Experimental determination of mass transfer coefficients of volatile sulfur odorants in biofilter media measured by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS)

Mass transfer from air to the liquid phase is an important process that may limit the efficiency of biological air filters used for abatement of odor from livestock production facilities. Mass transfer limitation is especially important for volatile sulfur compounds with relatively low aqueous solubility. A better understanding of limitations of mass transfer is therefore important in order to enhance the performance and design of biofilters. In this study, a method based on Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) has been developed in combination with a developed model to determine the mass transfer coefficients of volatile sulfur compounds for selected packing material used in biofilters. PTR-MS was used to measure breakthrough curves for sulfur compounds with adequate sensitivity, time resolution and reproducibility. The overall mass transfer coefficient for the selected biofilter media was then estimated by fitting an advection-dispersion equation modified for mass transfer between the gas and liquid phases to the measured profile of individual sulfur compound. Different injection strategies were evaluated and an optimal measurement procedure was developed. The method was validated by comparison of mass transfer coefficients to literature values for toluene, which was used as a reference compound in this study. By applying the method to compounds with different Henry's law constants, the application range of the method was demonstrated regarding solubility in water. This study demonstrates a method for determination of mass transfer coefficients of sparingly soluble gaseous compounds for selected biofilter media by applying PTR-MS in combination with modeling.