In order to ensure the stable and better working environment and reduce the treatment effect on the following treatment process,the working cycle,the flushing index,the flushing method and the control parameters of the biological contact oxidation process are discussed in this paper according to characteristics of the biological film.The result indicates that the bio-film flushing is based on the NH3-N concentration,the NH3-N removal rate and the running time.Only a quarter tank would be flushed every time,...