Determination of nitrification kinetics by the ANITA-DOstat biosensor

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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On-line determination of ammonia at low pptv mixing ratios in the CLOUD chamber

Atmospheric Measurement Techniques ◽

10.5194/amt-5-1719-2012 ◽

2012 ◽

Vol 5 (7) ◽

pp. 1719-1725 ◽

Cited By ~ 27

Author(s):

F. Bianchi ◽

J. Dommen ◽

S. Mathot ◽

U. Baltensperger

Keyword(s):

Detection Limit ◽

Liquid Phase ◽

Flow Rate ◽

Nucleation Rate ◽

Sampling Device ◽

High Tendency ◽

Mixing Ratios ◽

New Instrument ◽

On Line

Abstract. A new instrument for the on-line determination of ammonia was developed. Since ammonia is a rather sticky compound, sampling losses were minimised with a new sampling device where the ammonia was transferred to the liquid phase only 5 mm after the inlet tip. The liquid phase was then analyzed by long pathlength absorption spectrophotometry using the Berthelot reaction with phenol and hypochlorite as reagents. The measurements were made during the CLOUD3 campaign at CERN where the influence of ammonia on the nucleation rate was studied. At stable conditions the detection limit reached with this instrument was 35 pptv (air flow rate of 2 l min−1, liquid flow rate of 0.3 ml min−1), although occasionally the instrument was affected by background problems. The range of mixing ratios during this campaign was varied from the background contamination (<35 pptv) up to around 2 ppbv. The measured ammonia concentration was correlated with the rate of ammonia injected into the chamber, but with a response time of several hours due to the high tendency of ammonia to adsorb to or to desorb from surfaces. Since it was found that ammonia strongly increases the nucleation rate already at the lowest measured concentration, future work will focus on further decreasing the detection limit of the instrument.

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