Investigation of chemical-free nutrient removal and recovery from CO₂-rich wastewater

The feasibility of a bench-scale system for removal and recovery of phosphorus (P) as struvite from CO₂-rich wastewater was tested. A continuous 12 L reactor system combining a fluidized seedbed and aeration for pH increase was developed and tested using synthetic feed. For a 100 mL min⁻¹ influent rate, an aeration and recycle rate combination of 7 L min⁻¹ and 700 mL min⁻¹ was sufficient for increasing and maintaining the reactor pH from 6.7 to between 7.6 and 8.0. Significant P removal was achieved in 6 h runs without a seedbed (91–92%), while neither the struvite nor sand seedbeds improved P removal (91–96%). Struvite was recovered in all runs, with additional calcium (Ca) precipitation in the seedbed runs. Reactor operation was possible for an extended period of time, up to 46 h without any major adjustment during long-term run. The average P removal was 88%, and precipitate collected after 24 h was found to be mainly struvite, while the final precipitate had a Ca: total phosphorus molar ratio of 0.56 and also contained calcite. This study has demonstrated the technical feasibility of an aerated crystallization reactor system for chemical-free struvite removal and recovery from CO₂-rich wastewater such as stored livestock manure.