Phosphate precipitation with LEWA diaphragm pumps in sewage treatment plants

Phosphates are important nutrients for micro-organisms and aquatic plants. However, excessively large amounts of phosphate in waters can have devastating effects on the environment.

Therefore, the limit values for permissible phosphate rates have been reduced continuously over the last couple of years. This poses a challenge to operators of sewage treatment plants because they depend more than ever before on precise, efficient and reliable metering pumps.


LEWA pumps offer the following advantages for metering of media for phosphate precipitation in water treatment:

  • Exact metering of the precipitant (iron(III) chloride)
  • Absolutely reliable starting of the pump from every operating state; no positioning of the diaphragm required
  • The hermetic seal of the pump prevents the extremely aggressive precipitant from escaping
  • Patented sandwich diaphragm with DPS (Diaphragm Protection System) and diaphragm monitoring
  • Integrated pressure relief valve protects the pump against unacceptable overpressure situations (pressure surges/water hammers), which can cause damage to pumps or lines.
  • Lowest life cycle costs due to high energy efficiency, low maintenance costs and extremely long service life of the sandwich diaphragm
  • Highest reliability and availability even after operating error or in extreme operating states (such as a closed pressure or suction line)
  • Environmentally friendly thanks to high operating reliability and low power consumption


What happens during a phosphate precipitation?

A phosphate precipitation is a physico-chemical reaction in which salts of trivalent metals are used to precipitate phosphates. Non-hazardous iron (III) and aluminium salts are applied for this purpose. Injecting metal salts creates positively charged metal ions which react with negatively charged phosphate ions. The resulting difficultly soluble metal phosphate is precipitated in form of fine floc.

The precipitant has to be injected at the right point in order for the ions to react sufficiently. Subsequently, a flocculation phase ensues during which the fine precipitation products aggregate to settleable floc.



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