Volatile Sulfur Compounds from Livestock Production: Emission Control by Dissolved Metal Catalysts and Impact on Odor Removal Assessment

Publikation: ForskningPh.d.-afhandling

Volatile sulfur compounds, i.e. hydrogen sulfide, methanethiol and dimethyl sulfide have been identified as key odorants in livestock production due to their high concentration levels and low odor threshold values. At the same time their removal with abatement technologies based on mass transfer from a gas phase to a liquid phase, e.g. biotrickling filters, is decelerated due to their low partitioning coefficients. This can significantly limit the odor reduction obtained with these technologies. The present study examines the possibility of adding metal catalysts to enhance the mass transfer and, thus, odor removal in these systems. In this context, two processes based on the absorptive oxidation of sulfur compounds in trickling filters containing metal catalysts were examined. One process with iron chelated by ethylenediaminetetraacetic acid (EDTA) was shown to remove hydrogen sulfide efficiently, obtaining removal efficiencies in the range 80-99% for all process parameters tested. On the other hand, the removal of methanethiol was found to be limited compared to this and dimethyl sulfide was found to be unreactive. This process was tested in a full scale 3-stage biofilter, in which a removal of 89% was obtained during low air loads, while at higher air loads it was found difficult to maintain optimal pH and the efficiency decreased. A process based on cupric ions in the same lab-scale filter was found to remove both hydrogen sulfide and methanethiol more efficiently, with removal efficiencies exceeding 94% under all process conditions tested. The removal of dimethyl sulfide was in the range 20-40%. The main products determined were dimethyl disulfide, dimethyl trisulfide and elemental sulfur. Though a proportion of the removed hydrogen sulfide and methanethiol was found to form other gaseous sulfur products, it was estimated that the process would have a positive effect on odor levels, as the products have higher odor threshold values and are formed in lower concentrations. When considering abatement technologies it is necessary to consider the impact of the evaluation method. Presently, the development of abatement technologies is limited by the lack of an accurate and reliable method for quantifying the effect on odor. To measure the impact of air cleaning techniques on perceived odor, common practice in Europe is to store odor samples in sample bags and quantify them by dynamic olfactometry. In the present study, the recovery of 9 key odorants from livestock production in three olfactometers obtained from accredited odor laboratories and in sample bags of different materials and sizes were evaluated with proton-transfer-reaction mass spectrometry (PTR-MS). It was found that the original sample composition was significantly impaired due to adsorption and diffusion at the walls of the measuring equipment. Generally, sulfur compounds were best preserved in both olfactometers and sample bags, while carboxylic acids, 4-methylphenol and trimethylamine were found to undergo substantial losses. The main loss during dynamic olfactometry performed with the tested equipment was found to take place on stainless steel- and glass- surfaces in olfactometers and for sample bags, the degree of recovery was found to be PTFE>Tedlar>Nalophan and, shorter storage durations and a larger sample volume to surface area was found to significantly improve the recovery.  
Antal sider141
StatusAfsendt - 14 aug. 2017

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