Technical Field

This invention relates to a gas dissolution and bubble generator system and more particularly to an oxygen dissolution and micro/nano-bubble generator system for generating oxygen micro/nano-bubbles and an oxygen super-saturated aqueous medium. The invention also relates to a method of dissolving a gas in a liquid by the application of pressure to generate micro/nano-bubbles of the gas and in particular to a method of dissolving oxygen in an aqueous medium by the application of pressure, and generating oxygen micro/nano-bubbles.

Background of the Invention

The dissolution of gases in liquids is a system requirement in a number of industrial, horticultural and agricultural processes. For example, dissolved oxygen is widely used in many such processes with the result that there are numerous aqueous environments in which dissolved oxygen gas concentration is a critical factor. Such environments include the treatment of water for release to rivers and waterways in waste water treatment plants and biodigestion installations, vertical farming installations where oxygen levels in nutrient streams is diminished due to the elevated temperatures at which growing is optimised and fish farms where high concentrations of fish deplete the oxygen content of the water, leading to disease and poor growth.

In known systems, the addition of oxygen to the aqueous medium is traditionally done with compressed air plants which add both nitrogen and oxygen to water, which is at ambient pressure, in the form of bubbles. However, in such systems, the concentrations of dissolved oxygen achieved in the water tends to be low while the bubbles of oxygen do not persist in the water as they rapidly rise to the surface and quickly dissipate into the atmosphere. As a result, the systems can perform poorly.

An object of the invention is to overcome at least some of the problems of the prior art. Summary of the Invention

According to a first aspect of the invention there is provided an oxygen dissolution and bubble generator system for dissolving oxygen and generating oxygen bubbles in an aqueous medium comprising: an oxygen source; a pressurisable container for receiving the oxygen and an aqueous medium, a pressurizing source to increase the pressure in the pressurisable container to force dissolution of the oxygen in the aqueous medium and create bubbles in the aqueous medium following release of the increased pressure.

In one embodiment the oxygen source is an air compressor. In another embodiment, the oxygen source is an electrolyser for generating oxygen and hydrogen.

Preferably, the pressurizing source is configured to pressurize the aqueous medium.

Optionally, the pressurizing source comprises a pump communicable with the pressure cylinder.

In another embodiment, the electrolyser is the pressurizing source. Optionally, where the oxygen source is an electrolyser, the system further comprises a separator to separate oxygen from hydrogen. Suitably, the hydrogen is used elsewhere, leaving the oxygen to be dissolved in the aqueous medium.

Preferably, the invention further comprises a receiving environment to receive the aqueous medium from the pressure cylinder. More preferably, the receiving environment comprises a waste water treatment plant, a biodigestion plant or a farming system. Suitably, the farming system comprises a vertical farming system, a soil-based intensive farming system or a fish farming system.

The invention also extends to a method of dissolving oxygen bubbles in an aqueous medium comprising feeding oxygen from an oxygen source and aqueous medium from an aqueous medium source into a pressurisable container; increasing the pressure in the pressurisable container to force dissolution of the oxygen, and releasing the pressure to form micro- and/or nano-bubbles in the aqueous medium.

Preferably, the oxygen and the aqueous medium are separately fed into the pressurisable container.

In one embodiment, the oxygen source comprises an air compressor. Alternatively, the oxygen source comprises an electrolyser.

Preferably, the oxygen is fed into the pressurisable container at a relatively low pressure. Suitably, the low pressure is about 7 bar.

Advantageously, the pressure in the pressurisable container is increased to from about 15 to about 30 bar or more.

Preferably, the pressure is maintained at the increased pressure in the pressurisable container for a period to effect supersaturation of the aqueous medium. More preferably, the pressure is maintained at the increased pressure in the pressurisable container for a period of about two minutes or more.

Optionally, the aqueous medium is a waste water, a biodigestion or a farming aqueous medium.

In one embodiment, the aqueous medium is received into a receiving environment from the pressurisable container.

Suitably, the receiving environment comprises a waste water treatment plant, a biodigestion plant or a farming system. The systems and methods of the invention result in much smaller, more persistent micro/nano- oxygen bubbles compared with oxygen bubbles generated using the methods and systems of the prior art. In addition, the application of elevated pressure concurrently, super-saturates aqueous media with oxygen. The micro/nano-bubbles also exhibit a low buoyancy and, as a result, rise at a very slow rate in aqueous media. Accordingly, the bubbles persist in aqueous media and dissipate slowly thus optimising the performance of industrial, horticultural and agricultural process which rely on the use of dissolved and accessible oxygen. The oxygen source in the system of the invention can be derived from air, where the nitrogen is irrelevant to the desired function, or from water electrolysis where a combination of hydrogen and oxygen gases is generated. In some applications, both gases can be exploited if desired while in others the gases can be separated and the oxygen only used and the hydrogen deployed elsewhere as a fuel. Accordingly, the system of the invention can be based on the use of compressed air or can employ oxygen (and hydrogen) from an electrolyser-based system.

For example, in situations where there is no use for the hydrogen, or where its presence could be deemed hazardous, a system making use of compressed air at typical workshop pressures (7 bar max.) can be used as the feed-stock into a system which then increases the pressure to appropriate levels (15-30 bar or more) to force dissolution of the air-borne oxygen in a water or nutrient supply.

Alternatively, the system of the invention decomposes water into hydrogen and oxygen gases by electrolysis, making use of the self-pressurisation which occurs as a natural function of the electrolysis reaction, allowing dissolution of the gases in an aqueous solution at pressure, and subsequent release of that aqueous solution to the environment for which the system is designed. The highly oxygenated aqueous solutions produced in accordance with the invention provide both micro/nano-bubbles and super-saturated gas-rich solution to receiving technologies or environments thereby providing a significantly increased gas concentration for take-up by those organisms which are otherwise starved of gas. The systems and methods of the invention may be scaled for any application from small vertical farming installations up to waste water treatment plants, and have particular relevance to biodigestion installations, where electrolytically generated oxygen may be used to feed the bacteria and the electrolytically generated hydrogen used to enhance the methane produced by the system for power generation. Similarly, in situations where the oxygen is required for oxygenation of water in waterways, waste-water treatment plants, fish farms, etc. the hydrogen can be stored separately for use in other applications or sold as a commodity on relevant markets.

In situations where both electrolytically generated gases could be beneficially used, such as in biodigestion plants designed for the production of methane, there is no requirement for separation technologies to be employed in the system design, and a mixed oxygen/hydrogen gas can be supplied directly from the electrolyser where the oxygen is used to feed the bacteria and the hydrogen is used to enhance the methane.

Where the system of the invention is an air-based system which makes use of environmental air for the oxygenation of water, the system typically includes:

- an electrical power source;

- a control system to monitor pressures and valve timings, etc.;

- an air compressor to deliver air at around 7 bar pressure;

- a pressurisable container such as a pressure cylinder to receive air and an aqueous solution or water;

- a pressurising source in the form of a pump which is capable of pumping the aqueous solution to a sufficient pressure to force dissolution of the oxygen (from about 15 bar to about 30 bar or more pressure), and

- a release means or technology to provide the receiving environment with the super saturated medium.

Where the system of the invention includes an electrolyser to generate oxygen and hydrogen, the system can include:

- an electrical power source;

- a controller; - an electrolyser stack;

- a pressurisable container such as a pressure cylinder to receive gas and an aqueous solution or water;

- a pressure pump to supply the water-based medium to the pressure cylinder;

- an optional balance tube, and

- a release means in the form of a pressure release valve to allow the super-saturated solution to enter the treatment environment.

Where the gas mixture requires separation before being supplied to a treatment environment (e.g. a system configured for delivering an oxygen super-saturated solution of water, nutrient or other aqueous medium) the system can include:

- an electrical power source;

- a controller;

- an electrolyser stack of relatively complex design in which the oxygen and hydrogen are produced in separate streams of relatively high purity;

- a pressurisable container such as a pressure cylinder;

- a pressurising source in the form of a pressure pump to provide the liquid medium at pressure to the pressure cylinder, which delivers an increased pressure, appropriate for the treatment environment;

- alternatively, where the electrolyser stack is capable of delivering sufficient pressure i.e. can serve as a pressurising source, the water-based medium can be supplied to the pressure cylinder at low pressure, and the gas bubbled through it to attain the desired pressure;

- an optional timer which controls the duration over which the pressurised water is exposed to the pressurised gases;

- an optional release means or technology which releases the super-saturated liquid solution to the receiving environment at a rate appropriate to the application, and

- an optional receiving technology for the hydrogen produced in order to make use of its inherent energy.

Brief Description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view from above and one side of a first embodiment of a small scale micro/nano bubble generator system of the invention configured for use in a vertical farming system or a biodigestion system or similar in which oxygen and hydrogen are electrolytically generated and dissolved in water; to form a super saturated aqueous medium and micro/nano-bubbles upon release of pressure.

Figure 2 is a simplified perspective view from above and one side of the micro/nano bubble generator system of the invention in which a mixture of oxygen and hydrogen is electrolytically generated and dissolved in water, and

Figure 3 is a schematic view from the side of a second embodiment of a micro/nano bubble generator system of the invention in which electrolytically generated hydrogen and oxygen is cryogenically separated and the oxygen is dissolved in water and the hydrogen can be exploited for use in unrelated applications.

Detailed Description of the Invention

As shown in Figures 1 and 2, a first embodiment of a small scale electrolytic micro/nano bubble generator system of the invention configured, for example, for use in a vertical farming system or a biodigestion system or similar is generally indicated by the reference numeral 1 and is made up of an electrolyser stack 2 in which water is electrolytically decomposed into a mixed hydrogen and oxygen gas. Operation of the electrolyser stack 2 is controllable via a controller housed in a cabinet 3 which can include a PLC, a switch-gear and power supply unit (PSU). The controller can control the electrolyser stack 2 output, valve timings, sensor inputs, pump pressures and the like as required. The electrolyser stack 2 is in fluid communication with a separating tower/reservoir cylinder 4 of electrolyte via pipework 5 which is in turn in fluid communication via the pipework 5 with a bubbler 6 in which any carry-over electrolyte is captured for repatriation to the separating tower/reservoir cylinder 4 in order to avoid depletion of electrolyte salts.

Importantly, the bubbler 6 is connected via the pipework 5 to a pressurisable container such as a pressure cylinder 7 to which the gas generated by the electrolyser stack 2 and passed through the separating tower/reservoir 4 is initially supplied at a low pressure to the pressure cylinder (7) and is then subsequently pressurised by fluid (aqueous medium) which enters the pressure cylinder 7 via a media pressure pump 8. Accordingly, as shall be explained more fully below, the media pressure pump 8 provides pressurised fluid/aqueous medium to the pressure cylinder 7 after the pressure cylinder 7 has been filled with gas.

The micro/nano bubble generator system 1 is also optionally provided with a balance tube 9 in which level sensors are placed in order to avoid turbulence associated with circulating electrolyte and gases as they enter the separating tower/reservoir 4 from the electrolyser stack 2. Accordingly, gas-head and fluid are directly connected with those in the separating tower/reservoir 4 via the pipework 5 at the top and base in order to ensure that gas and fluid levels are equal in both.

The relatively simple system 1 of the present embodiment is of a relatively small scale and is suitable for use (for example) in a small, containerised biodigestion system such as might be deployed for handling food waste from a supermarket or restaurant.

If desired, the system 1 of the invention can be encased in a protective enclosure.

Figure 3 shows a schematic view from the side of a second embodiment of a micro/nano bubble generator system 1 of the invention in which hydrogen and oxygen has been electrolytically generated as outlined in Figures 1 and 2. However, in the present embodiment, the hydrogen and oxygen is cryogenically separated before the oxygen is dissolved in an aqueous medium to super-saturate it and the hydrogen is exploited for use in unrelated applications. Like numerals indicate like parts.

Accordingly, as shown in the drawing, the electrolytic micro/nano bubble generator system 1 is provided with an electrolyser stack 2 in which water is decomposed into a mixed hydrogen and oxygen gas for initial supply at a relatively low pressure to the pressure cylinder 7, a controller 3 (omitted for clarity), a separating tower/reservoir 4, pipework 5, a bubbler 6, the pressure cylinder 7, the pressure pump 8 and the optional balance tube 9. The electrolytic micro/nano bubble generator system 1 can be further provided with an optional gas dryer 10 (e.g. a desiccant based gas-drying cylinder 10) for the removal of water from the mixed gas stream. Other drying technologies that may be used as gas dryers 10 separately or in cooperation with desiccant include vortex tubes, cooling coils, coalescing filters, dashpots, etc.

The dryer 10 is in turn in fluid communication with a gas separator 11 via the pipework 5 to separate the gas mixture into separate streams of hydrogen and oxygen. Suitable gas separators are cryogenic or pressure/temperature swing adsorption means which effectively separate the gases. However, cryogenic separation is preferred.

Finally, the electrolytic micro/nano bubble generator system 1 is provided with a storage container 12 for storing the aqueous medium in which gas is to be dissolved.

The method of dissolving a gas in a liquid by the application of elevated pressure and in particular to a method of dissolving separated oxygen in an aqueous medium by the application of elevated pressure of the invention will now be described in relation to Figure 3.

Accordingly, generated and separated oxygen is fed at pressure into the pressure cylinder 7 where it is forced at pressure into dissolution with the aqueous medium to be oxygenated. This might be, for example, fluid from a water treatment plant, water from a fish farm or nutrient for a vertical farming or other horticultural system.

More particularly, the gas mixture is generated in the electrolyser stack 2 and passes to the separating tower/reservoir 4 where it separates from the electrolyte, passing to the bubbler 6 via the pipework 5. The gas mixture then travels from the bubbler 6 to the dryer 10 to be dried.

From the dryer 10, the gas mixture continues on to the separator 11 in which the oxygen is distilled out from the mixed gas stream, leaving pure hydrogen gas and liquid oxygen. Both gases exit the system through a heat exchanger (not shown) which can be incorporated in the separator 11 to leave the gases at close to ambient temperature. The oxygen stream then travels at system pressure to the pressure cylinder 7 in which it is mixed with a supply of liquid medium at pressure supplied by the pressure pump 8 from the storage container 12. The elevated pressures in the pressure cylinder 7 force dissolution of the oxygen into the pressurised aqueous medium. The rate of dissolution is dependent upon both pressure and duration prior to release to the receiving environment.

Upon release from the pressure cylinder 7, the liquid medium becomes depressurised and micro-bubbles of the dissolved oxygen appear in the liquid, turning it cloudy. These bubbles have very little buoyancy (being as small as they are) and are, therefore persistent in the liquid medium, rising slowly to the surface while cooperatively presenting a large surface area to the receiving environment. By surface energy, these minute bubbles adhere to the desired target surfaces depending on the treatment environment e.g. roots in vertical farming or bacteria in biodigestion systems thereby providing a more effective and accessible oxygen supply to the targets.

In addition to the provision of micro-bubbles, the effect of pressurisation on the liquid is to super-saturate it with the oxygen, thereby raising levels to a point significantly higher than can be obtained otherwise. This condition is more persistent than the micro-bubbles and can be seen to benefit the medium for a considerable time, dependent upon the degree of saturation, the temperature of the liquid and the elevation of the installation (ambient air pressure). The method of the invention was performed using the system 1 of the invention as outlined in the following Example:

Example 1 - Methodology Tests were carried out making use of an electrolyser-based system which generates mixed gas at a pressure of 7 bar (e.g. a system 1 as shown in Figures 1 and 2). The tests were performed at controlled, approximately ambient, temperatures. The mixed gas from the electrolyser stack 2 was delivered to a pressure-capable cylinder 7 in which it was pressurised to 15 bar by the pumping of water into the pressure cylinder 7. As the water volume in the pressure cylinder 7 increased, the gas volume decreased and its pressure increased to the target value (in this case) of 15 bar.

The pressurised cylinder 7 was allowed to remain at pressure for a period of about 2 minutes or more to allow the gases to dissolve in the water to a super-saturation point. The super-saturated water was then released from the pressure cylinder 7 into another container at ambient pressure.

The emerging super-saturated water was seen to have a ‘milky’ appearance created by the presence of micro/nano-bubbles in the stream. These persisted for a period of around 2 further minutes before their buoyancy eventually took them to the surface of the water and out into the surrounding environment. This differs significantly from the persistence of bubbles otherwise produced for aeration of water (or other aqueous solutions) which rapidly rise to the top and dissipate quickly.

After a total of approximately 5 minutes following release to the container (3 additional minutes after the nano-bubbles had dissipated), the water was tested with an oxygen concentration meter, with the following comparative results with other volumes of water as described: a. Tap water (straight from the tap and not exposed to air) - 7.71 ppm dissolved oxygen; b. Deionised water from purification system - 6.19ppm dissolved oxygen; c. Tap water (as above, but treated in Nano-bubble system) - 10.49ppm dissolved oxygen; d. Deionised water as above but processed through a mixed-gas system - 10.56ppm dissolved oxygen, where the test was carried out some 5 minutes after release from the pressurising system, and after all the micro-bubbles had dissipated by gravity to the surrounding environment.

These results suggest that a significant improvement in the dissolved oxygen content in water results from pressurisation of gases to a pressure of 15 bar, in the presence of water, and that the super-saturation persists for a considerable time. As both tests resulted in a similar resultant saturation level, it suggests that a maximum saturation at a given pressurisation level may be reached, no matter the saturation level at the start.

It is anticipated that even greater improvements in dissolution of gases may be obtained by the same method in any oxygen-depleted liquid or aqueous solution.

Example 2 - Vertical Farming

For vertical farming applications, small bubbles were seen to cling by surface energy to the roots of plants. The use of pressure to create such nano/micro bubbles also forced oxygen into super-saturated dissolution in the nutrient feed, thereby providing the growing environment with a more sustained, concentrated oxygen supply, even at the elevated temperatures which are maintained in such systems to promote better upper plant growth.

Example 3 - Water Treatment

As indicated above, as has been proven in various trial projects with bubbled oxygen at atmospheric pressure, the addition of oxygen (even in large bubble form) has improved the output and performance of the water purification operation in large waste treatment plants. However, in such trials, the majority of the oxygen is wasted to atmosphere as it rises to the surface. The benefit gained is thereby minimal relative to the volume of oxygen used.

However, where the oxygen is supplied to the water being treated in micro-bubble form in accordance with the invention, it adheres to the bacteria (which are cultivated and treasured by treatment plant operators), directly feeding them with the oxygen they need to carry out the purification process in a highly efficient manner. Furthermore, the oxygen-enriched media persists beyond the dissipation of any nano-micro bubbles to provide oxygenation to the receiving environment for a considerable time. Provision of oxygen in this type of environment can be economically achieved by either air compression or by use of electrolysis, where the oxygen addresses the water purification and the hydrogen goes to powering related technologies, fuelling delivery vehicles or to heating the premises, etc. as required.

Example 4 - Biodigestion

Oxygen super-saturated water in combination with the persistent micro/nano-bubbles in accordance with the invention satiates the bacteria (as in water treatment plants) in biodigestion installations, thereby clarifying the water in which they reside.

This allows the recirculation of the water through the system rather than having it externally treated (and replenished) at great expense. In such systems, where the methane produced is used to power electrical generators, a system which is electrolyser-based as described above can be employed if desired. In this case, the hydrogen rises within the unit to enhance the methane, while the oxygen improves the bacterial activity in the digestate and ‘ink’ above it.

Example 5 - Fish Farms

The water quality in high-concentration fish farms can become severely oxygen- depleted, leading to stress and disease in the fish stock. By deployment of a system of the invention which significantly enriches the oxygen content of the water, fish are maintained in good health and at greater concentration within the enclosed water environment whether fresh or seawater.

As in other applications, the hydrogen from an electrolyser system may be used to power other related technologies, e.g. for transportation and for heating, if desired. Example 6 - Soil-based intensive farming systems

In such systems, nutrient and oxygen-rich aqueous solutions are fed more directly to the roots of plants via in-ground supply systems. By provision of super-saturated water, such systems are more productive, and more viable in poor soils.