AU743075B1 - Control of algae and legionella - Google Patents

Description

P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: Feliciano R. Sagun Feliciano R. Sagun FREEHILLS CARTER SMITH BEADLE Level 32 MLC Centre Martin Place Sydney NSW 2000 Australia Control of Algae and Legionella The following statement is a full description of this invention, including the best method of performing it known to us Control of algae and legionella Field of the invention The present invention relates to a method to control and reduce populations of algae and bacteria in water.

Background of the invention Humans face an increasing challenge, to guarantee the supply of sufficient quantities of water as cities and populations grow. Ensuring this water is pure is critical, and requires us to control and minimise levels of contaminants such as algae and bacteria.

Algae contain a wide range of light-harvesting photosynthetic pigments the chlorophylls and carotenoids which harvest light energy for photosynthesis and growth. The abundance and diversity of aquatic algae varies from one environment to the next and is influenced most by light and nutrients. When nutrients are abundant, as occurs in some polluted waters, algal cell numbers can become great enough to produce obvious patches of algae. These "blooms" or "red tides," however, do not occur every time favourable conditions exist, and therefore it is difficult to explain or predict their occurrence.

While algae can be an abundant source of food, they can also be extremely harmful to humans. Some algae, for example, produce toxins that become concentrated in shellfish and finfish making them unsafe or poisonous for human consumption; paralytic shellfish poisoning is caused by the nerve toxin saxitoxin, probably the most toxic compound known, diarrheic shellfish poisoning is caused by okadaic acids that are produced by several algae, especially species of Dinophysis, while neurotoxic shellfish poisoning is caused by toxins produced in Gymnodinium breve, a red tide organism.

Algal blooms are due to short lived, sudden increases in phytoplankton abundance (more than ten times), which appear in a predictable sequence from small, chain-forming diatoms to large, centric diatoms to large dinoflagellates. Diatoms are either unicellular or colonial members of the algal division or phylum Bacillariophyta. Their silicified cell walls form pillbox-like shells (frustule) composed of overlapping halves (epitheca and hypotheca).

With the right temperature and nutrients, dinoflagellate populations can quickly multiply into dense blooms that discolour the seawater. Most plankton blooms are harmless, but in some circumstances they become so densely concentrated that they deplete the oxygen in the water.

On other occasions they can become dangerous to humans both directly and indirectly. Red tides for example can provide a source of airborne toxins or cause harm by poisoning the aquatic life in the region.

In large ecosystems (oceans) in particular there is little to be done to prevent or contain such events, but even in more controlled environments the task of controlling populations of algae is extremely difficult.

In internal waterways, such as rivers, lakes, dams and ponds, algal blooms can have a devastating effect on the environment. For example, in recent summers in Australia, blooms of blue-green algae have led to large-scale killings of fish and the poisoning of livestock. Inland population centres may also have their water supply interrupted due to algal blooms causing drinking water sources to become toxic.

While algae are better known to inhabit larger bodies of water, smaller, enclosed aquatic systems are home to many types of bacteria. One such bacteria is the Legionella pneumophila named following the outbreak of a severe respiratory illness Legionnaires' disease among delegates attending the 58th Annual Convention of the American Legion in Philadelphia USA in July 1976. L. pneumophila is the most commonly implicated of one of more than twenty currently recognised species in the genus Legionella.

Legionella is a bacteria naturally occurring in surface water and is widespread in the environment. It has been found in lakes, rivers, creeks, hot springs and other bodies of water and soils. Legionella is therefore also found in man made systems such as cooling towers associated with air conditioning and industrial processes, evaporative condensers, air washers, humidifiers, hot water heaters, spas, fountains, plumbing fixtures, as well as in reticulated warm water systems, where the temperature of the water is kept between 200C and 45 0 C. These man made systems can provide conditions that allow the bacteria to breed rapidly to large numbers.

People are infected with Legionella when they inhale contaminated aerosols containing these bacteria; there has been no reported person to person spread, nor does infection occur from drinking Legionella infected water.

Because of the susceptibility of water systems to provide favourable breeding conditions for bacteria, constant maintenance is of paramount importance. Some of the required tasks include frequent visual inspection, upkeep of the mechanical components, proper control of pH, control of dissolved solids, the minimisation of organic material such as decaying leaves in the water, and use of surfactants and biocides typically strong oxidants such as chlorine or bromine to prevent the proliferation of organisms in the water during operation. Some of the many requirements of biocides include efficacy against a wide range of bacteria, algae, protozoa and fungi, long activity time, lack of mammalian toxicity and environmental compatibility.

If normal maintenance procedures have been ineffective and high numbers of Legionella are found in a water system, a relatively simple procedure for disinfecting water systems with chlorine and detergent is available. This procedure, however, is not part of a routine ongoing maintenance program because equipment may become corroded.

One problem, however, with chemical control of Legionella is that particulate matter, such as scale, debris, slimes and the presence of other microorganisms such as protozoa have the potential to shield Legionella from biocides potentially resulting in their persistence and proliferation when biocide levels fall. One solution to the problem of dissolved solids in the water is to discharge a small percentage of the total volume to waste (bleed-off) and replace it with fresh water. This discharge has the effect of limiting the concentration of total dissolved solids and is usually controlled in association with chloride ion analysis of the water. The discharge itself, however, must be treated and disposed of appropriately.

In general therefore there is an opportunity to improve our methods for controlling and reducing populations of algae and bacteria in our water systems. The current methods, where they exist are unreliable and difficult to enforce.

It is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties or deficiencies associated with the prior art.

003931903v4.doc 4 Summary of the invention In a first aspect, the present invention provides a method for controlling or reducing populations of aquatic algae in a body of fresh water or non-saline water comprising the steps of oxygenating the body of water containing said algae, and introducing milkfish (Chanos Chanos) into the body of water to thereby control or reduce the population of algae.

Preferably, the method of the first aspect further comprises the step of allowing the population of algae to grow following commencement of oxygenation of the body of water and prior to the introduction of the fish.

More preferably, the method further comprises monitoring various parameters of the system including concentration of algae and size of the fish and removing the fish when they have reached a predetermined size or the amount of algae has been reduced to a satisfactory level.

The body of water can be of any suitable type including open or closed systems such as lakes, reservoirs, dams, cooling towers, evaporative condensers, air washers, humidifiers, hot water heaters, spas, fountains, plumbing fixtures, and bodies of cooling water used for other purposes such as plastic injection moulding.

The water may be sparged or otherwise aerated until the dissolved oxygen content is preferably between 4.0 and 7.5 ppm.

The concentration of algae may be allowed to reach a level such that it can sustain the introduction of some particular number of fish.

The fish may be removed from the body of water containing the algae either when the fish have grown to a predetermined size, or once the concentration of algae has been reduced to a satisfactory level, said level determined by the relevant regulatory body, or independent of such jurisdiction 0-100 algae/ml, preferably 0-10 algae/ml. If the fish reach a predetermined size prior to the algae reaching a satisfactory level, it is preferred that further fish are added to the body of water.

The milkfish added to the body of water will eat algae and will not be a predator !R /towards other aquatic life in the body of water.

7D* rf 003931903v4.doc Milkfish is especially preferred for use in fresh water systems because milkfish does not breed in fresh water. Thus, the milkfish will not increase in population in the body of water.

In a second aspect, the present invention provides a method for controlling the level of bacteria in a body of fresh water or non-saline water contained in a closed water system comprising introducing milkfish (Chanos Chanos) into the closed water system.

Closed water systems typically include a primary water containment vessel, with water flowing out of that vessel, through the system and back into the vessel. In such cases, it is preferred that the aquatic life is added to the primary containment vessel. It is also preferred that the primary containment vessel is fitted with egress prevent means to prevent egress of the aquatic life from the primary containment vessel. This will ensure that the aquatic life does not block any pipes or damage any pumps in the closed water system.

In another embodiment, the method of the second aspect further comprises directing a flow of water from the closed water system to a vessel containing the milkfish and returning water from the vessel to the closed water system. Preferably, this embodiment comprises removing water from the primary containment vessel to a second vessel, said second vessel containing said milkfish, and passing said water through the second vessel and returning it to the first. The closed water system may be of any suitable type including cooling towers, evaporative condensers, air washers, humidifiers, hot water heaters, spas, fountains, plumbing fixtures and bodies for cooling water for other purposes such as plastic injection moulding.

Claims or molluscs are preferably also added to the body of water. More preferably freshwater snails, especially paddy rice snails are used. Most preferably milkfish, in sustainable combination with any or all of the group of aquatic animals consisting of clams, molluscs or freshwater snails, especially paddy rice snails, are used.

The secondary containment vessel may be of any suitable type and in any suitable location. In one embodiment the secondary vessel is adjacent to the primary containment vessel. In another embodiment the secondary containment vessel may be removed from the primary containment vessel such as in the form of a decorative aquarium.

In both the first and second aspects of the present invention, it is preferred that the body of water be treated to reduce contaminants prior to introducing the aquatic life in the event that the body of water contains contaminants that are harmful to the aquatic life. For example, a body of water may contain high levels of herbicides or pesticides that are harmful to milkfish.

The body of water is preferably treated to reduce the levels of herbicides or pesticides therein.

The treatment method may be any suitable treatment method known to the person of skill in the art. Indeed, in the first aspect of the present invention, the treatment method may include or consist of the aeration step, as the aeration step will oxidise some contaminants.

In a third aspect of the invention there is provided a method where any silt, mud or particulates in the water are made to flocculate by use of an appropriate additive such that this solid matter collects on the bottom of the secondary vessel where it is processed by the aquatic life in the system, the aquatic life being chosen for their willingness to feed on bacteria in such conditions.

In a fourth aspect of the invention there is provided a water cleansing system comprising in part a tank adapted to housing fish and or other aquatic life, said tank being fitted with an inlet and outlet port, each containing a filter, said inlet and outlet ports being located on the tank such that the efficiency of cycling all the water through the tank is maximised.

The present invention will now be more fully described with reference to the accompanying Examples and drawings. It should be understood, however, that the description following is illustrative only and should not be taken in any way as a restriction of the generality of the invention described above.

Detailed description of the embodiments The present invention describes the use of aquatic life forms to control and reduce populations of algae and bacteria in water. Preferred aspects of the invention comprise the steps of; preparing a body of water containing said algae and/or bacteria, introducing aquatic life that feed on algae and/or bacteria to said body of water or directing the water to another containment vessel housing said aquatic life, monitoring various parameters of the system including the concentration of algae and/or bacteria and the disposition of the aquatic life, removing the aquatic life from the system either when they have reached some predetermined size or the amount of algae and/or has been reduced to a satisfactory level, or returning the removed quantity of water to the primary containment vessel.

Some forms of aquatic life suited to such an application include the milkfish, and various clams, other molluscs and snails.

Milkfish, also called bandeng, or bangos (Chanos chanos), is a silvery marine food fish that is the only living member of the family Chanidae (order Gonorhynchiformes). It is a toothless herbivore of 1 to 1.5 m when fully grown and may weigh as much as 15 kg. Found abundantly in the warmer regions of the western Pacific and Indian Oceans, the milkfish is often collected when young and raised for food in brackish or freshwater tropical ponds. It is ideally suited to such fish farms as it can withstand very shallow, warm (310 C) lagoon water. Also, milkfish grow rapidly and do not need expensive feeding programs. They will also tolerate crowding without being cannibalistic. Milkfish feed on the weed, plankton and detritus which reduces the amount of nutrients available to produce the unwanted algae and slime. They are relatively efficient at converting algae into animal protein, thus suggesting their use in milkfish aquaculture.

While the eggs of the milkfish are unable to survive in high salinity environments, the fish can be bred in brackish water and acclimatised to new, higher levels of salinity. In nature the milkfish offspring feed on microscopic plants. If food is plentiful and this varies greatly with the level of sophistication of the farming method the milkfish grows rapidly, reaching a weight of as much as 0.5 kg within the first six months. If the food is inadequate and they are held in overcrowded ponds, their growth will be stunted.

In the event that an algal bloom occurs on a waterway, such as an inland farm dam, the huge increase in algal biomass in the dam consumes essentially all of the oxygen in the water.

Simply introducing milkfish into this environment would quickly result in the milkfish dying.

As a first step in the method of the first aspect of the present invention, the dam is aerated. Aeration may be achieved by placing one or more spargers into the dam and pumping compressed air through the spargers. Alternatively, one or more water fountains or jets which pass a spray or jet of water upwardly into the air may also be used. Aeration causes further growth of algae as the. oxygen content of the water is raised.

After a suitable period of aeration, the milkfish may be introduced into the dam. The milkfish are preferably introduced at fingerling size so that a large number of milkfish can be introduced. The milkfish will immediately begin to eat the algae. Aeration should be maintained until the level of algae has been reduced sufficiently to prevent oxygen depletion in the water.

As another desirable aspect of the present invention, the milkfish may be culled or thinned as the algae are reduced to satisfactory levels. The culled or thinned milkfish may be sold as food or for processing into food products.

The milkfish are highly suited to this application. They are capable of survival in very warm and potentially highly saline environments. They are also herbivorous and therefore nonpredatory when confined and densely populated.

In a preferred embodiment of the second aspect of the present invention, a cooling water system of the air conditioning unit of a city office tower has a cooling water holding vessel.

Water from the vessel passes through a cooling tower and may be piped throughout the building. In order to avoid buildup of potentially harmful bacteria, such as Legionella, the cooling water holding vessel is fitted with an outlet pipe that directs water into a secondary vessel. The secondary vessel also has an outlet pipe that returns water to the cooling water holding vessel. The secondary vessel also contains a population of milkfish that consumes any algae present in the cooling water. Any bacteria that are being harboured by the algae will also be consumed, thereby reducing the amount of bacteria in the water.

Furthermore, one or both of the cooling water holdings vessel and the secondary vessel have clams or other molluscs therein which, process any mud or other particles in the cooling water, thereby removing bacteria from the water. To facilitate this process, the cooling water may be dosed with flocculant periodically to cause the mud or other particles to settle to the bottom of the vessel(s), where it can be processed by the molluscs. Freshwater clams and/or freshwater snails, especially paddy rice snails, are particularly suitable for this use.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.

Claims (16)

1. A method for controlling or reducing populations of aquatic algae in a freshwater or non-saline body of water comprising the steps of: oxygenating the body of water containing said algae, and introducing milkfish (Chanos Chanos) into the body of water to feed on said algae to the body of water to thereby control or reduce the population of algae.

2. A method according to claim 1 further comprising the step of allowing the population of algae to grow following commencement of oxygenation of the body o water and prior to the introduction of the milkfish.

3. A method according to claim 2 further comprising monitoring various parameters of the system including concentration of algae and size of the fish and removing the fish when they have reached a predetermined size or the amount of algae has been reduced to a satisfactory level.

4. A method according to any one of the preceding claims where the body of water is a lake, a reservoir, a dam, a cooling tower, an evaporative condenser, an air washer, a humidifier, a hot water heater, a spa, a fountain, or bodies of cooling water. A method according to any one of the preceding claims where the water is sparged or otherwise aerated until the dissolved oxygen content is preferably between and 7.5 ppm.

6. A method according to claim 3 where the milkfish are removed from the body of water containing the algae either when the fish have grown to a predetermined size, or once the concentration of algae has been reduced to a level of 0-100 algae/ml.

7. A method according to claim 7 wherein the milkfish are removed from the body of water when the concentration of algae has been reduced to a level of 0-10 algae/ml C'I Rje CD(003931903v4.doc 11

8. A method for controlling the level of bacteria in a body of freshwater or non-saline water contained in a closed water system comprising introducing milkfish (Chanos Chanos), into the closed water system.

9. A method according to claim 8 where the closed water system includes a primary water containment vessel, with water flowing out of that vessel, through the system and back into the vessel A method according to claim 9 where the milkfish are added to the primary containment vessel.

11. A method according to claim 10 where the primary containment vessel is fitted with egress prevention means to prevent egress of the milkfish from the primary containment vessel.

12. A method according to claim 8 further comprising directing a flow of water from the closed water system to a vessel containing milkfish, and returning water from said vessel to the closed water system.

13. A method according to claim 9 or claim 10 comprising removing water from the primary containment vessel to a second vessel, said second vessel containing said milkfish, and passing said water through the second vessel and returning it to the primary containment vessel.

14. A method according to any one of claims 8 to 13 where the closed water system comprises a cooling tower, an evaporative condenser, an air washer, a humidifier, a hot water heater, a spa, a fountain or a plumbing fixture. A method according to any one of claims 8 to 14 further comprising adding clams or molluscs that will feed on bacteria in typical conditions of the water system.

16. A method according to claim 15 wherein the molluscs are freshwater snails.

17. A method according to claim 13 where the secondary containment vessel is located remotely from the primary containment vessel and is in the form of a decorative aquarium. CD003931903v4.doc 12

18. A method according to claim 15 wherein silt, mud or particulates in the water are made to flocculate by use of a flocculant and the solid matter collects on the bottom of a vessel where it is processed by the milkfish, clams or molluscs.

19. A method substantially as hereinbefore described with reference to any one of the illustrative embodiments.