Phosphorus Recovery from Wastewater Treatment Plant by Using Waste Concretes

A new crystallization process is proposed to recover phosphorus from wastewater treatment plants using waste cement particles generated in aggregate recycling processes. Batch experiments were conducted with the waste cement particles for the phosphate recovery from potassium dihydrogen phosphate (KH2PO4) solutions as a model of wastewater. For an initial concentration of the phosphate of 50 mgP L-1, which is close to that in the water effluent produced in the sludge dewatering process, and an initial concentration of waste cement of 1.0 g L-1, approximately 50% of the phosphate was removed from the solution in 360 min. From the change over time in the concentrations of the phosphate, protons, and calcium ions, two reaction mechanisms can be considered: reaction at the surface of the waste cement particles, and the aqueous-phase reaction of the dissolved calcium hydroxide (Ca(OH)(2)) with the phosphate. The results of SEM and XRD analysis showed that the phosphorus was precipitated as hydroxyapatite (HAP) on the surface of the waste cement particles. The observed reaction rate of the phosphate recovery was comparable to those in the conventional HAP crystallization methods. Considering that costly additives such as a calcium source, e. g. calcium chloride, and seed materials are necessary for the conventional HAP crystallization methods, the present process is highly competitive due to the negligible cost of the waste cement.