10. Treatment Plants for Phosphorus
Removal from Wastewater
By Erik Arvin and Mogens Henze
Phosphorus is one of the vital macro nutrients for living organisms. Phosphorus in
itself is non-toxic. The problem with phosphorus arises when there is an excessive
input to aqueous recipients with the wastewater together with other nutrients, such
as nitrogen. The effect is eutrophication caused by a heavy growth of algae with a
subsequent, unwanted disturbance of the ecological balance of the recipient. A
consequence is, for example, that the living conditions for fish are deteriorated due
to oxygen depletion, etc. Moreover the recreational value of the waters is reduced
due to the turbid appearance and the smell of the water. If the water of the recipient
is also used as raw water for water supplies, serious technical and financial complications for the treatment of drinking water usually arise due to the unwanted tastes
and odours produced by the algae, and the organic materials.
In order to limit or prevent eutrophication, the phosphorus discharged with the
wastewater must be reduced. The discharged concentration of phosphorus can be
limited by reducing or eliminating the content of phosphorus in detergents. The
most widespread intervention is, however, the introduction of some kind of treatment process.
10.1. Mass balances for phosphorus removal
processes
No water treatment processes make phosphorus vanish into thin air. The purpose
of all the processes is to convert dissolved phosphates into suspended phosphorus
which can be retained, for example in a settler or in the soil.
Phosphorus in treatment plants is always phosphate in one form or the other. In Fig
10.1 we see a typical distribution of phosphorus components in municipal wastewater before and after a biological treatment. Polyphosphates are hydrolyzed to
orthophosphates and the major part of dissolved organic phosphates is also degraded to orthophosphates by the biological degradation of organic matter.
Suspended phosphates are normally considered to be organic phosphates, but they
may also include chemically precipitated orthophosphates and biologically bound
polyphosphates. The distribution of different phosphate fractions in the suspended
phosphate is normally less interesting as the suspended solids are separated from
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Removal from Wastewater
By Erik Arvin and Mogens Henze
Phosphorus is one of the vital macro nutrients for living organisms. Phosphorus in
itself is non-toxic. The problem with phosphorus arises when there is an excessive
input to aqueous recipients with the wastewater together with other nutrients, such
as nitrogen. The effect is eutrophication caused by a heavy growth of algae with a
subsequent, unwanted disturbance of the ecological balance of the recipient. A
consequence is, for example, that the living conditions for fish are deteriorated due
to oxygen depletion, etc. Moreover the recreational value of the waters is reduced
due to the turbid appearance and the smell of the water. If the water of the recipient
is also used as raw water for water supplies, serious technical and financial complications for the treatment of drinking water usually arise due to the unwanted tastes
and odours produced by the algae, and the organic materials.
In order to limit or prevent eutrophication, the phosphorus discharged with the
wastewater must be reduced. The discharged concentration of phosphorus can be
limited by reducing or eliminating the content of phosphorus in detergents. The
most widespread intervention is, however, the introduction of some kind of treatment process.
10.1. Mass balances for phosphorus removal
processes
No water treatment processes make phosphorus vanish into thin air. The purpose
of all the processes is to convert dissolved phosphates into suspended phosphorus
which can be retained, for example in a settler or in the soil.
Phosphorus in treatment plants is always phosphate in one form or the other. In Fig
10.1 we see a typical distribution of phosphorus components in municipal wastewater before and after a biological treatment. Polyphosphates are hydrolyzed to
orthophosphates and the major part of dissolved organic phosphates is also degraded to orthophosphates by the biological degradation of organic matter.
Suspended phosphates are normally considered to be organic phosphates, but they
may also include chemically precipitated orthophosphates and biologically bound
polyphosphates. The distribution of different phosphate fractions in the suspended
phosphate is normally less interesting as the suspended solids are separated from
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