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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/223269
Struvite precipitation in municipal wastewater treatment plants using a magnesium oxide by-product
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[eng] Phosphorus has been classified as a critical raw material by the European Union (EU) due to its economic importance, price volatility, and supply risks. This has driven research into alternative secondary sources for phosphorus recovery, particularly in wastewater treatment plants (WWTPs), where the majority of phosphorus losses occur. In the EU, approximately 54 % of imported phosphorus is lost through wastewater. Recovering phosphorus from these streams aligns with circular economy principles and enhances resource recovery.
Struvite precipitation is a promising approach for phosphorus recovery, with the potential to supply nearly 13 % of the EU’s phosphorus fertiliser demand. Additionally, phosphorus recovery can reduce its concentration in wastewater streams, leading to cost savings related to (i) chemical dosing for phosphorus removal and (ii) maintenance issues caused by uncontrolled struvite scaling in pipelines and equipment.
In recent years, there has been a significant increase in full-scale phosphorus recovery facilities. North America leads in struvite production, while the EU has the highest number of operational full-scale struvite recovery units. Currently, over 80 full-scale plants worldwide recover phosphorus from industrial and municipal wastewater, employing technologies such as PHOSPAQ®, ANPHOS®, NeReSys®, Struvia™, PHOSNIX®, Ostara Pearl®, and PhosphoGREEN. These processes use MgCl2, MgO, or Mg(OH)2 as magnesium sources and they primarily increase pH by CO2 stripping or by adding NaOH. However, reagent costs pose a major limitation, as magnesium and alkaline agents account for approximately 75 % of operating expenses, particularly in streams with low phosphorus concentrations.
This thesis investigates the feasibility of using an industrial by-product, low-grade magnesium oxide (LG-MgO), as a single reagent for phosphorus recovery via struvite precipitation. When added to anaerobic digestion supernatant, LG-MgO releases both magnesium and hydroxide ions, acting simultaneously as a magnesium source and an alkaline reagent. Phosphorus recovery yields ranged from 50 to 90 %, primarily influenced by the P:Mg molar ratio, the phosphorus concentration in the supernatant, and the reactivity of the LG-MgO used. The resulting precipitates consisted mainly of struvite, with a purity between 72 and 88 wt%.
Significantly, the findings support struvite precipitation in streams with low phosphorus concentrations when struvite seed is added, as these conditions promote particle growth. Moreover, the use of LG-MgO reduces operating costs. An economic analysis showed that the reagent cost to produce one tonne of struvite was significantly lower when using LG-MgO (73 €) compared to MgCl2·6H2O and NaOH (940 €) at a phosphorus recovery efficiency of approximately 90 %.
These findings highlight LG-MgO as a cost-effective alternative to conventional magnesium sources for struvite precipitation. Its application not only reduces operational costs but also adds value to an industrial by-product, promoting resource efficiency and advancing the circular economy.
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AGUILAR POZO, Verónica-belén. Struvite precipitation in municipal wastewater treatment plants using a magnesium oxide by-product. [consulta: 26 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/223269]