Struvite crystallization in a full scale plant after autotrophic nitrogen removal (ELAN process)

Morales, N.1, Vázquez-Padín, J. R.1, Rogalla, F.1, Crutchik, D.2, 3 and Garrido, J. M.2

1 FCC Aqualia,

2 Department of Chemical Engineering, Institute of Technology, University of Santiago de Compostela

3Faculty of Engineering and Sciences, Universidad Adolfo Ibáñez


A full scale struvite crystallization system is in operation in the Guillarei municipal WWTP (Northwest of Spain, influent flow 32500 m3/d) for the treatment of the centrate obtained after anaerobic sludge digestion. The precipitation process is carried out in a two-phase fluidized bed reactor connected to a gravity settler. Industrial grade Mg(OH)2 is added to the system as magnesium and alkali source.
In period I the centrate was directly fed to the crystallization plant; while in period II the centrate was pretreated by an autotrophic nitrogen removal process (the ELAN® process), the combination of the biological processes of partial nitrification and anammox performed in an SBR with granular biomass. This additional step removes around 80% – 90% of the ammonium and bicarbonate ions, reducing the needs of alkali addition for struvite crystallization. Phosphate concentration in the liquid effluent was around 15 mg P-PO43-/L when pH was controlled between 8.3-8.8, regardless of influent concentration. Struvite pellets with a size range of 0.5–5.0 mm, suitable to be used as agricultural fertilizer, were obtained.

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