Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2008
Publication Date: 10/27/2008
Citation: Loughrin, J.H., Lovanh, N.C., Arturo, Q., Rezaul, M. 2008. Sampling of Malodorous Compounds in Air Using Stir Bar Sorbtive Extraction. Transactions of the ASABE. Vol. 51(5): 1747-1752 Interpretive Summary: Silicone coated magnetic stir bars that adsorb odorous compounds were used to monitor malodors above a swine waste treatment lagoon. First the minimal amount of time for the stir bars to be exposed in order that amount of chemical compound on the stir bars would be proportional to its amount in the air was determined. The more volatile the compound, the faster this happened. In order to determine the volume of air sampled by the stir bars, our method was compared to a more standard one in which air was pulled through a tube containing an adsorbent for capturing odorous compounds. This comparison was hampered by the variability of the standard method. The standard method was more sensitive than were the stir bars, however. The adsorbent stir bars were placed 0.5 m and 1.5 m above the surface of the swine waste lagoon for four hour periods during the fall of 2007. As the lagoon cooled, malodorous compounds accumulated in the lagoon and as a result, greater amounts of compound were adsorbed onto the stir bars despite the cooler temperatures. These results indicate the waste treatment lagoons could actually emit more malodors during the fall and winter than during warmer seasons.
Technical Abstract: Twisters, (poly)-dimethylsiloxane-coated magnetic stir bars, were used to measure malodorous compounds in air. In initial experiments, a minimum deployment time was determined by preloading the stir bars with 10 compounds with a range of volatilities and polarities and then monitoring their loss. The rate of loss was dependent on compound volatility and the time for equilibrium to be attained varied widely, from 22 min for phenol to 210 min for skatole. In an attempt to relate the levels of compounds sorbed on to Twisters to their vapor phase concentrations, adsorption onto Tenax polymer was compared to absorption onto Twister stir bars. This comparison was rendered void at least in part by the relatively low reproducibility of the Tenax entrainments: coefficients of variations (CV) for Tenax analyses averaged over 100% whereas for Twisters the CVs averaged only about 40%. Twisters were deployed on portable magnetic stir plates 0.5 and 1.5 m above the surface of a wastewater lagoon serving as the primary waste receptacle of a 2,000-head farrowing operation. Two-three times as much compound was absorbed at 0.5 m than at 1.5 m. As the lagoon cooled, malodorous compounds accumulated in the lagoon and as a consequence, greater amounts of malodors were retained on the samplers even though air and wastewater temperatures had declined. These results indicate that Twisters can be used as equilibrium samplers in air to monitor relative emission rates from lagoons.