Optimization of struvite fertilizer formation from baker's yeast wastewater: growth and nutrition of maize and tomato plants

Struvite precipitate obtained from yeast industry anaerobic effluent with high ammonium nitrogen (NH4-N) was investigated for fertilizer effect on plant growth and nutrition according to applications of N, nitrogen/phosphorus/potassium (NPK), and control. Optimum struvite formation conditions were determined via Box-Behnken design. Optimum condition was obtained at pH 9.0 and Mg/N/P molar ratio of 1.5:1:1. Under these conditions, heavy metal concentrations in the obtained struvite precipitate (except Cu) were below the detection limits. In addition to high N, P, and Mg content, energy-dispersive X-ray (EDX) analysis showed that the struvite also included the nutritional elements Ca, K, Na, and Fe. X-ray diffraction (XRD) analysis revealed the complex structures of NaAl(SO4)(2)(H2O)(12), NaMn2+Fe2(PO4)(3), and (Na-2,Ca)O-2(Fe,Mn)O.P2O5 in the precipitate. High Na+ and Ca2+ concentrations in the anaerobic effluent reacted with phosphate during struvite precipitation. Different applications and struvite dosages significantly affected fresh and dry weights and nutrient element uptakes by plants (P < 0.05). N, P, and Mg uptakes of plants were significantly higher at struvite x2, x3, and x4 dosages compared with NPK application. For adequate nutrition and supply of optimum dry weight, struvite x2 dosage (5.71 g struvite/kg soil) was found appropriate for both maize and tomato plants.