Phosphate dynamics in an urban sewer: A case study of Nancy, France

Abstract : The nature of phosphate phases present in suspended matter, biofilm, and sediment of Greater Nancy sewer system, was investigated over a period of two years. The phosphate speciation was determined by two approaches: a direct identification of phosphorus mineral phases was conducted by Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-ray Spectroscopy (EDXS), whereas a chemical extraction of samples provided an estimate of phosphorus pools defined by the fractionation scheme. Quantitative analysis of 1340 individual particles allowed to draw a picture of phosphate species distributions along the sewer system and over time. Amorphous Ca-phosphates (brushite, whitlockite, octacalcium phosphate, Mg-brushite, hydroxyapatite and carbapatite) are ubiquitous although brushite dominated upstream, and octacalcium phosphate and apatite prevailed downstream and in sediments. Al-Ca-phosphate minerals such as foggite, bearthite, gatumbaite, and crandallite appeared downstream and in biofilms. Changes in Ca-phosphate phase distribution were related to phase transformations from brushite to hydroxyapatite that were shown to be kinetically driven. The restriction of Al-Ca-phosphates to downstream of the sewer system was most probably related to the lower pHs measured at these sites. The pH dependency was confirmed by stability calculations. TEM examination of chemical extraction residues revealed the presence of neoformed Al-Ca-phosphate species that invalidate the fractionation scheme. On the other hand, it confirmed that phosphate phases may undergo significant geochemical changes over a short time scale.
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J. Houhou, B.S. Lartiges, A. Hofmann, G. Frappier, J. Ghanbaja, et al.. Phosphate dynamics in an urban sewer: A case study of Nancy, France. Water Research, IWA Publishing, 2009, 43 (4), pp.1088-1100. ⟨10.1016/j.watres.2008.11.052⟩. ⟨hal-02264644⟩



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