Algaecides are chemicals that kill algae and blue or green algae, when
they are added to water. Examples are copper sulphate, iron salts, rosin
amine salts and benzalkonium chloride. Algaecides are effective against
algae, but are not very usable for algal blooms for environmental
reasons.
The problem with most algaecides is that they kill all
present algae, but they do not remove the toxins that are released by
the algae prior to death.
Antifoams
Foam is a mass of
bubbles created when certain types of gas are dispersed into a liquid.
Strong films of liquid than surround the bubbles, forming large volumes
of non-productive foam.
The cause of foam is a complicated study in
physical chemistry, but we already know that its existence presents
serious problems in both the operation of industrial processes and the
quality of finished products. When it is not held under control, foam
can reduce the capacity of equipment and increase the duration and costs
of processes.
Antifoam blends contain oils combined with small
amounts of silica. They break down foam thanks to two of silicone's
properties: incompatibility with aqueous systems and ease of spreading.
Antifoam compounds are available either as powder or as an emulsion of
the pure product.
Powder
Antifoam powder covers a group of
products based on modified polydimethylsiloxane. The products vary in
their basic properties, but as a group they introduce excellent
antifoaming in a wide range of applications and conditions.
The
antifoams are chemically inert and do not react with the medium that is
defoamed. They are odourless, tasteless, non-volatile, non-toxic and
they do not corrode materials. The only disadvantage of the powdery
product is that it cannot be used in watery solutions.
Antifoam
Emulsions are aqueous emulsions of polydimethylsiloxane fluids. They
have the same properties as the powder form, the only difference is that
they can also be applied in watery solutions.
When referring to
coagulants, positive ions with high valence are preferred. Generally
aluminium and iron are applied, aluminium as Al2(SO4)3- (aluin) and iron
as either FeCl3 or Fe2(SO4)3-. One can also apply the relatively cheap
form FeSO4, on condition that it will be oxidised to Fe3+ during
aeration.
Coagulation is very dependent on the doses of coagulants,
the pH and colloid concentrations. To adjust pH levels Ca(OH)2 is
applied as co-flocculent. Doses usually vary between 10 and 90 mg Fe3+/
L, but when salts are present a higher dose needs to be applied.
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