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A simple size-dependent compartmental model was developed to describe airborne dust exposure dynamics for the human respiratory tract (HRT) in mechanically ventilated swine buildings. Transport mechanisms of airborne dust for HRT include respiration, gravitational settling, turbulent diffusive deposition, inertial impaction, interception deposition loss, and dust clearance. The dominant deposition mechanism in the lung regions was found to be the inertial impaction rate, in which the order of magnitude ranged from 10 Ϫ3 to 10 Ϫ1 sec Ϫ1 . Results demonstrate that the extrathoracic region has a higher airborne dust mass lung/indoor ratios (0.71-0.87) than do the bronchial regions (0.41-0.74), the bronchiolar region (0.12-0.61), and the alveolar-interstitial region (0.01-0.49). The predictions from the HRT model agreed favorably with the experimental deposition profiles in the nasal passage, pharynx, bronchial, bronchiolar, and alveolar-interstitial regions, whereas the rms errors of the total deposition fraction between predicted values and ICRP66 and Non-ICRP66 were 0.15 and 0.07, respectively. Simulation results show that breathing via the nose has both a higher deposition fraction and a higher exposure dose in the size ranges 0.01-10 m than does breathing orally.

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The purpose of this research was to neutralize livestock-generated ammonia by using biofilters packed with inexpensive inorganic and organic packing material combined with multicultural microbial load at typical ambient temperatures. Peat and inorganic supporting materials were used as biofiltration matrix packed in a perfusion column through which gas was transfused. Results show the ammonia removal significantly fell in between 99 and 100% when ammonia concentration of 200 ppmv was used at different gas flow rates ranged from 0.030 to 0.060 m3 h(-1) at a fluctuating room temperature of 27.5 +/- 4.5 C (Mean +/- SD). Under these conditions, the emission concentration of ammonia that is liberated after biofiltration is less than 1 ppmv (0.707 mg m(-3)) over the period of our study, suggesting the usage of low-cost biofiltration systems for long-term function is effective at wider ranges of temperature fluctuations. The maximum (100%) ammonia removal efficiency was obtained in this biofilter was having an elimination capacity of 2.217 g m(-3) h(-1). This biofilter had high nitrification efficiencies and hence controlled ammonia levels with the reduced backpressure. The response of this biofilter to shut down and start up operation showed that the biofilm has a superior stability.

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