ABSTRACT
The production of N2 gas via anammox was investigated in sediment slurries at in situ NO2
− concentrations in the presence and absence of NO3
−. With single enrichment above 10 μM 14NO2
− or 14NO3
− and 15NH4
+, anammox activity was always linear (P < 0.05), in agreement with previous findings. In contrast, anammox exhibited a range of activity below 10 μM NO2
− or NO3
−, including an elevated response at lower concentrations. With 100 μM NO3
−, no significant transient accumulation of NO2
− could be measured, and the starting concentration of NO2
− could therefore be regulated. With dual enrichment (1 to 20 μM NO2
− plus 100 μM NO3
−), there was a pronounced nonlinear response in anammox activity. Maximal activity occurred between 2 and 5 μM NO2
−, but the amplitude of this peak varied across the study (November 2003 to June 2004). Anammox accounted for as much as 82% of the NO2
− added at 1 μM in November 2003 but only for 15% in May 2004 and for 26 and 5% of the NO2
− added at 5 μM for these two months, respectively. Decreasing the concentration of NO3
− but holding NO2
− at 5 μM decreased the significance of anammox as a sink for NO2
−. The behavior of anammox was explored by use of a simple anammox-denitrification model, and the concept of a biphasic system for anammox in estuarine sediments is proposed. Overall, anammox is likely to be regulated by the availability of NO3
− and NO2
− and the relative size or activity of the anammox population.
In situ FT-IR investigation of the reduction of NO with CO over Au/CeO2-Al2O3 catalyst in the presence and absence of H2
