Abstract
Urine diversion toilets and waterless urinals have received much attention lately to solve sanitation challenges in water scare countries. Separating the urine at source and treating the urine and solids separately has the impact of reducing water usage and reducing the burden on wastewater treatment systems. Source separated urine can be valorised by extracting struvite as fertiliser through crystallisation. A cost-effective magnesium (Mg) source is required for the process and depending on factors such as location and availability, an Mg source may be the difference between an economically viable process and one that is not. Different kinds of sources for Mg have been investigated, but none investigated fertiliser grade magnesium nitrate (Mg(NO3)2 ). In this study, struvite crystallisation using Mg(NO3)2 was investigated. The effect of four parameters namely residence time, pH, Mg: P ratio and stirring time on yield were studied. Residence time was determined to be the most influential parameter. The optimal pH, stirring speed, residence time and Mg:P ratio were found to be 9.5, 90 rpm, 24 min and 1.5 respectively. Stirring speed was found to have the least effect on yield and a minimal effect on crystal size distribution.
