AU649964B2 - Non-chemical water treatment for water supply system - Google Patents

Description

W'O 91/04229 PC'~/A U90/00420 -1- N/rJ-CHE-I:CAL- WATER TREATMENT FOA W,4TEK. SUPPLy/ !9YS TEM FIELD OF THE INVENTION This invention relates to an apparatus and non chemical method for the treatment of water, and relates particularly, although not exclusively to water treatment in cooling towers for: the prevention of dirt accumulation; the prevention of detectable microbial activity in return condenser water and; the prevention of scale and corrosion of air conditioning plant cooled by the cooling tower water (otherwise known as condenser water).

DISCUSSION OF THE PRIOR ART The invention or aspects of the invention have widespread application in, for example, domestic water supplies, fisheries, spas, swimming pools and any industrial or commercial application where algae, bacteria, viruses, or amoeba are undesirable in a water feeding system or supply. The following description will be given with particular reference to cooling towers in building air conditioniny plants, however it is to be understood that the invention is not limited to this application.

There is a constant volume of recirculating water in a cooling tower. This is typically 4000 40,000 litres which is pumped through "heat generating" refrigeration plant back to the cooling tower which cools the water by some 7 C. The flow rates through the condenser water pipes vary depending on the size of the plant but typically fall within the range of 3-140 litres per second.

The cooling tower is provid-d with a fill which is a series of wooden or plastic slats through or over which the water trickles to a tower basin. As it trickles to the basin .J )0 the evaporative effect of air cools the water. This is WO 91/04229 I"Cr/AU90/004 -2amplified by a large fan in the top of the cooling tower which sucks air through the tower fill out the top of the tower.

It is the action of air through the water and the splashing effect of water which causes aerosol droplets to form and it is these droplets which can contain legionella bacteria.

The droplets are able to be inhaled and can cause Legionnaire's disease which has a 20-30% mortality rate.

The condenser water is usually close to the ideal temperature range for bacterial growth and total bacterial counts(TBC) of 107 colony forming units per millilitre (cfu/ml) are not uncommon. TBC counts do not include legionella bacteria which need to be specifically cultured. Legionella bacteria have been found in large percentages of cooling towers (up to 100% in one study).

Scientists have found high levels of legionella bacteria in cooling towers that are clean and have low numbers of TBC.

There is no definitive scientific evidence to support the theory that legionella and TBC levels are inter-related.

The tower basin becomes dirty very quickly due to air borne particulate material which is deposited into the water.

Cleaning of cooling towers is particularly difficult as the basin is usually inaccessible due to the close proximity of the tower fill.

The continual evaporation of water from cooling towers causes a buildup of dissolved salts and chemicals conducive to scale formation and corrosion of copper and iron components of air conditioning plant.

Conventional water treatment of cooling towers is by the use of chemicals for scale, corrosion and microbial control.

These are applied in conjunction with a monthly inspection programme and manual cleaning as required.

3 The chemicals used for corrosion control include chromate and phosphanate based compounds. Chemicals used for microbial control include chlorine, quaternary ammonium based compounds, tin butyl oxide compounds, bromine, ozone and chlorine dioxide. Most of these chemicals are toxic and enter the environment either through drift from the cooling tower or bleed off to waste water. A number of the chemicals used for microbial control are oxidising agents and over a period of time cause corrosion and delignification of wooden structures. Some chemicals such as ozone degrade certain plastic materials including fibreglass.

Conventional water treatment of cooling towers relies upon continual dosing of anti-corrosive chemicals to cooling towers via dosing pumps interlocked to the condenser water pump. When the condenser water pump is activated by cooling demand the dosing pump automatically pumps anti-corrosive chemical into the condenser water.

Anti-microbial chemicals are similarly added although in many cases they are added monthly on a manual slug dose basis.

The build-up of total dissolved solids and suspended solids previously described is conventionally controlled in part by opening a valve to waste water causing an amount of "bleed off" to occur thus diluting the contaminants. Typically this is 50% of water consumption.

The present invention was developed with a view to providing a more effective and efficient method and system of treating water in the recirculating water supply system of a cooling tower, and in particular for inhibiting the contamination of cooling tower water with legionella bacteria, however as noted above the invention also has wider application.

SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided a method of water treatment for a water supply system, the method comprising the steps of: in-line ultraviolet (UV) light sterilisation of 0; 4 water flowing through the water supply system; mechanically agitating the water by directing water under pressure through a plurality of flexible sweeping tubes mounted adjacent a floor of a water reservoir provided in the water supply system so as to produce a random snake-like motion of the sweeping tubes thereby lifting settled dirt or biomass in the reservoir; and, filtering the agitated water to remove the suspended dirt ox biomass; whereby, in use, the combined effects of said steps of sterilisation, agitating and filtering can reduce the level of water borne bacteria and algae to negligible levels.

According to another aspect of the present invention there is provided a system of water treatment for a water supply system, the water treatment system comprising: in-line ultraviolet (UV) light sterilisation means for sterilising water flowing through the water supply system; mechanical agitating means comprising a water inlet pipe extending into a vessel of the water supply system, for feeding water under pressure into the vessel, a plurality of flexible sweeping tubes connected to the inlet pipe and adapted to sweep the vessel in a random snake-like motion as water from the inlet pipe is ejected from the ends of the tubes, and a ;-ater outlet for removing water from the vessel whereby, in use, the motion of the sweeping tubes agitates the water and causes settled dirt or biomass to become suspended in the water for removal from the vessel via the water outlet; and, filtering means connected to said water outlet for filtering the agitated water to remove the suspended dirt o' biomass; whereby, in use, the combined effects of said sterilising, agitating, and filtering can reduce the level of water borne bacteria and algae to negligible levels.

According to a further aspect of the present 7K> 5 invention there is provided a mechanical water cleaning apparatus for agitating water in a vessel of a water supply system, the apparatus comprising: a water inlet pipe extending into the vessel for feeding water under pressure into the vessel; a plurality of flexible sweeping tubes connected to said inlet pipe and adapted to sweep the vessel in a random snake-like motion as water from the inlet pipe is ejected from the ends of the tubes; and, a water outlet pipe for removing water from the vessel whereby, in use, the motion of the sweeping tubes agitates the water and causes settled dirt and biomass to become suspended in the water for removal via the outlet pipe.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the nature of the invention may be better ascertained preferred embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a cooling tower fitted with an embodiment of the invention. The UV steriliser prototype I is depicted; Figure 2 is a schematic diagram of a cooling tower fitted with a different embodiment of the invention.

The UV steriliser prototype II is depicted; Figure 3 is a plan view of the cooling tower mechanical cleaning system through section A-A of Figure 1; Figure 4 is a close up view of a cooling tower sweeper illustrated in Figure 3; Figure 5 is a side elevation of the UV steriliser prototype I; Figure 6 is a plan view B-B of the UV steriliser prototype I illustrated in Figure Figure 7 is a plan view of an O-ring type UV tube holder along B-B; Figure 8 is a sectional view of the UV steriliser prototype I along C-C of Figure 6; Figure 9 is an enlargec view of area A of Figure 8; and, \VO 91/04229 I"C*/A 090/004020 -6- Figure 10 is a side elevation of a removable UV tube holder; and, Figure 11 is a sectional view of the UV steriliser prototype II in a modular configuration; and, Figure 12 is a sectional view of the UV steriliser prototype II in a unitary configuration; and, Figure 13 is a plan view of the access hatch 102 in figures 12 and 13; and, Figure 14 is a end view along E-E in figure 11 of the UV tube 1 5 assembly; and, Figure 15 is a sectional view of a UV tube assembly along F-F in figure 14; and, Figure 16 is an enlarged view of area B of the UV tube assembly in figure DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to figure 1, cooling tower water 28 is drawn through the cooling tower sump 19 into the condenser supply pipe 3 through the condenser pump 26. It returns via the condenser return pipe 2. In small systems with up to 12 Ls-1 condenser pump flow rate, the UV steriliser prototype I 5 is installed in the condenser return pipe 2 and the entire condenser water flow is sterilised to a 99.9% kill efficiency per passage of water.

The water in the condenser return pipe 2 enters the top of the cooling tower 1 via the condenser pipe outlet 20 into header boxes 21. Header boxes 21 are covered (not illustrated) to prevent light entering and promoting algal growth, a known risk factor for legionella growth. The return condenser water 32 is sterilised to the extent that viable bacteria are not WO 91/04229 PC17/AU90/0020 -7detectable using standard analysis of 50-100 microlitres of condenser return water taken from sampling cock 33. The advantage of this is that there is no possibility of legionella becoming airborne and causing Legionnaires' disease as all bacteria are previously removed from the source which is recirculated condenser water.

The return condenser water 32 passes through distributor holes 31 into the tower fill 13 in a downward path 15 back to the tower basin 4 to repeat the cycle. The cooling tower fan 22 sucks air 14 through the tower side slats 34 through the tower fill 13 out through the fan cowling 35. The aerosols thus generated are safe by virtue of the sterile nature of the return condenser water 32.

Cooling tower and condenser water are part of the same body of recirculatinc water which is filtered to a minimum micron cutoff by a sand filter 8 thus removing suspended solids. Cooling tower mechanical cleaner supply water 30 passes to supply the side stream circuit pump 7. It then passes through the sand filter 8 to a magnetic or electrochemical corrosion and scale treatment unit 10, to an optional second UV steriliser prototype I 11 to the cooling tower mechanical cleaner return water 12. The optional second UV steriliser prototype I 11 is a fail-safe backup device to the first UV steriliser prototype I The magnetic or electrochemical water corrosion and scale treatment unit 10 is a proprietary device which causes scale forming ions to crystalise .from solution as filterable colloids and which also claim to generate free electrons into the water.

These prevent corrosion by mimicking the preferential supply of electrons to corrosive reactions by cathodic protection techniques. These technologies are well known to experts in the field.

The sand filter 8 contains an automatic back-flush system 9 (not illustrated in detail) commonly in use in other applications. Backflush water is directed via the back-flush VO 91/04229 POVAU90A ~O/004206 -8pipe 6 to a back-flush water recovery tank 23 mounted on top of the cooling tower 1.

The back-flush water passes through a graded sand bed 56 in the base of the back-flush water recovery tank 23 and gravity feeds back to the cooling tower via the recovery tank outlet pipe 24 thus conserving water. The suspended solids are retained on oL in the sand bed 56 for periodic manual removal approximately every six months.

The bleed-off pipe 57 leads to the bleed-off valve 29 to waste. The bleed-oil valve 29 is closed compared to conventional chemical water treatments which permit approximately 50% of water consumption to "bleed" to waste.

Drift eliminators 25 are not required to be relied on to prevent legionella drift because of the insignificant risk of legionella bacteria being present in drift.

A second alternative plumbing arrangement is illustrated in figure 2 whereby the side stream circuit pump 7 is eliminated. Supply suction is obtained from the condenser pump 26 by taking cooling tower mechanical cleaner supply water by suction at point 36 situated on the supply side of the condenser pump 26. The sand filter 8 is supplied by water under pressure taken from the condenser supply pipe at point 37 after the condenser pump 26. The flow rate of the side stream circuit is 3-12 Ls- depending on the size of the cooling tower 1.

The UV steriliser protot'ype II 101 contains UV tube assemblies 38 which are inserted into condenser return pipe 2 in systems with condenser flow rates greater than approximately 12 Ls- 1 ,thus achieving similar sterilisation specifications as in the abovementioned example of the UV steriliser prototype I.

The UV tube assemblies 38 permit sufficient amounts of UV light to be radiated in a cost efficient manner to sterilise the entire condenser water flow. Because they utilise existing pipework they are also space efficient which is an important commercial and physical consideration for many buildings, 9

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c II I~I i I I

I

The cooling tower mechanical cleaning system depicted in detail in figure 3 is designed for a very large tower and contains two cells within the tower separated by a cell dividing wall 47. Each cell is cleaned at separate times by timer controlled solenoids 39. The cooling tower mechanical cleaning return water 12 is fed via primary feeder lines 41 which feed to secondary feeder lines 42 located adjacent the floor of the tower basin 4. The primary and secondary feeder lines are suspended approximately 20 cm from the bottom of the tower basin 4 by supports and nylon ties (not illustrated).

Water under pressure passes to the cleaning sweepers 45 which agitate and mechanically scrape the wetted surfaces of the tower basin 4 suspending settled dirt and biological growth which may be loosely settled or adhered.

The suspended ma.erial enters the supply pickup pipes 46 suspended approximately 5 centimetres below the water in the tower basin 4 so as not to impede the cleaning sweepers 45. The supply pickup pipes 46 are in the immediate area of the suspended material which then enters into secondary supply linesi 20 48 and primary supply lines 44. The solids suspended in water supply the side stream circuit pump 7 and the sand filter 8 where suspended solids are removed from circulation.

Variable gate valves 40 and 43 provide means to adjust the flow rates through the return and supply circuits to ensure optimum performance of the cleaning sweepers 45 and the optimum amount of supply water to the side stream circuit pump 7.

The cleaner sweepers 45 are illustrated in some detail in figure 4 and comprise a piece of plastic tube 51 which 30 is approximately 12 mm outside diameter and 1 metre long. It is typically fitted with 6 interference fit nylon slider weigrhts 52 fastened firmly to the plastic tube 51. These nylon slider weights 52 permit minimal friction with the adjacent surface via a raised edge 53. They also weight the cleaner sweeper at the end and thus keep the end nozzle 54 under water. The end nozzle 54 contains a small orifice 55 which projects a forceful stream of water thus propelling the cleaner sweeper in a random snake like motion and cleaning the tower basin 4.

S. 0 00 0 cTA /4 10 The cleaner sweepers 45 and the supply pickup pipes 46 are located and designed so as to avoid the cleaner sweepers being hindered or impeded by obstructions in the tower basin 4. Long flexible pipe-like probes are inserted across the basin floor prior to installation and obstacles such as structural beams are mapped. A design plan tailored to that tower is devised so that in operation the cleaner sweepers 45 have an unimpeded sweep path over substantially the whole area of the tower basin floor, and are not likely to become intractably caught upon such obstacles or in corners.

The cooling tower mechanical cleaning system ensures that no pockets of dirt or sludge are left in corners 16, 17 or inaccessible still spots 18 of the tower basin 4. A minimum clearance rate of 0.3 kg m-2hr l of mixed sand and clay type soil (50:50) is achievable over the entire tower basin surface to absolute removal. This rate is generally sufficient to cope with dirt, sludge accumulating in a cooling tower but the clearance rate can be increased, if necessary, by increasing the flow rate through the cooling tower cleaning system and/or increasing the number of cleaner sweepers 45 and supply pickup pipes 46.

Referring now to figures 5, 6, 7, 8, 9 and 10 the UV steriliser prototype I comprises a water treatment vessel 58 with removable end plates 81 all made of marine grade aluminium, stainless steel, UV resistant fibreglass or some other UV resistant plastic, The end plates 81 are attached to the water treatment vessel 58 by flanged connections joined by some bolts and nuts 69 located evenly around the flange 78.

o* t 0 a The end plates 81 have a variable number (between 1- Ice- 6) of O-ring type UV tube holders 70 or of removable seal type UV tube holders 107 (see Figure 10) mounted to secure the glass sleeves 62 containing the UV tubes 90. The glass sleeves 62 are laminated with a thin layer of UV transparent fluorinated ethylene propylene known as TEFLONnm by the DUPONT Company.

S 35 TEFLON has 14d 91/0-1229 IPC1'/A L90/00420 -11unique properties in that it is UV light stable, transmits UV well and has well known non-stick properties. This maximises UV light transmission by reducing dirt and biofilm accumulation on the surface of the glass sleeve 62.

The electrodes of the UV tubes 63 are connected by standard electrical connections 71 to a power source(not illustrated). A cover 73 fits over the end plates 81 to conceal the electrical connections 71.

The water outlet pipe 109 contains a flange fitting 68 and also has a sampling cock 67 fitted for testing the sterility of the outlet water. The water treatment vessel 58 contains a removeable access hatch 65 for maintenance and inspection purposes which is secured by wing nuts 66 for easy operatic-; It is sealed by an O-ring (not illustrated) to the water treatment vessel 58.

Referring to figure 8, inlet water passes through the inlet flange 59 through inlet pipe 110, through a sieve screen through a conical venturi 86 into the inlet ena of the water treatment vessel 58. Water and impaction beads 83 are sucked into the region of the venturi effect 84. These impaction beads 83 are approximately 12 mm diameter plastic core, coated with a UV reflective substance such as aluminised paint. They do not substantially diminish t.he intensity of UV light in the the water treatment vessel 58.

The water and the impaction beads pass through a diffuser screen 80 which ensures that the water is not channeled unevenly through the water treatment vessel 58. The impaction beads randomly impact upon the glass sleeves 62 and have a cleaning effect. They pass towards the water outlet until they are deflected by a deflector sieve 87 through an impaction bead feeder line outlet 79 into an impaction bead feeder line 82 to the zone of the venturi effect 84 in the inlet pipe 110.

The water passes through the deflector sieve 87 to the outlet pipe 109 and is exposed to sufficient UV light to render \VO 91/04229 1,107AU9U0/00420 -12a 99.9% kill to all of the bacterial types present. Bacteria are not detectable by standard dipslide or agar plating methods.

Area A in figure 9 illustrates the O-ring type UV tube holder 70 which comprises a round plate with a central hole for the glass sleeve 62 to pass through. The O-ring UV tube holder is secured to the end plate 81 by bolts 94 and nuts 95. The edge of the O-ring type UV tube holder adjacent the end plate 81 is chamfered 108 to accommodate an O-ring 93. This O-ring is compressed against the glass sleeve 62 and the end plate 81 to create a water tight seal.

The UV tube 90 is located inside the outer glass sleeve 62 and is separated by a air space 91. The end of the UV tube contains a insulated end cap 111 from which projects an electrode 63 which provides current to an filament 92.

In an alternative embodiment of the invention the outer quartz glass sleeve 62 is absent so that UV tubes are directly in contact with water.

The removable seal type UV tube holder 107 illustrated in figure 10 is the preferred type as it is easily replaceable in the end plates 81 with threaded plugs. Thus the number of UV tubes can be easily increased or decreased according to the flow rate of treated water and the water quality.

A standard hydraulic seal 98 is activated by the water pressure inside the water treatment vessel 58 and seals in a watertight manner against the outer face of the outer glass sleeve 62 and against the seating faces 105 and 106 in the main body 99 of the removable seal type UV tube holder 107. When the water pressure is released inside the water treatment vessel 58 the hydraulic seal 98 releases and the outer glass sleeve 62 is easily slid from the removable seal type UV tube holders for maintenance and/ or replacement.

WO 91/04229 PCI'/IAU90/00420 -13- A threaded area 100 screws into the end plates 81 to provide a watertight seal between the gasket 76 and the end plate 81. A hexagon shaped area 75 is provided for tightening and loosening using standard spanners. A second threaded area 77 allows a cover 89 to be screwed into place thus locating the outer glass sleeve 62 and the UV tube (not illustrated) contained within the outer glass sleeve. A standard type spring loaded electrical terminal (not illustrated) is fixed to the cover 89 and allows a tolerance of some 5mm in the exact 1 0 location and length of the UV tube (not illustrated).

The UV steriliser prototype II 101 is a modular embodiment designed to sterilise large flow rates of condenser water.

Referring to figures 11, 12, 13, 14, 15 and 16 the device comprises a length of condenser water pipe 122 of variable width with UV tubes inside glass sleeves 123 arranged in UV tube assemblies 38 which can be inserted into existing condenser water pipes 122 to sterilise the entire condenser water flow. The advantages are that the UV tube assemblies can contain 1 or more UV tubes inside glass sleeves 123 depending on the condenser pipe size and water flow rate. Additional modules are easily inserted into the condenser water pipe to cope with various flow rates and water quality.

Access panels 102 are installed onto existing condenser water pipes 122. They are removable by wing nuts 121 which act to force the access panel against an O-ring seal (not illustrated) in a machined groove on the underside of the access panel 102 thereby sealing the condenser water inside the condenser pipe 122. The access panels 102 are of sufficient size so as to permit the installation of UV tube assemblies 38 inside the condenser water pipe 122.

The UV tube assembly 38 illustrated in figures 15 and 16 comprises two plastic mouldings 128 made of a suitable plastic material. This is preferably of high tensile strength, UV stable, machinable and a good electrical insulator. The plastic mouldings incorporate proprietary hydraulic gland seals 129 in the tube holding yoke 127 of the plastic moulding 128.

WVO 91/04229 1107'AU90/00420 -14- During assembly the UV tube inside a glass sleeve 123 is glued into a hole at adhesive bond 130 securing the UV tube inside glass sleeve 123 to the tube holding yoke 127. The adhesive used is silicone based or some other similar material which has good resistance to UV light and good adhesion to glass. The hydraulic seal 129 is then slid over the UV tube inside a glass sleeve 123 into its working location as illustrated.

Thus the spring loaded electrical connection 135 joining the UV tube electrode 131 to the electrical wire 132 is double insulated from the condenser water via an adhesive bond 130 and a hydraulic seal 129. The insulated electrical wire 132 to 1 5 terminal 133 provides a double insulated effect.

A hole in the condenser water pipe accommodates the fastening lug 120 of the mounting arm 124 of the UV tube assembly. The fastening lug 120 is sealed against the condenser water pipe 122 using a rubber washer or O-ring (not illustrated) and a nut 125 secures the fastening lug 120 firmly to the condenser water pipe 122.

A bead impaction system is used in the UV steriliser prototype II which is similar to that employed in the UV steriliser prototype I. It is used to clean the glass sleeves containing the UV tubes 123. The various components of this cleaning system are: impaction beads 134 a venturi device 113 operating which creates a low pressure venturi zone when water passes over the venturi device 113 in the direction 104 indicated; a sieve 114 which allows water passage but prevents impaction beads 134 from drifting past when the condenser water is not being pumped; a sieve 115 which allows water passage but directs impaction beads 134 to the impaction bead feeder line outlet 116.

'VO 91,04229 PCI*I/AUS0/004120 The unitary embodiment of the UV steriliser prototype II 118 whereby the modular UV tube assemblies 38 are modified to allow them to be connectible and inserted as one unit in a condenser water pipe 122 involves technology similar to that applied in the first modular embodiment 101 of the UV steriliser prototype I 101 and the details of the seals and connecting methods are not illustrated. The advantages are that fewer electrical connections are required.

A further modification to the UV steriliser prototype II is the shaping of the plastic mouldings 128 in a manner designed to minimise disruption to the laminar flow of the condenser water by incorporating a bulbous shape at the points of initial water contact tapering away to allow smooth water flow.

The UV steriliser prototypes I and II have a number of design aspects which enhance the efficiency of the devices. For example, were a single high efficiency UV tube to be located centrally in the UV steriliser prototype I, over five times the minimum lethal dose of UV light to kill legionella bacteria at a flow rate of 12.6Ls 1 would be delivered.

The units achieve sterilisation of water creating sufficient dosage of UV light to kill all types of bacteria found in cooling towers; ensuring that this dosage is delivered consistently in the most demanding of conditions experienced in cooling towers to the total condenser flow rate. This flow rate is substantial and typically ensures that in normal operation that the entire cooling tower 1 and condenser water volume is sterilised approximately 10 times per hour during operation.

A lethal dose of UV light can be continuously delivered by the UV sterilisers 101, 5 and 11 by: proper design of the water treatment vessel 58 and condenser pipe installations to ensure that the flow rate of water through UV light is sufficiently slow to allow sufficient exposure to UV light; NVO 91/04229 PCIV'AU90/00420 -16the condenser and cooling tower water 28 is continuously filtered by sand filter 8 to remove suspended solids and colloids which promote scale and corrosion formation in air conditioning plant and on proprietary electromagnetic and electrochemical water treatment devices and fouling of the glass tubes 62; settled and adhered bi-mass and scale is mechanically removed from the cooling toier 1 to minimise fouling of air conditioning plant and tower basin 4; a proprietary magnetic or electrochemical water corrosion and scale treatment unit 10 crystalises scale forming dissolved solids from the condenser and cooling tower water 28 and prevents the deposition of scale onto the glass sleeves 62 and air conditioning plant. These dissolved solids are deleterious in that they decrease UV light transmittance and promote fouling of the glass sleeves 62 containing the UV tube a thin layer of TEFLONT™i or some other similar material which allows a high level of UV light transmittance is applied to the outer surface of the glass sleeve 62 in contact with water. This has self-cleaning and non adhesive properties which minimise fouling and scaling normally associated with silica containing glass sleevrs 62. Silica is one of the elements which act as a binder for scale deposition.

An automated cleaning device comprises small plastic impaction beads which are recycled through the UV water treatment vessel and which randomly impact upon the glass sleeves 62 thus providing a mild abrasive cleaning action. This is incorporated in the water treatment vessel 58 and condenser pipe 122 to continually clean the surfaces of the glass sleeves 62.

The various aspects of the invention may be interrelated and when combined.result in: undetectable levels of water borne bacteria using standard analytical techniques; cooling towers and the condenser wate- contained therein are constantly in a very clean state without the need for manual cleaning; \WO 91/04229 PCII/A U90/00420 scale and corrosion of air conditioning plant are eliminated; significant water savings are achieved by eliminating water normally "bled off" to waste; and, no ch.icals are used thus the process is environmentally friendly.

The result of the combined action of the various aspects of the invention provides a chemical free water treatment system for cooling towers which does not rely upon chemicals being added; does not rely upon water bleed off to waste; does not rely upon manual cleaning; and provides efficient scale and corrosion control and; provides bacterial control to undetectable levels cf bacteria in condenser water outlet.

Claims (17)

1. A method of water treatment for a water supply system, the method comprising the steps of: in-line ultraviolet (UV) light sterilisation of water flowing through the water supply system; mechanically agitating the water by directing water under pressure through a plurality of flexible sweeping tubes mounted adjacent a floor of a water reservoir provided in the water supply system so as to produce a random snake-like motion of the sweeping tubes thereby lifting settled dirt or biomass in the reservoir; and, filtering the agitated water to remove the suspended dirt or biomass; whereby, in use, the combined effects of said steps of sterilisation, agitating and filtering can reduce the level of water borne bacteria and algae to negligible levels.

2. A method as defined in claim 1, further comprising the step of treating water flowing through said water supply system with electromagnetic or electrochemical means for crystallising scale-forming dissolved solids into suspended solids for removal by said step of filtering.

3. A method as defined in claim 1, wherein said step of in-line UV light sterilisation involves passing the water adjacent a UV light source located in a water supply pipe of the water supply system.

4. A method as defined in claim 1, wherein said step of filtering involves passing the water through a sand filter in a side stream circuit of the water supply system. A method as defined in claim 1, wherein said water supply system is a recirculating water supply system for a water cooling tower of an air conditioning plant, and said water reservoir is a basin in the cooling tower. 19

6. A system of water treatment for a water supply system, the water treatment system comprising: in-line ultraviolet (UV) light sterilisation means for sterilising water flowing through the water supply system; mechanical agitating means comprising a water inlet pipe extending into a vessel of the water supply system, for feeding water under pressure into the vessel, a plurality of flexible sweeping tubes connected to the inlet pipe and adapted to sweep the vessel in a random snake-like motion as water from the inlet pipe is ejected from the ends of the tubes, and a water outlet for removing water from the vessel whereby, in use, the motion of the sweeping tubes agitates the water and causes settled dirt or biomass to become suspended in the water for removal from the vessel via the water outlet; and, filtering means connected to said water outlet for filtering the agitated water to remove the suspended dirt or biomass; whereby, in use, the combined effects of said sterilising, agitating, and filtering can reduce the level of water borne bacteria and algae to negligible levels.

7. A system as defined in claim 6, wherein said in- line UV light sterilisation means comprises a UV light tube housed in a substantially transparent sleeve assembly for removably housing said LUV light tube and adapted to protect the light tube from exposure to water whereby, in use, th sleeve assembly can be immersed in flowing water with the cube therein radiating UV light into the flowing water in a region adjacent the sleeve assembly.

8. A system as defined in claim 7, wherein said sleeve assembly is in the form of a modular sleeve assembly comprising a pair of mouldings adapted to seal the ends of an elongate substantially transparent sleeve housing said UV light tube, and having electrical connecting means provided integral thereto for providing an electrical connection to the UV light tube, wherein said modular assembly can be located within a water supply pipe of said ~i Ac1 20 water supply system and electrical power supplied thereto through a wall of the pipe via said electrical connecting means.

9. A system as defined in claim 8, wherein said in- line UV light sterilisation means further comprises a plurality of impaction beads which recirculate in the flowing water in the region adjacent the sleeve assembly whereby, in use, the impaction beads randomly impact upon the sleeve housing said UV light tube to produce a cleaning effect. A system as defined in claim 6, wherein said water supply system is a recirculating water supply system for a water cooling tower of an air conditioning plant, and said vessel is a cooling tower basin, said inlet pipe being one of a plurality of pipes extending across the tower basin so that, in use, said sweeping tubes can sweep substantially the whole area of a floor of the tower basin.

11. A system as defined in claim 10, further comprising a side-stream water circuit, said filtering means comprising a sand filter located in said side-stream circuit for filtering the mechanically agitated water from the tower basin.

12. A system as defined in claim 11, wherein said side-stream circuit further comprises a back-flush system for directing back-flush water to a back-flush water recovering tank provided on top of the cooling tower, said recovering tank having a sand bed provided in the base thereof for filtering water that is gravity-fed back to the cooling tower.

13. A mechanical water cleaning apparatus for agitating water in a vessel of a water supply system, the apparatus comprising: a water inlet pipe extending into the vessel for feeding water under pressure into the vessel; a plurality of flexible sweeping tubes connected 21 to said inlet pipe and adapted to sweep the vessel in a random snake-like motion as water from the inlet pipe is ejected from the ends of the tubes; and, a water outlet pipe for removing water from the vessel whereby, in use, the motion of the sweeping tubes agitates the water and causes settled dirt and biomass to become suspended in the water for removal via the outlet pipe.

14. An apparatus as defined in claim 13, wherein said water inlet pipe is one of a plurality of inlet pipes extending through the vessel in such a manner as to permit said sweeping tubes to sweep substantially the whole area of a floor of a vessel. An apparatus as defined in claim 14, wherein each of said sweeping tubes comprises a flexible tube of plastics material provided with one or more weights fastened along its length, said weights providing minimal friction with a surface of said floor and ensuring the end of the tube remains under water.

16. An apparatus as defined in claim 15, wherein each sweeping tube is also provided with a nozzle at its free end, said nozzle having an orifice of reduced diameter compared to an internal diameter of the tube whereby, in use, a stream of water is projected forcefully from the orifice to propel the sweeping tube in said random snake- like motion.

17. An apparatus as defined in claim 16, wherein said water outlet pipe is one of a plurality of outlet pipes extending through the vessel adjacent regions swept by said sweeping tubes, said outlet pipes being located above said sweeping tubes so as not to impede the movement of the tubes.

18. An apparatus as defined in claim 17, wherein said water inlet pipe and water outlet pipe are each provided with a variable gate valve to adjust the flow rates of 22 water entering and leaving the vessel respectively whereby, in use, the performance of the sweeping tubes and the removal of suspended material can be optimised. 13. An apparatus as defined in claim 20, wherein said water supply system is recirculating water supply system for a water cooling tower of an air conditioning plant, and said vessel is a tower basin of the cooling tower. A method of water treatment substantially as herein described with reference to and as illustrated in any one or more of the accompanying drawings.

21. A system of water treatment substantially as herein described with reference to and as illustrated in any one or more of the accompanying drawings.

22. A mechanical water cleaning apparatus substantially as herein described with reference to and as illustrated in any one or more of the accompanying drawings. Dated this 4th day of March 1994. BIOLOGICAL CONTROL SYSTEMS PTY. LTD. By Its Patent Attorneys GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. V" •o h" o