Closing ammonia loop in efficient biogas production: Recycling ammonia pretreatment of wheat straw

Abstract

We propose an integrated system for simultaneous ammonia recovery, ammonia pretreatment, biogas upgrading, and fertiliser production in biogas production. Ammonia stripping and absorbing played an important role as they significantly affected the ammonia recovery and biogas upgrading performance. Ammonia stripping with biogas was used to remove ammonia from biogas slurry at various conditions. The ammonia removal efficiency reached 99.30% at 10% CO2 content, 90 °C and 6 h stripping time. Ammonia absorption of ammonia-bearing biogas achieved crystalline ammonium and biogas upgrading. The obtained crystalline ammonium was used for recovering ammonia. The ammonia pretreatment and anaerobic digestion results showed that wheat straw pretreated with 0.70% ammonia concentration and 105 °C obtained the highest biogas yield of 538.1 mL g−1, which was 31.9% higher than untreated wheat straw. The process in this study shows a great potential in biogas production by recycling ammonia for pretreatment of feedstocks and biogas purification associated with producing fertilisers.