AEROBIC DENITRIFIERS ISOLATED FROM AN ALTERNATING ACTIVATED-SLUDGE SYSTEM

One hundred and sixty-nine bacterial strains were isolated from activa ted sludge from a waste water treatment basin operating under alternat ing aerobic/anaerobic conditions. Sixteen strains from a subsample of 23 nitrogen oxide reducers were true respiratory denitrifiers, and all denitrified under both anaerobic and aerobic conditions. REP-PCR band analysis showed different patterns for all strains. One strain (strai n 1) produced large amounts of N2O and was studied in detail. Nitrous oxide was the major end product of denitrification by this strain, and NO2- was reduced more efficiently than NO3-. The aerobic denitrificat ion was most pronounced with NO2- as electron acceptor, and the reduct ion of NO2- was not coupled to NH4+ oxidation.