Glycinate-looping process for efficient biogas upgrading and phytotoxicity reduction of alkaline ashes

This paper proposed a glycinate-looping-based CO₂ mineralization process for efficient biogas upgrading and phytotoxicity reduction of alkaline ashes. Simultaneously CO₂ absorption and mineralization occurred by flowing artificial biogas through a single reactor filled with ashes and potassium glycinate solution. The technical feasibility and reaction mechanism was investigated using four ashes. Results showed that greater CO₂ removal efficiency and sequestration capacity were obtained in the glycinate-ash-CO₂ system than that in the traditional water-ash-CO₂ system. Glycinate played key roles in enhancing CO₂ mass transfer, Ca²⁺/Mg²⁺ leaching, and CaCO₃ formation. Maximal CO₂ removal of about 90% and CO₂ sequestration capacity of 275 g/kg was achieved at conditions of 55 °C, 0.5 M glycinate, and 100 g/L ash dosage. In addition, although the glycinate loss in the four carbonated ashes was >9.06 mg/g, a simple water wash could significantly reduce the glycinate loss to <3.66 mg/g. Furthermore, the phytotoxicity of carbonated biomass ash could be neglected if the ash dosage was controlled <100 g/L. Although the phytotoxicity of coal fly ashes can be reduced after carbonation reactions, only the application with a low dosage (<10 g/L) was acceptable in agriculture. The decreased phytotoxicity resulted from the reduced alkalinity and extraction of heavy metals of ashes in water after carbonation reactions.