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There are times in a 24 hr cycle when algal populations are depleting
oxygen from the system. On balance the proposition that algal populations
will contribute to aerobic activity is highly unlikely.
In relation to (c) the consequence of killing such a large volume of algae
needs to be understood before action is taken. The sudden death of this
number of algal cells is likely to result in the following:
· A release of all the toxins present in the algal cells at one time.
This of itself probably does not change the overall status of a system
as it is already likely to be highly contaminated with toxin. Killing all
the algae at one time will cause a spike in toxin that will stimulate
bacterial digestion of toxins already taking place.
· Oxygen levels are likely to be relatively low in a system of this type;
the death of large volumes of algae will cause these levels to decrease.
This may result in the death of fish.
Algae and Algal Blooms
Various Methods of treating algae also deserve consideration.
Some common options to consider are:
1. Copper Sulphate 2. Copper Sulphate and hypochlorite 3. Coptrol
1. Copper Sulphate
2. Copper Sulphate and hypochlorite
3. Coptrol
Point 1 Use of Copper sulphate in effluent systems.
A review of the chemistry of this approach is outlined below:
Effluent water is usually highly mineralised. When copper sulphate is
added to these environments copper sulphate reacts in the water.
Initially copper is released from the sulphate bond creating Cu++, at
the same time sulphate reacts with water creating mild sulphuric acid.
It is the Cu++ that is toxic to algae; however, its persistence in this
form has a very limited duration. Cu++ reacts with carbonates and
hydroxides in solution to form insoluble copper compounds which has
no algal toxicity. In most cases only 5% of the Copper ion from Copper
Sulphate remains in the Cu++ phase for 60 minutes. Most is lost as an
insoluble form in less than 60 minutes and never comes in contact with
the target algae.
Try conducting a pilot test using copper sulphate and watch for a cloudy
reaction,the reaction will be copper sulphate changing into an
insoluble copper carbonate/hydroxide compound.
In Australia Copper Sulphate is no longer approved for use in effluent
treatment systems.
Point 2
Hypochlorite, does not work as an efficient algaecide in fresh
water. When used in an organic rich environment as effluent it is
even less effective. Mixing Copper Sulphate and hypochlorite together
should be avoided. It will produce a highly noxious chlorine gas that
could cause significant health problems to anyone exposed to it.
Point 3 Coptrol
Has a number of major advantages.
Applying product over a large surface area will require either a large input
of labour or aerial application. Dosing marginally effective copper sulphate
from a boat is a highly labour intensive operation with the possibility of
health problems for those exposed to the lagoon for prolonged periods.
Application of Copper Sulphate by air also has serious issues. Reacting
copper crystals into slurry in an aircraft tank creates real potential for
corrosion in an aeroplane. There is also the question of the even
distribution of copper sulphate in such large volumes over such large areas.
By contrast Coptrol is a non corrosive liquid that can be readily applied
by air over large areas. For example Coptrol is routinely aerially applied
to rice production systems in Australia.
Coptrol is a liquid designed to remain stable in highly mineralised aquatic
environments without the risk of precipitation. It is ideally suited for use
in effluent pond systems as they are usually environments high in
carbonate and hydroxide anions. Application rates will depend on the likely
concentration of algae. Once the algal situation is brought under control
lower rates of application can be used to ensure ongoing control.
Coptrol works by accumulation of copper in the algal cell. The chelate acts
as a nutrient source for algae. This ensures the algae keeps accumulating
copper until it becomes toxic to the algae. The chelate protects the
copper from precipitation. Coptrol is approved for use in potable water
supplies in Australia.
In summary Coptrol is easier and cheaper to apply than the alternatives
and has a proven record dealing with algal problems in effluent systems.
To control algae add Coptrol at 8-10 litres per megalitre of water. Best
results are achieved when applying Coptrol by spraying the surface of
the water.
Click here for full application rates
Click here for Coptrol Bibliography
Click here for Coptrol Frequently Asked Questions.
Click here for Information on Coptrol and Environmental Safety