The ANITA biosensor, which measures ammonium oxidation rate by alkaline titration at constant pH, has been recently coupled to open respirometry making it possible to evaluate NH4+ oxidation kinetics by two different and completely independent techniques. This paper describes the use of a new instrument, also derived from the titration biosensor ANITA and named ANITA-DOstat, which incorporates dissolved oxygen (DO) control by H2O2 addition. The peroxide is very rapidly decomposed to H2O2 and O2 by bacterial catalase and supplies oxygen to the mixed liquor. The novelty lies not in the use of H2O2 addition as a source of oxygen for bacterial respiration, but in the measurement of kinetics by DOstat titrimetric respirometry which allows for evaluation of bacterial bio-oxidation parameters directly from the H2O2 flow rate at constant DO concentration. Preliminary results are presented on nitrification kinetics determination, for both ammonium oxidisers (AO) and nitrite oxidisers (NO), carried out by alkaline titration and by the new H2O2 DOstat titrimetric respirometry method.

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