PPO-based ion exchange membranes with distinct functional groups for bioelectrochemical systems: A comparative study of sulfonated and quaternized types in MFC and MEC modes

Comparison of water and salt transport properties of ion exchange, reverse osmosis, and nanofiltration membranes for desalination and energy applications

Ion transport through ion exchange membranes in Bioelectrochemical Systems (BESs) is different from other electrochemical cells as a result of the complex nature of the electrolyte, as the electrolytes in BESs contain many other cations and anions than H+ and OH−. Moreover, these other cations and anions are generally present in high concentrations and therefore determine the ion transport through the membrane. In this work, we provide a theoretical framework for understanding ion transport across ion exchange membranes in BESs. We show that the transport of cations and anions other than H+ and OH− determines the pH gradient between anode and cathode, and on top of that, also determines the membrane potential. Experimental data for microbial electrolysis cells with cation and anion exchange membranes are used to support the theoretical framework. In case of cation exchange membranes, the total potential loss consists of both the pH gradient and the concentration gradient of other cations, while in case of anion exchange membranes, the total potential loss is lower because part of the pH gradient loss can be recovered at the membrane. The presented work provides a better theoretical understanding of ion transport through ion exchange membranes in general and in BESs specifically.

Removal of organic matter and nitrogen in swine wastewater using an integrated ion exchange and bioelectrochemical system

Streams such as urine and manure can contain high levels of ammonium, which could be recovered for reuse in agriculture or chemistry. The extraction of ammonium from an ammonium-rich stream is demonstrated using an electrochemical and a bioelectrochemical system. Both systems are controlled by a potentiostat to either fix the current (for the electrochemical cell) or fix the potential of the working electrode (for the bioelectrochemical cell). In the bioelectrochemical cell, electroactive bacteria catalyze the anodic reaction, whereas in the electrochemical cell the potentiostat applies a higher voltage to produce a current. The current and consequent restoration of the charge balance across the cell allow the transport of cations, such as ammonium, across a cation exchange membrane from the anolyte to the catholyte. The high pH of the catholyte leads to formation of ammonia, which can be stripped from the medium and captured in an acid solution, thus enabling the recovery of a valuable nutrient. The flux of ammonium across the membrane is characterized at different anolyte ammonium concentrations and currents for both the abiotic and biotic reactor systems. Both systems are compared based on current and removal efficiencies for ammonium, as well as the energy input required to drive ammonium transfer across the cation exchange membrane. Finally, a comparative analysis considering key aspects such as reliability, electrode cost, and rate is made. This video article and protocol provide the necessary information to conduct electrochemical and bioelectrochemical ammonia recovery experiments. The reactor setup for the two cases is explained, as well as the reactor operation. We elaborate on data analysis for both reactor types and on the advantages and disadvantages of bioelectrochemical and electrochemical systems.

<p>Microbial fuel cells (MFCs) are a bioelectrochemical system where electrochemically active bacteria convert organic waste into electricity. Poly(vinyl alcohol) (PVA) and chitosan (CS) are polymers that have been studied as potential alternative ion exchange membranes to Nafion for many electrochemical systems. This study examined the optimal mixing ratio of PVA and chitosan CS in a PVA:CS composite membrane for MFC applications. PVA:CS composite membranes with 1:1, 2:1, and 3:1 ratios were synthesized and tested. The water uptake and ion exchange capacity, Fourier transform infrared spectra, and scanning electron microscopy images were analyzed to determine the physicochemical properties of PVA:CS membranes. The prepared membranes were applied to the ion exchange membrane of the MFC system, and their effects on the electrochemical performance were evaluated. These results showed that the composite membrane with a 3:1 (PVA:CS) ratio showed comparable performance to the commercialized Nafion membrane and produced more electricity than the other synthesized membranes. The PVA:CS membrane implemented MFCs produced a maximum power density of 0.026 mW cm<sup>−2</sup> from organic waste with stable performance. Therefore, it can be applied to a cost-effective MFC system.</p>

Recent developments in ion exchange : Elsevier Applied Science, London, 1987 (ISBN 1-85166-101-8). xi+423 pp. Price £45.00

Ion exchange membranes are used in practically every industry; however, most of them have defects such as low permeability and poor oxidation resistance. In this paper, cation-exchange membranes were prepared with poly (vinylidene fluoride) (PVDF) blended with nano-SiO2, nano-Al2O3 and nano-ZnO. Sulfonic acid groups were injected into the membrane prepared by styrene grafting and sulfonation. The methods used for characterizing the prepared membranes were Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and electrochemical measurements. Membrane performance, such as the ion exchange capacity (IEC), water uptake (WU), transport number, membrane permselectivity, membrane resistance, functional groups, and morphology were also evaluated. The hydrophilia, IEC, and permselectivity of cation-exchange membranes depended on the nanoparticle content of the membrane matrix. High transport property values were obtained, which increased with increasing nano-SiO2/Al2O3/ZnO weight fractions. Finally, the cation-exchange membranes prepared with 1.5% nano-SiO2, 2.0% nano-Al2O3 or 2.0% nano-ZnO all exhibited excellent membrane properties, including membrane permselectivity (PVDF/2% ZnO-g-PSSA membranes, 94.9%), IEC (PVDF/2% Al2O3-g-PSSA membranes, 2.735 mmol·g−1), and oxidation resistance (PVDF/1.5% SiO2-g-PSSA membranes, 2.33%). They can be used to separate applications in a variety of different areas, such as water treatment, electro-driven separation, heavy metal smelting, or other electrochemical processes.

Ion exchange equilibrium between ion exchange membrane and electrolyte solutions

A low cost cation exchange membrane to be used in a specific bioelectrochemical system has been developed using poly(ether ether ketone) (PEEK). This material is presented as an alternative to current commercial ion exchange membranes that have been primarily designed for fuel cell applications. To increase the hydrophilicity and ion transport of the PEEK material, charged groups are introduced through sulfonation. The effect of sulfonation and casting conditions on membrane performance has been systematically determined by producing a series of membranes synthesized over an array of reaction and casting conditions. Optimal reaction and casting conditions for producing SPEEK ion exchange membranes with appropriate performance characteristics have been established by this uniquely systematic experimental series. Membrane materials were characterized by ion exchange capacity, water uptake, swelling, potential difference and NMR analysis. Testing this extensive membranes series established that the most appropriate sulfonation conditions were 60 °C for 6 h. For mechanical stability and ease of handling, SPEEK membranes cast from solvent casting concentrations of 15%–25% with a resulting thickness of 30–50 µm were also found to be most suitable from the series of tested casting conditions. Drying conditions did not have any apparent impact on the measured parameters in this study. The conductivity of SPEEK membranes was found to be in the range of 10−3 S cm−1, which is suitable for use as a low cost membrane in the intended bioelectrochemical systems.

Relationships between transport and physical–mechanical properties of ion exchange membranes

The ion exchange membrane is a key component in many electrochemical membrane processes such as fuel cells, flow batteries and electrolysers. Typically, these ion exchange membranes are assembled in stacks and allow the transport of the charge carrying component, i.e. a cation (e.g. proton) or an anion, while retaining the other species and electrolytes preventing their crossover to the other side of the cell. Simultaneously electrons travel through an external circuit powering a device or to store energy.Conventional ion exchange membranes have two major problems: They are based on expensive materials (e.g. Nafion®e. PFSA; perfluorosulfonic acid) or on environmentally harmful chemicals and chemical reactions. Although due to its molecular structure and composition, PFSA membranes show good performances, the major limitation of PFSA membranes is the very high material costs often contributing for more than 35% to the total stack costs [1, 2].One of the major challenges of ion exchange membrane development is the tradeoff between high ion transport rates through the membrane while simultaneously preventing electrolyte crossover [3]. This talk will first present a comprehensive overview of required membrane characteristics and an extensive benchmark study of state-of-the-art performances of ion exchange membranes in different electro-membrane processes. Following on this, the challenges in ion exchange membrane development will be addressed and most importantly two new routes for the development of next generation ion exchange membranes will be presented and their characteristics will be compared to those of a series of extensively benchmarked commercially available ion exchange membranes.The first approach, electrospinning is an effective, versatile method to produce cheap ion exchange membranes [3-6]: Multiple polymers can be employed simultaneously during spinning and this is combined with high degrees of interchain entanglement. This results in an interconnected network of ionic pathways that promote high ionic conductivities confined in a matrix of an inert polymer that guarantees high rejections towards electrolytes to prevent crossover (Figure 1a). Moreover, it is a simple technique that can be easily adapted to large scale production.The second approach uses liquid crystalline (LC) polymers to make ion exchange membranes [7]. This approach has the potential to offer true molecular selectivity and a high degree of flexibility to actually tune this selectivity. LC polymer materials self-organize into structures with well defined isoporosity (Figure 1b). Subsequent template removal or chemical bond cleavage with an acid or base results in the formation of molecular pores. The pores of these materials can be functionalized and depending on the functionality, selectivity can be introduced. Depending on the bulkiness of the functional group also pore sizes can be smaller or bigger. Crosslinking of the formed structures allows control over the swelling of the material and with that reduces crossover. In this way one can rely on both charge-charge interactions as well on size sieving to separate species. The major challenge is the formation of organized structures over larger length scales and the identification of structure-property relationships and with that control over the membrane separation performance.Design principles of both newly developed membrane types are discussed, the membranes are extensively characterized and their performance in electrochemical processes is compared to that of conventional ion exchange membranes. The talk is concluded with a future outlook on the perspectives of ion exchanhe membrane development. T. Cho, et al., Energy Technol. 1 (2013) 596–608. https://doi.org/10.1002/ente.201300108.Lin, et al., J. Electrochem. Soc. 163 (2016) A5049–A5056. https://doi.org/10.1149/2.0071601jes.A. Hugo, et al., Journal of Membrane Science 566 (2018) 406. 10.1016/j.memsci.2018.09.006.Woo Park, et al., J. Membr. Sci. 541 (2017) 85–92. https://doi.org/10.1016/j.memsci.2017.06.086.Choi, et al., Macromolecules. 41 (2008) 4569–4572. https://doi.org/10.1021/ma800551w.J.B. Ballengee, P.N. Pintauro, Macromolecules. 44 (2011) 7307–7314. https://doi.org/10.1021/ma201684j.Kloos, et al., Journal of Membrane Science 620 (2021) 118849. https://doi.org/10.1016/j.memsci.2020.118849 Figure 1

ABSTRACTMost tropical plants produce fleshy fruits that are dispersed primarily by vertebrate frugivores. Behavioral disparities among vertebrate seed dispersers could influence patterns of seed distribution and thus forest structure. This study investigated the relative importance of arboreal seed dispersers and seed predators on the initial stage of forest organization–seed deposition. We asked the following questions: (1) To what degree do arboreal seed dispersers influence the species richness and abundance of the seed rain? and (2) Based on the plant species and strata of the forest for which they provide dispersal services, do arboreal seed dispersers represent similar or distinct functional groups? To answer these questions, seed rain was sampled for 12 months in the Dja Reserve, Cameroon. Seed traps representing five percent of the crown area were erected below the canopies of 90 trees belonging to nine focal tree species: 3 dispersed by monkeys, 3 dispersed by large frugivorous birds, and 3 wind‐dispersed species. Seeds disseminated by arboreal seed dispersers accounted for ca 12 percent of the seeds and 68 percent of the seed species identified in seed traps. Monkeys dispersed more than twice the number of seed species than large frugivorous birds, but birds dispersed more individual seeds. We identified two distinct functional dispersal groups, one composed of large frugivorous birds and one composed of monkeys, drop dispersers, and seed predators. These groups dispersed plants found in different canopy strata and exhibited low overlap in the seed species they disseminated. We conclude it is unlikely that seed dispersal services provided by monkeys could be compensated for by frugivorous birds in the event of their extirpation from Afrotropical forests.

Most tropical plants produce fleshy fruits that are dispersed primarily by vertebrate frugivores. Behavioral disparities among vertebrate seed dispersers could influence patterns of seed distribution and thus forest structure. This study investigated the relative importance of arboreal seed dispersers and seed predators on the initial stage of forest organization—seed deposition. We asked the following questions: (1) To what degree do arboreal seed dispersers influence the species richness and abundance of the seed rain? and (2) Based on the plant species and strata of the forest for which they provide dispersal services, do arboreal seed dispersers represent similar or distinct functional groups? To answer these questions, seed rain was sampled for 12 months in the Dja Reserve, Cameroon. Seed traps representing five percent of the crown area were erected below the canopies of 90 trees belonging to nine focal tree species: 3 dispersed by monkeys, 3 dispersed by large frugivorous birds, and 3 wind-dispersed species. Seeds disseminated by arboreal seed dispersers accounted for ca 12 percent of the seeds and 68 percent of the seed species identified in seed traps. Monkeys dispersed more than twice the number of seed species than large frugivorous birds, but birds dispersed more individual seeds. We identified two distinct functional dispersal groups, one composed of large frugivorous birds and one composed of monkeys, drop dispersers, and seed predators. These groups dispersed plants found in different canopy strata and exhibited low overlap in the seed species they disseminated. We conclude it is unlikely that seed dispersal services provided by monkeys could be compensated for by frugivorous birds in the event of their extirpation from Afrotropical forests.

Bioelectrochemical systems recover valuable components and energy in the form of hydrogen or electricity from aqueous organic streams. We derive a one-dimensional steady-state model for ion transport in a bioelectrochemical system, with the ions subject to diffusional and electrical forces. Since most of the ionic species can undergo acid-base reactions, ion transport is combined in our model with infinitely fast ion acid-base equilibrations. The model describes the current-induced ammonia evaporation and recovery at the cathode side of a bioelectrochemical system that runs on an organic stream containing ammonium ions. We identify that the rate of ammonia evaporation depends not only on the current but also on the flow rate of gas in the cathode chamber, the diffusion of ammonia from the cathode back into the anode chamber, through the ion exchange membrane placed in between, and the membrane charge density.

In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H2PO4 ‐), nitrate (NO3 ‐), and sulfate (SO4 2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha‐1 as triple superphosphate. The efficacy of the IEM was high (85% for SO4 2‐, and 92% for H2PO4 ‐ and NO3 ‐). Statistically significant correlations were obtained between the H2PO4 ‐ extracted by IEM and the H2PO4 ‐ obtained by the Bray P1 procedure (r2=0.936) and with the H2PO4 ‐ extracted using Saunders and Williams (1955) procedure (r2=0.370). The correlation obtained between the amount of NO3 ‐ extracted with IEM and that obtained using 2M potassium chloride (KCl) was also highly significant (r2=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the concentrations of soil available H2PO4 ‐, NO3 ‐, and SO4 2‐ ions, which are of great plant nutrition interest. Phosphorus extractable with IEM yielded a close relationship with biomass production and could be used for determining the P requirement of these forest trees.