Acid Phase Digestion: the Biological Solution for P Solubilization
An acid phase digester provides a low-oxygen and low pH environment. This facilitates the rapid release of orthophosphates in Bio-P sludge along with the dissolution of crystalized and organically bound phosphorus. Over 60% solubilization of P occurs in the acid phase digesters without using any additional chemicals. In non-Bio-P plants, up to 40% of the phosphorus solubilizes using an acid phase digester.
A CalPrex® reactor is placed between the acid phase and gas phase digesters. Sludge from the acid phase digester is dewatered. The centrate is sent to the CalPrex® reactor. The dissolved phosphorus in the centrate precipitates with the addition of calcium hydroxide and calcium chloride. By maintaining the pH of the solution at 6.5, phosphorus is recovered as a brushite crystal (CaHPO4· 2H2O). As a fertilizer, Brushite is as effective as other leading phosphate fertilizers on the market today.