ANAEROBIC AMMONIUM OXIDATION DISCOVERED IN A DENITRIFYING FLUIDIZED-BED REACTOR

Until now, oxidation of ammonium has only been known to proceed under aerobic conditions. Recently, we observed that NH4+ was disappearing f rom a denitrifying fluidized bed reactor treating effluent from a meth anogenic reactor. Both nitrate and ammonium consumption increased with concomitant gas production. A maximum ammonium removal rate of 0.4 kg N.m(-3).d(-1) (1.2 mM/h) was observed. The evidence for this anaerobi c ammonium oxidation was based on nitrogen and redox balances in conti nuous-flow experiments. It was shown that for the oxidation of 5 mol a mmonium, 3 mol nitrate were required, resulting in the formation of 4 mol dinitrogen gas. Subsequent batch experiments confirmed that the NH 4+ conversion was nitrate dependent. It was concluded that anaerobic a mmonium oxidation is a new process in which ammonium is oxidized with nitrate serving as the electron acceptor under anaerobic conditions, p roducing dinitrogen gas. This biological process has been given the na me 'Anammox' (anaerobic ammonium oxidation), and has been patented.