CalPrex™: Pre-Digestion P-Recovery

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).

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 35% 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). Without additional processing, Brushite, a phosphorus fertilizer, is available for growing plants.

High Efficiency P-Recovery and Digester Protection

  1. Over 60% Solubilzation of P in Bio-P Sludge
  2. Divert Over 50% of the Soluble P from the Digester
  3. Reduce 90% of the Soluble P in the CalPrex Reactor
  4. Reduce up to 50% of the Total P in Biosolids
  5. No Ammonium Required