[Laboratory-scale CANON Processes Applied to Wastewater Treatment Plants]

A laboratory-scale completely autotrophic nitrogen removal over nitrite (CANON) process was operated in a municipal wastewater treatment plant (WWTP). Sewage effluent treated by the anaerobic/oxic (A/O) process and was used to operate a WWTP to obtain the initial substance for the start-up of a CANON filter reactor. On the 48th day, the ammonia removal rate was measured at greater than 90% in successive 10 d samples and the nitrogen removal rate was greater than 70%. The CANON filter was successful at start up. From the 49^th to the 129^th day, the dissolved oxygen in the reactor was maintained at fairly low concentration of 0.2-0.5 mg·L^-1. The effluent contained nearly no ammonia and the maximum total nitrogen (TN) concentration was 15.6 mg·L^-1, which exceeded the national Class 1A Discharge Standards for pollutants from municipal wastewater treatment plants. Nitrite oxidizing bacteria (NOB) proliferated excessively in the reactor. Backwash was implemented on 129th, 169th and 213th days. The nitrogen removal rate was more than 70% for a long time and TN concentration in effluent was below 12 mg·L^-1. The nitrogen concentration in effluent fitted the national Class 1A Discharge Standards and the NOB were effectively inhibited. These results show that backwash has negligible on the structure of filter and its impact on the thickness of the bio-membrane and its functional bacteria was small, however, it is capable of effectively inhibiting the activity of the NOB. Periodically backwashing can be utilized as an engineering application to maintain stable operation of the CANON process.