Category: Water

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Polyelectrolyte coatings for ion-exchange membranes in electrodialysis

Reverse electrodialysis water purification

DOI: 10.13140/RG.2.2.20145.13929

Ion exchange membranes are key components for various electrochemical technologies in water treatment and energy storage, such as electrodialysis, membrane electrolysis, and flow batteries. These membranes are characterized by a high concentration of charged groups, which can be either cationic (positively charged) or anionic (negatively charged). The function of an ion exchange membrane is to facilitate the transport of counterions while limiting the loss of water and co-ions.

The efficiency of cation exchange membranes is affected by unwanted co-ion and water transport. The transport of hydroxide ions (OH−) through cation exchange membranes is of particular interest. Depending on the application, cation exchange membranes are designed either to selectively facilitate hydroxide transport or to minimize hydroxide loss. Therefore, improved ion exchange membranes must support such additional functionalities.

Researchers at Wageningen University have characterized ion exchange and water transport through both coated and uncoated cation exchange membranes. The scientists published their findings in the Journal of Membrane Science. In their study, they examined cation exchange membrane coating with polyelectrolytes made of polyallylamine and polystyrene sulfonic acid.

The researchers coated one side of commercial cation exchange membranes with double layers of these two polymers. They then studied ion and water transport in diffusion dialysis and electrodialysis. Diffusion dialysis involves passive ion transport driven by concentration gradients, while in electrodialysis, ion transport occurs actively and is powered by an applied current.

The coatings were evaluated for their selectivity for monovalent and divalent ions. This selectivity affects hydroxide transport and water permeability. Both are key factors for the efficiency of bipolar membrane electrodialysis, where solutions containing multivalent cations such as magnesium and calcium are treated.

Magnesium and calcium transport was significantly limited by the coatings, while sodium ion transport remained largely unaffected. This selectivity was attributed to the Donnan exclusion mechanism and differences in hydration shells, as multivalent ions have a higher resistance within the cation exchange membrane.

Orientation is crucial in this context. Coating alignment affected performance. Resistance increased in the direction of multivalent ion flow, which reduced the flow of magnesium ions. This finding is impotant for the design of devices for bipolar membrane electrodialysis.

Surprisingly, the coatings did not reduce water crossover. Denser layers remained the bottleneck. The hydroxide flow was somewhat higher in coated membranes exposed to extreme pH values. This was likely due to structural changes during the coating process.

The combination of a low-water-content cation exchange membrane with a coating could enable the direct use of untreated salt solutions in bipolar membrane electrodialysis. This would reduce pretreatment costs and improve sustainability. The Fuji CEM-12 proved to be a promising candidate for future designs with coatings.

Salt diffusion through uncoated cation exchange membranes was mainly determined by the type of anion, such as chloride, sulfate, or hydroxide. In addition, membrane properties, including water content and ionic charge density, had a significant influence. The ionic charge density determined the anion distribution within the cation exchange membranes.

In summary, the researchers coated various commercial cation exchange membranes multiple times on one side with polyelectrolytes. For uncoated cation exchange membranes, water permeability correlated well with  ionic membrane resistance. This correlation was due to both parameters being dependent on the water content of the membrane. Moreover, permeability for co-ions increased with a higher volume fraction of water in the membranes.

Osmotic water transport in cation exchange membranes was not affected by the multiple layers of polyallylamine and polystyrene sulfonic acid. The researchers recommended single layer coating of low-water-content cation exchange membranes to minimize the transport of hydroxides and problematic multivalent cations.

This work demonstrates that surface modification using polyelectrolyte layers can enhance the functionality of conventional membranes without significant trade-offs. Water transport remained a challenge but the ability to block multivalent ions while maintaining conductivity for sodium ions represented a major step toward more efficient and cost-effective dialysis systems.

At Frontis Energy, we are excited about the future application of multilayered membranes on an industrial scale.

Elozeiri et al. 2026, Water and co-ion transport across ion-exchange membranes coated with PAH/PSS polyelectrolyte multilayer in electrodialysis and diffusion dialysis, Journal of Membrane Science,741, 125072, DOI: 10.1016/j.memsci.2025.125072

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Transforming water systems with scalable membrane solutions

Fresh water from a faucet

DOI: 10.13140/RG.2.2.30211.46883

In a world increasingly defined by the need for cleaner processes, sustainable production, and advanced materials, membrane technology has emerged as a key enabler across multiple industries from water purification and energy generation to chemical separation and bioprocessing. Its high selectivity, compact footprint, and low energy requirements make it indispensable in meeting both environmental and performance demands.

At the heart of membrane fabrication lies a well-established method known as non-solvent-induced phase separation. This technique involves casting a polymer solution into a thin layer and exposing it to a non-solvent, typically through immersion or vapor contact, which triggers phase separation, forming a porous matrix with fine-tuned filtration properties. Due to its simplicity and scalability, this method has become a mainstay in industrial membrane production, offering reliable performance across many applications.­

However, as industries demand more specialized and high-efficiency membranes, researchers are continuously pushing the boundaries of conventional fabrication techniques. One of the most promising advancements is the spray-modified non-solvent-induced phase separation method, which swaps immersion for targeted non-solvent spraying. This subtle yet powerful modification enables patterned surface architectures, improved permeability, and reduced fouling, all while maintaining the advantages of scalable continuous production. Such innovation is instrumental in tailoring membranes to meet the complex needs of modern filtration systems.

Building on this progress, a recent study conducted by the Catholic University Leuven in Belgium successfully adapted the spray-modified non-solvent-induced phase separation technique to a roll-to-roll, 12-inch pilot-scale platform. This represents a meaningful advancement from laboratory concept to industrial feasibility. The findings were recently published in the Membranes. Through strategic variations in polymer concentration, molecular weight, and the inclusion of hydrophilic additives such as polyethylene glycol and polyvinylpyrrolidone, researchers fabricated defect-free, uniformly patterned polysulfone ultrafiltration membranes with remarkable performance gains. Notably, these membranes delivered up to 350% higher water flux compared to traditional flat membranes, attributed to their deep surface patterns—reaching 825 µm—and a porous, finger-like internal structure that enhances throughput without sacrificing rejection efficiency.

Among the additives tested, polyethylene glycol emerged as the standout, yielding membranes with high pure water permeance (over 1000 Liters/m²/hour/bar) and consistent protein rejection levels (around 90%). These membranes also demonstrated excellent structural fidelity and homogeneity, which are critical for ensuring long-term durability and process reliability. The study further identified operational parameters, such as optimal casting speed, non-solvent spray rate, and solution viscosity control, as essential contributors to reproducible membrane quality and process scalability.

This leap from bench to pilot scale carries profound industrial implications. The ability to continuously produce high-flux, anti-fouling membranes with precise structural characteristics offers industries a robust and scalable filtration solution. Applications span from municipal and industrial wastewater treatment to biopharmaceutical production and food processing—sectors where membrane performance can directly influence both environmental outcomes and operational costs.

In essence, the optimized spray-modified non-solvent-induced phase separation approach does more than enhance membrane metrics; it embodies the transition from research novelty to commercial readiness. By bridging the gap between design and deployment, this work lays a foundational blueprint for mass-producing advanced membranes that are not only efficient, but also economically and environmentally viable. It is a compelling example of how thoughtful engineering and process innovation can move technologies from promising prototypes to real-world solutions, thus shaping the future of filtration in a world that urgently needs it.

Frontis Energy envisions a world transformed by sustainable membrane innovations, where clean water, resource efficiency, and resilient infrastructure are accessible to all.

Ilyas, et al., 2025, Pilot-scale polysulfone ultrafiltrationpPatterned membranes: phase-inversion parametric optimization on a roll-to-roll casting system, Membranes 15, 8, 228, DOI: 10.3390/membranes15080228

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Advancing wastewater sustainability: Nafion-powered ammonium recovery

Wastewater treatment plant Bern

DOI: 10.13140/RG.2.2.24268.68488

With global population growth and the resulting increase in environmental stress, the need for sustainable wastewater treatment is becoming ever more urgent. Traditional methods focus on removing pollutants but often overlook the opportunity to recover valuable resources. One such resource is ammonium. This nitrogen-containing molecule promotes growth and is a key component of fertilizers. When mishandled, such as through over-fertilization, ammonium becomes one of the main contributors to nitrogen pollution.

A promising solution lies in bioelectrical systems. This umbrella term refers to innovative technologies that not only purify wastewater but also recover resources like ammonium. At the same time, bioelectrical systems generate clean energy such as electricity or biogas. The technology is based on galvanic cells, where the two cell chambers are often separated by a membrane. High-performance cation exchange membranes enable precise ion transport and system stability. The premium product among cation exchange membranes is Nafion, such as our Nafion 115 membrane.

At Frontis Energy, we have demonstrated that bioelectrochemical systems can remove ammonium from wastewater, offering an energy-efficient alternative to the energy-intensive Haber-Bosch process. To validate this concept, we developed microbiological electrolysis cells populated with microorganisms from oxygen-deprived marine sediments off the coast of Namibia. These sediments are naturally rich in ammonia and low in organic carbon, ideal conditions for microbes capable of anaerobic ammonium oxidation. For comparison, we also used conventional municipal wastewater to populate the electrodes.

Maintaining anoxic conditions was crucial to avoid nitrification, a process that transfers electrons directly to oxygen, bypassing the anode and resulting in energy loss and reduced hydrogen production. Instead, we regulated the anode potential between +150 mV and +550 mV, well below the redox potential required for water oxidation (+820 mV). This configuration enabled the oxidation of ammonium to nitrogen gas (N₂) at the anode, while hydrogen (H₂) or methane gas was produced at the cathode.

Central to this process is Nafion 115, a membrane made of perfluorosulfonic acid polymers (PFSA polymers). Its exceptional proton conductivity, chemical resistance, and mechanical robustness make it ideal for demanding wastewater environments. Nafion 115 acts like a selective gate, allowing ammonium ions (NH₄⁺) to migrate from the anode to the cathode while blocking competing ions and maintaining anoxic conditions. This selective transport, driven by electric field gradients and concentration differences, ensures efficient nutrient recovery and stable performance of the bioelectrical system.

A practical validation of this technology comes from our earlier report, in which researchers developed a two-chamber, anoxic bioelectrical reactor that continuously removed ammonium at a rate of about 5 g/m³/day. Their system converted over 97% of the ammonium directly into nitrogen gas. This transformation occurred without the formation of harmful byproducts like nitrite or NOx gases. Particularly impressive was the energy consumption, just 0.13 kWh per kilogram of nitrogen removed. That is a 35-fold reduction compared to conventional aeration, which typically requires around 5 kWh/kg.

These results highlight the transformative potential of bioelectrical systems. As mentioned earlier, significant energy is used to remove nitrogen from wastewater, only to make it available again via the Haber-Bosch process, accounting for 1–2% of global energy consumption. Bioelectrical systems offer a circular alternative: by coupling ammonium oxidation with hydrogen production, wastewater treatment plants could become net energy producers. The generated hydrogen and biogas can be used directly for electricity generation and ultimately to reduce greenhouse gas emissions.

With the right biofilms, well-controlled electrode potentials, and robust membranes like Nafion 115, ammonium can serve as a clean, resource-efficient alternative to water electrolysis. This underscores the potential of bioelectrical systems to build a circular water economy, where waste is treated as a resource.

This technology reflects Frontis Energy’s commitment to promoting clean, efficient, and circular solutions that turn ecological challenges into sustainable opportunities.

Siegert and Tan, 2019, Electric stimulation of ammonotrophic methanogenesis, Frontiers in Energy Research 7:17, DOI: 10.3389/fenrg.2019.00017

Image: Wastewater treatment plant Bern

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Advances in ammonium recovery with bioelectrical systems

DOI: 10.13140/RG.2.2.30016.19204

In recent decades, the focus of wastewater treatment has shifted from mere disposal to the recovery of valuable resources. This approach aims to harness energy and nutrients found in wastewater. Among emerging technologies are bioelectrical systems, which can recover not only energy and carbon but also valuable compounds like ammonium. Nitrogen bound in ammonium is a key component of fertilizers. Today, two-thirds of this resource are produced through the highly energy-intensive Haber-Bosch process using natural gas extracted from air. Fertilizer production significantly contributes to anthropogenic CO₂ emissions and, ultimately, to global warming.

Bioelectrical systems for ammonium recovery are classified into microbial fuel cells and microbial electrolysis cells. In both, electrogenic microorganisms oxidize organic matter in wastewater into carbon dioxide and protons. Exoelectrogens, also known as anode-respiring bacteria, use the anode as an electron acceptor instead of oxygen, thereby gaining energy for their metabolic processes.

By combining microbial activity with electrochemical processes, chemical reactions in wastewater treatment are catalyzed efficiently. This novel biocatalytic application still faces challenges in terms of optimization for practical use. At Frontis Energy, we have already demonstrated through a patented process that ammonium can be effectively removed from wastewater using bioelectrical systems. We are currently working on scaling this method for industrial deployment. However, a comprehensive understanding of the underlying processes and recovery mechanisms is still lacking.

A new study conducted by the Autonomous University of Barcelona investigated the development and optimization of bioelectrical systems aimed at recovering ammonium from wastewater in an energy-efficient and concentrated form. The findings were recently published in Bioelectrochemistry. Using a three-chamber configuration with a hydrophobic membrane, the researchers systematically examined the influence of different levels of electric current and ammonium concentrations on recovery efficiency. The system achieved its highest ammonium recovery rate of 55 g/m²/day at a current of 75 mA. Overall, a 97% removal of ammonium from a 0.3% solution was attained.

Notably, electrons flow from the anode to the cathode via an external circuit, where they react with an electron acceptor. In ammonium recovery systems, ammonium ions migrate from the anode to the cathode through a cation exchange membrane, driven by concentration gradients and the electric field, allowing them to accumulate in the cathode chamber.

While this ion transport mechanism supports efficient ammonium recovery, the researchers found that high-performance operation led to material wear at the cathode. This highlights the need to balance operational intensity with material durability. Consequently, the team explored different cathode materials and voltages. Stainless steel electrodes operated at 1.4 V yielded the best results, achieving a removal rate of 21 g/m²/day and a recovery rate of 17 g/m²/day, primarily due to enhanced cation migration resulting from higher current density.

Long-term experiments revealed that higher ammonium concentration in the anolyte significantly improves selective migration of ammonium ions through the cation exchange membrane, further boosting system performance. Operating at 1.4 V increased recovery efficiency and reduced energy consumption per gram of nitrogen—making the process more cost-effective and environmentally friendly.

These insights underscore the practical potential of bioelectrical systems as a pioneering solution for sustainable nitrogen recovery. By fine-tuning material selection, system design, and operational parameters, high ammonium removal and recovery rates can be achieved with minimal energy input.

From an industrial perspective, this study represents a scalable advance in resource recovery within existing wastewater treatment infrastructures. If scaled, the technology could reduce reliance on the energy-intensive Haber-Bosch process.

Since concentrated ammonium is a commercially viable product, its recovery reduces operational costs for wastewater treatment plants. If the scaled-up process maintains its long-term stability and low energy demand, these would be compelling arguments for adopting bioelectrical technologies as part of a circular economy.

At Frontis Energy, we see great potential in scaling this technology and making a meaningful contribution to sustainable wastewater treatment.

Ul, et al. 2025, Electrochemical and bioelectrochemical ammonium recovery from N-loaded streams using a hydrophobic membrane, Bioelectrochemistry, Volume 166, 109013, DOI: 10.1016/j.bioelechem.2025.109013.

Image: Shutterstock

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From waste heat to ultrapure water: A new technology transforming renewable hydrogen

DOI: 10.13140/RG.2.2.36620.17281

Hydrogen (H₂), produced using renewable energy, has emerged as a possible alternative to fossil fuel. This versatile molecule can serve as an energy carrier, an efficient storage solution, and a sustainable feedstock for transportation, chemical processing, and energy systems worldwide.

Unlike fossil fuels, hydrogen produces no harmful emissions when used. It can be generated using electrolyzers running on renewable energy and abundant water as feedstock. It then becomes a renewable and sustainable energy source, reducing reliance on depleting fossil fuel reserves, helping combat climate change. Consequently, hydrogen production has become a key priority on the political agenda of numerous countries.

However, the water used in electrolyzers must be ultrapure in order to protect the electrodes of electrolyzers from poisoning and avoid chloride oxidation to chlorine. Abundant seawater adds several challenges when directly fed to electrolyzer plants for hydrogen production, making highly pure water, specifically ultrapure water, an expensive necessity. Ultrapure water is produced in a series of steps, including pretreatment to remove suspended solids and desalination to eliminate salts, organics, and colloidal particles. Polishing techniques such as deionization, degasification, and ultraviolet treatment are then used to achieve the required quality. Among these processes, desalination is particularly critical for removing most impurities.

Reverse osmosis, especially seawater reverse osmosis, is a widely used desalination technology but has notable drawbacks, such as requiring high-pressure operation (high energy consumption), intensive pretreatment, and producing concentrated brine, which can harm marine ecosystems when discharged. Membrane distillation has gained attention as an alternative for producing high-quality water and supporting recovery applications. It operates at lower temperatures and has the ability to utilize waste heat.

Membrane distillation is a thermal separation process where a vapor pressure difference across a hydrophobic membrane causes liquid particles to phase change and pass through as gas. Operating at ambient pressure and utilizing low-temperature heat sources (<90 °C), membrane distillation offers significant advantages. However, research on membrane distillation as a viable alternative to reverse osmosis for ultrapure water production remains limited, particularly in areas such as module design and techno-economic analysis.

A group of researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany, has explored the potential of membrane distillation as a cost- and energy-efficient alternative to reverse osmosis for producing ultrapure water for proton exchange membrane (PEM) electrolyzers. The findings were recently published in the Desalination Journal. They introduced membrane distillation as a possible alternative to reverse osmosis for ultrapure water production. But here is the twist: the membrane distillation system ingeniously taps into waste heat from a 5 MW proton exchange membrane electrolyzer, transforming what would typically be an efficiency liability into an asset for sustainability. So far, their results are impressive—membrane distillation not only produces exceptional distillate (<3 μS/cm) but does so at a cost ranging from €2.33 to €2.85 per ton of distillate, compared to reverse osmosis’s €2.80 to €5.51. Using membrane distillation, seawater desalination could be 50% or more cheaper.

Economic analyses highlight that membrane distillation’s cost-effectiveness is driven by its low electrical energy requirements and optimized short-channel module design. Its impressive energy efficiency, enabled using low-grade thermal energy, establishes membrane distillation as a highly versatile and environmentally friendly solution that aligns seamlessly with the vision for renewable hydrogen production. This study positions membrane distillation as more than just an alternative to reverse osmosis: it is a smarter and greener approach to ultrapure water production.

Their findings have the potential to reshape the industrial approach to ultrapure water production. By demonstrating an efficient use of waste heat and providing a more economical solution, it offers industries a pathway to lower operational costs while advancing sustainability. This aligns particularly well with sectors striving for greener operations, such as renewable hydrogen production and other energy-intensive applications. Moreover, the adoption of membrane distillation could catalyze innovation in system design and integration, encouraging industries to optimize processes and reduce dependence on traditional, energy-intensive methods. This shift can contribute to broader sustainability goals and improve the economic feasibility of renewable energy initiatives.

At Frontis Energy, we are committed to advancing sustainable and green energy solutions by embracing innovative technologies like membrane distillation, bringing us closer to a sustainable future.

Schwantes et al. 2025 Thermally driven ultrapure water production for water electrolysis – A techno-economic analysis of membrane distillation, Desalination, Volume 608, 118848, DOI: 10.1016/j.desal.2025.118848.

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Pilot-scale decentralized bioelectric treatment of domestic wastewater

Pine Creek wastewater treatment plant

DOI: 10.13140/RG.2.2.10734.98888

Growing urban populations and rising demands on water infrastructure make decentralized wastewater treatment an urgent research priority. Conventional centralized plants are often energy intensive and limited in their ability to recover valuable resources.

Exploring integrated bioelectric systems offers a pathway to not only improve nutrient removal but also generate useful byproducts such as biogas and hydrogen. Pilot-scale studies are required to demonstrate feasibility, optimize reactor design, and assess performance under realistic operating conditions.

Researchers at the Mexican Institute of Water Technology (IMTA) in Jiutepec , Mexico, addressed the pressing need for sustainable, modular solutions. They recently published their pilot in the journal Bioprocess and Biosystems Enginee­ring. Their system could possibly serve households, hotels, and other facilities where both wastewater volumes and energy demands converge.

An integrated, decentralized treatment system consisting of an electrolysis reactor, an anaerobic biofilm reactor, and an aerobic moving-bed reactor was tested at pilot scale. The total volume was 50 liters, with 10.4 liters allocated to the electrolysis chamber. Domestic wastewater was treated while simultaneously producing hydrogen.

The system comprised the following individual reactors

  1. An electrolysis chamber with graphite felt anode and cathode and a cation exchange membrane (CMI‑7000S),
  2. A fixed-bed reactor with polyurethane foam as carrier material,
  3. An aerobic moving-bed reactor with modified LDPE carrier elements (≈1,500 m²/m³ specific surface area) and targeted aeration,
  4. A high-performance sedimentation unit.

The system was installed in a tank and operated under continuous flow at two different rates. The hydraulic retention time was 0.75 or 1.5 days. Applied voltages ranged from 0.7 to 1.0 V. Various organic loads (chemical oxygen demand, COD) of 0.2–0.44 kg/m³/d were also investigated.

Contamination Removal
COD 81–84%
BOD₅₀ 84–85%
TSS 76–88%
TN 53–68%
NH₄⁺ 88–98%
TP 11–30%

With increasing load, the treatment rated tended to decrease. Current densities reached up to 0.41 A/m² with a maximum hydrogen production rate of 0.007 L/L/d (absolute: 0.072 L/d). The higher voltage of 1.0 V promoted hydrogen formation as well as nitrogen and phosphorus conversions. A control phase without applied voltage was used to isolate the contribution of voltage to treatment performance.

This voltage-free control quantified the actual contribution of the electrochemical field. No current flow or hydrogen production occurred. Organic load removal continued, but only through conventional steps. Nitrogen and phosphorus conversions were significantly reduced, especially ammonium removal. Overall, the system showed lower treatment performance without applied voltage.

Microbial electrolysis in the combined system did not merely add passive biofilm volume. Under applied voltage it provided an independent functional contribution to nitrogen and phosphorus conversion and energy recovery. Without voltage, the microbial electrolysis cell behaved hydraulically like an additional reactor space but lost its added value as a bioelectric unit.

The study demonstrated that integrated bioelectrolysis combinations at small pilot scale can achieve high organic degradation rates and relevant nitrogen conversions, while simultaneously producing hydrogen or biogas. This makes the approach suitable as a low-energy, modular pre- and main treatment for domestic wastewater with potential for useful gas recovery. The hotel industry is particularly interesting as a market, given the necessary flow volumes and corresponding gas demand.

Phosphate removal was too low (11–30%) to meet regulatory requirements. Post-treatment in municipal wastewater plants remained necessary. Higher organic loads worsened nutrient and solids removal, making the system only partially suitable for industrial wastewater with higher loads. For discharge and reuse standards, additional post-treatment steps were also required in industrial applications.

The pilot-scale integration of bioelectric reactors into domestic wastewater treatment marks an exciting step toward industrialization of sustainable water management. By coupling high organic removal efficiencies with simultaneous hydrogen generation, this approach demonstrated how treatment systems can evolve from purely consumptive infrastructure into resource-recovering platforms.

At Frontis Energy we believe that, while challenges remain, particularly in phosphorus removal and scaling to higher organic loads, the promise of modular, low-energy systems that deliver both clean water and usable energy is compelling. The next phase will involve refining nutrient conversion, optimizing reactor design for larger volumes, and exploring real-world applications in sectors such as hospitality and decentralized communities. This trajectory points toward a future where wastewater treatment is not just a necessity but a driver of circular economy innovation.

Estrada-Arriaga, et al. 2024, Performance of a pilot-scale microbial electrolysis cell coupled with biofilm-based reactor for hou­sehold wastewater treatment: simultaneous pollutant removal and hydrogen production. Bioprocess and Biosystems Enginee­ring, 47, 1929–1950, DOI: 10.1007/s00449-024-03079-0

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Poly-electrolyte layers determine the efficiency of desalination membranes

Increasing water scarcity and pollution with micropollutants are responsible for the increasing cost of drinking water. Desalination of sea water and better wastewater treatment are necessary to counter this trend. Membranes can desalinate and remove most wastewater pollution. However, a lot of energy is required. Therefore, modern membranes must be more efficient in order to achieve satisfactory results.

Nano-filtration membranes consisting of poly-electrolytic layers are a promising approach to treat water more efficiently. Accordingly, the composition of poly-electrolytic layers has stirred up much interest in the production of nano-filtration membranes. Such membranes are manufactured layer by layer, which enables a good tuning of membrane properties for different purposes.

Commercially available nano-filtration membranes are usually a trade-off between high water permeability and good salt retention (desalination). This trade-off impacts either the quality or the volume of the cleaned water. Nano-filtration membranes that are produced in layer by layer can have a positive impact on this trade-off balance due to the formation of nano scaled layers. It is important to know which component plays a crucial role in the layer forming process.

A research group of the Technical University Eindhoven in the Netherlands had therefore undertaken the task of examining these layer components more closely. They specifically investigated the poly-electrolyte concentration. It is known that a higher poly-electrolyte concentration produces thicker layers. However, their impact on the membrane performance has so far been unknown. They now published their work, in which the researchers used two well-known strong poly-electrolytes: PDADMAC and PSS (polydiallyldimethylammonium chloride and poly(sodium-4-styrene sulfonate)). The membrane output was examined with regard to water permeability, the molecular weight cutoff and salt retention.

In the first double layer, the membranes made with a 50 mM saline solution showed a lower water permeability and molecular weight cutoff, as well as better salt retention (magnesium sulfate) due to the higher poly-electrolyt concentration. After a certain number of double layers, the molecular weight cutoff and the salt retention efficiency for all poly-electrolyte concentration leveled off. The higher the poly-electrolyte concentration, the sooner the plateau value was reached.

The membranes prepared with a 1 M salt concentration had a lower or comparable salt retention efficiency with one exception. The scientists concluded that the poly-electrolyte concentration significantly changed the membrane properties. A plateau was reached with seven or more double layers. The thicker layers showed a lower water permeability than those that were coated with poly-electrolyte solutions using a 50 mM salt concentration. Due to the reduced swelling of these membranes, they all had better salt retention efficiency, with the exception of magnesium chloride.

The results showed that increasing the poly-electrolyte concentration also increased the amount of poly-electrolyte adsorption. Due to a higher coating thickness, this led to lower permeability with pure water. However, this did not lead to a lower molecular weight cutoff or salt retention. The additional poly-electrolyte adsorption resulted in fewer links between the individual layers. The higher diffusivity of PDADMAC compared to PSS resulted in highly positively charged membranes, which in turn led to a better salt retention of magnesium and sodium chloride.

Overall, increased poly-electrolyte concentration and the salt concentration influenced the membrane charge exclusion significantly due to a higher charged surface, which led to better salt retention. However, the membrane size exclusion has not changed, which led to the same plateau values. The study presented here will allow chemists to produce better tuned desalination membranes, which will reduce the energy requirement and raw material requirements during production.

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Bio-electric systems help PFAS removal

Per- and polyfluoroalkyl substances (PFAS) have been manufactured for various applications for many decades. These include medical applications, such as implants and catheters, or consumer products for firefighting, plastics, cookware, and cosmetics. Likewise, PFAS are required in countless industrial applications, such as in the automotive industry, the chemical industry and the energy sector, including hydrogen electrolysis and fuel cells (e.g. Nafion™). They help apparatuses to function properly, reduce wear and the risk of accidents. The widespread use of PFAS has led to traces of these substances entering the environment worldwide. Typical sites with higher environmental PFAS concentrations include airports, chemical plants, fire brigades, military facilities etc.

The long-term health effects of these substances are currently a matter of controversy, particularly with regard to their chemical stability (a desired property).

In addition to completely avoiding their entry into the environment, PFAS can also be eliminated from it. For example, activated charcoal is often used to adsorb PFAs onto it. However, this method is not efficient in soils. Ideally, the activated carbon itself would have to be further processed in order to reuse PFAS. This process is very energy intensive.

As for many treatment processes, microbes can be used also for PFAS. Such biological methods are called bioremediation. However, the carbon-fluorine (C-F) bonds in PFAS are among the strongest covalent bonds in organic chemistry. In addition, there are very few naturally occurring C-F bonds in nature. They only occur in small concentrations. A prominent example is fluoroacetic acid, a highly toxic compound produced by the South African poisonous gifblaar. Few microorganisms with the ability to break the C-F bond have been identified. Thus, bioremediation of PFAS is possible but a slow process.

As already described in our previous articles, bio-electrical systems can accelerate microbial conversion processes. With bio-electrical systems it is possible to offer microbes a greater electrochemical potential gradient. Since this leads to larger energy gain in microbial metabolism, such metabolic rates can be accelerated. This process is successfully employed to clean industrial waste water.

In bio-electrical systems, microorganisms along with contaminants are placed in an electrochemical apparatus. The electrodes of such a system serve as electron donors or acceptors. The biodegradation is can be measured via the electric current.

Indeed, bio-electric systems have been used to degrade fluorinated alkanes. For example, the anti-inflammatory drug dexamethasone was successfully eliminated using such an apparatus. As proposed for bio-electrical liquid fuel, designer microbiomes could also be studied for PFAS. Other drug residues, such as Prozac™, should also be examined to ensure absence from the environment.

At Frontis Energy we are looking forward to new developments for PFAS removal in bio-electrical systems.

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Decentralized waste energy systems produce biogas where it is needed

Among others, the current European energy crisis was caused by a surge in demand after the pandemic, the embargo on Russia, the reluctance of investors to finance fossil energy projects and the throttling of production by the OPEC countries. In this complex situation, European countries are forced to develop alternatives and renewable energy sources. At the same time, however, natural gas is difficult to replace in many industries. One exception is the food and beverage industry, which sits enormous untapped resources of biogas in their wastewater.

Wastewater is a resource of which 380 billion m³ are produced worldwide. It contains valuable nutrients and energy. Global production is projected to increase by 51% by 2050. Wastewater treatment consumes about 3-4% of the energy generated globally. The full reeovery of the energy that is contained in this wastewater would completely offset the energy consumption of its treatment and in many cases even produce a surplus. In addition, the entire global water treatment is estimated to account for up to 5% of man-made CO2 production. Unfortunately, many businesses and municipalities do not invest in complex and expensive wastewater treatment technologies and continue to waste this valuable resource. The European Biogas Association estimates that by 2050, a maximum of 65% of gas requirements (~167 billion m³) could be covered by biogas.

Europe is the largest cheese maker in the world. More than 9 million tons of cheese are produced annually. With every ton of cheese, 9 m³ of cheese whey remain. Despite its high nutritional value, whey is often treated like wastewater for various reasons. Yet, the very high organic load in the whey makes it difficult to treat. Wasted whey can also be used for biogas production. In addition to whey, regular wastewater is also produced by cheese makers. For example, a medium-sized cheese factory pays 1.5 million euros a year for its waste water. Reducing these costs by producing biogas would turn dairy industry wastewater into a valuable resource.

This situation is similar in many other food and beverage sectors such as breweries, distilleries, winemakers, bakeries etc. All of these sectors have high energy requirements. Renewable electrical energy cannot meet this need. The market for wastewater treatment in Europe and the US is around 12 billion euros.

Traditional wastewater treatment is a cascaded process including aeration and anaerobic sludge digestion followed by incineration. These methods often consume more than 70% of the energy in a wastewater treatment plant. If contaminants such as high-energy total organic carbon or ammonia were converted into biogas before the process, at least 80% of the energy needed for wastewater treatment could be saved. It is absurd that this energy is removed from the wastewater using even more energy.

An ever-increasing number of sewage treatment plants already recover the resources contained in their wastewater, apart from the water itself. The oldest recivered products are biogas and fertilizers made from sewage sludge. Due to its heavy metal content such as copper and mercury, sewage sludge is no longer used as fertilizer but incinerated.

Biogas is particularly popular in Europe as the produced volumes and prices are high enough to compete with natural gas. Biogas is also a green alternative to natural gas as no additional CO2 is emitted. (Hence, it is often called Renewable Natural Gas in North America.) A disadvantage of classic biogas is the CO2 and sulfide content. Another disadvantage is that anaerobic digestion is the terminal treatment step, wasting valuable wastewater resources in the preceding treatment. Finally, the size and complexity of current digestion requires significant commitment from users when it comes to capital expenditures. Most food manufacturers prefer to focus on making food rather than cleaning their wastewater.

Novel high-performance biogas reactors solve these problems through miniaturization. A 20-fold size reduction is achieved compared to conventional systems. The new technology used was developed in Japan in the early 1990s and is called microbial electrolysis. The electrolysis of wastewater is catalyzed by electroactive microorganisms on the anode (the positive electrode). The reaction products are CO2 (from organic matter) and nitrogen gas (N2 from ammonia).

Principle of a microbial electrolysis reactor. On the left anode, the organic material is oxidized to CO2. The free electrons are absorbed by the anode and transported to the cathode. Hydrogen gas (H2) is released there. CO2 and hydrogen form methane, the final microbial reaction product.

At the same time, hydrogen gas (H2) is generated at the cathode (the negative electrode). This hydrogen reacts with CO2 to form methane. The final methanation step completes the biocatalytic treatment of the wastewater. Gas grid injection is one possible use. But for cheese makers, the gas would be used on site to generate electricity and/or heat.

The reaction is accelerated using an applied voltage and is based on the laws of thermodynamics. As a result, the reactor volume can be reduced. The size reduction has several advantages. First, it makes biogas accessible in markets where it was previously not possible due to the high investment costs. Second, it enables higher throughput at a lower cost. Smaller units are mobile and can be shared, moved or rented. After all, food manufacturers want to do what they do best, which is to make food.

 

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Novel membranes from plant waste filter heavy metals from water

Unfortunately, water pollution is still an issue in many places. Heavy metals are a group of water pollutants that can accumulate in the human body and causing cancer and other diseases. Existing technologies for heavy metal removal, however, are very energy intensive.

Scientists from the Nanyang Technological University in Singapore and the Swiss Federal Institute of Technology Zurich (ETHZ) have created a new membrane out of byproducts from the vegetable oil industry. The membrane removes heavy metals from contaminated water. The team discovered that proteins, which originated from peanut or sunflower oil production bind heavy metal ions very effectively. In their tests, they showed that this adsorption process can purify contaminated water so much that it fulfills drinking water quality standards.

The researchers see their membranes as an inexpensive, simple, sustainable and scalable solution for heavy metal removal from water. Their results were published in the Chemical Engineering Journal.

The new protein based membranes were generated by an environmentally friendly process and needed little energy for their use. This makes them a promising water purification solution for industrialized nations as well as less developed countries.

The production of commercial vegetable oils generates protein rich waste products. These remnants remain from the raw plant after the oil extraction. For their membranes, the research team used sunflower and peanut oils. After the proteins had been extracted, they were transformed into nano-amyloid fibrils. These are rope-like structures built from tightly intertwined proteins. The protein fibrils strongly attract heavy metals and act like a molecular sieve. In the published experiments, the membranes removed up to 99.89 percent of heavy metals.

Among the three metals tested, lead and platinum were filtered most effectively, followed by chrome. Since platinum is often used as a catalyst in fuel cells or electrolyzers, the new membrane would be an elegant and cheap method to recover this metal.

The researchers combined the extracted amyloid fibrils with activated carbon. Due to the high surface volume ratio of the amyloid fibrils, they are particularly suitable for adsorption large amounts of heavy metals. The filter can be used for all types of heavy metals. In addition, organic pollutants such as perfluoralkyl and polyfluoralkyl compounds are filtered as well. These chemicals are used for a variety of consumer and industrial products, as well as in nafion membranes of fuel cells.

The concentration of heavy metals in contaminated water determines how much volume the membrane can filter. A hybrid membrane made of sunflower amyloids requires only 16 kg of protein to filter a swimming pool contaminated with 400 parts lead per billion. One kilogram of sunflower extract yields about 160 g of protein. The protein-rich sunflower and peanut oils are inexpensive raw materials. Since this is the first time that amyloid fibrils were obtained from sunflower and peanut proteins, the process must still be scaled and industrialized.

However, due to its simplicity and minimal use of chemical reagents, the process seems easy to scale. This makes it possible to recycle the waste product for further applications and to fully exploit such industrial food waste. The filtered metals can also be extracted and further recycled. After filtration, the membrane with the captured metals can simply be burned and leaving behind only the metals.

While toxic metals such as lead or mercury need safe disposal, other metals such as platinum can be re-used in the production of electronics and other high value devices, such as fuel cells. The recovery of the precious platinum, which costs 30,000 euros per kg, only requires 32 kg of protein, while the recovery of gold, which corresponds to almost 55,000 euros per kg, only requires 16 kg of protein. In view of the costs of less than 1 euro per kg of protein, the advantages are enormous.

The co-author of the article, Raffaele Mezzenga, had already discovered in 2016 that whey proteins from cow milk had similar properties. Back then, the researchers noticed that proteins from plant oil seeds could also have similar properties.

Another great advantage is that, unlike other methods such as reverse osmosis, this filtration does not require electricity. Gravity is completely sufficient for the entire filtration process. The method is also suitable for water purification in poorly developed areas.

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