Combined Oxygen and Nitrous Oxide Microsensor for Denitrification Studies

Abstract

The construction of a microsensor which can be used to measure O 2 and N 2 O simultaneously is described. The microsensor exhibited a linear response to both O 2 and N 2 O, and the response to N 2 O was independent of the O 2 concentration and vice versa. The N 2 O detection limit of a microsensor with a tip diameter of 20 μm was around 1 μmol liter −1 . The signals for O 2 and N 2 O were affected by hydrogen sulfide, but other interfering agents were not observed in the biofilms and sediments analyzed. Microprofiles of O 2 and N 2 O were measured in a biofilm which was exposed to acetylene to block the N 2 O reductase activity of denitrifying bacteria. O 2 penetrated about 0.5 mm into the biofilm and was not affected by acetylene, but the N 2 O concentration at 1.4 mm depth increased from 32 to 411 μmol liter −1 after the addition of the inhibitor. The shape of the N 2 O profile after the addition of acetylene showed that denitrification (denitrifying activity) was detectable in all anoxic layers of the biofilm.