Treatment Plants for Phosphorus Removal from Wastewater
relatively large pore volume in the plastics layer, a combined plastics/ sand filter can
retain considerably larger volumes of sludge than a traditional sand filter.
The precipitation and flocculation mechanisms in a contact filter fully correspond
to those in the other precipitation processes. Ferric salts are often used as a precipitant.
Ponds
This type of process can be used for polishing or as the primary part of the
phosphorus precipitation process. The function depends on the size of the pond and
the chemical dosing. A soil pond as shown in Fig 10.20 functions as a large secondary clarifier for the chemical floes which are formed by the supplementary addition
of chemicals. If the soil pond is made sufficiently big, it will, in fact, function as an
algae pond. In that case, it may not be necessary to add chemicals to the influent of
the pond. On the other hand it may be necessary to establish a chemical precipitation plant for the separation of the algae in the effluent from the pond.
As precipitant, iron and aluminium salts may be used. The chemical sludge has to
be removed from the bottom of the pond at (large) intervals.
Infiltration
Here it is the capacity of the soil to bind phosphate which is used. In order for the
process to function, a preceding treatment is required where particles and most of
the organic matter are removed. The ponds are often operated intermittently, with
rest periods of 1-2 weeks. In these periods the pond remains dry, and the upper
strata are oxidized which prevents clogging caused by micro-organisms which
grow on the organic matter deposited.
These processes are widespread in the southern part of Europe, see Fig 10.21.
10.4. Design of plants for phosphorus removal
10.4.1 Chemical precipitation
Design can be carried out in two levels
I. Total phosphorus.
II. Dissolved plus suspended phosphorus.
Design based on total phosphorus is the easier, however, the more unreliable of the
two methods.
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relatively large pore volume in the plastics layer, a combined plastics/ sand filter can
retain considerably larger volumes of sludge than a traditional sand filter.
The precipitation and flocculation mechanisms in a contact filter fully correspond
to those in the other precipitation processes. Ferric salts are often used as a precipitant.
Ponds
This type of process can be used for polishing or as the primary part of the
phosphorus precipitation process. The function depends on the size of the pond and
the chemical dosing. A soil pond as shown in Fig 10.20 functions as a large secondary clarifier for the chemical floes which are formed by the supplementary addition
of chemicals. If the soil pond is made sufficiently big, it will, in fact, function as an
algae pond. In that case, it may not be necessary to add chemicals to the influent of
the pond. On the other hand it may be necessary to establish a chemical precipitation plant for the separation of the algae in the effluent from the pond.
As precipitant, iron and aluminium salts may be used. The chemical sludge has to
be removed from the bottom of the pond at (large) intervals.
Infiltration
Here it is the capacity of the soil to bind phosphate which is used. In order for the
process to function, a preceding treatment is required where particles and most of
the organic matter are removed. The ponds are often operated intermittently, with
rest periods of 1-2 weeks. In these periods the pond remains dry, and the upper
strata are oxidized which prevents clogging caused by micro-organisms which
grow on the organic matter deposited.
These processes are widespread in the southern part of Europe, see Fig 10.21.
10.4. Design of plants for phosphorus removal
10.4.1 Chemical precipitation
Design can be carried out in two levels
I. Total phosphorus.
II. Dissolved plus suspended phosphorus.
Design based on total phosphorus is the easier, however, the more unreliable of the
two methods.
337