GB2356860A

GB2356860A - Flotation system for purifying a liquid

Info

Publication number: GB2356860A
Application number: GB0019939A
Authority: GB
Inventors: Peter Inatius Swan; Richard Pierpont Moore
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-08-16
Filing date: 2000-08-15
Publication date: 2001-06-06
Anticipated expiration: 2020-08-15
Also published as: GB0019939D0; GB2356860B

Abstract

A method of purifying a liquid by dissolved air flotation (DAF) in which a liquid, saturated with dissolved air under pressure is released directly into the liquid to be treated vis at least one injection nozzle 4, in which the degree of opening of the nozzle 4 may be remotely varied, thereby providing the facility to remotely adjust the pressure of the air solutionised liquid. Also disclosed is means to combine flotation and filtration wherein the impurities in the water rise to the surface of the liquid due to the flotation process, and the liquid flows over the top 35 of a division wall into a body of liquid 33 above the top 9 of a filter bed. The liquid may then pass through the filter bed 2 into a filter distribution and collecting system 3. A coagulant may be used. A method of removing the accumulated float from dissolved air purification systems by using wipers is also claimed.

Description

2356860 FLOTATION SYSTEM and ELEMENTS RELATIVE THERETO.

This invention relates to the system of removing impurities from a liquid by first causing them to be carded to its surface on fine gas bubbles and known as "DAF" or "dissolved air flotation" so named on account of the means to produce the fine gas bubbles that involves dissolving or solutionising the gas under pressure prior to its introduction and release into the liquid to be processed.

The invention specifically relates to different steps in the process including the means to dissolve the air into the pressurised liquid, the means to release the pressurised air saturated liquid into the liquid to be processed, the different means to remove the floated material and the means to connect a dissolved air flotation stage with a specific type of rapid gravity filter.

Referring first to the means to introduce the gas into the liquid; systems to effect this include the abstraction and pressurisation of a percentage of the liquid to be processed, the introduction of gas under pressure to the said percentage, its solutionising in a solutionising chamber and its return and release into the main body of the liquid.

The solutionising pressure chamber, in this instance according to this aspect of the invention, would be an elongated vertical cylindrical container with pressurised re-circulating liquid entering at the top and activating an eductor system that induces or assists the induction or aspiration of air into the center of an annular incoming jet that carries the aspirating air as well as air above the liquid, into the body of liquid in the container the level of which is maintained at the point for maximum induction, the system thus providing maximum contact between water and air under pressure to assist the dissolving action, recirculating and mixing both within the container before the saturated dissolved air liquid exits from the base of the container..

A major aspect of the invention relates to the means whereby a dissolved air flotation system is linked with a specific type of rapid gravity filter, namely a downflow rapid gravity filter in which the filter bed is located at a relatively high level, employs a relatively low backwash rate, has a controlled normal operating water level just below the crest level of the expended washwater receiving channel which channel extends across the whole of one side of the filter bed and may be common to adjoining filters since it is open and its outlet flow unisolated as is the case with Moore Airlift Rapid Gravity Filters with their typical structures such as an inlet channel on one side of the filter bed and a waste or expended backwash water channel on the opposite side of the filter bed separated there from by retaining walls again with a relatively shallow closely controlled normal operating liquid level a few centimetres below the crest of the expended washwater outlet, the normal operating water level being raised to backwash and employing the special filter washing techniques of Moore Filters which are ideally adapted to accommodate an adjoining DAF" stage.

The invention provides for the linking of a specific design of filtration stage with a dissolved air flotation stage in which the actual flotation stage occurs in a primary channel adjacent to the filter bed with a common operating liquid level above the devision wall so that floated material from the flotation stage accumulates on the surface of the liquid and the effluent from the flotation stage flows over the devision wall in to the liquid above the filter bed that comprises particulate material suitable to remove filterable impurities that may remain in the effluent from the flotation stage. After passing downwards through the filtration stage the filtrate is collected by the underbed collection distribution system of the filter and delivered therefrorn via outlet control to storage or use.

1 L) Removal of both floated material and expended backwashing liquid is effected into the waste channel adjoining the filter compartment located on the opposite side of the filter compartment to the flotation channel. In both cases the said channels extend across the full width of the adjoining filter compartment so that inflow to the flotation channel whilst removing floated material or backwashing the filter creates a cross current assisting the said operations.

Because operating liquid level above the fitter bed is maintained just below the crest of the waste channel. This facilitates floated material or scum removal that may be required more frequently than filter backwashjng. It also facilitates and speeds up the backwashing process as will be shown later.

Regarding the removal of scum the invention includes a number of systems depending on operating conditions It is possible on account of the closeness of the operating water level to the crest of the waste channel that build up of floated material will cause it to automatically discharge over the crest.

Or discharge may be effected by periodically raising the water level; this may be automated by, for instance, suitable control of the filter outlet valve.

The movement of scum may be impeded by a tendency to adhere to the side walls and the invention includes means to break the adherence periodically as required.

The invention also includes mechanically motivated scum wiping means.

According to this aspect of the invention, a floating material removal system includes a flexible, scum wiping blade that transverses the width of the structure, is carried by a trolley system mounted on wheels, resting on opposite sides of the surround of the flotation structure, is guided by wheels or skids bearing against the side walls of the structure and is caused to reciprocate across the surface of the liquid and wipe the floated material into a receiving trough or channel; the wiper blade is mounted on a swivelling member that spans the structure, with bearing means whereby single central rope drive means from a central arm on the swivelling member, with stops that limit the swivelling action, causes the said member to rotate or swivel so that when travelling towards the scum removal trough, the blade engages the scum and when moving away from the trough, the blade is lifted above the scum by reverse pull of the rope drive As mentioned, the invention requires the top or normal operating water level above the filter to be accurately controlled, regardless of the build up of float and the invention includes means to do so accurately, utilising a Moore Diaphragm Valve or other specialist valve, controlling the filter outlet and paced by the filter top water level.

Since the filter top water level may have float build up interfering with top water level sensing, means to overcome this problem includes the provision of a separate float chamber with level communicating conduit to reflect the water level and the water level transmitted via a float with its vertical stem threading a liquid retaining tube piercing the floor of the float chamber to motivate a pilot valve controlling the Moore Diaphragm valve below or other means to pace the filter outlet valve in accordance with the required operating water level.

Incoming liquid to be treated is delivered evenly across the bottom of the flotation channel where the said liquid is subjected to admixture with a percentage of air saturated liquid that on release creates a bloom of minute bubbles to effectively perform the flotation function. of ensnaring coagulated impurities and carrying these to the surface of the liquid..

The entrance to the flotation channel may take alternative forms but in all cases the incoming liquid to be processed, either enters or is directed initially to the bottom of the flotation channel where it has been or is about to be subjected to admixture with the percentage recirculated air saturated liquid.

The flotation process is dependent on the liquid to be processed having been dosed with a coagulant and the impurities in the liquid being captured by flocculent particles; preferably this occurs prior to the entry of the liquid into the flotation channel but the invention also provides for conditioning to occur in the actual flotation channel based on the prior administration of a quick acting coagulant and the provision of mixing or conditioning vanes in the flotation channel the depth and volume of which could be increased.

In this regard Moore Airlift Filters with washwater storage below the filter bed lend themselves structurally to such a channel see Fig 4.

Fig 4 also shows media loss prevention means (45) a very important aspect in efficient filter backwashing and one that has received previous attention S.A.

patent No.82770 and U.S. patent No.4,478,726 (Moore) who also originated the provision of a sloping approach to the washwater outlet crest 12 now enhanced.

# -6 J1 The filter of the invention is equipped with means to effect backwashing of the filter bed including an underbed distribution system that includes means to evenly distribute air agitation of the filter bed, the necessary compressors or blowers, washwater motivation means, valves, piping and controls and may also use the special backwashing techniques applicable to Moore filter patents.

For example In a preferred design of the filter this would embody the process described in South African Patent No.9318195 whereby the backwash water supply is housed in a common compartment spanning a bank of filters and the backwash flow is motivated therefrom by displacement with compressed air which may utilise the same blower that effects filter bed agitation.

In other words the filter of the invention has the facilities to periodically cleanse the filter bed of collected impurities as required.

The special design of the washwater weir wall with an inclined section preceding the crest of the weir sill has been enhanced by the thickening of the rear of the wall and the top thereof to provide an increased width of slope and media loss prevention characteristic enabling special air water wash combination techniques.and the operating liquid depth above the filter applicable to the specialized flotation filter of the invention.

Coming to a very important aspect of the invention and of the flotation process generally, namely, the method of releasing pressurised dissolved air liquid into the body of liquid to be subject to flotation It is recognised that a shearing action at the point of release is advantageous and that the sizing of the release aperture is critical in maintaining pressure and in releasing the correct amount of dissolved air liquid.

To this end it is advantageous to provide control and adjustment of the said aperture.

Further in order to spread the effectiveness of introducing the pressurised dissolved air liquid into the body of liquid to be subject to flotation, it can as is the case in the present invention, be most advantageous to have a number of release points.

Since the provision of a number of release points reduces the individual size of each and since the orifices of such points may have relatively narrow openings, the invention includes means to remotely adjust, to periodically clear, or in a further step to automatically clear such blockages.

Further it is important that the correct pressure is maintained in the pressurised air solutionizing process of dissolved air flotation and as mentioned this is a function of the said release pointis.

In a very important aspect of the invention preset pressure of the air solutionising system is automatically maintained regardless of variations of flow in the system. This is achieved by controlling the opening of the said release point/s of the system by having a closure member of the said release points motivated by the pressure of the pressurised air solutionizing system such that any reduction in the pressure of the said system causes closure of the release points and vice versa for increases in pressure resulting in automatic preset pressure restoration.

In its simplest form the pressure is preset, in a further form the preset pressure is adjustable and in a still further form it is remotely adjustable.

An automatic preset pressure form of the invention comprises a diaphragm having connected to its one face motivating means to vary the opening of the release point/s of the pressurised air solutionising system to which pressure the same face of the diaphragm is also subject, with the opposite face of which diaphragm being subject to the required preset force or pressure, the preset pressure being elastic in that it permits movement of the diaphragm to control the opening of the release points to restore the preset pressure that would otherwise vary with fluctuations in flow.

The elastic preset pressure to which said opposite face of the diaphragm is subject may be provided by various means. It may be provided by a spring in combination with the body of liquid into which the pressurised air saturated liquid is released or in combination with the pressure of the air in which latter event the said opposite face of the diaphragm would face an enclosed compartment, connected to atmosphere; alternatively preset compressed air pressure connected to the said enclosed compartment without the spring will perform the required function or again reduced pressure drawn from the pressurised air saturated liquid itself and connected to the said enclosed compartment in combination with a spring.

The invention includes means to adjust the automatically maintained preset pressure setting - in its simplest form by adjusting a fixed initial setting by changing the strength of the said spring or by providing means to adjust the tension thereof - or by providing means to adjust the preset pressure in the said compartment or compartments, which means facilitates adjustment by remote control.

A simple form of the invention comprises a tubular manifold that distributes and releases pressurised air saturated liquid into the body of liquid to be subject to flotation via a number of release apertures the degree of opening of which depends on the position of matching apertures on a sliding sleeve within the said manifold which sleeve is mechanically linked either to manual means to adjust its position and consequently the preset pressure or to the said mechanically linked diaphragm that may then jointly control all the release points in accordance With the above described functions. In the latter event all the said release points are jointly controlled by the preset pressure in a single diaphragm compartment.

In another form of the invention the manifold that distributes pressurised air saturated liquid may be connected to a number of individual release points, each release point being fitted with its own individual diaphragm motivation, so that the preset pressure of each release point may be individually or jointly set or controlled or remotely set by a single preset pressure source connected to the said compartments.

To summarise this aspect of the invention includes several means to remotely preset or automatically control the aperturels of the release pointis and the pressure of the said pressurised air saturated liquid.

ILLUSTRATED EXAMPLES OF THE INVENTION AND RELATED ELEMENTS Fig. 1 illustrates in vertical cross-section a structure 1, with a flotation system in channel 30 and a particulate filter bed 2, in an adjoining compartment with a common liquid level 11 above the devision wall 35 where floating material or scum 10 accumulates and in this Fig is shown being removed by reciprocating scum wiping system 19 into channel 13 that also serves to receive expended wash water from the filter.

In Fig 1, 8 is a conduit supplying liquid to be treated via valve 7 into dispersion header 4 that is shown enclosing dispersion header 6M that receives pressurised air saturated liquid and releases this through remotely controlled release orifices along the length of header 6M through corresponding orifices in dispersion header 4 (see enlarged Fig 8 that also shows alternative individual, jointly controlled, release orifice units for spreading the delivery of the said air saturated liquid across the length of the base of channel 30 and its intimate admixture with incoming liquid),. Fig 7 shows a still further alternative inlet and mixing arrangement for channel 30, possibly the most important step in the efficiency of the whole process. (Figs 9, 10 and 11 illustrate enlarged detail of the release nozzles of the invention.) For the flotation action to be initiated at this stage it is assumed that the entering liquid to be purified has been coagulated but in any case a quick acting coagulant or coagulant aid may be administered at 31 and baffles at 5 in channel 30 assist the coagulation process as well as the contact between liquid and micro bubbles. The impurities captured by the micro bubbles rise to the surface of the liquid and the effluent from the flotation process flows over the top 35 of the devision wall into the body of liquid 33 above the top 9 of the filter bed. The liquid may then pass through filter bed 2 into filter distribution and collecting system 3 and out of the filter via duct 47 and outlet valve 16 paced by the water level 11, accurately controlled within close limits via level communication pipe 14, stilling box 15 and water level transmission unit 18.

When required for backwashing a filter bed air agitating supply is admitted via valve 34 and backwash water via valve 17. Before backwashing, scum wiper system 19 may be activated or, if the scum is first freed of adherence to the side walls the level 11 of the liquid above the filter may be raised to discharge scum or floated accumulation 10 over weir lip 12 using incoming liquid from channel 30 to create a cross current.

Fig. 4 illustrates in cross-section a preferred embodiment of the invention in which a Type 3 Moore Airlift Rapid Gravity Filter is combined with a flotation process step.

The identifying numbers of Fig. 1 above relate to similar functions and parts of the filter of Fig.4 except that a mechanical scum removal system has not been illustrated. Additional components include a common washwater storage compartment 44 beneath the filter, that contains filtered water from the filtration stage and that can serve additional filter units, and from which, when backwashing, backwash water is displaced by compressed air, (connections not shown). The unit of Fig 4 illustrates a single or multiple weir type inlet 43, with isolator 7, that discharges behind inlet flow deflector 48 delivering across the bottom of inlet/reaction channel 30 where it is subject to admixture wilth air saturated liquid from release points on compressed air saturated liquid manifold 6M against deflecting shroud 42. Enlarged detail and description in

Fig 7 As before the effluent from the flotation channel flows over the enlarged top of the wall 35 that devides the flotation channel 30, from the filter bed 2, provides a velocity controlled smooth inlet to the filter chamber, and when backwashing J -12- deflects rising backwash water advantageously, Due to its width and shape the top of wall 35 also precludes media entering the inlet channel during air agitation of the filter; any media coming to rest thereon is returned to the filter bed by incoming flow.

The widening of the top of the washwater weir wall at 45 provides increased slope distance to the slope 46 that inhibits the loss of media during backwashing.

In all inlet arrangements it is necessary that the liquid to be treated enters or is directed to and spread across the base of the flotation channel 30, that it is efficiently mixed with air saturated liquid at a low level in this channel and that the channel has sufficient depth. Further for maximum efficiency the liquid to be treated should be adequately coagulated and preconditioned, although the invention does provide for some conditioning in the flotation channel.

Figs. 7 is an enlarged cross sectional elevation of a preferred type of inlet arrangement with a drowned inlet weir 43 (to deter floc break up) discharging behind deflecting plate 48 that spreads the incoming flow along the floor 51 of the flotation channel but which has in this instance, a shaped discharge end that acts as a shroud to deflect the multiple issuing jets from the release points of the pressurised air saturated liquid manifold 6M to just above the incoming liquid. Even preferable, the multiple individual orifice release system of the invention located just above the incoming liquid.

In all preferred cases the pressurised air saturated liquid with remotely adjustable multiple discharge points delivers across the whole length of the flotation channel.

Fig 8 indicates an enlarged detail of the inlet shown in Fig 1 with air saturated liquid manifold 6M (of the type illustrated in Figs 9 or 10) located inside inlet manifold 4 with the remote controlled multiple jets of its release points, surrounded by the discharge orifices of the inlet manifold, directed downwards for dispersion against the floor 51 of the flotation channel 30.

Fig 8 further illustrates an alternative system for the release of the pressurised air saturated liquid with the multiple deployment of individual release orifices of the type illustrated in Fig 11 arranged across channel 30 with air saturated liquid header 6M located outside the channel as well as preset compressed air header 90, the pressure of which jointly controls all the release orifices.

3 Figs 9, 10 and 11 relate to the means to release the pressurised air saturated liquid in Missolved Air Flotation" and illustrate in cross section, examples of this important aspect of the invention, namely the means to control a release orifice and jointly control a number of release orifices.

Fig 9 illustrates a manually remote controlled manifold 6M that receives the pressurised air saturated liquid for dispersion and release via orifices 54 the openings of which may be jointly manually controlled and set by hand lever 62, magnified movement scale 60, lock 61 and lever extension 59 that motivates an inner sliding sleeve 56, with orifices 55, corresponding with orifices 54 in manifold 6M such that the movement of orifices 55 controls the degree of opening of orifices 54. 58 is the fulcrum of lever 59 and 64 the linkage point that transmits movement to sleeve 56 via rod 65 and gland 63.

Lever 59 may extend to above the water line and the throttled orifice setting be readily adjusted or orifice blockage cleared by the momentary opening of release orifices 55 at any time.

14- The movement of sleeve 56 may be electrically, hydraulically or otherwise power motivated to be remotely controlled or be automated for instance to have orifice blockage cleared automatically when triggered by rise in pressure in manifold 6M or of the pressurised air saturated liquid.

In a further important inventive step of the dissolved air flotation process where a percentage of the liquid to be processed is pressurised to be saturated with air, it is important that the designated percentage be maintained regardless of variations in flow and that the designated air solutionising pressure be maintained in the air saturating system and the invention includes means to control the said release orifice/s of the pressurised air saturated liquid to fulfil this requirement.

Examples of such means are illustrated in figs 10 and 11 Fig 10 illustrates a multiple release orifice system similar to that of Fig 9 except that in this instance the release orifices 54 in the manifold 6M discharge vertically against shroud 42 (with positional locating pins 82 and light retaining springs 81) and the sliding orifice aperture control member 56 is motivated, via rod 65, by the differential forces on diaphragm 57 resulting from the pressure from the manifold 6M on one face of the diaphragm and the opposing preset force of spring 66 together with the pressure (or absence thereof) on the opposite face of the diaphragm in compartment 79, to automatically maintain the preset pressure in manifold 6M and incidentally in the air saturating system by regulating the degree of opening of release orifices 54 to restore or correct any variation from the preset pressure.

The setting of the said preset pressure may be altered by changing the spring 66, by adjusting the strength of spring 66, by spring tensioning screw 80, or by altering the back pressure in compartment 79.

The back pressure in compartment 79 may be static with connection 91 open to the liquid in which the manifold 6M is immersed or open to atmosphere via a conduit connected to 91, the preset force being provided by spring 66.

Alternatively in another aspect of the invention the spring may be replaced by a supply of compressed air, 89, connected via conduit 90 to compartment 79 the preset pressure of which may be remotely set or adjusted by pressure reducing valve 87 and needle bleed valve 85 and indicated on pressure gauge 86. In addition to automatically maintaining the preset pressure in manifold 6M and the air saturating system, partial blockage of the release orifices would be automatically compensated for by their degree of opening, also may be automatically periodically opened and flushed by the release of pressure in compartment 79 for example by solenoid valve branching off connecting conduit 90.

Fig 11 is a primary example of this latter aspect of the invention applicable to friction free control of individual release points where each release point orifice 54 is individually controlled by orifice closure member 55, motivated by diaphragm 57 via connecting rod 65 in accordance with the opposing forces applied to each side of the diaphragm 57 and resulting from the pressure in the manifold 6M, applicable to the upper face of the diaphragm via connection 613, and the opposing preset force resulting from spring 66 and or the pressure in compartment 79 applied to the opposite side of the diaphragm which pressure could be from the liquid in which the unit is functioning or from a source of compressed air as previously described.

In a further feature of the invention where no compressed air source is available the preset pressure may be remotely set by utilising the pressure in manifold 6M via connection 6A isolating valve 83 strainer 84 throttling needle valve 85 preset pressure indicating gauge 86 and pressure regulating release valve 87 with bleed discharge 88, the preset pressure being conveyed via branch conduit 92 and connection 91 to compartment 79 where it is operative in conjunction with spring 66 on the opposing side of the diaphragm to automatically maintain the preset pressure of the air saturated compressed air system.

In the ideal multi release point dispersion of the air saturated liquid, the individual release point example of Fig 11 may be duplicated any number of times along manifold 6M fed by branch connections 613 in which case the preset pressure of the individual release points may be jointly set by a single preset pressure setting system commonly connected to each.

The example of Fig 11 is illustrated as part of a jointly remotely controlled multi release point system however the unit may operate singly to control release of the full pressurised saturated air liquid supply connected directly to the unit with all the remote control benefits of the invention..

The earlier description of fig 1 omitted a description of the mechanical scum removal system of the invention illustrated in Figs 1,2 and 3. In this system a movable trolley 19, mounted on wheels 25, that rest on the filter surround 29, with side guide wheels or skids 26, reciprocates to and fro across the structure, wiping scum or collected floating material 10 over lip 12 into the scum removal channel 13 The scum skimming trolley 19 is motivate by rope drive 20 (driven by geared motor drive means 21) that motivates the trolley via arm 22 on swivelling sleeve 27 that in turn carries scum blade 23 to depend into liquid surface 11 when travellingtowards lip 12 and propel scum thereto and to swivel clear of liquid level 11 when the scum has been wiped over 12 and automatic reversing rope drive 20 pulls over arm 22 and causes trolley 19 to reverse and travel away from lip 12.

Whereas Fig. 1 illustrates the trolley structure in cross section elevation, Fig. 3 and 2 have been prepared to indicate the trolley structure in plan and end elevation and in these Figs., 25 are four support wheels operative an structure surround 29 with guide wheels 26 operative against the side of the structure 29. 40 are cross- members that carry the wheels and column 28 that spans the structure and threads swivelling collars 27 and 27a from which flexible scum wiper blade 23 depends and to which swivelling drive arm 22 is attached.

The swivelling action of the scum blade that engages the scum in forward motion and is lifted clear in reverse motion is a special feature of the invention and Figs. 5 and 6 have been prepared in enlarged cross-section to indicate in Fig. 5 the position of the blade in forward motion and in Fig. 6 its position when the trolley is reversing and the change over action caused by the pull of the rope drive in forward motion Fig. 5 and reverse Fig. 6, the collar 27 swivelling about column 28 until reaching stops 41, attached to column 28 and transferring drive to the trolley. 39 are weights to assist in ensuring positive swivelled position and the trolley may have initial inertia or friction means to ensure swivel change over before commencing to travel.

In the above arrangement column 28 is fixed to the trolleys. In the alternative arrangement column 28 (with wiper 23 and drive arm 22 attached) swivels in end bearings mounted on the trolleys which are joined, by two fixed cross-members from which stops 41 are mounted.

With regard to the pressurised air solutionising process of the invention, that relates to the percentage liquid that is circulated to produce pressurised dissolved air, Fig. 12 indicates in vertical section an air dissolving system 1-18- comprising enclosed pressurised container 68, with an incoming delivery, 75 for circulating liquid under pressure that feeds a velocity accelerating approach cone 69 to an eductor, 78, that produces an annular jet and induces air via central air inlet tube 70 and carries this to the base of the said container from where it is dispersed and deflected by circular baffle 77 back up into the body of liquid, the top water level of the body of liquid in the container being maintained at optimum by a float valve, 72 that vents excess air via exhaust pipe 71. Air exhaust valve 72 is mounted on an arm with fulcrum at 73 and is motivated by float 74 responsive to the level of the liquid in the said container and providing leverage to motivate air exhaust valve 72.

Depending on the relative delivery pressure applied to the incoming circulating liquid 75 in relation to the pressure maintained in container 68, eductor 78 would be capable of inducing an excess of air over and above that which can be dissolved in the circulating liquid with the excess vented by air exhaust valve 72 and the level of liquid in container 68 automatically maintained at the required level.

The air solutionising system can operate alternatively by pressurising the incoming air supply 70 so that the pressure differential necessary to drive eductor 78 is less but even in these circumstances a pressure differential should be maintained to provide the annular jet that carries the incoming air to the bottom of container 68 and contributes to the air solutionising efficiency of the system.

The outer periphery of the annular jet further induces air from above the liquid in the container carrying this also in the form of fine bubbles into the body of liquid in the container to again assist the solutionising efficiency of the system.

Circulating liquid containing dissolved air exits from behind the baffle 77 j -19- in the base of the container at 76.

The system requires that the quantity of air entering the pressurised container 68 to be in excess but only slightly in excess of that which can be solutionised in the circulating liquid.

-20

Claims

1.

A method of purifying a liquid that includes the step of subjecting the liquid to admixture with a second liquid (or a recirculated portion of the same liquid) that has been pressurised, saturated with dissolved air under pressure and then released directly into the said liquid to be purified via an injection nozzle, in which the degree of opening of which nozzle may be remotely varied, thereby providing the facility to remotely adjust the pressure of the air solutionised liquid that is controlled by the degree of opening of the nozzle..

2.

A method of purifying a liquid as claimed in claim 1 including means to automatically vary the opening of the said nozzle in order to restore the preset pressure of the air solutionising liquid in the event of variations in flow thereof.

3.

A method of purifying a liquid as claimed in claim 2 in which more than one or several of the said injection nozzles are jointly controlled by common means.

4.

A method of purifying a liquid as claimed in claim 3 in which the several said nozzles are located in a row spanning a channel or elongated compartment and discharge the said pressurised air saturated liquid into the liquid to be purified at a low level.

5.

A method of purifying a liquid as claimed in claim 4 in which the row of injection nozzles may comprise individual units jointly controlled and connected to the conduit delivering the said pressurised air saturated liquid or the row of injection nozzles may comprise orifices in the conduit delivering the pressurised air saturated liquid which conduit then has a slideable inner member that varies the opening of the orifices in accordance with motivation applied to the inner member.

6.

A method of purifying a liquid as claimed in claim 5 in which the means to preset and automatically maintain a preset pressure in the pressurised air saturated liquid includes an enclosed structure devided by a diaphragm into two compartments which diaphragm includes connected thereto on one side means to vary the opening of the said nozzles as well as an opening force applied thereto by the pressure of the air saturated liquid to which that side compartment is connected and which opening force is opposed by a closure force on the opposite side of the diaphragm such that a balance of forces is achieved when the opening of the nozzlels releases only the amount of pressurised air saturated liquid that corresponds to the retention of the required preset pressure of the pressurised air saturated liquid and is determined by the amount of preset closure force applied.

7.

A method of purifying a liquid as claimed in claim 6 in which the said mobile closure force is provided by a spring that may also have an adjustment to vary the force that may also be augmented or determined by connecting its compartment to the liquid in which the injection nozzle is submerged or to atmosphere.

8.

A method of purifying a liquid as claimed in claim 6 in which the said closure force applied to the diaphragm is provided by compressed air the pressure of which applied to the diaphragm may be remotely set and varied to vary the required pressure of the said pressurised air saturated liquid.

9.

A method of purifying a liquid as claimed in claim 8 in which the said compressed air closure force is jointly applied to any number of individual injection nozzles controlling outlets from the said pressurised air saturated liquid.

10.

A method of purifying a liquid as claimed in claim 8 in which the method to provide an adjustable preset compressed air closure force includes a compressed air supply at adequate pressure, means to adjust the pressure of the compressed air supply, including adjustable pressure reducing means, means to indicate the reduced regulated pressure (or preset pressure) and means to vent pressure in order to reduce regulated pressure when required.

11.

A method of purifying a liquid as claimed in claim 8 in which the said closure force is obtained from the said pressurised air saturated liquid, reduced in pressure en route so as to provide means to vary the pressure and resultant force setting in combination with a spring that augments the reduced force.

12.

A method of purifying a liquid and of obtaining a preset closure force as described in claim 11 in which the said closure force is jointly applied to any number of individual injection nozzles.

13.

A method of purifying a liquid as claimed in claim 5 in which the motivation applied to the said inner member of the said conduit with multiple orifices is provided by an external hinged arm or lever that is attached to the said inner sleeve with sealing gland means and which arm extends upwards to above the liquid level and is provided with locking adjustment means with calibrated indication of the degree of opening of the nozzle orifices, magnified by the degree of leverage.

14.

A method of purifying a liquid as claimed in claim 1 relating to the method of saturating the said dissolved air liquid with air and which method comprises pressurising the liquid prior to its entry to a vertical enclosed cylindrical saturating tank in which the said liquid enters the saturating tank centrally at the top through a velocity increasing cone with a throat annularly surrounding a central air inlet tube inducing air directly from the atmosphere, or augmented from a pressunsed air source, in quantities slightly in excess of the amount of air to be taken into solution and directing the air liquid mixture vertically downwards via a velocity reducing tube to the center of a circular baffle on the base of the saturator that redirects the air/liquid flow upwards for possible re-entry into the initial stream via an annular gap at the maximum velocity point of the incoming stream that may also serve to induce air trapped in the upper portion of the saturator at a controlled level with the said excess air vented by a float controlled outlet at the designed operating level of the liquid in the saturator which is at the said gap or throat of the venturi type unit that combines the triple function of inducting (or assisting the induction) of air into the saturator causing the liquid in the saturator to recirculate and inducing air into solution from that trapped in the upper part of the saturator and then following remixing and intimate contact, causing delivery of the pressurised air solutionised liquid from the annular area surrounding the said baffle, into an outlet conduit near the bottom of the saturator.

15.

A method of purifying a liquid that combines:- coagulating the liquid, introducing the coagulated liquid evenly into an elongated chamber at a low level of the chamber, causing the liquid to mix with a released recirculated portion of the subsequently purified liquid which portion contained dissolved air saturated under pressure, causing impurities to attach to the resulting micro bubbles and to rise to the surface of the liquid, causing the liquid to flow over an opening between the surface of the liquid and the top of a dividing wall between the said elongated chamber and a chamber containing a rapid gravity particulate filter, causing the liquid to flow through the filter, be collected by the under bed reticulation system of the filter, be delivered therefrom via a filtered water outlet controller paced by the water level in the filter to maintain the water level in the filter just below the level of the weir crest of a channel extending along the opposite side of the filter chamber to the filter inlet and the purpose of which channel is to periodically receive floating impurities that accumulate on the surface of the liquid above the filter and also expended filter backwash water as required during the backwashing of the filter, and preventing the loss of filter media during the backwashing procedure (that may also include agitating the filter media with compressed air) by providing media loss prevention means between the filter chamber and the expended washwater receiving channel.

16.

A method of purifying a liquid according to claim 15 in which the media loss prevention means is comprised by a sloping approach to the crest of the devision wall between the filter chamber and the expended washwater receiving channel augmented by increased thickening of the devision wall or the thickening of the top of the wall to accommodate increased amount of slope over and above what would be applicable from the thickness of applicable walls in normal civil structure.

17.

A method of media loss prevention as claimed in claim 16 in which the increased slope to the crest of the said division wall is provided by the provision of an angled plate attached to the division wall, that may also be shaped to provide beach means accommodating the expulsion of float.

18.

A method of purifying a liquid as claimed in claim 15 in which the top of the said dividing wall between the said elongated chamber and the said filter chamber is widened so that when backwashing the filter, filter media are retained thereon and cannot reach the said elongated chamber and is subsequently carded back into the filter chamber by the inlet flow.

19.

A method of purifying a liquid as claimed in claim 15 in which the method of introducing the said coagulated liquid evenly at a low level throughout the length of the said elongated chamber comprises the provision of a baffle or baffle wall behind which the coagulated liquid is initially introduced and below which the coagulated liquid flows into the said elongated chamber.

20.

A method as claimed in claim 19 in which the method by which the said coagulated liquid is initially introduced is by means of a weir or drowned weir or weirs behind the said baffle that may constitute similar inlets to parallel purification units to equally divide the overall flow thereto.

21.

A method of removing accumulated float from dissolved air purification systems in which a carriage bearing float wiping means attached to an arm or arms depending from swivelling means, is caused to reciprocate over the float area by rope drive means attached to an opposite arm of the swivelling means such that when the carriage is being driven by the said swivelling drive arm towards the float exit means, the float wiper has swivelled to engage the float and when travelling in the opposite direction away from the float exit means, by reason of the pull of the drive rope in that direction the float wiper means is caused to swivel free of the float.

22.

A method of removing accumulated float from dissolved air purification systems as claimed in claim 21 in which the reciprocating carriage that carries float wiper means, also carries means to sever the adhesion of accumulated float to the side walls.

23.

A method of removing accumulated float from dissolved air purification systems as claimed claim 22 in which the float removal operation is intermittent and on initiation, the means of severing the float from the side walls is operative during the initial reciprocation of the carriage which is in reverse so that on it's forward float wiping removal stroke the accumulated float has been freed from adhesion to the side walls.

24.

A method of purifying a liquid according to claim 15 in which the compressed air source that is used to agitate the filter media is also used to motivate the back washwater flow to the filter by displacing filtered water from the said filter, stored in an airtight chamber beneath the fitter chamber and which said airtight chamber is adjoined by the lower portion of the said elongated chamber into which the said coagulated liquid is introduced and whereby the depth of the said elongated chamber is increased in an economic structure.