Use of carbon dioxide evolution rate for determining heterotrophic yield and characterising denitrifying biomass

The aim of this work was to show the potentiality of carbon dioxide evolution rate measurement (CER) in characterisation of heterotrophic biomass, especially in anoxic conditions, in view of modelling and design denitrifying processes. The carbon dioxide evolution rate (CER) was determined in a respirometer by infrared analysis associated to a modelling technique. During anoxic and aerobic batch experiments CER was qualitatively correlated with other respirometric methods (OUR and NUR) and with organic carbon consumption. Yield coefficients were determined under aerobic (Y_H) and anoxic (Y_HD) conditions by means of carbon balances using CER and organic carbon measurements. Compared to the COD balances, accuracy of the yield estimation was improved and results obtained were not significantly different. Measured anoxic yields were systematically lower than aerobic ones, and the observed ratios between them were in the range from 0.66 to 0.85. By comparing aerobic and anoxic CER, two methods were proposed to determine the correction factor for anoxic growth η_g. The first results obtained were consistent with those given by the classical method (NUR/OUR).