Capacitive processes for carbon capture and energy recovery from CO2 emissions : Shaping a new technology going from water to gas applications
Legrand, Louis J.P. - \ 2020
Wageningen University. Promotor(en): C.J.N. Buisman, co-promotor(en): H.V.M. Hamelers; M. Tedesco. - Wageningen : Wageningen University - ISBN 9789463954891 - 218
New insights on the estimation of the anaerobic biodegradability of plant material : Identifying valuable plants for sustainable energy production
Pabón-Pereira, Claudia P. ; Hamelers, H.V.M. ; Matilla, Irene ; Lier, Jules B. van - \ 2020
Processes 8 (2020)7. - ISSN 2227-9717
Anaerobic digestion - Biodegradability - Fiber degradation - Lignocellulosics
Based on fifteen European plant species, a statistical model for the estimation of the anaerobic biodegradability of plant material was developed. We show that this new approach represents an accurate and cost-eective method to identify valuable energy plants for sustainable energy production. In particular, anaerobic biodegradability (Bo) of lignocellulosic material was empirically found to be related to the amount of cellulose plus lignin, as analytically assessed by the van Soest method, i.e., the acid detergent fiber (ADF) value. Apart from being theoretically meaningful, the ADF-based empirical model requires the least eort compared to the other four proposed conceptual models proposed, as individual fractions of cellulose, hemicellulose, and lignin do not need to be assessed, which also enhances the predictive accuracy of the model's estimation. The model's results showed great predictability power, allowing us to identify interesting crops for sustainable crop rotations. Finally, the model was used to predict Bo of 114 European plant samples that had been previously characterized by means of the van Soest method.
Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture
Shu, Qingdian ; Legrand, Louis ; Kuntke, Philipp ; Tedesco, Michele ; Hamelers, Hubertus V.M. - \ 2020
Environmental Science and Technology 54 (2020)14. - ISSN 0013-936X - p. 8990 - 8998.
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.
Exploiting Donnan Dialysis to enhance ammonia recovery in an electrochemical system
Rodrigues, Mariana ; Sleutels, Tom ; Kuntke, Philipp ; Hoekstra, Douwe ; Heijne, Annemiek ter; Buisman, Cees J.N. ; Hamelers, Hubertus V.M. - \ 2020
Chemical Engineering Journal 395 (2020). - ISSN 1385-8947
Ammonia recovery - Donnan dialysis - Electrochemical system
A hydrogen recycling electrochemical system (HRES) can be used for energy efficient removal of TAN (Total ammonia nitrogen, ammonium and ammonia) from wastewater. When a current is applied, a concentration gradient of cations builds up between catholyte and feed solution. When no current is applied, cations (Na+ and K+) diffuse back to the feed solution from the catholyte as a result of the concentration difference. These cations will be exchanged for other cations (NH4 + and H+) to maintain electroneutrality: a phenomenon known as Donnan Dialysis. In this study, Donnan Dialysis was explored as a strategy to enhance the TAN removal efficiency in an HRES. In continuous operation, Donnan Dialysis did not clearly affect TAN removal efficiency. In batch operation, Donnan Dialysis resulted in (10 ± 2) % higher removal efficiency compared to operation without Donnan Dialysis. By analyzing transport numbers of the different cations, we show that in batch mode, Donnan Dialysis indeed exchanges mostly NH4 + with Na+ and K+. In continuous mode, however, more protons were transported from anode to cathode. Batch operation with Donnan Dialysis achieved similar removal to continuous operation but consumed less energy (between 7.8 kJ gN −1 and 10.1 kJ gN −1) than continuous operation. Donnan Dialysis can be a good strategy to enhance TAN recovery in batch operation mode since additional ammonium was removed at a lower energy input.
Role of ion exchange membranes and capacitive electrodes in membrane capacitive deionization (MCDI) for CO2 capture
Legrand, L. ; Shu, Q. ; Tedesco, M. ; Dykstra, J.E. ; Hamelers, H.V.M. - \ 2020
Journal of Colloid and Interface Science 564 (2020). - ISSN 0021-9797 - p. 478 - 490.
Carbon electrodes - Donnan model - Electrochemical carbon capture - MCDI
Recently we showed that membrane capacitive deionization (MCDI) can be used to capture CO2, but we found that the performance decreases with decreasing current density. In the present study, we investigate the effect of electrodes and ion exchange membranes by performing experiments with two membranes (CO2-MCDI), with one membrane (cation or anion exchange membrane), and without membranes (CO2-CDI). We find that the anion exchange membrane is essential to keep high CO2 absorption efficiencies (Λa=nCO2(g)/ncharge), while the absorption efficiency of the CO2-CDI cell was lower than expected (Λa≈0.5 for CO2-MCDI against Λa≈0.18 for CO2-CDI). Moreover, we theoretically investigate ion adsorption mechanisms in the electrodes by comparing experimental data of a CO2-CDI cell with theoretical results of the classic amphoteric-Donnan model developed for conventional CDI. By comparing the experimental results with the amph-D model, we find that the model overestimates the absorption efficiency in CO2-CDI experiments. To understand this discrepancy, we investigate the effects of other phenomena, i.e., (i) low ion concentration, (ii) passive CO2 absorption, and (iii) the effect of acid-base reactions on the chemical surface charge.
Theory of Ion and Electron Transport Coupled with Biochemical Conversions in an Electroactive Biofilm
Lichtervelde, A.C.L. De; Heijne, A. Ter; Hamelers, H.V.M. ; Biesheuvel, P.M. ; Dykstra, J.E. - \ 2019
Physical Review Applied 12 (2019)1. - ISSN 2331-7019
An electroactive biofilm is a porous layer of bacteria covering an electrode, which plays an important role in bioelectrochemical systems, such as in the microbial fuel cell. We derive a dynamic model of ion transport, biochemical reactions, and electron transport inside such a biofilm. After validating the model against data, we evaluate model output to obtain an understanding of the transport of ions and electrons through a current-producing biofilm. For a system fed with a typical wastewater stream containing organic molecules and producing 5 A m−2, our model predicts that transport of the organic molecules is not a limiting factor. However, the pH deep within the biofilm drops significantly, which can inhibit current production of such biofilms. Our results suggest that the electronic conductivity of the biofilm does not limit charge transport significantly, even for a biofilm as thick as 100 μm. Our study provides an example of how physics-based modeling helps to understand complex coupled processes in bioelectrochemical systems.
Electrical energy from CO2 emissions by direct gas feeding in capacitive cells
Legrand, L. ; Schaetzle, O. ; Tedesco, M. ; Hamelers, H.V.M. - \ 2019
Electrochimica Acta 319 (2019). - ISSN 0013-4686 - p. 264 - 276.
Capacitive cell - Capacitive deionization - CO - Membrane potential - Mixing energy
This work demonstrates the possibility to harvest electrical power from CO2 emissions by feeding CO2 and air gas directly into a capacitive cell. Hamelers et al. previously showed, that the available mixing energy of CO2 emitted into the air can be converted into electricity, but at high energy costs for gas-sparging in the process. In the present work, electrical power is generated by feeding the gas directly into the capacitive cell. We investigated three different cell designs (namely, “conventional”, “flow-by(wire)”, and “flow-by(flat)”), by changing both electrode and cell geometry. The flow-by(flat), inspired from fuel cell design, showed the best performance thanks to a high membrane potential (≈190 mV), which is the highest value so far reported from CO2 and air. A maximum membrane permselectivity between CO2 and air of 90% was obtained, i.e., almost double of values reported in previous studies. On the contrary, the “conventional” cell design gave poor performance due to non-optimal gas flow in the cell. We highlight the importance of water management and internal electrical resistance, to indicate directions for future developments of the technology.
The RED Fouling Monitor : A novel tool for fouling analysis
Bodner, E.J. ; Saakes, M. ; Sleutels, T. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2019
Journal of Membrane Science 570-571 (2019). - ISSN 0376-7388 - p. 294 - 302.
Fouling analysis - Ion-exchange membranes - Organic fouling - RED Fouling Monitor - Salinity gradient
RED is a technology for harvesting energy using the salinity gradient between river (RW) and seawater (SW). Membrane fouling can decrease the net power density. Fouling inhibition might be indispensable. For implementing antifouling strategies more detailed insights upon fouling are required. In RED stacks investigations of single membranes are practically impossible. We introduce the RED Fouling Monitor, in which one side of a single ion-exchange membrane in contact to a foulant-containing feed stream can be studied under OCV and current conditions. Fouling is detectable in four configurations: (1) SW/AEM, (2) RW/AEM, (3) SW/CEM and (4) RW/CEM. Functionality is provided by a novel flow-through salt bridge enabling ionic connection and the incorporation of reference electrodes in close proximity to the membrane surface. The results indicate a stable, reproducible performance under un-fouled conditions. Upon SDBS exposure RW/AEM fouling showed a more pronounced fouling response than SW/AEM fouling. Fouling is partly attributable to the current density and the current field direction. An irreversible, internal fouling of the AEM is indicated when exposed to SDBS in SW. RW/AEM fouling shows to be reversible. With prospect to future systematic investigations this tool can be used to test various configurational, operational designs, different pre-treatment schemes and the fouling potential of feed streams at different seasons. This will result in valuable insights for new constructional sites for future RED plants.
Solvent-Free CO2 Capture Using Membrane Capacitive Deionization
Legrand, L. ; Schaetzle, O. ; Kler, R.C.F. De; Hamelers, H.V.M. - \ 2018
Environmental Science and Technology 52 (2018)16. - ISSN 0013-936X - p. 9478 - 9485.
Capture of CO2, originating from both fossil fuels, such as coal combustion, and from renewables, such as biogas, appears to be one of the greatest technological challenges of this century. In this study, we show that membrane capacitive deionization (MCDI) can be used to capture CO2 as bicarbonate and carbonate ions produced from the reaction of CO2 with water. This novel approach allows capturing CO2 at room temperature and atmospheric pressure without the use of chemicals. In this process, the adsorption and desorption of bicarbonate ions from the deionized water solution drive the CO2(g) absorption-desorption from the gas phase. In this work, the effects of the current density and the CO2 partial pressure were studied. We found that between 55 and 75% of the electrical charge of the capacitive electrodes can be directly used to absorb CO2 gas. The energy requirement of such a system was found to be ∼40 kJ mol-1 at 15% CO2 and could be further improved by reducing the ohmic and non-ohmic energy losses of the MCDI cell.
Energy-Efficient Ammonia Recovery in an Up-Scaled Hydrogen Gas Recycling Electrochemical System
Kuntke, Philipp ; Rodrigues, Mariana ; Sleutels, Tom ; Saakes, Michel ; Hamelers, Hubertus V.M. ; Buisman, Cees J.N. - \ 2018
ACS sustainable chemistry & engineering 6 (2018)6. - ISSN 2168-0485 - p. 7638 - 7644.
Ammonia recovery - Electrochemical system - Hydrogen recycling - Up-scaling
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 gN/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/gN (15.6 kW h/kgN) at 50 A/m2 (prototype) to 23.4 kJ/gN (6.5 kW h/kgN) 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 gN/(m2 day) were obtained across the CEM. The TAN recovery was limited by TAN transport from the feed to concentrate compartment.
Concentration Gradient Flow Batteries : salinity gradient energy systems as environmentally benign largescale electricity storage
Egmond, Willem Johannes van - \ 2018
Wageningen University. Promotor(en): C.J.N. Buisman, co-promotor(en): H.V.M. Hamelers. - Wageningen : Wageningen University - ISBN 9789463438421 - 160
The total amount of energy derived from wind turbines and solar panels is rapidly growing. Since these sources of energy are intermittent in nature, supply and demand of energy show an increasing mismatch. To accommodate efficient, large scale use of intermittent renewable energy sources such as wind and sun, energy storage systems are necessary. One of the primary drivers for the increasing use of renewable energy sources is concern about the quality of our environment. Therefore, it is vital that energy storage systems storing sustainable energy, are sustainable themselves. Creating storage systems using abundant, environmentally friendly materials is therefore an important prerequisite for a sustainable energy supply. This thesis aims to explore the potential of the Concentration Gradient Flow Battery (CGFB) as large-scale electricity storage technology. A CGFB stores energy in aqueous solutions of salt (typically NaCl) and uses ion exchange membranes to extract energy from the solutions.
Chapter 1 (Introduction) introduces the need of energy storage. Available energy storage technologies are compared in terms of technical performance but also in terms of safety, environment and political aspects. The CGFB is introduced and explained. Finally, a theoretical background on how a salinity gradient can create a useable voltage across ion exchange membranes is presented.
In Chapter 2 (The Concentration Gradient Flow Battery as electricity storage system: Technology potential and energy dissipation) a working prototype is constructed and tested. This chapter explains how a CGFB works in more detail and the theoretical maximum energy density of the battery is explored (~3.2 kWh m-3 for NaCl). The maximum energy density is shown to vary as function of salt concentrations, volume ratio between salt and fresh solution and salt type. A model is introduced which includes the major dissipation factors; internal resistance, water transport and co-ion transport. Experimental work is performed to validate the model. A wide range of salt concentrations (0-3 m NaCl) and current densities (-49 to +33 A m-2) is chosen. From this work, an optimal working range is identified where the concentrate concentrations preferably do not exceed the 1 m. At higher concentrate concentrations water transport and co-ion transport are found to increase heavily decreasing the energy efficiency of the battery.
In chapter 2 it was shown that the CGFB works best at low (<1 m) concentrations. At low concentrations, internal resistance and water transport are shown to be the most important dissipation factors. In chapter 3 (Energy efficiency of a Concentration Gradient Flow Battery at elevated temperatures), a more specific working range (0-1 m) is explored in more detail. Mass transport is measured accurately and an improved experimental approach allows to determine losses by water transport, internal resistance and co-ion transport in more detail. Chapter 3 shows for both the charge and discharge step the energy efficiency and quantifies the losses at each moment in time. The effect of current density and state-of-charge on power density and energy efficiency is analysed. It is shown that it is not efficient to either completely discharge or charge a CGFB. An optimal working domain is identified (Δm > 0.5 and η > 0.4) where the CGFB delivers best performance in terms of energy efficiency (max. discharge η of 72%) and power density (max. discharge power density, 1.1 W m-2). Tests are also performed at different temperatures (10, 25 and 40 ˚C) to measure the effect of temperature on mass transport, internal resistance and power density. Finally, it is shown that water transport is a major issue in the operation of a CGFB where it causes hysteresis (after discharge the battery does not return to its original state), lower efficiency and leads to decreased energy density.
To improve the performance of a CGFB, it is necessary to decrease water transport across the membranes. Chapter 4 (Tailoring ion exchange membranes to enable low osmotic water transport and energy efficient electrodialysis) introduces modified membranes with a polymer mesh inside with a very small open area (2, 10, 18 and 100% open area). The membranes are prepared by casting an ionomer solution over a polymeric mesh. The material, open area and surface properties of the mesh are changed and the effect on electrical resistance, water transport properties and the efficiency of the charge process are investigated. Comparing a meshed membrane with a homogeneous membrane, the osmotic water transfer coefficient of the meshed membrane is shown to be reduced up to a factor eight. Decreasing the open area of the mesh decreases the water permeability of the membrane but adversely increases electrical resistance. The membranes are tested at different current densities (5-47.5 A m-2). Chapter 4 shows that at low current densities (5-25 A m-2) the meshed membranes outperform the homogeneous membranes in terms of energy efficiency (at a Δc of 0.7 M, maximum energy efficiency η = 67 % for the meshed membranes and η = 50 % for the homogeneous membranes). Also, the meshed membranes outperform the homogeneous membranes in terms of diluate yield across all tested current densities (diluate yield of 78-87% for the meshed membranes, 43-76% for the homogeneous membranes). Using a meshed membrane in a CGFB will lead to less issue with hysteresis. In addition, the relation between material and surface property of the mesh and the ionomer resin is investigated. The type of material (PA or PET) is shown to affect the water permeability of the meshed membrane. It is shown that in some cases, compared to a non-treated mesh, a chemically treated mesh (2 M NaOH treatment) yields lower water permeability membranes. Finally, when optimized ion exchange resin is used it is expected that the water permeability can be reduced even further.
Chapter 2 and chapter 3 show that the CGFB is able to store energy in NaCl solutions which has significant environmental benefits. The measured power density is relatively low and energy density is limited because high concentrations cannot be used. In chapter 5 (Performance of an environmentally benign Acid Base Flow Battery at high energy density) the process is changed to significantly improve power density and energy density while maintaining the environmental benefits. The adjusted system uses three energy storage solutions instead of two and stores most energy in a proton and hydroxyl ion concentration gradient. To create protons and hydroxyl ions (during charge) and to let the ions recombine to pure water again (during discharge) a bipolar membrane is added. Chapter 5 shows that the theoretical maximum energy density of the adjusted system (called Acid Base Flow Battery, ABFB) is over three times higher than the theoretical maximum of the original CGFB (chapter 2, maximum energy density of the CGFB is ~3.2 kWh m-3 and ~11.1 kWh m-3 for the ABFB). In addition, experiments demonstrate that the ABFB reaches a power density which is about a factor four higher compared to the original CGFB (3.7 W m-2 compared to 0.9 W m-2 of membrane area). The main dissipation sources are identified and quantified (energy lost by; co-ion transport 39-65%, ohmic resistance 23-45% and non-ohmic resistance 4-5%). The low selectivity of the membranes to protons and hydroxyls lead to a low coulombic efficiency (13-27 %). The ABFB has potential to be improved significantly. Development of better proton blocking anion exchange membranes and hydroxyl ion blocking cation exchange membranes would increase ABFB performance. Also decreasing the thickness of membranes and compartments would increase ABFB performance as it would lead to lower internal resistance energy losses. In addition, higher current densities would help reduce energy losses by co-ion transport.
Chapter 6 (General discussion and outlook) discusses important aspects of CGFB technology from a societal and commercial point of view. Costs and revenues of energy storage systems are very important drivers and can largely determine the chance of success for a storage technology. First a theoretical background of costs calculations for energy storage systems is presented. Next, the costs of future CGFB systems is calculated and compared to competing technologies. In terms of costs, the ABFB outperforms the CGFB system (0.259 and 0.366 € kWh-1 cycle-1 respectively). Also, possible revenue sources are discussed. Stacking of multiple revenue streams is possible and recommended to increase profitability. Both systems cannot yet generate a profit as costs are too high and single revenue streams are low. However, although difficult, based on the costs calculations, when performance is increased, costs can be reduced and multiple revenue streams are stacked, a commercially viable CGFB/ABFB system is estimated to be feasible. Besides technical and costs aspects, also sustainability of energy storage systems is of major importance. The energy consumption of the production and use of storage systems over their lifetime is analysed and the potential of a CGFB system is discussed. Also, choice in material and system design is discussed. Finally, the size of storage technologies is important. Therefore, the size of a future CGFB system is estimated and discussed with the help of case studies. For diurnal energy storage, the size of a CGFB/ABFB is deemed acceptable given that performance is increased. Seasonal energy storage is not feasible in terms of size without significant technological improvement.
Energy storage with CGFB systems is shown possible. There is a clear need for increased technical performance and reduced costs to create a profitable CGFB. Yet, because of the exciting benefits across different aspects such as safety, environment and politics, CGFB technology is worth continued research.
Performance of an environmentally benign acid base flow battery at high energy density
Egmond, W.J. van; Saakes, M. ; Noor, I. ; Porada, S. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2018
International Journal of Energy Research 42 (2018)4. - ISSN 0363-907X - p. 1524 - 1535.
acid base flow battery - bipolar membrane - co-ion transport - energy efficiency - ion exchange membranes - renewable energy storage - sustainable materials
An increasing fraction of energy is generated by intermittent sources such as wind and sun. A straightforward solution to keep the electricity grid reliable is the connection of large-scale electricity storage to this grid. Current battery storage technologies, while providing promising energy and power densities, suffer from a large environmental footprint, safety issues, and technological challenges. In this paper, the acid base flow battery is re-established as an environmental friendly means of storing electricity using electrolyte consisting of NaCl salt. To achieve a high specific energy, we have performed charge and discharge cycles over the entire pH range (0–14) at several current densities. We demonstrate stable performance at high energy density (2.9 Wh L−1). Main energy dissipation occurs by unwanted proton and hydroxyl ion transport and leads to low coulombic efficiencies (13%–27%).
(Bio)electrochemical ammonia recovery : progress and perspectives
Kuntke, P. ; Sleutels, T.H.J.A. ; Rodríguez Arredondo, M. ; Georg, S. ; Barbosa, S.G. ; Heijne, A. Ter; Hamelers, Hubertus V.M. ; Buisman, C.J.N. - \ 2018
Applied Microbiology and Biotechnology 102 (2018)9. - ISSN 0175-7598 - p. 3865 - 3878.
Ammonia recovery - Bioelectrochemical systems - Electrochemical systems - Total ammonia nitrogen - Wastewater treatment
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.
Tailoring ion exchange membranes to enable low osmotic water transport and energy efficient electrodialysis
Porada, S. ; Egmond, W.J. van; Post, J.W. ; Saakes, M. ; Hamelers, H.V.M. - \ 2018
Journal of Membrane Science 552 (2018). - ISSN 0376-7388 - p. 22 - 30.
Electrical resistance - Electrodialysis - Ion exchange membrane - Osmosis - Water desalination
Ion exchange membranes have been applied for water desalination since the 1950s in a process called electrodialysis, ED. Parallel to the transport of ions across ion exchange membranes, water molecules are transported from diluate to concentrate compartments reducing ED efficiency. In this study tailor made meshed membranes were prepared by embedding polymeric meshes with significantly reduced open area into an ion conductive polymer. These membranes were characterized to assess their transport properties. It is shown that by changing mesh open area, material and surface properties, it is possible to significantly reduce osmotic water transport. Polyamide mesh embedded in a cation exchange polymer showed an eightfold decrease of the water mass transport coefficient. Unexpectedly, osmotic water transport was not affected when the same mesh material was embedded in an anion exchange polymer. A decrease of the osmotic water transport for meshed anion exchange membranes was achieved by using a polyethylene terephthalate mesh. Despite the associated electrical resistance increase, application of meshed membranes increased diluate yield and allowed for more energy efficient operation in case ED is confined to a low current density regime.
Membrane Selectivity Determines Energetic Losses for Ion Transport in Bioelectrochemical Systems
Sleutels, Tom H.J.A. ; Heijne, Annemiek ter; Kuntke, Philipp ; Buisman, Cees J.N. ; Hamelers, Hubertus V.M. - \ 2017
ChemistrySelect 2 (2017)12. - ISSN 2365-6549 - p. 3462 - 3470.
BES - ion exchange membrane - MEC - MET - MFC
Ion transport through ion exchange membranes in Bioelectrochemical Systems (BESs) is different from other electrochemical cells as a result of the complex nature of the electrolyte, as the electrolytes in BESs contain many other cations and anions than H + and OH − . Moreover, these other cations and anions are generally present in high concentrations and therefore determine the ion transport through the membrane. In this work, we provide a theoretical framework for understanding ion transport across ion exchange membranes in BESs. We show that the transport of cations and anions other than H + and OH − determines the pH gradient between anode and cathode, and on top of that, also determines the membrane potential. Experimental data for microbial electrolysis cells with cation and anion exchange membranes are used to support the theoretical framework. In case of cation exchange membranes, the total potential loss consists of both the pH gradient and the concentration gradient of other cations, while in case of anion exchange membranes, the total potential loss is lower because part of the pH gradient loss can be recovered at the membrane. The presented work provides a better theoretical understanding of ion transport through ion exchange membranes in general and in BESs specifically.
Hydrogen Gas Recycling for Energy Efficient Ammonia Recovery in Electrochemical Systems
Kuntke, Philipp ; Rodríguez Arredondo, Mariana ; Widyakristi, Laksminarastri ; Heijne, Annemiek ter; Sleutels, Tom H.J.A. ; Hamelers, Hubertus V.M. ; Buisman, Cees J.N. - \ 2017
Environmental Science and Technology 51 (2017)5. - ISSN 0013-936X - p. 3110 - 3116.
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 56.3 kJ 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 independence of organic matter compared to bioelectrochemical systems. (Chemical Equation Presented).
Load ratio determines the ammonia recovery and energy input of an electrochemical system
Rodríguez Arredondo, Mariana ; Kuntke, Philipp ; Heijne, Annemiek Ter; Hamelers, Hubertus V.M. ; Buisman, Cees J.N. - \ 2017
Water Research 111 (2017). - ISSN 0043-1354 - p. 330 - 337.
Complete removal and recovery of total ammonia nitrogen (TAN) from wastewaters in (bio)electrochemical systems has proven to be a challenge. The system performance depends on several factors, such as current density, TAN loading rate and pH. The interdependence among these factors is not well understood yet: insight is needed to achieve maximum ammonium recovery at minimal energy input. The aim of this study was to investigate the influence of current density and TAN loading rate on the recovery efficiency and energy input of an electrochemical cell (EC). We therefore defined the load ratio, which is the ratio between the applied current and the TAN loading rate. The system consisted of an EC coupled to a membrane unit for the recovery of ammonia. Synthetic wastewater, with TAN concentration similar to urine, was used to develop a simple model to predict the system performance based on the load ratio, and urine was later used to evaluate TAN transport in a more complex wastewater. High fluxes (up to 433 gN m−2 d−1) and recovery efficiencies (up to 100%) were obtained. The simple model presented here is also suited to predict the performance of similar systems for TAN recovery, and can be used to optimize their operation.
In-situ carboxylate recovery and simultaneous pH control with tailor-configured bipolar membrane electrodialysis during continuous mixed culture fermentation
Arslan, D. ; Zhang, Y. ; Steinbusch, K.J.J. ; Diels, L. ; Hamelers, Hubertus V.M. ; Buisman, C.J.N. ; Wever, H. de - \ 2017
Separation and Purification Technology 175 (2017). - ISSN 1383-5866 - p. 27 - 35.
Bipolar membrane - Electrodialysis - Fermentation - ISPR - Short chain carboxylates
Anaerobic fermentation of organic waste streams by mixed culture generates a mixture of short chain carboxylic acids. To avoid inhibitory effects of the acids or their consumption in internal conversion reactions in the mixed culture environment, in-situ recovery of acids can be beneficial. In this study, electrodialysis with bipolar membranes (EDBM) was applied to a mixed culture fermentation on organic waste streams using a novel EDBM stack with “direct contact” operation mode. We could demonstrate simultaneous recovery of carboxylates from the fermenter by the EDBM stack while in-situ generation and transport of hydroxyl ions to the fermenter allowed direct pH control. Experiments showed productivity increase after EDBM coupling to the fermenter, and complete elimination of external base consumption. It was also observed that EDBM was able to drive the mixed culture fermentation towards acetate and propionate type of carboxylates.
Energy efficiency of a concentration gradient flow battery at elevated temperatures
Egmond, W.J. van; Starke, U.K. ; Saakes, M. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2017
Journal of Power Sources 340 (2017). - ISSN 0378-7753 - p. 71 - 79.
Aqueous electrolyte - Charge/discharge efficiency - Concentration gradient flow battery - Large scale electricity energy storage - Reverse electrodialysis - Stationary batteries
Fast growth of intermittent renewable energy generation introduces a need for large scale electricity storage. The Concentration Gradient Flow Battery (CGFB) is an emerging technology which combines Electrodialysis with Reverse Electrodialysis into a flow battery which is able to safely store very large amounts of energy in environmental friendly NaCl solutions. In this work, (dis)charge efficiency, energy density and power density are both theoretically and experimentally investigated. Fifteen constant current experiments (−47.5 to +37.5 A m−2) are performed at 40 °C and two experiments (−32.5 and 15 A m−2) at 10 and 25 °C. The magnitudes of the three main energy dissipation sources (internal resistance, water transport and co-ion transport) are measured and mitigation strategies are proposed. The effect of current density, state of charge and temperature on the dissipation sources is analysed. Water transport is shown to cause hysteresis, lower (dis)charge efficiencies and lower energy capacity. At constant current and with increasing temperature, internal resistance is reduced but unwanted water transport is increased. This study reports charge efficiencies up to 58% and discharge efficiencies up to 72%. Full charge or discharge of the battery is shown inefficient. The optimal operating range is therefore introduced and identified (concentration difference Δm > 0.5 and energy efficiency η > 0.4).
On the origin of the membrane potential arising across densely charged ion exchange membranes : How well does the teorell-meyer-sievers theory work?
Galama, A.H. ; Post, J.W. ; Hamelers, H.V.M. ; Nikonenko, V.V. ; Biesheuvel, P.M. - \ 2016
Journal of Membrane Science & Research 2 (2016)3. - ISSN 2476-5406 - p. 128 - 140.
Donnan equilibrium - Ion exchange membranes - Nernst-planck equation - Teorell-meyer-sievers (TMS) theory
A difference in salt concentration in two solutions separated by a membrane leads to an electrical potential difference across the membrane, also without applied current. A literature study is presented on proposed theories for the origin of this membrane potential (Φm). The most well-known theoretical description is Teorell-Meyer-Sievers (TMS) theory, which we analyze and extend. Experimental data for Φm were obtained using a cation exchange membrane (CMX, Neosepta) and NaCl solutions (salt concentration from 1 mM to 5 M). Deviations between theory and experiments are observed, especially at larger salt concentration differences across the membrane. At a certain salt concentration ratio, a maximum in Φm is found, not predicted by the TMS theory. Before the maximum, TMS theory can be used as a good estimate of ?m though it overestimates the actual value. To improve the theory, various corrections to TMS theory were considered: A) Using ion activities instead of ionic concentration in the external solutions leads to an improved prediction; B) Inhomogeneous distribution of the membrane fixed charge has no effect on Φm; C) Consideration of stagnant diffusion layers on each side of the membrane can have a large effect on Φm; D) Reducing the average value of the fixed membrane charge density can also largely affect ?m; E) Allowing for water transport in the theory has a small effect; F) Considering differences in ionic mobility between co-ions and counterions in the membrane affects Φm significantly. Modifications C) and F) may help to explain the observed maximum in Φm.
Gas-permeable hydrophobic membranes enable transport of CO2 and NH3 to improve performance of bioelectrochemical systems
Sleutels, Tom H.J.A. ; Hoogland, Biense ; Kuntke, P. ; Heijne, A. ter; Buisman, C.J.N. ; Hamelers, Hubertus V.M. - \ 2016
Environmental Science : Water Research & Technology 2 (2016). - ISSN 2053-1400 - p. 743 - 748.
Application of bioelectrochemical systems (BESs), for example for the production of hydrogen from organic waste material, is limited by a high internal resistance, especially when ion exchange membranes are used. This leads to a limited current density and thus to large footprint and capital costs. Ion transport between anode and cathode compartment is one of the factors determining the internal resistance. The aim of this study was to reduce the resistance for ion transport in a microbial electrolysis cell (MEC) through the ion exchange membrane by shuttling of CO2 and NH3 between anode and cathode. The transport of these chemical species was enabled through the use of a hydrophobic TransMembraneChemiSorption module (TMCS) that was placed between anolyte and catholyte circulation outside the cell. The driving force for transport was the pH difference between both solutions. The transport of CO2 and NH3 resulted in an increase in current density from 2.1 to 4.1 A m−2 for a cation exchange membrane (CEM) and from 2.5 to 13.0 A m−2 for an anion exchange membrane (AEM) at 1 V applied voltage. The increase in current density was the result of a lower ion transport resistance through the membrane; this resistance was 60% lower for the CEM, as a result of NH3 recycling from cathode to anode, and 82% for the AEM, as a result of CO2 recycling from anode to cathode with TMCS, compared to experiments without TMCS.
Gas-permeable hydrophobic tubular membranes for ammonia recovery in bio-electrochemical systems
Kuntke, P. ; Zamora, P. ; Saakes, M. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2016
Environmental Science : Water Research & Technology 2 (2016)2. - ISSN 2053-1400 - p. 261 - 265.
The application of a gas-permeable hydrophobic tubular membrane in bio-electrochemical systems enables efficient recovery of ammonia (NH3) from their cathode compartments. Due to a hydrogen evolution reaction at the cathode, no chemical addition was required to increase the pH for continuous NH3 recovery from wastewater.
Revisiting Morrison and Osterle 1965 : The efficiency of membrane-based electrokinetic energy conversion
Catalano, J. ; Hamelers, H.V.M. ; Bentien, A. ; Biesheuvel, Maarten - \ 2016
Journal of Physics-Condensed Matter 28 (2016)32. - ISSN 0953-8984
charged nanopore - desalination - electrokinetic energy conversion
We revisit Morrison and Osterle (1965) who derived a phenomenological expression for the 'figure-of-merit' βEK of the electrokinetic energy conversion (EKEC) of a pressure difference into electric energy (and vice versa) using charged nanotubes, nanopores or ion-exchange membranes. We show the equivalence with Morrison and Osterle of a novel expression of βEK derived by Bentien et al (2013). We analyze two physical models for ionic and solvent flow which directly relate βEK to nanopore characteristics such as pore size and wall charge density. For the uniform potential model, we derive an analytical expression as a function of pore size, viscosity, ion diffusion coefficients and membrane charge density, and compare results with the full space-charge model by Osterle and co-workers as a function of pore size and ion diffusion coefficient. We present a novel expression for βEK for salt solutions with ions with unequal diffusion coefficients (mobilities) and show that to increase βEK the counterion mobility must be low and the coion mobility high.
The concentration gradient flow battery as electricity storage system : Technology potential and energy dissipation
Egmond, W.J. Van; Saakes, M. ; Porada, S. ; Meuwissen, T. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2016
Journal of Power Sources 325 (2016). - ISSN 0378-7753 - p. 129 - 139.
Aqueous based battery - Flow batteries - Ion-exchange membranes - Large scale electricity energy storage - Reverse electrodialysis - Salinity gradient energy
Unlike traditional fossil fuel plants, the wind and the sun provide power only when the renewable resource is available. To accommodate large scale use of renewable energy sources for efficient power production and utilization, energy storage systems are necessary. Here, we introduce a scalable energy storage system which operates by performing cycles during which energy generated from renewable resource is first used to produce highly concentrated brine and diluate, followed up mixing these two solutions in order to generate power. In this work, we present theoretical results of the attainable energy density as function of salt type and concentration. A linearized Nernst-Planck model is used to describe water, salt and charge transport. We validate our model with experiments over wide range of sodium chloride concentrations (0.025-3 m) and current densities (-49 to +33 A m-2). We find that depending on current density, charge and discharge steps have significantly different thermodynamic efficiency. In addition, we show that at optimal current densities, mechanisms of energy dissipation change with salt concentration. We find the highest thermodynamic efficiency at low concentrate concentrations. When using salt concentrations above 1 m, water and co-ion transport contribute to high energy dissipation due to irreversible mixing.
Selective short-chain carboxylates production : A review of control mechanisms to direct mixed culture fermentations
Arslan, D. ; Steinbusch, K.J.J. ; Diels, L. ; Hamelers, H.V.M. ; Strik, D.P.B.T.B. ; Buisman, C.J.N. ; Wever, H. De - \ 2016
Critical Reviews in Environmental Science and Technology 46 (2016)6. - ISSN 1064-3389 - p. 592 - 634.
Biomass conversion - carboxylates - mixed culture fermentation - operational parameters - organic waste - volatile fatty acids
Anaerobic digestion of organic residual streams can be directed to produce carboxylates such as acetate, propionate, and n-butyrate, which can be either directly used in industry or converted into other valuable compounds. This paper reviews the studies working with mixed culture conversion of organic substrates toward carboxylates. It draws connections between standard fermentation parameters and the carboxylate product concentrations and composition. The use of more concentrated carbohydrate-rich substrates, at longer residence times and at neutral pH ranges, stimulates total acid production. When increasing pH to the neutral range, acetate and propionate fractions are elevated. High propionate concentrations and fractions are infrequently reported and mainly appear on high-protein-containing feedstock. High n-butyrate fraction <70% is usually found when pH > 6, at longer retention times or organic loading rates, under CO2 atmosphere or on substrates with high lactate concentrations. The review concludes with prospects for further developments related to the carboxylate platform.
On-line method to study dynamics of ion adsorption from mixtures of salts in capacitive deionization
Dykstra, J.E. ; Dijkstra, J. ; Wal, A. van der; Hamelers, H.V.M. ; Porada, S. - \ 2016
Desalination 390 (2016). - ISSN 0011-9164 - p. 47 - 52.
Capacitive Deionization - Electrosorption - Ionic mixtures - Salt removal - Selective ion removal
Capacitive Deionization (CDI) is a water desalination technology that adsorbs ions into two oppositely polarized porous carbon electrodes, under the action of an applied voltage. Here, we introduce a novel method to analyze the effluent concentration of multiple ionic species in mixtures of salt solutions by directing the outflow of a CDI cell to an inductively coupled plasma optical emission spectroscopy (ICP-OES) instrument. Compared to previous methods based on manual sampling, the on-line use of ICP-OES allows collecting more accurate time-dependent ion adsorption data, and therefore, ion dynamics can be studied even at very short half-cycle times. We use this method to study ion adsorption from a mixed solution containing two monovalent cations with similar radius, namely potassium and sodium. We find that potassium ions are preferentially adsorbed over sodium ions, due to their higher mobility. Furthermore, we compare our experimental findings with a novel multicomponent electromigration model that calculates dynamic adsorption of ions from solutions of multiple salts. Whereas we find good agreement between data and theory at low half cycle times, we observe a considerable discrepancy at higher values.
Chain Elongation with Reactor Microbiomes: Open-Culture Biotechnology To Produce Biochemicals
Angenent, L.T. ; Richter, H. ; Buckel, W. ; Spirito, C.M. ; Steinbusch, K.J.J. ; Plugge, C.M. ; Strik, D.P.B.T.B. ; Grootscholten, T.I.M. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2016
Environmental Science and Technology 50 (2016)6. - ISSN 0013-936X - p. 2796 - 2810.
Chain elongation into medium-chain carboxylates, such as n-caproate and n-caprylate, with ethanol as an electron donor and with open cultures of microbial consortia (i.e., reactor microbiomes) under anaerobic conditions is being developed as a biotechnological production platform. The goal is to use the high thermodynamic efficiency of anaerobic fermentation to convert organic biomass or organic wastes into valuable biochemicals that can be extracted. Several liter-scale studies have been completed and a first pilot-plant study is underway. However, the underlying microbial pathways are not always well understood. In addition, an interdisciplinary approach with knowledge from fields ranging from microbiology and chemical separations to biochemistry and environmental engineering is required. To bring together research from different fields, we reviewed the literature starting with the microbiology and ending with the bioprocess engineering studies that already have been performed. Because understanding the microbial pathways is so important to predict and steer performance, we delved into a stoichiometric and thermodynamic model that sheds light on the effect of substrate ratios and environmental conditions on product formation. Finally, we ended with an outlook
Parallel up-scaling of Capacitive Mixing (CapMix) system enhances the specific performance
Liu, Fei ; Donkers, Tim F.W. ; Wagterveld, R.M. ; Schaetzle, Olivier ; Saakes, Michel ; Buisman, Cees J.N. ; Hamelers, Hubertus V.M. - \ 2016
Electrochimica Acta 187 (2016). - ISSN 0013-4686 - p. 104 - 112.
Capacitive Donnan Potential - Capacitive Mixing - Ion exchange membrane - Salinity gradient energy - Wire-shaped electrode
Given the considerable amount of energy dissipated in the salinity gradient at the point where a river flows into the sea, we investigate the technology of capacitive mixing (CapMix), an attractive technology for generating electrical power from this gradient. We determine the performances of multiple wire-shaped electrode pairs connected either in series or in parallel in a CapMix system. The bundles of pairs were immersed in synthetic river and seawater. Pairs connected in parallel and placed next to each other allowed for 18% more energy extraction than the total energy extracted by the same number of pairs individually. An even higher additional energy gain is possible if contact resistances are further minimized. The improvement is due to the additional flow paths for ions between electrode pairs in parallel connection, reducing the total internal resistance. The highest power density achieved (in terms of the mass of activated carbon material used) was 2.7 mW/g, which was higher than the power densities that have been achieved previously using a flat plate CapMix cell (1.26 mW/g) and a wire electrode cell (0.34 mW/g). The lower ohmic resistance in the parallel system was identified using a current distribution model and experimental measurements.
Theory of Water Desalination by Porous Electrodes with Immobile Chemical Charge
Biesheuvel, P.M. ; Hamelers, H.V.M. ; Suss, M.E. - \ 2015
Colloids and Interface Science Communications 9 (2015). - ISSN 2215-0382 - p. 1 - 5.
In capacitive deionization (CDI), water is desalinated by storing ions in electrical double layers (EDLs) within the micropores of charged porous carbon electrodes. Recent experiments using chemically modified electrodes have shown differing, novel phenomena such as "inverted CDI," "enhanced CDI," and "inversion peaks." We here present an EDL and dynamic model which includes immobile chemical charge in the micropores and show that the models predict these disparate experimental observations. Our model also makes predictions for a previously undiscovered operational regime with higher salt adsorption, which we term extended voltage CDI.
Analysis of bio-anode performance through electrochemical
Heijne, A. ter; Schaetzle, O.C. ; Gimenez, S. ; Navarro, L. ; Hamelers, B. ; Fabregat-Santiago, F. - \ 2015
Bioelectrochemistry 106 (2015)part A. - ISSN 1567-5394 - p. 64 - 72.
In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm- 2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture. In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm- 2. The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 O·cm2 and 34 O·cm2, respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the Butler–Volmer relationship that needs further exploration.
Energy from CO2 using capacitive electrodes – A model for energy extraction cycles
Paz-García, J.M. ; Dykstra, J.E. ; Biesheuvel, P.M. ; Hamelers, H.V.M. - \ 2015
Journal of Colloid and Interface Science 442 (2015). - ISSN 0021-9797 - p. 103 - 109.
A model is presented for the process of harvesting electrical energy from CO2 emissions using capacitive cells. The principle consists of controlling the mixing process of a concentrated CO2 gas stream with a dilute CO2 gas stream (as, for example, exhaust gas and air), thereby converting part of the released mixing energy into electrical energy. The model describes the transient reactive transport of CO2 gas absorbed in water or in monoethanolamine (MEA) solutions, under the assumption of local chemical equilibrium. The model combines the selective transport of ions through ion-exchange membranes, the accumulation of charge in the porous carbon electrodes and the coupling between the ionic current and the produced electrical current and power. We demonstrate that the model can be used to calculate the energy that can be extracted by mixing concentrated and dilute CO2 containing gas streams. Our calculation results for the process using MEA solutions have various counterintuitive features, including: 1. When dynamic equilibrium is reached in the cyclical process, the electrical charge in the anode is negative both during charging and discharging; 2. Placing an anion-exchange membrane (AEM) in the system is not required, the energy per cycle is just as large with or without an AEM.
Carbon nanotube yarns as strong flexible conductive capacitive electrodes
Liu, F. ; Wagterveld, R.M. ; Gebben, B. ; Otto, M.J. ; Biesheuvel, P.M. ; Hamelers, H.V.M. - \ 2015
Colloids and Interface Science Communications 3 (2015). - ISSN 2215-0382 - p. 9 - 12.
Carbon nanotube (CNT) yarn, consisting of 23 µm diameter CNT filaments, can be used as capacitive electrodes that are long, flexible, conductive and strong, for applications in energy and electrochemical water treatment. We measure the charge storage capacity as function of salt concentration, and use Gouy–Chapman–Stern theory to describe the data. CNT yarn can also be used as conductive scaffold for the application of a porous activated carbon (AC) layer. We show the potential of CNT yarn for the generation of electrical energy from environmental entropy differences, by coating yarn (both with and without AC coating) with ion-exchange membranes (IEMs) and generating power from the salt concentration difference between river water and seawater. The use of flexible and conductive CNT yarns as capacitive electrodes and electrode scaffolds breaks with the paradigm of planar static electrodes, and opens up a range of alternative designs for electrochemical cells with enhanced performance.
Advancing CapMix for electricity generation : system operation, cell design and material selection
Liu, F. - \ 2015
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Bert Hamelers. - Wageningen : Wageningen University - ISBN 9789462573079 - 164
hernieuwbare energie - bio-energie - energiebronnen - capacitantie - vermenging - zout water - zoet water - elektrodialyse - biobased economy - renewable energy - bioenergy - energy sources - capacitance - mixing - saline water - fresh water - electrodialysis - biobased economy
Capacitive energy extraction of the mixing process, also referred as Capacitive Mixing (CapMix), is a novel and promising technology that can convert salinity gradient power into electricity directly. This technology uses two porous activated carbon electrodes. The energy extraction is directly linked to the mixing process, while no emission of greenhouse gases and no thermal pollution occur. This emerging CapMix technology is still immature. In order to transform the proof-of-principle into a viable technology, many questions remain to be answered, not only in science (i.e. understanding what is happening), but also in technology (i.e. how to design and manufacture the system). In this thesis, the author investigated the optimized way to operate the system. Moreover, models were developed to understand the physical-chemical process; material including ion exchange membranes and activated carbon electrodes were evaluated; and the innovative cell design was made.
Fluidized Capacitive Bioanode As a Novel Reactor Concept for the Microbial Fuel Cell
Deeke, A. ; Sleutels, T.H.J.A. ; Donkers, T.F.W. ; Hamelers, B. ; Buisman, C.J.N. ; Heijne, A. ter - \ 2015
Environmental Science and Technology 49 (2015)3. - ISSN 0013-936X - p. 1929 - 1935.
waste-water treatment - electricity-generation - power-generation - iron reduction - scaled-up - performance - carbon - resistance - membranes - biofilms
The use of granular electrodes in Microbial Fuel Cells (MFCs) is attractive because granules provide a cost-effective way to create a high electrode surface area, which is essential to achieve high current and power densities. Here, we show a novel reactor design based on capacitive granules: the fluidized capacitive bioanode. Activated carbon (AC) granules are colonized by electrochemically active microorganisms, which extract electrons from acetate and store the electrons in the granule. Electricity is harvested from the AC granules in an external discharge cell. We show a proof-of-principle of the fluidized capacitive system with a total anode volume of 2 L. After a start-up period of 100 days, the current increased from 0.56 A/m2 with 100 g AC granules, to 0.99 A/m2 with 150 g AC granules, to 1.3 A/m2 with 200 g AC granules. Contact between moving AC granules and current collector was confirmed in a control experiment without biofilm. Contribution of an electro-active biofilm to the current density with recirculation of AC granules was limited. SEM images confirmed that a biofilm was present on the AC granules after operation in the fluidized capacitive system. Although current densities reported here need further improvement, the high surface area of the AC granules in combination with external discharge offers new and promising opportunities for scaling up MFCs.
Extraction of Energy from Small Thermal Differences near Room Temperature Using Capacitive Membrane Technology
Sales, B.B. ; Burheim, O.S. ; Porada, S. ; Presser, V. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2014
Environmental Science & Technology Letters 1 (2014)9. - ISSN 2328-8930 - p. 356 - 360.
charged membranes - performance - electrodes - systems
Extracting electric energy from small temperature differences is an emerging field in response to the transition toward sustainable energy generation. We introduce a novel concept for producing electricity from small temperature differences by the use of an assembly combining ion exchange membranes and porous carbon electrodes immersed in aqueous electrolytes. Via the temperature differences, we generate a thermal membrane potential that acts as a driving force for ion adsorption/desorption cycles within an electrostatic double layer, thus converting heat into electric work. We report for a temperature difference of 30 degrees C a maximal energy harvest of similar to 2 mJ/m(2), normalized to the surface area of all the membranes.
Capacitive bioanodes for electricity storage in Microbial Fuel Cells
Deeke, A. - \ 2014
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Bert Hamelers; Annemiek ter Heijne. - Wageningen : Wageningen University - ISBN 9789462571105 - 151
afvalwaterbehandeling - organische stof - brandstofcellen - energiebronnen - elektriciteit - opslag - energiegebruik - elektrodes - elektrolyten - bio-energie - onderzoek - biobased economy - waste water treatment - organic matter - fuel cells - energy sources - electricity - storage - energy consumption - electrodes - electrolytes - bioenergy - research - biobased economy
Denkend aan het opraken van de fossiele brandstoffen, wordt de noodzaak om naar hernieuwbare alternatieven te kijken alleen maar groter. Zon, wind, water en biomassa zijn al hernieuwbare bronnen die actueel gebruikt worden. Maar voor zonne-, wind- en waterenergie beperkt die discontinue aanwezigheid de verdere ontwikkeling en wordt de noodzaak voor elektriciteitsopslag benadrukt. Een andere technologie voor hernieuwbare elektriciteitsopwekking is de microbiële brandstofcel (MFC). In een MFC worden de organische bestanddelen van het afvalwater rechtstreeks in elektrische energie omgezet. MFCs zijn een opkomende technologie van de afgelopen 10 jaar en vele onderzoekers hebben onderzoek gedaan naar de verbetering van de stroomdichtheid en het vermogen. De continue verwerking van het afvalwater vraagt om opslag van het afvalwater of om opslag van de geproduceerde elektriciteit. Opslag van de elektriciteit kan bewerkstelligd worden door het combineren van een MFC met een condensator.
Carbon flow electrodes for continuous operation of capacitive deionization and capacitive mixing energy generation
Porada, S. ; Hamelers, H.V.M. ; Bryjak, M. ; Presser, V. ; Biesheuvel, P.M. ; Weingarth, D. - \ 2014
Journal of Materials Chemistry. A, Materials for energy and sustainability 2 (2014)24. - ISSN 2050-7488 - p. 9313 - 9321.
graphite powder suspensions - activated carbon - electrochemical polarization - salinity differences - porous-electrodes - constant-current - co2 capture - desalination - ions - performance
Capacitive technologies, such as capacitive deionization and energy harvesting based on mixing energy (“capmix” and “CO2 energy”), are characterized by intermittent operation: phases of ion electrosorption from the water are followed by system regeneration. From a system application point of view, continuous operation has many advantages, to optimize performance, to simplify system operation, and ultimately to lower costs. In our study, we investigate as a step towards second generation capacitive technologies the potential of continuous operation of capacitive deionization and energy harvesting devices, enabled by carbon flow electrodes using a suspension based on conventional activated carbon powders. We show how the water residence time and mass loading of carbon in the suspension influence system performance. The efficiency and kinetics of the continuous salt removal process can be improved by optimizing device operation, without using less common or highly elaborate novel materials. We demonstrate, for the first time, continuous energy generation via capacitive mixing technology using differences in water salinity, and differences in gas phase CO2 concentration. Using a novel design of cylindrical ion exchange membranes serving as flow channels, we continuously extract energy from available concentration differences that otherwise would remain unused. These results may contribute to establishing a sustainable energy strategy when implementing energy extraction for sources such as CO2-emissions from power plants based on fossil fuels.
Two-stage medium chain fatty acid (MCFA) production from municipal solid waste and ethanol
Grootscholten, T.I.M. ; Strik, D.P.B.T.B. ; Steinbusch, K.J.J. ; Buisman, C.J.N. ; Hamelers, B. - \ 2014
Applied Energy 116 (2014)1. - ISSN 0306-2619 - p. 223 - 229.
clostridium-kluyveri - carboxylic-acids - carbon-dioxide - elongation - biomass - inhibition - caprylate - caproate - bacteria - acetate
Chain elongation is an anaerobic fermentation that produces medium chain fatty acids (MCFAs) from volatile fatty acids and ethanol. These MCFAs can be used as biochemical building blocks for fuel production and other chemical processes. Producing MCFAs from the organic fraction of municipal solid waste (OFMSW) is attractive because it combines waste treatment with biochemical production. We investigated whether higher MCFA production rates can be achieved from OFMSW by applying a two-stage conversion, consisting of the OFMSW acidification step followed by chain elongation, compared to a single-stage system. We obtained higher MCFA production rates with a two-stage system than with a single-stage system. The obtained caproate concentrations were above the solubility of caproic acid in water. Furthermore, this work discussed competitive processes for MCFA production and shows how these processes can be controlled in a two-stage system. Finally an outlook was given on research required to prevent too much production of the intermediate co-product butyrate instead of MCFAs, which occurred several times during the experiment.
Energy from CO2 using capacitive electrodes – Theoretical outline and calculation of open circuit voltage
Par-Garcia, J.M. ; Schaetzle, O. ; Biesheuvel, P.M. ; Hamelers, H.V.M. - \ 2014
Journal of Colloid and Interface Science 418 (2014). - ISSN 0021-9797 - p. 200 - 207.
anion-exchange membranes - porous-electrodes - carbamate formation - aqueous-solution - acid anions - monoethanolamine - equilibrium - absorption - simulation - capture
Recently, a new technology has been proposed for the utilization of energy from CO2 emissions (Hamelers et al., 2014). The principle consists of controlling the dilution process of CO2–concentrated gas (e.g., exhaust gas) into CO2–dilute gas (e.g., air) thereby extracting a fraction of the released mixing energy. In this paper, we describe the theoretical fundamentals of this technology when using a pair of charge–selective capacitive electrodes. We focus on the behavior of the chemical system consisting of CO2 gas dissolved in water or monoethanolamine solution. The maximum voltage given for the capacitive cell is theoretically calculated, based on the membrane potential. The different aspects that affect this theoretical maximum value are discussed.
Harvesting Energy from CO2 Emissions
Hamelers, H.V.M. ; Schaetzle, O. ; Paz-García, J.M. ; Biesheuvel, P.M. ; Buisman, C.J.N. - \ 2014
Environmental Science & Technology Letters 1 (2014)1. - ISSN 2328-8930 - p. 31 - 35.
water salinity difference - capacitive deionization - carbon electrodes - extraction - power - capture
When two fluids with different compositions are mixed, mixing energy is released. This holds true for both liquids and gases, though in the case of gases, no technology is yet available to harvest this energy source. Mixing the CO2 in combustion gases with air represents a source of energy with a total annual worldwide capacity of 1570 TWh. To harvest the mixing energy from CO2-containing gas emissions, we use pairs of porous electrodes, one selective for anions and the other selective for cations. We demonstrate that when an aqueous electrolyte, flushed with either CO2 or air, alternately flows between these selective porous electrodes, electrical energy is gained. The efficiency of this process reached 24% with deionized water as the aqueous electrolyte and 32% with a 0.25 M monoethanolamine (MEA) solution as the electrolyte. The highest average power density obtained with a MEA solution as the electrolyte was 4.5 mW/m2, significantly higher than that with water as the electrolyte (0.28 mW/m2).
Clean energy generation using capacitive electrodes in reverse electrodialysis
Vermaas, D.A. ; Bajracharya, S. ; Bastos Sales, B. ; Saakes, M. ; Hamelers, B. ; Nijmeijer, K. - \ 2013
Energy & Environmental Science 6 (2013)2. - ISSN 1754-5692 - p. 643 - 651.
sustainable power-generation - pressure-retarded osmosis - salinity gradients - water - density - difference
Capacitive reverse electrodialysis (CRED) is a newly proposed technology to generate electricity from mixing of salt water and fresh water (salinity gradient energy) by using a membrane pile as in reverse electrodialysis (RED) and capacitive electrodes. The salinity difference between salt water and fresh water generates a potential difference over ion selective membranes, which can be used as a renewable power source. The strength and unique characteristic of CRED in comparison to the other technologies is that it allows multiple membrane cells between a single set of electrodes and at the same time avoids redox reactions using capacitive electrodes. The capacitive electrodes use activated carbon on a support of Ti/Pt mesh to store ions and their charge. A periodic switching of the feed waters, combined with a switching of the direction of the electric current, ensures that the capacitive electrodes do not get saturated. The large membrane pile enables the electrodes to be charged more than in previous approaches for capacitive mixing. As a consequence, the energy cycle of CRED has a larger range in both voltage and accumulated charge compared to previous capacitive mixing technologies. The power density obtainable with CRED stacks with capacitive electrodes is an order of magnitude higher than in previous attempts for capacitive energy extraction and close to or even better than similar RED stacks with conventional redox based electrode systems. CRED is considered to be a stable, safe, clean and high performing technology to obtain energy from mixing of salt water and fresh water.
|Bioelectrochemical production of caproate and caprylate from acetate
Eerten-Jansen, M.C.A.A. van; Heijne, A. ter; Grootscholten, T.I.M. ; Steinbusch, K.J.J. ; Sleutels, T.H.J.A. ; Hamelers, B. ; Buisman, C.J.N. - \ 2013
Correction to Bioelectrochemical Production of Caproate and Caprylate from Acetate by Mixed Cultures
Eerten-Jansen, M.C.A.A. van; Heijne, A. ter; Grootscholten, T.I.M. ; Steinbusch, K.J.J. ; Sleutels, T.H.J.A. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
ACS sustainable chemistry & engineering 1 (2013)8. - ISSN 2168-0485 - p. 1069 - 1069.
Development of a mixed culture chain elongation process based on municipal solid waste and ethanol
Grootscholten, T.I.M. - \ 2013
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Bert Hamelers. - Wageningen : Wageningen UR - ISBN 9789461737809 - 190
afvalbeheer - afvalverwerking - keukenafval - bio-energie - fermentatie - ethanol - waste management - waste treatment - kitchen waste - bioenergy - fermentation - ethanol
Keywords: mixed culture fermentation; Carboxylates; Caproate; Heptanoate; ethanol; OFMSW
To reduce dependence on oil, alternative fuel and chemical production processes are investigates. In this thesis, we investigated the production of medium chain fatty acids (MCFAs) using an anaerobic chain elongation process from the organic fraction of municipal solid waste (OFMSW) and (diluted) ethanol.By using OFMSW for the production of MCFAs, OFMSW can be valorised. Moreover, the food-fuel discussion can be avoided, as long as the ethanol is not produced from food resources. Investigations included studies about single stage and two-stage systems, methods to reduce impact of competitive processes within the desired mixed microbial culture and kinetic considerations. As result, the MCFA productivity was improved more than 100-fold compared to the productivity at the start of the investigations. Consequently, the potential of the mixed culture chain elongation process as alternative for anaerobic digestion has increased.
Increase of power output by change of ion transport direction in a plant microbial fuel cell
Timmers, R.A. ; Strik, D.P.B.T.B. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
International Journal of Energy Research 37 (2013)9. - ISSN 0363-907X - p. 1103 - 1111.
long-term performance - bioelectrochemical systems - exchange membranes - electrolysis cells - iron reduction - rice plants - electricity - cathode - rhizodeposits - generation
The plant microbial fuel cell (PMFC) is a technology for the production of renewable and clean bioenergy based on photosynthesis. To increase the power output of the PMFC, the internal resistance (IR) must be reduced. The objective of the present study was to reduce the membrane resistance by changing the transport direction of cations in the direction of the established concentration gradient. Two setups, a MFC and PMFC, were designed with one anode and two cathode compartments to demonstrate the effect of changing the transport direction. This design allowed changing the direction of transport of cations by switching the cathode compartment that functions as cathode. The change between cathode 1 and cathode 2 enhanced the power output of the PMFC by 398%. More specifically, after changing transport direction, the increase in power output was due to the reduction of IR (normalized to membrane area) from 4.3 O m2mem to 1.2 O m2mem in the PMFC. Consecutive changes of cathodes resulted in an increase of generated power with cathode 1 while this power decreased for cathode 2. During the consecutive changes, the average power output remained constant 0.0362¿±¿0.0005 W m-2mem; this was 246% higher than the initial power output with cathode 1
Capacitive technology for energy extraction from chemical potential differences
Bastos Sales, B. - \ 2013
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Bert Hamelers. - S.l. : s.n. - ISBN 9789461737380 - 120
capacitantie - bio-elektrische potentiaal - hernieuwbare energie - energiebronnen - zoutgehalte - elektrische kracht - temperatuur - capacitance - bioelectric potential - renewable energy - energy sources - salinity - electric power - temperature
This thesis introduces the principle of Capacitive energy extraction based on Donnan Potential (CDP) to exploit salinity gradients. It also shows the fundamental characterization and improvements of CDP. An alternative application of this technology aimed at thermal gradients was tested.
Chapter 2 introduces the principle and initial tests. The entropy increase of mixing two solutions of different salt concentrations can be harnessed to generate electrical energy. Worldwide, the potential of this resource, the controlled mixing of river and seawater, is enormous, but existing conversion technologies are still complex and expensive. Here we present a small-scale device that directly generates electrical power from the sequential flow of fresh and saline water, without the need of auxiliary processes or converters. The device consists of a sandwich of porous “supercapacitor” electrodes, ion-exchange membranes, and a spacer and can be further miniaturized or scaled-out. Our results demonstrate that alternating the flow of saline and fresh water through a capacitive cell allows direct autogeneration of voltage and current and consequently leads to power generation. Theoretical calculations aid in providing directions for further optimization of the properties of membranes and electrodes.
In Chapter 3, traditional electrochemical techniques (galvanostatic charge–discharge and cyclic voltammetry) were used to investigate intrinsic properties of this open system. This study demonstrates the feasibility to characterize the capacitive behavior of the cell in low concentration (0.5 M). Presence of membranes, as well as the possibility of having the electrolyte flowing through the cell was investigated. In the studied cell, the presence of membranes showed a limitation by the anion exchange membrane at low current densities but no effect at high current densities. The flow rate did not influence the capacitance of the system either.
Chapter 4uses again a stack of eight cells coupled in parallel to investigate the viability of this technology. An average power density of 0.055W/m2was obtained during the peak of the different cycles, though reasonable optimization suggests an expectation of 0.26W/m2at 6.2 A/m2. It was found that 83 ± 8% of the theoretical driving potential was obtained during the operating process. By studying the polarization curves during charging and discharging cycles, it was found that optimizing the feed fluid flow is currently among the most beneficial paths to make CDP a viable salinity difference power source. Another parallel route for increasing the efficiency is lowering the internal ohmic resistances of the cell by design modifications.
A modification is proposed in Chapter 5, approaching the electrodes geometry that has a relevant impact on internal resistance and overall performance in CDP. In this work, we present the first effort to use wire-shaped electrodes and its suitability for improving CDP. Analytical evaluation and electrical measurements confirm a strong nonlinear decrease in internal resistance for distances between electrodes smaller than 3 mm. We also demonstrate that we get more power per material invested when compared to traditional flat plate designs. These findings show the advantages of this design for further development of CDP into a mature technology.
Alternatively, in Chapter 6, we present a new principle for producing electricity from low temperature differences by using an affordable assembly combining ion exchange membranes and supercapacitor carbon electrodes. Our proposed design involves two isolated salty solutions, with equal concentration but different temperatures. The operation consists of an alternately and cyclic exposure of the electrodes to these electrolytes. This difference in temperature generates a thermomembrane potential that acts as a driving force for ionic adsorption/desorption cycles on the electrodes. Our simple system is interesting for exploiting the potential of low temperature waste heat. When two volumes with equal concentration have different temperatures, it is possible to immerse a pair of electrodes (anode and cathode) into the low temperature one and have ion adsorption. An electric current is then generated in the external circuit to achieve electro neutrality. After saturation, the same electrodes are immersed in the high T volume and then ions desorb from the electrodes and are released to the volume, leading to a reverse electric current in the external circuit compared to the first step. These experiments prove the principle and the direct dependence of the temperature gradient for energy extraction.
Finally, Chapter 7discusses the internal energy losses identified and faced throughout this thesis. We summarize the solutions encountered for the major contributions hindering the CDP performance and give suggestions to further develop the technology.
Selective carboxylate production by controlling hydrogen, carbon dioxide and substrate concentrations in mixed culture fermentation
Arslan, D. ; Steinbusch, K.J.J. ; Diels, L. ; Wever, H. de; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
Bioresource Technology 136 (2013). - ISSN 0960-8524 - p. 452 - 460.
sequencing batch reactor - biohydrogen production - biological production - waste-water - bacteria - glucose - acid - bioconversion - butyrate - caproate
This research demonstrated the selective production of n-butyrate from mixed culture by applying 2 bar carbon dioxide into the headspace of batch fermenters or by increasing the initial substrate concentration. The effect of increasing initial substrate concentration was investigated at 8, 13.5 and 23 g COD/L with potato processing waste stream. Within 1 week of incubation, n-butyrate fraction selectively increased up to 83% by applying 2 bar hydrogen or 78% by applying carbon dioxide into the headspace whereas it was only 59% in the control reactor. Although the fraction of n-butyrate was elevated, the concentration remained lower than in the control. Both the highest concentration and fraction of n-butyrate were observed under the highest initial substrate concentration without headspace addition. The concentration was 10 g COD/L with 73% fraction. The operational conditions obtained from batch experiments for selective n-butyrate production were validated in a continuous process.
Steady-state performance and chemical efficiency of Microbial Electrolysis Cells
Sleutels, T.H.J.A. ; Heijne, A. ter; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2013
International Journal of Hydrogen Energy 38 (2013)18. - ISSN 0360-3199 - p. 7201 - 7208.
fuel-cells - bioelectrochemical systems - waste-water - biocatalyzed electrolysis - exchange membranes - electrical-current - power-generation - ion-transport - cathode - methane
The objective of this paper was to study MEC performance at steady-state conditions in continuous mode and to analyse MEC performance in terms of chemical efficiency. At steady-state operation, a current density of 10.2 A m-2 (applied voltage 1.0 V) for a set-up with an AEM was produced, compared to 7.2 A m-2 for a set-up with a CEM. For all applied voltages, total internal resistance for the AEM configuration was lower than or the CEM configuration. Therefore, energy input for the AEM configuration is lower than for the CEM configuration. In case a CEM is used, the conductivity in the cathode reaches high values: >130 mS cm-1. This conductivity is mainly caused by the presence of Na+ (7.8 g L-1), K+ (12.2 g L-1) and OH- (8.3 g L-1). Furthermore, MECs perform better at high buffer and electrolyte concentrations. However, as current density does not increase proportionally with increase in chemicals, the effectiveness of chemical addition decreases when more chemicals are added. Therefore, addition of chemicals and buffer does not necessarily enhance performance but increases operational costs.
Influence of the thickness of the capacitive layer on the performance of bioanodes in Microbial Fuel Cells
Deeke, A. ; Sleutels, T.H.J.A. ; Heijne, A. ter; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
Journal of Power Sources 243 (2013). - ISSN 0378-7753 - p. 611 - 616.
waste-water treatment - energy-storage - operation - power
Earlier it was shown, that it is possible to operate a Microbial Fuel Cell with an integrated capacitive bio-anode with a thickness of 0.5 mm and thereby to increase the power output. The integrated capacitive bioanode enabled storage of electricity produced by microorganisms directly inside an MFC. To increase the performance of this integrated storage system even more; the thickness of the capacitive electrode was varied: 0.2 mm, 0.5 mm and 1.5 mm. Each of these capacitive electrodes was tested in the MFC setup during polarization curves and charge–discharge experiments for the steady-state current density and the maximum charge recovery. The capacitive electrode with a thickness of 0.2 mm outperformed the other electrodes in all experiments: it reached a maximum current density of 2.53 Am-² during polarization curves, and was able to store a cumulative total charge of 96013 cm-² during charge–discharge experiments. The highest relative charge recovery for this electrode was 1.4, which means that 40% more current can be gained from this capacitive electrode during intermittent operation compared to continuous operation of a noncapacitive electrode. Surprisingly it was possible to increase the performance of the MFC through decrease of the thickness of the capacitive electrode.
Resilience of roof-top Plant-Microbial Fuel Cells during Dutch winter
Helder, M. ; Strik, D.P.B.T.B. ; Timmers, R.A. ; Reas, S.M.T. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
Biomass and Bioenergy 51 (2013). - ISSN 0961-9534 - p. 1 - 7.
time-domain reflectometry - electricity production - temperature - performance - biofilm
The Plant-Microbial Fuel Cell (P-MFC) is in theory a technology that could produce sustainable electricity continuously. We operated two designs of the P-MFC under natural roof-top conditions in the Netherlands for 221 days, including winter, to test its resilience. Current and power densities are not stable under outdoor conditions. Highest obtained power density was 88 mW m-2, which is lower than was achieved under lab-conditions (440 mW m-2). Cathode potential was in our case dependent on solar radiation, due to algae growth, making the power output dependent on a diurnal cycle. The anode potential of the P-MFC is influenced by temperature, leading to a decrease in electricity production during low temperature periods and no electricity production during frost periods. Due to freezing of the roots, plants did not survive winter and therefore did not regrow in spring. In order to make a sustainable, stable and weather independent electricity production system of the P-MFC attention should be paid to improving cathode stability and cold insulation of anode and cathode. Only when power output of the Plant-Microbial Fuel Cell can be increased under outdoor conditions and plant-vitality can be sustained over winter, it can be a promising sustainable electricity technology for the future