Simultaneous current generation and ammonia recovery from real urine using nitrogen-purged bioelectrochemical systems

Abstract

Bioelectrochemical systems (BESs) offer a strategy for treating source-separated urine with current generation, but the high content of ammonia is still a challenge for sustainable maintenance of BESs due to ammonia inhibition. Therefore, an integrated BES setup was developed to overcome this problem by ammonia recovery. This setup, working in closed circuit mode with nitrogen purging (CN), allowed for the produced ammonia to be continuously channeled to an absorption bottle. In addition, control reactors in closed circuit (CC) or in open circuit mode (OC) were also run for comparison. A maximum power density of 310.9 ± 1.0 mW m⁻² was obtained for the CN reactor, and 127.1 ± 0.9 mW m⁻² was obtained for the CC reactor. Total nitrogen (TN) removal efficiency (84.9% ± 2.2%) from urine was considerably higher in the CN reactor than it was in the CC (29.7% ± 6.7%) or OC (30.0% ± 8.2%) reactor. In the CN reactor, 52.8% ± 3.6% of the TN was recovered in the form of NH₃-N, with a NH₃ recovery rate of 435.7 ± 29.6 gN m⁻³ d⁻¹. The improved performance of the CN reactor was attributed to the mitigation of ammonia inhibition to the anode electro-activity. 16S rDNA sequencing showed that no Anammox and nitrifiers were detected on the anodes and cathodes. Overall, nitrogen purging provides the urine-fed BESs with a useful approach for maintaining the system performance by ammonia recovery.