P-RoC - Phosphorus Recovery from Wastewater by Crystallisation of Calcium Phosphate Compounds

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 wasteand industrial process waters by applying calcium silicate hydrate (CSH) compounds or synthesised tobermorite pellets as crystallisation seed materials. At first, the experiments were performed in fixed bed reactors in laboratoryand 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, the efficiency 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 DOCand 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 phosphate rock 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.