Processing of the liquid fraction
Struvite precipitation (magnesium ammonium phosphate)
Objective
Recovery of nitrogen and phosphorus from a liquid fraction in the form of a phosphate of magnesium, nitrogen and phosphorus (MAP, struvite).
Inlets
Liquid streams rich in P and N, products of other processes
Efficiency
The main limitation in slurries is the concentration of P. High removal of N and P can be achieved if the initial concentrations are correct for a complete reaction (>95%)
Weaknesses
Risk of ammonium volatilization in highly aerated reactors or with CO2 stripping;
Products
Struvite (MgNH4PO4·6H2O)
Other outlets
Treated liquid effluent
Consumption
Energy: Low
Water: Not applicable
Reagents: Medium
Investment
Thames Water Engineering: €0.40/m3 (precipitation reactor); Pig slurry plant: €4.85-7.25/m3 (Crystallization reactor); €2.41-3.62/m3 (crystallization reactor). Quantifiable income: from the sale of struvite (€200/ton)
Operation
Cost of reagents: MgO (€0.6/kg)/H3PO4 (€0.8/L)/NaOH (€0.2/L); >€1/m3 if MgO by-products are used; Reagents required for precipitation: €6/kg of NH4+ or €48/m3 (if the slurry has 8 kg N/m3)
Observations
The pH is one of the main factors because it changes the concentration of free ions available for the reaction, and affects the solubility of struvite;
To favor its precipitation, it is recommended to raise the pH to values
To favor its precipitation, it is recommended to raise the pH to values
Combination with other technologies
1. Acidification -> Separation -> Struvite precipitation;
2. Separation by pressing -> nitrification-denitrification -> Struvite precipitation;
2. Separation by pressing -> nitrification-denitrification -> Struvite precipitation;
Download the file here
TRL - 9
Status Consolidated
Complexity Medium
Information made by:
BETA Tech Center