Abstract

Phosphorus (P) recovery from waste water must become a predominant goal of all countries to face the limited resources of this essential nutrient. The induced crystallisation of calcium phosphates straight from the waste water phase applying tobermorite-rich calcium silicate hydrate compounds (CSH) from the construction industry as the trigger material has proved to be a suitable method. Laboratory and semi-technical scale experiments were carried out in fixed bed, stirred reactor and expanded bed mode. P-loads of the crystallisation substrates of up to 13 wt-% total P (P-tot) (30 wt-% P2O5) were achieved.

Recycling options of the generated products, both as substitute for phosphate rock in the phosphate industry and as a new fertiliser in agriculture, were demonstrated. Indicative operating and investment costs were estimated for conversion of conventional waste water treatment plants (WWTP) designed for nutrient removal and P-precipitation with iron and aluminium reagents to the proposed new crystallisation technology for simultaneous P-removal and P-recovery.