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

Abstract

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.