Autotrophic ammonium removal from reject water: partial nitrification and anammox in one-reactor versus two-reactor systems.

Removal of total nitrogen from anaerobically digested sludge reject water by a fully autotrophic process in either one- or two-reactor systems was compared. Autotrophic nitrogen removal is currently most often applied in the one-reactor system primarily in the DEMON configuration. The two-reactor systems had a similar nitrogen removal rate to the one-reactor systems. It was evident that the limiting step was partial nitrification. Increase in partial nitrification can be difficult in a one-reactor system, where the overall conditions, such as the oxygen concentration or substrate concentrations, would progress to full nitrification. The partial nitrification of the two-reactor system may be improved by adjusting key parameters: the un-ionized form of the substrates, the oxygen concentration or the solids residence time. The impact of two process configurations on the operational stability and process performance was presented based on two cases--DEMON and the SHARON-ANAMMOX process.