The impact of oxygen penetration on the estimation of denitrification rates in anoxic processes

Increasingly stringent effluent nitrogen criteria require that appropriate assessments of denitrification rates be made to facilitate the design of wastewater treatment systems. A zero-head-space reactor was used in comparative denitrification studies as a reference system that totally excludes oxygen. An open reactor and a reactor with a floating lid were also operated simultaneously to determine how oxygen input into typical laboratory reactors might influence observed denitrification results. Preclarified influent and activated sludge from a denitrifying domestic wastewater treatment plant were used as the carbon and biomass source, and KNO₃ was used as the nitrate source. The impact of oxygen penetration proved to be highly dependent on the denitrification rate. The influence of the design of the experimental system was small when rapid nitrate consumption occurred, whereas oxygen penetration had a severe impact at low denitrification rates.