Advanced control of electric current in BIO-electrochemical systems

Abstract

A bio-electrochemical electrode current control system for improving the performance of bio-electrochemical systems is provided. The system comprises at least a pair of bio- electrochemical electrodes disposed inside a vessel of a bio-electrochemical system. The bio- electrochemical electrodes have a large surface area in contact with an operating fluid disposed in the vessel. An electric power source is operatively connected to each pair of the at least a pair of bio-electrochemical electrodes such that in operation the bio- electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes have a polarity corresponding to one anode and one cathode. A polarity switching circuitry is interposed between the electric power source and each pair of the at least a pair of bio- electrochemical electrodes for simultaneously switching the polarity of the bio- electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes. A processor is operatively connected to the polarity switching circuitry. The processor is adapted for controlling the polarity switch such that the polarity is repeatedly switched after elapse of a preset switching time interval greater than about one second. In operation, the operating fluid is bio-electrochemically processed while the electric current is provided to each pair of the at least a pair of bio-electrochemical electrodes such that the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bio- electrochemical electrodes is repeatedly switched.

Description

[0001] ADVANCED CONTROL OF ELECTRIC CURRENT IN BIO-ELECTROCHEMICAL SYSTEMS

[0002] FIELD

[0003] The present application relates to the field of bio-electrochemical systems, and more particularly to an advanced current control system and method for controlling provision of electric current to bio-electrochemical electrodes employed in bio-electrochemical systems.

[0004] BACKGROUND

[0005] Bio-Electrochemical Systems (BES), such as microbial electrolysis cells (MEC), and microbial electrosynthesis cells (MES) represent a new approach to combining microbial and electrochemical reactions for enhancing bioconversions and extending the range of bioproducts. Advantages of using BES systems in various applications such as, for example, biomethane and biohydrogen production, biodegradation of organic wastes, bio-extraction of metals, and CO2 conversion, are well established. However, most applications are still under development and a suitable control of the electric current, which is a key parameter affecting BES performance, has not yet been determined.

[0006] Current experimental MEC and MES setups are operated either at a constant applied voltage or constant applied current. While one parameter is fixed, the second is allowed to fluctuate and adapt to variations in the setup electrical properties. The constant current mode of operation is used more often than the constant voltage mode of operation for both MEC and MES operation.

[0007] Complex water chemistry, which is typical for many practical applications such as, for example, wastewater treatment, and bio-electrosynthesis, often creates precipitation and deposition of various elements and / or compounds dissolved in the process water on or around the electrodes due to oxidation at the anode and reduction at the cathode. This process results in electrode fouling and can severely affect the BES performance. Most often, either the electrode performance deteriorates over time or the bio-electro transformation rates decline.

[0008] Over time, microbial populations at each electrode of an MEC become highly specialized with anodophilic microorganisms using the anode as a terminal electron acceptor and cathodophilic microorganisms receiving electrons from the cathode. Parasitic cathodic reactions include, but are not limited to, the formation of elemental metals as disclosed in:

[0009] Kim, J.R., J.M. Regan, and B.E. Logan, Analysis of ammonia loss mechanisms in microbial fuel cells treating animal wastewater. Biotechnol. Bioeng., 2007;

[0010] Kuntke, P., et al., Hydrogen production and ammonium recovery from urine by a Microbial Electrolysis Cell. Int. J. Hydrogen Energ, 2014. 39: p. 4771-4778;

[0011] Villano, M., et al., Carbon and nitrogen removal and enhanced methane production in a microbial electrolysis cell. Bioresour. Technol., 2013. 130: p. 366-371;

[0012] Zhan, G., et al., Anodic ammonia oxidation to nitrogen gas catalyzed by mixed biofilms in bioelectrochemical systems. Electrochim. Acta, 2014. 135: p. 345-350;

[0013] Cecconet, D., A. Callegari, and A.G. Capodaglio, Bioelectrochemical Systems for Removal of Selected Metals and Perchlorate from Groundwater: A Review. Energies, 2018. 11: p. 2643; and,

[0014] Luo, H., et al., Heavy metal recovery combined with H2 production from artificial acid mine drainage using the microbial electrolysis cell. J. Hazardous Materials, 2014. 270: p. 153-159, and bio-electrochemical denitrification as disclosed in:

[0015] Clauwaert, P., et al., Biological denitrification in microbial fuel cells. Environ. Sci. Technol., 2007. 41: p. 3354-3360.

[0016] At the anode, side reactions include bio-electrochemical removal of ammonium as disclosed in:

[0017] Kuntke, P., et al., Hydrogen production and ammonium recovery from urine by a Microbial Electrolysis Cell. Int. J. Hydrogen Energ, 2014. 39: p. 4771-4778.

[0018] At both electrodes, polar molecules that don’t directly participate in bio-electrochemical reactions can accumulate. This accumulation typically results in decreased active electrode area, which in turn reduces the overall bio-electrochemical activity. Hydroponic food grown in the Arctic and in small and remote communities is currently limited by a number of factors, among which are availability, cost of water and fertilisers, and disposal of nutrient waste. Extensive plant growth in hydroponic systems and high density of plants leads to the production of root exudates, which are organic carbon compounds such as, for example, simple sugars, organic acids, and amino acids, released throughout the plant growth cycle. These exudates, if allowed to accumulate, inhibit plant growth and yield. As a consequence, commercial hydroponic growers discard or partially replace the hydroponic feed-solution every 2-4 weeks, thus wasting water and fertiliser, which can be costly in areas such as the Arctic, where water is scarce and fertilisers are expensive. Moreover, disposal of nutrient-rich water creates environmental problems.

[0019] Known attempts to reduce removal of essential nutrients when treating hydroponic waters include application of AC current for electro-oxidation of the exudates. Here, AC current is used to reduce oxidation and reduction reactions that lead to the removal of nitrogen and phosphorus as well as essential metal ions from the hydroponic feed solution as disclosed in:

[0020] Talukder, M.R., et al., Electro-degradation of culture solution improves growth, yield and quality of strawberry plants grown in closed hydroponics. Scientia Horticulturae, 2019. 243: p. 243-251.

[0021] However, when AC current is used in an electrochemical process, it is typically aimed at electrochemically oxidizing (destroying) organic compounds. Electrochemical oxidation uses high applied voltage (well above 2V) and, consequently, uses a significantly large amount of energy. Also, the process produces substantial amounts of oxygen and hydrogen due to water electrolysis.

[0022] Biogas production from organic waste material using Anaerobic Digestion (AD) is a well- known commercial technology that is broadly used in the industry. However, existing AD systems typically produce a methane yield that is lower than the theoretical methane yield.

[0023] Typically, the methane yield of an existing AD system is 0.15-0.25 L per g Chemical Oxygen Demand (COD) consumed, which is substantially lower than the theoretical methane yield of 0.35 L / g COD under Standard Temperature and Pressure (STP) conditions. Moreover, existing AD systems experience poor process stability, especially during operation at high organic loads. To avoid reactor failure anaerobic digesters are often operated at significant underloading conditions.

[0024] Enhanced AD processes with bio-electrodes (microbial electrosynthesis) added to the reactor were demonstrated in laboratory tests. However, the long-term stability of such systems can be problematic due to declining electrode performance over time. This declining performance is caused, among other things, by electrochemical reactions leading to accumulation of polar molecules at the electrode surface and formation of insoluble compounds. This accumulation results in decreased active electrode area and reduces the overall bio-electrochemical activity, as well as may limit transport of nutrients and gasses through porous (3 -dimensional) electrodes.

[0025] Several existing publications proposed combining AD with MEC electrodes placed either directly in the AD unit or in an additional reactor connected to the AD unit as disclosed in:

[0026] Colantoni S, Santiago 6, Weiler JR, Knoll MT, Lapp CJ, Gescher J, et al., Comparative study of bioanodes for microbial electrolysis cells operation in anaerobic digester conditions. Journal of Environmental Chemical Engineering, 2024;12:113071;

[0027] Alonso, R.M., et al., Integrating microbial electrochemical technologies with anaerobic digestion to accelerate propionate degradation. Fuel, 2020. 267: p. 117; and,

[0028] Bo, T., et al., A new upgraded biogas production process: Coupling microbial electrolysis cell and anaerobic digestion in single-chamber, barrel-shape stainless steel reactor. Electrochem. Communications, 2014. 45: p. 67-70.

[0029] There is a lack of long-term demonstration of such system performance, including operation on real waste material. However, at least partial removal of phosphorus, accompanied by struvite formation, is expected at the cathode as disclosed in:

[0030] Cusick, R.D. and B.E. Logan, Phosphate recovery as struvite within a single chamber microbial electrolysis cell. Biores. Technol., 2012. 107: p. 110-115.

[0031] Also, bio-electrochemical removal of ammonium at the anode has been demonstrated as disclosed in:

[0032] Kim, J.R., J.M. Regan, and B.E. Logan, Analysis of ammonia loss mechanisms in microbial fuel cells treating animal wastewater. Biotechnol. Bioeng., 2007; Kuntke, P., et al., Hydrogen production and ammonium recovery from urine by a Microbial Electrolysis Cell. Int. J. Hydrogen Energ, 2014. 39: p. 4771-4778;

[0033] Villano, M., et al., Carbon and nitrogen removal and enhanced methane production in a microbial electrolysis cell. Bioresour. Technol., 2013. 130: p. 366-371; and, Zhan, G., et al., Anodic ammonia oxidation to nitrogen gas catalyzed by mixed biofilms in bioelectrochemical systems. Electrochim. Acta, 2014. 135: p. 345-350.

[0034] Furthermore, various electrochemical reactions result in solids formation on the surface of both electrodes. Such a layer of inert materials significantly decreases the efficiency of the electrodes. While nitrogen and phosphorous removal can be advantageous, the reduced electrode surface results in decreased efficiency and requires electrode replacement.

[0035] There is a need for improving the performance of bio-electrochemical systems. For example, there is a need in hydroponic systems for removing root exudates from the hydroponic feed solution while retaining the beneficial nutrients therein. There is also a need in AD systems for improving process stability, increasing methane yield, and reducing electrode fouling.

[0036] This background information is provided for making information believed by the applicant to be of possible relevance to the present application. No admission is necessarily intended, nor should be constmed, that any of the preceding information constitutes prior art against the subject matter presented herein.

[0037] SUMMARY

[0038] An aspect of the present application is to provide an advanced control system and method for controlling provision of electric current to bio-electrochemical electrodes employed in bioelectrochemical systems.

[0039] In a first example implementation, the advanced control system and method for controlling provision of electric current to bio-electrochemical electrodes has been applied in hydroponic systems such that root exudates are removed from the hydroponic feed solution, while the beneficial nutrients remain retained therein.

[0040] In a second example implementation, the advanced control system and method for controlling provision of electric current to bio-electrochemical electrodes has been applied in anaerobic digester systems such that process stability is improved, methane yield is increased, and electrode fouling is reduced.

[0041] In accordance with one aspect, the present application provides a bio-electrochemical electrode current control system for improving the performance of bio-electrochemical systems. The system comprises at least a pair of bio-electrochemical electrodes disposed inside a vessel of a bio-electrochemical system. The bio-electrochemical electrodes have a large surface area in contact with an operating fluid disposed in the vessel. An electric power source is operatively connected to each pair of the at least a pair of bioelectrochemical electrodes such that in operation the bio-electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes have a polarity corresponding to one anode and one cathode. A polarity switching circuitry is interposed between the electric power source and each pair of the at least a pair of bio-electrochemical electrodes for simultaneously switching the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes. A processor is operatively connected to the polarity switching circuitry. The processor is adapted for controlling the polarity switch such that the polarity is repeatedly switched after elapse of a preset switching time interval greater than about one second. In operation, the operating fluid is bio-electrochemically processed while the electric current is provided to each pair of the at least a pair of bioelectrochemical electrodes such that the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes is repeatedly switched.

[0042] In accordance with the aspect, the present application further provides a bio-electrochemical electrode current control method. At least a pair of bio-electrochemical electrodes is placed into an operating fluid of a bio-electrochemical system. Electric current is provided to each pair of the at least a pair of bio-electrochemical electrodes such that in operation the bioelectrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes have a polarity corresponding to one anode and one cathode. The provision of the electric current is switched such that the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes is simultaneously switched. The polarity is repeatedly switched after elapse of a preset switching time interval greater than about one second. The operating fluid is bio-electrochemically processed while the electric current is provided to each pair of the at least a pair of bio-electrochemical electrodes such that the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bioelectrochemical electrodes is repeatedly switched.

[0043] Optionally, a potentiostat power supply with a reference electrode may be employed to serve as a control to maintain the constant voltage application.

[0044] The bio-electrochemical electrode current control system and method described herein have been applied and tested in a hydroponic system and an anaerobic digester system. The test results for the hydroponic system have revealed that employment of the present current control system and method provides a yield without changing the hydroponic feed-solution for 60 days that is comparable or even higher than the yield of a conventional hydroponic system with a complete change of the hydroponic feed-solution every 14 days. Test results for the anaerobic digester system have revealed a methane yield increased by at least about 25-30% and improved reactor stability at high organic loads.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Drawings of embodiments are provided herewith and briefly described as follows:

[0047] Figures 1 and 2 are schematic diagrams of a first example implementation of the bioelectrochemical electrode current control system in two types of hydroponic systems described herein;

[0048] Figure 3 is schematic diagram of a second example implementation of the bioelectrochemical electrode current control system in an anaerobic digester system described herein;

[0049] Figures 4 and 5 are schematic diagrams of a polarity switching circuitry of the current control system illustrated in Figures 1 to 3 in two modes of operation;

[0050] Figures 6 and 7 illustrate a voltage and a current diagram, respectively, for a constant voltage mode of operation of the current source of the current control system illustrated in Figures 1 to 3; and,

[0051] Figures 8 and 9 illustrate a current and a voltage diagram, respectively, for a constant current mode of operation of the current source of the current control system illustrated in Figures 1 to 3.

[0052] DETAILED DESCRIPTION

[0053] Disclosed herein is a bio-electrochemical electrode current control system for improving the performance of bio-electrochemical systems. The system comprises at least a pair of bioelectrochemical electrodes disposed inside a vessel of a bio-electrochemical system. The bio-electrochemical electrodes have a large surface area in contact with an operating fluid disposed in the vessel. An electric power source is operatively connected to each pair of the at least a pair of bio-electrochemical electrodes such that in operation the bioelectrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes have a polarity corresponding to one anode and one cathode. A polarity switching circuitry is interposed between the electric power source and each pair of the at least a pair of bioelectrochemical electrodes for simultaneously switching the polarity of the bioelectrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes. A processor is operatively connected to the polarity switching circuitry. The processor is adapted for controlling the polarity switch such that the polarity is repeatedly switched after elapse of a preset switching time interval greater than about one second. In operation, the operating fluid is bio-electrochemically processed while the electric current is provided to each pair of the at least a pair of bio-electrochemical electrodes such that the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bioelectrochemical electrodes is repeatedly switched.

[0054] Optionally, a potentiostat power supply with a reference electrode may be employed to serve as a control to maintain the constant voltage application.

[0055] Figures 1 and 2 illustrate a first example implementation of the bio-electrochemical electrode current control system in two types of hydroponic systems.

[0056] Figure 3 illustrates a second example implementation of the bio-electrochemical electrode current control system in an anaerobic digester system.

[0057] Figures 4 and 5 illustrate polarity switching circuitry in two modes of operation.

[0058] Figures 6 and 7 illustrate a voltage and a current diagram, respectively, for a constant voltage mode of operation of the current source. Figures 8 and 9 illustrate a current and a voltage diagram, respectively, for a constant current mode of operation of the current source.

[0059] The basic concept of the bio-electrochemical electrode current control system and method is to control the current of a MEC, a MES, and other similar BESs, using Low Frequency Alternating Current (LF-AC). Applicant has found that provision of LF-AC can significantly alter both microbial populations and bio-electrochemical transformation pathways. The provision of LF-AC current can support electroactive populations capable of acting as electron donors and electron acceptors. This duality can result in a more robust electroactive microbial biofilm. Furthermore, the provision of LF-AC can reduce certain bio-electrochemical reactions such as, for example, reduction of nitrates, nitrites, phosphates and metal ions at the cathode and oxidation of ammonium at the anode. At the same time, since oxidation of organic molecules such as, for example, organic wastes, is an irreversible bioreaction leading to CO2 formation, this bioreaction occurs at both electrodes, at least during the time period when each electrode operates as an anode. This enables the adaptation of the provision of LF-AC for treating a hydroponic feed-solution such that the toxic root exudates are removed through electrochemical oxidation while the nutrients remain retained therein.

[0060] Furthermore, the provision of LFAC also can reduce the formation of elemental metals and insoluble metal salts that accumulate at the cathode surface and decrease the active electrode surface area over time leading to reduced electroactivity. This characteristic in concert with the above characteristics enables the application of LF-AC in anaerobic digester systems where the provision of the LF-AC can be adapted for improving process stability, increasing methane yield, reducing electrode fouling, and reducing electric power consumption.

[0061] In a first example implementation the advanced control system and method for controlling provision of electric current as LF-AC to bio-electrochemical electrodes has been applied in hydroponic systems such that root exudates are removed from the hydroponic feed solution, while the beneficial nutrients remain retained therein which can be implemented in thin film hydroponic systems, as shown in Figure 1, or in deep-water hydroponic systems, as shown in Figure 2. The thin film hydroponic system typically comprises a growing vessel 10 having disposed therein a hydroponic feed-solution 12 comprising water having dissolved therein elements (nutrients) that are beneficial for growing hydroponic plants 14 disposed in the growing vessel 10 such that at least a portion of their roots are in contact with the hydroponic feed-solution 12. A bio-electrochemical processing vessel 16 is operatively connected to the growing vessel 10, for example, via a pipe connected to first port 16A. Second port 16B is connected to the growing vessel 10 via a recirculation pipe and pump 18, thus forming a closed circuit for circulating the hydroponic feed-solution 12 from the growing vessel 10 to the bio-electrochemical processing vessel 16 and back to the growing vessel 10 after bio-electrochemical processing of the same for removing the root exudates. The hydroponic feed-solution 12 may be circulated continuously or in predetermined time intervals.

[0062] At least a pair of bio-electrochemical electrodes 20 having a separator 22 sandwiched therebetween are disposed inside the bio-electrochemical processing vessel 16 for bio- electrochemically processing the hydroponic feed-solution 12. The bio-electrochemical electrodes 20 have a large surface area in contact with the hydroponic feed-solution 12 and are provided, for example, as MECs or MESs. The electric current is provided to the bioelectrochemical electrodes 20 as LF-AC using bio-electrochemical electrode current control system 100 which will be described hereinbelow. The LF-AC may be provided continuously or in predetermined intervals, for example, in predetermined intervals coinciding with the predetermined intervals for circulating the hydroponic feed-solution 12.

[0063] Alternatively, in the deep-water hydroponic system the bio-electrochemical electrodes 20 having a separator 22 sandwiched therebetween are disposed in the bottom of the growing vessel 10, as shown in Figure 2. Again, the electric current is provided to the bioelectrochemical electrodes 20 as EF-AC using the bio-electrochemical electrode current control system 100 which will be described hereinbelow. The EF-AC may be provided continuously or in predetermined intervals.

[0064] In a second example implementation the advanced control system and method for controlling provision of electric current as EF-AC to bio-electrochemical electrodes has been applied in anaerobic digester systems such that process stability is improved, methane yield is increased, and electrode fouling is reduced. An anaerobic digester system comprises anaerobic digester 30 operated, for example, in an upflow configuration, as shown in Figure 3. Eiquid organic waste 31 is provided to the anaerobic digester 30 via input port 32 disposed at the bottom thereof. Biogas, mainly comprising methane (CH4) and carbon dioxide (CO2), is removed from the anaerobic digester 30 via port 40 disposed at the top thereof. The anaerobic digester 30 may further comprise sample port 34 and effluent port 36. A recirculating port 38 may be operatively connected to the input port 32 via pump 39 for recirculating the liquid organic waste 31.

[0065] At least a pair of bio-electrochemical electrodes 20 are disposed one above the other inside a mid-section of the anaerobic digester 30, as shown in Figure 3. The bio-electrochemical electrodes 20 have a large surface area in contact with the liquid organic waste 31 and are provided, for example, as MECs or MESs. The electric current is provided to the bioelectrochemical electrodes 20 as LF-AC using the bio-electrochemical electrode current control system 100 which will be described hereinbelow. The LF-AC may be provided continuously or in predetermined intervals.

[0066] It is noted that the advanced control system and method for controlling provision of electric current as LF-AC to bio-electrochemical electrodes may also be applied in anaerobic digester systems with the anaerobic digester being provided in a horizontal flow configuration with a series of compartments constituting three-dimensional electrodes.

[0067] The bio-electrochemical electrode current control system 100 comprises an electric power source 102 which is operatively connected to each pair of the at least a pair of bioelectrochemical electrodes 20 such that in operation the bio-electrochemical electrodes 20 of each pair of the at least a pair of bio-electrochemical electrodes 20 have a polarity corresponding to one anode and one cathode. Polarity switching circuitry 104 such as, for example, a Double Pole Double Throw (DPDT) switch is interposed between the electric power source 102 and each pair of the at least a pair of bio-electrochemical electrodes 20 for simultaneously switching the polarity of the bio-electrochemical electrodes 20 of each pair of the at least a pair of bio-electrochemical electrodes 20, as shown in Figures 4 and 5. Processor 108 is operatively connected to the polarity switching circuitry 104 and is adapted for controlling the polarity switching circuitry such that the polarity is repeatedly switched after elapse of a preset switching time interval Ts greater than about one second. While the hydroponic feed-solution 12 or the liquid organic waste 31 is bio-electrochemically processed the electric current is provided to each pair of the at least a pair of bioelectrochemical electrodes 20 such that the polarity of the bio-electrochemical electrodes 20 of each pair of the at least a pair of bio-electrochemical electrodes 20 is repeatedly switched. The electric current may be provided from a direct current source 102 in a constant voltage mode of operation such that during switching the electric current is provided as successive pulses. The resulting voltage and current at the bio-electrochemical electrodes 20 are shown in Figures 6 and 7, respectively. The instant polarity switching results in a significant surge of current due to capacitive properties of the electrode materials. Also, biofilm formation on the cathode surface is expected to increase electrode capacitance. To reduce or avoid spikes due to in-rush current, the provision of the electric current may be interrupted for a preset delay time interval TD between adjacent pulses allowing for charge dissipation and resulting in smaller peaks at the beginning of each pulse, as shown in Figure 7. Electroactive microorganisms can take advantage of this charge and continue oxidative (at the anode) and reductive (at the cathode) reactions. The dashed lines in Figure 6 show the voltage at the bio-electrochemical electrodes 20 when disconnected from the current source 102.

[0068] Optionally, the polarity switching circuitry may be adapted such that the current is gradually increased to a maximum value instead of an instant jump.

[0069] Alternatively, the electric current may be provided from a direct current source 102 in a constant current mode of operation such that during switching the electric current is provided as successive pulses. The resulting current and voltage at the bio-electrochemical electrodes 20 are shown in Figures 8 and 9, respectively. Since the current is kept constant, spikes due to in-rush current do not occur in the constant current mode of operation. However, the provision of the electric current may still be interrupted for a preset delay time interval TD between adjacent pulses in order to optimize the electric power consumption.

[0070] Optimal parameters for the switching time interval Ts, the delay time interval TD, the voltage, and the current can be determined empirically based on, for example, maximizing the COD removal in hydroponic systems, maximizing the methane yield in anaerobic digester systems, or optimizing the electric power consumption.

[0071] The optimal parameters may be preprogrammed in processor 108 with the same being provided, for example, as a Field Programmable Gate Array (FPGA).

[0072] Alternatively, the system 100 may comprise a computer 106 having the processor 108 disposed therein. The computer comprises a polarity switching software component comprising processor instructions for controlling the polarity switching circuitry 104 in dependence upon user input data received from a human interface device 110 such as, for example, a touch screen or a monitor with keyboard, operatively connected to the processor 108. Employment of a computer 106 enables a user to change the parameters, for example, to adjust system performance.

[0073] Further alternatively, the system 100 may comprise at least a sensor 112 operatively connected to the processor. The at least a sensor 112 is adapted for sensing information indicative of a status of operation of the bio-electrochemical system and for providing system status data in dependence thereupon. The polarity switching software component comprises processor instructions for controlling the polarity switching circuitry 104 in dependence upon the system status data. For example, the electric power provided to the bio-electrochemical electrodes 20 of a hydroponic system may be sensed and the parameters for the switching time interval Ts and the delay time interval TD may be determined such that electric power consumption is optimized. In another example, the biogas mass flow and the methane concentration of the biogas produced in an anaerobic digester system may be sensed and the parameters for the switching time interval Ts and the delay time interval TD may be determined such that the methane yield is maximized.

[0074] To provide a large surface area in contact with the hydroponic feed-solution 12 or the liquid organic waste 31, the bio-electrochemical electrodes 20 may be made, for example, of: a porous material; as a three-dimensional lattice structure; as a series of two-dimensional lattice structures; as a series of sheets; or, as cylinders. Materials such as, for example, carbon felt, carbon paper, carbon fibers, granular carbon, conductive polymers (Poly Active Acid (PEA) or PolyPropylene (PP) with added carbon black powder) may be used.

[0075] The separator 22 is made of a suitable material, such as a dielectric material. In some embodiments, the separator 22 may be, for example, a geotextile or a proton exchange membrane.

[0076] The switching time interval Ts may be varied between about 1 second and about 24 hours, typically between about 15 seconds and about 30 minutes.

[0077] In MECs the applied voltage is below the onset of water electrolysis (theoretically around 1.23V, practically above 1.5V), hence release of O2 is avoided and the anode is a bioanode, it receives electrons from biodegradable organics. In microbial electrosynthesis the applied voltage is above the water electrolysis threshold (theoretically around 1.23 V, practically 1.5- 17V,). Use of MES cells may be feasible if a small amount of oxygen or oxygen radicals is required.

[0078] The controlled provision of electric current as LF-AC to bio-electrochemical electrodes has been applied in a hydroponic system and tested for lettuce cultivation as follows:

[0079] Negative control (no hydroponic feed-solution change for 60 days);

[0080] Positive control (complete hydroponic feed-solution change every 14 days); and, Hydroponic system with LF-AC implementation (no hydroponic feed-solution change for 60 days).

[0081] Results summary:

[0082] Using the hydroponics system with UF-AC implementation the production of leaves (dry weight) increased by 15-30% and roots (also dry weight) increased by 38-48% vs Negative control, which is comparable with to the production of the Positive control.

[0083] Therefore, the consumption of nutrients and wastewater disposal is substantially reduced, as the hydroponic feed-solution 12 has never been discarded.

[0084] The controlled provision of electric current as EF-AC to bio-electrochemical electrodes has also been applied in an anaerobic digester system and tested for biogas production from food waste. Here, the methane yield increased by 25-30% and reactor stability improved at high organic loads.

[0085] Since numerous bio-electrochemical systems such as, for example, wastewater treatment systems, hydrocarbon removal systems, and carbon dioxide conversion systems, are based on bio-electrochemical processes that are similar to the bio-electrochemical processes of the hydroponic system and the anaerobic digester system as described hereinabove, a sound prediction can be made that the controlled provision of electric current as EF-AC to bioelectrochemical electrodes can also be beneficial for numerous other bio-electrochemical systems. The above disclosure and figures are intended to be illustrative and not exhaustive. The description will suggest many variations and alternatives to one of ordinary skill in the art. Those familiar with the art may recognize other equivalents to the specific embodiments described herein within, without departing from the scope thereof.

Claims

What is claimed is:

1. A bio-electrochemical electrode current control system comprising: at least a pair of bio-electrochemical electrodes disposed inside a vessel of a bioelectrochemical system, the bio-electrochemical electrodes having a large surface area in contact with an operating fluid disposed in the vessel; an electric power source operatively connected to each pair of the at least a pair of bio-electrochemical electrodes such that in operation the bio-electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes have a polarity corresponding to one anode and one cathode; a polarity switching circuitry interposed between the electric power source and each pair of the at least a pair of bio-electrochemical electrodes for simultaneously switching the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bioelectrochemical electrodes; and, a processor operatively connected to the polarity switching circuitry, the processor being adapted for controlling the polarity switching circuitry such that the polarity is repeatedly switched after elapse of a preset switching time interval greater than about one second.

2. The system of claim 1 wherein the electric power source is a direct current source adapted for constant voltage or constant current operation.

3. The system of claim 1 wherein the bio-electrochemical electrodes are microbial electrolysis cell electrodes or microbial electrosynthesis cell electrodes.

4. The system of claim 3 wherein the bio-electrochemical electrodes are made: of a porous material; as a three-dimensional lattice structure; as a series of two-dimensional lattice structures; as a series of sheets; or as cylinders.

5. The system of claim 1 wherein the polarity switching circuitry is a double pole double throw switch.

6. The system of claim 1 comprising a computer having the processor disposed therein, wherein the computer comprises a polarity switching software component comprising processor instructions for controlling the polarity switching circuitry in dependence uponuser input data received from a human interface device operatively connected to the processor.

7. The system of claim 6 comprising at least a sensor operatively connected to the processor, the at least a sensor being adapted for sensing information indicative of a status of operation of the bio-electrochemical system and for providing system status data in dependence thereupon, and wherein the polarity switching software component comprises processor instructions for controlling the polarity switching circuitry in dependence upon the system status data.

8. The system of claim 1 wherein the bio-electrochemical system is one of: a hydroponic system; an anaerobic digestor system; a wastewater treatment system; a hydrocarbon removal system; and, a carbon dioxide conversion system.

9. A bio-electrochemical electrode current control method comprising: placing at least a pair of bio-electrochemical electrodes into an operating fluid of a bio-electrochemical system; providing electric current to each pair of the at least a pair of bio-electrochemical electrodes such that in operation the bio-electrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes have a polarity corresponding to one anode and one cathode; switching the provision of the electric current such that the polarity of the bioelectrochemical electrodes of each pair of the at least a pair of bio-electrochemical electrodes is simultaneously switched, wherein the polarity is repeatedly switched after elapse of a preset switching time interval greater than about one second; and, bio-electrochemically processing the operating fluid while the electric current is provided to each pair of the at least a pair of bio-electrochemical electrodes such that the polarity of the bio-electrochemical electrodes of each pair of the at least a pair of bioelectrochemical electrodes is repeatedly switched.

10. The method of claim 9 wherein the electric current is provided from a direct currentsource in a constant voltage or constant current mode of operation.

11. The method of claim 9 wherein during switching the electric current is provided as successive pulses.

12. The method of claim 11 wherein between adjacent pulses the provision of the electric current is interrupted for a preset delay time interval.

13. The method of claim 9 wherein the switching of the provision of the electric current is controlled using a processor operatively connected to a polarity switching circuitry.

14. The method of claim 13 comprising: providing a computer having the processor disposed therein; receiving user input data from a human interface device operatively connected to the processor; and, executing a polarity switching software component for controlling the polarity switching circuitry in dependence upon the user input data.

15. The method of claim 14 comprising: providing at least a sensor operatively connected to the processor; using the at least a sensor sensing information indicative of a status of operation of the bioelectrochemical system and providing system status data in dependence thereupon; and, executing the polarity switching software component for controlling the polarity switching circuitry in dependence upon the system status data.

16. The method of claim 9 wherein the bio-electrochemical electrodes are placed into an operating fluid of one of: a hydroponic system; an anaerobic digestor system; a wastewater treatment system; a hydrocarbon removal system; and, a carbon dioxide conversion system.

17. The method of claim 9 wherein the bio-electrochemical system is a hydroponicsystem and the operating fluid is a hydroponic feed solution, and wherein the hydroponic feed solution is bio-electrochemically processed for removing the organic root exudates by electrochemically oxidizing the same.

18. The method of claim 17 wherein the preset switching time interval is determined such that removal of the organic root exudates is maximized while the hydroponic plant nutrients remain retained in the hydroponic feed solution.

19. The method of claim 17 comprising: sensing the electric current provided to the bio-electrochemical electrodes; and, determining the preset switching time interval such that electric power consumption is optimized.

20. The method of claim 9 wherein the bio-electrochemical system is an anaerobic digester system and the operating fluid is organic waste, and wherein the organic waste is anaerobically digested for producing methane.

21. The method of claim 20 comprising : sensing a biogas mass flow; sensing a methane concentration of the biogas; and, determining the preset switching time interval such that the methane production is maximized.

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