Anaerobic ammonium oxidation, nitrification and removal of COD was studied at ambient temperature (18 °C ± 3) in an anoxic/aerobic granular sludge reactor during 390 days. The reactor was operated in a sequencing fed batch mode and was fed with acetate and ammonium containing medium with a COD/N ratio of 0.5 [g COD/gN]. During influent addition, the medium was mixed with recycled effluent which contained nitrate in order to allow acetate oxidation and nitrate reduction by anammox bacteria. In the remainder of the operational cycle the reactor was aerated and controlled at a dissolved oxygen concentration of 1.5 mg O(2)/l in order to establish simultaneous nitritation and Anammox. Fluorescent in-situ hybridization (FISH) revealed that the dominant Anammox bacterial population shifted toward Candidatus "Brocadia fulgida" which is known to be capable of organotrophic nitrate reduction. The reactor achieved stable volumetric removal rates of 900 [g N(2)-N/m(3)/day] and 600 [g COD/m(3)/day]. During the total experimental period Anammox bacteria remained dominant and the sludge production was 5 fold lower than what was expected by heterotrophic growth suggesting that consumed acetate was not used by heterotrophs. These observations show that Anammox bacteria can effectively compete for COD at ambient temperatures and can remove effectively nitrate with a limited amount of acetate. This study indicates a potential successful route toward application of Anammox in granular sludge reactors on municipal wastewater with a limited amount of COD.
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