Hydrogen Gas Recycling for Energy Efficient Ammonia Recovery in Electrochemical Systems

Treatment techniques and resource recovery of source-separated urine: a bibliometric analysis and literature review

Human urine, which is high in nutrients, acts as a resource as well as a contaminant. Indiscriminate urine discharge causes environmental pollution and wastes resources. To elucidate the research status and developmental trajectory of source-separated urine (SSU) treatment and recovery, this study was based on the Web of Science Core Collection (WOSCC) database and used the bibliometric software VOSviewer and CiteSpace to conduct a comprehensive and in-depth bibliometric analysis of the related literature in this field. The findings revealed a general upward trend in SSU treatment and recovery from 2000 to 2023. The compendium of 894 scholarly articles predominantly focused on the disciplines of Environmental Sciences, Environmental Engineering, and Water Resources. China and the USA emerged as the foremost contributors. Keyword co-occurrence mapping, clustering, and burst analysis have shown that the recovery of nitrogen and phosphorus from urine is currently the main focus, with future prospects leaning toward the retrieval of biochemicals and chemical energy. This study systematically categorizes and compares the developmental status, current advancements, and research progress in this field. The findings of this study provide a valuable reference for understanding developmental pathways in this field of research.

Gas permeable membrane electrode assembly with in situ utilization of authigenic acid and base for transmembrane electro-chemisorption to enhance ammonia recovery from wastewater

Ammonia recovery from wastewater is of great significance for aquatic ecology safety, human health and carbon emissions reduction. Electrochemical methods have gained increasing attention since the authigenic base and acid of electrochemical systems can be used as stripper and absorbent for transmembrane chemisorption of ammonia, respectively. However, the separation of electrodes and gas permeable membrane (GPM) significantly restricts the ammonia transfer-transformation process and the authigenic acid-base utilization. To break the restrictions, this study developed a gas permeable membrane electrode assembly (GPMEA), which innovatively integrated anode and cathode on each side of GPM through easy phase inversion of polyvinylidene fluoride binder, respectively. With the GPMEA assembled in a stacked transmembrane electro-chemisorption (sTMECS) system, in situ utilization of authigenic acid and base for transmembrane electro-chemisorption of ammonia was achieved to enhance the ammonia recovery from wastewater. At current density of 60 A/m2, the transmembrane ammonia flux of the GPMEA was 693.0 ± 15.0 g N/(m2·d), which was 86 % and 28 % higher than those of separate GPM and membrane cathode, respectively. The specific energy consumption of the GPMEA was 9.7∼16.1 kWh/kg N, which were about 50 % and 25 % lower than that of separate GPM and membrane cathode, respectively. Moreover, the application of GPMEA in the ammonia recovery from wastewater is easy to scale up in the sTMECS system. Accordingly, with the features of excellent performance, energy saving and easy scale-up, the GPMEA showed good prospects in electrochemical ammonia recovery from wastewater.

Enhancing selective ammonium transport in membrane electrochemical systems

Recovering ammonia nitrogen from wastewater is a sustainable strategy that simultaneously addresses both nitrogen removal and fertilizer production. Membrane electrochemical system (MES), which utilizes electrochemical redox reactions to transport ammonium ions through cation exchange membranes, has been considered as an effective technology for ammonia recovery from wastewater. In this study, we develop a mathematical model to systematically investigate the impact of co-existing ions on the transport of ammonium (NH4+) ions in MES. Our analysis elucidates the importance of pH values on both the NH4+ transport and inert ion (Na+) transport. We further comprehensively assess the system performance by varying the concentration of Na+ in the system. We find that while the inert cation in the initial anode compartment competes with NH4+ transport, NH4+ dominates the cation transport in most cases. The transport number of Na+ surpasses NH4+ only if the fraction of Na+ to total cation is extremely high (>88.5%). Importantly, introducing Na+ ions into the cathode compartment significantly enhances the ammonia transport due to the Donnan dialysis. The analysis of selective ion transport provides valuable insights into optimizing both selectivity and efficiency in ammonia recovery from wastewater.

A stacked transmembrane electro-chemisorption system connected by hydrophobic gas permeable membranes for on-site utilization of authigenic acid and base to enhance ammonia recovery from wastewater

The ammonia recovery from wastewater via electrochemical technologies represents a promising way for wastewater treatment, resource recovery, and carbon emissions reduction. However, chemicals consumption and reactors scalability of the existing electrochemical systems have become the key challenges for their development and application. In this study, a stacked transmembrane electro-chemisorption (sTMECS) system was developed to utilize authigenic acid and base on site for enhancing ammonia recovery from wastewater. The easily scaled up system was achieved via innovatively connecting the cathode chamber in a unit with the anode chamber in the adjacent unit by a hydrophobic gas permeable membrane (GPM). Thus, authigenic base at cathodes and authigenic acid at anodes could be utilized as stripper and absorbent on site to enhance the transmembrane chemisorption of ammonia. Continuous power supply, reducing the distances of electrodes to GPM and moderate aeration of the catholyte could promote ammonia recovery. Applied to the ammonia recovery from the simulated urine, the sTMECS under the current density 62.5 A/cm2 with a catholyte aeration rate of 3.2 L/(L⋅min) for operation time 4 h showed the transmembrane ammonia flux of 26.00 g N/(m2·h) and the system energy consumption of 10.5 kWh/kg N. Accordingly, the developed sTMECS system with chemicals saving, easy scale-up and excellent performance shows good prospects in recovering ammonia from wastewater.

Energy Efficient Carbon Capture through Electrochemical pH Swing Regeneration of Amine Solution

Carbon capture is widely acknowledged as a promising strategy for achieving negative emissions. Electrochemical carbon capture technologies are considered a viable alternative to conventional temperature swing processes. Among these, employing the hydrogen oxidation and hydrogen evolution reactions as a redox couple, along with an ion exchange membrane, offers an effective means of establishing a pH swing for desorbing CO2 and regenerating the alkaline solvent. However, the practical scalability of this approach is impeded by challenges such as high energy demands resulting from a high pH differential between anodic and cathodic environments and operation with solutions with a low conductivity, required to obtain an acceptable current yield. To address these limitations, this study introduces an innovative anion exchange membrane (AEM)-based electrochemical process for solvent regeneration. Our research demonstrates the advantageous utilization of amines as chemical buffers. Selecting an amine solution with a favorable pKa (∼7 to 10) helps in maintaining bicarbonate as the predominant carbon species within the system, thereby ensuring a high current yield (>80%) across various operational conditions (current, load ratio, and solution concentration). Furthermore, our analysis indicates that the use of amine solutions effectively reduces the overpotential of the hydrogen evolution reaction due to a lower local pH. This results in a minimum energy requirement of 63 kJ/mol at a current density of 20 A/m2 to regenerate the solution (MDEA) while maintaining high (>99%) product (CO2) purity.

Long-Term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

Nitrogen in wastewater has negative environmental, human health, and economic impacts but can be recovered to reduce the costs and environmental impacts of wastewater treatment and chemical production. To recover ammonia/ammonium (total ammonia nitrogen, TAN) from urine, we operated electrochemical stripping (ECS) for over a month, achieving 83.4 ± 1.5% TAN removal and 73.0 ± 2.9% TAN recovery. With two reactors, we recovered sixteen 500-mL batches (8 L total) of ammonium sulfate (20.9 g/L TAN) approaching commercial fertilizer concentrations (28.4 g/L TAN) and often having >95% purity. While evaluating the operation and maintenance needs, we identified pH, full-cell voltage, product volume, and water flux into the product as informative process monitoring parameters that can be inexpensively and rapidly measured. Characterization of fouled cation exchange and omniphobic membranes informs cleaning and reactor modifications to reduce fouling with organics and calcium/magnesium salts. To evaluate the impact of urine collection and storage on ECS, we conducted experiments with urine at different levels of dilution with flush water, extents of divalent cation precipitation, and degrees of hydrolysis. ECS effectively treated urine under all conditions, but minimizing flush water and ensuring storage until complete hydrolysis would enable energy-efficient TAN recovery. Our experimental results and cost analysis motivate a multifaceted approach to improving ECS's technical and economic viability by extending component lifetimes, decreasing component costs, and reducing energy consumption through material, reactor, and process engineering. In summary, we demonstrated urine treatment as a foothold for electrochemical nutrient recovery from wastewater while supporting the applicability of ECS to seven other wastewaters with widely varying characteristics. Our findings will facilitate the scale-up and deployment of electrochemical nutrient recovery technologies, enabling a circular nitrogen economy that fosters sanitation provision, efficient chemical production, and water resource protection.

Pulsed electric field drives chemical-free membrane stripping for high ammonia recovery from urine

Recovering ammonia from waste streams (e.g., urine) is highly desirable to reduce natural gas-based NH3 production and nitrogen discharge into the water environment. Electrochemical membrane stripping is an attractive alternative because it can drive NH4+ transformation to NH3 via cathodic OH- production; however, the conventional configurations suffer from relatively low ammonia recovery (<80 %) and significant acid/material usage for ammonia adsorption. To this end, we develop a novel stack system that simply uses an oxygen evolution reaction to in-situ produce acid from water, enabling chemical-free ammonia recovery from synthetic urine. In batch mode, the percentage removal and recovery increased respectively from 74.5 % to 97.9 % and 81.8 % to 92.7 % when the electrode pairs increased from 2 to 4 in the stack system. To address the gas-sparging issue that deteriorated ammonia recovery in continuous operation, pulsed electric field (PEF) mode was applied, resulting in ∼100 % recovery under optimized conditions. At an ammonia removal rate of 35.1 g-N m-2 h-1 and electrical energy consumption of 28.9 kWh kg-N-1, our chemical-free system in PEF mode has achieved significantly higher ammonia recovery (>90 %) from synthetic urine. The total cost to recover 1 kg of NH3-N from real human urine was $15.9 in the proposed system. Results of this study demonstrate that this novel approach holds great promise for high ammonia recovery from waste streams, opening a new pathway toward sustainable nitrogen management.

Electrochemically selective ammonium recovery from wastewater via coupling hydrogen bonding and charge storage

Electrochemical ammonium (NH4+) storage (EAS) has been established as an efficient technology for NH4+ recovery from wastewater. However, there are scientific difficulties unsolved regarding low storage capacity and selectivity, restricting its extensive engineering applications. In this work, electrochemically selective NH4+ recovery from wastewater was achieved by coupling hydrogen bonding and charge storage with self-assembled bi-layer composite electrode (GO/V2O5). The NH4+ storage was as high as 234.7 mg N g-1 (> 102 times higher than conventional activated carbon). Three chains of proof were furnished to elucidate the intrinsic mechanisms for such superior performance. Density functional theory (DFT) showed that an excellent electron-donating ability for NH4+ (0.08) and decrease of diffusion barrier (22.3 %) facilitated NH4+ diffusion onto electrode interface. Physio- and electro-chemical results indicated that an increase of interlamellar spacing (14.3 %) and electrochemical active surface area (ECSA, 388.9 %) after the introduction of GO were responsible for providing greater channels and sites toward NH4+ insertion. Both non-ionic chemical-bonding (V5+=O‧‧‧H, hydrogen-bonding) and charge storage were contributed to the higher capacity and selectivity for NH4+. This work offers underlying guideline for exploitation a storage manner for NH4+ recovery from wastewater.

Hybrid Donnan dialysis-electrodialysis for efficient ammonia recovery from anaerobic digester effluent

Ammonia recovery from wastewater is crucial, yet technology of low carbon emission and high ammonia perm-selectivity against complex stream compositions is urgently needed. Herein, a membrane-based hybrid process of the Donnan dialysis-electrodialysis process (DD-ED) was proposed for sustainable and efficient ammonia recovery. In principle, DD removes the majority of ammonia in wastewater by exploring the concentration gradient of NH₄ ⁺ and driven cation (Na⁺) across the cation exchange membrane, given industrial sodium salt as a driving chemical. An additional ED stage driven by solar energy realizes a further removal of ammonia, recovery of driven cation, and replenishment of OH^- toward ammonia stripping. Our results demonstrated that the hybrid DD-ED process achieved ammonia removal efficiency >95%, driving cation (Na⁺) recovery efficiency >87.1% for synthetic streams, and reduced the OH^- loss by up to 78% compared to a standalone DD case. Ammonia fluxes of 98.2 g_N m^-2 d^-1 with the real anaerobic digestion effluent were observed using only solar energy input at 3.8 kWh kg_N ^-1. With verified mass transfer modeling, reasonably controlled operation, and beneficial recovery performance, the hybrid process can be a promising candidate for future nutrient recovery from wastewater in a rural, remote area.

A novel sustainable N recycling process: Upcycling ammonia to ammonium fertilizer from dilute wastewater and simultaneously realizing phenol degradation via a visible solar-driven PECMA system with efficient Ag2S-BiVO4 photoanodes

The selective recovery of NH₄⁺ as N fertilizers from dilution wastewater is a promising but challenging topic. Herein, a novel visible-light driven photo-electrochemical membrane stripping cell (designated "PECMA") with Ag₂S-BiVO₄ heterojunction photoanode was proposed to recover ammonium from dilute wastewater, which comprised an anode chamber for organics treatment, intermediate chamber for separating ammonium, cathode chamber for upcycling NH₄⁺ into NH₃, and recovery chamber for converting NH₃ into (NH₄)₂SO₄. The NH₄⁺ is concentrated by 21.5 times and recovered as (NH₄)₂SO₄ with a concentration of 7103 mg L^-1 after 10 cycles. At a current density of 3.86 A m^-2, PECMA system achieves excellent NH₄⁺ removal and recovery rates of 97.5 and 37.2 g N m^-2 d^-1 in 100 mg_N L^-1 wastewater. Moreover, PECMA degrades refractory organic pollutants through ClO· generated by Ag₂S-BiVO₄ photoanode, which effectively decompose phenol to CO₂ with a degradation rate of 93 %. Although tested as a proof-of-concept, the hybrid system opens up a novel field involving a sunlight-water-energy nexus, promising high efficiency NH₄⁺ recovery and wastewater remediation.

Protonic Ceramic Electrochemical Cells for Synthesizing Sustainable Chemicals and Fuels

Protonic ceramic electrochemical cells (PCECs) have been intensively studied as the technology that can be employed for power generation, energy storage, and sustainable chemical synthesis. Recently, there have been substantial advances in electrolyte and electrode materials for improving the performance of protonic ceramic fuel cells and protonic ceramic electrolyzers. However, the electrocatalytic materials development for synthesizing chemicals in PCECs has gained less attention, and there is a lack of systematic and fundamental understanding of the PCEC reactor design, reaction mechanisms, and electrode materials. This review comprehensively summarizes and critically evaluates the most up-to-date progress in employing PCECs to synthesize a wide range of chemicals, including ammonia, carbon monoxide, methane, light olefins, and aromatics. Factors that impact the conversion, selectivity, product yield, and energy efficiencies are discussed to provide new insights into designing electrochemical cells, developing electrode materials, and achieving economically viable chemical synthesis. The primary challenges associated with producing chemicals in PCECs are highlighted. Approaches to tackle these challenges are then offered, with a particular focus on deliberately designing electrode materials, aiming to achieve practically valuable product yield and energy efficiency. Finally, perspectives on the future development of PCECs for synthesizing sustainable chemicals are provided.

Integrated membrane electrochemical reactor-membrane distillation process for enhanced landfill leachate treatment

Treatment of recalcitrant landfill leachate (LFL) induces huge energy consumption and carbon emissions due to its complex composition. Although membrane distillation (MD) exhibits good potential in LFL treatment with waste heat utilization, membrane fouling and ammonia rejection are still the major problems encountered that hinder its application. Herein, membrane electrochemical reactor (MER) was coupled with MD for simultaneous membrane fouling control and resource recovery. LFL pretreatment with membrane-less electrochemical reactor (EO) and without pretreatment were also purified by MD for comparison. Results showed that the MER-MD system rejected almost all COD_Cr, total phosphorus, metal salts, and ammonia nitrogen (increased by 33.5%-43.5% without chemical addition), and recovered 31% of ammonia nitrogen and 48% of humic acid in the raw LFL. Owing to the effective removal of hardness (61%) and organics (77%) using MER, the MER-MD system showed higher resistance to the membrane wetting and fouling, with about 61% and 14% higher final vapor flux than those of the MD and EO-MD systems, respectively, and the pure water flux could be fully recovered by alkaline solution cleaning. Moreover, SEM-EDS, ATR-FTIR and XRD characterization further demonstrated the superiority of the MD membrane fouling reversibility of the MER-MD system. Energy consumption and carbon emissions analysis showed that the MER-MD system reduced the total energy consumption/carbon emissions by ∼20% and ∼8% compared to the MD and EO-MD systems, respectively, and the ammonia nitrogen recovered by MER could offset 8.25 kg carbon dioxide equivalent. Therefore, the introduction of MER pretreatment in MD process would be an option to decrease energy consumption and reduce carbon emissions for MD treatment of LFL.

Recent Advances in Bioelectrochemical Systems for Nitrogen and Phosphorus Recovery Using Membranes

Bioelectrochemical systems (BESs) have emerged as a technology that is able to recover resources from different kinds of substrates, especially wastewater. Nutrient recovery, mostly based on membrane reactor configuration, is a clear niche for BES application. The recovery of nitrogen or phosphorus allows for treatment of wastewater while simultaneously collecting a concentrated stream with nutrients that can be reintroduced into the system, becoming a circular economy solution. The aim of this study is to review recent advances in membrane-based BESs for nitrogen and phosphorus recovery and compare the recovery efficiencies and energy requirements of each system. Finally, there is a discussion of the main issues that arise from using membrane-based BESs. The results presented in this review show that it would be beneficial to intensify research on BESs to improve recovery efficiencies at the lowest construction cost in order to take the final step towards scaling up and commercialising this technology.

Membrane Technologies for Nitrogen Recovery from Waste Streams: Scientometrics and Technical Analysis

The concerns regarding the reactive nitrogen levels exceeding the planetary limits are well documented in the literature. A large portion of anthropogenic nitrogen ends in wastewater. Nitrogen removal in typical wastewater treatment processes consumes a considerable amount of energy. Nitrogen recovery can help in saving energy and meeting the regulatory discharge limits. This has motivated researchers and industry professionals alike to devise effective nitrogen recovery systems. Membrane technologies form a fundamental part of these systems. This work presents a thorough overview of the subject using scientometric analysis and presents an evaluation of membrane technologies guided by literature findings. The focus of nitrogen recovery research has shifted over time from nutrient concentration to the production of marketable products using improved membrane materials and designs. A practical approach for selecting hybrid systems based on the recovery goals has been proposed. A comparison between membrane technologies in terms of energy requirements, recovery efficiency, and process scale showed that gas permeable membrane (GPM) and its combination with other technologies are the most promising recovery techniques and they merit further industry attention and investment. Recommendations for potential future search trends based on industry and end users' needs have also been proposed.

Direct Air Capture Using Electrochemically Regenerated Anion Exchange Resins

Direct air capture (DAC) aims to remove CO₂ directly from the atmosphere. In this study, we have demonstrated proof-of-concept of a DAC process combining CO₂ adsorption in a packed bed of amine-functionalized anion exchange resins (AERs) with a pH swing regeneration using an electrochemical cell (EC). The resin bed was regenerated using the alkaline solution produced in the cathodic compartment of the EC, while high purity CO₂ (>95%) was desorbed in the acidifying compartment. After regenerating the AERs, some alkaline solution remained on the surface of the resins and provided additional CO₂ capture capacity during adsorption. The highest CO₂ capture capacity measured was 1.76 mmol·g^-1 dry resins. Moreover, as the whole process was operated at room temperature, the resins did not show any apparent degradation after 150 cycles of adsorption-desorption. Furthermore, when the relative humidity of the air source increased from 33 to 84%, the water loss of the process decreased by 63%, while CO₂ capture capacity fell 22%. Finally, although the pressure drop of the adsorption column (5 ± 1 kPa) and the energy consumption of the EC (537 ± 33 kJ·mol^-1 at 20 mA·cm^-2) are high, we have discussed the potential improvements toward a successful upscaling.

Electrocatalytic Upcycling of Nitrate Wastewater into an Ammonia Fertilizer via an Electrified Membrane

Electrochemically upcycling wastewater nitrogen such as nitrate (NO₃^-) and nitrite (NO₂^-) into an ammonia fertilizer is a promising yet challenging research topic in resource recovery and wastewater treatment. This study presents an electrified membrane made of a CuO@Cu foam and a polytetrafluoroethylene (PTFE) membrane for reducing NO₃^- to ammonia (NH₃) and upcycling NH₃ into (NH₄)₂SO₄, a liquid fertilizer for ready-use. A paired electrolysis process without external acid/base consumption was achieved under a partial current density of 63.8 ± 4.4 mA·cm^-2 on the cathodic membrane, which removed 99.9% NO₃^- in the feed (150 mM NO₃^-) after a 5 h operation with an NH₃ recovery rate of 99.5%. A recovery rate and energy consumption of 3100 ± 91 g-(NH₄)₂SO₄·m^-2·d^-1 and 21.8 ± 3.8 kWh·kg^-1-(NH₄)₂SO₄, respectively, almost outcompete the industrial ammonia production cost in the Haber-Bosch process. Density functional theory (DFT) calculations unraveled that the in situ electrochemical conversion of Cu²⁺ into Cu¹⁺ provides highly dynamic active species for NO₃^- reduction to NH₃. This electrified membrane process was demonstrated to achieve synergistic nitrate decontamination and nutrient recovery with durable catalytic activity and stability.

Effects of Current on the Membrane and Boundary Layer Selectivity in Electrochemical Systems Designed for Nutrient Recovery

During electrochemical nutrient recovery, current and ion exchange membranes (IEM) are used to extract an ionic species of interest (e.g., ion) from a mixture of multiple ions. The species of interest (ion 1) has an opposing charge to the IEM. When ion 1 is extracted from the solution, the species fractions at the membrane and the adjunct boundary layers are affected. Hence, the species transport through the electrochemical system (ES) can no longer be described as electrodialysis-like. A dynamic state is observed in the compartments, where the ionic species are recovered. When the boundary layer-membrane interface is depleted, the IEM is at maximum current. If the ES is operated at a current higher than the maximum current, the fluxes of both ion 1 and other competing ions, with the same charge (ion 2), occur. This means, for example, ion 1 will be recovered, and the concentration of ion 2 will build up in time. Therefore, a steady state is never reached. Ideally, to prevent the effect of limiting current at the boundary layer-membrane interface, ES for nutrient recovery should be operated at low currents.

Electrochemically mediated precipitation of phosphate minerals for phosphorus removal and recovery: Progress and perspective

Phosphorus (P) is an essential element for the growth and reproduction of organisms. Unfortunately, the natural P cycle has been broken by the overexploitation of P ores and the associated discharge of P into water bodies, which may trigger the eutrophication of water bodies in the short term and possible P shortage soon. Consequently, technologies emerged to recover P from wastewater to mitigate pollution and exploit secondary P resources. Electrochemically induced phosphate precipitation has the merit of achieving P recovery without dosing additional chemicals via creating a localized high pH environment near the cathode. We critically reviewed the development of electrochemically induced precipitation systems toward P removal and recovery over the past ten years. We summarized and discussed the effects of pH, current density, electrode configuration, and water matrix on the performance of electrochemical systems. Next to ortho P, we identified the potential and illustrated the mechanism of electrochemical P removal and recovery from non-ortho P compounds by combined anodic or anode-mediated oxidation and cathodic reduction (precipitation). Furthermore, we assessed the economic feasibility of electrochemical methods and concluded that they are more suitable for treating acidic P-rich waste streams. Despite promising potentials and significant progress in recent years, the application of electrochemical systems toward P recovery at a larger scale requires further research and development. Future work should focus on evaluating the system's performance under long-term operation, developing an automatic process for harvesting P deposits, and performing a detailed economic and life-cycle assessment.

State of the art of urine treatment technologies: A critical review

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.

Bipolar Membrane Electrodialysis for Ammonia Recovery from Synthetic Urine: Experiments, Modeling, and Performance Analysis

Recovering nitrogen from source-separated urine is an important part of the sustainable nitrogen management. A novel bipolar membrane electrodialysis with membrane contactor (BMED-MC) process is demonstrated here for efficient recovery of ammonia from synthetic source-separated urine (∼3772 mg N L^-1). In a BMED-MC process, electrically driven water dissociation in a bipolar membrane simultaneously increases the pH of the urine stream and produces an acid stream for ammonia stripping. With the increased pH of urine, ammonia transports across the gas-permeable membrane in the membrane contactor and is recovered by the acid stream as ammonium sulfate that can be directly used as fertilizer. Our results obtained using batch experiments demonstrate that the BMED-MC process can achieve 90% recovery. The average ammonia flux and the specific energy consumption can be regulated by varying the current density. At a current density of 20 mA cm^-2, the energy required to achieve a 67.5% ammonia recovery in a 7 h batch mode is 92.8 MJ kg^-1 N for a bench-scale system with one membrane stack and can approach 25.8 MJ kg^-1 N for large-scale systems with multiple membrane stacks, with an average ammonia flux of 2.2 mol m^-2 h^-1. Modeling results show that a continuous BMED-MC process can achieve a 90% ammonia recovery with a lower energy consumption (i.e., 12.5 MJ kg^-1 N). BMED-MC shows significant potential for ammonia recovery from source-separated urine as it is relatively energy-efficient and requires no external acid solution.

Anaerobic digestion of organic waste: Recovery of value-added and inhibitory compounds from liquid fraction of digestate

Anaerobic digestion, as an eco-friendly waste treatment technology, is facing the problem of low stability and low product value. Harvesting value-added products beyond methane and removing the inhibitory compounds will unleash new vitality of anaerobic digestion, which need to be achieved by selective separation of certain compounds. Various methods are reviewed in this study for separating valuable products (volatile fatty acids, medium-chain carboxylic acids, lactic acid) and inhibitory substance (ammonia) from the liquid fraction of digestate, including their performance, applicability, corresponding limitations and roadmaps for improvement. In-situ extraction that allows simultaneous production and extraction is seen as promising approach which carries good potential to overcome the barriers for continuous production. The prospects and challenges of the future development are further analyzed based on in-situ extraction and economics.

Donnan Dialysis for scaling mitigation during electrochemical ammonium recovery from complex wastewater

Inorganic scaling is often an obstacle for implementing electrodialysis systems in general and for nutrient recovery from wastewater specifically. In this work, Donnan dialysis was explored, to prevent scaling and to prolong operation of an electrochemical system for TAN (total ammonia nitrogen) recovery. An electrochemical system was operated with and without an additional Donnan dialysis cell, while being supplied with synthetic influent and real digested black water. For the same Load Ratio (nitrogen load vs applied current) while treating digested black water, the system operated for a period three times longer when combined with a Donnan cell. Furthermore, the amount of nitrogen recovered was higher. System performance was evaluated in terms of both TAN recovery and energy efficiency, at different Load Ratios. At a Load Ratio 1.3 and current density of 10 A m^-2, a TAN recovery of 83% was achieved while consuming 9.7 kWh kg_N^-1.

The Application of Cation Exchange Membranes in Electrochemical Systems for Ammonia Recovery from Wastewater

Electrochemical processes are considered promising technologies for ammonia recovery from wastewater. In electrochemical processes, cation exchange membrane (CEM), which is applied to separate compartments, plays a crucial role in the separation of ammonium nitrogen from wastewater. Here we provide a comprehensive review on the application of CEM in electrochemical systems for ammonia recovery from wastewater. Four kinds of electrochemical systems, including bioelectrochemical systems, electrochemical stripping, membrane electrosorption, and electrodialysis, are introduced. Then we discuss the role CEM plays in these processes for ammonia recovery from wastewater. In addition, we highlight the key performance metrics related to ammonia recovery and properties of CEM membrane. The limitations and key challenges of using CEM for ammonia recovery are also identified and discussed.

Electrochemical In Situ pH Control Enables Chemical-Free Full Urine Nitrification with Concomitant Nitrate Extraction

Urine is a valuable resource for nutrient recovery. Stabilization is, however, recommended to prevent urea hydrolysis and the associated risk for ammonia volatilization, uncontrolled precipitation, and malodor. This can be achieved by alkalinization and subsequent biological conversion of urea and ammonia into nitrate (nitrification) and organics into CO₂. Yet, without pH control, the extent of nitrification is limited as a result of insufficient alkalinity. This study explored the feasibility of an integrated electrochemical cell to obtain on-demand hydroxide production through water reduction at the cathode, compensating for the acidification caused by nitritation, thereby enabling full nitrification. To deal with the inherent variability of the urine influent composition and bioprocess, the electrochemical cell was steered via a controller, modulating the current based on the pH in the bioreactor. This provided a reliable and innovative alternative to base addition, enabling full nitrification while avoiding the use of chemicals, the logistics associated with base storage and dosing, and the associated increase in salinity. Moreover, the electrochemical cell could be used as an in situ extraction and concentration technology, yielding an acidic concentrated nitrate-rich stream. The make-up of the end product could be tailored by tweaking the process configuration, offering versatility for applications on Earth and in space.

Donnan Dialysis-Osmotic Distillation (DD-OD) Hybrid Process for Selective Ammonium Recovery Driven by Waste Alkali

This work proposed an innovative and energy-efficient Donnan Dialysis (DD) and Osmotic Distillation (OD) hybrid process for alkali-driven ammonium recovery from wastewater. The efficiency and feasibility of ammonium removal and recovery from synthetic and real wastewater using NaOH and waste alkali were investigated. Ammonium in the feed first transported across the cation exchange membrane and accumulated in the receiver chamber. It is then deprotonated as ammonia, passing through the gas permeable membrane and finally is fixed as ammonium salt in the acid chamber. Our results indicated that employing waste alkali (red mud leachate) as driving solution led to excellent ammonium recovery performances (recovery efficiency of >80%), comparable to those of NaOH solution. When the initial ammonium concentration was 5 and 50 mM, the waste alkali driven DD-OD process achieved acceptable NH₄⁺-N flux density of 16.8 and 169 g N m^-2 d^-1, at energy cost as low as 8.38 and 2.06 kWh kg^-1 N, respectively. Since this alkali driven DD-OD hybrid process is based on solute concentration (or partial pressure) gradient, it could be an energy-effective technology capable of treating wastewaters containing ammonium using waste alkali to realize nutrients recovery in a sustainable manner.

Gas-diffusion-electrode based direct electro-stripping system for gaseous ammonia recovery from livestock wastewater

Livestock wastewater (LW) typically contains a substantial amount of NH₄⁺ that can potentially be recovered and used in fertilizers or chemicals. In an attempt to recover NH₄⁺ from LW, a novel electrochemical approach using a gas diffusion electrode (GDE) was developed and its efficacy was demonstrated in this study. The GDE-based electrochemical device, when operated at an air-flow rate of 20 mL/min, was free of back-diffusion flux, which is a fatal drawback of any membrane-based NH₄⁺ separation approach. Continuous operation resulted in a nitrogen flux of 890 g N/m²d with synthetic LW and 770 g N/m²d with real LW at a current density of 10 mA/cm². The electrochemical energy input was 7.42 kWh/kg N with synthetic LW and 9.44 kWh/kg N with real LW. Compared with the traditional stripping method, the GDE-based electrochemical system has a certain potential to be competitive, in terms of energy consumption. For instance, a rough-cost estimate based only on operating costs regarding chemical usage, air blowing, and water pumping revealed that the system consumed 13.44 kWh/kg N, whereas the conventional stripper required 27.6 kWh/kg N. This analysis showed that an electrochemical approach such as our GDE-based method can recover NH₃, (particularly in gaseous form) from LW. In addition, with the future development of a smart operation method, as proposed and demonstrated in this study, the cost-effective implementation of a GDE-based method is feasible.

Electrochemical recovery of H2 and nutrients (N, P) from synthetic source separate urine water

This study examined an electrochemical method of H₂ production and nutrient recovery from synthetic source separated urine (SSU). The efficacy of H₂ production was examined through hydrogen recovery experiments (HRE) using Ni foam electrodes. Similarly, nutrient (N and P) recovery was also examined in post-nutrient recovery experiments (NRE) with sacrificial Mg electrodes. To achieve higher nutrient recovery in the post-nutrient recovery process, the most important operating parameters (initial solution pH (pH_i) and current density) were optimized. Optimization of NRE revealed that > 90% NH₃-N and PO₄^3--P could be recovered at 8 mA cm^-2 with a pH_i of 6-8. Notable NH₃-N and PO₄^3--P reduction were observed at an equimolar Mg²⁺ dissolution ratio (1:1) of Mg²⁺:NH₄⁺ and a 1.1:1 ratio of Mg²⁺:PO₄^3- respectively. However, poor total Kjeldahl nitrogen (TKN) reduction was observed. Thus, we anticipate that direct electrochemical conversion of urea to N₂ at the anode followed by H₂ generation at the cathode is a more sustainable way to reduce TKN. Batch HRE showed that the initial TKN, 1094 mg L^-1 (934 mg L^-1 from urea-N and 160 mg L^-1 from NH₄Cl), was significantly reduced to 360 mg L^-1 by Ni-Ni electrolysis, whereas around 53.8 g H₂ gas was received from this Ni-Ni electrolysis system with a flow rate of 5-5.8 g mol^-1 day^-1. Overall, this work produced a 68% reduction in TKN due to electrochemical conversion of urea into H₂.

Minimal Bipolar Membrane Cell Configuration for Scaling Up Ammonium Recovery

Electrochemical systems for total ammonium nitrogen (TAN) recovery are a promising alternative compared with conventional nitrogen-removal technologies. To make them competitive, we propose a new minimal stackable configuration using cell pairs with only bipolar membranes and cation-exchange membranes. The tested bipolar electrodialysis (BP-ED) stack included six cell pairs of feed and concentrate compartments. Critical operational parameters, such as current density and the ratio between applied current to nitrogen loading (load ratio), were varied to investigate the performance of the system using synthetic wastewater with a high nitrogen content as an influent (NH₄ ⁺ ≈ 1.75 g L^-1). High TAN removal (>70%) was achieved for a load ratio higher than 1. At current densities of 150 A m^-2 and a load ratio of 1.2, a TAN transport rate of 1145.1±14.1 g_N m^-2 d^-1 and a TAN-removal efficiency of 80% were observed. As the TAN removal was almost constant at different current densities, the BP-ED stack performed at a high TAN transport rate (819.1 g_N m^-2 d^-1) while consuming the lowest energy (18.3 kJ g_N ^-1) at a load ratio of 1.2 and 100 A m^-2. The TAN transport rate, TAN removal, and energy input achieved by the minimal BP-ED stack demonstrated a promising new cell configuration for upscaling.

Technologies for the recovery of nutrients, water and energy from human urine: A review

The global demand for a constant supply of fertilizer is increasing with the booming of the population. Nowadays more focus is given to the recovery and reuse of the nutrients rather than synthesis of the fertilizer from chemicals. Human urine is the best available resource for the primary macronutrients (Nitrogen, Phosphorus and Potassium) for the fertilizer as it contains 10-12 g/L nitrogen, 0.1-0.5 g/L phosphorous and 1.0-2.0 g/L potassium. For the recovery of these nutrients from human urine, various technologies are available which requires source separation and treatment. . In this review, a wide range of the technologies for the treatment of source-separated human urine are covered and discussed in detail. This review has categorized the technologies based on the recovery of nutrients, energy, and water from human urine. Among the various technologies available, Bio-electrochemical technologies are environmental friendly and recovers energy along with the nutrients. Forward Osmosis is the best available technology for the water recovery and for concentrating the nutrients in urine, without or minimal consumption of energy. However, experimental work in this technology is at its prior stage. A single technology is still not sufficient to recover nutrients, water and energy. Therefore, integration of two or more technologies seems essential.

Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture

CO2 capture from the atmosphere (or direct air capture) is widely recognized as a promising solution to reach negative emissions, and technologies using alkaline solutions as absorbent have already been demonstrated on a full scale. In the conventional temperature swing process, the subsequent regeneration of the alkaline solution is highly energy-demanding. In this study, we experimentally demonstrate simultaneous solvent regeneration and CO2 desorption in a continuous system using a H2-recycling electrochemical cell. A pH gradient is created in the electrochemical cell so that CO2 is desorbed at a low pH, while an alkaline capture solution (NaOH) is regenerated at high pH. By testing the cell under different working conditions, we experimentally achieved CO2 desorption with an energy consumption of 374 kJ·mol-1 CO2 and a CO2 purity higher than 95%. Moreover, our theoretical calculations show that a minimum energy consumption of 164 kJ·mol-1 CO2 could be achieved. Overall, the H2-recycling electrochemical cell allowed us to accomplish the simultaneous desorption of high-purity CO2 stream and regeneration of up to 59% of the CO2 capture capacity of the absorbent. These results are promising toward the upscaling of an energy-effective process for direct air capture.

Technologies for biological removal and recovery of nitrogen from wastewater

Water contamination is a growing environmental issue. Several harmful effects on human health and the environment are attributed to nitrogen contamination of water sources. Consequently, many countries have strict regulations on nitrogen compound concentrations in wastewater effluents. Wastewater treatment is carried out using energy- and cost-intensive biological processes, which convert nitrogen compounds into innocuous dinitrogen gas. On the other hand, nitrogen is also an essential nutrient. Artificial fertilizers are produced by fixing dinitrogen gas from the atmosphere, in an energy-intensive chemical process. Ideally, we should be able to spend less energy and chemicals to remove nitrogen from wastewater and instead recover a fraction of it for use in fertilizers and similar applications. In this review, we present an overview of various technologies of biological nitrogen removal including nitrification, denitrification, anaerobic ammonium oxidation (anammox), as well as bioelectrochemical systems and microalgal growth for nitrogen recovery. We highlighted the nitrogen removal efficiency of these systems at different temperatures and operating conditions. The advantages, practical challenges, and potential for nitrogen recovery of different treatment methods are discussed.

Urine in Bioelectrochemical Systems: An Overall Review

In recent years, human urine has been successfully used as an electrolyte and organic substrate in bioelectrochemical systems (BESs) mainly due of its unique properties. Urine contains organic compounds that can be utilised as a fuel for energy recovery in microbial fuel cells (MFCs) and it has high nutrient concentrations including nitrogen and phosphorous that can be concentrated and recovered in microbial electrosynthesis cells and microbial concentration cells. Moreover, human urine has high solution conductivity, which reduces the ohmic losses of these systems, improving BES output. This review describes the most recent advances in BESs utilising urine. Properties of neat human urine used in state-of-the-art MFCs are described from basic to pilot-scale and real implementation. Utilisation of urine in other bioelectrochemical systems for nutrient recovery is also discussed including proofs of concept to scale up systems.

Competition of electrogens with methanogens for hydrogen in bioanodes

Bioelectrochemical systems (BES) can provide an energy efficient way to recover nutrients from wastewaters. However, the electron donors available in wastewater are often not sufficient to recover the total amount of nutrients. This work investigates hydrogen (H₂) as an additional substrate for bioanodes. This hydrogen can be produced in the fermentation of complex organic waste or could be recycled from the cathode. Understanding how to influence the competition of electroactive microorganisms (EAM) with methanogens for H₂ gas from different sources is key to successful application of H₂ as additional electron donor in bioelectrochemical nutrient recovery. Ethanol (EtOH) was used as model compound for complex wastewaters since it is fermented into both acetate and H₂. EtOH was efficiently converted into electricity (e^-) by a syntrophic biofilm. Total recovered charge from 1 mM EtOH was 20% higher than for the same amount of acetate. This means that H₂ from EtOH fermentation was converted by EAM into electricity. Low EtOH concentrations (1  mM) led to higher conversion efficiencies into electricity than higher concentrations (5 and 10  mM). Thermodynamic calculations show this correlates with a higher energy gain for electrogens compared to methanogens at low H₂ concentrations. Cumulatively adding 1 mM EtOH without medium exchange (14 times in 14 days) resulted in stable conversion of H₂ to e^- (67%-77% e^-) rather than methane. With H₂ gas as electron donor, 68 ± 2% H₂ was converted into e^- with no carbon source added, and still 53 ± 5% to e^- when 50  mM bicarbonate was provided. These results show that under the provided conditions, electrogens can outcompete methanogens for H₂ as additional electron donor in MECs for nutrient recovery.

Building an operational framework for selective nitrogen recovery via electrochemical stripping

Recovering nitrogen from wastewater can simultaneously fulfill the roles of traditional removal technologies such as nitrification-denitrification and fertilizer production processes such as Haber-Bosch. We have recently demonstrated a proof-of-concept for selective recovery of the fertilizer ammonium sulfate via electrochemical stripping, a combination of electrodialysis and membrane stripping. In this study, we furthered electrochemical stripping from concept to informed practice by investigating the effects of influent concentration (30, 300, and 3000 mg N/L), catholyte temperature (15, 23, and 35 °C), and gas permeable membrane choice on electrochemical nitrogen removal and recovery. We also proposed and validated a nitrogen mass transport model for the experimental results, providing mechanistic rationale behind observed effects of varying operating parameters. While changing operating parameters did affect performance, electrochemical stripping exhibited robust performance over a range of realistic ambient temperatures, three gas permeable membranes, and three orders of magnitude of influent concentrations. Practically, these results demonstrate that electrochemical stripping is viable across a range of waste streams and resilient to fluctuations in temperature and nitrogen concentration; they also establish operational trade-offs between residence time and energy consumption. As a result of this work, electrochemical stripping continues to mature from concept to practice and provides lessons for developing other resource recovery technologies.

Hydrophobic Gas Transfer Membranes for Wastewater Treatment and Resource Recovery

Gaseous compounds, such as CH₄, H₂, and O₂, are commonly produced or consumed during wastewater treatment. Traditionally, these gases need to be removed or delivered using gas sparging or liquid heating, which can be energy intensive with low efficiency. Hydrophobic membranes are being increasingly investigated in wastewater treatment and resource recovery. This is because these semipermeable barriers repel water and create a three-phase interface that enhances mass transfer and chemical conversions. This Critical Review provides a first comprehensive analysis of different hydrophobic membranes and processes, and identifies the challenges and potential for future system development. The discussions and analyses were grouped based on mechanisms and applications, including membrane gas extraction, membrane gas delivery, and hybrid processes. Major challenges, such as membrane fouling, wetting, and limited selectivity and functionality, are identified, and potential solutions articulated. New opportunities, such as electrochemical coating, integrated membrane electrodes, and membrane functionalization, are also discussed to provide insights for further development of more efficient and low-cost membranes and processes.

Continuous Ammonia Recovery from Wastewaters Using an Integrated Capacitive Flow Electrode Membrane Stripping System

We have previously described a novel flow-electrode capacitive deionization (FCDI) unit combined with a hydrophobic gas-permeable hollow fiber membrane contactor (designated "CapAmm") and presented results showing efficient recovery of ammonia from dilute synthetic wastewaters (Zhang et al., Environ. Sci. Technol. Lett. 2018, 5, 43-49). We extend this earlier study here with description of an FCDI system with integrated flat sheet gas permeable membrane with comprehensive assessment of ammonia recovery performance from both dilute and concentrated wastewaters. The integrated CapAmm cell exhibited excellent ammonia removal and recovery efficiencies (up to ∼90% and ∼80% respectively). The energy consumptions for ammonia recovery from low-strength (i.e., domestic) and high-strength (i.e., synthetic urine) wastewaters were 20.4 kWh kg^-1 N and 7.8 kWh kg^-1 N, respectively, with these values comparable to those of more conventional alternatives. Stable ammonia recovery and salt removal performance was achieved over more than two days of continuous operation with ammonia concentrated by ∼80 times that of the feed stream. These results demonstrate that the integrated CapAmm system described here could be a cost-effective technology capable of treating wastewaters and realizing both nutrient recovery and water reclamation in a sustainable manner.

Continuous Ammonia Recovery from Wastewaters Using an Integrated Capacitive Flow Electrode Membrane Stripping System

We have previously described a novel flow-electrode capacitive deionization (FCDI) unit combined with a hydrophobic gas-permeable hollow fiber membrane contactor (designated "CapAmm") and presented results showing efficient recovery of ammonia from dilute synthetic wastewaters (Zhang et al., Environ. Sci. Technol. Lett. 2018, 5, 43-49). We extend this earlier study here with description of an FCDI system with integrated flat sheet gas permeable membrane with comprehensive assessment of ammonia recovery performance from both dilute and concentrated wastewaters. The integrated CapAmm cell exhibited excellent ammonia removal and recovery efficiencies (up to ∼90% and ∼80% respectively). The energy consumptions for ammonia recovery from low-strength (i.e., domestic) and high-strength (i.e., synthetic urine) wastewaters were 20.4 kWh kg^-1 N and 7.8 kWh kg^-1 N, respectively, with these values comparable to those of more conventional alternatives. Stable ammonia recovery and salt removal performance was achieved over more than two days of continuous operation with ammonia concentrated by ∼80 times that of the feed stream. These results demonstrate that the integrated CapAmm system described here could be a cost-effective technology capable of treating wastewaters and realizing both nutrient recovery and water reclamation in a sustainable manner.

A dual ammonia-responsive sponge sensor: preparation, transition mechanism and sensitivity

PDMS-PU (polydimethylsiloxane-polyurethane) sponge decorated with In(OH)3 (indium hydroxide) and BCP (bromocresol purple) particles is shown to be a room-temperature ammonia sensor with high sensitivity and excellent reproducibility; it can accomplish real-time detection and monitoring of ammonia in the surrounding environment. The superhydrophobic and yellowish In(OH)3-BCP-TiO2-based ammonia-responsive (IBT-AR) sponge changes to a purple superhydrophilic one when exposed to ammonia. Notably, after reacting with ammonia, the sponge can recover its original wettability and color after heating in air. The wettability, color and absorption signal of IBT-AR sponge have been measured for sensing ammonia using the water contact angle, macroscopic observation and UV-vis absorption spectrometry, respectively. The minimum ammonia concentrations that can be detected by the sponge wettability, color and absorption signal are 0.5%, 1.4 ppm and 50 ppb, respectively. This kind of sponge with smart wettability and color is a promising new ammonia detector.

Energy-Efficient Ammonia Recovery in an Up-Scaled Hydrogen Gas Recycling Electrochemical System

Nutrient and energy recovery is becoming more important for a sustainable future. Recently, we developed a hydrogen gas recycling electrochemical system (HRES) which combines a cation exchange membrane (CEM) and a gas-permeable hydrophobic membrane for ammonia recovery. This allowed for energy-efficient ammonia recovery, since hydrogen gas produced at the cathode was oxidized at the anode. Here, we successfully up-scaled and optimized this HRES for ammonia recovery. The electrode surface area was increased to 0.04 m² to treat up to 11.5 L/day (∼46 g_N/day) of synthetic urine. The system was operated stably for 108 days at current densities of 20, 50, and 100 A/m². Compared to our previous prototype, this new cell design reduced the anode overpotential and ionic losses, while the use of an additional membrane reduced the ion transport losses. Overall, this reduced the required energy input from 56.3 kJ/g_N (15.6 kW h/kg_N) at 50 A/m² (prototype) to 23.4 kJ/g_N (6.5 kW h/kg_N) at 100 A/m² (this work). At 100 A/m², an average recovery of 58% and a TAN (total ammonia nitrogen) removal rate of 598 g_N/(m² day) were obtained across the CEM. The TAN recovery was limited by TAN transport from the feed to concentrate compartment.

(Bio)electrochemical ammonia recovery: progress and perspectives

In recent years, (bio)electrochemical systems (B)ES have emerged as an energy efficient alternative for the recovery of TAN (total ammonia nitrogen, including ammonia and ammonium) from wastewater. In these systems, TAN is removed or concentrated from the wastewater under the influence of an electrical current and transported to the cathode. Subsequently, it can be removed or recovered through stripping, chemisorption, or forward osmosis. A crucial parameter that determines the energy required to recover TAN is the load ratio: the ratio between TAN loading and applied current. For electrochemical TAN recovery, an energy input is required, while in bioelectrochemical recovery, electric energy can be recovered together with TAN. Bioelectrochemical recovery relies on the microbial oxidation of COD for the production of electrons, which drives TAN transport. Here, the state-of-the-art of (bio)electrochemical TAN recovery is described, the performance of (B)ES for TAN recovery is analyzed, the potential of different wastewaters for BES-based TAN recovery is evaluated, the microorganisms found on bioanodes that treat wastewater high in TAN are reported, and the toxic effect of the typical conditions in such systems (e.g., high pH, TAN, and salt concentrations) are described. For future application, toxicity effects for electrochemically active bacteria need better understanding, and the technologies need to be demonstrated on larger scale.