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Ozone treatment in Aquaculture

A replacement for malachite in fungal treatment ?

Ozone has strong cleaning and disinfection properties which will rapidly kill viruses, bacteria, fungi and protozoa's.  Basically ozone has the same properties as chlorine,  but with seven times the oxidation capacity. Ozone is used in many aquaculture situations for the treating of water,  in these system ozone is used to help prevent disease developing by increasing the redox potential of the water.  The ozone will crack organic molecules and thereby disinfect the water.  However too high a redox potential, or ozone level, will also start to oxidise the surface  of aquatic animals.  There is therefore a limit to the concentration of ozone and the time of exposure that needs to be calculated

Mechanism

Ozone is a gas that when dissolved into the water, will rapidly degrade back to oxygen and free radicals of oxygen atoms.  The free radicals increase the oxidation potential of the water,  and this effect can be measured by using a simple redox monitor.  The redox potential of freshwater and seawater is around 200 to 330mv  The table below gives some basic guidelines,  the information has been generated from data collected from fish farms that have had accidents with regards to their water disinfection in salmonid systems.  The data has not been quantified and as such it is only a rough guideline.

<350mv                     safe for continuous exposure

350 to 450mv            irritation to the fish, may case moralities from continuous exposure

450-550mv               serious irritation of fish gills and surface tissue, will cause moralities after 24 hours exposure

550 -650mv               serious irritation to fish,  may cause moralities after approx. 6 hours exposure

>650mv                    complete disinfection of water, 100% fish moralities after approx. 6 hours

OZ500 systems

The OZ500 is a small ozone generator with 3/8" hose connections in stainless steel.  The equipment has been designed for use with dry air or oxygen.  If Dryden air is used,  the air must be dried to -50 deg C due point using a silica gel drier,  or PSA drier. Oxygen generators, provide dry oxygen, or oxygen from cylinders and cryogenic tanks are okay. The oz500 connects to your oxygen supply using a 3/8" hose. If oxygen is used, the supply must be fitted with a 2 stage regulator with  needle valve,m the regulator should be set to 3 bar as a  maximum. The flow of gas can be measure using a rotometer. The OZ500 is connected to the ozone supply and the discharge from the generator is connected to a Dryden Aqua DAD6 ceramic oxygen diffuser. The oz500 is powered by 240v ac or 110v ac,  the unit should be protected from water spray and the elements.

1. Connect the oxygen supply to the OZ500 and the ozone out-let to a ceramic diffuser

2. Place the diffuser in the fish tank or cage to be treated

3. Make sure the needle valve on the oxygen regulator is closed, and then turn on the two stage regulator with the maximum pressure set at 3 bar

4. Open the rotometer needle valve to give an oxygen flow of approx. 1 to 2 litres per minute

5. Make sure that the oxygen is can be seen bubbling out of the diffuser, the bubble pattern is very fine, so it may be difficult to see.  Always insure that the diffuser is under water before the gas supply is turned on.

6. Turn on the power to the ozone generator, and then slowly rotate the ozone production dial to maximum.  The ozone generator will make a buzzing sound. An RCD (residual current devise) should be used with the ozone generator. The ozone generator is not water proof so it will need protection from the elements and water spray.

Ozone treatment of Tanks and Cages

TV is the treatment valve based on the following equation.

TV (treatment value)    =   C (concentration of ozone  in mg/l)) x time (minutes)

As a guideline the TV value for salmonids above 5g in size is approximately 3.

The maximum amount of ozone produced by the ozone generator is 1.0 g per hour, so if the flow of water through the fish tank is 10 cubm/hr,  the concentration of ozone in the water will be approximately 0.1mg/l.  If the TV value is 3,  then the exposure time is 3 / 0.1 = 30 minutes

In large tanks or cages,  the very small ozone generator will have virtually no impact on water quality or redox potential.  However the fish will occasionally swim through the ozone bubble stream, and as the ozone bubbles break on the surface of the fish,  the ozone will be administered directly onto the fish.  The exposure level is extremely low,  however the fish may regard the oxygen/ozone bubble stream as a cleaning station and will actively seek it out  if they have any ectoparasites or skin infections.  It is therefore important the diffuser is always used in the same position.

disclaimer

Health and safety precaution should be exercised when using oxygen and ozone. The use and application of ozone as detailed on this page has not been quantified or certified,  the use of the technique is therefore at the sole discretion of the user.  Dryden Aqua can accept no responsibility or consequential loss.

References

Disinfection of fish farms

Surface disinfection of Atlantic halibut Hippoglossus hippoglossus eggs with ozonated sea-water inactivates nodavirus and increases survival of the larvae

Diseases of Aquatic Organisms (ISSN: 0177-5103)  Inter-Research, Oldendorf/Luhe, 2000 January 24

Specifications