Oxidation behavior of ammonium in a 3-dimensional biofilm-electrode reactor

Excess nitrogenous compounds are detrimental to natural water systems and to human health. To completely realize autohydrogenotrophic nitrogen removal, a novel 3-dimensional biofilm-electrode reactor was designed. Titanium was electroplated with ruthenium and used as the anode. Activated carbon fiber felt was used as the cathode. The reactor was separated into two chambers by a permeable membrane. The cathode chamber was filled with granular graphite and glass beads. The cathode and cathode chamber were inhabited with domesticated biofilm. In the absence of organic substances, a nitrogen removal efficiency of up to 91% was achieved at DO levels of 3.42±0.37 mg/L when the applied current density was only 0.02 mA/cm². The oxidation of ammonium in biofilm-electrode reactors was also investigated. It was found that ammonium could be oxidized not only on the anode but also on particle electrodes in the cathode chamber of the biofilm-electrode reactor. Oxidation rates of ammonium and nitrogen removal efficiency were found to be affected by the electric current loading on the biofilm-electrode reactor. The kinetic model of ammonium at different electric currents was analyzed by a first-order reaction kinetics equation. The regression analysis implied that when the current density was less than 0.02 mA/cm², ammonium removal was positively correlated to the current density. However, when the current density was more than 0.02 mA/cm², the electric current became a limiting factor for the oxidation rate of ammonium and nitrogen removal efficiency.