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P-RoC - Phosphorus Recovery from Wastewater by Crystallisation of Calcium Phosphate Compounds
U. Berg*1, G. Knoll**, E. Kaschka**, V. Kreutzer***, D. Donnert*, P.G. Weidler* and R. Nüesch*
* Institute for Technical Chemistry - Water- and Geotechnology Division (ITC-WGT), Forschungszentrum Karlsruhe GmbH, P.O. Box 36 40, D-76021 Karlsruhe, Germany; 1 corresponding author: Dr. Ute Berg (e-mail:ute.berg@itc-wgt.fzk.de; dietfried.donnert@gmx.de; peter.weidler@itc-wgt.fzk.de; rolf.nueesch@itc-wgt.fzk.de) ** Posch & Partners, Consulting Engineers, Sebastian-Kneipp-Weg 17, A-6026 Innsbruck, Austria; (e-mail: knoll@pap.co.at; kaschka@pap.co.at) *** Institute of Sanitary Engineering and Water Pollution Control, University of Natural Resources and Applied Life Sciences (BOKU), Muthgasse 18,A-1190 Vienna, Austria; (e-mail: verena.kreutzer@lycos.at)

Abstract The P-RoC process – the phosphorus recovery straight from the aqueous phase by crystallisation of calcium phosphate – was developed in order to simultaneously remove and recover phosphorus from municipal waste- and industrial process waters by applying calcium silicate hydrate (CSH) compounds or synthesised tobermorite pellets ascrystallisation seed materials. At first, the experiments were performed in fixed bed reactors in laboratory- and in pilot scale. In continuation stirred reactor technique was developed and optimised in order to reduce operation and maintenance efforts of the process. Apart from the composition and grain size of the seed materials and the hydraulic retention time (HRT) in the reactor, theefficiency and longevity of the P-RoC process was mainly controlled by the initial P concentration of the wastewater. P-RoC proved to be feasible to treat also highly DOC- and P-enriched process waters. Total P (P-tot) contents in the generated crystallisation products of at least 10-11% P-tot were achieved in long-term fixed bed experiments, which was promising for the substitution of natural phosphaterock in the phosphorus industry. Mineralogical investigations (FTIR-ATR, XRD) proved the formation of hydroxyapatite-(HAP) like coatings onto the surface of the seed materials using municipal wastewater. Using industrial process water, the crystallisation product formed was brushite. Keywords Calcium phosphate; crystallisation; phosphorus recovery; Phostrip; process water

INTRODUCTION Facing thefiniteness of the natural resources of phosphorus as an essential nutrient and indispensable fertiliser component in agriculture (ATV, 2003), the declared objective of all industrialised countries should be the sustainable use of available phosphorus sinks. Municipal wastewater treatment plants (WWTP) or phosphorus-rich industrial process waters, serving as major sinks for phosphate, offer highlypotential sources for the generation of P-rock substitutes or new fertilisers. Phosphorus recovery straight from the liquid phase offers the noteworthy advantage that phosphate is already dissolved. It just has to be scavenged, either by the precipitation of struvite (Heinzmann, 2001), requiring a constant stoichiometrical ratio of magnesium, ammonium and phosphorus (Ueno and Fuji, 2001), or bythe formation of calcium phosphate, e.g. by crystallisation. For that, the properties of the seed material, initiating the kinetically controlled crystallisation process as well as serving as carrier for the generated calcium phosphate compounds, play a decisive role. Crystallisation has already been realised in full-scale using sand (Giesen, 1999), calcite (Donnert and Salecker, 1999) orsynthesised spherical tobermorite pellets (Moriyama et al., 2001, 2003) as seed materials. However, preliminary CO2-stripping and/or adjustment of the pH-value, prior to the

calcium phosphate precipitation were required. Furthermore, the pH-value had to be re-adjusted prior to discharge. The objective of this study was to develop a simple technology for phosphorus recovery from municipal waste- and...