The invention relates to a bio-electrochemical system (BES) for recovery of components and/or generating electrical energy from a waste stream. Such component may relate to ammonia (NH ₃ ) and/or ammonium (NH ₄ ⁺ ) such that the system provides for ammonia and/or ammonium recovery. Waste stream may involve municipal waste water and industrial waste water, for example.

Conventional systems for recovering components involve the use of so-called strippers, for example for recovery of ammonia gas and/or ammonium solution. Such process is energy intensive and, furthermore, requires large amounts of chemicals.

WO 2013/105854 discloses a method for ammonia gas and/or ammonium solution recovery from an ammonium comprising fluid and bio-electrochemical system capable of performing such method. The method involves providing an anode compartment with an anode and a cathode compartment with a cathode, with both compartments being separated by an ion- exchange membrane, and extracting ammonia gas from the cathode compartment. This method enables ammonium-nitrogen (NH ₃ and NH ₄ ⁺ ) recovery from an ammonium comprising fluid.

An objective of the present invention is to provide a bio-electrochemical system for recovery of components from a waste stream that is more effective and more energy efficient as compared to conventional methods.

This object is achieved with the bio-electrochemical system (BES) for recovery of components or generating electrical energy from a waste stream according to the invention, the system comprising a reactor that comprises:

an anode compartment with an anode;

- a cathode compartment with a cathode, wherein at least one of the anode and cathode is a bio-electrode;

a circuit connecting the anode and the cathode, the circuit comprising a power source for providing an electric current or a resistor;

an ion-exchange membrane separating the anode and cathode compartments; and - a flow channel defining hydrophobic membrane configured for gas extraction and/or reactant supply.

In the case of component recovery, for example ammonia and/or ammonium recovery, involving the system according to the present invention, the term "ammonium" will be understood as NH ₄ ⁺ ions, and "ammonia" will be understood as NH ₃ (for example in the gas phase (g) or in solution (aq)). The term "nitrogen recovery" will be understood as the recovery of a nitrogen comprising compound, such as ammonium and/or ammonia (NH ₃ ) and/or nitrogen (N ₂ ). Waste streams may involve municipal waste waters and industrial waste waters, for example. This may involve ammonia and/or ammonium rich waste water streams such as the effluent of an anaerobic digester, urine treatment etc. Industrial waste waters may relate to waste waters from food processing, paper industry, and agriculture. It will be understood that also other waste water streams, preferably with a substantial amount of a component, such as ammonia and/or ammonium, can be treated in the bio-electrochemical system according to the present invention.

The at least one ion exchange membrane separating the anode and cathode compartments is preferably one or more of the following: a cation exchange membrane (CEM), an anion exchange membrane (AEM), a bipolar exchange membrane (BEM) or a charge mosaic membrane (CMM). In one of the presently preferred embodiments according to the invention, the membrane separating the anode compartment from the cathode compartment comprises a CEM, since transfer of NH ₄ ⁺ from the anode compartment is most efficient using a CEM.

In use, some of the cations are transported from the anode to the cathode, for example protons (H ⁺ ). For example, protons are produced in the anode compartment due to an oxidation reaction and pass through the membrane to the cathode compartment. Transport of cations other than H ⁺ and NH ₄ ⁺ will lead to an increase in the pH of the liquid in the cathode compartment, which will influence the equilibrium between ammonium and ammonia (NH ₄ ⁺ + OH <— > NH ₃ + H ₂ 0) resulting in a higher ammonia concentration once the pH is higher than the pKa of ammonia (pKa = 9.25).

The use of a flow channel defining hydrophobic membrane enables gas extraction from the compartment and/or reactant supply. It is shown that this significantly improves the overall efficiency of the reactions that take place in the bio-electrochemical system according to the present invention. Therefore, the efficiency of such system is improved due to the use of the one or more flow channel defining hydrophobic membranes.

More specifically, in the described embodiment of the present invention ammonium can be recovered by over the hydrophobic membrane as ammonia gas, involving the reaction NH ₄ ⁺ + OH — > NH ₃ + H ₂ 0. Additionally, the reason why there is a high pH in the cathode liquid is that the reduction process occurs under neutral to alkaline conditions and there is insufficient H ⁺ or NH ₄ ⁺ transport through the ion exchange membrane to compensate/buffer the production OH from the oxygen reduction reaction (MFC) or hydrogen evolution reaction (MEC). Oxygen reduction reaction (ORR) at neutral or alkaline conditions at the cathode involves 0 ₂ + 2H ₂ 0 + 4e— > 40H , and hydrogen evolution reaction (HER) at neutral or alkaline conditions at the cathode involves 2H ₂ 0 + 2e— > H ₂ + 20H . Dependent of the type of membrane different ions are being transported through the anion exchange membrane (AEM), mostly OH from cathode to bonus compartment or anode compartment increasing the pH in the liquid. The cathode pH is also high at this point. CEM - cations, mostly NH ₄ ⁺ and other metal ions (Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ ) that may lead to a pH increase in the bonus or cathode compartment. Once there is an equilibrium between the concentration of ions in anode compartment liquid and cathode compartment liquid the charge transport through the cation exchange membrane (CEM) will substantially/exclusively involve NH ₄ ⁺ and H ⁺ as NH ₄ ⁺ + OH— > NH ₃ + H ₂ 0, and ammonia is removed by the TMCS (hydrophobic membrane) and H ⁺ + OH— > H ₂ 0. At this point the pH of the cathode should be stable and be defined by the buffer capacity and the most dominate species in the cathode, which should be ammonium/ammonia (pKa = 9.25) which leads to a pH around 9.25. This illustrates an operation with the system according to the present invention.

In the system according to the invention the hydrophobic membrane can be placed at different positions in the system. The hydrophobic membrane can be placed in the cathode compartment with a cation exchanging membrane separating the anode compartment from the cathode compartment. In addition, or alternatively, the hydrophobic membrane can be positioned in the anode compartment with an anion exchange membrane separating the anode compartment and the cathode compartment. Furthermore, in addition or alternatively, the hydrophobic membrane can be positioned in another (intermediate) compartment. It will be understood that this specific design can be optimized in relation to relevant parameters including the type of waste water and the specific components and concentrations therein. Preferably, the hydrophobic membrane enables transmembrane chemisorption (TMCS).

In the presently preferred embodiment the hydrophobic membrane is provided as a number of tubular elements from a hydrophobic membrane material. Preferably, the tubular elements are shaped as hollow fiber flow channels, tubular members or straw like channels. The tubular elements can optionally be bundled. It will be understood that other designs for the hydrophobic membrane can also be envisaged in accordance with the present invention.

The bio-electrode is an electrode that is provided with micro-organisms, such as (electro- active) bacteria or electrogens. Often, the bio-electrode comprises a biofilm on the electrode. The micro-organisms catalyze the reactions at the anode and/or cathode, thereby improving the energy efficiency. The micro-organisms brake down "complex" organic compounds. Such organic compounds may comprise acetate or other fatty acids, creatinine, organic acids, creatine or sugars, for example.

The bio-electrochemical system according to the present invention is different from conventional microbial electrolysis cells (MECs) and conventional microbial fuel cells (MFCs).

The system according to the invention is capable of recovering components as was already described. For this purpose the system differs from conventional MECs, for example. In conventional MECs a voltage is applied for electrolysis of water to produce H ₂ . Usually the anode is provided as a bio-electrode to oxidize organic compounds for electron production. The electrons are used to reduce protons (H ⁺ ions) or water (H ₂ 0) at the cathode to hydrogen gas (H ₂ ). The goal of MECs is to produce a product at the cathode, in most cases hydrogen. In contrast, the system and method according to the invention is aimed at ammonia and/or ammonium recovery, for example in the form of ammonium sulphate, ammonium nitrate, ammonium phosphate, or ammonium chloride solution. For example, the recovery of ammonia and/or ammonium from a wastewater occurs in a final step, wherein the volatile ammonia is transported over the

hydrophobic membrane and absorbed, in an absorption process, in an acid solution such as sulphuric, nitric, phosphoric and/or hydrochloric acid. Dependent on the used acid solution in the absorption process this results in a solution of ammonium -sulphate, -nitrate, -phosphate, -chloride.

The system according to the invention can be used in a configuration in which it is capable of generating electrical energy. In conventional MFCs the organic compounds are consumed by the bacteria to produce (bio-anode) electrons and/or consume (bio-cathode) electrons to produce a current. This requires providing oxygen to the cathode compartment. In the system according to the invention the oxygen can be supplied with the use of a flow channel defining hydrophobic membrane. This provides an effective and efficient way to supply oxygen to the cathode and generate electrical energy.

In a further preferred embodiment the system is used for both component recovery and generating electrical energy. Oxygen is supplied to the cathode compartment by an oxygen inlet and/or a hydrophobic membrane, thereby enabling the system to operate in an MFC configuration. The reaction components can be used for the recovery involving a flow channel defining hydrophobic membrane. Optionally, a hydrophobic membrane is used both for oxygen supply and component recovery.

The aforementioned applications of the system and method according to the invention will be described in more detail in relation to some specific embodiments that are illustrated in the drawings.

In use, in nitrogen recovery, at the anode of the bio-electrochemical system according to the present invention organic matter is oxidized, preferably resulting in the production of H ⁺ and C0 ₂ . At the cathode a reduction reaction is performed, preferably resulting in OH and H ₂ production. This results in pH increase in the cathode compartment thereby shifting the equilibrium between ionic ammonium towards ammonia (aq). The ammonia is transported over the hydrophobic membrane. Preferably, in the flow channel defining hydrophobic membrane ammonia is subsequently chemosorbed in an acid, for example H ₂ S0 ₄ , to ammonium, for example producing ammonium sulphate.

The bio-electrochemical system according to the present invention enables an effective recovery of components, such as ammonia and/or ammonium. Due to the electrons production of the bacteria, the required voltage which has to be applied across the anode and the cathode is reduced, thereby decreasing the power consumption of the system. This achieves an efficient system. Furthermore, the amount of chemicals that are required is significant reduced as compared to conventional system. Preferably no (additional) chemicals, for example for increasing the pH in the cathode compartment, are introduced in the system according to the invention.

As an alternative to providing the circuit connecting the anode and the cathode with a power source, a resistor can be provided. By providing the system with oxygen electrical energy can be generated. Oxygen can be provided with the flow channel defining hydrophobic membrane configured for reactant supply.

As already mentioned a further interesting embodiment can be achieved by including a (additional) flow channel defining hydrophobic membrane enabling component recovery.

Preferably, the waste water supplied to the bio-electrochemical system according to the invention comprises providing urine as ammonium comprising fluid, or a flow wherein preferably the urine concentration is high, most preferably close to or equal to 100%. Urine comprises relatively high levels of nitrogen in the form of urea. Urea decomposes to ammonia and ammonium. For example, waste water treatment plants have to remove considerable amounts of ammonium and ammonia due to urine. In particular since approximately 80% of nitrogen in waste water originates from urine. The system according to the invention and the method associated therewith is in particular suitable for this task.

In a preferred embodiment according to the present invention the method comprises providing an ammonium comprising fluid having an ammonium-nitrogen concentration > 0.5 g/1, preferably > 1 g/1, more preferably > 5 g/1 and most preferably > 10 g/1.

Preferably, in use the applied voltage is in the range of 10 mV - 50 V, more preferably 50 mV - 10 V and most preferably 100 mV - 5 V, for example IV - 2V. The voltage preferably is in the range of 0.6-1.2 V and supplied by a DC power supply or potentiostat.

In a presently preferred embodiment according to the invention the bio-electrochemical system further comprises an intermediate compartment between the anode and cathode compartments, the intermediate compartment comprising separating ion-exchange membranes.

The intermediate compartment preferably receives waste water. In a presently preferred embodiment, wherein the bio-electrochemical system recovers ammonia, the ammonia is removed from the waste water flow where after the waste water flow is provided to the anode compartment wherein organic manner is preferably oxidized involving a bio-catalyzed oxidation reaction. Cations like Na ⁺ , K ⁺ are transported through the cation exchange membrane separating the intermediate from the anode compartment, and for example OH is transported through the anion exchange membrane separating the intermediate compartment from the cathode compartment resulting in a pH increase of the intermediate compartment thereby enhancing the deprotonation of ionic ammonium into ammonia (aq). Preferably, the hydrophobic membrane is positioned in the intermediate compartment. Providing the flow channel defining hydrophobic membrane in the intermediate compartment enables diffusion transport of ammonia from the intermediate compartment towards the flow channel defined by the hydrophobic membrane. In this flow channel subsequently chemosorption of ammonia into an acid as ammonium takes place. This provides a compact design and improved performance of a bio-electrochemical system for component recovery.

Optionally, an additional anode is provided in the reactor of the system of the present invention. Preferably, the additional anode is provided in an intermediate compartment enabling decomposing ammonia into nitrogen gas and, depending on the configuration, hydrogen and water. This improves the overall performance of the bio-electrochemical system according to the present invention. Further effects and advantages for such additional anode are described in WO

2013/105854 for such additional anode.

In a presently preferred embodiment according to the present invention the hydrophobic membrane is positioned adjacent to a separating ion-exchange membrane.

By positioning the hydrophobic membrane close to a separating ion-exchange membrane the flow channel provides at an optimal location for optimal ion concentrations, for example a location having a relatively high OH concentration and highest pH. This renders the bio- electrochemical system according to the invention even more effective.

Preferably, the hydrophobic membrane is integrated with a separating ion-exchange membrane. This further improves the efficiency of the hydrophobic membrane and provides an effective means to assemble the reactor according to the present invention involving ion-exchange membranes and at least one hydrophobic membrane.

In the presently preferred embodiment according to the present invention the anode comprises a bio-electrode.

Providing the anode as a bio-electrode results in a so-called bio-anode where electro-active micro-organisms at the bio-anode catalyze the anodic reaction, thereby improving the overall energy efficiency. This results in a more efficient oxidation of organic compounds at the anode and associated component recovery, for example ammonia and/or ammonium. As already mentioned, the bio-anode potential lowers the voltage which has to be applied across the anode and cathode. This decreases the power consumption of the system resulting in an efficient recovery.

In a further preferred embodiment according to the present invention the bio- electrochemical system further comprises a number of additional reactors with a flow channel defining hydrophobic membrane extending through more than one of the reactors.

By providing a number of reactors, for example a stack of reactors, an effective upscaling of the system can be achieved. By extending the hydrophobic membrane through more than one of the reactors an effective and efficient recovery system can be provided. In a further preferred embodiment according to the present invention the anode and/or cathode is integrated with the hydrophobic membrane.

By integrating the cathode with the hydrophobic membrane, in one of the presently preferred embodiments oxygen can be supplied to the cathode. This obviates the need of dissolving/sparging/aeration of oxygen or air into the catholyte media in the cathode compartment. Preferably, the cathode is directly integrated with membrane fibers of the hydrophobic membrane, optionally using a carbon based catalyst, optionally enriched with noble metals, for direct integration. This enables oxygen reduction at the cathode in an effective manner.

In a further preferred embodiment according to the present invention the hydrophobic membrane is configured for extracting C0 ₂ from the electrolyte of the anode compartment and enriching electrolyte of the cathode compartment.

By providing a hydrophobic membrane in or connected to the anode compartment the electrolyte of the anode compartment can be brought into contact with the hydrophobic membrane, thereby enabling extraction/transfer of C0 ₂ . More specifically, the flow through the flow channel as defined by the hydrophobic membrane comprises electrolyte from the cathode compartment using the C0 ₂ to acidify/buffer/counteracting the hydroxyl ion production at the cathode by recycling the electrolyte of the cathode compartment through the flow channel defining hydrophobic membrane. This achieves extracting C0 ₂ from the electrolyte from the anode compartment and enriching the electrolyte of the cathode compartment.

In a further preferred embodiment according to the present invention, the bio- electrochemical system further comprises a fuel cell or engine configured for generating electricity with gasses removed from the reactor.

By generating electricity using hydrogen fuel, for example, electricity can be generated to further improve the overall energy efficiency of the bio-electrochemical system according to the present invention. This may even result in a stand-alone application that can be operated in remote areas.

It will be understood that the different features that are described can be applied in the system, and method, according to the invention when applied for component recovery, electrical energy generation and/or a combination thereof.

The invention further relates to a method for recovery of components or generating electrical energy from a waste stream, comprising the steps of:

- providing a bio-electrochemical system as described above;

- supplying a waste stream to the reactor;

- supplying a reactant to and/or extracting a gas from the reactor with the flow channel defining hydrophobic membrane; and

- operating the reactor. The method provides the same effects and advantages as those described for a bio- electrochemical system.

In a presently preferred embodiment the recovery of the components involves recovery of ammonia. For example, the method treats urine that comprises several organic compounds and having an ammonium-nitrogen concentration as high as 10 g/1, for example. Also other ammonium comprising waste streams can be treated. Furthermore, energy can be gained from the process, and organic material and ammonia and/or ammonium can be removed from the (waste) fluid.

In a further embodiment electrical energy is generated by providing oxygen to the reactor, preferably by a flow channel defining hydrophobic membrane.

In a further embodiment electrical energy is generated by providing oxygen to the reactor and recovering components, such as ammonia, thereby combining the two aforementioned embodiments.

In further embodiments according to the invention C0 ₂ and/or NH ₃ are recycled and transported in the system. This provides an efficient process by decreasing the internal resistance of the system.

An alternative method and/or system for recovery of components from a waste stream, without requiring the use of a bio-electrode as described in the aforementioned presently preferred embodiments of the invention, involves a reactor that comprises:

an anode compartment with an anode;

- a cathode compartment with a cathode;

a circuit connecting the anode and the cathode, the circuit comprising a power source for providing an electric current;

an ion-exchange membrane separating the anode and cathode compartments; and a hydrophobic membrane configured for gas extraction and/or reactant supply.

In such electrochemical system the reactions that are involved are electrochemical and no microorganisms are involved. In the case of ammonia nitrogen recovery from a waste water in this electrochemical system water electrolysis will most likely take place, involving oxygen production at the anode and H ₂ production at the cathode.

In one of the presently preferred embodiments the system comprises an electrochemical cell and a membrane unit with at least one hydrophobic membrane that are coupled. The hydrophobic membrane allows ammonia gas to pass and transfer from the catholyte towards the acid in the other compartment.

In experiments it was shown that an effective ammonia removal and/or recovery is possible, especially from concentrated streams, such as urine. The method and system achieve high recovery rates at low power inputs as compared to conventional nitrogen removal processes. Furthermore, results showed that the electrochemical system with the hydrophobic membrane can be used advantageously. Features from one or more of the preferred embodiments of the bio- electrochemical system and method that were described earlier can also be applied in the alternative electrochemical system with hydrophobic membrane. Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

- Figure 1 A shows a reactor with the hydrophobic membrane in the cathode compartment enabling component recovery;

- Figure IB shows a reactor with the hydrophobic membrane in the cathode compartment enabling generating electrical energy;

- Figure 1C shows a reactor with the hydrophobic membrane in the cathode compartment enabling both component recovery and generating electrical energy;

- Figure 2 shows an alternative reactor according to the invention with the hydrophobic membrane in the anode compartment;

- Figure 3 shows an alternative embodiment of the hydrophobic membrane positioned in an intermediate compartment;

- Figure 4 shows a design of a hydrophobic membrane in a compartment;

- Figure 5 shows a number of stacked reactors according to the invention;

- Figure 6A shows a hydrophobic membrane integrated with the cathode in an embodiment for generating electrical energy;

- Figure 6B shows a hydrophobic membrane integrated with the cathode in an embodiment for generating electrical energy and component recovery;

- Figure 7 shows a reactor with a separate anode compartment for C0 ₂ removal with a hydrophobic membrane; and

- Figure 8 A-E illustrates some experimental results with a reactor of figure 1 ;

- Figure 9 shows an alternative system.

The figures comprise some of the relevant reactions that may take place in the system according to the invention. For illustrative purposes the reactions are presented with their components only, without showing the exact stoichiometric balanced reactions.

Bio-electrochemical system 2 (figure 1A) comprises reactor 4 with anode compartment 6 which comprises bio-anode 8 with bio film 10. Reactor 4 further comprises cathode compartment 12 with cathode 14. Anode 8 and cathode 14 are connected with circuit 16 involving power source 18a. Anode compartment 6 and cathode compartment 12 are separated with cation exchange membrane 20. Hydrophobic membrane 22 defining flow channel 24 is positioned in cathode compartment 12. Waste water inlet 26 is connected to anode compartment 6 that further comprising waste water outlet 28. Optionally gas outlet 30 is provided in cathode compartment 12. In use, in system 2 as illustrated in figure 1A, is capable of component recovery. At anode 8 bio-catalyzed anode reactions take place that involve oxidation of organic matter resulting in a production of H ⁺ and C0 ₂ . _. Cations like NH ₄ ⁺ and Na ⁺ transfer through membrane 20 towards cathode compartment 12. At cathode 14 reduction reactions reduce water in OH and H ₂ . This increases the pH in cathode compartment 12. In cathode compartment 12 ionic ammonium is deprotonated into ammonia (aq) with OH . Due to the ammonia-ammonium equilibrium NH ₃ and H ₂ 0 is produced, with NH ₃ diffusing over hydrophobic membrane 22 into flow channel 24.

Preferably, flow channel 24 receives acid through inlet 32 enabling chemosorbing ammonia into ammonium with H ⁺ and leaving at ammonium outlet 34. It will be understood that other configurations can also be envisaged, for example including positioning hydrophobic membrane 22 outside cathode compartment 12 and involving a hydraulic connection between membrane 22 and compartment 12.

System 2 as illustrated in figure IB is capable of generating electrical energy. Oxygen (0 ₂ ) is supplied to cathode compartment 12 by inlet 29 and/or hydrophobic membrane 24 to enable the oxygen reduction reaction (0 ₂ + 2H ₂ 0 + 4e— > 40H ) producing OH . Unspecified ions Q+ and Q- are transported over the anion/cation selective membrane 20 in accordance with the electric field. In the illustrated embodiment system 2 acts as a MFC with resistor 18b included in circuit 16. This enables production of electrical energy.

By providing hydrophobic membrane 24 it is possible to combine electrical energy generation with component recovery, such as ammonia and/or ammonium, in system 2 (figure 1C). Oxygen reduction takes place (0 ₂ + 2H ₂ 0 + 4e— > 40H ) in cathode compartment 12. In the illustrated embodiment oxygen is only supplied by membrane 24. It will be understood that oxygen can, alternatively or in addition thereto, be supplied with a separate inlet 29 and/or an additional flow channel defining hydrophobic membrane. At anode 8 bio-catalyzed anode reactions take place that involve oxidation of organic matter resulting in a production of H ⁺ and C0 ₂ . _. Cations like NH ₄ ⁺ and Na ⁺ transfer through membrane 20 towards cathode compartment 12. In cathode compartment 12 ionic ammonium is deprotonated into ammonia (aq) with OH . Due to the ammonia-ammonium equilibrium NH ₃ and H ₂ 0 is produced, with NH ₃ diffusing over hydrophobic membrane 22 into flow channel 24. Preferably, flow channel 24 receives acid through inlet 32 enabling chemosorbing ammonia into ammonium with H ⁺ and leaving at ammonium outlet 34.

Further embodiments according to the invention will be described and/or illustrated disclosing further features. It will be understood that these features can be combined to provide even further embodiments. Also, it will be understood that these features can be applied to configurations capable of component recovery, electrical energy generation and/or the combination thereof. Alternative system 42 (figure 2) comprises reactor 44 comprising similar components as mentioned relation to system 2 illustrated in figure 1 A-C. The differences between system 42 illustrated in figure 2 and system 2 illustrated in figure 1 will be described. Anode compartment 6 and cathode compartment 12 are separated by anion exchange membrane 46. Hydrophobic membrane 22 is positioned in anode compartment 6. The same reactions can take place in reactor 44 as described in relation to reactor 4. OH is transferred over anion exchange membrane 46. In the illustrated embodiment the membrane fibers are positioned close to anion exchange membrane 46 where the OH concentration and the pH in the anode compartment is the highest, thereby allowing ammonia recovery from the anode compartment in an effective manner. This specific location for hydrophobic membrane 22 is preferably close to membrane 46 allowing for ammonia recovery from anode compartment 6 which is usually acidifying due to the anodic reactions. It will be understood that membranes 20, 46 can optionally be integrated with hydrophobic membrane 22.

System 52 (figure 3) comprises reactor 54 with similar components as described before in relation to systems 2, 42 that are illustrated in figures 1 , 2. Reactor 54 comprises an additional intermediate compartment 56 that is separated with anion exchange membrane 58 from cathode compartment 12 and cation exchange membrane 60 from anode compartment 6. Hydrophobic membrane 22 is in the illustrated embodiment positioned in intermediate compartment 56. The same or similar reactions can take place in reactor 54 as described for reactors 4, 44. It will be understood that anions like OH may transfer over anion exchange membrane 58 and cations like Na ⁺ can transfer over cation exchange membrane 60 towards intermediate compartment 56. This improves the overall performance of the bio-electrochemical system 52 and allows for a compact design.

Hydrophobic membrane 22 (figure 4) is preferably provided in a straw-type configuration. In the illustrated embodiment one straw-hydrophobic membrane 22 is shown in reactors 4, 44, 54. It will be understood that any number of hydrophobic membranes 22 can be provided in compartments of reactors 4, 44, 54. Optionally, additional hydrophobic membranes 22 can be provided in other compartments of reactors 4, 44, 54.

Bio-electrochemical system 72 (figure 5) comprises a number of reactors 74, 76 with one hydrophobic membrane 22 extending through reactors 74, 76. This enables upscaling of bio- electrochemical system 72 in an effective and efficient manner.

In a further alternative embodiment system 82 with reactor 84 (figure 6A) comprises cathode system 86. Cathode system 86 comprises cathode 88 and hydrophobic membrane 90 that have been integrated. This enables supply of oxygen (0 ₂ ) to cathode system 12.

It will be understood that cathode system 86 can also be provided tothe other bio- electrochemical system configurations 2, 42, 52, 72. In the illustrated embodiment cathode system 86 supplies oxygen to the cathode compartment, thereby enabling reduction at cathode 86. Unspecified ions Q+ and Q- are transported over the anion/cation selective membrane in accordance with the electric field. In the illustrated embodiment system 82 acts as a MFC with a resistor included in the circuit. This enables production of electrical energy. By providing an additional hydrophobic membrane, as shown in one or more of the other embodiments, recovery of components, such as ammonia and/or ammonium can be achieved.

In an alternative configuration (figure 6B) cathode system 86 is combined with flow channel defining hydrophobic membrane 24 as illustrated in figure 1A, for example. This enables an effective electrical energy generation with cathode system 86 in combination with component recovery as described in relation to figure 1A and figure 1C.

A further alternative system 92 (figure 7) provides reactor 94 with separate membrane module 96. Membrane module 96 is connected with input 98 receiving electrolyte from anode compartment 6 and returning treated electrolyte through exit 100 to anode compartment 6.

Hydrophobic membrane 102 is positioned in module 96 and is, in use, supplied with electrolyte from cathode compartment 12 at its input 104. The (enriched) electrolyte leaves membrane 102 through exit 106 to cathode compartment 12. System 92 is advantageously used for acidifying/ buffering the cathode counteracting the hydroxyl ion production at the cathode and thereby lowering losses due to an increasing pH.

As already mentioned features of embodiments described and/or illustrated can be combined and/or applied in other configurations according to the invention. For example, more than one hydrophobic membrane 24 can be provided in a system according to the invention.

Experiments have been performed with reactors shown in figures 1-7. In an ammonia removal experiment from human urine as waste stream with bio-electrochemical system 2 illustrated in figure 1 , the current was measured during operation (figure 8 A) during a time period of more than 20 days showing measured currents in the range of 0.2-0.35A. The recovery percentage of nitrogen from the influent in the experiment lies between 30 -55 (figure 8B) and COD removal between 20 -50 (figure 8D). The so-called coulombic efficiency (figure 8C) determined from the COD removal and the measured current lies between 50% -100%. The transport efficiency over cation exchange membrane 20 (figure 8E) is between 40% and 100% during the experiment based on transported charge (coulombs) in the form of ammonium and current.

The experiment illustrates the possible use of the configurations according to the present invention. The use of hydrophobic membrane 22 provides improved results of the process in bio- electrochemical system 2 as compared to a configuration without any hydrophobic membrane 22. Experiments with system 92 (figure 7) involving a hydrophobic membrane module 96 and a CEM or AEM separating the anode and cathode compartments, show the effect of recycling of C0 ₂ and NH ₃ on current production. Results show that membrane module 96 can transport the C0 ₂ produced at the anode to the cathode, but can also be used to recycle NH ₃ from cathode back to anode. Both processes reduce the resistance for ion transport over the membrane, and thereby significantly increase the current produced by an MEC at the same applied voltage.

Runs were performed with the reactor comprising an AEM or CEM, respectively. In both reactor type a first run was performed without, and a second run with membrane module. Anolyte and catholyte were recirculated on respective sides of the module to allow gas exchange between both liquids. During start-up, the bioanode was allowed to develop and reach stable anode potential and current production. After start-up, each experiment was started by refreshing the catholyte with a fresh 10 mM NaCl solution and applying -I V between anode and cathode using a power source (Delta Elektronika ES 030-5). The experiment was finished when steady state conditions were reached in which current density, pH and all other ion concentrations in anode and cathode compartment were constant,

For the reactor with CEM, the module led to an increase in current density from 2.1 to 4.1 A m ² . For the reactor with AEM, the module led to an increase in current density from 2.5 to 13.0 A m ² . Therefore, current density was significantly increased for both reactor types when C0 ₂ was transported to the cathode.

The experiments show that the transport of C0 ₂ from anode to cathode via the hydrophobic membrane module decreases the internal resistance of the reactor. The mechanism is that chemical species are exchanged between anolyte and catholyte, thereby introducing extra ionic species as charge carrier in the electrolyte.

Alternative electrochemical system 102 (figure 9) comprises electrochemical cell 104 and membrane unit 106 with hydrophobic membrane 108. Influent 110 is provided to anode compartment 112 with pump 114 and recirculated with pump 116. Effluent is removed at outlet 118. Catholyte is recirculated through cathode compartment 120 with pump 122. Compartments 112, 120 are separated with membrane 124. Membrane unit 106 comprises first compartment 126 for catholyte and second compartment 128 for acid that is recirculated with pump 130 and is provided with outlet 132. Membrane 108 separates first and second compartments 126, 128.

System 102 was operated at room temperature (23.4 ± 1.1 °C). Anode compartment 112 of electrochemical cell 104 had a continuous inflow of fresh medium, while both the cathode compartment 120 and membrane unit 106 were operated in batch mode. All three liquids (anolyte, catholyte and acid) were recirculated over their respective compartments at 70 ml rnin ¹ . The anolyte inflow rate was either 1.1 ml min ¹ or 0.2 ml min \ resulting in a hydraulic retention time (HRT) of 3.0 and 16.7 h, respectively. The effluent from anode compartment 112 was collected in a closed container sealed with a water lock. Both anode and cathode recirculation vessels had a vent to let the produced gasses escape.

Each experiment was finished when both anode and cathode pH, as well as anode and cathode potentials, were constant. Two types of wastewater were used as anolyte during the experiments: a simplified synthetic wastewater and pre -treated human urine. The synthetic wastewater was composed of sodium carbonate and ammonium carbonate to study and model the ammonium transport processes in the system. Human urine was used to evaluate total ammonia nitrogen (TAN) transport in a more complex mixture of cations and anions. Before starting each experiment, samples were taken from both influent containers and recirculation vessels. At the completion of one hydraulic retention time (HRT), a sample was taken from the anolyte recirculation and from the acid. At the end of the experiment, two samples were taken from both anode and cathode recirculation vessels, acid, and the anolyte effluent container.

There are two fluxes of nitrogen in the system: NH ₃ over hydrophobic membrane 108

(JNH3, TMCS) and TAN over (cation) exchange membrane 124 (J _T AN)- For a steady state with respect to TAN, both fluxes need to be approximately the same. Results showed in the experiments that there was a direct linear relationship with a slope of 1.06 and a R ² of 0.98 for the synthetic wastewater data points, which indicates near steady state. Therefore, system 102 effectively transports ammonia from the influent to the acid. Afterwards, experiments using urine were done to evaluate TAN transport of a more complex wastewater. The experiments with urine further confirmed that TAN transport reached a steady state.

System 102 efficiently transported TAN from the influent to the acid, and TAN transport reached steady state in both synthetic wastewater and urine. High fluxes (up to 433 gN m ² d ^"1 ) and recovery efficiencies (> 89%) were obtained.

The present invention is by no means limited to the above described preferred

embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged. For example, the bio-electrochemical system 2, 42, 52, 72, 82, 92 can be operated batch wise or continuously with a waste stream that may comprise ammonium.