Annex 4: Removal of Phosphate from water
Total phosphate includes; organic phosphate found in plankton, algae and bacterial cell biomass,
inorganic phosphate such as struvite, and soluble reactive phosphate referred to as ortho-phosphate.
AFM® will mechanically filter the water down to less than 1 micron when coupled with pre-coagulation
and flocculation. The removal of organic and inorganic phosphate is usually better than 95%.
AFM® will also directly adsorb orthophosphate PO 42- in the AFM® stern layer; the capacity for adsorption
is low, but sufficient to make an impact on concentrations remaining after a precipitation stage with ferric,
lanthanum or magnesium.
Sand works very well for phosphate removal; the main issue with sand is that it becomes a biofilter in
wastewater. This leads to transient wormhole channelling of unfiltered water through the filter bed and
premature blockage of the media. Phosphate also forms a hard scale that bonds on to sand, making it
very difficult to remove the precipitate from the surface of the sand. The bed can turn into a solid mass
which makes it impossible to filter the water and very difficult to remove the sand. This problem does
not occur with AFM®, the AFM® will capture the precipitate but it does not form a bond the with the
media surface, so a regular back-washing will remove the precipitate and adsorbed ortho-phosphate.
Wastewater treatment
AFM® provides a sustainable and efficient means of removing phosphate from wastewater.
There are three main approaches, all of which involve the precipitation of phosphate to form an insoluble
salt, by the addition of; ferric to form ferric phosphate, lanthanum to form lanthanum phosphate or
magnesium to form struvite.
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Page 36 of 44
At Dryden Aqua we have been using Lanthanum salts (NoPhos) to remove phosphate in the aquarium
and aquaculture industry for over 20 years. Lanthanum is injected into the water at a 1:1 stoichiometric
ratio to remove phosphate to achieve concentration below 0.01 mg/l. NoPhos must be injected into the