Nitrate reduction by organotrophic Anammox bacteria in a nitritation/anammox granular sludge and a moving bed biofilm reactor

► Nitritation/anammox process in granular and biofilm system was studied. ► Nitrate production in both systems was 40-68% lower than expected. ► Sludge production would be higher if heterotrophs were the main VFAs degraders. ► The dominant Anammox bacterium is known to be capable of oxidizing VFAs. ► Anammox bacteria effectively competed-out heterotrophic denitrifying bacteria.