Alcaligenes faecalis C16 was found to have the ability to heterotrophically nitrify and aerobically denitrify. In order to further understand its nitrogen removal ability and mechanism

the growth and ammoniumremoval response were investigated at different C/N ratios and ammoniumconcentrations in the medium with citrate and acetate as carbon source separately. Furthermore

experiments of nitrogen sources

production of nitrogen gas and enzyme assay were conducted. Results show that the bacterium converts NH

4

+

-N and produces NH

2

OH during the growing phase and nitrite accumulation is its distinct metabolic feature. A. faecalis C16 is able to tolerate not only high ammonium concentration but also high C/N ratio

and the ammonium tolerance is associated with carbon source and C/N ratio. The nitrogen balance under different conditions shows that approximately 28%-45% of the initial ammonium is assimilated into the cells

44%-60% is denitrified and several percent is converted to nitrification products. A. faecalis C16 cannot utilize hydroxylamine

nitrite or nitrate as the sole nitrogen source for growth. However

nitrate can be used when ammonium is simultaneously present in the medium. A possi

ble pathway for nitrogen removal by C16 is suggested. The preliminary enzyme assay provides more evidence for this nitrogen removal pathway.