Thematic training material for the use of struvite as fertilizer has been published


Struvite is an ammonia and magnesium phosphate hexahydrate (NH4MgPO4·6H2O). When ammonia and phosphate are found in solution, they can be removed by adding a magnesium salt, under controlled conditions, and white glowing crystals of struvite can then be recovered. One of the main advantages of recovering struvite from waste flows is the high selectivity of the reaction therefore the recovered product will not contain heavy metals either organic residues at significant concentrations. Struvite has low solubility in water but a high solubility in acidic solution, thus the humic acids are very efficient in increasing the solubility of struvite in the soil and this genuine slow-release fertiliser character prevents plant’s roots from burning even if applied in excess. Besides, the low solubility in water will prevent P losses due to filtrations or runoffs. In addition, conventional fertiliser manufacturing processes are energy-intensive involving mining, long transport distances, thermal processes, and in some cases direct combustion of fossil fuels for product manufacture (e.g. urea production). In contrast, struvite recovery facility operates on a total installed electrical capacity of around 25 horsepower.

Examples for struvite products available on the NUTRIMAN Farmer Platform:

The struvite selected in NUTRIMAN is available either at Spain or Belgium.

The struvite recovered from urban wastewater by “PHORWater” process (ID:208) is made starting from the WWTP side streams. An elutriation process has been developed in order to increase the P availability. The struvite obtained contains 5% N (w/w), 29% P2O5 (w/w), < 1.0% K2O (w/w) with a TOC < 0,8%.

The struvite recovered from pig manure digestate by “REVAWASTE” process (ID:250) is made starting from the pig manure. The struvite obtained contains 5% N (w/w), 28% P2O5 (w/w), < 1.0% K2O (w/w).

The struvite recovered from urban wastewater by “Canal de Isabel II S.A.” process (ID:251) is made from the WWTP side streams. The struvite obtained contains 5% N (w/w), 28% P2O5 (w/w), < 1.0% K2O (w/w).

The struvite recovered from wastewater by “NuReSys” process (ID:293) is made from the side streams from either industrial or urban WWTP. The struvite obtained contains 5% N (w/w), 29% P2O5 (w/w), < 1.0% K2O (w/w).

Fields of application in agriculture: 

The struvite (ID:208-250-251-293) is usually applied at 0,1 t/ha to provide P and N to the soil, according to soil quality, season and crop uptake. It is specially recommended for permanent grassland, cereals for the production of grain, root crops and plants harvested green from arable land by area. The product is very suitable for top-dressing application and can be blended with other solid fertilisers but, it can also be dissolved in a slightly acidic solution. Therefore, traditional agricultural machinery can be used for the application and it is recommended to be applied before seeding/planting.

Benefits for farmers:

Struvite (ID: 208, 250, 251 and 293) are white solids, odorless and easy to handle, even though they come from residual flows. Due to its genuine slow release property, nutrients are efficiently used by crops because it meets nutritional demands of crops in a better way and prevents the burning of plant roots, even when applied in excess quantities. Struvite guarantees a slow but steady nutrient supply and reduces nutrients runoff, consequently is not only good for the economics of the farm, but also for its sustainable agronomy. In addition, Cd has not been detected and the amount of organic matter is very low, so it is a secure environmentally friendly product. Finally, struvite is a recovered product with steady composition. Most of the commercial phosphates have variable composition and do not constitute a defined chemical entity instead they are mixtures of monocalcium phosphate, bicalcium phosphate, phosphoric acid, calcium carbonate and impurities but struvite offers a very steady composition, even though the recovery technology used may be different.

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