Simultaneous biogas upgrading, CO₂ sequestration, and biogas slurry decrement using biomass ash

A novel system for simultaneous biogas upgrading, CO₂ sequestration, and biogas slurry decrement was established by adding biomass ash into biogas slurry to form a renewable CO₂ mixture absorbent. After CO₂ saturation, the CO₂-rich mixture absorbent could be applied for plant growth. When the mass ratio of liquid to solid was 4:1, CO₂ absorption capacity of this mixture absorbent reached up to 97.33 g-CO₂/kg-biomass-ash, which was about 135% higher than that of the biomass ash-water mixture. The highest value of 129.94 g-CO₂/kg-biomass-ash was obtained at a liquid-solid ratio of 99:1. When the TS concentration of anaerobic digestion feedstock was higher than 16 wt% and the water content of CO₂-rich absorbent was about 50 wt%, more than 80% of biogas slurry can be adsorbed by the biomass ash. If the biomass ash with a CO₂ absorption capacity of 100 g-CO₂/kg was adopted and its transportation distance was less than 45 km, the biogas upgrading cost could be lower than the global average level (about RMB¥ 0.7/Nm³-biogas) when using the novel system proposed in this study.