Assessing Nutrient Recovery from Piggery Effluents

The past few decades has seen an increase in livestock intensification within the Australian pig industry, which has lead to a waste management problem due to increased volumes of nutrient rich effluent leaving these facilities. Land application of these nutrient-rich effluents is economically and environmentally unsustainable in some circumstances. One promising alternative is to remove the nitrogen and phosphorus compounds by co-crystallising these compounds with magnesium, producing magnesium ammonium phosphate, commonly called struvite. Rigorous design of a struvite crystalliser requires detailed knowledge of crystallisation thermodynamics and kinetics, which depend on factors such as temperature, solution oversaturation and pH. The present study aims to evaluate struvite precipitation potential, using the Visual MINTEQ modelling package. A solution speciation model of struvite precipitation in different phases has been developed. This model indicates that across a wide range of pH (6-14) various other crystals form along with struvite, whereas struvite formation is dominant in the pH range of 7.75-9.27. Solution speciation modelling indicates that a Magnesium Ion Selective Electrode can be used to infer struvite supersaturation, enabling better modelling and control of crystal growth kinetics. A brief thermodynamic investigation on piggery wastewater collection pond will be performed using this model.