OPTIMIZATION OF ALKALINE–THERMAL HYDROLYSIS TO OBTAIN STRUVITE FROM DIGESTED SLUDGE USING A BOX–BEHNKEN DESIGN: SOLUBILIZATION OF NUTRIENTS AND METALS

In this study, we investigated ways by which to optimize metals and nutrients solubilization from sewage sludge using alkaline–thermal hydrolysis the Box–Behnken design. We also examined through struvite crystallization recovery of solubilized hydrolyzed liquid determined effect NaOH concentration, liquid/solid ratio, temperature on process. Nutrients was positively affected decreasing liquid/sludge ratio increasing concentration. Ca, Al, Zn increased with temperature. The optimum condition for 0.7 M a 5/1 mL/g at 35 °C. EDS analyses obtained under conditions showed that mass percentage C, P, Fe, K decreased compared digested sludge. Under conditions, removal efficiencies NH4+ PO43- precipitation were 57.43 79.22% N:Mg:P molar 1:1:1, 73.31 99.02% 1:1.5:1, respectively. XRD dry precipitate hazenite in addition formation 1:1:1.