The change of biodegradation activity of activated sludge was studied during nitrification and denitrification course to remove organic matters in a SBR reactor by determination of TTC-ETS activity at various concentrations of NH+4   - N and organics in influent.The experimental results show that TTC-ETS activity could be a good indicator for the biological reactions progress in SBR process; in a period of the process biological activity for biodegradation of organic matter

nitrification and denitrification decreased gradually from 39.68 mg·(g·h)-1 to 21.89 mg·(g·h)-1 and last to 6.58 mg·(g·h)-1 at COD and concentration of NH+4   -N 300 mg·L-1  and 40 mg·L-1

respectively.For TTC-ETS activity there appeared in general characteristic points with the progress of the process

which pointed toward the start and end of different reaction stages.It was found that operational conditions had no significant influence on the change rule of TTC-ETS activity

but could affect the time appearing these characteristic points.These characteristic points on DO

ORP and pH curves marked different reaction stages

and there was a good correlation between the times they appeared and TTC-ETS activity

COD

as well as three nitrogen curves (ammonia

nitrate and nitrite).