Ion Exchange Capacity Of Membranes Research Articles

Morphology and methanol permeability of sulfosuccinic acid cross‐linked polyvinyl alcohol and polyvinyl alcohol/Nafion nanofibrous membranes

AbstractCross‐linking of polyvinyl alcohol (PVA) and polyvinyl alcohol/Nafion (PVA/Nafion) electrospun nanofibers with sulfosuccinic acid (SSA) was investigated to assess their characterization and the effects of cross‐linking on the methanol permeability performance of the nanofibrous membranes. SSA was directly incorporated into the electrospinning polymer solution. The morphology, chemical functional groups, thermal stability, water stability and water swelling of the resulting nanofibers were examined. The effects of SSA concentration on ion exchange capacity (IEC) and methanol permeability of the nanofibrous membranes were discussed. Bead‐free and smooth nanofibers were produced for all SSA concentrations with a mean nanofiber diameter of 240–270 nm. It was shown that 15% SSA concentration was suitable for preserving the morphology of PVA nanofibers against water, while the morphology of PVA/Nafion nanofibers was preserved even without cross‐linking. The increase in SSA concentration led to increase in swelling in water. SSA cross‐linking was also shown to increase the thermal stability of the produced nanofibers. IEC increased by the increase in SSA concentration, while increase in SSA concentration led to a decrease in methanol permeability.

Advanced hybrid membrane constructed with silicon carbide, graphene oxide and functionalized silicon carbide for vanadium permeability, proton conductivity to battery and fuel cell applications

The energy sector is currently exploring eco-friendly energy conversion and storage devices, as an alternative to traditional fossil fuel devices. A unique hybrid proton exchange membrane is developed for proton exchange membrane fuel cells (PEMFC) and vanadium redox flow battery (VRFB) application. Polymeric nanocomposite membranes are effective for the selective and controlled transportation of ions between the electrodes. This study utilizes various modifiers such as GO, SGO, SPES, and SiC, to modify the PES polymer matrix. Analysis of the functional groups confirmed the presence of modifiers and hydroxyl groups on the nanocomposite membrane. Additionally, the use of Field Emission Scanning Electron Microscopy (FESEM) validated the existence of honeycomb and sponge-like voids as well as the surface morphology on the membrane surface. The incorporation of modifiers into the nanocomposite membrane matrix serves as a reliable barrier for the transport of vanadium ions, leading to a significant reduction in vanadium ion permeability across the membrane. The mechanical properties and ion exchange capacity of nanocomposite membranes are enhanced, while the permeability of VO2+ decreases compared to that of the bare PES membrane. The enhancement of proton conductivity is further achieved with the utilization of modifiers in PES polymer. As compared to bare PES membrane, PES/SPES + SGO (5%) exhibits less than half the permeability for vanadium, and PES/SiC shows 44.03 % elongation means twice of bare PES membrane.

Comparative study of random and block SPEEK copolymers for high-temperature proton exchange membrane electrolysis

Traditionally, High-temperature proton Exchange Membrane Electrolysis (HT-PEME) has relied on costly and exceptionally hydrogen-permeable PFSA ionomers like Nafion®, Flemion®, and Aciplex®. Sulfonated Poly (ether ether ketone) (SPEEK) membranes have been developed as potential substitutes for the highly hydrogen permeable Nafion® membranes. The ion exchange capacity (IEC) of SPEEK membranes has been varied, ranging from 0.5 to 2.2 meq/g, to enhance their performance. Furthermore, the incorporation of ion-conducting units into these polymers is explored using both random and block copolymerization approaches. At 75 °C, SPEEK membranes exhibit significantly lower hydrogen diffusivity (35–50 barriers) compared to Nafion® and Flemion® membranes (∼202 barriers). Among SPEEK yttria-stabilized zirconia membranes (YSZM), those produced through random copolymerization exhibit marginally greater proton-to-hydrogen selectivity than YSZM derived from block SPEEK copolymers with a similar ion exchange capacity (IEC). This could be ascribed to the improved hydrogen-blocking capability resulting from an underdeveloped hydrophilic component. Among the SPEEK membranes tested, the random SPEEK membrane with an IEC of approximately 1.9 meq/g demonstrates superior performance (6.8 A/cm2) compared to a similarly thick (∼45 μm) Flemion® membrane (4.4 A/cm2) at 2.2 V. However, during an accelerated stress test involving 410 successive fluctuating flow densities of 2.8 and 0.04 A/cm2 imitating the alternating period's cycles of a water electrolyzer, the random SPEEK membrane exhibits a higher degradation rate (860 μV/h) compared to Flemion® and Nafion® (505 μV/h).

Static and dynamic properties investigation of modified polyethersulfone membrane for direct methanol fuel cell applications

The present study's main focus is understanding the impact of modification, especially through phosphoric acid and acetic acid, on polyethersulfone (PES) membranes for direct methanol fuel cell application, as sulfonation is the preferred modification method. The cross-linking introduces the sulfonate, phosphonate, and carboxylate group in the polymer matrix, while the membrane's semi-crystalline nature and homogeneous surface are confirmed through instrumental analysis. The high ion exchange capacity and water retention capacity of the phosphoric acid cross-linked PES membrane (PPES-2) reveal its potentiality. The impact of different hydration levels and temperatures on proton conductivity indicates that based on the operating conditions, the cross-linked membrane can be used, such as at high temperatures and 50 % hydration level, the PPES-2 membrane shows high proton conductivity as well as has low methanol crossover due to the presence of hydroxyl group. At the same time, the acetic acid-treated PES (CPES-2) membrane shows high proton conductivity at 50 % hydration level and low temperature. The same is confirmed through molecular dynamic simulation by understanding their dynamic and static properties. The PPES-2 membrane shows maximum power density (0.34 Wcm−2). In conclusion, the study indicates that PES modification can be done through phosphorylation and carboxylation, apart from sulfonation.

How can we design anion-exchange membranes to achieve longer fuel cell lifetime?

The substantial advancements and availability of new cost-effective materials have drawn significant attention to the anion-exchange membrane fuel cell (AEMFC) technology. The anion exchange membrane (AEM) is a core component in AEMFCs, essential for conducting hydroxide ions and controlling water transport between the fuel cell electrodes. In this study, we apply a numerical model to investigate the relationship and sensitivity of AEMFC performance and its stability to key AEM properties. Our findings show that membrane maximum hydration level (λmax) has the most significant impact on AEMFC lifetime, followed by membrane ion-exchange capacity, water diffusivity, and membrane thickness. We also demonstrate the significance of improving the stability of the functional group to AEMFC lifetime, while AEM hydroxide conductivity shows a negligible effect on AEMFC lifetime. Finally, we provide a simple algebraic functional relationship between key dimensionless parameters as well as a machine learning-based analysis of the relationship between AEM parameters and AEMFC lifetime. Through these analyses, we calculate the lifetime of selected membranes from the literature and compare them to the measured operation time. This study summarizes and highlights important AEM property targets suggested to improve AEM design to boost the performance stability of AEMFCs.

Novel Proton Exchange Membranes Based on Sulfonated Poly(acrylonitrile-co-glycidyl methacrylate)/Poly(vinyl chloride) Composite

In this study, novel proton exchange membranes (PEMs) based on a composite of sulfonated polyacrylonitrile (SPAN), sulfonated polyglycidyl methacrylate (SPGMA), or sulfonated poly(acrylonitrile-co-glycidyl methacrylate) (SP(AN-co-GMA))/polyvinyl chloride (PVC) were developed to be used for direct methanol fuel cells (DMFCs). After polymerization and sulfonation of the prepared polymers, the polyelectrolyte membranes were prepared by the casting and solvent evaporation technique for sulfonated homo- or co-polymers with polyvinyl chloride (PVC) composites. The resulting membranes were characterized by Fourier infrared and Raman spectral analyses, X-ray diffractometry, and scanning electron microscopy. The findings of this study reveal that both the thermal stability and ion exchange capacity of the composite membranes based on sulfonated copolymers were higher than that of their corresponding composites based on sulfonated homopolymers. In this context, the weight loss percentage of the prepared composite polyelectrolyte membranes did not exceed 12% of their initial weights. The IEC of all the composite membranes ranged from 0.18 to 0.48 meq/g. Thus, the IEC value increased with the increasing proportion of the glycidyl methacrylate comonomer. Moreover, the prepared PEMs based on SP(AN-co-GMA)/PVC composites showed lower methanol permeability (8.7 × 10−7 cm2/s) than that of the Nafion membranes (3.39 × 10−6 cm2/s). Therefore, these prepared PEMs are a good candidate for DMFCs applications.

A comparative study on sPEEK‐based composite membranes with various inorganic fillers using different preparation routes for DMFCs

AbstractIn this study, proton‐conducting sulfonated polyether ether ketone (sPEEK) membranes including tungstic acid, organically modified montmorillonite, and silicon dioxide were prepared using solution casting method for direct methanol fuel cells. All obtained composite membranes had adequate thermal stability for fuel cells, and their surfaces became more hydrophilic due to the incorporation of additives. The ion exchange capacities of the composite membranes were found to be very close to the sPEEK membrane. While the proton conductivity of the sPEEK membrane was 8.6 mS cm−1, the addition of additives led to an enhancement in the proton conductivity values. Among the prepared composite membranes, sPEEK‐H2WO4‐5 had the highest proton conductivity (36.5 mS cm−1) which was comparable to Nafion117 in water at room temperature. On the other hand, the methanol permeabilities of the composite membranes were in the same order compared to sPEEK but showed minor changes depending on the added materials and their compositions. Among the membranes obtained by solution casting, sPEEK‐H2WO4‐5 was found to be the best composite membrane due to its high proton conductivity and acceptable methanol permeability. Layer‐by‐layer modified sPEEK membranes were also obtained in the study for comparison and it was found that sPEEK‐PAH/H2WO4‐2 displayed the best selectivity value.

Low water swelling polyaromatic proton exchange membranes

A carbon-carbon linked polyaromatic electrolyte was designed and synthesized for proton exchange membranes. The facile synthesis consists of a metal-free Friedel-Crafts polymerization and a direct post-sulfonation. To prevent the random sulfonation, the trifluorobuanone monomer was incorporated as a spacer to sterically confine the sulfonated area. Hydrophobic/hydrophilic separation was observed in the polymer's microstructure. The membrane (ion exchange capacity = 1.88 mmolg−1) displayed low water swelling (area swelling = 38.0% at 80 °C) at a slightly higher proton conductivity than Nafion 212. Tensile strength of 39.3 MPa and elongation at break of 67.0% were confirmed by stress-strain measurements. The membrane electrode assembly afforded an electrolyzing performance of 4.6 A cm−2@2.0 V while Nafion 212 was 3.6 A cm−2@2.0 V under the same testing conditions. The 45 μm film exhibited better stability than Nafion 212 (∼50 μm) both in the preliminary in-situ cyclic accelerated stress test and the 800-h galvanostatic evaluation. The degradation rate of our thin membrane in the 800-h test was comparable to that of Nafion 115 (∼125 μm).

Study on the Treatment of Refined Sugar Wastewater by Electrodialysis Coupled with Upflow Anaerobic Sludge Blanket and Membrane Bioreactor.

In this paper, refined sugar wastewater (RSW) is treated by electrodialysis (ED) coupled with an upflow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). The salt in RSW was first removed by ED, and then the remaining organic components in RSW were degraded by a combined UASB and MBR system. In the batch operation of ED, the RSW was desalinated to a certain level (conductivity < 6 mS·cm-1) at different dilute to concentrated stream volume ratios (VD/VC). At the volume ratio of 5:1, the salt migration rate JR and COD migration rate JCOD were 283.9 g·h-1·m-2 and 13.84 g·h-1·m-2, respectively, and the separation factor α (defined as JCOD/JR) reached a minimum value of 0.0487. The ion exchange capacity (IEC) of ion exchange membranes (IEMs) after 5 months of usage showed a slight change from 2.3 mmol·g-1 to 1.8 mmol·g-1. After the ED treatment, the effluent from the tank of the dilute stream was introduced into the combined UASB-MBR system. In the stabilization stage, the average COD of UASB effluent was 2048 mg·L-1, and the effluent COD of MBR was maintained below 44-69 mg·L-1, which met the discharge standard of water contaminants for the sugar industry. The coupled method reported here provides a viable idea and an effective reference for treating RSW and other similar industrial wastewaters with high salinity and organic contents.

Sulfonated branched poly(arylene ether ketone sulfone) proton exchange membranes: Effects of degree of branching and ion exchange capacity

Sulfonated branched polymers exhibit substantial potential for application as proton exchange membranes (PEMs). Most studies develop branched polymer PEMs by regulating the degree of branching (DB), without considering another important factor, i.e., the ion exchange capacity (IEC). Herein, we report on a systematical comparison regarding the effects of DB and IEC on the branched polymer PEMs and a solution to advance the properties of PEMs. To accomplish this, two series of branched poly(arylene ether ketone sulfone)s containing densely sulfonated tetraarylmethane units were synthesized. The DB and IEC were controlled in the range of 5–10 % and 1.41–1.94 meq g−1, respectively. It was found that both increasing DB and IEC of membranes promoted water absorption, proton conductivity, single-cell performance, denser distribution of microscopic hydrophilic phase, and also reduced the mechanical property. Furthermore, the strengthening via increased DB maintained dimensional stability and improved oxidative stability, while the impact of IEC was the opposite. Ultimately, a polymer membrane bearing optimal DB (7.5 %) and IEC (1.94 meq g−1) exhibited the highest proton conductivity (134.5 mS cm−1) and maximum power density (426.8 mW cm−2), satisfactory dimensional change (18.8 % in-plane, 27.2 % through-plane, and 79.5 % volume) at 80 ℃, and sufficient thermal, oxidative, and mechanical stability. This work is expected to serve as a guide for designing and synthesizing the DB and IEC of sulfonated branched polymer PEMs.

Influence of sulfonated SBA - 15 on fuel cell performance of sulfonated polysulfone electrolyte membranes

The prepared mesoporous SBA-15 (Santa Barbara Amorphous-15) was sulfonated and used as filler for the preparation of sulfonated polysulfone based composite electrolyte membranes. The SBA-15 and polysulfone were sulfonated using 3-mercaptopropyl trimethoxysilane and trimethylsilyl chlorosulfonate, respectively. The different weight percentages (1, 3, and 5 wt%) of sulfonated SBA-15 (SSBA-15) were used to prepare composite electrolyte membranes. Water uptake, ion exchange capacity, swelling ratio and proton conductivity of the composite membranes were studied for assessing the suitability of the electrolyte membranes for use in fuel cells. Characterization techniques such as FT-IR, XRD, SEM, TEM and Brunauer–Emmett– Teller were used to study the physico-chemical properties of the electrolyte membranes. TEM and BET analysis showed that SBA -15 retained its mesoporous structure even after sulfonation process. The prepared membranes were then tested in an in-house built single-cell fuel cell using hydrogen as fuel and oxygen as the oxidant. The fuel cell study showed that the presence of Sulfonated SBA-15 in the polymer matrix provided additional ion exchange sites and retained water for proton transfer which resulted in higher power density of 815 mW/cm2 with SPSU + 3% SSBA-15 membrane as compared with Nafion 117®.

On the Characterization of Membrane Transport Phenomena and Ion Exchange Capacity for Non-Aqueous Redox Flow Batteries

The development of high-performance membrane materials for non-aqueous redox flow batteries (NAqRFBs) could unlock a milestone towards widespread commercialization of the technology. Understanding of transport phenomena through membrane materials requires diagnostic tools able to monitor the concentrations of redox active species. While membrane characterization in aqueous media focused the attention of the scientific community, dedicated efforts for non-aqueous electrolytes remain poorly developed. Here, we develop new methodologies to assess critical membrane properties, namely ion exchange capacity and species transport, applied to NAqRFBs. In the first part, we introduce a method based on 19F-NMR to quantify ion exchange capacity of membranes with hydrophobic anions commonly used in non-aqueous systems (e.g., PF6 − and BF4 −). We find a partial utilization of the ion exchange capacity compared to the values reported using traditional aqueous chemistry ions, possibly limiting the performance of NAqRFB systems. In the second part, we study mass transport with a microelectrode placed on the electrolyte tank. We determine TEMPO crossover rates through membranes by using simple calibration curves that relate steady-state currents at the microelectrode with redox active species concentration. Finally, we show the limitations of this approach in concentrated electrolyte systems, which are more representative of industrial flow battery operation.

Anion Exchange Membranes Incorporating Multi N-Spirocyclic Quaternary Ammonium Cations via Ultraviolet-Initiated Polymerization for Zinc Slurry-Air Flow Batteries

Four anion exchange membranes (AEMs) incorporating multi N-spirocyclic quaternary ammoniums via an ultraviolet (UV)-curing method were prepared and tested as separators in zinc (Zn) slurry-air flow batteries (referred to here as ZSAFBs), an environmentally friendly, high specific energy, and low cost energy storage device. The multi N-spirocyclic cations chain was grafted onto the PPO backbone via a hexyl spacer and its chain length, and the thus membrane ion exchange capacity was tuned by varying the molar ratio between the hexyl diallyl ammonium grafted on PPO and the diallyl piperidinium monomer. This rationally designed 3D polymer results in a membrane with a well-developed phase separation morphology, as confirmed by atomic force microscopy, with a high hydroxide ion conductivity and low zincate ion diffusion coefficient, i.e., the PO-6CH2-3x membrane exhibited 19 mS/cm and 2.3 × 10–12 m2/s at 20 °C, respectively. The membranes exhibited great alkaline stability, with PPO-6CH2-3x showing less than 8% drop in ionic conductivity after 2 weeks of accelerated degradation test (1 M KOH, 60 °C). The ZSAFB cell assembled with the PPO-6CH2-3x membrane exhibited an excellent maximum power density (153 mW/cm2), surpassing those of the reported values, making it a very promising membrane material for rechargeable ZSAFBs.

Standard Operating Protocol for Ion-Exchange Capacity of Anion Exchange Membranes

Ion-exchange capacity (IEC) is the measure of a material’s capability to displace ions formerly incorporated within its structure. IEC is a key feature of anion-exchange membranes (AEM), as it determines the AEM’s ability to conduct the ions required to sustain the electrochemical reactions where they are utilized. As an intrinsic property, measuring the IEC accurately is essential to study AEMs and understand their performance within devices. In this method article, a facile and accurate standard operating procedure (SOP) to measure the IEC of AEMs is proposed. When compared to conventional acid-base back-titration or Mohr titration, the proposed method combines the fast reaction between silver and halide ions and the accuracy of the potentiometric titration, providing a convenient and precise protocol for researchers in the field.

Imidazole-doped proton conducting composite membranes fabricated from double-crosslinked poly(vinyl alcohol) and zeolitic imidazolate framework

Proton conducting membranes were fabricated from double-crosslinked poly(vinyl alcohol) and zeolitic imidazolate framework (ZIF). The effect of the ZIF type (ZIF-8, ZIF-67, and a 1:1 wt/wt. mixture (ZIF-mix)) on water uptake, ion exchange capacity, proton conductivity, and oxidative stability of the composite membranes was studied. The membrane comprising ZIF-mix exhibited the highest proton conductivity, suggesting a synergistic effect between ZIF-8 and ZIF-67. The influence of ZIF-mix content on the membrane properties was further investigated, and the optimum loading was 7.5%. The introduction of ZIF-mix provided an improvement in proton conductivity and mechanical strength. Moreover, all composite membranes demonstrated low water uptake, low methanol uptake, adequate thermal stability, and high oxidative stability. To the best of our knowledge, this was the first time a ZIF-mix composite membrane was doped with imidazole to improve proton conductivity under non-humidified conditions. The proton conductivity of the imidazole-doped 7.5%ZIF-mix membrane increased with increasing imidazole content and temperature.

Interface electrode and enhanced actuation performance of SiO2-GO/PFSA-based IPMC soft actuators

In this study, ‘three-dimensional structure’ nanohybrid particle (SiO2-GO) were synthesized by in situ hydrolysis and composited with perfluorosulfonic acid (PFSA) to increase the water uptake (WUP) and ion exchange capacity (IEC) of the cast membranes. Ionic polymer metal composite (IPMC) soft actuators were fabricated based on the cast pure PFSA, GO/PFSA and SiO2-GO/PFSA membranes. The morphology and properties of IPMC were researched, and the relationship between them was analyzed in this article. The mechanism of SiO2-GO particles enhancing the properties of IPMC was revealed. The effects of incorporating GO and SiO2-GO on IPMC actuators were analyzed using physicochemical and electromechanical measurements comparing with the corresponding behavior of pure PFSA-based IPMC actuators. Morphology of IPMC showed effective incorporation of GO and SiO2-GO and clarified the dependency of Pt interface electrode on the SiO2-GO content of the PFSA membranes. The addition of SiO2-GO increased dramatically the WUP and IEC of the PFSA membranes and autuation performance of the IPMC actuators. The IPMC with 1 wt% SiO2-GO showed superb properties. The displacement of 1 wt% SiO2-GO under 3 V AC voltage reached 28.4 mm, which is 3.2 times higher than that of the pure PFSA. The maximum displacement under DC voltage reached 44.7 mm (5.5 V), and the blocking force reached 43.2 mN (5 V), which increased respectively 1.1 times and two times.

Enhanced performance of novel carbon nanotubes - sulfonated poly ether ether ketone (speek) composite proton exchange membrane in mfc application

Sulfonated poly ether ether ketone (SPEEK) nanocomposite proton exchange membrane (PEM) was prepared by incorporating multi-walled carbon nanotubes (CNT) at different weight percentages for microbial fuel cell (MFC) applications. Physico-chemical, thermal, mechanical and morphological characteristics of the prepared CNT-SPEEK composite membranes were analyzed using various techniques. Further, the water uptake capacity, Ion exchange capacity (IEC) and MFC performance of the CNT-SPEEK composite membranes were evaluated and compared with the pristine SPEEK membrane. Results show that incorporation of CNTs in SPEEK membranes exhibited a better water uptake capacity (34.18%–36.02%) and IEC (1.94–2.15 meq/g) compared to the SPEEK membrane. Improvement in membrane properties resulted in 2-fold higher power density compared to SPEEK membrane. Composite membrane with 0.75% CNT-SPEEK produced the higher power density (1.77 W/m2) in comparison with all the membranes evaluated. Chemical oxygen demand (COD) removal efficiency values of the MFC with SPEEK composite membranes were also found to be around 90%. Overall, the results reveal that CNT-SPEEK composite membrane as a potential PEM for MFC applications.

New insights into the definition of membrane cleaning strategies to diminish the fouling impact in ion exchange membrane separation processes

Ion exchange membranes represent the main core of a number of separation processes such as electrodialysis, diffusion dialysis and Donnan dialysis, among others, at which the key role of these membranes is to control the transport of ionic species and their selective separation simultaneously. However, the ion exchange capacity, selective separation, stability and durability of ion exchange membranes in separation processes are especially limited under the use of natural feedwaters due to their heterogeneous and multivalent ionic composition, which leads to several fouling issues. This effect provokes a clear undesirable evolution with time in the initial membrane properties and characteristics, thus significantly decreasing the overall process performance in several applications. As a consequence, not only a further understanding of the fouling mechanisms and the interactions between foulant(s) and membrane(s) is crucial, but also development of adequate membrane cleaning protocols to alleviate the fouling impact after prolonged operations. Therefore, the aim of the present review is to define efficient membrane cleaning strategies to control and mitigate the impacts of fouling phenomena on ion exchange membranes in separation processes, paying special attention to the type of membrane, its characterization (before and after cleaning) and the target application. Herein, promising membrane cleaning approaches reported in the recent years are summarized and discussed. Alternative physical, chemical and mechanical cleanings (or their combination) can be considered, even though the control of the number of cleaning cycles, cleaning conditions and combination of cleaning approaches seem to be essential to achieve an optimum global cleaning efficiency. To sum up, although further research in understanding the role of fouling in material stability and degradation after cleaning is still needed, this review provides novel insights into the definition of the most appropriate membrane cleaning strategy in different ion exchange membrane separation processes.

Testing a simple Lee's disc method for estimating throuh-plane thermal conductivity of polymeric ion-exchange membranes

Thermal conductivity of a material is a critical parameter for using it in non-isothermal applications. The new emphasis on using ion-exchange membranes as thermoelectric materials makes necessary to study the relation between thermal and structure properties. Here, through-plane thermal conductivity of different polymeric ion-exchange membranes was measured by a rapid experimental method using a simple Lee's Disc apparatus. Membranes with different structures and thicknesses in the interval 25–700 micrometers were analysed with the aim of testing the feasibility of the method in this kind of samples. Thermal conductivity of the investigated membranes was found to vary from as low as 0.03 up to as high as 0.41 W K−1m−1, depending on the type of membrane. Membranes with reinforcement in their structure presented lower values of the through-plane thermal conductivity. Although the thermal conductivity mainly depended on the composition of the membrane matrix, larger thermal resistances were estimated, in general, for membranes with higher density and thickness. No significant influence of the membrane ion-exchange capacity was observed for homogeneous and reinforced membranes, but a positive correlation was observed for heterogeneous membranes. The results obtained for homogeneous Nafion membranes were compared with values given in the literature for these same membranes, finding a good agreement. A thickness-dependent thermal conductivity was estimated for these membranes, suggesting that a size effect may play an important role in this kind of membranes. Despite its simplicity, the method allows to make a good estimation for the value of the through-plane thermal conductivity of polymeric ion-exchange membranes.

Novel electro-ion substitution strategy in electrodialysis for ammonium recovery from digested sludge centrate in coastal regions

Membrane fouling has been the primary challenge limiting the application of electrodialysis (ED) technologies in wastewater treatment, particularly the wastewater containing abundant dissolved organic matter, such as the digested sludge centrate. This study proposed an electro-ion substitution modified electrodialysis (EIS-ED) system that can recover NH4+ from the sludge centrate in coastal wastewater treatment plants (WWTPs), with negligible membrane fouling and scaling formed. In this system, the sludge centrate flowed between two cation-exchange membranes (CM), alongside the seawater providing Na+ as the substitution of NH4+. According to the experimental data and modeling, EIS-ED recovered more than 70% of NH4+ from the sludge centrate with an energy consumption of 2.03 kWh/kg NH4+-N, which was 14% lower than the conventional ED. Membranes, solutions and electrodes were the three major contributors of the linear ohmic resistance in the EIS-ED process. EIS-ED significantly resisted membrane fouling by means of electrostatic repulsion between the CM and negatively charged compounds, including particles and dissolved organic matter, and membrane scaling was also mitigated. After a treatment of 20 L sludge centrate, no significant decrease of membrane ion-exchange capacity was observed in the EIS-ED, while a decrease of 5.3% was found in the conventional ED. Accordingly, the potential application prospect of EIS-ED was proposed, which can recover at least 70% of NH4+ from the sludge centrate and reduce 10–20% of the NH4+ loading to the mainstream processes in coastal WWTPs.