There is an urgent need to develop odor reduction technologies for animal production facilities, and this requires a reliable measurement technique for estimating the removal of odorants. The purpose of the present experiment was to investigate the application of proton-transfer-reaction mass spectrometry (PTR-MS) for continuous measurements at a biofilter from SKOV A/S installed at a pig production facility. PTR-MS was able to handle the harsh conditions with high humidity and dust load in a biofilter and provide reliable data for the removal of odorants, including the highly odorous sulfur compounds. The biofilter removed 80-99% of carboxylic acids, aldehydes, ketones, phenols, and indoles and ca. 75% of hydrogen sulfide. However, only ~0-15% of methanethiol and dimethyl sulfide was removed. In conclusion, PTR-MS is a promising tool that can be used to improve the development of biological air cleaning and other odor reduction technologies toward significant odorants.

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Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water were followed and related to bacterial activity in a 14-d anoxic decomposition experiment. For the experiment 0.2-m filtered pore water from a coastal marine sediment was inoculated with native sediment bacteria. The initial composition of DON was characterized by a high contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and urea, which together accounted for 82% of the DON pool. During the experiment, 54% of the DON was used by bacteria, indicating that DON was readily available to bacterial degradation. The consumption of DFAA and DCAA accounted for more than half of the DON consumed. The unidentified DON pool accounted for 33% of the net DON consumption, and the unidentified DON pool was fully depleted by the end of the experiment. Systematic changes in the amino acid composition occurred with time of incubation, as demonstrated by use of a principal component analysis based on the mole percent contribution of amino acids. The results indicated that amino acids of both the DFAA and the DCAA pools were useful indicators of the diagenetic state of DON. The present study presents the first direct evidence of short-term (within 14 d) changes in DFAA and DCAA of the DON pool. These changes were similar to decompositional changes in the molecular composition of amino acids observed in traditional studies of bulk sediment diagenesis.At present, the majority of marine dissolved organic nitrogen (DON) has not been characterized at a molecular level. However, the chemical identity of DON may be a key in understanding the mechanisms by which DON is formed and used. Several different strategies have been used to gain insight into these topics. Amon and Benner (1996) proposed a size-reactivity continuum model, which links the physical size of organic matter to its diagenetic state. The model suggests a decrease in size with increasing diagenesis and chemical alteration, but it does not explain a mechanism for the observed production of biorefractory low-molecular-weight (LMW) dissolved organic matter (DOM) or the observed 1 Corresponding author (Bente.Lomstein@biology.au.dk). AcknowledgmentsWe thank Annie Sølling and Rikke O. Holm for skillful technical assistance and two anonymous reviewers for their constructive comments.

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