Struvite crystallization under a marine/brackish aquaculture condition

Area of Science:

• Environmental Chemistry
• Materials Science

Background:

• Phosphate recovery from wastewater is crucial for resource management and pollution control.
• Struvite (ammonium magnesium phosphate) precipitation is a common method for phosphate removal.

Purpose of the Study:

• To investigate struvite formation and characteristics in a digester under brackish conditions.
• To understand the influence of wastewater characteristics on phosphate precipitate composition.

Main Methods:

• Analysis of digester contents and synthetic brackish water.
• Thermodynamic calculations for solubility product and enthalpy change.
• X-ray diffraction (XRD) for mineral identification.
• Investigation of crystal size dependence on pH and temperature.

Main Results:

• Struvite formed in the digester at pH 7.7, lowering phosphate concentration.
• Under brackish conditions, thermodynamic solubility product was 10(-13.06) and enthalpy change was 25.7 kJ/mol.
• Crystal size decreased with pH and increased with temperature.
• Struvite and dittmarite were predominant in digester filtrates, while struvite and newberyite precipitated from synthetic waters.
• Ammonia-containing precipitates dominated under high ammonium conditions.

Conclusions:

• Digesters can provide suitable conditions for struvite formation.
• Wastewater characteristics critically affect phosphate precipitate nature.
• Controlling conditions like pH, temperature, and ammonium concentration can optimize phosphorus recovery.