Investigation of optimum conditions for the recovery of magnesium ammonium phosphate from human urine using the Box-Behnken design

Abstract

Urine from domestic wastewater greatly increases the nutritional value of wastewater. Urine has a high concentration of nutrients and minerals that can be utilized as plant growth agents, according to a chemical analysis. Due to its high phosphate, nitrogen, and potassium content, human urine can serve as a sustainable substitute for chemical fertilizers. Struvite, also referred to as MAP, can be considered as a sustainable fertilizer and it is a magnesium ammonium phosphate crystal with the chemical formula of MgNH4PO4·6H2O. Struvite may be formed from many types of wastewater, one inexpensive and reliable source for struvite formation being human urine. However, struvite formation requires an external magnesium supply due to the extremely low concentration of magnesium in human urine. In this work, magnesium ammonium phosphate was precipitated from human urine by examining the effects of Mg2+ dose, temperature, and pH on struvite crystals. Several experiments for struvite precipitation were created using the Box-Behnken design. Struvite crystals formed upon the addition of a magnesium source at 20 °C, pH 10, and a mole ratio of 1:1. The results show that the large-scale application and nutrient recovery of struvite crystals from human urine are promising.