Article

Passive Separation of Recovered Ammonia from Catholyte for Reduced Energy Consumption in Microbial Electrolysis Cells

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Ammonia recovery using microbial electrolysis cells (MECs) is of great interest due to potentially high energy efficiency. However, separating the recovered ammonia from MEC catholyte demands energy input via gas stripping or solution mixing. In this study, a passive separation method has been investigated to greatly reduce energy input for ammonia recovery. By exposing the cathode electrode directly to the gas phase, the passive separation led to comparable current generation to that with the active aeration, through the mutual influence of catholyte pH and conductivity. With the active aeration, the percentage of nitrogen in the catholyte (1–4%) was much lower than that in the MEC catholyte with the passive separation (21.1 ± 4.8%). Although the active aeration could achieve a higher ammonia recovery efficiency of 90.1 ± 1.3%, the energy consumption with the passive separation was only 1.3 kW h per kg N recovery, significantly lower than 2.3 kW h per kg N recovery with the active aeration. These results have demonstrated the effectiveness of passive separation as a simple method to collect the recovered ammonia with high energy efficiency.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Hence, there is a great demand for nitrogen recovery from other resources and wastewater is considered as a sustainable resource of ammonia (Solon et al., 2019). Qin et al. (2018) investigated the use of passive separation and active aeration methods in an MEC for ammonia recovery by ascertaining the influence of catholyte pH and conductivity. The recovery process of nitrogen via redox reactions at cathode and anodes of MEC system is illustrated in Fig. 2 (Xiao et al., 2016). ...
... In MFCs, oxygen acts as oxidizing agents and induces the flow of electrical current; however, MFCs must be supplied with a minimum amount of current in order to carry out the required bioelectrolytic reactions. MFCs are claimed to be more effective as a biosensor with a faster and more sensitive response (Adekunle et al., 2019), but MECs are more effective in terms of resource recovery (Qin et al., 2018). ...
... In advanced bioreactor configurations such as the microbial fuel cells (MFCs), ammonia can be recovered by the cathodic reduction reaction (ammonium ions to ammonia gas) and it can be separated by stripping. A previous study reports that the energy requirement is 4.9 kWh/(kg N) in microbial fuel cells (MFCs) and 1.3 kWh/(kg N) in microbial electrolysis cells (MECs) for ammonia recovery (Qin et al., , 2018. Another recent study proposes a novel method for the recovery of ammonia from urine using transmembrane chemisorption (TMCS) ( (Zamora et al., 2017). ...
Article
In recent years, due to rapid globalization and urbanization, the demand for fuels, energy, water and nutrients has been continuously increasing. To meet the future need of the society, wastewater is a prominent and emerging source for resource recovery. It provides an opportunity to recover valuable resources in the form of energy, fertilizers, electricity, nutrients and other products. The aim of this review is to elaborate the scientific literature on the valorization of wastewater using wide range of treatment technologies and reduce the existing knowledge gap in the field of resource recovery and water reuse. Several versatile, resilient environmental techniques/technologies such as ion exchange, bioelectrochemical, adsorption, electrodialysis, solvent extraction, etc. are employed for the extraction of value-added products from waste matrices. Since the last two decades, valuable resources such as polyhydroxyalkanoate (PHA), matrix or polymers, cellulosic fibers, syngas, biodiesel, electricity, nitrogen, phosphorus, sulfur, enzymes and a wide range of platform chemicals have been recovered from wastewater. In this review, the aspects related to the persisting global water issues, the technologies used for the recovery of different products and/or by-products, economic sustainability of the technologies and the challenges encountered during the valorization of wastewater are discussed comprehensively.
... Nitrogen is one of the major nutrients used as a fertilizer, and nowadays it is commercially produced via the Haber-Bosch process with significant energy consumption. 117 The demand for nitrogen fertilizer is expected to increase at an average annual growth rate of 1.5% over the following decade. 118 The issue of producing ammonia in a sustainable manner represents a global challenge. ...
... However, high energy input via solution mixing or gas stripping is required to separate the recovered ammonia from the MEC catholyte. Qin et al. 117 exposed the cathode directly to the gas phase to achieve passive separation, which was comparable with current generation using active aeration in the MEC. The percentage of nitrogen in the MEC catholyte with passive separation was 21.1 ± 4.8%. ...
Article
Microbial electrolysis cell (MEC) has been studied in a wide range of potential applications such as recalcitrant pollutants removal, chemicals synthesis, resources recovery and biosensors. However, MEC technology is still in its infancy stage and poses serious challenges towards practical large‐scale applications. To understand the diversified applications of MEC, this review aims exploring MEC applications in the following contexts: an overview of MEC for energy generation and recycling such as hydrogen, methane, formic acid and hydrogen peroxide; contaminant removal, specifically complex organic pollutants and inorganic pollutants; as a sensor; as well as resource recovery. New concepts of MEC technology; configuration optimization; electron transfer pathways in biocathode, and coupling with other technologies for value‐added applications such as MEC‐anaerobic digestion, MEC‐MFC, MEC‐MDC and Bio‐E‐Fenton system are discussed. Finally, challenges and outlooks are suggested. The review aims to assist researchers and engineers to understand the latest trends in MEC technologies and applications. This article is protected by copyright. All rights reserved.
... According to the statistics, about 30% of total ammoniumnitrogen in fertilizers flowed eventually into wastewater streams [1,2]. The robust denitrification technologies such as nitrificationdenitrification, anaerobic ammonia oxidation, and breakpoint chlorination have been developed to remove reactive nitrogen (NO 3 À , NO 2 À , NH 4 þ , NH 3 , and urea) as N 2 [3,4]. ...
... Anode: ammonia electro-oxidation reaction 2NH 3(aq) þ 6OH À / N 2(g) þ 6H 2 O þ 6e À E 0 ¼ À0.77 V/SHE (1) Cathode: hydrogen evolution reaction (HER) 6H 2 O þ 6e À / 3H 2(g) þ 6OH À E 0 ¼ À0.83 V/SHE (2) Overall: ammonia electrolysis cell ...
... This recovery process can be highly energy efficient. It was reported that ammonia recovery would require 4.9 kWh/(kg N) in an MFC or 1.3 kWh/(kg N) in an MEC with passive aeration (Qin et al., 2018). A recent study has demonstrated ammonia recovery in a scaled-up system (5 L) with 31% ammonia removal and 31% ammonia recovery by using TransMembraneChemiSorption (TMCS) membrane module in a two-stage treatment of urine waste (Zamora et al., 2017). ...
Article
Bioelectrochemical systems (BES) have been extensively studied for resource recovery from wastewater. By taking advantage of interactions between microorganisms and electrodes, BES can accomplish wastewater treatment while simultaneously recovering various resources including nutrients, energy and water (“NEW”). Despite much progress in laboratory studies, BES have not been advanced to practical applications. This paper aims to provide some subjective opinions and a concise discussion of several key challenges in BES-based resource recovery and help identify the potential application niches that may guide further technological development. In addition to further increasing recovery efficiency, it is also important to have more focus on the applications of the recovered resources such as how to use the harvested electricity and gaseous energy and how to separate the recovered nutrients in an energy-efficient way. A change in mindset for energy performance of BES is necessary to understand overall energy production and consumption. Scaling up BES can go through laboratory scale, transitional scale, and then pilot scale. Using functions as driving forces for BES research and development will better guide the investment of efforts.
... Consequent upon the implications of the unregulated discharge of nutrient-rich wastewater, poor access to fertilizer in the developing countries and the impending high fertilizer cost on global food security, researchers are investigating different procedures for the recovery of the nutrient fraction for reuse as fertilizer in agriculture Pradhan et al. 2017;Munir et al. 2017;Huang et al. 2017; Van der Grift et al. 2016), or extraction onto a solid phase material Scott et al. 2020;Lu et al. 2020;Martin et al. 2020;Kotoulas et al. 2019;Das et al. 2017;Lei et al. 2019;Ye et al. 2018;Qin et al. 2018;Merino-Jimenez et al. 2017;Oon et al. 2017;Nancharaiah et al. 2016). An overview of research efforts, in the last few decades, on the concept of resource recovery from wastewater showed that great efforts have been expended. ...
Article
Nutrient recovery from wastewater and recycling nutrients as soil fertilizers is a major challenge for the future circular economy. This is motivated by unregulated discharge of wastewater, poor access to fertilizers in developing countries and high fertilizer costs. Here, we review protocols of nutrient recovery from major wastewater sources such as agriculture, domestic and industrial wastewater. We provide an update on the reuse of the recovered nutrient as fertilizers in agriculture. Many effective strategies have been developed for nutrient recovery from wastewater. The reuse potential of the recovered nutrient as fertilizer is often based on postulations. Plant growth and yield potentials with recovered nutrients are either similar or better than that of the conventional fertilizer, in few experimental cases. Evaluation of reuse potentials of the recovered nutrient should involve field trials and not just pot experiments. The contamination of the recovered nutrient with toxic compounds should be avoided.
... The power production (P G , kW) by MFC was quantified by (Qin et al., 2018) ...
Article
Maintaining low concentrations of nitrogen compounds in aquaculture water is a key requirement for a recirculating aquaculture system (RAS), due to the potential detrimental effects of ammonia or nitrate on fish growth and metabolic activities. Herein, a microbial fuel cell (MFC) was investigated to accomplish the removal of either nitrate or ammonia from real RAS water (with simulated daily nitrate/ammonium accumulation) while generating electricity, via aerobic nitrification in the cathode, electricity/concentration driven transport across anion exchange membrane, and subsequent heterotrophic denitrification in the anode chamber. The experiment went through two stages, nitrate removal (Stage I) and ammonia removal (Stage II). In Stage I when daily nitrate addition was performed to mimic nitrate accumulation (0.050 kg NO3−-N m−3 NCC d−1, NCC: net cathodic chamber volume) in the MFC cathode, a stable current density of 12.48 A m−3 could be achieved with a 73.3% nitrate removal and 91.3% COD removal at the end of day 15. To better mimic ammonium accumulation in the RAS effluent without a biofilter, daily ammonium addition (0.050 kg NH4+-N m−3 NCC d−1) was performed in the cathode in Stage II. The MFC system achieved a total inorganic nitrogen removal rate of 0.051 kg N m−3 NCC d−1, and a COD removal efficiency of 91.8% with a current density of 74.00 A m−3. A preliminary analysis of energy balance indicated that the proposed MFC could potentially achieve energy-positive RAS water treatment with a net energy production of 7.50 × 10−3 kWh m−3 treated RAS water or 0.145 ± 0.031 kWh kg−1 removed nitrogen. The results of this study indicate that MFCs have a potential to treat RAS water with simultaneous energy recovery.
... Microbial electrochemical systems, such as microbial electrolysis cells (MECs) and 100 microbial fuel cells (MFCs), have recently received much attention for energy neutral wastewater 101 treatment and value-added resources recovery [19,20]. Studies have also demonstrated that 102 microbial electrochemical systems can simultaneously recover nutrients from wastewater, which 103 makes them more attractive over other nutrients recovery technologies [21][22][23][24][25][26]. In dual-chamber 104 microbial electrochemical systems having cation exchange membrane (CEM), efficient cathodic 105 nitrogen recovery could be attained due to ammonium transport from the anode to the cathode 106 chamber for meeting charge neutrality [23,24]. ...
Article
A two-step sidestream process was investigated for nitrogen (N) and phosphorous (P) recovery from digested sludge centrate. In the first step, a dual-chamber microbial electrolysis cell (MEC) was used for N recovery on the cathode. In the second step, P was recovered as solid precipitates by the addition of Ca2+ or Mg2+ salts in the anodic effluent. The operation of MEC with centrate indicate that N transport from the anode to the cathode chamber is primarily driven by anodic electron transport rather than diffusional transport. Low concentration of readily biodegradable organics in centrate significantly hindered current density (<0.15 A/m2) and led to trivial N recovery on the cathode chamber. The addition of primary sludge fermentation liquor (25 vol%) with centrate as an exogenous source of readily biodegradable organics substantially increased current density up to 6.4 A/m2, along with high TAN removal efficiency of 53±5%. The energy requirement was calculated at 5.8±0.1 kWh/kg-TAN; however, the recovered H2 gas from the cathode was adequate to offset this energy input completely. The addition of Ca2+ salt at a Ca: P molar ratio of 3:1 was optimum for P recovery from the anodic effluent; Mg: P molar ratio of 2:1 was found to be optimum for Mg2+ salt addition. However, optimum doses of both salts resulted in maximum P recovery efficiency of ∼85%, while Mg2+ addition provided an additional 38% TAN removal. These results demonstrate that microbial electrolysis followed by chemical precipitation can promote sustainable nutrients recovery from centrate at municipal wastewater treatment plants where sludge fermentation has already been adopted to provide readily biodegradable carbon source in the biological nutrient removal process.
... Over the years, the concept of nutrient recovery and reuse has been promoted through the development of innovative technologies. Such technologies include the use of biological nutrient uptakes ( [11][12][13][14], Zhou et al., 2015 [15],), bioelectrochemical Systems (BES) nutrient uptake [16][17][18][19], chemical precipitation [20], electrocoagulation [21,22], adsorption and ion exchange [23][24][25][26][27]. ...
... Periodic or continuous removal of the recovered ammonia out of an MDC will help to reduce the concentration gradient and thus lead to less backward flux. This can be realized by a few methods such as active aeration, passive collection, and membrane diffusion (Qin et al., , 2018Tarpeh et al., 2018). Second, due to the complex composition of real wastewater for ammonia recovery, other cations such as Na + , Ca 2+ , and Mg 2+ would compete with ammonium ions for currentdriven migration. ...
Article
Full-text available
Microbial desalination cells (MDCs) have been studied as an emerging technology to accomplish simultaneous wastewater treatment and saline water desalination. A good amount of effort has been invested to understand fundamental problems and develop functional systems of the MDC technology. However, a revisit of MDCs’ desalination function reveals that the unique requirements like co-location of wastewater and saline water will greatly limit the application of this technology. In addition, the relatively low desalination rate of MDCs will result in a large reactor size and thus higher capital cost. Because of the need for wastewater (as a substrate for electricity generation), the MDC technology may have a promising niche of application for resource recovery from wastewater. A proper design of MDCs will allow the current-driven separation of ammonia, phosphorus, and volatile fatty acids (VFAs) from wastewater for further recovery. Based on the literature data, we conduct a case study analysis of mass flow for MDC-based resource recovery and demonstrate the potential of this function. Resource recovery can be a new function of interest to MDCs and worth further exploration of its technical and economic feasibility.
... Making use of ammonia in clean energy applications is especially interesting due to the high volumetric energy density of ammonia (12.9 MJL -1 ) [2,5,[14][15][16][17][18]. This is relatively high compared to other conventional fuels such as hydrogen, methanol and ethanol [2,19]. ...
Article
Full-text available
Wastewater can contain high amounts of ammonia which can pose as a great safety threat if released into natural waters. The electrochemical oxidation of ammonia offers a viable strategy to remove high concentrations and provides an attractive method for wastewater treatment. However, finding a highly efficient and low-cost catalyst is imperative for overcoming the sluggish nature of ammonia oxidation reaction. Herein, a modified A- and B-site perovskite is proposed as a catalyst for the oxidation of ammonia, making it suitable as an anode in an ammonia electrolyser. A series of La1-yNi0.6Cu0.4-xFexO3-δ (x = 0, 0.05 and 0.10; y = 0, 0.05 and 0.10) perovskite materials were synthesised by a conventional sol–gel method. Amongst those tested oxides, La0.9Ni0.6Cu0.35Fe0.05O3-δ was found to have superior activity towards the electrooxidation of ammonia due to an optimised amount of Fe doping and the presence of oxygen vacancies introduced by an A-site deficiency. Subsequently, La0.9Ni0.6Cu0.35Fe0.05O3-δ was employed as an anode in an ammonia electrolyser where the ammonia removal efficiency reached 95.4 % in simulated wastewater after 80 hr and a substantial reduction in real wastewater was also observed. These results demonstrate that the A-site deficient perovskite materials are a viable electrode for the removal of ammonia in a practical energy setting and paves way for future applications.
... wastewaters, digestate, acidogenic fermentate); moreover, by the presence of a cation exchange membrane, ammonium nitrogen can be also removed and recovered from the liquid stream [30] by exploiting its migration for electoneutrality mantaince. Ammonium nitrogen is usually present at high concentration in the AD effluents due to the protein hydrolysis [31]; the ammonium recovery from AD process can be used for agricultural purpose or other biotechnological applications [32,33]. The ammonium migration along with the other ionic species different from proton and hydroxyls, directly promotes the pH split phenomenon in the MEC which causes the alkalinity production in the cathodic chamber that eventually results in an important additional CO 2 removal mechanism [34,35]. ...
Article
The experimental study reports the performance of a three-chamber Microbial Electrolysis Cell equipped with a two-side cathode, which combines the COD removal in the intermediate anodic chamber, the CO2 removal from a gas mixture in the two-side cathode and the recovery of ammonium as a concentrate solution. The MEC anode was fed by a synthetic dark fermentation effluent with a nitrogen load rate of 1.7 g N/Ld while the two-side cathode was operated with a gas mixture containing CO2. Indeed, the MEC configuration permitted the CO2 removal maximization from a N2/CO2 gaseous mixture simulating a biogas in terms of carbon dioxide composition, while the ammonium migration through the cation exchange membrane allowed for the recovery of a 5 times concentrated solution of ammonium. The +0.20 V vs SHE potentiostatic anodic condition and the two different galvanostatic conditions allowed the removal of 4.21 gCO2/Ld while 700 mg N/Ld were recovered as a concentrated ammonium solution. The current increase set by galvanostatic operation promoted the CO2 removal and ammonium recovery increase by the 113 % and 27 % in comparison with the potentiostatic condition. An increase of the energy consumption was promoted by the galvanostatic condition due to the loss of bioelectrochemical COD oxidation in favour of water oxidation which in turn was caused by the anodic overpotential decrease from 0.85 to 0.52 V.
... By the adoption of a passive aeration the nitrogen percentage in the catholyte increased from 4 ± 1 to 21 ± 5%. Moreover, despite the active aeration achieved an ammonia recovery efficiency of 90 ± 1%, the energy consumption resulted lowered from 2.3 to 1.3 kWh/kgN recovery with the active aeration [115]. The alkalinisation of the catholyte has been also tested in single chamber MEC for the precipitation of struvite; even if no ion exchange membranes are present in a single chamber configuration, it has been demonstrated that local alkalinisation in the area near the cathodic surface is interesting for the struvite precipitation caused by a local pH increase [116]. ...
Article
Typical reactions in bioelectrochemical systems (BESs) promote the phenomenon of the pH split between anode and cathode. The pH split results in an undesirable phenomenon which has stimulated several technological solutions to limit its effects, particularly for energy-producing bioelectrochemical systems (BESs). On the other hand, several applications of energy-consuming BESs exploited the pH split to integrate different operations using the bioelectrochemical reactions. Those additional operations, which are directly related to the electric field generated by the bioelectrochemical interphases, include target products extraction, concentration, and recovery. This review offers a comprehensive overview of the different bioelectrochemical applications in which the pH split is used for the integration of bioelectrochemical reactions with products concentration and recovery. By discussing the phenomenon of the pH split in BESs, this paper presents an alternative view to stimulate new niches of applications for the bioelectrochemical processes.
... Integrated MESC and anaerobic fermentation process increase reaction efficiency as the commercial application of MESC are restricted due to low creation rate and high Ref. [63][64][65][66]. ...
Article
Full-text available
In the last decade, there is extensive research carried out for improving the Microbial electrochemical systems (MES) performance in terms of both wastewater treatment and product generation along with its upscaling for industrial application. During the scale-up of these technologies, various economic problems regarding process feasibility have been faced. This economic feasibility needs to be valued in terms of efficiency and environmental sustainability, because of which these technologies have been studied in the first place. A systematic review was conducted highlighting both parameters, i.e., the economics and environmental sustainability in the form of techno-economic assessment of these systems and also showing a comparative study between microbial fuel cells, microbial electrolysis cells, microbial electrosynthesis cells, and microbial desalination cells against the conventional technologies on the basis on these parameters. Based on the study, the conventional technologies require less operational and maintenance cost but also less environmentally sustainable in comparison to these MES. The most common tool for the assessment of the environmental performance of a process or product is the Life Cycle Analysis (LCA). This article summarizes the techno-economic assessment of microbial fuel cells, Microbial electrolysis cells, microbial electrosynthesis cells, and microbial desalination cells. This article concludes that further research is required in terms of scale-up and reducing the overall costs of these MES for efficiently incorporating for practical usage.
... Microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) also provide a sustainable tool for wastewater treatment (Li et al., 2014a;Ren et al., 2017;Qin et al., 2018). There is an increasing gap between the reserves of nutrients and the growing demand for their supply because of the gradual depletion of nutrients reserves. ...
Chapter
Wastewater treatment plants produce large volumes of sludge on a daily basis as a by-product containing soluble and insoluble impurities. The proper management of sewage sludge is a main issue to control environmental pollution and limit negative impacts on human health. However, sludge is rich in nutrients such as nitrogen and phosphorous and contains valuable organic matter that is useful. Due to this, management of sewage sludge includes its regulated reuse in agriculture in such a way as to prevent any harmful effect on the environment and living beings. Different strategies have emerged for sewage sludge management. These strategies are crucial for the sustainability aspects of sludge management. The importance of sewage sludge as a valuable source of nutrients and energy is elaborated, as well as a potential risk related to the application of these strategies.
Article
Landfill leachate is a type of complex organic wastewater, which can easily cause serious negative impacts on the human health and ecological environment if disposed improperly. Electrochemical technology provides an efficient approach to effectively reduce the pollutants in landfill leachate. In this review, the electrochemical standalone processes (electrochemical oxidation, electrochemical reduction, electro-coagulation, electro-Fenton process, three-dimensional electrode process, and ion exchange membrane electrochemical process) and the electrochemical integrated processes (electrochemical-advanced oxidation process (AOP) and biological electrochemical process) for landfill leachate treatment are summarized, which include the performance, mechanism, application, existing problems, and improvement schemes such as cost-effectiveness. The main objective of this review is to help researchers understand the characteristics of electrochemical treatment of landfill leachate and to provide a useful reference for the design of the process and reactor for the harmless treatment of landfill leachate.
Article
Wastewater contains a significant amount of recoverable nitrogen. Hence, the recovery of nitrogen from wastewater can provide an option for generating some revenue by applying the captured nitrogen to producing bio-products, in order to minimize dangerous or environmental pollution consequences. The circular bio-economy can achieve greater environmental and economic sustainability through game-changing technological developments that will improve municipal wastewater management, where simultaneous nitrogen and energy recovery are required. Over the last decade, substantial efforts were undertaken concerning the recovery of nitrogen from wastewater. For example, bio-membrane integrated system (BMIS) which integrates biological process and membrane technology, has attracted considerable attention for recovering nitrogen from wastewater. In this review, current research on nitrogen recovery using the BMIS are compiled whilst the technologies are compared regarding their energy requirement, efficiencies, advantages and disadvantages. Moreover, the bio-products achieved in the nitrogen recovery system processes are summarized in this paper, and the directions for future research are suggested. Future research should consider the quality of recovered nitrogenous products, long-term performance of BMIS and economic feasibility of large-scale reactors. Nitrogen recovery should be addressed under the framework of a circular bio-economy.
Article
Nutrients removal and recovery from surface water are attracting wide attention as nutrients contamination can cause eutrophication even threaten human health. In this study, a novel in-situ photomicrobial nutrient recovery cell (PNRC) was developed, which employed the self-generated electric field to drive nutrient ions to migrate and subsequent recovery as microalgae biomass. At an external resistance of 200 Ω, the current density of the PNRC reactor reached 2.0 A m-2, more than 92% of ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), and total phosphorus (TP) were separated from eutrophic water, which represented <0.19 mg L-1 of NH4+-N, <0.23 mg L-1 of NO3--N, <0.02 mg L-1 of TP were left in the eutrophic water effluent. Meanwhile these separated NH4+-N, NO3--N, and TP were highly enriched in the cathode and anode chambers, and further removed from the system with the removal efficiencies of 91.8%, 90.6%, and 94.4%. The analysis of microbial communities unraveled that high nitrate removal was attributed to the abundant denitrifying bacteria (Thauera, Paracoccus, Stappia, and Azoarcus). The removal of ammonia was attributed to the algae assimilation (69.3%) and nitrification process (22.5%), and the phosphorus removal was mainly attributed to C. vulgaris. The preliminary energy balance analysis indicated that the electricity generation and biodiesel production could achieve energy neutrality theoretically, further demonstrating the huge potential of the PNRC system in cost-effective nutrients recovery from eutrophic water.
Article
Here a three-chamber microbial electrolysis cell (MEC) has been developed to couple the CO 2 removal from a gas mixture to the ammonium nitrogen recovery. The here proposed MEC adopted an innovative two-side cathode configuration, where two identic cathodic chambers are connected in parallel by a titanium wire and separated from an intermediate anodic compartment by an anion and a cation exchange membrane (AEM and CEM). The two-side configuration has been proposed as a post treatment unit capable to perform the biogas upgrading through the CO 2 reduction and removal into the cathodic chambers as well as the ammonium recovery from a liquid waste stream due to its migration for the electroneutrality maintenance of the cell. The experiments have been conducted at two different anodic potential (i.e. +0.2 and −0.1 V vs Standard Hydrogen Electrode SHE), using a synthetic feeding solution and a gas mixture simulating a domestic wastewater and a biogas, respectively. The results obtained using the new configuration have been also compared to the performances reported in a previous work where a three – chamber MEC, characterized by the presence of an intermediate accumulation chamber, was aimed to the CO 2 removal and to nitrogen recovery; this comparison highlighted higher performances of the two-side configuration in terms of methane production, CO 2 removal and energy consumption, keeping the same anodic performances.
Article
A nickel (Ni)-graphene oxide (GO) dispersed carbon film was prepared by the carbonization of the phenolic precursor-based polymer. Three dimensional (3D) micropillars were fabricated on the carbon film using laser ablation technique. The micropillars-engraved film was used as electrodes in a single chamber microbial electrolytic cell (MEC) for hydrogen (H 2 ) production. Besides promoting biofilm formation at anode, the 3D micropillars provided relatively more exposure to the in situ dispersed electrocatalytic Ni nanoparticles (NPs) and electroconductive GO in the carbon film. The Tafel slope of ∼49 mV dec ⁻¹ indicated that Heyrovsky reaction or electrochemical desorption was the rate determining step for H 2 evolution. A H 2 production rate of 4.22 ± 0.21 m ³ m ⁻³ d ⁻¹ was measured at 0.8 V in the prepared electrode-based MEC. Whereas the overall H 2 and cathodic recoveries were measured to be 92.3 ± 2.77% and 98.7 ± 0.99%, respectively, the Coulombic and overall energy efficiencies were determined to be 93.5 ± 2.81% and 72.2 ± 3.61%, respectively. The relatively higher efficiency of the MEC was ascribed to the synergistic contributions of the 3D micropillars, Ni NPs and GO, indicating the prepared electrode to be a viable alternative to the expensive noble metal-based electrodes used in MECs for H 2 production.
Chapter
Electrochemical membrane technology for environmental remediation repository of basic knowledge and recent progress is reviewed in this chapter. The chapter summarizes the key processes in the use of electrochemical membranes, focusing on their need in electrodialytic and the electrocatalytic remediation of contaminated media. The fundamentals (including materials and reactor design) of the electrodialytic remediation technology are presented with consideration given to the critical operating parameters and performance indicators, mathematical simulation/modeling methods, and recent advances in electrodialytic remediation research. Meanwhile, two membrane technologies (i.e., the 3D electrochemical system and the proton-conducting membrane cell) for electrocatalytic remediation of contaminated media under different scenarios are briefly described. Finally, the chapter ends with a critical discussion on the challenges of and the perspectives for future study in electrochemical membrane technology for the purpose of environmental remediation.
Chapter
Rapid population growth and economic development, globally, have intensified the need for water reclamation to conserve and extend water supplies, especially in arid and semiarid regions. Microbial desalination cell (MDC), as an emerging electrochemical membrane technology that generates electricity through the bioelectrochemical oxidation of organics in wastewater, offers simultaneous wastewater treatment, electricity generation, and desalination with low energy consumption and high performance. In this review, we discuss the MDC fundamental principle, electroactive microorganisms, electrode materials, recently developed configurations, and optimized operational conditions that improve MDC performance. This review also acknowledges the emerging applications of MDC for municipal/industrial wastewater, seawater/brackish water desalination, water softening, heavy metal removal, chemical production, and resources recovery. The review further identifies the potential for integration of MDC with existing desalination technologies such as reverse osmosis and forward osmosis. Finally, the practical needs, technological barriers, and research priorities in both material development and process design for the promotion of MDC in practical application are discussed.
Article
Although ammonia recovery from wastewater can be environmentally friendly and energy efficient compared to the conventional Haber-Bosch process, there is a lack of research on the reuse of the recovered ammonia to exhibit a complete picture of resource recovery. In this study, a microbial electrochemical system (MES) was used to recover ammonia from a mixture of anaerobic digester (AD) centrate and food wastewater at a volume ratio of 3:1. More than 60% of ammonia nitrogen was recovered with energy consumption of 2.7 kWh kg⁻¹ N. The catholyte of the MES, which contained the recovered ammonia, was used to prepare fertilizers to support the growth of a model plant Arabidopsis thaliana. It was observed that A. thaliana grown on the MES generated fertilizer amended with extra potassium, phosphorus, and trace elements showed comparable sizes and an even lower death rate (0%) than the control group (24%) that was added with a commercial fertilizer. RNA-Seq analyses were used to examine A. thaliana genetic responses to the MES generated fertilizers or the commercial counterpart. The comparative study offered metabolic insights into A. thaliana physiologies subject to the recovered nitrogen fertilizers. The results of this study have demonstrated the potential application of using the recovered ammonia from AD centrate as a nitrogen source in fertilizer and identified the necessity of supplementing other nutrient elements.
Chapter
The excess availability of wastewater and reduction in the energy resources has initiated a new thought process of ‘waste to energy’. The green technology like solar and wind system utilises natural unending resources for production of valuable energy. To utilise waste as a source of energy we require process that a convert the chemical energy trapped in waste to green energy. The conventional technologies like anaerobic digestor produce methane, but the purity of product and time duration taken for the production makes the system unsustainable. The new bio-electrochemical system has been rectified as a potential process that can utilise waste, produce valuable products and is being optimised towards sustainability. This chapter presents a comparative review with respect to this new technology and its ability for resource recovery.
Article
Maintaining low concentrations of nitrogen compounds in aquaculture water is a key requirement for a recirculating aquaculture system (RAS), due to the potential detrimental effects of ammonia or nitrate on fish growth and metabolic activities. Herein, a microbial fuel cell (MFC) was investigated to accomplish the removal of either nitrate or ammonia from real RAS water (with simulated daily nitrate/ammonium accumulation) while generating electricity, via aerobic nitrification in the cathode, electricity/concentration driven transport across anion exchange membrane, and subsequent heterotrophic denitrification in the anode chamber. The experiment went through two stages, nitrate removal (Stage I) and ammonia removal (Stage II). In Stage I when daily nitrate addition was performed to mimic nitrate accumulation (0.050 kg NO3⁻-N m⁻³ NCC d⁻¹, NCC: net cathodic chamber volume) in the MFC cathode, a stable current density of 12.48 A m⁻³ could be achieved with a 73.3% nitrate removal and 91.3% COD removal at the end of day 15. To better mimic ammonium accumulation in the RAS effluent without a biofilter, daily ammonium addition (0.050 kg NH4⁺-N m⁻³ NCC d⁻¹) was performed in the cathode in Stage II. The MFC system achieved a total inorganic nitrogen removal rate of 0.051 kg N m⁻³ NCC d⁻¹, and a COD removal efficiency of 91.8% with a current density of 74.00 A m⁻³. A preliminary analysis of energy balance indicated that the proposed MFC could potentially achieve energy-positive RAS water treatment with a net energy production of 7.50 × 10⁻³ kWh m⁻³ treated RAS water or 0.145 ± 0.031 kWh kg⁻¹ removed nitrogen. The results of this study indicate that MFCs have a potential to treat RAS water with simultaneous energy recovery.
Article
This work achieved nitrogen recovery from the wastewater treatment by the bioelectrochemical system with the concept of biohythane generation. In this study, 3D network electrode could improve the biohythane generation to reduce energy consumption of the nitrogen recovery, achieving the highest biohythane production rate at 0.123 m³ m⁻³ treated wastewater to obtain energy consumption at 0.77 kWh kg⁻¹ N under 0.8 V, significantly lower than other traditional technologies (at about 1.3 to 14 kWh kg⁻¹ N). Further microbial analysis was processed for voltage optimization, and 0.8 V was proved as best voltage for high abundance of Geobacter over Methanosarcina. Correlation factor and heatmap analysis indicated that the suitable voltage could benefit Geobacter growth for higher energy recovery. Furthermore, genera of Bacteroides and Azospirillum were found as key species. This study proved that the biohythane generation concept could outstandingly reduce the energy consumption for higher nitrogen recovery from wastewater treatment.
Article
Full-text available
Energy self-sufficiency is a highly desirable goal of sustainable wastewater treatment. Herein, a combined system of a microbial fuel cell and an intermittently aerated biological filter (MFC-IABF) was designed and operated in an energy self-sufficient manner. The system was fed with synthetic wastewater (COD = 1000 mg L(-1)) in continuous mode for more than 3 months at room temperature (~25 °C). Voltage output was increased to 5 ± 0.4 V using a capacitor-based circuit. The MFC produced electricity to power the pumping and aeration systems in IABF, concomitantly removing COD. The IABF operating under an intermittent aeration mode (aeration rate 1000 ± 80 mL h(-1)) removed the residual nutrients and improved the water quality at HRT = 7.2 h. This two-stage combined system obtained 93.9% SCOD removal and 91.7% TCOD removal (effluent SCOD = 61 mg L(-1), TCOD = 82.8 mg L(-1)). Energy analysis indicated that the MFC unit produced sufficient energy (0.27 kWh m(-3)) to support the pumping system (0.014 kWh m(-3)) and aeration system (0.22 kWh m(-3)). These results demonstrated that the combined MFC-IABF system could be operated in an energy self-sufficient manner, resulting to high-quality effluent.
Article
Full-text available
The paper examines the main physico-chemical processes for nitrogen removal from wastewaters, considering both those that have been long known, and are still widely applied at the industrial scale, and those that are still at research level. Special attention is paid to the latest technological developments, as well as to operational problems and fields of application. The processes considered are briefly summarized as follows: ammonia air and steam stripping; ammonia vacuum distillation; ammonia precipitation as struvite; ammonia and nitrate removal by selected ion exchange; breakpoint chlorination; chloramines removal by selected activated carbon; ammonia adsorption on charcoal; chemical reduction of nitrate; advanced oxidation processes to convert ammonia and organic-N into nitrogen gas or nitrate. Special attention is given to advanced oxidation processes as great research efforts are currently addressed to their implementation. These specifically include ozonation, peroxon oxidation, catalytic wet air oxidation, photo-catalytic oxidation and electrochemical oxidation.
Article
Full-text available
Activated carbon (AC) has been demonstrated as a promising cathode catalyst for microbial fuel cells (MFCs). A simple and effective dipping method was developed and examined for coating AC with better control of the loading rate than the commonly used brushing method.
Article
Full-text available
On 13 October 1908, Fritz Haber filed his patent on the ``synthesis of ammonia from its elements'' for which he was later awarded the 1918 Nobel Prize in Chemistry. A hundred years on we live in a world transformed by and highly dependent upon Haber-Bosch nitrogen.
Article
Full-text available
Humans create vast quantities of wastewater through inefficiencies and poor management of water systems. The wasting of water poses sustainability challenges, depletes energy reserves, and undermines human water security and ecosystem health. Here we review emerging approaches for reusing wastewater and minimizing its generation. These complementary options make the most of scarce freshwater resources, serve the varying water needs of both developed and developing countries, and confer a variety of environmental benefits. Their widespread adoption will require changing how freshwater is sourced, used, managed, and priced.
Article
Bioelectrochemical systems (BES) can recover ammonia from wastewater driven by electricity generation. However, energy consumption of such an approach has not been well evaluated. In this study, the effects of several key operating factors including catholyte aeration rate, external voltage, and external resistance on both ammonia recovery and energy consumption were systematically investigated. A mathematical model developed for ammonia removal/recovery in BES was applied to help interpret the experimental results. It was found that a high aeration rate in the catholyte could facilitate ammonia recovery. An aeration rate of 100 mL min⁻¹ resulted in the lowest energy consumption of 4.9 kWh kg⁻¹ N recovery among the tested aeration rates. A low external resistance facilitated the ammonia recovery via higher current generation, while a moderate external voltage (e.g., 0.5 V) helped to achieve low energy consumption. The highest ammonia recovery rate of 7.1 g N m⁻² d⁻¹ was obtained with energy consumption of 5.7 kWh kg⁻¹ N recovery. Therefore, there is a trade-off between energy consumption and ammonia recovery.
Article
Recycling of hydrogen gas (H2) produced at the cathode to the anode in an electrochemical system allows for energy efficient TAN (Total Ammonia Nitrogen) recovery. Using a H2 recycling electrochemical system (HRES) we achieved high TAN transport rates at low energy input. At a current density of 20 A m-2, TAN removal rate from the influent was 151 gN m-2 d-1 at an energy demand of 26.1 kJ gN-1. The maximum TAN transport rate of 335 gN m-2 d-1 was achieved at a current density of 50 A m-2 and an energy demand of 56.3kJ gN-1. High TAN removal efficiency (73-82%) and recovery (60-73%) were reached in all experiments. Therefore, our HRES is a promising alternative for electrochemical and bioelectrochemical TAN recovery. Advantages are the lower energy input and lower risk of chloride oxidation compared to electrochemical technologies, and high rates and independency of organic matter compared to bioelectrochemical systems.
Article
The food security of a booming global population demands a continuous and sustainable supply of fertilisers. Their current once-through use [especially of the macronutrients nitrogen (N), phosphorus (P), and potassium (K)] requires a paradigm shift towards recovery and reuse. In the case of source-separated urine, efficient recovery could supply 20% of current macronutrient usage and remove 50-80% of nutrients present in wastewater. However, suitable technology options are needed to allow nutrients to be separated from urine close to the source. Thus far none of the proposed solutions has been widely implemented due to intrinsic limitations. Microbial electrochemical technologies (METs) have proved to be technically and economically viable for N recovery from urine, opening the path for novel decentralised systems focused on nutrient recovery and reuse. Copyright © 2015 Elsevier Ltd. All rights reserved.
Article
This study has presented a proof-of-concept system for the self-sustained supply of ammonium-based draw solute for wastewater treatment through coupling a microbial electrolysis cell (MEC) and forward osmosis (FO). The MEC produced an ammonium bicarbonate draw solute via recovering ammonia from a synthetic organic solution, which was then applied in the FO for extracting water from the MEC anode effluent. The recovered ammonium could reach a concentration of 0.86 mol L–1, and with this draw solution, the FO extracted 50.1 ± 1.7% of the MEC anode effluent. The lost ammonium during heat regeneration could be supplemented with additional recovered ammonium in the MEC. The MEC achieved continuing treatment of both organic and ammonium in the returned feed solution mixed with fresh anolyte, although at lower efficiency compared to that with completely fresh anolyte. These results encourage further investigation to optimize the coordination between MEC and FO with improved performance.
Article
Removal of nitrogen compounds from wastewater is essential to prevent pollution of receiving water bodies (i.e. eutrophication). Conventional nitrogen removal technologies are energy intensive, representing one of the major costs in wastewater treatment plants. For that reason, innovations in nitrogen removal from wastewater focus on the reduction of energy use. Bioelectrochemical systems (BESs) have gained attention as an alternative to treat wastewater while recovering energy and/or chemicals. The combination of electrodes and microorganisms has led to several methods to remove or recover nitrogen from wastewater via oxidation reactions, reduction reactions and/or transport across an ion exchange membrane. In this study, we give an overview of nitrogen removal and recovery mechanisms in BESs based on state-of-the-art research. Moreover, we show an economic and energy analysis of ammonium recovery in BESs and compare it with existing nitrogen removal technologies. We present an estimation of the condi
Article
Nutrient removal and recovery has received less attention during the development of bioelectrochemical systems (BES) for energy efficient wastewater treatment, but it is a critical issue for sustainable wastewater treatment. Both nitrogen and phosphorus can be removed and/or recovered in a BES through involving biological processes such as nitrification and bioelectrochemical denitrification, the NH4(+)/NH3 couple affected by the electrolyte pH, or precipitating phosphorus compounds in the high-pH zone adjacent a cathode electrode. This paper has reviewed the nutrients removal and recovery in various BES including microbial fuel cells and microbial electrolysis cells, discussed the influence factors and potential problems, and identified the key challenges for nitrogen and phosphorus removal/recovery in a BES. It expects to give an informative overview of the current development, and to encourage more thinking and investigation towards further development of efficient processes for nutrient removal and recovery in a BES.
Article
The use of spiral spacers to create a helical flow for improving electricity generation in microbial fuel cells (MFCs) was investigated in both laboratory and on-site tests. The lab tests found that the MFC with the spiral spacers produced more electricity than the one without the spiral spacers at different recirculation rates or organic loading rates, likely due to the improved transport/distribution of ions and electron mediators instead of the substrates because the organic removal efficiency was not obviously affected by the presence of the spiral spacers. The energy production in the MFC with the spiral spacers reached 0.071 or 0.073kWh/kg COD in either vertical or horizontal installment. The examination of the MFCs installed in an aeration tank of a municipal wastewater treatment plant confirmed the advantage of using the spiral spacers. Those results demonstrate that spiral spacers could be an effective approach to improve energy production in MFCs.
Article
The scope of this study was ammonium ions removal from synthetic aqueous solutions by raw and pretreated natural zeolite, Transcarpathian mordenite under static and dynamic conditions. The cation exchange capacity of the Transcarpathian mordenite regarding ammonium ions was evaluated as 1.64 meq/g at 1000 mg/l initial NH4–N concentration. The dynamic exchange capacity exceeded one estimated in equilibrium study at the same initial concentration that may be conditioned by the constant removal of ion exchange products. Ammonium uptake rate was controlled by particle diffusion with diffusion coefficients determined in the range of 0.7–3.6 × 10−12 m2/s. Efficiency of ammonium sorption may be improved by slowing down of initial solution rate in the column test and non-significantly by NaCl and HCl pretreatment of the mordenite. Ammonium sorption by the mordenite increased from the coarser to the finer fraction but this dependence became weaker to low flow rates. It was established that hydrogen ions displaced exchangeable cations on the mordenite in distilled water and hydrochloric acid with destroy of the zeolite framework structure in the last case. NH4+-ions removal from aqueous solutions occurs mainly by ion exchange with Na+- and Ca2+-ions at the practically equal parts of them because of the weakest affinity of the mordenite to these cations.
Article
Equilibrium gas phase concentration of ammonia in dilute solution has been measured as a function of total ammonia + ammonium concentration (0.002–0.10 M), pH (6–10) and temperature (278.8−290.6 K). Henry's Law is obeyed under these conditions and may be expressed as In KH(M atm−1) = 4092/T −9.70 with a relative standard error of less than 5 %, in good agreement with NBS thermodynamic data. Convenient generation of trace levels of ammonia (1.33 × 10−8–7.77 × 10−4 atm) using a porous membrane tube is described.
Article
Recently, several novel and cost-effective biological nitrogen elimination processes have been developed, including partial nitritation, nitrifier denitrification, anaerobic ammonium oxidation (Anammox), and its combined system (completely autotrophic nitrogen removal over nitrite, Canon). This paper deals with a review of novel biological nitrogen elimination technologies under anaerobic or oxygen limited conditions. The conventional nitrogen removal process (nitrification and denitrification), aerobic denitrification and other lithoautotrophic denitrification are also discussed briefly. The target of the novel process is the biological removal of nitrogen compounds from concentrated waste streams such as anaerobic digestion sludge liquor, etc. The review addresses the specifics of process, microbial diversity, performance characteristics and the future challenges for application.
Article
Nitrogen recovery through NH(3) stripping is energy intensive and requires large amounts of chemicals. Therefore, a microbial fuel cell was developed to simultaneously produce energy and recover ammonium. The applied microbial fuel cell used a gas diffusion cathode. The ammonium transport to the cathode occurred due to migration of ammonium and diffusion of ammonia. In the cathode chamber ionic ammonium was converted to volatile ammonia due to the high pH. Ammonia was recovered from the liquid-gas boundary via volatilization and subsequent absorption into an acid solution. An ammonium recovery rate of 3.29 g(N) d(-1) m(-2) (vs. membrane surface area) was achieved at a current density of 0.50 A m(-2) (vs. membrane surface area). The energy balance showed a surplus of energy 3.46 kJ g(N)(-1), which means more energy was produced than needed for the ammonium recovery. Hence, ammonium recovery and simultaneous energy production from urine was proven possible by this novel approach.
Article
This work examines a pH control method using ammonium (NH(4)(+)) as a sustainable proton shuttle in a CEM-equipped BES. Current generation was sustained by adding NH(3) or ammonium hydroxide (NH(4)OH) to the anolyte, controlling its pH at 7. Ammonium ion migration maintained the catholyte pH at approximately 9.25. Such NH(4)(+)/NH(3) migration accounted for 90±10% of the ionic flux in the BES. Reintroducing the volatilized NH(3) from the cathode into the anolyte maintained a suitable anolyte pH for sustained microbial-driven current generation. Hence, NH(4)(+)/NH(3) acted as a proton shuttle that is not consumed in the process.
Article
Ammonium recovery using a two chamber microbial fuel cell (MFC) was investigated at high ammonium concentration. Increasing the ammonium concentration (from 0.07 to 4 g ammonium-nitrogen/L) by addition of ammonium chloride did not affect the performance of the MFC. The obtained current densities by DC-voltammetry were higher than 6A/m(2) for both operated MFCs. Also continuous operation at lower external resistance (250 Ω) showed an increased current density (0.9A/m(2)). Effective ammonium recovery can be achieved by migrational ion flux through the cation exchange membrane to the cathode chamber, driven by the electron production from degradation of organic substrate. The charge transport was proportional to the concentration of ions. Nonetheless, a concentration gradient will influence the charge transport. Furthermore, a charge exchange process can influence the charge transport and therefore the recovery of specific ions.
Article
The green alga Scenedesmus was investigated for its ability to remove nitrogen from anaerobic digestion effluent possessing high ammonium content and alkalinity in addition to its growth characteristics. Nitrate and ammonium were indistinguishable as a nitrogen source when the ammonium concentration was at normal cultivation levels. Ammonium up to 100ppm NH(4)-N did not inhibit cell growth, but did decrease final cell density by up to 70% at a concentration of 200-500ppm NH(4)-N. Inorganic carbon of alkalinity in the form of bicarbonate was consumed rapidly, in turn causing the attenuation of cell growth. Therefore, maintaining a certain level of inorganic carbon is necessary in order to prolong ammonia removal. A moderate degree of aeration was beneficial to ammonia removal, not only due to the stripping of ammonium to ammonia gas but also due to the stripping of oxygen, which is an inhibitor of regular photosynthesis. Magnesium is easily consumed compared to other metallic components and therefore requires periodic supplementation. Maintaining appropriate levels of alkalinity, Mg, aeration along with optimal an initial NH(4)(+)/cell ratio were all necessary for long-term semi-continuous ammonium removal and cell growth.
Article
The analysis of different removal and recovery techniques for nutrients in urine shows that in many cases recovery is energetically more efficient than removal and new-production from natural resources. Considering only the running electricity and fossil energy requirements for the traditional way of wastewater treatment and fertiliser production, the following specific energy requirements can be calculated: 45 MJ kg-1N for denitrification in a WWTP, 49 MJ kg-1P for P-precipitation in a WWTP, 45 MJ kg-1N for N-fertiliser and 29 MJ kg-1P for P-fertiliser production. These numbers are higher than the values derived for thermal volume reduction of urine (35 MJ kg-1N for eliminating 90% water) or production of struvite (102 MJ kg-1N, including 2.2 kg P). Considering only the electricity and fossil energy for the traditional way of wastewater treatment and fertiliser production, the energy value of 1 PE urine is 0.87 MJ PE-1d-1 (fertiliser value: 0.44, wastewater treatment: 0.43 MJ PE-1d-1). A more detailed life cycle assessment (LCA) of the entire urine collection system, including the required materials and the environmental burden, support the energy analysis. The LCA compares conventional denitrification in a wastewater treatment plant with collecting urine in households, reducing the volume by evaporation and using it as a multi-nutrient fertiliser. The primary energy consumption for recovery and reuse of urine, including the nutrients N, P and K, is calculated with 65 MJ kg-1N, compared with 153 MJ kg-1N derived for the conventional 'recycling over the atmosphere'.
Article
Due to the excellent proton conductivity of Nafion membranes in polymer electrolyte membrane fuel cells (PEMFCs), Nafion has been applied also in microbial fuel cells (MFCs). In literature, however, application of Nafion in MFCs has been associated with operational problems. Nafion transports cation species other than protons as well, and in MFCs concentrations of other cation species (Na+, K+, NH4+, Ca2+, and Mg2+) are typically 10(5) times higher than the proton concentration. The objective of this study, therefore, was to quantify membrane cation transport in an operating MFC and to evaluate the consequences of this transport for MFC application on wastewaters. We observed that during operation of an MFC mainly cation species other than protons were responsible for the transport of positive charge through the membrane, which resulted in accumulation of these cations and in increased conductivity in the cathode chamber. Furthermore, protons are consumed in the cathode reaction and, consequently, transport of cation species other than protons resulted in an increased pH in the cathode chamber and a decreased MFC performance. Membrane cation transport, therefore, needs to be considered in the development of future MFC systems.
Article
Ammonia losses during swine wastewater treatment were examined using single- and two-chambered microbial fuel cells (MFCs). Ammonia removal was 60% over 5 days for a single-chamber MFC with the cathode exposed to air (air-cathode), versus 69% over 13 days from the anode chamber in a two-chamber MFC with a ferricyanide catholyte. In both types of systems, ammonia losses were accelerated with electricity generation. For the air-cathode system, our results suggest that nitrogen losses during electricity generation were increased due to ammonia volatilization with conversion of ammonium ion to the more volatile ammonia species as a result of an elevated pH near the cathode (where protons are consumed). This loss mechanism was supported by abiotic tests (applied voltage of 1.1 V). In a two-chamber MFC, nitrogen losses were primarily due to ammonium ion diffusion through the membrane connecting the anode and cathode chambers. This loss was higher with electricity generation as the rate of ammonium transport was increased by charge transfer across the membrane. Ammonia was not found to be used as a substrate for electricity generation, as intermittent ammonia injections did not produce power. The ammonia-oxidizing bacterium Nitrosomonas europaea was found on the cathode electrode of the single-chamber system, supporting evidence of biological nitrification, but anaerobic ammonia-oxidizing bacteria were not detected by molecular analyses. It is concluded that ammonia losses from the anode chamber were driven primarily by physical-chemical factors that are increased with electricity generation, although some losses may occur through biological nitrification and denitrification.