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Phosphorus removal and induced precipitation in aerobic granular sludge process for wastewater treatment

Manas, Angela. Phosphorus removal and induced precipitation in aerobic granular sludge process for wastewater treatment. PhD, Institut National Polytechnique de Toulouse, 2011

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Official URL: http://ethesis.inp-toulouse.fr/archive/00001801/

Abstract

Over the last decade, aerobic granulation processes have araised as a promising technology for treating wastewater effluents containing high nitrogen, phosphorus and carbon concentrations. The microbial complexity of granules and the mechanisms by which they acquire excellent settleability properties, still constitute important research goals to investigate. This thesis is focused on a mechanism that has been little addressed in literature, that is, phosphate precipitation in the core of aerobic granules. Different analytical techniques, sometimes adapted for the first time to this type of systems, like Raman spectroscopy, have let an exhaustive characterization of biominerals in the core of granules. Analyses performed on aerobic granules grown with synthetic fed in a lab-scale SBR (Sequential Batch Reactor), revealed a calcium phosphate core made of hydroxyapatite [Ca5(PO4)3(OH)]. This precipitation phenomenon is induced by local pH and supersaturation gradients issued of biological reactions inside granules. The study of the biomineralization phenomenon has been extended into anaerobic granules coming from UASB reactors at different cheese wastewater treatment plants. A physico-chemical model has been described in a form of matrix with AQUASIM® software, and coupled with a thermodynamic database (PHREEQC®), in an attempt to hypothesize the mechanisms that influence the biomineralization phenomena. It has been proposed the formation of an amorphous precursor (ACP) prior hydroxyapatite precipitation in the core of granules, suggesting the thermodynamic constant (pKsp|20ºC=28.07±0.58) and kinetic constants at different operating conditions. It has been also estimated the contribution of the biomineralization to the overall phosphorus removal process (up to 46% at the operating conditions tested), thanks to the development and study of a GSBR (Granular Sludge Batch Reactor) in labscale, for more than 900 days. The fate of the biomineralization process in granules, regarding the contribution to their stabilization and physical properties, has been also dealt in this thesis. The reactor stability and performances have been assessed by alternating anoxic/aerobic and anaerobic/aerobic cycles, in sights of a future industrial application. The induction of precipitation by local variation of pH and supersaturation issued of biological reactions has been here introduced, although it will need further investigation.

Item Type:PhD Thesis
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Institution: Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
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Research Director:
Spérandio, Mathieu and Biscans, Béatrice
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