AU675512B2

AU675512B2 - Treatment of swimming pool water

Info

Publication number: AU675512B2
Application number: AU61774/94A
Authority: AU
Inventors: Dudley John Mills
Original assignee: Dudley Mills Pty Ltd; Innovez Pty Ltd
Current assignee: Dudley Mills Pty Ltd; Innovez Pty Ltd
Priority date: 1993-02-24
Filing date: 1994-02-24
Publication date: 1997-02-06
Anticipated expiration: 2014-02-24
Also published as: AU6177494A

Description

TITLE TREATMENT OF SWIMMING POOL WATER

TECHNICAL FIELD

This invention relates to compositions and methods for use in the treatment o swimming pool water. More particularly, it is concerned with the control of alga growth in chlorinated or unchlorinated fresh- or salt-water artificial swimming pools, and/or the reduction of the concentration of unpleasant chloramines in chlorinate pools.

The term 'algal growth' refers to the growth of aquatic algae and alga-like euglen species, together with the aquatic plant, animal or bacterial life-forms which ar associated with them. These organisms may be free-floating or may attach to the walls and bottoms of swimming pools.

BACKGROUND TO THE INVENTION

Algal growth in swimming pools leads, first, to a coating of slime on the walls and bottom, then, to an unpleasant green discolouration of the water and, finally, to the proliferation of micro-organisms and other aquatic life forms, some of which may be pathogenic for humans. The conventional ways of controlling such growth are chemical and mechanical in nature. The chemical approach is to add toxins, such a chlorine and algacides, to the pool water to kill the algae. The mechanical approach is to scrub the bottom and sides of the pool, by hand or with a moving suction-head to dislodge the algae and to pump the pool water through a filter to remove the free floating or dislodged material. Almost all pool owners use both chemical an mechanical treatments, though many have reservations about the wisdom of using algacides in their pools, from the standpoint of the health of swimmers,.

Pool owners generally recognise that the effort and expense needed to achieve given level of control over algal growth increases with the age of a pool and with poo usage. It is also generally appreciated that the water of well-used pools tends t develop an unpleasant acrid odour and to irritate the eyes and skin of swimmers, i being known that this is due to relatively high concentrations of chloramines in suc pools. The recommended treatment is an extended period of super-chlorinatio (during which the pool cannot be used), but the chloramine — and algal growth problems soon return after such a treatment. The situation is essentially the same fo fresh and salt pools.

5 Despite the widespread recognition of these pool maintenance problems, I have been unable to uncover any prior art which addresses them.

OBJECTIVE OF THE INVENTION

The objective of the invention is to provide methods and compositions for use in the lOtreatment of swimming pools to facilitate the control of algal growth, and/or the reduction of chloramines, without reliance upon the use of toxins, mechanical scrubbing or super-chlorination.

OUTLINE OF INVENTION

15 In contrast to the known art and current practice, the present invention is based upon the simple idea that algae in swimming pools may be starved rather than poisoned in order to control their growth. This invention therefore essentially comprises compositions and methods for removing from solution in pool waters one or more dissolved nutrients essential for algal growth. Hitherto, the concentration of dissolved 0 nutrients in swimming pools has tended to build-up over time, resulting in the ever- increasing pool management problems noted above.

The nutrients which I most prefer to target are those containing phosphorus, particularly phosphate, and (to a lesser degree) those containing nitrogen (including 5chloramines), but any of a number of other nutrients may be targeted. The phosphate nutrients may be removed from solution by ion-exchange with a particulate solid or by precipitation with a dissolved compound. The key nitrogenous nutrients (nitrates, nitrites and chloramines) tend to be chemically unstable and may be broken down with the aid of catalysts to release nitrogenous gases. I have found, first, that lanthanide, 0yttrium, zirconium and/or zirconyl compounds are very effective in scavenging phosphates from swimming pools for the purpose of controlling algal growth and, second, that these compounds (particularly the lanthanides) are useful in catalysing the breakdown of the unpleasant chloramines in pool water.

The nutrient elements required by algae (ranked in order of the atomic percentage 5 required) are generally taken to be carbon (as carbon dioxide and carbonate in water), hydrogen and oxygen (mainly as water), potassium, sodium, nitrogen (mainly as nitrates, nitrites and ammonia), sulfur (mainly as sulphates), calcium, magnesium, chlorine (as chloride), phosphorous (mainly as phosphate ions H₃P0₄, H₂P0₄ ^', HP0₄ ^2", P0₄ ^3") silicon, strontium, bromine and a variety of trace elements including iron, lOcopper, molybdenum, zinc, tin, etc. In principle, one or more of these nutrient elements could be targeted for removal but, bearing in mind that concentrations in water of only a few parts per billion (ppb) for many nutrients may be sufficient to support algal growth, the removal of most of these nutrients presents practical difficulties. Hydrogen and oxygen, as the basic constituents of water and as dissolved

15atmospheric oxygen, are clearly impractical targets. Carbon is also impractical as it is present in water as dissolved C0₂ (which can be re-supplied from the atmosphere) and, moreover, is often added as a bicarbonate to raise or buffer the pH of pool water. On the other hand, the trace elements are also impractical targets because they are readily oversupplied by small amounts of garden litter and soil carried into the pool. 0This leaves the nutrient elements present in intermediate amounts (eg, potassium, sodium, nitrogen, sulfur, calcium, magnesium, chlorine, phosphorus, silicon, strontium and bromine) as being more suitable targets. Of this group, potassium, sodium, calcium, magnesium, chlorine, silicon, strontium and bromine are not propitious as their precipitates are partially soluble in water at normal pH and/or they are often 5 present in many parts per million (ppm) in pool waters. Though it is feasible to target sulphates in waters with naturally low sulfur (< 100 ppm) by precipitation using barium or calcium compounds, the residual solubility of these precipitates and their large mass present a problem. Also, sulfur is often added to pools as NaHS0₄ to control pH or as a contaminant of other pool chemicals. I therefore prefer to target phosphorus and 0 nitrogen because the former can form highly insoluble phosphates and the latter can be removed as a gas, even in the presence of chlorine used for sterilisation. In a survey of swimming pools, I found phosphate concentrations ranging from a fe ppb to over 1000 ppb and I also found that the reported effort and cost of controllin algal growth correlated with phosphate concentration. Few pool owners perceived a algae problem when phosphates were below about 20 ppb but most were acutel aware of one at concentrations around 400 ppb and above. Phosphates are mainl introduced into swimming pools by the sweat and urine of swimmers, exudate fro overhanging trees, rain water and, ironically, from the breakdown products of po chemicals (such as cleaning agents) introduced by pool owners.

Phosphates and some other nutritional ions can be precipitated from water at roughl neutral pH with a variety of iron, aluminium and calcium solutions, but large volume of reagents (relative to the amount of phosphorus removed) are required, the resultan floes are unpleasant and tend to block pool filters. It is difficult to reduce th phosphate concentration in the pool water to below about 50 ppb in this way, concentration which is not low enough to stop algal growth. I prefer to use the solubl salts (eg the chlorides) of yttrium, zirconium, zirconyl and/or the lanthanide element to effect precipitation as they have high specific affinity for phosphates, thei precipitates are highly insoluble in pool water and they can reduce phosphat concentrations to below 5 ppb. Lanthanum chloride is particularly suitable.

Phosphorus ions may also be removed from pool waters by exchange with the anion of an insoluble paniculate material mixed (or otherwise brought into contact) with th pool water. As the anion displaced by phosphate is not important, there are man candidate compounds available, but few are highly specific for phosphate and fewe still are capable of forming stoichiometric phosphates when the concentration o phosphates in water is less than 10 ppb. Again, I have found that many insolubl lanthanide, yttrium, zirconium and zirconyl salts have these desirable propertie — especially lanthanum carbonate, La₂(C0₃)₃. It is also envisaged, however, that th active compound — for example, La₂(C0₃)₃ — may be formed in situ within the poo water by the addition of a precursor — for example, La_j>0₃ or LaCL₃. Turning now to the problem of nitrogenous nutrients and chloramines: Besides being contributed by the sweat and urine of users, nitrogen is introduced into swimming pools by the use of algacides based on amino complexes, flocculants based upon polyacrylamides or polyamines and nitrogenous garden fertilisers. The ke nitrogenous nutrients are thus nitrates, nitrites and chloramines; chloramines being formed by the reaction of chlorine and ammonia which is therefore not a key nutrient. I have found nitrogen concentrations around 15 ppm in many well-used pools where the effects of chloramines are objectionable to swimmers.

It is fortunate that the key nitrogenous nutrients — particularly, chloramines — happen to be chemically unstable and, therefore, may be removed by promoting their breakdown (releasing nitrogenous gas) with a suitable catalyst. The overall reactions involved include the following which can be considerably accelerated by the use of rare earth (and other) catalysts: N0₃ ²- + 2H⁺ => N0₂T + H_zO

N0₂ ² + 2H⁺ => NOt + H₂0 2N0₂ ²- + 8H⁺ => N₂T + 4H₂0 2NH₃ + 3CI₂ => 2N₂t + 6HCI Ideally, catalysts for such reactions in pool water will have two possible oxidation states at about pH 7 which can be switched by nitrogen and chlorine ions to break down chloramines. Lanthanide elements, such as cerium, praseodymium, terbium and lanthanum can switch between +4 and +3 oxidation states at about neutral pH, the +4 cations of the catalyst acting as electron acceptors for electrons from the nitrogen (at -3) of chloramines, and the resultant +3 cation of the catalyst then being switched back to +4 in the presence of chlorine.

While it is difficult to remove sufficient nitrogen in this way to control algal growth (without the use of specialised reactors), I have found that the break down o chloramines in pool water is significantly accelerated by the presence of the above- mentioned lanthanides, particularly lanthanum. Cerium and other rare earth catalysts are generally present in commercial grade lanthanum oxide to a minor degree. Thus, the acceleration of chloramine breakdown is a fortunate side-benefit of the use o commercial-grade lanthanum chloride, oxide or carbonate for the removal of phosphates from pool waters to control algal growth.

The matter of formulation of treatment compositions will now be considered. The precipitates produced using soluble lanthanides (eg the chlorides) have a very small particle size (< 5μm). They therefore cloud the pool water, settle slowly and tend to block common pool filters. Similar problems arise from the use of commercial grade insoluble compounds (such as lanthanum oxide or lanthanum carbonate) in the ion- exchange process, as they also have a large proportion of fine particles (< 10 μm). However, such fine particles are highly reactive so that phosphate removal is rapid. I therefore prefer to use a variety of specially formulated ion-exchange compositions which offer a beneficial compromise between reactivity and ease of removal:

1 Using hydrocyclones or air classifiers, classified paniculate ion-exchange material substantially composed of particles within the size range 10-50 μm may be produced. Such a material will remove phosphate from pool water as is settles over a few hours (eg, overnight) and can be vacuumed to waste or to the filter to remove it from the pool.

2 The particles of unclassified commercial-grade powders can be agglomerated into clumps larger than 100 μm (and, preferably, less than 2500 μm) and used in the same manner as the classified composition. Alternatively, the agglomerated composition may be added to the pool filter. Agglomeration can be effected by mixing with a suitable binder such as polyacrylamide. The amount required is very small, between 0.01% and 1% by weight of the active agent generally being sufficient.

3 Fine reagent particles may be agglomerated with larger and essentially inert porous carrier particles, such as those of diatomaceous earth. Preferably, the conglomerate particles are at least 100 μm in size. (Agglomeration may be achieved as indicated above.)

4 The particles of unclassified commercial-grade powders may be incorporated within a carrier matrix, preferably a hydrophilic and porous organic or siliceous polymer, such as polystyrene or an aluminate-silicate gel. The resultant conglomerate particles (hereinafter called beads) will normally have a relative density significantly greater than unity and will preferably have a particle size greater than 100 μm. Such a composition having a particle-size range of 150-2500 μm is well suited as a phosphate-adsorbing additive for pool filters.

5 The beads of the last-mentioned composition may be formulated to have a density significantly less than unity — that is, to float. This may be done by incorporating air into the beads. Such beads can be readily skimmed from the surface of the pool or collected in the skimmer-box.

6 Finally, commercial-grade powders may be formulated with flocculants which (when dispersed in the pool) capture the fines, linking them to the more coarse particles and bringing them down together.

These methods of formulating particulate compositions are generally well known to those skilled in the handling of powdered materials and therefore need little further elaboration. It will also be well appreciated by those skilled in the art that such compositions can be presented as pastes or slurries rather than as free-flowing powders. Moreover, those skilled in the ion-exchange art will be aware that formulations employing suitably-sized reagents or beads can be held in a reactor column and cycled between phosphate-adsorption and reagent re-generation. For example, carrier particles containing 'spent' lanthanum can be conveniently regenerated by washing, first, with a hydroxide and/or carbonate solution at pH 10+ and then with a bicarbonate/carbonate solution at about pH 8 to regenerate lanthanum carbonate.

A variety of organic polymers suitable for use in the beads are known. Australian patent 534337 to ICI, for example, discloses a method for incorporating ferromagnetic, activated carbon and the like particulate ion-exchange absorbents within porous polymer beads for use in water treatment. This patent also discloses the use of weighting agents such as zircon to achieve the desired bead density. Australian patent 548852 to ICI and CSIRO discloses a 'plum-pudding' amphoteric ion-exchange resin incorporating synthetic ion-exchange components within a porous polymeric matrix. A process for incorporating non-polymeric agents into a porous polymeric matrix disclosed in these ICI patents. It involves adding minerals as fine powders to the monomeric reagents, solutions and/or emulsions to form a slurry which is then polymerised to form beads in which the particulate agent is incorporated in a disperse condition.

I further envisage that polymer or siliceous beads can be mixed in a (preferabl aqueous) solution containing a liquid pre-cursor which impregnates them so that th finely divided active agents can be formed in situ by precipitation from the pre-cursor The pre-cursor may be, for example, lanthanum chloride, the precipitant could b sodium bicarbonate and the precipitated reagent could be lanthanum carbonate. Th active agents may also be precipitated (in finely-divided particulate form) into or ont a porous particulate carrier (such as diatomaceous earth) of the desired particle size. They may be applied as a coating on the larger carrier particles by mixing in a slurr of a suitable binder such as poiyacrylamide. The binder may be applied as monomer which is polymerised in situ to hold the reagent particles in place, but th coating must be porous and hydrophiiic.

As known in the art, the level of cross-linking and porosity of such polymer beads can be varied to suit the application. Beads intended for cycled ion-exchange column need to be more robust than those intended for once-only use in a swimming pool o for one-time use in a swimming pool filter.

Safety considerations favour the use of ion-exchange compounds such as lanthanu oxide/carbonate rather the precipitants such as lanthanum or zirconium chloride, bu there may still be a concern that the carbonates and oxides will be converted to th chlorides in stomach acid. The ion-exchange reagents may therefore be formulate with a non-toxic sulphate compound so that any chloride which forms in the stomach is immediately converted to the innocuous sulphate. Aluminium sulphate is convenient sulphate to employ because it is useful (upon dissolution) as a flocculan and as a pH buffer for pool waters. Safety and convenience considerations als suggest that the particulate ion-exchange compositions should be formulated a aqueous slurries or pastes rather than free-flowing fine powders. The phosphate scavenging ability of the preferred reagents will be seriously impaired in water that is too acid (< pH 6) or too alkaline (> pH 10). While pools with these characteristics have been seen, they are characteristically poorly buffered so that a small amount of material with good pH buffering capabilities (such as sodium carbonate or aluminium hydroxide) will be able to hold the pool pH at between pH 6.5 and pH 8 (preferably at pH 7.6) for sufficient time for the phosphate scavenging reaction to be completed and chloramines substantially reduced. The compositions may therefore be formulated to include such a pH buffer and, if formulated as a paste or slurry, will themselves have a pH with this range.

The ratios or proportions of the components can vary widely but will normally be based upon the amount of active agent required to react with substantially all of the phosphate within a pool. This, in turn, will depend upon the choice of active agent as activity can vary widely within the group of agents identified. Where a flocked carrier formulation is employed, it has been found that the carrier and the flocculant each need to be between one and three times the weight of the active compound. A similar amount of pH buffer may be needed, but it will he appreciated that AI₂(S0₄)₃ will serve effectively as (i) a flocculant, (ii) a pH buffer and (iii) a shield in the event of ingestion. Of course, sufficient water will be needed to create a slurry or paste of the desired consistency.

It will be appreciated from the above that a variety of different methods for treating swimming pools are envisaged, methods which may be used alone or in combination with one another: 1 Liquid precipitants or finely-divided ion-exchange/catalyst reagents may be mixed directly into the pool (eg, using the pool pump with the filter by-passed) to remove the target nutrient(s) from the pool water by precipitation or by ion-exchange. The particulate reaction products may then be physically removed from the pool by vacuuming-to-waste or by circulating the pool water through the pool filter. 2 Finely-divided reagents may be mixed directly into the pool (as above) together with a flocculating agent, allowed to settle as a floe and then removed from the pool. The flocculating agent may be of the well known types using iron or aluminium salts or long-chain organic molecules. For example, when AICI₃ is added to water of about neutral pH, an AI(OH)₃ floe is formed which, when settling, brings down much of the suspended particulate matter in the water.

3 Heavy, agglomerated reagent particles (with or without a carrier) or composite beads incorporating reagents may be added directly to the pool water, allowed to settle and then removed by vacuuming.

4 Agglomerated or composite beads (as in #3) may be added to the pool filter and pool water circulated through the filter to remove the target nutrients.

5 Light agglomerated or composite beads may be added to the pool, allowed to rise to the surface and skimmed off.

6 The ion-exchange/catalyst material may be contained in a separate reactor vessel and pool water circulated there-through, with or without the cyclic regeneration of the material.

DESCRIPTION OF EXAMPLES

Having broadly portrayed the nature of the present invention, particular examples of the use of the invention will now be described by way of illustration only.

Example 1 A 50,000 litre (I) uncovered swimming pool located in a suburban garden is used almost daily in the summer months by a family with children who are usually joined by friends in the pool at the weekends. On first inspection, the water was dull but not noticeably green, though there was a patina of algal growth on the walls, and both the walls and the bottom were slimy to touch. The pool was fitted with a diatomaceous earth filter, a roof-mounted solar heater and pump system with a capacity of 10,000 Itr/hr and a moving suction-head bottom-cleaner. Maintenance was heavy: the filter was operated for at least 8 hours per day (usually with the moving suction-head in action) and backwashed on the average once every 10 days; the sides of the pool were manually scrubbed with a long-handled brush at least once a week; 300 gm hypochlorite was added daily with 10 to 50 grams of cyanurate stabiliser, 50 to 200 grams of sodium bisulphate and 50 to 200 ml of algacide. In addition, floating leaf and insect litter was removed at least once a day using a long-handled net. The pool had a strong chloramine odour and the users complained of stinging eyes. Measurement revealed a water temperature of 25 °C, a pH of 6.5, chlorine at 1.5 ppm, 'combined chlorine' (an indicator of chloramines) at 1.8 ppm and phosphorus as phosphates at 450 ppb (ie, approximately 25 gm of phosphorus in the pool).

Given the user's wish not to interrupt pool usage, the filter supports were inspected to ensure that there were no holes or tears and a slurry of 150 gm of lanthanum carbonate power (with a particle size of about 5 μm) was prepared and added to a fresh diatomaceous earth filter bed by pouring the slurry into the skimmer box while the pump was circulating water through the filter. The filter was then operated 14 hours per day for a week (while chlorine addition was maintained) and then backwashed, at which time the phosphate concentration had been reduced to about 2 ppb, combined chlorine was about 650 ppb, the water was noticeably more clear, the walls were no longer slimy to touch, there was no visible trace of algae, there was no odour of chloramines and the pool pH had naturally risen to 7.5. Thereafter, only 450 gm hypochlorite was added per week, no other chemicals were used (including lanthanum carbonate), the filter was operated only one or two hours per day (usually without the suction-head), wall-brushing was undertaken only once every four weeks, filter backwashing was needed only after 105 days. The pool still had no noticable chloramine odour, appeared crystal-clear and sparkling and the users reported much more comfortable and pleasant swimming without eye-sting or the need to use goggles. At the end of the season, after more than three months of use with this low level of maintenance, phosphate concentrations had risen to about 100 ppb and detectable slime had returned to the sides of the pool.

Example 2

An uncovered suburban pool of 20,000 with a sand filter is used for only one or two weeks a summer when grandchildren visit the elderly owners; it is generally unused for 11 months of the year and occasionally not used at all for 23 months. The owners wish to keep the pool looking clean but find the cost and effort of pool maintenance a heavy burden. When inspected, the walls and bottom of the pool were green with algae, though they were still visible. The pool was said to have been in this condition for some months. Maintenance comprised adding 200 gm hypochlorite to the pool waiting for a day, then running the filter a few hours once a week until it neede backwashing and then backwashing the filter. Phosphorus * as phosphate wa measured at 50 ppb (approximately 1 gm phosphorus in the pool), pH at 7.5 an chlorine at 0.4 ppm (the day after the last treatment).

The pool was treated as follows: the algae was killed by the addition of 1 kg o hypochlorite. After 24 hours, the walls and bottom of the pool were scrubbed with long-handled brush and the debris allowed to settle for a further day before being vacuumed to waste. The filter was then run for a 8 hours, backwashing twice. Give the use of La^CO_j)., as the active phosphate-scavenging agent, the amount require was estimated by assuming that La would couple stochiometrically to the pool P an allowing a safety factor of 2. A slurry was prepared using diatomaceous earth as carrier for the La₃(C0₃)₃ and AI(OH)₃ as a linker and flocculant in the following manner. Given that LaP0₄ will be formed, the actual weight ratio of La to P will be theoretically 4.5 gm:1 gm; ie, approximately 10 gm equivalent weight of La will be required, allowing for the safety factor. Assuming that the La is added in the form of o La;,(C0₃)₃ the weight of these compounds required will be, respectively, about 11 gm and 17 gm.

The flocculant used in this example was AI(OH)₃, and assuming that AI:La is 2:1 , it was calculated that 10 gm AI(OH)₃ was required. Adding the Al to the composition as AI₂(S0₄)₃, about 44 gm will be required, ignoring water of hydration. In this example, diatomaceous earth was used as the carrier, at least the same amount as the AI₂(S0₄)₃ and LagOg or LaCI₃ combined being required. In this example, about 60 g of diatomaceous earth was used. The AI₂(S0₄)₃ and the LaCI₃ are first each separately mixed with 100 ml water, then combined and the diatomaceous earth is added. This slurry was found to have a pH of about 4. To raise this pH and to provide the pH buffering capacity needed within the pool, an aqueous solution of Na₂CO₃ was added to the slurry (while stirring) to bring the pH to 8. About 125 g N^COa in 200 ml water was required. The resultant slurry to be added to the pool was about 500 ml and weighed about 0.8 kg. It had the following component moieties: S0₄ ^2", AI(OH)₃, La₂(C0₃)₃,C0₃ ^2" (assuming an excess of Na^O., was employed, as is desirable), H₂0, Cl^" (if LaCI₃ was used) and Na⁺.

The slurry was mixed in the pool using the pool pump with the filter by-passed, the slurry being poured into the skimmer box, and the pump was left running to continue the mixing for a few minutes and the water was uniformly cloudy. The pump was then turned off and the floe allowed to form and settle overnight, at which time the pool water was clear and a layer of whitish-grey floe was evident on the bottom. After this floe was vacuumed to waste, the walls and bottom of the pool were lightly scrubbed again and filter was operated for about five hours. Pool phosphate concentrations were monitored after initiation of the treatment and were found to have dropped within a few minutes to about 3-4 ppb, indicating a very rapid and effective scavenging action. At the end of the treatment (with the water thoroughly mixed), the pool appeared crystal clear and the phosphate concentration was found to be 1 ppb. The only maintenance then undertaken for the next 12 months was to hand-skim the pool of leaves and insects and to operate the filter and suction-head a few hours per week, backwashing being require about once a month. Since the pool was not being used, hypochlorite was not added and no other chemicals were used. After 12 months the phosphate concentration was found to be about 8 ppb and the pH 7.5, the water still being clear. All that was required before the pool was used again was to add 200 gm of hypochlorite.

Example 3

Styrene-based polymeric ion-exchange beads of 250-700 μm incorporating up to 75% lanthanum carbonate particles of 5-10 μm were made in the manner disclosed in Example 12 of Australian patent No 534337. 250 g of the beads were added to the sand filter of a pool like that of Example 1 and the filter was operated continuously for four days. Phosphate concentrations in the pool water were monitored during this time and were found to fall logarithmically from 400 ppb to 30 ppb in a manner consistent with the assumption that the phosphate removal efficiency of the beads within the filter was 90-95%. Example 4

The beads formed in accordance with Example 3 were recovered by back-washing the sand filter, about 90% (w/w) being recovered. These beads were washed in tap water to remove surface contaminants and added to a beaker containing 500 ml of an δaqueous solution of sodium hydroxide and carbonate at pH 12 and stirred for 10 minutes at 30°C. to convert the lanthanum phosphate to lanthanum hydroxide/carbonate. The beads were then filtered and transferred to 500 ml of an aqueous solution of sodium carbonate/bicarbonate at 30°C and pH 7 to convert the lanthanum hydroxide to lanthanum carbonate , the pH being reduced to about 8 in so 0doing.

The re-charged beads were then washed in distilled water at pH 7.5, removed and dried. 1 gm of the dried beads were then added to a flask containing 5000 ml of distilled water at 20°C, and buffered with sodium bicarbonate to pH 7.5. 1 ml of 0.01 % 5pool hypochlorite was then added to raise the chlorine content of the water to 2 ppm to simulate a normal pool. Sodium phosphate was then added to the water (to simulate a phosphate nutrient concentration of 400 ppb and the water was stirred for 30 minutes while 10 ml samples water were taken every minute.

0 An equal weight of virgin beads formed as described in Example 3 were subjected to the same treatment as the reformed beads. The results indicated that the capacity of the reformed beads to scavenge phosphate was about 92% of that of the virgin beads and that (assuming the lost capacity was due to leaching and/or poisoning of the active agent from the reformed beads) there was no measurable difference in the 5 specific rate of uptake of phosphate between the virgin and the reformed beads.

Example 5

Silicate-aluminate beads were formed as follows. A 2:1 aluminate-silicate mix was formed and 100 gm was added to 900 ml of an aqueous sodium hydroxide solution 0 of pH 12 to make up approximately 1000 ml of alumino-silieate solution. 100 gm of -20 μm lanthanum carbonate powder and 10 gm sodium carbonate (to ensure excess carbonate) were thoroughly mixed into the solution and hydrochloric acid was gradually added to return the pH to 7.5-8.0 and set the gel. After setting, the gel wa macerated and sieved to produce a first fraction of 20-200 μm, a second fraction o 200-2500 μm and a third fraction of >2500 μm which was returned for furthe maceration. 5 Laboratory evaluation using simulated pool water confirmed that substantially all of th lanthanum carbonate in the beads of -2500 μm was accessible by phosphate ions an that the rate of reaction varied only slightly more than inversely as the square of th bead diameter. The matrix material therefore appeared to present little inhibition t 10the ion-exchange process. Reactivity was confirmed by mixing beads of the firs fraction directly into a simulated pool and allowing them to settle, and by adding bead of the second fraction to a sand filter and passing pool water through it. The latte beads could be readily removed from the filter by normal backwashing.

15 Summary of Benefits of the Examples

The benefits evident from Examples 1 and 2 over the conventional pool management methods include the following:

1. Management of a swimming pool to achieve a given level of water quality is simplified and rendered less expensive, requiring less labour, materials an

20 energy.

2. The pool can be left unattended and unused for longer periods of time withou fear of an algal bloom.

3. Fewer toxic chemicals in lesser amounts are required.

4. There is less environmental impact from discharged pool waters, and from th 25 storage, transport, use, and spillage of pool chemicals.

5. The risk of poisoning from toxic chemicals is reduced.

6. Less chlorine smell and less "stinging eyes" resulting from chloramines.

7. Capital expenditure on automatic chlorine/ozone generators and mechanica sweepers can be reduced.

308. Less energy for pumping of water is required. 9. Less wear on pumping and filtration systems. Though a range of preferred and possible pool treatment methods and compositions have been offered, chemists will appreciate that many modifications to these methods and compositions — along with many alternatives — are possible without departing from the broad and general principle of controlling algal growth in swimming pools by removing nutrients essential for the algae.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

1. A method of treating swimming pool water comprising the step of removing from solution in the pool water at least one nutrient which is essential for algal growth.

52. A method according to claim 1 comprising the step of mixing or otherwise contacting the pool water with a finely divided particulate material which is insoluble in pool water having a pH between 6.5 and 8.0, to effect the removal of phosphate ions from solution by a process of ion exchange with said material thereby converting said material to an insoluble particulate phosphate. 0

3. A method according to claim 1 comprising the step of mixing a water-soluble substance with the pool water to precipitate phosphate dissolved in the pool water from solution as a particulate phosphate material which is insoluble in pool water at pH 6.5 to pH 8.0. 5

4. A method according to claim 1 comprising the step of mixing or otherwise contacting the pool water with a liquid or particulate substance to catalyse or accelerate the breakdown of dissolved nitrate/nitrite and chloramine nutrients so as to release gaseous nitrogen from the pool water. 0

5. A method according to claim 1 comprising the step of mixing or otherwise contacting with the pool water a finely-divided particulate insoluble material including one or more lanthanide, yttrium, zirconium or zirconyl compounds (other than phosphates) to effect the removal of phosphate ions from solution by ion exchange 5 and to catalyse the breakdown of chloramines within the pool water.

6. A method according to claim 1 comprising the steps of: mixing into the bulk of the pool water a first substance including finely-divided particulate insoluble lanthanide, yttrium, zirconium or zirconyl compounds (other 0 than phosphates), mixing into the bulk of the pool water (together with or separately from the first substance) a second substance including a soluble compound to cause the flocculation and settling of the first substance, and removing the flocculant, together with the reacted and any unreacted first substance, from the pool water by suction to waste or by filtration.

7. A method according to claim 1 comprising the steps of:

• mixing into the bulk of the pool water a finely-divided insoluble particulate lanthanide, yttrium, zirconium or zirconyl compound (other than a phosphate) aggregated into composite particles, beads or clumps containing macro-pores, allowing the composite particles to settle out while removing dissolved phosphate from the pool water by ion exchange and while catalysing the breakdown of nitrogenous ions to release nitrogen from the pool water, and removing the composite reacted and any unreacted particles from the pool water by suction to waste or by filtration.

8. A method according to claim 1 comprising the steps of:

• mixing into the bulk of the pool water a finely-divided insoluble particulate lanthanide, yttrium, zirconium or zirconyl compound (other than a phosphate) aggregated into composite particles, beads or clumps containing macro-pores, said particles, beads or clumps being less dense than water, allowing the composite particles to rise to the surface of the pool while removing dissolved phosphate from the pool water by ion exchange and while catalysing the breakdown of nitrogenous ions to release nitrogen from the pool water, and skimming the composite reacted and any unreacted particles from the surface of the pool water.

9. A method according to claim 1 for use in pools which have a filter connected for the circulation of pool water, said method comprising the steps of: adding to the filter and retaining therein particles of an insoluble particulate lanthanide, yttrium, zirconium or zirconyl compound (other than a phosphate), circulating pool water through the filter to contact said insoluble particles to effect the removal of phosphate ions from the pool water and to catalyse the breakdown of chloramines therein, and backwashing the filter to remove said particles (reacted and unreacted) therefrom.

10. A method according to claim 1 comprising the step of: circulating the pool water through a reactor vessel having a bed formed from particles of lanthanum carbonate to remove phosphate ions from the water and/or to catalyse the breakdown of chloramines in the pool water.

11. A method according to claim 10 including the steps of:

• stopping the circulation of pool water through said vessel, washing the reactor contents with a hydroxide and/or carbonate solution at a pH of at least 10, washing the reactor contents with a bicarbonate/carbonate solution at pH 6.0 -

8.5 to regenerate the lanthanum carbonate, and re-circulating the pool water through said reactor vessel to remove further phosphates therefrom.

12. A composition for use in the treatment of swimming pool water comprising a reagent adapted, upon admixture with the water, to remove from solution by precipitation, ion-exchange or conversion to gas at least one nutrient critical for algal growth.

13. A composition according to claim 12 wherein the reagent is selected from the group comprising lanthanide, yttrium, zirconium and zirconyl compounds (other than the phosphates) and is adapted to effect the removal of phosphate ions from solution in the pool water by precipitation or ion-exchange and/or is adapted to catalyse the reakdown of nitrogenous ions and dissolved nitrogenous complexes to effect the release of nitrogen from the pool water as a gas. 14. A composition according to claim 13 wherein the reagent is a finely-divide insoluble particulate material having an average particle size between 10 and 50 μ .

15. A composition according to claim 13 or 14 characterised in that:

5» the reagent particles are incorporated within and/or bonded to the surface o porous and hydrophilic beads of organic or siliceous polymeric material

16. A composition according to claim 13 or 14 characterised in that: the reagent particles are agglomerated into clumps by a hydrophilic and porous 10 binder material.

17. A composition according to claim 15 or 16 wherein the clumps or bead (respectively) have an average particle size of between 100 and 2500 μm

1518. A composition according to any one of claims 15 wherein the carrier or matrix material comprises diatomaceous earth, silica gel or cross-linked polystyrene.

19. A composition according to any one of claims 13 to 18 wherein the reagent comprises lanthanum carbonate.

20

20. A composition according to any one of claims 13 to 19 wherein the reagen comprises one or more particulate lanthanide catalysts, including lanthanum carbonate.

2521. A composition according to any one of claim 13 to 20 including: a soluble aluminium compound adapted to form a floe when the composition is added to pool water.

22. A composition according to any one of claims 13 to 21 including: 30* a water-soluble pH buffer adapted to hold the pH of the pool water between 7 and 8 during the reaction of the reagent with the dissolved nutrient or nutrients in the water. 23. A composition according to any one of claims 13 to 22 including: a water-soluble non-toxic sulphate compound, the equivalent weight of the sulphate being at least equal to that of the reagent.

24. A composition according to claim 13 including: a particulate lanthanum carbonate reagent having a particle size less than 20 μm, aluminium sulphate as a flocculating agent, * a particulate siliceous carrier or diluent having a particle size less than 50 μm, and sodium carbonate as a pH buffer, the composition being formulated as a slurry, paste or a flowable dry particulate material.

25. A composition according to claim 24 wherein the weight of carrier to that of the reagent (when dry) is 1 :1 to 3:1 , the weight of the flocculant to the weight of the reagent (when dry) is 1 :1 to 3:1 and the weight of the pH buffer (when dry) to the weight of the reagent is 1 :1 to 3:1.