Showing papers by "Bo Thamdrup published in 2011"
TL;DR: The introduction of the STOX (switchable trace oxygen) sensor has lowered the level for accurate quantification by a factor of 1000, and they can be used for monitoring O(2) dynamics during laboratory incubations of low-O( 2) media such as OMZ water.
Abstract: Until recently, it has not been possible to measure O(2) concentrations in oxygen minimum zones (OMZs) with sufficient detection limits and accuracy to determine whether OMZs are anoxic or contain 1-2 μM O(2). With the introduction of the STOX (switchable trace oxygen) sensor, the level for accurate quantification has been lowered by a factor of 1000. By analysis with STOX sensors, O(2) can be prevented from reaching the sensing cathode by another cathode (front guard cathode), and it is the amplitude in signal by polarization/depolarization of this front guard that is used as a measure of the O(2) concentration. The STOX sensors can be used in situ, most conveniently connected to a conventional CTD (conductivity, temperature, and depth analyzer) along with a conventional oxygen sensor, and they can be used for monitoring O(2) dynamics during laboratory incubations of low-O(2) media such as OMZ water. The limiting factors for use of the STOX sensors are a relatively slow response, with measuring cycle of at least 30 s with the current design, and fragility. With improved procedures for construction, the time for a complete measuring cycle is expected to come down to about 10 s.
36 citations
01 Jan 2011
TL;DR: In this article, anaerobic ammonium oxidizing bacteria are not known to metabolize N2O, but the existence of an oxygen free zone would permit complete expression of a denitrification pathway by heterotrophic bacteria and hence remove any N2Os which is transiently produced in the inner (aerobic) sections of the biofilm.
Abstract: nitritation/anammox biofilms DTU Orbit (24/12/2018) Production and mitigation of N2O in sequentially membrane-aerated redox-stratified nitritation/anammox biofilms Combining partial nitritation with anaerobic ammonium oxidation maybe a costand energy-efficient alternative to remove reduced nitrogen from nitrogen rich waste streams. However, increased N2O emissions (upto several % of the incoming N flux) have been observed for reactors performing partial nitritation, which is likely due to the stimulatory effect of combined elevated nitrite and ammonium concentrations and reduced oxygen concentrations on nitrous oxide formation by ammonium oxidizing bacteria. Because increased N2O emission may be inherent to partial nitrification systems, we have explored how these emissions can be mitigated by performing autotrophic nitrogen removal in one reactor systems by combining aerobic and anaerobic ammonium oxidizing bacteria within one redox-stratified biofilm. In such biofilms, a section of the biofilm is at all times maintained under anaerobic (free of oxygen invasion) conditions. Although anaerobic ammonium oxidizing bacteria are not known to metabolize N2O, we speculate that the existence of oxygen free zone would permit complete expression ofa denitrification pathway by heterotrophic bacteriaand hence remove any N2O which is transiently produced in the inner (aerobic) sections of the biofilm. We have successfully operated such membrane –aerated redox-stratifed biofilm reactors performing completely autotrophic N removal and have monitored N2O dynamics. Successful community control required periodic aeration. N2O emissions were detected, but only in the inner cores of the fiber bundles, and only transiently, upon initiation or cessation of aeration. Bulk phase N2O concentrations were significantly lower than expected based on transient evolution rates, suggesting a removal mechanism. Emitted N2O fluxes represented less than 0.02 % of the converted ammonium N. Anoxic batch incubations with biofilm samples revealed a significant N2O assimilatory activity. Anoxic incubations with N-15 enriched nitrite, nitrate, or ammonium, in presence or absence of acetate revealed the following: a very high conversion of original nitrite or nitrate N to N2O over N2, no stimulatory activity of acetate addition, a very different isotopic abundance in the formed N2 and N2O, and no conversion of ammonium N to N2O. These results confirm that N2O production was most likely to ammonium oxidizers, and that the heterotrophs contributed to N2O attenuation. The spatial structure of these biofilms may, therefore, be especially suitable to minimize N2O emissions.
1 citations