Enhancement of nitrogen removal in a novel anammox reactor packed with Fe electrode.

Slow proliferation of anammox bacteria is a major problem limiting the wider application of anammox technology in practical wastewater treatment. A novel anammox reactor packed with a Fe electrode was developed for enhancing anammox consortium activity and accelerating the startup of anammox process. After 125 days' operation, total nitrogen removal rate achieved 1209.6 mg N/L/d in this hybrid reactor (R1), which was significantly higher than that in a control anammox reactor without Fe electrode (R2, 973.3 mg N/L/d). Raising the voltage applied for the electrode in a given extent (≤0.6 V) enhanced the performance of the reactor, while the voltage more than 0.8 V reduced the anammox performance. Scanning electron microscope (SEM) observation along with transmission electron microscope (TEM) analysis of the sludge taken from the reactors revealed that a more compacted microbial community structure was formed in R1. Fluorescence in situ hybridization (FISH) together with DNA analysis indicated that anammox bacteria were highly enriched with the presence of the Fe electrode.