Abstract:
Recently there is a process in which ammonia is converted to dinitrogen gas by autotrophic bacteria utilizing aerobic autotrophic
produced nitrite as an electron acceptor under anaerobic condition. The sequencing batch biofilm reactor , SBBR was employed
in this work to investigate the autotroph nitrification and denitrification process to remove nitrogen under different air supply. The
air supply was controlled at different three ways, one was continuous supplying by control dissolved oxygen at 1.5 mg/l , two was
continuous supplying at dissolved oxygen greater than 2.0 mg/l and the other was on/off air supplying by maintaining dissolved
oxygen during aerated period at about 2 mg/l. There were two types of microbial sludge originated taken from the same municipal
treatment plant and before immobilized on fibrous media, acclimatized in the specific autotrophic substrate with ammonia as substrate
but with different air supply condition : one is MC1, continuous supplying with excess air for 5 months and the other is MC2, on/off
air supplying for 2 weeks. The SBBRs were controlled at two different hydraulic retention time (HRT) and 48 hour. The results at hy
draulic retention time of 24 hour showed that the nitrogen removal by MC2 was better than by MC1 and SBBRs continuous supplied
with air at dissolved oxygen 1.5 mg/L showed slightly better nitrogen removal than the other two sets, the nitrogen removal efficiencies
were 53 and 67 percent for MC1 and MC2 , respectively. In SBBRs with continuous air supplying at dissolved oxygen greater than
2.0 mg/l, the nitrogen removal efficiencies were 21 and 63 percent for MC1 and MC2 , respectively, and with on off air supplying, the
nitrogen removal efficiencies were 51 and 55 percent for MC1 and MC2, respectively. There was no nitrite accumulated and mainly
nitrogen compound in the effluent was the remaining influent ammonia .The results at hydraulic retention time 48 hour showed that there
was no significant difference on nitrogen removal between SBBRs immobilized with MC1 and MC2. The highest nitrogen removal
of 86 and 85 percent for MC1 and MC2 were obtained in SBBRs operated with alternating aeration . The nitrogen removed in SBBRs
operated with continuous air supply at 1.5 mg/L dissolved oxygen were 80 and 81 and at 2.0 mg/L dissolved oxygen were 65 and 62
by MC1 and MC2 , respectively. The ammonia was completely removed at HRT 48 hour. The chemoautotroph which can oxidize
ammonia by utilizing nitrite as an electron acceptor (ANAMMOX) could be identified in all experiments by Fluorescent in situ hybridization,
FISH technique.