Introduction
The main problem associated with the presence of phosphorus in water is that it, being a nutrient required for growth, is often responsible for the extravagant growth of aquatic life, also called eutrophication. This reduces the quality of the receiving water and the suitability for reuse. For this reason in many countries effluent standards have been implemented with regard to phosphorus.
Initially the methods used for phosphorus removal were all based on physical-chemical treatment, especially the addition of metal salts. There are several important disadvantages to chemical phosphorus removal:
- The high costs of the consumed chemicals
- A significant increase of the excess sludge production (metal-hydroxides and metal phosphates)
- The accumulation of ions (increased salt content) may seriously restrict the reuse of the effluent.
At present, the preferred alternative is biological excess phosphorus removal, where the activated sludge system is operated in such a way that a biomass with an increased phosphorus content develops. The accumulated phosphorus is subsequently removed from the wastewater through discharge with the excess sludge. If the biological removal capacity is insufficient, supplementary chemical dosing may be applied.
Contents of this section
Biological phosphorus (bio-P) removal
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Nutrient removal - design case
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