- Nutrient Recovery Process


Many wastewater treatment plants concentrate large quantities of nitrogen and phosphorus in their sludge dewatering streams. The dissolved nutrients promote the formation of obstructive struvite scale in piping, pumps and valves resulting in severe impacts to plant reliability, efficiency and operating and maintenance costs.

Ostara’s Pearl Process resolves struvite issues and provides a comprehensive approach to nutrient management. The technology is based on controlled chemical precipitation in a fluidized bed reactor that recovers struvite in the form of highly pure crystalline pellets or “prills.” Nutrient-rich feed streams are mixed with magnesium chloride and, if necessary, sodium hydroxide and then fed into the Pearl reactor where minute particles or struvite “seeds” begin to form. Like a pearl, these seeds grow in diameter until they reach the desired size – 1.0 mm to 3.5 mm – which is precisely controlled by varying key parameters. In a municipal wastewater treatment plant, up to 90 per cent of the phosphorus and 40 per cent of the ammonia load is removed from sludge dewatering liquid using this process and the resulting product is marketed as a commercial fertilizer called Crystal Green.


  • Removes phosphorus and ammonia loads
  • Prevents struvite scale formation
  • Recovers nutrient value
  • Promotes environmental sustainability
  • Provides attractive whole-life financial value

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