wen-Yu Zhang, Xiao-Di Hao, Eiji Iritani and Nobuyuki Katagiri

Membranes 2023, 13(1), 74; https://doi.org/10.3390/membranes13010074 - 07 Jan 2023

Cited by 2 | Viewed by 1698

Abstract

The recycling of extracellular polymeric substances (EPSs) from excess sludge in wastewater treatment plants has received increasing attention in recent years. Although membrane separation has great potential for use in EPS concentration and recovery, conventional membranes tend to exhibit low water flux and high energy consumption. Herein, electrospun nanofiber membranes (ENMs) were fabricated using polyvinylidene fluoride (PVDF) and used for the recovery of EPSs extracted from the excess sludge using the cation exchange resin (CER) method. The fabricated ENM containing 14 wt.% PVDF showed excellent properties, with a high average water flux (376.8 L/(m²·h)) and an excellent EPS recovery rate (94.1%) in the dead-end filtration of a 1.0 g/L EPS solution at 20 kPa. The ENMs displayed excellent mechanical strength, antifouling properties, and high reusability after five recycles. The filtration pressure had a negligible effect on the average EPS recovery rate and water flux. The novel dead-end filtration with an EPS filter cake on the ENM surface was effective in removing heavy-metal ions, with the removal rates of Pb²⁺, Cu²⁺, and Cr⁶⁺ being 89.5%, 73.5%, and 74.6%, respectively. These results indicate the potential of nanofiber membranes for use in effective concentration and recycling of EPSs via membrane separation. Full article

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

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