Abstract:

22 nitrate reducing strains were isolated using dilute soil suspension spread plate techniques from soil that sampled from the rhizosphere of Arundo donax L.. Denitrifying bacterium strain LZ-14 with faster gas producing and higher nitrogen removal efficiency was screened. The cells of strain LZ-14 were Gram negative, facultative anaerobic, mobile and short rodshaped. The effects of the C／N ratio and pH on the growth and denitrification process of strain LZ-14 were  respectively investigated with acetate and nitrate as the sole carbon and nitrogen source. The results showed that the optimal C／N ratio was 5 and TN removal rate of 845％ was achieved in 36 hours with complete removal of 150?mg／L nitrateN. The best initial pH range for strain LZ-14 was 7 to 8, also nearlyno cell growth and denitrification could be detected. It was also found that thenitrogen removal process mainly appened in the growth phase of 12～36 hours with a considerable amount of nitrite accumulation which can be completely reduced in the later 24 hours.

Key words: denitrifying bacteria; screen; n(C)／n(N); pH; biological nitrogen removal