LAUSR

Abstract It was observed in previous studies that optical dissolved oxygen (DO) sensors were measuring values up to 1 mg O2/L in anoxic mixed liquor samples containing nitrite (NO2−). Based on these observations of false DO measurements it was hypothesized that NO2−, N2O, or NO were interfering with the DO sensors. A variety of DO probes were tested for interference while measuring NO2−, N2O, and NO. It was concluded that NO causes a positive inference with some models of optical DO probes. In bench-scale denitrification tests, 25 mg/L of NO2− led to the production of enough NO to cause a DO sensor reading of 1 mgO2/L. These findings are important for any wastewater treatment process that is utilizing online DO measurements in the presence of NO such as shortcut nitrogen removal processes.