Dynamic modelling and simulation of nutrient recovery from piggery effluent

Livestock intensification in Australia has led to increased nutrient loading, where the major nutrients present are ammonium and phosphate. In this and other wastewater systems, it is possible to precipitate ammonia and phosphorus as a magnesium salt, commonly known as struvite. While the possibility of this recovery scheme is known, very little appears in the available literature related to the rigorous design of such systems, in particular the dynamic modelling and simulation of this system. This paper initially focuses on the investigation of growth kinetics of struvite based on the crystal size distribution (CSD) of the growing crystal population. The parameters involved in this study of the crystal growth are supersaturation, seed size and variety, and degree of agitation. The second feature of this work is the presentation of a dynamic model of a struvite recovery unit, incorporating. The proposed model is a continuous-discrete system, in which the effluent flows continuously through the unit, while the growing crystals are held-up within the reactor, undergoing periodic harvesting. The third element of this paper relates to the dynamic simulation of the proposed recovery unit, using the gPROMS dynamic simulation package. Dynamic simulation has the potential to deliver greater insight into this system, leading to more effective and rigorous designs of full-scale struvite recovery units. This results through the evaluation of a variety of "what-if' scenarios, including the effect of hydraulic and nutrient loading on nutrient recovery