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J Environ Manage. 2017 Jul 1;196:340-346. doi: 10.1016/j.jenvman.2016.12.074. Epub 2017 Mar 16.

Sludge management modeling to enhance P-recovery as struvite in wastewater treatment plants.

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Dpto. de Ingeniería Química, Universitat de València, Avinguda de la Universitat s/n, 46100, Burjassot, Valencia, Spain. Electronic address:
Instituto de Ingeniería del Agua y Medio Ambiente, IIAMA, Universitat Politècnica de València, Camí de Vera, s/n, 46022, Valencia, Spain.
Dpto. de Ingeniería Química, Universitat de València, Avinguda de la Universitat s/n, 46100, Burjassot, Valencia, Spain.
Depuración de Aguas del Mediterráneo (DAM), Avenida Benjamín Franklin, 21, 46980, Parque Tecnológico, Paterna, Valencia, Spain.


Interest in phosphorus (P) recovery and reuse has increased in recent years as supplies of P are declining. After use, most of the P remains in wastewater, making Wastewater Treatment Plants (WWTPs) a vital part of P recycling. In this work, a new sludge management operation was studied by modeling in order to recover P in the form of struvite and minimize operating problems due to uncontrolled P precipitation in WWTPs. During the study, intensive analytical campaigns were carried out on the water and sludge lines. The results identified the anaerobic digester as a "hot spot" of uncontrolled P precipitation (9.5 gP/kg sludge) and highlighted possible operating problems due to the accumulation of precipitates. A new sludge line management strategy was simulated therefore using DESASS© software, consisting of the elutriation of the mixed sludge in the mixing chamber, to reduce uncontrolled P precipitation and to obtain a P-rich stream (primary thickener supernatant) to be used in a crystallization process. The key operating parameters were found to be: the elutriation flow from the mixing chamber to the primary thickener, the digestion flow and the sludge blanket height of the primary thickener, with optimized values between 70 and 80 m3/d, 90-100 m3/d and 1.4-1.5 m, respectively. Under these operating conditions, the preliminary results showed that P concentration in the primary thickener overflow significantly increased (from 38 to 100 mg PO4-P/L), which shows that this stream is suitable for use in a subsequent crystallization reactor to recover P in the form of struvite.


Crystallization; Nutrient recovery; Sludge treatment; Uncontrolled precipitation; Urban WWTP

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