Thermodynamic Assessment of Effects of Solution Conditions on Precipitation and Recovery of Phosphorus from Wastewater

Abstract

Abstract Chemical modeling calculations and batch tests were carried out to investigate the effect of solution chemistry on formation of phosphate precipitation in synthetic flushed dairy manure wastewater for phosphorus recovery. Saturation index (SI) of different calcium phosphate precipitates in solution with a PO43− concentration range of 0.032–9.8 mM (1–300 mg P/L), Ca/P molar ratio of 1–20, pH value of 5.0–12.0, and the CO32− concentration of 0–100 mM was calculated separately using the geochemical aquatic modeling program, PHREEQC. Results show that the SI of calcium phosphate is the logarithmic function of Ca2+ and PO43− concentration, increasing with the increase of Ca2+ and PO43− concentrations. SI of calcium phosphate is the polynomial function of the solution pH value. SIs of hydroxyapatite (HAP) and tricalcium phosphate (TCP) increase with the growth of the pH value, while the SIs of octacalcium phosphate (OCP) and dicalcium phosphate dehydrate (DCPD) reach the maximum value at pH 9.0–9.5 and...