Techno-economic evaluation of ammonia recovery from biogas slurry by vacuum membrane distillation without pH adjustment

Abstract

A techno-economic evaluation of ammonia recovery from biogas slurry without pH adjustment by vacuum membrane distillation was performed in this study. After experimentally exploring the effects of key operation parameters on the ammonia separation performance, we conducted the orthogonal experiments to obtain the optimal operation conditions. The results indicated that the maximum ammonia separation factor can reach up to 8.05 under the optimal conditions, implying the technical feasibility of ammonia recovery from biogas slurry without pH adjustment by vacuum membrane distillation. We also investigated the economic evaluation of this ammonia recovery system for NH4HCO3 production considering different pH adjustment methods and heat sources. When the total ammonia nitrogen content is 2 g-N/L and heat is supplied by natural gas combustion, the profit of this ammonia recovery system is about $0.4/m3-biogas slurry for the case without pH adjustment, while the profit decreases greatly to about $-2.06/m3-biogas slurry for the case using NaOH to increase pH value and $-0.06/m3-biogas slurry for CaO addition case. Sensitivity analysis illustrated that the membrane lifetime is the most significant impact factor at a fixed initial total ammonia nitrogen content of biogas slurry. With an increase of initial total ammonia nitrogen content of biogas slurry from 0.5 to 4.0 g-N/L, the profit increases gigantically from $-0.71/m3-biogas slurry to $1.88/m3-biogas slurry. The study can provide a green and sustainable nitrogen fertilizer production process.