CalPrex: Pre-Digestion P-Recovery

THE PROBLEM
Phosphorus Solubilization Limits Recovery Efficiency

Typical struvite based phosphorus recovery technologies recover only 15-30% of the phosphorus entering wastewater treatment plants (including Bio-P plants). Recoverable crystals are only available from soluble and reactive phosphorus (orthophosphate).

THE SOLUTION
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.

THE BENEFITS
High Efficiency P-Recovery and Digester Protection

     Over 60% Solubilzation of P in Bio-P Sludge
     Divert Over 50% of the Soluble P from the Digester
     Reduce up to 50% of the Total P in Biosolids
     Reduce Struvite Buildup in the Methane Digester
     No Ammonium Required