WO2009121123A1

WO2009121123A1 - Non-toxic liquids for water treatment

Info

Publication number: WO2009121123A1
Application number: PCT/AU2009/000385
Authority: WO
Inventors: Graham George Strachan
Original assignee: Ultimate Nominees Pty Ltd
Priority date: 2008-04-01
Filing date: 2009-03-31
Publication date: 2009-10-08

Abstract

A liquid suspension for treatment of bodies of water and water systems containing algae or cloudy water, said systems containing a flocculant, preferably aluminium potassium sulphate, and a mineral, preferably calcium sulphate, admixed in a liquid, preferably water, and optionally containing a viscosity modifier, preferably a clay mineral.

Description

NON-TOXIC LIQUIDS FOR WATER TREATMENT

Field of the Invention

The present invention relates to a method of treating bodies of water or water systems containing algae, and primarily to a means of treating algae in bodies of water or water systems by causing the algae to flocculate to the bottom of the water body. It also relates to treatment of cloudy water in bodies of water or water systems.

Background of the Invention A vast amount of effort and money is expended in attempting to treat algae in waterways. Blooms of algae normally form in warm weather conditions - particularly in bodies of water which are stagnant. Algal growth is exacerbated by the inflow of nutrient-rich water, such as that which occurs from agricultural farmland which has been excessively fertilized. A number of methods are available for algae treatment.

Algaecides are commonly used to kill algae, but they have some major disadvantages:

• the dead algae release toxins into the water as they decompose nitrogen and phosphorus can also be released back into the water, thereby creating an environment for further algal growth

• algaecides only affect the algae which is currently in the water system i.e. they do not kill subsequent blooms

• finally, there is a growing awareness of the negative environmental impacts of adding toxic chemicals to waterways. Alum (aluminium potassium sulphate) or various other salts of aluminium or iron are often used for algae treatment. However, although these products can coagulate the algae particles, it can take several days or weeks before the algae eventually settle to the bottom of the body of water. In addition, aluminium and iron salts are acidic, and their use can impact on the natural balance of aquatic life in the body of water if used excessively.

Inert minerals such as bentonite or zeolite can also be utilised. These products eventually settle the algae, but they are slow-working. Various 'active' minerals such as calcium carbonate, calcium hydroxide or gypsum can be used. One can refer to these as 'active' because they react with phosphorus-containing compounds in the water to form calcium phosphate, which settles to the bottom. Over time, the reduction in phosphorus will starve the algae and it will die, but the timeframe can be several weeks.

None of these methods is used universally, as they all have disadvantages as outlined above.

There is a need for a product which brings together the advantages of these approaches without the corresponding disadvantages. Summary of the Invention

According to one aspect of this invention there is provided a liquid suspension for treatment of bodies of water or water systems containing algae, said suspension comprising a flocculant and a mineral admixed in a liquid, preferably water. The key differences from the traditional treatments are that the product is supplied as a relatively or substantially stable liquid, i.e., there is no need for on-site blending into a slurry, and the components are applied in a single application.

Throughout this document, alum (aluminium potassium sulphate) and gypsum (calcium sulphate) are used in the examples, but other flocculants and minerals could be substituted.

A range of minerals, both inert and active, can be used in the formulation. They can be selected from the group comprising calcium sulphate, kaolin, feldspar, bentonite, and talc. The main exceptions are alkaline minerals such as calcium carbonate or calcium hydroxide, which react with the acidic flocculant.

Inert minerals such as zeolite can also be used, but they do not have the longer term benefit of reacting with phosphorus-containing compounds in the water. It has been found that the most suitable mineral is calcium sulphate in its various forms, including gypsum. Being neutral, it does not react with the flocculant in the suspension. It has the additional benefit of reacting with excess phosphorus-containing compounds in the water over time: the phosphorus-containing compounds are converted to calcium phosphate (which is insoluble), thereby restricting future algal growth. Anhydrite, the nearly anhydrous form of calcium sulphite works in a similar manner to gypsum.

Any suitable flocculant could be used instead of alum in the formulation. These include other aluminium salts, including aluminium sulphate, ferric aluminium sulphate or related compounds of aluminium possessing another cation, or iron salts. However, iron salts tend to impart an undesirable pale brown colour to the water.

The suspension can be poured into the water and it will spread to form a cloud which will flocculate the algae. Alternatively, if poured behind a boat the propeller action will spread the product very effectively.

This invention dramatically reduces the equipment required, the time involved, and also results in a much faster and complete treatment of the algae.

It will be appreciated that the ability to apply the flocculant and the mineral simultaneously is in itself advantageous. If a mineral and a flocculant are applied separately, the time duration between the applications can mean that the complementarity of the two products is reduced because the product applied first has dissipated before the second product is applied.

It has also been found that the quantity of flocculant required to settle the algae is significantly lower when the mineral is present throughout the water column than when it has been allowed to settle to the bottom.

This invention acts to remove algae in the following way:

• the aluminium in the aluminium salt reacts in the water body to form aluminium hydroxide - a fluffy, white gelatinous product • the aluminium hydroxide attaches to the algae. Ordinarily, the aluminium hydroxide/algae particles would float in the water for an extended period

• however, the gypsum is also attracted to the aluminium hydroxide. The gypsum drags down the resulting combination, which settles out to the bottom of the water body.

Alum is used as a mordant in dyeing i.e. it binds the dye to the fabric. Its role in the current application may be seen to be similar - it binds the algae and the gypsum together to form a precipitate which drops to the bottom of the water.

Unlike algaecides, the method does not kill the algae. The method can also be used to clarify water containing very fine suspended solids. In addition to the active components, additives such as a dispersant and a viscosity modifier can be incorporated to impart stability to the suspension.

A slurry of gypsum in liquid alum generally will settle out of suspension in a few hours. As such it must be used relatively quickly. The alum imparts a fairly low pH of around 2.8 to the liquid, and it is very difficult to find a thickener which will be effective in such a low pH environment which does not require heating of the whole mix (e.g. gelatine).

However, it has been found that the addition of a small quantity of a clay mineral will suspend the gypsum. In addition, the clay mineral assists in the flocculation of the algae. As a refinement to this invention, an algaecide could be included in this suspension to enhance its performance if the killing of algae was not an issue.

To prepare approximately 1 litre of a typical liquid suspension, the following method can be used:

• to 500 ml of water, add 400 gm of fine gypsum and blend in well

• slowly add 100 gm of alum while stirring. The alum will froth initially, but will settle down over time

• slowly add 40 gm of Attagel 30 powder and blend until uniform

• if necessary to reduce foaming, add small quantity of defoamer such as Cognis Foamaster AP.

If the product is overdosed, the pH of the water may be reduced below a desirable level, as the alum in the formulation has a strong acidifying effect. The pH can be corrected by the addition of hydrated lime or caustic soda, but this tends to negate the 'one step' benefit of the formulation. However, the presence of algae in the water tends to raise the pH of the water in the first place, so the pH-lowering effect of this formulation is beneficial to the extent that it can help to take the pH back to its pre-algae level. A preferred formulation comprises:

This formulation provides the gypsum and alum in suitable proportions to allow the existing algae to settle, as well as providing surplus gypsum to react with future phosphorus inflows.

It has been found that the suspension remains stable for several weeks, which is sufficient for most applications.

Theoretically there is no upper limit to the concentration of gypsum in the formulation, as higher concentrations in the liquid will simply provide more surplus gypsum to settle on the algae at the bottom of the water body. However, it is believed that there may be a trade-off in terms of the rate at which the water clarifies: excess gypsum in the formulation may take a day or two to settle out. Other formulations could be prepared within the following concentrations of components:

At one extreme, these ranges allow for the liquid to be supplied in a very thin, dilute form which may be advantageous for certain applications where the product can be pumped and/or sprayed directly on to the water. At the other extreme, it may be advantageous to supply it as a paste in order to reduce freight costs. The paste could be re-constituted to a thin liquid with the addition of water at the destination.

They also allow for a wide variation in the gypsum /alum ratio to suit specific situations.

Between 50-150 litres of the suspension according to the invention should be sufficient to treat one megalitre of water. The effective dose rate depends on the concentration of the algal bloom. However, as algae moves up and down through the water column as part of its lifecycle, it is possible that the surface area may in fact be more relevant than the total volume. If a small amount of the suspension is stirred into the algae-containing water at the top of a flask, for example, it will generate activity throughout the water column.

According to another aspect of the invention suspensions prepared as aforesaid may be used to clarify cloudy water. According to another aspect of the invention there is provided a liquid suspension for treatment of bodies of water or water systems containing algae or cloudy water, said suspension comprising at least one fiocculant as hereinbefore described and at least one mineral as hereinbefore described admixed in a liquid, preferably water. The key advantages of this invention are:

• two or more components can be applied simultaneously to the water body

• as the product is in liquid form, there is no need for the handling of powders or for slurry mixing on site • when applied simultaneously, the interaction of the fiocculant and the mineral is more effective than if they are applied at different times (and certainly more effective than if only one or the other is applied), requiring less of each component to achieve a given result

• settlement of the algae is very rapid - usually just a few minutes - compared with a timeframe of several days or more for traditional methods

• it can also be used to clarify turbid water which may not have an algal problem. Description of Embodiments and Experiments

In developing and refining this invention, five sets of experiments on algae-infested water were carried out. One set of the experiments was also carried out on cloudy water without algae being present in the water. In each case, the experiments were carried out in a 1 litre glass cylinder.

Temperatures were maintained at 22⁰C - 25°C, and the glass cylinders were placed near a window to allow sufficient natural light.

Results from each of these are summarised below.

Experiment No 1: to gauge the impact of varying particle sizes of gypsum only (i.e. without the addition of alum).

In each case, 10 gm of gypsum was stirred into the water at the top of the column and the effect observed.

1000 micron = 1 mm The main conclusion from these experiments was that the finer gypsum had a greater impact on the algae, but not to a level which would make gypsum a viable product to remove algae by itself.

It is apparent that the finer the gypsum, the greater is the opportunity for each gypsum particle to be attached to the algae.

Gypsum did not have a significant impact on the pH of the water.

Experiment No 2: to gauge the impact of alum only (i.e. without the addition of gypsum).

These experiments showed that alum was effective at coagulating the algae when applied at a rate of more than about 2 gm per litre. However, the algae remained in suspension in the water column, which makes the treatment ineffective from a commercial viewpoint. In addition, the pH of the water dropped to 6.2 when 2 gm of alum were applied. In most commercial applications, it is desirable for the pH to remain above about 6.5.

Experiment No 3: to gauge the impact of applying both gypsum and alum. As about 2 gm of alum was found to coagulate most of the algae albeit without settling the algae to the bottom (Experiment 2), a third set of experiments was conducted by first applying 2 gm of alum to the water, and then applying increasing quantities of gypsum to the water. The aim was to determine the appropriate quantity of gypsum required to settle the coagulated algae to the bottom of the cylinder. Fine gypsum was used in these experiments, based on the results of Experiment 1.

It was concluded from this third set of experiments that 4 gm of gypsum in combination with 2 gm of alum was sufficient to settle all of the algae to the bottom (i.e. a ratio of 2 parts gypsum to 1 part alum) within 15 minutes of application.

However, the addition of 8 gm of gypsum (i.e. a ratio of 4 parts gypsum to 1 part alum) presented a surprising result. It was observed that the 'surplus' gypsum settled to the bottom as a blanket over the settled algae. This raises the prospect that the addition of surplus gypsum - above the quantity required in conjunction with the alum to settle the algae - can have two benefits: firstly, that the algae can be prevented from floating to the surface because of the blanket; and secondly, that the gypsum blanket is available to react with any phosphorus-containing compounds which may come into the water at a later time. In this second case, the phosphorus-containing compounds will react with the gypsum (calcium sulphate) to form calcium phosphate, which is insoluble and will drop to the bottom of the water. As algae requires phosphorus as a nutrient in its lifecycle, future algal growth will be discouraged.

It was found that the gypsum blanket remained in place for some weeks, and that the algae did not re-float to the surface. Therefore the combination of alum and gypsum forms a very effective

'package' to settle the existing out of the water, as well as providing a means of limiting future algal growth.

Experiment No 4: to formulate the gypsum and alum into a stable liquid suspension. Using the preferred ratio of 4 parts fine gypsum to 1 part alum, a fourth set of experiments was carried out with the aim of determining how to formulate a liquid comprising a suspension of the gypsum and a solution of the alum which remained stable over time.

Using a liquid comprised of 50% water, 40% gypsum and 10% alum (i.e. with the gypsum and alum present in the ratio of 4: 1), it was found that the gypsum settled rapidly to the bottom of the liquid. Reducing the quantity of water imparted a higher viscosity to the liquid, but it also tended to thicken up dramatically over time.

Various viscosity modifiers were trialled. The pH of the liquid was less than 3.0, which meant that most standard viscosity modifiers were ineffective.

It was found that Attapulgite clay thickeners were the most effective, as they can withstand the low pH of the suspension without degradation. The formulation is not as effective in salt water. It is surmised that the sodium chloride impedes the reaction which takes place in fresh water.

Experiment No. 5: to compare the effectiveness of the combined formulation with the effectiveness of the alum and gypsum added separately. Eight (8) gm of gypsum was added to algae-infested water and stirred in. After 1 day, 2 gm of alum were also stirred in. Although the addition of the alum precipitated some of the algae, there was still a significant quantity floating in the water after several hours. Much of the gypsum had settled to the bottom of the water before the alum was added, thereby negating the complementary effect.

Experiment 3 above with both the gypsum and the alum being added together at the same quantities as in this current experiment, completely cleared the water of algae.

This demonstrates that the application of the two active components simultaneously was more effective than their separate addition.

Experiment No. 6: to determine the impact of the formulation on cloudy water.

The preferred formulation was added to cloudy water at a dosage of 10 gm per litre of water. It was found that a similar result was achieved as when algae was in the water i.e. it flocculated the fine particles to the bottom of the glass cylinder within a few minutes.

It is to be understood that the invention may embrace many further modifications as would be readily apparent to persons skilled in the art and which would be deemed to reside within the broad scope and ambit of the invention. The preferred embodiment described above is by way of example only and is not to be considered as limiting.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form or suggestion that the prior art forms part of the common general knowledge in Australia or elsewhere.

Claims

1. A liquid suspension for treatment of bodies of water and water systems containing algae or cloudy water, said suspension comprising a flocculant and a mineral in a liquid.

2. A liquid suspension as claimed in claim 1 , wherein said flocculant is selected from the group comprising aluminium salts and iron salts.

3. A liquid suspension as claimed in claim 2, wherein said flocculant is one of aluminium potassium sulphate, or aluminium sulphate, or aluminium ferric sulphate.

4. A liquid suspension as claimed in claim 1, wherein said at least one mineral is selected from the group comprising non-alkaline minerals.

5. A liquid suspension as claimed in claim 4, wherein said at least one mineral is selected from the group comprising calcium sulphate (anhydrous or hydrated), zeolite, kaolin, feldspar, bentonite, and talc.

6. A liquid suspension as claimed in any preceding claim, wherein is added a viscosity modifier.

7. A liquid suspension as claimed in claim 6, wherein said viscosity modifier is a clay mineral.

8. A liquid suspension for treatment of bodies of water or water systems containing algae or cloudy water, wherein said suspension contains between 10 and 70% of calcium sulphate by weight, 2 and 40% of aluminium potassium sulphate by weight, between 1 and 10% a viscosity modifier by weight, with the remainder being water.

9. A liquid suspension for treatment of bodies of water or water systems containing algae or cloudy water, said suspension comprising 38% by weight of calcium sulphate, 10% by weight of aluminium potassium sulphate, 4% by weight of viscosity modifier, with the remainder being made up of water.

10. A liquid suspension for the treatment of bodies of water or water systems containing algae or cloudy water, said suspension being prepared by adding approximately 40% by weight of calcium sulphate to 50% by weight of water, blending well, slowly adding approximately 10% by weight of aluminium potassium sulphate with stirring, slowing adding approximately 4% by weight of Attagel 30 powder, and blending the suspension until uniform.

11. A method of treatment of bodies of water or water systems containing algae or cloudy water, wherein a liquid suspension, in accordance with any one of the preceding claims, is added to the body of water or water system to be treated, either by pouring into the body of water or water system or by agitating the suspension following the pouring into the body of water or water system.

12. A liquid suspension for treatment of bodies of water or water systems containing algae or cloudy water, wherein said suspension contains between 10 and 70% by weight of a mineral, between 12 and 40% by weight of a flocculant, between 1 and 10% by weight of a viscosity modifier, with the remainder being water.

13. A liquid suspension as claimed in any one of claims 1 to 7 wherein at least one additional flocculant as hereinbefore described and/or at least one additional mineral as hereinbefore described is present.