Struvite precipitation from urine - Influencing factors on particle size

Journal article (2010)

Authors

Mariska Ronteltap Mariska Ronteltap Eawag - Swiss Federal Institute of Aquatic Science and Technology, ETH Zürich, IHE Delft Institute for Water Education
Max Maurer Max Maurer Eawag - Swiss Federal Institute of Aquatic Science and Technology
Rainer Hausherr Rainer Hausherr Eawag - Swiss Federal Institute of Aquatic Science and Technology, Swiss Federal Nuclear Safety Inspectorate
Willi Gujer Willi Gujer Eawag - Swiss Federal Institute of Aquatic Science and Technology, ETH Zürich
Affiliation
External organisation
Phosphorus recovery Struvite Supersaturation Crystal size Urine
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Published Date

2010-3

Language

English

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Abstract

Struvite crystallisation is a fast and reliable phosphorus removal and recovery process for concentrated waste streams - such as hydrolysed human urine. In order to optimise P-elimination efficiency, it is beneficial to obtain larger particle sizes: they are easier to separate and less prone to wash-out than smaller particles. This paper presents the results of a study on the effect of process parameters on particle size in a single step struvite precipitation. Crystals formed in batch experiments with real hydrolysed urine were shown to have an average size of >90 μm at pH 9 and 20 °C. This is reduced to 45 μm when changing stirrer type. Particle size increases with lower supersaturation. The results showed that under otherwise constant conditions, particle size decreases with lower temperature and has a minimum between pH 9 and 10. Deviating trends are observed at pH <8. Struvite formation in a CSTR (continuously stirred tank reactor) process was shown to be a reliable stable process that does not require any pH control. A method based on conductivity measurement is presented to estimate ionic strength, which is needed for equilibrium calculations.