Phosphorus removal from soy protein wastewater using novel crystallisation technology

The objective of this work was to identify and implement a treatment method that would reduce the phosphorus (P) content of soy protein isolate manufacturing wastewater to an average of 2 mg L(-1) total P without increasing soluble salts in order to comply with discharge and receiving-water requirements. A novel crystallisation technology was evaluated through pilot studies that demonstrated these objectives could be met. Rapid settling (3.6 cm min(-1)) and filterable particles (65% filter cake dry solids content) were produced with lime precipitation at 10.0-10.2 pH in the high-aspect ratio, draft tube crystalliser (HARDTAC). Crystal growth in the full-scale system has yielded mean particle sizes of >60 microm. Also, minimal carbonate removal resulted in residual sludge generation of 0.6-0.8 g and lime consumption of 0.40-0.75 g per litre treated, which is substantially less than with a complete softening reaction. This paper describes the technical evaluation and full-scale treatment system that has been in operation since late 2005.