Struvite formation occurs by dosing magnesium salts if the ammonium required for struvite formation is present in the water. The phosphate concentration can generally be reduced to 0.2-0.5 mg/L. The bulk of the phosphate is removed in the form of pellets from the reactor. Effluent filtration is usually required to remove suspended phosphate flocs that are present as carry over from the reactor.
The heart of the Crystalactor treatment plant is the pellet reactor, partially filled with suitable seed material such as sand, garnet, or small crushed pellets.
The water is pumped in an upward direction, maintaining the pellet bed in a fluidised state. In order to crystallise metal salts on the pellet bed, a driving force is created by a reagent dosage, usually lime or magnesium hydroxide, or a combination of caustic soda and magnesium chloride is applied. The pellets grow and move towards the reactor bottom.
At regular intervals, a quantity of the largest fluidised pellets is discharged from the reactor and fresh seed material is added. After atmospheric drying, easy-to-handle and virtually water-free pellets are obtained.
The Crystalactor is most suited to treat flows with phosphate concentrations above 25 mg/L PO4-P. In municipal waste water treatment plants it can be used to treat a concentrated phosphate flow produced by biological phosphate removal. /L. The required low effluent concentrations are usually achieved by filtration of the effluent.