Energy-positive nitrogen removal from reject water using a tide-type biocathode microbial electrochemical system

A tide-type biocathode microbial electrochemical system (TBMES) employing intermittent air accessible method was constructed for simultaneous carbon and nitrogen removal. The nitrification and denitrification processes occurred in cathode chamber were enhanced by raising frequency of catholyte feeding-draining process and lowering external resistance. At external resistance of 5 Ω and frequency of 8 cph, the TBMES removed 99.3 ± 0.3% of COD and 57.7 ± 1.1% of total nitrogen when treating synthetic medium with COD/N ratio of 3.0, concomitantly, a maximum power density of 10.6 W m⁻³ was achieved. Comparable performances were obtained for reject water treatment with a relatively lower COD/N ratio of 2.5, which were 88.6 ± 1.3%, 53.2 ± 3.8% and 8.9 ± 0.2 W m⁻³ for COD removal, total nitrogen removal and maximum power density. The feeding-draining process consumed 14.3% of the total energy produced, and thus obviated energy-intensive aeration and achieved net energy output.