WO2011011829A1

WO2011011829A1 - A bioelectrochemical cell system

Info

Publication number: WO2011011829A1
Application number: PCT/AU2010/000959
Authority: WO
Inventors: Ka Yu Cheng; Ralf Cord-Ruwisch
Original assignee: Murdoch University
Current assignee: Murdoch University
Priority date: 2009-07-29
Filing date: 2010-07-29
Publication date: 2011-02-03
Anticipated expiration: 2012-01-29
Also published as: AU2010278674A1

Abstract

A bioelectrochemical cell system comprising: an upper portion; a lower portion adapted to retain an aqueous solution; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the bioelectrochemical cell, the first zone and the second zone of the electrode are in electrical communication and, in use, the first zone of the electrode is at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell such that, the first zone is anodic, and wherein at least part of the second zone of the electrode is remote from the aqueous solution such that, the second zone is cathodic.

Description

A Bioelectrochemical Cell System

Field of the Invention

The present invention relates to a bioelectrochemical cell system and methods for treating aqueous solutions, such as wastewater.

Background Art

Wastewater is typically treated to remove undesirable contents and provide an effluent that can safely be returned to the environment. Bacteria can assist in this process, particularly in respect of breaking-down ammonia that may be present in the wastewater. The biological reaction by which ammonia is removed involves the conversion, first, aerobically, of the ammonia and other nitrogen-containing compounds to nitrates through bacterial nitrification; followed by a second step in which anoxic bacterial denitrification converts the nitrates into nitrogen gas, which is then separated from the wastewater. These two processes have mutually exclusive requirements. Nitrification is performed under aerobic conditions by slow-growing autotrophic nitrifying bacteria, using oxygen to convert ammonia to nitrite and then to nitrate. In contrast, denitrification is performed by heterotrophic bacteria that require anoxic conditions and a source of electrons, typically organic material to convert nitrate into nitrogen gas. The electrons are usually provided in the form of oxidisable organic and inorganic compounds in the wastewater.

The activated sludge (AS) process is currently the most widely adopted biological process for wastewater treatment. It is an energy intensive process, in which air (oxygen) is actively transported, either by surface turbines or submerged diffusers, into wastewater, in order to maintain an aerobic system and the activated sludge (a highly concentrated bacterial consortium) in suspension. The activated sludge degrades the organic contaminants in the wastewater by using dissolved oxygen as the terminal electron acceptor. For each m³ of wastewater approximately 8 m³ of air is required (Lee and Lin (2000) Handbook of Environmental Engineering Calculations). Such an active aeration process leads to about 60-80% of the total operational cost of the entire wastewater treatment process. The energy demand of aeration in AS processes lies fundamentally on the mass transfer of air to water. A certain amount of mechanical energy must be supplied to transport a unit volume of air into a unit mass of wastewater. This energy is directly proportional to the height of the aeration basin, and hence the depth of the wastewater. However, due to limited oxygen transfer efficiency (OTE) only part of the oxygen in the transferred air is accessible to the bacteria in the wastewater. Although OTE can be maximized by reducing the size of the air bubble, oxidizing power (as oxygen) is still lost in the process. Such a loss represents a significant problem with the AS method of wastewater treatment.

Some technologies use "oxygen-equivalents" instead of transferring oxygen from a gas- into a liquid-phase, required for the organic removal in a wastewater. The "oxygen-equivalents" can be indirectly supplied in the form of an electron accepting (i.e. oxidizing) surface (e.g. inert carbon electrode), in order to optimize aeration efficiency or to minimize aeration without compromising treatment efficiency.

Reported approaches have included bioelectrochemical cell systems (BESs), such as microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). They are bioelectrochemical processes that allow a direct conversion of chemical energy stored in a chemical compound into electrical energy, with MFC used for a net production of electricity and MEC for a production of gas as a by-product. MFC and MEC are seen as a potential clean technology to recover valuables from wastewaters. For example, the use of MFCs for treating aqueous solutions, such as wastewater, results in the production of energy from organic material present in wastewater.

To generate electric current, a BES has several features. Firstly, an electron donor (e.g. organics present in a wastewater) is oxidized by an electrochemically active anodophilic biofilm which can subsequently transfer the liberated electrons to an electrode (anode). Secondly, these electrons at the anode are driven by a potential gradient and flow toward a cathode via an external conductive circuit. Electrical energy is thereby generated if a suitable resistive load is located between the two electrodes. Thirdly, the electrons at the cathode react with a soluble electron accepting species (e.g. oxygen) which itself becomes reduced. The continuous generation of electricity in a BES is possible only when the ionic charges between the anode and cathode are balanced. Therefore, for each electron flowing across the external circuit, either a positively or a negatively charged ionic species must be transferred from the anode to the cathode or vice versa. These systems are limited in performance and cost by several intrinsic technical problems.

BES processes regardless of design, for example trickling filter or sequencing batch reactor, are limited by: (1) the poor cathodic reaction of oxygen reduction; and (2) the build-up of a pH gradient between anode and cathode over time, which leads to an increased voltage loss (i.e. overpotential) of the BES. Further, it is this so-called pH splitting phenomenon, which can block the electron flow and operation of the BES. The continual need for pH control is known to be a significant cost and energy factor in BES wastewater treatment.

Ideally, either a proton (H+) or a hydroxide ion (OH-) serves as the migrating ionic species. However, under BES operating conditions (predominately at neutral pH) protons are continuously consumed for the reduction of oxygen or generation of hydrogen gas, for example, at a cathode, and also the concentrations of both protons and hydroxide ions are several order of magnitudes lower compared to most other ionic species. This results in a preferential migration of other ionic species to maintain electroneutrality of the system, causing acidification and alkalization at the anode and cathode, respectively. Such pH splitting phenomena leads to a decrease in the driving force of the system (i.e. potential difference between anode and cathode), as each unit of pH gradient represents an over- potential (i.e. potential loss) of 59 mV according to Nernst equation. Subsequently, the current is diminished and hence diminishing the wastewater treatment performance. Correcting the pH by acid/ base dosing or addition of a concentrated buffer (e.g. phosphate buffer) is impractical and costly.

A loop-concept has been proposed as a solution to overcome the aforementioned pH limitation during BES operation (Freguia et al., (2007b) Sequential anode-cathode configuration improves cathodic oxygen reduction and effluent quality of microbial fuel cells, Wat. Res., 42, 1387-1396). Specifically, the acidified anodic effluent is used as the influent for the cathode compartment in a two-compartment configuration. However, such operation depends heavily on mechanical pumping of wastewater through the system (Clauwaert et al. (2009) Litre-scale microbial fuel cells operated in a complete loop. Appl. Microbiol. Biotechnol., 82, 241-247 and Freguia et al. (2007b) Sequential anode-cathode configuration improves cathodic oxygen reduction and effluent quality of microbial fuel cells, Wat. Res., 42, 1387-1396). Wastewater needs to be lifted up from the bottom inlet to the top of the anodic compartment, from which the anodic effluent overflows and trickles over an air exposed cathode. The energy required to lift a unit volume (i.e. a unit weight) of wastewater upward within the anodic compartment is directly proportional to the compartment's height, the up scaling potential for this kind of configuration is significantly limited by increasing costs. Further, separation of anode and cathode in both systems requires the use of sophisticated ionic exchange membranes, which are expensive.

Apart from the pH splitting limitation, the high over-potential associated with the cathodic oxygen reduction at graphite and carbon electrodes often limits the BES performance. Although modifying the cathode with a platinum catalyst is a proven way to alleviate such over-potential limitation, the use of platinum cannot be justified in BES processes because of costs and environmental impact in its production.

Single chamber and membraneless upflow BES, in which liquid from the anode flowed into the cathode has been illustrated to suffer from oxygen reflux from cathode to anode, which was alleviated by inserting compounds such as glass wool between the compartments thereby increasing the internal resistance of the system resulting in low performance (Jang JK, Pham TH, Chang IS, Kang KH, Moon H, Cho KS et al. (2004) Construction and operation of a novel mediator- and membrane-less microbial fuel cell. Process Biochemistry 39: 1007-1012.). Liu and Logan (Liu H, Logan BE (2004) Electricity generation using an air-cathode single chamber microbial fuel cell in the presence and absence of a proton exchange membrane. Environmental Science & Technology 38: 4040-4046) omitted the membrane from a BES in order to promote cation transport from anode to cathode. They achieved a higher performance in terms of power output in comparison to a membrane containing system but the crossover of reduced substrate from the anode to the cathode compartment caused efficiency decreases.

Despite the advantages presented above, it can be seen that the current waste treatment methods suffer from at least three economically significant problems, namely pH splitting, a membrane is still needed to separate anodes and cathodes, and extensive uplifting or re- circulating of wastewater is required.

The above discussion of the background art is intended only to facilitate an understanding of the present invention. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application. Disclosure of the Invention

The present invention provides a bioelectrochemical cell system comprising: an upper portion; a lower portion, adapted to retain an aqueous solution; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the cell, the first zone and the second zone of the electrode are in electrical communication and, in use, the first zone of the electrode is at least partially immersed in an aqueous solution retained in the lower portion of the cell such that, the first zone is anodic, and wherein at least part of the second zone of the electrode is remote from the aqueous solution such that, the second zone is cathodic. In one form of the invention, the bioelectrochemical cell system comprises: an upper portion; a lower portion, adapted to retain an aqueous solution; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the bioelectrochemical cell, the first zone and the second zone of the electrode are in electrical communication and, in use, the first zone of the electrode is at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell such that, the first zone is anodic, and wherein at least part of the second zone of the electrode is remote from the aqueous solution such that, the second zone is cathodic.

In one embodiment of the present invention, when in use, the first zone and the second zone of the electrode of the bioelectrochemical cell system alternate, such that the second zone is at least partially immersed in an aqueous solution retained in the lower portion and at least part of the first zone of the electrode is remote from the aqueous solution. The aqueous solution circulates with the first zone and the second zone of the electrode alternating in position, thereby reducing the build-up of a pH gradient between first and second zone. In one embodiment of the present invention, when in use, the first zone and the second zone of the electrode of the bioelectrochemical cell system alternate position, such that the first zone of the electrode is completely immersed in the aqueous solution retained in the lower portion of the bioelectrochemical cell and the second zone of the electrode is completely remote from the aqueous solution. .

The bioelectrochemical cell system of the present invention, by providing for the first zone and the second zone of the electrode to alternate in position, alleviates the need for an ion exchange membrane or separator interposed between the first zone and the second zone of the electrode. Furthermore, the bioelectrochemical cell system of the invention may be operated without the mechanical recirculation of the aqueous solution, such as wastewater. The bioelectrochemical cell system of the present invention ameliorates the three economically significant problems described within the prior art.

In a further embodiment of the present invention, the first zone and the second zone of the electrode of the bioelectrochemical cell system are adapted to be both anodic and cathodic. The electrode of the present invention may be formed from any material that is conductive. In one form of the invention, the electrode is formed from material selected from the group: stainless steel, carbon fibre, graphite, granular graphite and combinations thereof.

In one embodiment, the electrode is rotatably provided within the bioelectrochemical cell and the bioelectrochemical cell system further comprises a rotating means for rotating the electrode. The rotating means may be located outside the bioelectrochemical cell or within the upper portion of the bioelectrochemical cell, such that when in use, the rotating means is above the level of aqueous solution present therein. In a preferred embodiment of the present invention, the electrode is rotatably provided within the bioelectrochemical cell and the bioelectrochemical cell system further comprises a rotating means for rotating the electrode such that, when in use, the first zone and the second zone rotate by 180°.

In one embodiment of the present invention, the bioelectrochemical cell system further comprises a biological support mounted to the electrode of the bioelectrochemical cell. In a preferred form of the invention, the biological support is adapted to support a biofilm. In a further embodiment of the present invention, a biofilm is provided on at least part of the biological support mounted to the electrode of the bioelectrochemical cell system, such that in use, the biofilm is adapted to subject the electrode to a polarization potential when the first zone or second zone of the electrode is at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell.

In a preferred embodiment of the present invention, the electrode of the bioelectrochemical cell system, when in use, is rotated such that a biofilm is established thereon and the electrode intermittently serves as the anode and the cathode alternately by rotation. The use of biofilms in any of the preceding bioelectrochemical cell systems does not necessarily contribute to the improvement in the electrochemical rates at the electrodes, but to the biological production of electricity and/or gas by-products. The bioelectrochemical cell system may further comprise an electrical circuit in communication with the electrode. The bioelectrochemical cell system may further comprise a catalyst on the electrode. In a preferred embodiment, the lower portion of the bioelectrochemical cell is adapted to contain micro-organisms, such that, in use, the micro-organisms catalyze transfer of electrons from the aqueous solution retained in the lower portion of the bioelectrochemical cell to the electrode, and to the circuit. In an alternative embodiment, the upper portion is adapted to contain microorganisms such that, in use, the micro-organisms catalyze transfer of electrons from the electrode to an electron acceptor remote from the aqueous solution.

In an alternative embodiment, the bioelectrochemical cell system may contain microorganisms in the upper portion and the lower portion of the bioelectrochemical cell, such that, in use, the micro-organisms of the upper portion catalyze transfer of electrons from the electrode to an electron acceptor and the micro-organisms of the lower portion catalyze transfer of electrons from the aqueous solution retained in the lower portion of the bioelectrochemical cell to the electrode.

The bioelectrochemical cell system of the present invention may further comprise an electrical power supply electrically connected to the electrical circuit, wherein in use, voltage is applied from the electrical power supply between either the first zone or the second zone of the electrode, being the zone that is at least partially immersed, in the aqueous solution retained in the lower portion of the bioelectrochemical cell and the zone at least partially remote from the aqueous solution, such that the zone remote from the aqueous solution is cathodic, thereby promoting chemical synthesis and/or fermentation and/or biotransformation of the aqueous solution in the lower portion of the cell.

In a preferred embodiment, the bioelectrochemical cell system of the present invention provides for both nitrification and denitrification processes in the upper portion of the bioelectrochemical cell. The upper portion of the bioelectrochemical cell may be oxygenated, aerated or open to the air, or alternatively enclosed. The bioelectrochemical cell system of the present invention may also provide for conversion of nitrate or nitrite to nitrogen in the lower portion of the cell.

In one form of the invention, the bioelectrochemical cell system further comprises an inlet and an outlet, wherein in use, a quantity of the aqueous solution enters the bioelectrochemical cell through the inlet, and a quantity of the aqueous solution departs through the outlet.

The present invention further provides for a method for treating an aqueous solution, the method comprising the steps of: providing a quantity of an aqueous solution to a bioelectrochemical cell, the bioelectrochemical cell comprising an upper portion; a lower portion adapted to retain an aqueous solution; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the bioelectrochemical cell, the first zone and the second zone being in electrical communication; providing an electrical circuit in communication with the electrode; at least partially immersing the first zone of the electrode in the quantity of aqueous solution such that at least part of the second zone of the electrode is remote from the aqueous solution, wherein the first zone allows transfer of electrons released from the aqueous solution to the circuit and the second zone allows transfer of electrons from the circuit to the aqueous solution; after a predetermined period, at least partially alternating the first zone and the second zone of the electrode such that the second zone is at least partially immersed in the aqueous solution and such that the first zone is partially remote from the aqueous solution, wherein the second zone allows transfer of electrons released from the aqueous solution to the circuit and the first zone allows transfer of electrons from the circuit to the aqueous solution.

In a preferred embodiment, the method for treating an aqueous solution further comprises an electrical power supply in electrical connection with the first and the second zone of the electrode, wherein the method further comprises the step of enhancing an electrical potential between first and the second zone, such that the zone at least partially immersed in the aqueous solution is anodic and such that the zone at least partially remote from the aqueous solution is cathodic. The enhancement of the electrical potential between first and the second zones of the embodiment may in turn enhance chemical synthesis and/or fermentation and/or biotransformation occurring in the aqueous solution contained within the cell.

In one embodiment of the invention, the method comprises the step of connecting an electrical load to the electrical circuit, wherein an electrode zone, being the first or second zone, at least partially immersed in the aqueous solution is anodic and the bioelectrochemical cell generates electrical current detectable at the load.

In a further embodiment, the method of the present invention comprises the step of detecting the electrical current at the load. In a further embodiment, the electrical current detected at the load may be used as a source of electricity. In a further embodiment, the electrical current detected at the load may be measured in a chemical or biochemical sensing device.

Preferably, the electrode is provided rotatably within the bioelectrochemical cell. Preferably, the electrode is provided with a biofilm mounted thereon. In one embodiment, the upper portion of bioelectrochemical cell is adapted to enable both nitrification and denitrification processes. In one embodiment, the lower portion is adapted to enable conversion of nitrate and/or nitrite to nitrogen.

The present invention further provides a method for generating gas by-products and electricity by treatment of an aqueous solution, the method comprising the steps of: providing a quantity of an aqueous solution to a bioelectrochemical cell, the bioelectrochemical cell comprising an upper portion; a lower portion adapted to retain an aqueous solution, the bioelectrochemical cell having a wall generally enclosing and defining an interior space adjacent an interior surface of the wall, and defining an exterior; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the cell, the first zone and the second zone being in electrical communication; providing an electrical circuit in communication with the electrode; providing micro-organisms to the bioelectrochemical cell, wherein the aqueous solution is oxidizable by an oxidizing activity of the micro-organisms; at least partially immersing the first zone of the electrode in the aqueous solution such that at least part of the second zone of the electrode is remote from the aqueous solution, wherein the first zone allows transfer of electrons released from the aqueous solution to the circuit and the second zone allows transfer of electrons from the circuit to the aqueous solution; incubating the aqueous solution oxidizable by the micro-organisms under oxidizing conditions such that electrons are produced and at least a portion of the electrons produced are transferred to the anodic zone and then the circuit; and after a predetermined period, at least partially alternating the first zone and the second zone of the electrode such that the second zone is at least partially immersed in the aqueous solution and such that the first zone is partially remote from the aqueous solution, wherein the second zone allows transfer of electrons released from the aqueous solution to the circuit and the first zone allows transfer of electrons from the circuit to the aqueous solution; and activating the electrical power supply to increase a potential between the anodic and cathodic zones of the electrode, such that at least a portion of electrons and protons combine to produce a gas by-product, wherein the zone at least partially immersed in the aqueous solution is anodic and such that, the zone at least partially remote from the aqueous solution is cathodic.

In one form of the invention, the bacteria provided to the bioelectrochemichal cell are anodophilic bacteria. In a preferred form of the invention, the anodophilic bacteria are adapted to generate methane or hydrogen gas.

The method for generating gas by-products and electricity by treatment of an aqueous solution may further comprise the step of rotatably providing the electrode to the bioelectrochemical cell. In a further embodiment, the method of the present invention further comprises a biofilm mounted on the rotatably provided electrode. In one embodiment, the upper portion is adapted to enable both nitrification and denitrification processes and the lower portion is adapted to enable conversion of nitrate and/or nitrite to nitrogen.

In a preferred embodiment, the method for generating gas by-products and electricity during treatment of an aqueous solution, further comprises a biofilm mounted on the cathodic zone of the electrode, such that the cathodic zone of the electrode is a biocathode, and the catalytic effect of the biofilm and the energy value of the gas by-product allows for a more energy efficient cathode, compared to a traditional oxygen-cathode.

The bioelectrochemical cell system of the present invention may operate as a microbial fuel cell, producing electricity from organic pollutants, without the poor cathodic reaction of oxygen reduction; and a build-up of a pH gradient between an anode and a cathode over time, which leads to a reduction in the activity of electrochemically active bacteria. The bioelectrochemical cell system of the invention may use electrical energy as a source of reducing power in chemical, fermentation or biotransformation reactions and may use aqueous solutions, such as wastewater as electron mediators and a catalyst, to produce electricity and/or gas by-products. Various catalysts are suitable for use in the bioelectrochemical cell system in accordance with the invention. For example, the catalyst may comprise an oxidoreductase (e.g., fumarate reductase) bound to the electrode. The catalyst may also comprise bacterial cells disposed in the lower portion of the cell. Non- limiting examples of bacterial cells include cells of Actinobacillus succinogenes, cells of Escherichia coli, and sewage sludge.

Advantageously, the bioelectrochemical cell system of the present invention does not require ionic exchange membranes to separate the anode and cathode. Rather, the electrode zones of the present invention may act as both an anode and a cathode, whereby alternating electrode zones results in polarity inversion on both the first and second zones of the electrode, leading to increasing pollutant removal rate. Preferably, pumps are used to achieve aqueous solution flow in the present invention and the establishment of anodophilic/ cathodophilic biofilm The aqueous solution employed any of the preceding methods is preferably an aqueous solution product from agricultural, mining (alumina, gold, nickel processing), food processing or beverage (brewing and winery) production industries. In an embodiment of the invention, the aqueous solution is wastewater. The following description expounds on the invention in terms of its use in the treatment of wastewater. The invention is not however limited only in this context. A person of skill reading this application will and should recognise and understand that a wide varieties of liquids may be employed in the method of the invention without departing from the employed methodology.

The term "wastewater" as used herein refers to a mixture of water and dissolved or suspended solids. It is generally water, derived from residential, business or industrial sources, which may contain a variety of waste products such as soap, chemicals or manure. It may be derived from a wide variety of sources, for example effluent from agricultural sources such as animal farming practices including piggeries, aquaculture sources, poultry farms and dairy farms. Industrial wastewater and effluent from sources such as paper and pulp mills, sugar refineries, abattoirs, food processing and manufacturing industries, effluent from the tanning industry, the defence industry (e.g. munitions production), the food industry, the agriculture industry, the chemical industry (e.g. manufacturing of fertilizers) and mining may be treated using the present method. Effluent from human sources such as sewerage facilities and domestic grey and black water is also included within the meaning of the term. Storm water, surface water, and groundwater infiltration, particularly if it is contaminated by organic or chemical substances, may also fall within the meaning of the term wastewater. Preferably, the wastewater to be treated using the method of the present invention is wastewater derived from a municipal wastewater treatment facility, such as sewage. It is contemplated that the methods of the present invention are suitable for removal of nitrogenous matter, carbonaceous matter, matter containing phosphate, and/or mixtures thereof from aqueous waste generated by, for example, domestic, agricultural, mining or industrial processes. Wastewater can also include natural or modified water bodies such as aquifers, lakes, ponds, pools, lagoons, rivers or run-offs and leachates from material that is in contact with water, as long as it contains ammonia, or other nitrogen substances and organic compounds.

The "biofilm" employed by the present invention, is a structured community of microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface.

Biofilm based bioelectrochemical cell may increase the biomass 'concentration' compared to a similar sized suspended culture reactor and hence may have lower footprint requirements. This is of particular interest with increasingly dense urban populations, as the volume of wastewater to be treated is high while the land available for treatment is low. Biofilms may also assist in the regulation of population characteristics, for example, the maintenance of a high level of nitrifiers without sludge bulking. The use of biofilms may also reduce the amount of wastewater liquor which is retained in suspended culture aerobic nitrifying reactors and is therefore not available to be denitrified. In addition, the use of a biofilms may also eliminate the need for settling and clarification of treated wastewater. Even with the use of biofilms though, there will still be a need for periodic cleaning of biofilm growth to prevent clogging. The biomass may be composed of any population of micro-organisms that are able to perform denitrification of the wastewater being treated, i.e. the conversion of oxidised nitrogen to a gaseous end product and that are able to convert ammonia to nitrate. For example, the biomass may be composed of microbes such as bacteria, fungi and archaea. Preferably, the biomass is composed principally of bacteria. However, any microbe that is capable of denitrifying wastewater may be used.

Other aspects and advantages of the invention will become apparent to those skilled in the art from a review of the ensuing description, which proceeds with reference to the following illustrative drawings.

Best Mode(s) for Carrying Out the Invention General

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variation and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features. The entire disclosures of all publications (including patents, patent applications, journal articles, laboratory manuals, books, or other documents) cited herein is expressly incorporated herein by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness. No admission is made that any of the references constitute prior art or are part of the common general knowledge of those working in the field to which this invention relates.

Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as "comprises", "comprised", "comprising" and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean "includes", "included", "including", and the like; and that terms such as "consisting essentially of and "consists essentially of have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.

Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

Detailed Description of the preferred embodiments

The present invention will now be described with reference to four embodiments, and the following figures, in which:

Figure 1 is a schematic diagram of an electrode disc set according to the present invention; with an o-ring and a small extension of the stainless steel mesh.

Figure 2 is a schematic diagram of a batch bioelectrochemical cell system according to the present invention operated for electricity generation. Figure 3 is a schematic diagram of an alternate batch bioelectrochemical cell system according to the present invention operated for electricity generation.

Figure 4 is a schematic diagram of an alternate batch bioelectrochemical cell system according to the present invention operated for electricity generation. Figure 5 is a schematic diagram of an alternate batch bioelectrochemical cell system according to the present invention coupled with a potentiostat for enhanced cathodic oxygen reductions at a chemostat mode operated to overcome the thermodynamic constraint of the poor cathodic oxygen reduction.

The description of the embodiments should not be understood as limiting the foregoing general description of the invention.

In Figure 2, there is shown a bioelectrochemical cell system for treating an aqueous solution in accordance with a first embodiment of the present invention. The bioelectrochemical cell (cell) 10 comprises a vessel 9, provided with an inlet and an outlet (not shown). The cell 10 comprises an upper portion 11 ; a lower portion 12 adapted to retain an aqueous solution; and a plurality of electrodes 30 provided within the cell. As can best be seen in Figure 1 , each of the electrodes 30 comprises a first zone 31 and a second zone 32.

In the embodiment illustrated, each of the electrodes is provided in the form of a rotatable electrode disc assembly comprising at least one disc. Figure 1 further shows the rotatable electrode disc 30 consisting of two zones, being a first zone 31 and a second zone 32. Each of the first and second zones 31 and 32 consists of a stainless steel current collecting mesh 35. Electrically conductive carbon fibre sheet is mounted onto both sides of the mesh. The first zone 31 and the second zone 32 are separated by a central shaft 34 and an O-ring 33. The first and second zones 31 and 32 are in electrical communication via the stainless steel mesh 35,. As shown in Figure 2, the vessel 9 of the first embodiment comprises a cylindrical Perspex transparent water pipe (298 mm length; 140 mm diameter) with its two ends covered by two separate square Perspex side plates 13 (160 x 160 mm). A rubber O-ring is located between each side plate and the centre pipe to assure air and water tightness. The rotatable electrode disc assembly 34 comprises a Perspex horizontal central rotatable shaft 36 (see Figure 1). Two separate stainless steel current collecting strips are independently mounted onto the upper and lower sides of the shaft (not shown). As illustrated, in the first embodiment, 20 sets of rotatable electrode discs 30 are mounted onto the central rotatable shaft 36 (see Figure 2). A Perspex plastic o-ring is used to connect each pair of electrode discs 30 with the central shaft 36 and to maintain a constant distance with the neighbouring discs. In this preferred embodiment, the estimated total projected surface area (immersed in an aqueous solution) of the 20 disc halves is 947 cm². This value is used for calculating the current and power densities. The total working volume of the cell is used to calculate acetate or COD removal rates and hydraulic retention time of the system when operated at continuous mode.

Upon providing an aqueous solution to the cell, such that a portion of a zone of the electrode disc 32 is immersed in the solution, this allows an ionic contact between the zone 31 at least partially remote from the solution (such that the zone is cathodic) and the zone at least partially immersed in the solution 32 (such that the zone in anodic). The system does not require the use of a membrane or separator. The electrical circuit 14 in electrical communication with the electrode zones 31 and 32; therefore electrical energy is generated if a suitable resistive load is located between the two zones 31 and 32 of the electrode 30. The reference electrode 15 allows the potential of the cell to be determined. Figure 3 illustrates a second embodiment of the present invention, comprising a stepper motor unit 16 consisting of a stepper motor, a stepper motor driver, and an analog output card is mounted onto the side plate of the cell. A gear disc (one-to-seven reduction) is used to convey the mechanical action of the motor 16 to the central rotatable shaft 36. The stepper motor 16 and its driver is calibrated such that upon receiving a proper signal from the analog output card (such as Labjack™), the central rotatable electrode disc assembly can be precisely rotated for a fixed degree (e.g. full turn, 360°; half turn, 180°, etc) at predetermined time intervals.

In use, the first zone of the electrode 32 can rotate from being at least partially immersed in an aqueous solution retained in the lower portion of the cell 10 such that the first zone is anodic, to being at least partially remote from the aqueous solution such that, the zone 32 is cathodic. Similarly, the second zone of the electrode 31 can rotate from being at least partially remote from the aqueous solution such that, the zone is cathodic, to being at least partially immersed in an aqueous solution retained in the lower portion of the cell 10 such that the second zone 31 is anodic. Further, a computer program 17, such as LabVIEW™ (version 7.1 National Instrument) can be used to control and monitor the cell, for example, the program can be used to control the alternating of the electrodes 30, as illustrated in a third embodiment of the present invention (see Figure 4). The computer program LabVIEW™ can be used to increase voltage to achieve fixed anodic and cathode potentials, record current, cell voltage, anodic potential and cathodic potential, record dissolved oxygen, record hydrogen gas production and record the pH of the cell.

In a fourth embodiment of the present invention, the cathodic reaction can be enhanced upon providing additional voltage to the system. A potentiostat 20 can be used to provide extra power supply for the system, as illustrated in Figure 5, thereby avoiding the thermodynamic constraint of the poor cathodic oxygen reduction and allowing higher anodic potential.

The working (41), counter (42) and reference electrodes (43) of the potentiostat 20 are connected to the at least partially immersed in an aqueous solution first electrode zone 32, the at least partially remote from the aqueous solution second electrode zone 31 and the reference electrode 15, respectively.

Hn use, the first zone of the electrode 32 can rotate from being at least partially immersed in an aqueous solution retained in the lower portion of the cell 10 such that the first zone is anodic, to being at least partially remote from the aqueous solution such that, the zone 32 is cathodic. Similarly, the second zone of the electrode 31 can rotate from being at least partially remote from the aqueous solution such that, the zone is cathodic, to being at least partially immersed in an aqueous solution retained in the lower portion of the cell 10 such that the second zone 31 is anodic. As the electrode zones alternate between being anodic and cathodic, a computer 17 controllable relay switch 25 can be used to synchronize the control by the potentiostat 20, such that whichever electrode is at least partially immersed in an aqueous solution retained in the lower portion of the cell 10 can always act as the working anodic electrode, while the electrode at least partially remote from the aqueous solution always act as the counter cathodic electrode.

In a further embodiment of this invention describes a wastewater treatment apparatus. Specifically, it describes the conversion of organic matters in wastewaters into a form of energy, such as electricity or gas by-products. Further, it describes an anoxic reactor through which wastewater which has previously been nitrified may be denitrified. It is not intended that these embodiments be limiting, as other anoxic, anaerobic and aerobic processes in which a microorganism is provided with a reciprocating biofilm support in order to encourage a biological reaction through the apparatus described in this document are intended to fall within the disclosure of the invention.

Examples The following examples serve to more fully describe the manner of using the biolelectrochemical cell system of the present invention, and the methods of the present invention. This description is included solely for the purposes of exemplifying the present invention. It is understood that these methods in no way serve to limit the true scope of this invention, but rather are presented for illustrative purposes.

The nature of the present invention means that a wide variety of experimental conditions can be selected.

Bacterial Seeding Inoculum and Synthetic wastewater

A return activated sludge collected from domestic wastewater treatment plant (sequencing batch reactors activated sludge process) was used as the initial inoculums. It was stored at 4°C prior use.

A synthetic wastewater used consisted of (mg L^'1): NH₄CI 125, NaHCO₃ 125, MgSO₄ TH₂O 51 , CaC|₂-2H₂O 300, FeSO₄-7H₂O 6.25, and 1.25 ml. L^"1 of trace element solution, which contained (g L^"1): ethylene-diamine tetra-acetic acid (EDTA) 15, ZnSO₄-7H₂O 0.43, CoCi₂-6H₂0 0.24, MnC,₂-4H₂O 0.99, CuSO₄ SH₂O 0.25, NaMoO₄-2H₂O 0.22, NiCI₂ GH₂O 0.19, NaSeO₄-IOH₂O 0.21 , H₃BO₄ 0.014, and 0.050. Either sodium acetate (5 to 10 mM) or glucose (10 mM) was added as the electron donor.

Yeast extract (0.1-1 g L^"1 279 final concentration) was added as bacterial growth supplement. Unless otherwise stated, the initial pH of the synthetic wastewater was adjusted to 6.9-7.2 using either 1 M HCI or 4M NaOH.

Process Monitoring and Control

Voltage signals were recorded at fixed time intervals via the LabVIEW™ program interfaced with a high precision voltage data acquisition board (DAQ) (National Instrument NI4350). All electrode potential (mV) herein refers to values against Ag/AgCI reference electrode (ca. +197 mV vs. standard hydrogen electrode).

Bioelectrochemical Cell

The bioelectrochemical cells were inoculated with synthetic wastewater containing 10% (v/v) of a return activated sludge collected from a local municipal wastewater treatment plant. The initial two months, the cells were operated in batch mode. A variable external resistor (5 - 1 M ohm) was used to connect the first zone and the second zone of the electrode. The cells were operated at ambient room temperature (22 - 25° C) and atmospheric pressure. Polarization curve analysis was performed regularly to evaluate performance over time. The analysis was done by decreasing the external resistance of the cell from 1 M to 5 ohm in a stepwise manner. For each external resistance setting, at least 5 min waiting period was given to obtain steady state values of current (I) and voltage (V). These values were used to calculate the corresponding power output (P) according to an equation of P=V^*I. Power and current densities were obtained by normalizing the P and I with the projected surface area of the submerged half discs. Correlation between the submerged anode potential and the current density was further obtained from the data of the polarization curve analysis. This correlation is useful to evaluate anodophilic activities of the electrochemically active biofilm in a cell.

Example 1 : Cathodic Oxygen Reduction Using an External Power Supply

In order to overcome the thermodynamic constraint of the poor cathodic oxygen reduction of the bioelectrochemical systems of the prior art, a potentiostat was used to provide extra power supply for the process. The working, counter and reference electrodes of the potentiostat were connected to the immersed electrode zone, the aqueous solution remote zone of the electrode and the reference electrode, respectively. As the electrode zones would be alternated regularly between the aqueous solution in the lower portion of the cell and the upper portion of the cell, at least partially remote from the aqueous solution, the electrode zones would serve alternately as an anode and cathode, a computer controllable relay switch was used to synchronize the control by the potentiostat. Such that whichever electrode zone that was immersed in the aqueous solution could always act as the working electrode (anode) while the air-exposed discs always act as the counter electrode (cathode).

Example 2: Anaerobic Operation of the Upper portion of the Bioelectrochemical Cell

By enclosing the bioelectrochemical cell, there is an opportunity to recycle, recover or control of gaseous by-products. It is possible that by maintaining the upper portion of the cell under anaerobic condition and applying a suitable external electrical power, the cathodic zone of the electrode of the cell can generate hydrogen gas, an added-value by-product that is of commercial interest. To obtain anaerobic condition in the upper portion of the cell, the upper portion was purged with pure nitrogen gas (1 L min^"1) for at least 10 min. Example 3: Scanning Electron Microscopy of Biofilm-Electrode

In order to observe the difference between the morphology of the electrode biofilm cultivated under oxic and anaerobic cathodic conditions, the biofilm electrodes collected under these two conditions were examined by using scanning electron microscopy (SEM) (Philips XL 20 Scanning Electron Microscope). At appropriate time points as specified in the article, a small piece of carbon sheet was cut with a sterile stainless steel scissor. The electrode samples were fixed in 3 % glutaraldehyde in 0.025 M phosphate buffer (pH 7.0), overnight at 4⁰C C. The samples were then rinsed three times (5 min each time) with 0.025 M phosphate buffer (pH 7.0) before they were subjected to dehydration procedure through a series of ethanol solution (each solution was changed two times and each change was 15 min): 30, 50, 70, 90 and 100%. The 100% ethanol solution was replaced with amyl acetate (two changes, 15 min each). The samples were critical point dried before they were mounted to SEM specimen holder with contact adhesive. The samples were then sputter coated with gold before being subjected to SEM observation. Abiotic plain carbon sheet were treated with the same procedures and served as the Control.

Example 4: Operating the Bioelectrochemical Cell for Electricity Generation

It is shown that there is evidence of electrochemical reduction of the submerged anode electrode. Decrease of the anode potential and the build up of cell voltage could indicate whether the cell was capable of generating electricity. Hence, the effect of activated sludge (10%, v/v) on the initial build up of the submerged anode potential and cell voltage of the cell was evaluated. At an external resistance of 1M ohm, the activated sludge could decrease the anode potential from about +40 to a steady level of -453 mV within 16 hours. In the absence of activated sludge, the anode potential remained at level between +40 and +50 mV, suggesting that the electrochemical reduction of the anode (aqueous solution immersed zone of the electrode) was caused by the metabolic activity of the activated sludge. Hence, the proposed cell allows electricity generation using activated sludge as the bacterial catalyst.

Example 5: Increased Anodophilic Activity increases Current and Power Output The improvement of current and power output of the bioelectrochemical cell can be due to an improved anodophilic activity of the biofilm over time. Anodophilic activity of biofilms can be visualized from a plot of current versus anodic potential (Cheng et al., 2008). In general improved anodophilic activity is indicated by an increase of current without a significant polarization of the biofilm-anode (i.e. anodic potential becomes more positive). The results indicate anode polarization was decreased over time. For instance, an increase of current density from the lowest to the highest point (by decreasing the external resistance) resulted in an anode polarization of +244 mV (i.e. from -400 to -156 mV) at Day 1. While at Day 38 and 50, the anode polarizations reduced to +107 and +77 mV, respectively. This result suggests that the biofilm became more anodophilic over time. Example 6: Transfer of "Oxygen Equivalents" via Conductive Electrode (as Electron Flow) increases Acetate Removal

To test the effect of current on acetate oxidation in the bioelectrochemical, acetate concentrations were monitored over a batch cycle with two external resistance settings (2 ohm and 1M ohm). During the batch, the discs were rotated once every 15 min.

Upon acetate addition, the aqueous solution immersed anodic electrode zone potentials in both resistance settings decreased from -50 mV to about -490 mV. Current generation was negligible at 1M ohm. While at 2 ohm, acetate addition could immediately increase the current from 0.18 to 3.4 mA within an hour. Thereafter, a gradual, linear increase of current was observed until a maximal level of 5.8 mA was reached at 12.3 h. Upon acetate depletion, the current decreased to its background level.

The acetate removal rates at external resistances of 1M and 2 ohm were 0.32 and 0.43 mM^• h^"1, respectively. This current generation in the cell could lead to a 34% increase of acetate removal. A background acetate removal rate of 0.21 mM^• h^"1 was observed without electrode rotation and current generation (1 M ohm), suggesting that the regular electrode rotation (a full turn per 15 min) could already increase the acetate removal rate by 53%. Such enhancement is due to an enhanced mass transfer of oxygen from air into the wastewater by the electrode rotation. Example 7: Intermittent Flipping the Electrode Discs allows Alternate Current

Generation

To test whether a biofilm could alternately catalyze an anodic and a cathodic reaction in the bioelectrochemical, the electrode discs were flipped (180 °) once per hour, such that the electrode zones alternated between acting as an anode partially immersed in the aqueous solution and a cathode, at least partially remote from the aqueous solution. The hourly flipping of the electrode discs at 2 ohm could reverse the current (ranged from -6.7 to +7.5 mA), indicating that a biofilm could alternately catalyze the current under alternating anodic- cathodic conditions.

Example 8: Electrochemically Assisted Anode Facilitates the Establishment of

Anodophilic Biofilm

The potential of the submerged anode disc was controlled by the potentiostat at -300 mV. In the absence of acetate, a background current of less than 3 mA was observed. Acetate addition immediately increased the current to about 40 mA within 15 min. Thereafter, the current was continuously increased to a maximal level of about 60 mA within lOhours. Acetate depletion resulted in a gradual decline of current to its original level. The maximal current was ranged from 60 to 70 mA. It was about 10 times higher than that previously obtained.

Example 9: Energy Evaluation of the Bioelectrochemical Cell (Oxygen as the Cathodic Electron Acceptor)

To determine whether the proposed bioelectrochemical cell process can be used as an alternative technology to the conventional AS processes, the treatment performance and energy requirement of the process are compared with that of conventional AS processes as reported in the literature (Table 1).

The COD removal rate obtained from the bioelectrochemical cell fall within the range of the conventional AS processes, indicating that the bioelectrochemical cell process is equally good as compared to the AS processes in removing organic pollutants from the wastewater. In terms of energy usage, the bioelectrochemical cell process demonstrated better efficiency (0.47 kWh kg COD^'1) compared to the AS processes (0.7 to 2 kWh kg COD^"1). Further, the bioelectrochemical cell process also demonstrated at least 5 times less energy demand per volume of wastewater treated as compared to the AS processes (88 vs. 430 kWh ML^"1) (Table 1).

Table 1 : Treatment performance and energy requirement of the bioelectrochemical cell process and conventional activated sludge (AS) processes.

b Adapted from (Logan et al., 2006)

c Adapted from (Tchobanoglous et al., 2003)

d Adapted from (Keighery, 2004)

# COD content of acetate was estimated assuming 1.067 g COD per 1.0 g acetate.

¥ The values include the energy consumption by the stepper motor (0.083 Wh per one rotation). Applications of the present invention may vary in size from commercial plants to personal use units for example, for use on a small boat.

Modifications and variations such as would be apparent to the skilled addressee are considered to be within the scope of the present invention.

Claims

The Claims Defining the Invention are as Follows:

1. A bioelectrochemical cell system comprising: an upper portion; a lower portion adapted to retain an aqueous solution; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the bioelectrochemical cell, the first zone and the second zone of the electrode are in electrical communication and, in use, the first zone of the electrode is at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell such that, the first zone is anodic, and wherein at least part of the second zone of the electrode is remote from the aqueous solution such that, the second zone is cathodic.

2. A bioelectrochemical cell system according to claim 1 , characterised in that the bioelectrochemical cell system does not comprise an ion exchange membrane or separator disposed between the first zone and the second zone of the electrode.

3. A bioelectrochemical cell system according to claim 1 or 2, characterised in that the first zone of the electrode and the second zone of the electrode are adapted to alternate position, such that, in use, the second zone becomes at least partially immersed in an aqueous solution retained in the lower portion and at least part of the first zone of the electrode becomes remote from the aqueous solution.

4. A bioelectrochemical cell system according to claim 1 , characterised in that the first and second electrode zones are adapted to be both anodic and cathodic.

5. A bioelectrochemical cell system according to any one of the preceding claims characterised in that the electrode is rotatably provided within the bioelectrochemical cell.

6. A bioelectrochemical cell system according to claim 5, characterised in that the bioelectrochemical cell further comprises a rotating means for rotating the electrode by 180°.

7. A bioelectrochemical cell system according to claim 1, characterised in that a biological support is mounted to the electrode of the bioelectrochemical cell, the biological support being adapted to support a biofilm.

8. A bioelectrochemical cell system according to claim 7, comprising a biofilm on at least part of the surface of the electrode, such that in use, the biofilm is adapted to subject the electrode to a polarization potential when the first zone or second zone is at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell.

9. A bioelectrochemical cell system according to claim 1 , characterised in that the lower portion of the bioelectrochemical cell is adapted to contain micro-organisms, such that, in use, the micro-organisms catalyze transfer of electrons from the aqueous solution retained in the lower portion of the bioelectrochemical cell to the electrode, and to the circuit.

10. A bioelectrochemical cell system according to claim 1 , characterised in that the lower portion contains micro-organisms that catalyze transfer of electrons from the aqueous solution retained in the lower portion of the bioelectrochemical cell to the electrode.

11. A bioelectrochemical cell system according to any one of the preceding claims comprising an electrical power supply electrically connected to the electrical circuit, wherein in use, electrical voltage is applied from the electrical power supply between the zone of the electrode at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell and the zone at least partially remote from the aqueous solution, such that the zone remote from the aqueous solution is cathodic, thereby promoting chemical synthesis of the aqueous solution in the lower portion of the cell.

12. A bioelectrochemical cell system according to any one of the preceding claims comprising an electrical power supply electrically connected to the electrical circuit, wherein in use electrical voltage is applied from the electrical power supply between the zone of the electrode at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell and the zone at least partially remote from the aqueous solution, such that the zone remote from the aqueous solution is cathodic, thereby promoting fermentation of the aqueous solution in the lower portion of the cell.

13. A bioelectrochemical cell system according to any one of the preceding claims comprising an electrical power supply electrically connected to the electrical circuit, wherein in use electrical voltage is applied from the electrical power supply between the zone of the electrode at least partially immersed in an aqueous solution retained in the lower portion of the bioelectrochemical cell and the zone at least partially remote from the aqueous solution, such that the zone remote from the aqueous solution is cathodic, thereby promoting biotransformation of the aqueous solution in the lower portion of the cell.

14. A method for treating an aqueous solution, the method comprising the steps of: providing a quantity of an aqueous solution to a bioelectrochemical cell, the bioelectrochemical cell comprising an upper portion; a lower portion adapted to retain an aqueous solution; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the cell, the first zone and the second zone being in electrical communication; providing an electrical circuit in communication with the electrode; at least partially immersing the first zone of the electrode in the aqueous solution such that at least part of the second zone of the electrode is remote from the aqueous solution, wherein the first zone allows transfer of electrons released from the aqueous solution to the circuit and the second zone allows transfer of electrons from the circuit to the aqueous solution; after a predetermined period, at least partially alternating the first zone and the second zone of the electrode such that the second zone is at least partially immersed in the aqueous solution and such that the first zone is partially remote from the aqueous solution, wherein the second zone allows transfer of electrons released from the aqueous solution to the circuit and the first zone allows transfer of electrons from the circuit to the aqueous solution.

15. A method for generating gas by-products and electricity by treatment of an aqueous solution, the method comprising the steps of: providing a quantity of an aqueous solution to a bioelectrochemical cell, the bioelectrochemical cell comprising an upper portion; a lower portion adapted to retain an aqueous solution, the bioelectrochemical cell having a wall generally enclosing and defining an interior space adjacent an interior surface of the wall, and defining an exterior; and an electrode, the electrode having a first zone and a second zone, wherein, the electrode is provided within the bioelectrochemical cell, the first zone and the second zone being in electrical communication; providing an electrical circuit in communication with the electrode; providing micro-organisms to the bioelectrochemical cell, characterised in that the aqueous solution is oxidizable by an oxidizing activity of the micro-organisms; at least partially immersing the first zone of the electrode in the aqueous solution such that at least part of the second zone of the electrode is remote from the aqueous solution, wherein the first zone allows transfer of electrons released from the aqueous solution to the circuit and the second zone allows transfer of electrons from the circuit to the aqueous solution; incubating the aqueous solution oxidizable by the micro-organisms under oxidizing conditions such that electrons are produced and at least a portion of the electrons produced are transferred to the anodic zone and the circuit; and after a predetermined period, at least partially alternating the first zone and the second zone of the electrode such that the second zone is at least partially immersed in the aqueous solution and such that the first zone is partially remote from the aqueous solution, wherein the second zone allows transfer of electrons released from the aqueous solution to the circuit and the first zone allows transfer of electrons from the circuit to the aqueous solution; and activating the electrical power supply to increase potential between the anodic and cathodic zones of the electrode, such that at least a portion of electrons and protons combine to produce a gas by-product, wherein the zone at least partially immersed in the aqueous solution is anodic and such that, the zone at least partially remote from the aqueous solution is cathodic.

16. A method according to claim 14 or 15 characterised in that the bioelectrochemical cell comprises an electrical power supply in electrical connection with the first and the second zone of the electrode, and the method further comprises the step of enhancing an electrical potential between first and the second zones of the electrode.

17. A method of according to claims 15 or 16 further comprising the steps of: providing anodophilic bacteria in the bioelectrochemical cell, characterised in that the aqueous solution is oxidizable by an oxidizing activity of the anodophilic bacteria and wherein the bioelectrochemical cell further comprises a wall generally enclosing and defining an interior space adjacent an interior surface of the wall, and defining an exterior; incubating the aqueous solution oxidizable by the anodophilic bacteria under oxidizing reactions conditions such that electrons are produced and at least a portion of the electrons produced are transferred to the anodic zone and the circuit; and activating an electrical power supply to increase potential between the anodic and cathodic zones of the electrode, such that at least a portion of electrons and protons combine to produce methane or hydrogen gas.

18. A method according to any one of claims 14 to 17, characterised in that the electrode is rotatably provided within the cell.

19. A method according to any one of claims 14 to 18, characterised in that the bioelectrochemical cell further comprises a rotating means for rotating the electrode by 180°.

20. A method according to any one of claims 22 to 30, wherein the electrode has a biofilm mounted thereon.

21. A method according to any one of claims 22 to 32, wherein, in use the bioelectrochemical cell is a biosensor.

22. A method according to any one of the preceding claims wherein the aqueous solution is wastewater.