Struvite - Phosphate and Nitrate
Struvite is a substance which is produced from a combination of Mg(OH)2 and phosphate, and is formed as a slowly growing crystal. This process can be used to obtain phosphate from waste water (dephosphation) and from manure, by creating struvite and removing this from such materials.
Struvite therefore contains magnesium and phosphate and is thus a first-rate slow-acting fertilizer and can be used for example as a fertilizer for hydrocultures.
Phosphate and nitrate
Decreasing the phosphate quantity in manure is advantageous to the farmer in that he can apply more m³ of manure to the ground. According to the fertilizer legislation, it is not the quantity of manure but the quantity of phosphate, and to a lesser degree the nitrate quantity, which is defining for the assimilation of the manure quantity on the land. The law states that the phosphate and nitrate amounts are dependent on the crop which is being cultivated. Generally speaking, it is the phosphate amount which is the restricting factor for the permitted number of m³ of manure, the nitrate quantity thus also being restricted. By actively controlling the ratio of phosphate to nitrate, an optimum fertilizer product is created, and more manure can be applied to the land. The extra amount of manure which can be used ensures that sufficient phosphate and nitrate are present, d thus no extra nitrate in the form of fertilizer is required.
Obstacle
After the addition of Mg(OH)2 and a quantity of air, struvite crystals are rapidly formed. The formed crystals increase in size and subside to the ground due to the increased weight. Unfortunately this crystal formation occurs not just in the substance itself, but also against the walls or other parts with which it comes in contact. The crystal attachment is such that a layer is formed which increases in thickness, thus slowing the operation of the entire installation.
Advantages
One of the advantages of struvitising is the increase in value of the manure (decrease in sale cost) by the correct phosphate-nitrate ratio and the struvite can, moreover, be sold as fertilizer.
The process occurs quite quickly. Approximately 1000 tons of manure can be processed in a week. Thus, with a mobile installation and a number of manure sacks a large quota of a farmer`s manure can be struvitised for temporary storage. Another option is to connect a mini-installation to an attenuator. Attenuated manure can be struvitised more easily.