ENRICHIMENT OF ANAEROBIC AMMONIUM OXIDIZING (ANAMMOX) BACTERIA FROM ACTIVATED SLUDGE USING CONTINUOUS CULTIVATION SYSTEM.

Enrichment of anaerobic ammonium-oxidizing (anammox) bacteria was performed in a continuous-feeding anaerobic culture using a fixed bed reactor. As a seed sludge, three different types of sludge were used: sewage, digestion and nitrification sludge. About four months later, simultaneous removal of ammonia and nitrite and production of a little amount of nitrate, peculiar to anammox reactions, were observed in all the reactors where the different seed sludges were inoculated. The ratio of the amount of nitrite removed to that of removed ammonium was 0.98 - 1.26; and the ratio of the amount of nitrate produced to that of removed ammonium was 0.14 - 0.20. These ratios are similar to those obtained for anammox reactions in previous reports. Furthermore, 16S rRNA gene analysis confirmed the enrichment of anammox bacteria in each culture. In particular, a new cluster of anammox bacteria, which have 93.8 - 95.3% similarity with Candidatus Brocadia anammoxidans, was created within the Planctomycetes using clones obtained from the enrichment culture started from sewage sludge.When anammox bacteria-enriched sludge was used for continuous wastewater treatment with gradual increase of ammonia and nitrite concentrations, the denitrification rate reached 9.8 kg-N/m3/d in 97days.