Electrochemical removal of phosphate in the presence of calcium at low current density: Precipitation or adsorption?
Lei, Yang ; Geraets, Emilio ; Saakes, Michel ; Weijden, Renata D. van der; Buisman, Cees J.N. - \ 2020
Water Research 169 (2020). - ISSN 0043-1354
Calcium phosphate - Electrochemical - Local pH - Low current - Phosphorus recovery
Phosphorus removal and recovery from waste streams are crucial to prevent eutrophication and sustain fertilizer production. As has been shown in our previous papers, electrochemical treatment has the potential to achieve this goal. However, the adoption of electrochemical approach is limited by its high energy consumption. Here, we investigate the possibility of electrochemical phosphorus removal at extremely low current density using graphite felt as the cathode. We found a current density as low as 0.04 A/m2 can enhance the removal of phosphate in our electrochemical system. The removal of phosphate at extremely low current density resulted from electrochemical induced calcium phosphate precipitation and not by electrochemical adsorption. Electrochemical treatment of real domestic wastewater at 0.2 A/m2 almost eliminates the precipitation of Mg(OH)2 and limits the formation of CaCO3. The recovered precipitates are dominated by calcium phosphate (59%), followed by 35% CaCO3 and 6% Mg(OH)2. The specific energy consumption of this newly electrochemical system is between 4.4 and 26.4 kW h/kg P, which is 2 orders of magnitude lower than our previous system (110–2238 kW h/kg P). Key factors for this improvement prove to be enlarged precipitation area and hydroxide flux retardation by graphite felt. Practically, our study offers a potential way to reduce the energy consumption in electrochemical removal of phosphate by using a graphite felt cathode and at a current density below 0.2 A/m2. Fundamentally, our study contributes to the understanding of adsorption and precipitation in electrochemical removal of phosphate at an extremely low current density and with carbon-based electrodes.
Electrochemically mediated calcium phosphate precipitation from phosphonates: Implications on phosphorus recovery from non-orthophosphate
Lei, Yang ; Saakes, Michel ; Weijden, Renata D. van der; Buisman, Cees J.N. - \ 2020
Water Research 169 (2020). - ISSN 0043-1354
Calcium phosphate - Local high pH - Organic phosphorus - Oxidation - Precipitation
Phosphonates are an important type of phosphorus-containing compounds and have possible eutrophication potential. Therefore, the removal of phosphonates from waste streams is as important as orthophosphate. Herein, we achieved simultaneously removal and recovery of phosphorus from nitrilotris (methylene phosphonic acid) (NTMP) using an electrochemical cell. It was found that the C–N and C–P bonds of NTMP were cleaved at the anode, leading to the formation of orthophosphate and formic acid. Meanwhile, the converted orthophosphate reacted with coexisting calcium ions and precipitated on the cathode as recoverable calcium phosphate solids, due to an electrochemically induced high pH region near the cathode. Electrochemical removal of NTMP (30 mg/L) was more efficient when dosed to effluent of a wastewater treatment plant (89% in 24 h) than dosed to synthetic solutions of 1.0 mM Ca and 50 mM Na2SO4 (43% in 168 h) while applying a current density of 28 A/m2 and using a Pt anode and Ti cathode. The higher removal efficiency of NTMP in real waste water is due to the presence of chloride ions, which resulted in anodic formation of chlorine. This study establishes a one-step approach for simultaneously phosphorus removal and recovery of calcium phosphate from non-orthophosphates.
Electrochemical phosphorus removal and recovery
Lei, Yang - \ 2019
Wageningen University. Promotor(en): C.J.N. Buisman, co-promotor(en): R.D. van der Weijden; M. Saakes. - Wageningen : Wageningen University - ISBN 9789463950473 - 247
Phosphorus removal and recovery from waste streams is essential for closing the loop of phosphorus. In this thesis, we propose an innovative membrane-free electrochemical system, which can potentially achieve the removal and recovery of phosphorus from wastewaters in the form of recoverable calcium phosphate. We studied the fundamentals, efficiency, and energy consumption of electrochemical phosphorus removal and recovery in both synthetic solutions and real wastewaters. We showed electrochemically induced calcium phosphate precipitation depends on the local pH. We demonstrated the feasibility of electrochemical phosphorus recovery for both orthophosphate and no-orthophosphates. We concluded that a low current density and high phosphorus concentration enables energy-efficient phosphorus recovery. To our knowledge, this is the first systematic study focusing on electrochemical phosphorus removal and recovery. The insights we have gained from this thesis present therefore a significant step towards the potential application of this new technique.
Calcium Carbonate Packed Electrochemical Precipitation Column: New Concept of Phosphate Removal and Recovery
Lei, Yang ; Narsing, Santosh ; Saakes, Michel ; Weijden, Renata D. Van Der; Buisman, Cees J.N. - \ 2019
Environmental Science and Technology 53 (2019)18. - ISSN 0013-936X
Phosphorus (P) is a vital micronutrient element for all life forms. Typically, P can be extracted from phosphate rock. Unfortunately, the phosphate rock is a nonrenewable resource with a limited reserve on the earth. High levels of P discharged to water bodies lead to eutrophication. Therefore, P needs to be removed and is preferably recovered as an additional P source. A possible way to achieve this goal is by electrochemically induced phosphate precipitation with coexisting calcium ions. Here, we report a new concept of phosphate removal and recovery, namely a CaCO3 packed electrochemical precipitation column, which achieved improved removal efficiency, shortened hydraulic retention time, and substantially enhanced stability, compared with our previous electrochemical system. The concept is based on the introduction of CaCO3 particles, which facilitates calcium phosphate precipitation by buffering the formed H+ at the anode, releases Ca2+, acts as seeds, and establishes a high pH environment in the bulk solution in addition to that in the vicinity of the cathode. It was found that the applied current, the CaCO3 particle size, and the feed rate affect the removal of phosphate. Under optimized conditions (particle size, <0.5 mm; feed rate, 0.4 L/d; current, 5 mA), in a continuous flow system, the CaCO3 packed electrochemical precipitation column achieved 90 ± 5% removal of phosphate in 40 days and >50% removal over 125 days with little maintenance. The specific energy consumptions of this system lie between 29 and 61 kWh/kg P. The experimental results demonstrate the promising potential of the CaCO3 packed electrochemical precipitation column for P removal and recovery from P-containing streams.
The granular capacitive moving bed reactor for the scale up of bioanodes
Borsje, Casper ; Sleutels, Tom ; Saakes, Michel ; Buisman, Cees J.N. ; Heijne, Annemiek ter - \ 2019
Journal of Chemical Technology and Biotechnology 94 (2019)8. - ISSN 0268-2575 - p. 2738 - 2748.
activated carbon - bioelectrochemical system - capacitive bioanode - gas lift reactor - granular bed - microbial electrochemical technology
BACKGROUND: Scaling up bioelectrochemical systems for the treatment of wastewater faces challenges. Material costs, low conductivity of wastewater and clogging are issues that need a novel approach. The granular capacitive moving bed reactor can potentially solve these challenges. In this reactor, capacitive activated carbon granules are used as bioanode material. The charge storage capabilities of these capacitive granules allow for the physical separation of the charging and the discharging process and therefore a separation of the wastewater treatment and energy recovery process. RESULTS: This study investigates the performance of the granular capacitive moving bed reactor. In this reactor, activated granules were transported from the bottom to the top of the reactor using a gas lift and settled on top of the granular bed, which moved downwards through the internal discharge cell. This moving granular bed was applied to increase the contact time with the discharge anode to increase the current density. The capacitive moving bed reactor (total volume 7.7 L) produced a maximum current of 23 A m−2 normalized to membrane area (257 A m−3granules). Without granules, the current was only 1.4 A m−2membrane. The activity of the biofilm on the granules increased over time, from 436 up to 1259 A m−3granules. A second experiment produced similar areal current density and increase in activity over time. CONCLUSION: Whereas the produced current density is promising for further scaling up of bioanodes, the main challenges are to improve the discharge of the charged granules and growth of biofilm on the granules under shear stress.
Energy Efficient Phosphorus Recovery by Microbial Electrolysis Cell Induced Calcium Phosphate Precipitation
Lei, Yang ; Du, Mengyi ; Kuntke, Philipp ; Saakes, Michel ; Weijden, Renata van der; Buisman, Cees J.N. - \ 2019
ACS sustainable chemistry & engineering 7 (2019)9. - ISSN 2168-0485 - p. 8860 - 8867.
amorphous calcium phosphate - bioelectrochemical - energy consumption - local high pH - phosphate removal
Phosphorus (P) removal and recovery from waste streams is essential for a sustainable world. Here, we updated a previously developed abiotic electrochemical P recovery system to a bioelectrochemical system. The anode was inoculated with electroactive bacteria (electricigens) which are capable of oxidizing soluble organic substrates and releasing electrons. These electrons are then used for the reduction of water at the cathode, resulting in an increase of pH close to the cathode. Hence, phosphate can be removed with coexisting calcium ions as calcium phosphate at the surface of the cathode with a much lower energy input. Depending on the available substrate (sodium acetate) concentration, an average current density from 1.1 ± 0.1 to 6.6 ± 0.4 A/m 2 was achieved. This resulted in a P removal of 20.1 ± 1.5% to 73.9 ± 3.7%, a Ca removal of 10.5 ± 0.6% to 44.3 ± 1.7% and a Mg removal of 2.7 ± 1.9% to 16.3 ± 3.0%. The specific energy consumption and the purity of the solids were limited by the relative low P concentration (0.23 mM) in the domestic wastewater. The relative abundance of calcium phosphate in the recovered product increased from 23% to 66% and the energy consumption for recovery was decreased from 224 ± 7 kWh/kg P to just 56 ± 6 kWh/kg P when treating wastewater with higher P concentration (0.76 mM). An even lower energy demand of 21 ± 2 kWh/kg P was obtained with a platinized cathode. This highlights the promising potential of bioelectrochemical P recovery from P-rich waste streams.
Influence of Cell Configuration and Long-Term Operation on Electrochemical Phosphorus Recovery from Domestic Wastewater
Lei, Yang ; Remmers, Jorrit Christiaan ; Saakes, Michel ; Weijden, Renata D. Van Der; Buisman, Cees J.N. - \ 2019
ACS sustainable chemistry & engineering 7 (2019)7. - ISSN 2168-0485 - p. 7362 - 7368.
Calcium phosphate - Current density - Electrode distance - Energy consumption - Local high pH
Phosphorus (P) is an important, scarce, and irreplaceable element, and therefore its recovery and recycling are essential for the sustainability of the modern world. We previously demonstrated the possibility of P recovery by electrochemically induced calcium phosphate precipitation. In this Article, we further investigated the influence of cell configuration and long-term operation on the removal of P and coremoved calcium (Ca), magnesium (Mg), and inorganic carbon. The results indicated that the relative removal of P was faster than that of Ca, Mg, and inorganic carbon initially, but later, due to decreased P concentration, the removal of Ca and Mg became dominant. A maximum P removal in 4 days is 75% at 1.4 A m -2 , 85% at 8.3 A m -2 and 92% at 27.8 A m -2 . While a higher current density improves the removal of all ions, the relative increased removal of Ca and Mg affects the product quality. While the variation of electrode distance and electrode material have no significant effects on P removal, it has implication for reducing the energy cost. A 16-day continuous-flow test proved calcium phosphate precipitation could continue for 6 days without losing efficiency even when the cathode was covered with precipitates. However, after 6 days, the precipitates need to be collected; otherwise, the removal efficiency dropped for P removal. Economic evaluation indicates that the recovery cost lies in the range of 2.3-201.4 euro/kg P, depending on P concentration in targeted wastewater and electrolysis current. We concluded that a better strategy for producing a product with high P content in an energy-efficient way is to construct the electrochemical cell with cheaper stainless steel cathode, with a shorter electrode distance, and that targets P-rich wastewater.
Fate of calcium, magnesium and inorganic carbon in electrochemical phosphorus recovery from domestic wastewater
Lei, Yang ; Hidayat, Ipan ; Saakes, Michel ; Weijden, Renata van der; Buisman, Cees J.N. - \ 2019
Chemical Engineering Journal 362 (2019). - ISSN 1385-8947 - p. 453 - 459.
Acidification - Amorphous calcium phosphate - Brucite - Calcite - pH - Phosphate recovery
Calcium (Ca), magnesium (Mg), phosphate and (bi)carbonate are removed simultaneously in electrochemical recovery of phosphorus (P) from sewage. However, the fate of these ions is not completely understood yet. In this paper, through wastewater acidification and current density altering, we clarified the precipitation process and electrochemical interaction of phosphate and coexisting ions. The removal of P is attributed to amorphous calcium phosphate (ACP) formation, whereas the removal of bicarbonate is mainly due to calcite (CaCO3) formation and acid-base neutralization. While both ACP and calcite results in Ca removal, Ca predominantly ends up in calcite. For Mg, it is exclusively removed as brucite (Mg(OH)2). Regardless of the acidification, 53 ± 2% P and 32 ± 1% Mg were removed in 24 h at 8.3 A/m2. By contrast, in response to the acidification, the removal of Ca dropped from 42% to 19%. The removal of Mg depends on the current density, with less than 5% removed at 1.4 A/m2 but 70% at 27.8 A/m2 in 24 h. Based on the precipitation mechanisms, the formation of calcite and brucite can be reduced by acidification and operating at a relatively low current density, respectively. Accordingly, we achieved the lowest Ca/P molar ratio (1.8) and the highest relative abundance of ACP in the precipitates (75%) at bulk pH 3.8 with a current density of 1.4 A/m2.
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.
Is There a Precipitation Sequence in Municipal Wastewater Induced by Electrolysis?
Lei, Yang ; Remmers, Jorrit Christiaan ; Saakes, Michel ; Weijden, Renata D. van der; Buisman, Cees J.N. - \ 2018
Environmental Science and Technology 52 (2018)15. - ISSN 0013-936X - p. 8399 - 8407.
Electrochemical wastewater treatment can induce calcium phosphate precipitation on the cathode surface. This provides a simple yet efficient way for extracting phosphorus from municipal wastewater without dosing chemicals. However, the precipitation of amorphous calcium phosphate (ACP) is accompanied by the precipitation of calcite (CaCO3) and brucite (Mg(OH)2). To increase the content of ACP in the products, it is essential to understand the precipitation sequence of ACP, calcite, and brucite in electrochemical wastewater treatment. Given the fact that calcium phosphate (i.e., hydroxyapatite) has the lowest thermodynamic solubility product and highest saturation index in the wastewater, it has the potential to precipitate first. However, this is not observed in electrochemical phosphate recovery from raw wastewater, which is probably because of the very high Ca/P molar ratio (7.5) and high bicarbonate concentration in the wastewater resulting in formation of calcite. In the case of decreased Ca/P molar ratio (1.77) by spiking external phosphate, most of the removed Ca in the wastewater was used for ACP formation instead of calcite. The formation of of brucite, however, was only affected when the current density was decreased or the size of cathode was changed. Overall, the removal of Ca and Mg is much more affected by current density than the surface area of cathode, whereas for P removal, the reverse is true. Because of these dependencies, though there is no definite precipitation sequence among ACP, calcite, and brucite, it is still possible to influence the precipitation degree of these species by relatively low current density and high surface area or by targeting phosphorus-rich wastewaters.
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.
Interaction of calcium, phosphorus and natural organic matter in electrochemical recovery of phosphate
Lei, Yang ; Song, Bingnan ; Saakes, Michel ; Weijden, Renata D. van der; Buisman, Cees J.N. - \ 2018
Water Research 142 (2018). - ISSN 0043-1354 - p. 10 - 17.
Buffer - Calcium phosphate - Co-precipitation - Electrochemical precipitation - Natural organic matter
To address the issues of eutrophication and the potential risk of phosphorus (P) shortage, it is essential to remove and recover P from P-containing streams to close this nutrient cycle. Electrochemical induced calcium phosphate (CaP) precipitation was shown to be an efficient method for P recovery. However, the influence of natural organic matter (NOM) is not known for this treatment. In this paper, the behavior of NOM and its effect on CaP precipitation was studied. In contrast to studies where NOM hindered CaP precipitation, results show that the interaction of NOM with CaP improves the removal of P, independent of the types of NOM. The P removal at the average increased from 43.8 ± 4.9% to 58.5 ± 1.2% in the presence of 1.0 mg L−1 NOM. Based on the yellow color of the CaP product, NOM is co-precipitated. The bulk solution pH with and without buffers has totally different effects on the precipitation process. Without buffer, CaP precipitates on the cathode surface in a wide pH range (pH 4.0–10.0). However, the precipitation process is completely inhibited when the bulk solution is buffered at pH 4.0 and 6.0. This is probably due to neutralization of OH− by the buffers. Regardless of the presence or absence of NOM and solution pH, the recovered products are mainly amorphous CaP unless the electrolysis time was increased to seven days with 4.0 A m−2, in which crystalline CaP formed. These findings advance our understanding on the interaction of Ca, P and NOM species for the application of electrochemical method for P recovery from real wastewater.
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%).
Effects of current density, bicarbonate and humic acid on electrochemical induced calcium phosphate precipitation
Lei, Yang ; Saakes, Michel ; Weijden, Renata D. van der; Buisman, Cees J.N. - \ 2018
Chemical Engineering Journal 342 (2018). - ISSN 1385-8947 - p. 350 - 356.
Bicarbonate - Electrochemical - Humic acid - Phosphate removal - Precipitation
Phosphorus (P) removal and recovery from sewage as calcium phosphate (CaP) by chemical precipitation is a widely used method. To avoid the addition of chemicals to increase the pH of the bulk solution and the need for a further separation step in conventional chemical precipitation process, we developed an electrochemical method, which can locally increase the pH near a Ti cathode. The separation of product and liquid then happens simultaneously by accumulating CaP at the electrode surface. The current density plays a crucial role in this system. A current density of 19 A/m2 results in the formation of crystalline CaP rather than amorphous CaP, but it does not enhance the removal of P in 24 h. Moreover, the current efficiency decreases with increasing current density. Furthermore, the increased H2 production at high current density may push the precipitated CaP back to the bulk solution, resulting in its dissolution. In the presence of bicarbonate (1–5 mM) or humic acid (1–20 mg/L), the removal of P was higher. This is probably due to the inhibited CaP precipitation in the bulk solution which in turn leaves more Ca and P ions available for the local precipitation on the cathode. However, bicarbonate at high concentration (10 mM) dropped P removal from 52 to 25%. This is caused by competition of carbonate and phosphate with the free Ca2+ ions and also by buffering the producted hydroxide ions at the cathode. The study shows that P can be removed as CaP by electrochemical precipitation at low current densities at common concentrations of bicarbonate and humic acid.
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.
Gas diffusion electrodes improve hydrogen gas mass transfer for a hydrogen oxidizing bioanode
Rodenas, Pau ; Zhu, Fangqi ; Heijne, Annemiek ter; Sleutels, Tom ; Saakes, Michel ; Buisman, Cees - \ 2017
Journal of Chemical Technology and Biotechnology 92 (2017)12. - ISSN 0268-2575 - p. 2963 - 2968.
BES - copper - gas diffusion electrode, MET
Background: Bioelectrochemical systems (BESs) are capable of recovery of metals at a cathode through oxidation of organic substrate at an anode. Recently, also hydrogen gas was used as an electron donor for recovery of copper in BESs. Oxidation of hydrogen gas produced a current density of 0.8 A m-2 and combined with Cu2+ reduction at the cathode, produced 0.25 W m-2. The main factor limiting current production was the mass transfer of hydrogen to the biofilm due to the low solubility of hydrogen in the anolyte. Here, the mass transfer of hydrogen gas to the bioanode was improved by use of a gas diffusion electrode (GDE). Results: With the GDE, hydrogen was oxidized to produce a current density of 2.9 A m-2 at an anode potential of –0.2 V. Addition of bicarbonate to the influent led to production of acetate, in addition to current. At a bicarbonate concentration of 50 mmol L-1, current density increased to 10.7 A m-2 at an anode potential of –0.2 V. This increase in current density could be due to oxidation of formed acetate in addition to oxidation of hydrogen, or enhanced growth of hydrogen oxidizing bacteria due to the availability of acetate as carbon source. The effect of mass transfer was further assessed through enhanced mixing and in combination with the addition of bicarbonate (50 mmol L-1) current density increased further to 17.1 A m-2. Conclusion: Hydrogen gas may offer opportunities as electron donor for bioanodes, with acetate as potential intermediate, at locations where excess hydrogen and no organics are available.
Prototype of a scaled-up microbial fuel cell for copper recovery
Rodenas Motos, Pau ; Molina, Gonzalo ; Heijne, Annemiek ter; Sleutels, Tom ; Saakes, M. ; Buisman, Cees - \ 2017
Journal of Chemical Technology and Biotechnology 92 (2017)11. - ISSN 0268-2575 - p. 2817 - 2824.
BES - copper - MET - MFC
Background: Bioelectrochemical systems (BESs) enable recovery of electrical energy through oxidation of a wide range of substrates at an anode and simultaneous recovery of metals at a cathode. Scale-up of BESs from the laboratory to pilot scale is a challenging step in the development of the process, and there are only a few successful experiences to build on. This paper presents a prototype BES for the recovery of copper. Results: The cell design presented here had removable electrodes, similar to those in electroplating baths. The anode and cathode in this design could be replaced independently. The prototype bioelectrochemical cell consisted of an 835 cm2 bioanode fed with acetate, and a 700 cm2 cathode fed with copper. A current density of 1.2 A/−2 was achieved with 48 mW m−2 of power production. The contribution of each component (anode, electrolytes, cathode and membrane) was evaluated through the analysis of the internal resistance distribution. This revealed that major losses occurred at the anode, and that the design with removable electrodes results in higher internal resistance compared with other systems. To further assess the practical applicability of BES for copper recovery, an economic evaluation was performed. Conclusion: Analysis shows that the internal resistance of several lab-scale BESs is already sufficiently low to make the system economic, while the internal resistance for scaled-up systems still needs to be improved considerably to become economically applicable.
Electrochemical Induced Calcium Phosphate Precipitation : Importance of Local pH
Lei, Yang ; Song, Bingnan ; Weijden, Renata D. van der; Saakes, M. ; Buisman, Cees J.N. - \ 2017
Environmental Science and Technology 51 (2017)19. - ISSN 0013-936X - p. 11156 - 11164.
Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.
Ammonia recovery from urine in a scaled-up Microbial Electrolysis Cell
Zamora, Patricia ; Georgieva, Tanya ; Heijne, Annemiek ter; Sleutels, Tom H.J.A. ; Jeremiasse, Adriaan W. ; Saakes, Michel ; Buisman, Cees J.N. ; Kuntke, Philipp - \ 2017
Journal of Power Sources 356 (2017). - ISSN 0378-7753 - p. 491 - 499.
Ammonia recovery - Microbial Electrolysis Cells - Up-scaling bioelectrochemcial systems - Urine treatment
A two-step treatment system for nutrient and energy recovery from urine was successfully operated for six months. In the first step, phosphorus (P) was recovered as struvite (magnesium ammonium phosphate or MAP) in a MAP reactor. The effluent of this MAP reactor was used for total ammonia-nitrogen (TAN) recovery and hydrogen production in a Microbial Electrolysis Cell (MEC). This MEC was coupled to a Transmembranechemisorption (TMCS) module, in which the TAN was recovered as an ammonium sulphate solution. The MEC had a projected surface area of 0.5 m2 and was operated at different urine dilutions. The system was stable during the operation on 2 times diluted and undiluted urine at an applied voltage of 0.5 V with an average current density of 1.7 ± 0.2 A m−2. During stable current production, the TAN transport efficiency over the CEM was 92 ± 25% and the TAN recovery was 31 ± 59%. In terms of energy efficiency, the electrical energy required for the TAN recovery was 4.9 ± 1.0 MJ kgN−1, which is lower than competing electrochemical nitrogen removal/recovery technologies. Overall, this study shows, for the first time, the application of a scaled-up MEC for nutrient recovery from urine.
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).