Promoting the nitrogen removal of anammox process by Fe-C micro-electrolysis.

In this study, a process that combines iron-carbon micro-electrolysis (IC-ME) with the anammox process was successfully established for promoting nitrogen removal, especially the removal of nitrate by-product. Compared with the conventional anammox process, the average total nitrogen removal efficiency of the combined system increased from 64.6% to 90.2% and 83.8% when the system was effectively operated for 4 days (Phase 2) and 13 days (Phase 3), respectively. In this combined system, IC-ME played a dual role: 1) converting the nitrate to ammonia as the nitrogen substrate for further degradation, and 2) producing Fe2+, Fe3+ and H2 for the nitrogen removal processes of NH4+ oxidation with Fe3+ reduction (Feammox), nitrate-dependent Fe2+ oxidation (NDFO), and denitrification, in addition to the anammox process. Microbial analysis using 16S rRNA high-throughput sequencing revealed Candidatus Kuenenia and Candidatus Brocadia as the major anammox genera, accounting for 1.01% and 0.15%, respectively.