Iron
Most surface waters contain very
low concentrations of iron. Some
anoxic ground waters, however,
contain considerable iron in a dissolved
form. When the water is
aerated the iron is oxidized to a
rust-colored precipitate of iron
oxide. Dissolved iron is considered to be of relatively low toxicity
to most aquatic organisms. Solid
precipitates of iron oxide are even
less toxic but may coat the gills of
fry and interfere with respiration.
Dense precipitates of iron oxide
also may cover eggs and hinder
gas exchange and suffocate the
eggs. Total iron concentrations
should be less than about 0.5 ppm
for hatchery water supplies.
The simplest system used to remove
iron is to pump the water
into a small reservoir pond (0.5 to
1 acre) where the dissolved iron is
oxidized and some of the iron
oxide precipitate settles out. Some
of the remaining precipitate can be
removed using sand filters. An alternate
method is to oxidize the
iron by vigorously aerating the
water in a tank or chamber prior
to sand filtration. Complete removal
of iron is difficult regardless
of the system used