Abstract:In the biogas project, determining how to treat the biogas slurry with large volume is one of big issues. Additionally, biogas upgrading is always required for increasing the heat value of biogas. A concept was proposed by coupling the water recovery using forward osmosis and CO2 chemical absorption, in which the CO2-rich solvent from CO2 chemical absorption process was adopted as the draw solution to recover water from biogas slurry in forward osmosis. The feasibility of water recovery from biogas slurry by using CO2-rich solvent as the draw solution in addition to concentrating the biogas slurry was experimentally investigated. In terms of the water flux, concentration ratio of biogas slurry, rejection ratio of ammonia nitrogen and CO2 absorbent transfer flux from the draw solution to biogas slurry, effects of the type and mass fraction of draw solution and other key operation parameters on water recovery performance in forward osmosis were explored. Results showed that CO2-rich solvent can be adopted as the draw solution to successfully reclaim water from biogas slurry and simultaneously concentrate the biogas slurry in forward osmosis. Additionally, the water flux transferred from biogas slurry from the draw solution increases with the mass fraction, flow rate and temperature of draw solution. Correspondingly, the concentration ratio of biogas slurry was increased, however, the rejection ratio of ammonia nitrogen in biogas slurry was decreased and the absorbent transfer flux of CO2 absorbent was increased. When the CO2-rich potassium glycinate with 2.5mol/L and 0.5mol/mol CO2 loading was adopted as the draw solution in the forward osmosis, the initial water flux from biogas slurry was about 8.05L/(m2·h) at the conditions of 70℃ and 150mL/min for draw solution, and ambient temperature and 150mL/min for biogas slurry. After 4h operation, the concentration ratio and ammonia nitrogen rejection ratio of biogas slurry can reach 1.18 and 84.13%, respectively. Notably, the CO2 absorbent transfer flux was only 2.94g/(m2·h). The research result may provide a technical support for concentrating biogas slurry and recovering water from biogas slurry.
