Today's agriculture is highly dependent on phosphate fertilizers to
feed a growing world population with dwindling cultivation areas.
Most fertilizers are produced from phosphate ores, and since phosphorous (P) is a limited resource, current reserves are estimated to run
out within the next 50 to 100 years (Cordell et al., 2009). To avoid
future scarcity, sustainable recovery and recycling techniques are
needed to preserve this vital element. One possible approach is the
precipitation of struvite, also known as magnesium ammonium
phosphate hexahydrate (MgNH4PO4 6H2O). It can be crystallized
from nutrient-rich wastewater that contains high concentrations of
ammoniacal nitrogen and phosphate ions, by adding a low-grade
magnesium oxide (MgO) as a precursor. This MgO source derives from
the magnesite industry, both via recycling and as a by-product
(Quintana et al., 2003), is safe and suits agricultural restrictions.
Struvite can be used as a slow-release fertilizer and is a potential
substitute for conventional fertilizers.