WATER TREATMENT METHOD FOR POOLS, SPA BATHS AND THE LIKE

This invention relates to methods and apparatus for the treatment of pools, spa baths and the like to suppress the growth of bio-organisms. More particularly, it relates to methods and apparatus for suppressing bio-organism growth by dissolving ozone into water flows.

In the operation of pools, spa baths and the like, nutrients may be present in the initial water charge and are subsequently added by airborne transportation and by lavage from the bodies and clothing of users. Bio-organisms are seeded into the water charge in the same way. Particularly where the water charge is heated, bio-organisms may grow rapidly, causing water discolouration, bio film slime on surfaces and undesirable odour. More importantly, the warm environment of heated pools, spa baths and the like may support the growth of Legionella pneumophila, the causative organism of Legionnaire's Disease. It is therefore normal practice to inhibit the growth of such bio-organisms by treating the water charge with a suitable biocidal process. Biocidal processes which have been employed include chlorination (by air injection, titration of sodium hypochlorite or electrolysis of dissolved sodium chloride); bromination (by titration of suitable bromine salts, such as potassium bromide or sodium bromide); oxygenation (by air injection, oxygen injection, ozone injection, titration of hydrogen peroxide and irradiation with ultra-violet light); or cuprification (by the titration of copper oxide or the electrolytic dispersion of copper ions from copper metal). hi the case of ozone injection, ozone kills bacteria by rupturing their cell walls, a process to which micro-organisms cannot develop immunity. Residual ozone concentrations greater than or equal to 0.4 mg/L have been shown to result in a 100% kill in two to three minutes of Pseudomonas florescens (a biofilm producer) in a biofilm, while residual concentrations of as little as 0.1 mg/L will remove 70% to 80% of the biofilm in a three-hour exposure. Studies have also shown that ozone concentrations of less than 0.1 mg/L will reduce the populations of Legionella pneumophila by 80%. Ozone injection normally occurs in the form of bubbles dispersed into a circulating water flow, hi a typical treatment system, water is drawn from a pool, spa bath or the like by a suitable pump, passed through suitable air

injection means (usually a form of venturi or inductor) in which said bubbles of ozonated air are entrained in it and then returned to the main part of the water charge of said pool, spa bath or the like. Ozone dissolved into said circulated water flow from said bubbles of ozonated air is highly reactive with biological organisms present in said water charge and exerts a lethal effect upon them. Obviously, the resultant biocidal process occurs in both water circulating in the conduits of a said treatment system and within the main part of the water charge of a said pool, spa bath or the like. Undissolved bubbles of air, containing some ozonated air, are discharged into said main water part with said circulating water flow, rise to the surface and are dissipated into the ambient air. Said ozonated air is generated by passing ambient air through suitable means in which part of the atmospheric oxygen is converted to ozone. Such ozone generating means are well known in the art, the most common operating principles being corona discharge and photo-dissociation by ultra-violet irradiation. Examples of water treatment systems in pools, spa baths and the like which incorporate ozone injection as a biocidal process are those taught by Bodenstein in US 4,752,401, Hargrove in US 4,761,838, Conrad in US 5,032,292, Leaverton et al in US 5,665,228, Martin et al in US 6,129,850, 6,372,148, 6,500,332 and 6,699,441, Garair in US 6,277,288 and 6,517,713, Barnes in US 6,405,387 and 6,723,233, and Collins in US 6,800,205. In the water treatment system taught by Bodenstein, circulating water is exposed to light from one or more ultra-violet lamps which directly converts dissolved oxygen into ozone, rendering contact means unnecessary. Ultra-sonic energy is employed to remove particles from the lamp surfaces and copper ions are electrolytically dispersed from copper electrodes to inhibit the growth of algae. While this system creates no air bubbles in the circulating water, immersed ultra-violet lamps require a level of management which renders their use impractical in domestic applications. In the system taught by Hargrove, ozonated air generated by an ozone generator is dispersed into circulating water flow, no particular provision being made for the generation of a fine dispersion, for the use of dedicated contact means or for the removal of free (undissolved) air prior to discharge of flow into the main part of the water charge of a spa bath, hi the method taught by Conrad, ozonated air from an ozone generator is dispersed into circulating water flow with particular attention being

directed towards the periodical modification of flow paths to minimise the growth of bio-organisms. No particular provision is made for the generation of a fine dispersion, for the use of dedicated contact means, or for the removal of free (undissolved) air prior to discharge of flow into the main part of the water charge of a spa, therapy pool or bath. In the system taught by Leaverton et al, ozonated air generated by an ozone generator is dispersed by a first ozone injector into a primary circulating water flow, with right angle bends being provided to break ozone bubbles into smaller bubbles. Free (undissolved) air is captured in an ozone recapturing unit and directed to a second ozone injector in a secondary circulating water flow. Apart from said right angle bends, no particular provision is made for the generation of a fine dispersion, for the use of dedicated contact means, or, notwithstanding the use of said ozone recapturing unit, the removal of residual, free (undissolved) air prior to discharge of flow into the main part of the water charge of a hydrotherapy spa. In the apparatus taught by Martin et al, ozonated air from an ozone generator is dispersed into circulating water flow through a venturi, particular attention being directed to the form of said ozone generator. No particular provision is made for the generation of a fine dispersion, for the use of dedicated contact means, or for the removal of free (undissolved) air prior to discharge of flow into the main part of the water charge of a spa or hot tub. In the method and apparatus taught by Garair, ozonated air from an ozone generator is dispersed into circulating water flow through a venturi. No particular provision is made for the generation of a fine dispersion or for the removal of free (undissolved) air prior to discharge of flow into the main part of the water charge of a swimming pool, pond or the like. Dedicated contact means are provided in the form of a simple, cylindrical tank, air bubbles being retained in said contact means simply by a downward, swirling flow. In a first form of apparatus taught by Barnes, ozonated air from an ozone generator is dispersed into a secondary circulating water flow by a venturi, provision being made to controllably aerate said water flow. Said secondary water flow is discharged into a primary circulating water flow and no particular provision is made for the generation of a fine dispersion, for the use of dedicated contact means, or for the removal of free (undissolved) air prior to discharge of flow into the main part of the water charge of a spa or hot tub. Provision is made to discharge ozonated air into conduits in their empty state for sterilisation

purposes. In a second form of apparatus taught by Barnes, ozonated air from an ozone generator is dispersed into circulating water flow through a venturi, no particular provision being made for the generation of a fine dispersion. Dedicated contact means are provided in the form of a serpentine length of conduit and free (undissolved) air is separated in an air removing column and recirculated to said ozone generator. Said air removing column is described in detail in US 6,342,154 (Barnes) and takes the form of a cylindrical, gravity separation tank which, '...separates undesirable bubbles from the water'. Obviously, without provision to discharge separated air to atmosphere, continued, uncontrolled recirculation would lead to discharge of normal and ozonated air, together with circulated water, into the main part of the water charge of a spa or hot tub. More importantly, continued recirculation of air, as proposed by this invention, would lead to a depletion of oxygen, a reduction in ozone output and a concomitant diminution in biocidal effect. Similarly, in this invention, provision is made to discharge ozonated air into conduits in their empty state for sterilisation purposes. In a method and means taught by

' Collins, ozonated air from an ozone generator is dispersed into circulating water flow through a venturi, no particular provision being made for the generation of a fine dispersion, for the use of dedicated contact means, or for the removal of free

(undissolved) air prior to discharge of flow into the main part of the water charge of a pool or spa. Provision is made to admit a regulated flow of ambient air into said flow of ozonated air. It will be appreciated that, in all of the examples cited, little effective provision is made for the generation of a fine bubble dispersion, for the use of dedicated contact means, or for the removal of free (undissolved) air prior to discharge of flow into the main part of the water charge of a pool or spa. Most accept the quality of bubble dispersion achieved at discharge with sharp conduit directional changes being employed in some cases to provide subsequent bubble breakdown by shearing effects. Dedicated contact means, where provided, take the form of a simple, cylindrical tank or serpentine conduit section. Where air separation means are provided, none is able to positively prevent the entry of free, ozonated air bubbles into the main part of the water charge of a pool or spa.

While ozone injection is a suitable biocidal process for use in the treating the water charge in a pool, spa bath or the like, it has a particular disadvantage. This is

the fact that ozone dissipated from said water charge in the form of undissolved bubbles acts to attack the materials of upholstery, coverings and some fittings, leading to their rapid embrittlement and subsequent failure. This effect is exacerbated in spa pools which are usually covered when not in use to minimise exposure of the water charge to light, which may act to promote algal growth. The first object of the present invention is therefore to provide method and apparatus which permit the use of ozone injection as a biocidal process in the treatment of water in a pool, spa bath or the like without the said deleterious effects upon the said materials. A second object of the present invention is to provide means to generate a consistent, fine bubble dispersion of ozonated air. A third object of the present invention is to provide effective contact means. A fourth object of the present invention is to provide means for the consistent removal of free (undissolved) ozonated air prior to discharge of circulating water flow into the main part of the water charge of a pool or spa.

According to the present invention, a flow of water is drawn from a pool, spa bath or the like by a suitable pump and passed through suitable air injection means in which a flow of ozonated air generated by suitable ozone generation means is dispersed into it in the form of finely divided bubbles. From said air injection means, said water flow and said entrained ozonated air bubbles pass in turbulent flow to contact means which act to extend the contact time of said ozonated air with said water, thereby promoting dissolution of ozone into said water. From said contact means, said ozonated water flow and said entrained ozonated air bubbles pass to separation means which act to strip out said ozonated air bubbles and disperse said stripped air into the ambient air well clear of said pool, spa bath or the like. Said air injection means, said contact means and said separation means all take several alternative embodiments. Provision is also optionally made to filter or heat said circulating water flow, to dose it with chemical biocide or perfume or to treat it with metal ions, or the like.

The various aspects of the present invention will be more readily understood by reference to the following description of preferred embodiments given in relation to the accompanying drawings in which:

Figure 1 is a longitudinal schematic view of a water circulation and ozonation system of conventional arrangement for a pool, spa bath or the like;

Figure 2 is a longitudinal schematic view of a first embodiment of a water circulation and ozonation system for a pool, spa bath or the like made in accordance with the present invention;

Figure 3 is a longitudinal schematic view of a second embodiment of a water circulation and ozonation system for a pool, spa bath or the like made in accordance with the present invention;

Figures 4a and 4b are, respectively, longitudinal and transverse cross- sectional views of a hydrocyclone device used to disperse ozonated air into a circulating water flow; Figures 4c, 4d and 4e are cut-away views of the device depicted at

Figures 4a and 4b showing flow paths;

Figure 5 is a side view of a multi-path contact unit used in the present invention;

Figure 6 is a longitudinal cross-sectional view of a jet ventilator-type unit used to disperse ozonated air into a circulating water flow;

Figure 7 is a longitudinal cross-sectional view of a venturi-type unit used to disperse ozonated air into a circulating water flow;

Figure 8 is a vertical schematic view of a form of contact unit used in the present invention; Figure 9b is a face view of a mixing device employed as a contact unit used in the present invention and Figures 9a and 9c are transverse cross- sectional views at right angles of the same device;

Figures 10a, 10b and 10c are fragmentary isometric, side and vertical views of mixing devices in another form of contact unit used in the present invention;

Figure 11 is a longitudinal cross-sectional view of another form of contact unit used in the present invention;

Figures 13a and 13b are, respectively, vertical and transverse cross- sectional views of a bubble separation unit used in the present invention; Figures 13c, 13d, 13e and 13f are transverse cross-sectional views of parts of coalescing plates of the unit depicted at Figures 13a and 13b;

Figure 14a is a longitudinal cross-sectional view of an alternative form

of bubble separation unit used in the present invention;

Figures 14b and 14c are, respectively, longitudinal and transverse cross-sectional views of the bubble separation unit depicted at Figure 14a;

Figure 15a is a fragmentary isometric view of separation elements of an alternative form of bubble separation unit used in the present invention;

Figure 15b is a face view of a sheet of the separation elements depicted at Figure 15a;

Figure 16 is a vertical cross-sectional view of another alternative form of bubble separation unit used in the present invention. With reference to Figure 1, a water circulation and ozonation system of conventional arrangement for a pool spa bath or the like is depicted. Said system comprises shell 1, main part of water charge 2, water outlet conduit 3, circulating pump 4, filter 5, first delivery conduit 6, air dispersion unit 7, final delivery conduit 8, air inlet conduit 9, ozone generation unit 10, ozone delivery conduit 11, control unit 12, power supply and control conductors 13 and power supply conductors 14. In operation, said circulating pump draws water from water from said shell via said outlet conduit and delivers it via said first delivery conduit to said venturi device. Said filter is situated in said first delivery conduit and is of one of the types well known in the art. In alternative embodiments, said filter is situated upstream of said circulating pump. Electrical power and control signals are supplied to said control unit via conductors 13 and said control unit supplies power to said ozone generator via conductors 14. Air enters said ozone generator via conduit 9 and ozonated air is delivered to said air dispersion unit via conduit 11, influenced by a depression generated by said air dispersion unit. Water containing dissolved ozone and entrained bubbles of ozonated air is delivered to said water charge via said final delivery conduit.

With reference to Figure 2, a water circulation and ozonation system for a pool, spa bath or the like made in accordance with the present invention is depicted. Said system comprises shell 1, main part of water charge 2, water outlet conduit 3, circulating pump 4, filter 5, first delivery conduit 6, air dispersion unit 7, second delivery conduit 15, contact unit 16, intermediate conduit 17, air separation unit 18, vent line 19, final delivery conduit 8, air inlet conduit 9, ozone generation unit 10,

ozone delivery conduit 11, control unit 12, power supply and control conductors 13 and power supply conductors 14. In operation, said circulating pump draws water from said shell via said water outlet conduit and delivers it via said first delivery conduit to said air dispersion unit. Said filter is situated in said first delivery conduit and is of one of the types well known in the art. Electrical power and control signals are supplied to said control unit via conductors 13 and said control unit supplies power to said ozone generator via conductors 14. Air enters said ozone generator via conduit 9 and a flow of ozonated air is delivered to said air dispersion unit via conduit 11, influenced by a depression generated by said air dispersion unit, and is entrained in said water flow in the form of finely-divided bubbles. Water containing dissolved ozone and entrained bubbles of ozonated air is delivered via said second delivery conduit to said contact unit where further dissolution of said ozone into said water flow takes place. From said contact unit, said water containing dissolved ozone and entrained bubbles of ozonated air is delivered via said intermediate conduit to said air separation unit, in which free, undissolved air bubbles are stripped out, the separated gaseous components being vented off through said vent line. From said air separation unit, said water flow passes via said final delivery conduit to said water charge. In the preferred embodiment, said vent line is made sufficiently long to carry said vented ozonated air well clear of said pool, spa bath or the like and optionally discharges into a wall, sub-floor or ceiling space. Air entering said ozone generator via conduit 9 is cleaned by suitable filtration means (not shown) to minimise fouling of components of said ozone generation unit. Operation of said ozone generator is optionally manually controlled or is controlled automatically through said control unit by a preset timing device (not shown), by reference to a dissolved oxygen sensor (not shown) preferably positioned in outlet conduit 3, or by any combination of these control means.

With reference to Figure 3, a modified form of the water circulation and ozonation system for a pool, spa bath of Figure 2 is depicted. Said system comprises shell 1, main part of water charge 2, water outlet conduit 3, circulating pump 4, filter 5, final delivery conduit 8, first delivery conduit 6, air dispersion unit 7, second delivery conduit 15, contact unit 16, intermediate conduit 17, air separation unit 18, vent line 19, recirculation conduit 20, final delivery conduit 8, air inlet conduit 9,

ozone generation unit 10, ozone delivery conduit 11, control unit 12, power supply and control conductors 13 and power supply conductors 14. In operation, said circulating pump draws a supply of water from said shell via said water outlet conduit and delivers it via said filter and said final delivery conduit back to said water charge. Simultaneously, a flow of water is tapped off said final delivery conduit immediately upstream of said filter and passes via first delivery conduit 6 to said air dispersion unit. A suitable restriction is provided, as required, at said take-off point to said filter to ensure that the desired volume of flow is achieved through first delivery conduit 6. hi the preferred embodiment, said filter is situated downstream of said pump and is of one of the types well known in the art. hi an alternative embodiment, said filter is situated upstream of said pump. Electrical power and control signals are supplied to said control unit via conductors 13 and said control unit supplies power to said ozone generator via conductors 14. Air enters said ozone generator via conduit 9 and a flow of ozonated air is delivered to said air dispersion unit via conduit 11, influenced by a depression generated by said air dispersion unit, and is entrained in said water flow in the form of finely-divided bubbles. Water containing dissolved ozone and entrained bubbles of ozonated air is delivered via second delivery conduit 15 to said contact unit where further dissolution of said ozone into said water flow takes place. From said contact unit, said water containing dissolved ozone and entrained bubbles of ozonated air is delivered via intermediate conduit 17 to said air separation unit, in which free, undissolved air bubbles are stripped out, the separated gaseous components being vented off through said vent line. From said air separation unit, said water flow passes via recirculation conduit 20 to a point in said outlet conduit adjacent said shell. In the preferred embodiment, said vent line is made sufficiently long to carry said vented ozonated air well clear of said pool, spa bath or the like and optionally discharges into a wall, sub-floor or ceiling space. Air entering said ozone generator via conduit 9 is cleaned by suitable filtration means (not shown) to minimise fouling of components of said ozone generation unit. Operation of said ozone generator is optionally manually controlled or is controlled automatically through said control unit by a pre-set timing device (not shown), by reference to a dissolved oxygen sensor (not shown) preferably positioned in outlet conduit 3, or by any combination of these control means, hi this embodiment, the flow of circulating water tapped off said final

delivery conduit and circulated via said air dispersion unit, contact unit, air separation unit and recirculation conduit is controlled in the range of 10% to 50% of the total flow generated by said circulating pump.

With further reference to Figure 3, diversion of part of the circulating water flow and its separate ozonation allows the provision of an extended residence time in said contact unit and permits the use of an embodiment of said contact unit with a smaller working capacity. In an alternative embodiment, a suitable valve (not shown) is provided in first delivery conduit 6 adjacent its said tapping off point, said valve being employed to cut off said diverted part of said circulating water flow. Obviously, said water circulation and ozonation system may also optionally incorporate chlorination, heating, electro-separation, perfuming, dispersion of metal ions or other forms of water treatment which are well known in the art.

With reference to Figures 4a to 4e, in one embodiment, said air dispersion unit takes the form of a hydrocyclone-type bubble generator generally of the form as taught by Ohnari in US 6,382,601. hi this embodiment, circular accommodation cylinder 23 formed in base 25 communicates with covered inverted conical cylinder 22. Water inlet duct 30 discharges tangentially into said accommodation cylinder through port 31, a flow of water being supplied to said inlet duct through fitting 24. Air inlet port 21 positioned on the axis of said conical cylinder and passing through its closure 48 is connected to said ozone generator via conduit 11 (as depicted in Figures 2 and 3) and communicates suction generated by said bubble generator. Lateral discharge ports 27, 28, 29, 46 pass radially outwards from central reflux port 32 and discharge through fittings 26, 33, 34. The arrows 38, 40 indicate a swirling, ascending liquid flow; the arrows 39 and 42 indicate a swirling, descending liquid flow; 41 is a swirling cavity under negative pressure; 43, 44, 45 indicate a gas vortex flow; and 47 indicates a cut-off sector, hi operation, the flow of water from said inlet duct enters said accommodation cylinder tangentially, generating said swirling, ascending liquid flow within the outer part of the interior of conical cylinder 22. When said swirling, ascending liquid flow reaches the upper end of said conical cylinder, it flows inwardly as indicated by arrow 35 and begins to descend while swirling. Descending vortex flow 37 formed within said swirling descending liquid flow draws in air through air inlet port 21 and entrains it in the form of small bubbles,

said vortex flow reducing in diameter and rapidly accelerating in rotational speed as it descends towards and enters said central reflux port under negative pressure. A difference in swirling velocity occurs between that of swirling cavity 41 and horizontal gas vortex flow 45, resulting in said vortex flow being forcibly cut off at point 44, thereby generating a stream of micro bubbles which are discharged entrained in said water flow through discharge port 46. The arrow 36 indicates a dissolving gas component. Where only a single discharge port is required, discharge ports 27, 28, 29 are deleted. The complete text of US 6,382,601 is incorporated herein by way of reference. With reference to Figure 6, in an alternative embodiment, said air dispersion unit takes the form of a jet regulator-type unit generally of the form as taught by Flieger in US 6,588,682. In this embodiment, said air dispersion unit is accommodated within bosses 57, 58 formed on the ends, respectively, of conduits 51, 52, said bosses being joined by male threaded part 61 of boss 58 being screwed into complementary female threaded part 65 of boss 57. Perforated plates 49, 50, each having apertures staggered in relation to the other are accommodated within collar 60.

Concentric, terraced partitions 62 joined by thin, radially-arranged webs 63 are installed as a block, captured between gasket 64 seated against a shoulder in boss 58 and collar 60. Said perforated plates are captured between a flange of collar 60 and gasket 59 seated against a shoulder in boss 57. Air shroud 53 surrounding said terraced partitions is fixed to said concentric, terraced partitions by the outermost said radially arranged webs, a plurality of suitable apertures 54 permitting ingress of air from plenum chamber 56 into the interior of said air shroud. A flow of air is admitted to said plenum chamber via inlet duct 55. hi operation, a flow of water through conduit 51 is emitted in the form of discrete jets from said apertures in perforated plate 50. The energy of said jets induces a flow of air inwards through apertures 54 to be entrained with said water flow. Said jets discharge over said concentric, terraced partitions, thereby being split, broken up and thoroughly mixed with said induced air flow. Said aerated water flow passes along the parallel annular spaces between the downstream parts of said concentric, terraced partitions and discharged into conduit

52 in the form of a coherent stream. The complete text of US 6,588,682 is incorporated herein by way of reference.

With reference to Figure 7, in an alternative embodiment, said air dispersion unit takes the form of a venturi-type unit. In this embodiment, venturi 69 is formed between bodies 70, 71, the mating faces of said bodies being formed such that, when they abut, concentric plenum 72 is formed between them with narrow air slot 73 passing inwardly from said plenum into the throat of said venturi. Said bodies are secured together by a plurality of suitable fastenings (positions indicated in broken line 76) passing through their flanges 77, 78. Inlet duct 11 permits a flow of ozonated air into said plenum. Spigots 74, 75 are provided, respectively, on bodies 70, 71 for attachment of conduits 6, 15. In operation, a flow of water passing through said venturi induces a depression at its throat. Said depression induces a flow of air in through inlet duct 11 and via plenum 72 and air slot 73. Said flow of air is discharged from said air slot into said water flow in the form of a thin sheet which is subjected to intense shearing, said shearing acting to disperse and entrain said air into said water flow in the form of fine, well mixed bubbles. In all said embodiments, if required, one or more separate drive pumps are employed to provide a more energetic flow of water through said air dispersion unit than that provided by said circulating pump.

With reference to Figure 5, to promote thorough dissolution of ozone from said ozonated air in said circulating water flow, said flow of aerated water from said air dispersion units is directed to a suitable contact unit. In one embodiment, said contact unit takes the form of a plurality of contact ducts preferably combined with a venturi-type air dispersion unit. In this embodiment, a flow of water from conduit 6 passes via venturi unit 7, where it is aerated by a flow of ozonated air entering via inlet duct 11. From said venturi unit, said water flow passes to plenum 66 and thence to contact ducts 67. In the preferred embodiment, said contact ducts range in number from one to five and are spirally arranged to reduce the overall length of said contact unit and promote mixing. From said contact ducts, said water flow passes via plenum 68 to conduit 15. The combined capacity of said contact ducts is made such that the velocity of flow of said water through them is reduced and its residence time commensurately increased. Obviously, said air dispersion unit associated with this embodiment may be situated anywhere upstream of said contact unit.

With reference to Figure 8, in an alternative embodiment, said contact unit

takes the form of a canister 79 of suitable capacity filled with spheres 80 of a suitable diameter. Said spheres are made from a suitable material and rest upon a supporting floor 81 made from a suitable sheet material pierced by narrow, closely-spaced slots which are not effectively obstructed by said spheres, hi an alternative embodiment, said supporting floor is made from a stiff wire mesh material. In operation, a flow of aerated water from air dispersion unit 7 passes via conduit 15 to the region beneath said supporting floor and thence through said floor into said canister. Said water flows upwardly through said canister through the interstices between said spheres, its flow velocity being reduced and its residence time being increased, while mixing and pressure changes so generated promote dissolution of said ozone. Passing to the apex of the conical roof 82 of said canister, said flow of water exits via water outlet conduit 83 carrying with it any free, undissolved air bubbles. In the present invention, said flow of water then passes to a bubble separation unit (not shown) in which said free, undissolved air bubbles are removed. With reference to Figures 9a, 9b and 9c, in an alternative embodiment, said contact unit takes the form of canister 92 of suitable capacity containing a plurality of stacked static mixer arrays, generally of the form taught by Berner et al in US 5,489,153. Said static mixer arrays comprise square or rectangular grids, built up from interconnected supporting elements 84, 85 of a suitable thin, flat strip material arranged perpendicularly to one another. Deflection elements 86 are fixed to said supporting elements and act to deflect axial fluid flow 87 through canister 92 into opposing cross flows 88, 89, localised vortices 90 and streaming vortices 91. In the preferred embodiment, said deflection elements of alternate said stacked mixer arrays are arranged such that said cross flows, localised vortices and streaming vortices of one array work in the opposite sense to those of the immediately preceding (upstream) array. Said embodiment acts to reduce flow velocity and increase residence time, while the mixing and pressure changes so generated act to promote dissolution of said ozone. The complete text of US 5,489,153 is incorporated herein by way of reference. With reference to Figures 10a, 10b and 10c, in an alternative embodiment, said contact unit takes the form of a vessel of suitable capacity (not shown) containing a plurality of static mixer elements, generally of the form taught by Davis et al in US

5,971,603. This embodiment is somewhat similar in form to that described in relation to Figure 8, excepting that said spheres are replaced by suitable elongated baffles 93 arranged such that their longitudinal axes are more or less normal to the direction of flow, the arrangement of baffles in each row being more or less normal to that of baffles in adjacent rows. Said baffles are of a teardrop cross-sectional shape, with a narrow part 95 orientated upstream (relative to flow direction) and a broad, rounded part 96 orientated downstream, such that, in their assembled form, they define flow pathways 94 converging at the angle α which promote elongation and dispersive mixing of flow. Said embodiment acts to reduce flow velocity and increase residence time, while the mixing and pressure changes so generated act to promote dissolution of said ozone. The complete text of US 5,971,603 is incorporated herein by way of reference.

With reference to Figure 11, in an alternative embodiment, said contact unit takes the form of a static mixer comprising one or more tubular ducts 97 of suitable capacity and circular cross-sectional shape, the ends of said ducts being closed by plugs 99 incorporating inlet 100 and outlet 101 fittings. Accommodated within said tubular ducts are spiral mixing elements 98 made by twisting long strips of a suitable, thin, more or less rigid material. The edges of said mixing elements make a close fit with the inner wall surfaces of said tubular ducts and the pitch of their said spiral forms is such as to provide maximum rotation of flow without material flow impedance. Said embodiment acts to reduce flow velocity and increase residence time, while the mixing and pressure changes so generated act to promote dissolution of said ozone.

With reference to Figure 12, after passing through said contact unit, said flow of aerated water is directed to a suitable air separation unit in which free, undissolved air bubbles are removed. In one embodiment, said air separation unit takes the form of a canister 104 of suitable capacity in which are accommodated a plurality of stacked, conical coalescer plates 102, 103. Said coalescer plates are made from a suitable thin sheet material and, in the preferred embodiment, are provided with downwardly-directed dimples to generate turbulence in the flow over their surfaces.

The angle at the apex of a said coalescer plate varies in the range 100° to 160° and said plates are supported in their regular spatial relationship by two or more axially-

arranged supporting posts (not shown) passing upwardly through said plates and fixed to either or both of conical roof 115 and floor 108 of said canister. Flow deflector body 109 is provided fixed to floor 108, water inlet conduit 105 enters said canister at its base and water outlet conduit 107 exits said canister at a point on its side wall a suitable distance below said conical roof. Deflector coalescer plates 102 make a close fit with the inner side wall surfaces of said canister and have a relatively large central aperture (as indicated in broken line 111). Collector coalescer plates 103, interleaved with said deflector coalescer plates, have a substantial annular opening 122 between their outer edges and the inner side wall surfaces of said canister and are provided with small bubble release apertures 110 at their apices. Bubble duct 112 is fixed to the apex of the uppermost said collector coalescer plate and inverted conical shield 113 is fixed to the upper end of said bubble duct. Float 117 is fixed to the free end of arm 118 which is, in turn, pivotally supported at pivot 119 fixed to said conical roof. Needle valve 116 (shown schematically) is pivotally supported on said arm and, when said float is raised by an elevated water level, acts to close the outlet of air release conduit 106. One or more drainage apertures 114 are provided at the base of said inverted conical shield adjacent said bubble duct, hi alternative embodiments, said needle valve is replaced by any other form of valve capable of being operated by a float, said valves being well known in the art. hi operation, water enters said canister through water inlet conduit 105, flows up over flow deflector body 109 and follows the general flow path indicated by arrows 120, 121, passing up under deflector coalescer plates 102 to central apertures 111, thence downwardly under collector coalescer plates 103 to annular openings 122 and so on. During the passage of said water flow between said coalescer plates, free bubbles tend to separate out onto the under surfaces of said coalescer plates where they combine or coalesce to form larger bubbles. Said coalesced bubbles rising to the edges of central apertures 111 or to bubble release apertures 110 then rise upwardly through successive bubble release apertures and thence via bubble duct 112 to accumulate in the apex of conical roof 115. When sufficient air has accumulated under said conical roof, said float drops and said needle valve is opened, thereby permitting said collected air to exit via air release conduit 106. As air exits in the manner described, the level of water in said canister rises above water outlet conduit 107 and said float commences to rise until

the opening of said air release conduit is closed by needle valve 116. When sufficient air has again accumulated, said float again drops, thereby releasing further air through said air release conduit, and so on. Inverted conical shield 113 protects said float, needle valve and arm from water turbulence. Drainage apertures 114 are provided in said inverted conical shield to permit water to drain from said shield as said water level drops at a time when said bubble duct is obstructed by a continuous, upwardly flowing stream of air bubbles. Said embodiment of air separation unit is effective in the removal of free, undissolved air bubbles from said water flow while providing minimal impedance to flow. With reference to Figures 13a, 13b, 13c, 13d, 13e and 13f, in an alternative embodiment, said air separation unit takes the form of a canister 123, 123a of suitable capacity in which are accommodated a plurality of stacked, parallel coalescer plates 124. Said coalescer plates are made from a suitable thin sheet material and, in the preferred embodiment, are provided with downwardly-directed dimples to generate turbulence in the flow over their surfaces. The longitudinal axes of said coalescer plates are inclined at an angle which, in alternative embodiments, varies in the range 10° to 40° and said plates are supported in their regular spatial relationship by two or more axially-arranged supporting posts (not shown) passing upwardly through said plates and fixed to either or both of inclined roof 125 and inclined floor 126 of said canister. Said canister is supported on flat floor 127. Said coalescer plates are made with a cross-sectional shape in the form of an inverted shallow V with a longitudinal medial ridge 132, their side edges making a close fit with the inner side wall surfaces of said canister. Said inverted V form of said coalescer plates is shallowest at their lower ends (as depicted in Figure 13c, being a section on A-A), less shallow centrally (as depicted in Figure 13 d, being a section on B-B), and less shallow again at then- upper ends (as depicted in Figure 13e, being a section on C-C). A bubble guide 128, in the form of a narrow, inverted U-shaped channel, is provided at the upper end of each said coalescer plate, positioned on its centreline and extending outwardly beyond the upper edges 131 of said coalescer plate to project through suitable apertures 130 provided in flow partition 129. hi an alternative embodiment, said bubble guides are made tubular. The edges of said flow partition are fixed to said inclined floor, the sides and said inclined roof of said canister, said flow partition being orientated

parallel to the end wall 123a of said canister, thereby effectively creating vertical bubble duct 135 between it and said end wall. In the preferred embodiment said flow partition is provided at its upper end with an angled part 133 to create air collection chamber 134. A substantial aperture is provided between the upper edges 131 of said coalescer plates and said flow partition, thereby effectively creating vertical water exit duct 136. A substantial aperture is provided between the lower edges 137 of said coalescer plates and said end wall of said canister, thereby creating vertical water inlet duct 138. Water inlet conduit 139 enters said canister at its base and water outlet conduit 141 exits said canister at a point on its side wall a suitable distance below said inclined roof. The inner end of said water inlet conduit is provided with a curved part 140 which directs flow upwardly into vertical water inlet duct 138. Float 142 is fixed to the free end of arm 143 which is, in turn, pivotally supported at pivot 144 fixed to flow partition angled part 133. Needle valve 145 (shown schematically) is pivotally supported on said arm and, when said float is raised by an elevated water level, acts to close the outlet of air release conduit 146. In alternative embodiments, said needle valve is replaced by any other form of valve capable of being operated by a float, said valves being well known in the art. In operation, water enters said canister through water inlet conduit 139, 140, flowing up vertical water inlet duct 138 and following the general flow path indicated by arrows 147, passing between coalescer plates 124 and thence to vertical water exit duct 136 following the general flow path indicated by arrows 148, 149. During the passage of said water flow between said coalescer plates, free air bubbles tend to separate out onto the under surfaces of said coalescer plates where they combine or coalesce to form larger bubbles which migrate inwardly to collect at the longitudinal medial ridges 132 of said coalescer plates. Said coalesced bubbles then migrate upwardly along said medial ridges of said coalescer plates to bubble guides 128 which carry them through said apertures in said flow partition whence they are released to rise upwardly through bubble duct 135 to collect in air collection chamber 134. When sufficient air has accumulated under said inclined roof, said float drops and said needle valve is opened, thereby permitting said collected air to exit via air release conduit 146. As air exits in the manner described, the level of water in said canister rises above water outlet conduit 141 and said float commences to rise until the opening of said air release conduit is closed by needle

valve 145. When sufficient air has again accumulated, said float again drops, thereby releasing further air through said air release conduit, and so on. Said embodiment of air separation unit is effective in the removal of free, undissolved air bubbles from said water flow while providing minimal impedance to flow. With reference to Figures 14a, 14b and 14c, in an alternative embodiment, said air separation unit takes the form of a long, free- vortex hydrocyclone, generally of the form taught by Tuszko et al in US 6,071,424. Said hydrocyclone comprises basically cylindrical upper part 150 and conical part 151, the combined lengths of which are approximately five times the diameter of said cylindrical part. Said upper cylindrical part is closed at its upper end by partition 169 and incorporates axially- positioned overflow duct 154, which passes through said partition, and tangentially arranged inlet duct 153, which discharges into said cylindrical part through a discharge port (depicted as 166 in Figures 14b and 14c) immediately beneath said partition. Said hydrocyclone also comprises underflow duct 152 made contiguous with the small end said conical part and vortex bed 155 positioned towards the lower end of said conical part. Said vortex bed is made from a suitable material, is circular in plan form and is optionally made flat, conical, hemispherical or in other suitable form. Said vortex bed has a diameter of approximately one third of that of said conical part at its location and is secured in position within said conical part by one or more narrow wings or struts 156 passing from said vortex bed to the inner surfaces of said conical section. With particular reference to Figures 14b and 14c, in an alternative embodiment, inlet duct 170 is approximately volute in plan form and converges in cross-section towards discharge port 166. Said inlet duct and said cylindrical upper part are closed by a single cover plate 164. Fixed to said cover plate is sleeve mounting flange 163 which supports axially-located cylindrical sleeve 162, the diameter of said sleeve being such as to not obstruct flow in through discharge port 166. Said cylindrical sleeve extends downwardly into said upper cylindrical part to a point a suitable distance below discharge port 166 and supports at its upper end vortex finder mounting flange 159. Captured between said vortex finder mounting flange and closure plate 158 is vortex finder flange 161 which supports axially- located vortex finder 160. Said vortex finder is made with a small internal diameter, in the range 5 to 20 per cent of the internal diameter of said upper cylindrical part and

extends downwardly into said cylindrical sleeve to a point approximately level with the lower edge of said discharge port. Overflow duct 154 is provided in closure plate 158. The embodiment described provides the advantages of interchangeability between said cylindrical sleeve and said vortex finder with others of different lengths and diameters. An inlet conduit (not shown) is connected to inlet flange 165. In a preferred embodiment, moulded liner 167 defines the internal shaping and dimensions of inlet duct 170 and said cylindrical upper part. Said moulded liner is replaceable simply by removing cover plate 164. Said cylindrical upper part is fixed to a separately made said conical part at flange 168, said conical part optionally having a similarly replaceable moulded liner (not shown). In operation, water flow into said cylindrical upper part through discharge port 166 generates and maintains a vortex within said unit, forces generated by said vortex leading to rapid migration of free gas bubbles to the core of said vortex and the establishment of an air column 157 extending more or less throughout the length of said core. Said air column, stabilised at its lower end by the presence of vortex bed 155, extends upwardly to vortex finder 160 through which air from said air column is free to vent as it is generated. Said embodiment of air separation unit is effective in the removal of free, undissolved air bubbles from said water flow while providing minimal impedance to flow. The complete text of US 6,071,424 is incorporated herein by way of reference. With reference to Figures 15a and 15b, in an alternative embodiment, said air separation unit takes the form of a canister of suitable capacity (not shown) in which are accommodated stacked sheets of moulded coalescing elements generally of the form taught by Pelton et al in US 5,762,810. In this embodiment, said sheets of coalescing elements are moulded from a suitable material and made with a vertical depth in the range 10 millimetres to 25 millimetres. Said sheets of coalescing elements are of an identical, grid-like formation, their horizontal parts incorporating a plurality of uniformly-spaced openings or perforations 171, said openings or perforations coinciding with the identical perforations of said sheets of coalescing elements stacked above and below. The upper and lower edges of the vertical parts of said sheets of coalescing elements are cut away to create a plurality of recesses or indentations 175, 176 symmetrically adjacent said openings or perforations. Said recesses or indentations are made more or less semi-circular such that, when said

sheets of coalescing elements are stacked, circular openings are created permitting a horizontal flow of water between said sheets. In their said stacked configuration, said sheets of coalescing elements are supported one from another by the abutment of small horizontal surfaces 173, 174. When said sheets of coalescing elements are accommodated within said canister, their side edge surfaces 172 make a close fit with the inner side wall surfaces of said canister. Suitable flow distribution and collection spaces (not shown) are provided between end edge surfaces 177 of said sheets of coalescing elements and the inner end wall surfaces of said canister. In operation, water enters said canister through a water inlet conduit (not shown), is distributed throughout said flow distribution space, passes across said stacked sheets of coalescing elements in horizontal flow via said circular openings, and thence collects in said flow collection space and exits via a water outlet conduit (not shown). During said passage of said water flow between said stacked sheets of coalescing elements, free air bubbles tend to separate out and attach themselves to said coalescing elements where they combine or coalesce to form larger bubbles which migrate upwardly through openings or perforations 171 to accumulate at the uppermost part of said canister. In the preferred embodiment, said canister is made with a conical or pyramidical roof (not shown) which is provided with a float-operated valve (not shown) of the type described in relation to Figure 16 employed to release air accumulated beneath said roof into an air release conduit (not shown). Said embodiment of air separation unit is effective in the removal of free, undissolved air bubbles from said water flow while providing minimal impedance to flow. The complete text of US 5,762,810 is incorporated herein by way of reference.

With reference to Figure 16, in an alternative embodiment, said air separation unit takes the form of a canister 178 of suitable capacity in which is accommodated one or more suitable filtration elements 186. Said filtration elements are preferably pleated to provide increased surface area and are made from filter media having a suitable pore size and low surface energy characteristics. Said filtration elements are enclosed in a forarninous casing 185 which incorporates upper cap 188 and lower cap 187. Said canister is provided with filter support 181 fixed to its floor 179 and side walls, suitable apertures 182 being provided in said filter support to permit a flow of water into the interior of said filter. The upper surface of said filter support is

provided with locating shoulder 184 to accurately locate said lower cap and groove 183 to accommodate a suitable seal (not shown) which seals said filter support to said lower cap. The upper opening of said canister is closed by cover 200 which is secured in place on flange 204 by a plurality of suitable fastenings (positions indicated in broken line 191), a suitable gasket 190 being provided between said cover and said flange. Locating shoulder 192 is provided on said cover to accurately locate said upper cap and groove 189 to accommodate a suitable seal (not shown) which seals said cover to said upper cap. Water inlet conduit 198 enters said canister at its base and water outlet conduit 199 exits said canister at a point on its side wall a suitable distance below said cover. Float 194 is fixed to the free end of arm 195 which is, in turn, pivotally supported at pivot 196 fixed to air collection chamber 180. Said air collection chamber takes the form of an inverted cone formed on the upper surface of said cover. Needle valve 197 (shown schematically) is pivotally supported on said arm and, when said float is raised by an elevated water level, acts to close the outlet of air release conduit 193. In alternative embodiments, said needle valve is replaced by any other form of valve capable of being operated by a float, said valves being well known in the art. hi operation, water enters said canister through water inlet conduit 198, flows up through apertures 182 in said filter support and follows the general flow path indicated by arrows 201, 202, 203, passing outwardly through said filter and thence via annular water collection chamber 205 to water outlet conduit 199. During the passage of said water flow through said filter, free air bubbles are captured on the inner surfaces of said filter elements and combine or coalesce to form larger bubbles which migrate upwardly to accumulate in said air collection chamber. When sufficient air has accumulated in said air collection chamber, said float drops and said needle valve is opened, thereby permitting said accumulated air to exit via air release conduit 193. As air exits in the manner described, the level of water in said canister rises above water outlet conduit 199 and said float commences to rise until the opening of said air release conduit is closed again by needle valve 197. When sufficient air has again accumulated, said float again drops, thereby releasing further air through said air release conduit, and so on. Said embodiment of air separation unit is effective in the removal of free, undissolved air bubbles from said water flow while providing minimal impedance to flow.