Submersible microbial desalination cell for simultaneous ammonia recovery and electricity production from anaerobic reactors containing high levels of ammonia

• Novel submersible microbial desalination cell as a new method for ammonia recovery.
• In situ lowering ammonia level in anaerobic reactor by ammonia recovery.
• Current driven NH4+ migration and free NH3 diffusion for ammonia transportation.
• Initial ammonia level and external resistance affected the ammonia recovery.
• Coexistence of other cations had no negative effect on the ammonia transportation.

High ammonia concentration in anaerobic reactors can seriously inhibit the anaerobic digestion process. In this study, a submersible microbial desalination cell (SMDC) was developed as an innovative method to lower the ammonia level in a continuous stirred tank reactor (CSTR) by in situ ammonia recovery and electricity production. In batch experiment, the ammonia concentration in the CSTR decreased from 6 to 0.7 g-N/L during 30 days, resulting in an average recovery rate of 80 g-N/m2/d. Meanwhile, a maximum power density of 0.71 ± 0.5 W/m2 was generated at 2.85 A/m2. Both current driven NH4+ migration and free NH3 diffusion were identified as the mechanisms responsible for the ammonia transportation. With an increase in initial ammonia concentration and a decrease in external resistance, the SMDC performance was enhanced. In addition, the coexistence of other cations in CSTR or cathode had no negative effect on the ammonia transportation.

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