Influence of Sludge Dewatering Filtrate Components on Phosphorus Recovery in Form of Struvite

Effects of the constitutes of sludge dewatering filtrate on phosphorus recovery in form of struvite (MgNH₄PO₄·6H₂O) were studied by using batch stirring reactors.The results showed that with keeping stirring speed at 200 rpm,stirring time at 180 min and precipitation time at 60 min in all experiments,pH of sludge dewatering filtrate rose after stirring without reagent addition;however,it was not enough to form struvite.When the concentration of PO₄^3- was at 4.00 mmol/L,more than 90% of the PO₄^3- was recovered. But only the initial concentration of Mg²⁺ in sludge dewatering filtrate exceeded above 5.00 mmol/L,the reaction between Ca²⁺ and PO₄^3- was inhibited distinctly and the ratio of the recovery molar concentration of PO₄^3-、Mg²⁺ and NH₄⁺ could nearly reach 1:1:1.which means that the most quantity struvite were formed. When pH ranged from 10.0 to 10.5,the most quantity of struvite formed.Turbidity of sludge dewatering filtrate had negative effect on the recovery of Mg²⁺ and struvite formation.