Application of carbon dioxide stripping for struvite crystallization — I: Development of a carbon dioxide stripper model to predict CO₂ removal and pH changes Available to Purchase

This research investigated the feasibility of stripping CO₂ from the digester supernatant to raise the pH, thereby reducing the caustic chemical usage. In this study, a cascade CO₂ stripper was first designed and tested, with three different synthetic solutions in a struvite recovery, crystal reactor: (1) tap water saturated with CO₂, (2) NaHCO₃ solution saturated with CO₂, and (3) NaHCO₃ + NH₄Cl solution saturated with CO₂. It was found that the removal efficiency of the CO₂ stripper was dependant on several parameters, such as the characteristics of the influent, including total alkalinity, temperature, and initial concentration of dissolved CO₂ gas, influent flow rate, effluent recycle rate, aeration rate, and baffle numbers in the stripper. Based on the performance of the stripper on the three synthetic solutions, a CO₂ stripping model was developed using these parameters. This model was subsequently tested in a pilot-scale facility, to predict the amount of CO₂ removal possible.