The air velocity determined the time for toluene to reach Table 2 Diffusion

# The air velocity determined the time for toluene to

• 9

This preview shows page 7 - 9 out of 9 pages.

The air velocity determined the time for toluene to reach Table 2. Diffusion coefficients ( D ) in water at 10 5 cm 2 sec 1 . Gas D Ref. MT 1.48 15 DMS 1.34 16 DMDS 1.01 15 O 2 2.01 17 Toluene 0.85 17 Figure 4. MIMS data compared with model data at 10 cm from the top of the filter bed. The area beneath the model data 1 and 2 curves is the same as the area beneath the MIMS data curve because the model 1 and 2 concentration data continue with a long tail. Model data 1 simulate the BF with a K L a and air velocity of 0.0088 sec 1 and 0.103 m sec 1 , respectively. Model data 2 simulated the BF with a K L a and air velocity of 0.0088 sec 1 and 0.037 m sec 1 , respectively. Nielsen et al. 160 Journal of the Air & Waste Management Association Volume 59 February 2009 Downloaded by [University of California, San Diego] at 07:10 08 October 2015 a peak and the K L a value determined the height of the retention profile. A metric for determining the degree of fit between model and MIMS data was not developed. It was assumed that the degree of fit could be inspected by adjusting K L a and velocity with 4 and 3 digits, respectively, and making sure that no other reasonable combinations of K L a and velocity in the model would get closer to the height of the peak than the estimated values of K L a and velocity. Data from the MIMS showed that the area beneath the toluene versus time graph in the MIMS was the same before the BF and at a 10-cm depth of the BF and therefore it could be assumed that toluene was not degraded by bacteria in the BF. The K L a and air velocity found by this method are close to the predicted values. If the K L a value of O 2 is calculated using toluene as a reference gas, the K L a of O 2 in the BF is 0.0147 sec 1 , which is not far from other reported values. For example, Hellinga et al. 8 used a K L a for O 2 of 0.023 sec 1 found in a study of a bubble aerator, whereas Nikakhtari and Hill 19 found K L a values of O 2 dependent on superficial air velocities and up to 0.021 sec 1 in an airlift bioreactor with a packed bed. Deront et al. 20 found K L a values of O 2 up to 0.05 sec 1 in a cocur- rent packed bed column with 1-mm diameter glass spheres, whereas Poughon et al. 21 found K L a values of O 2 dependent on gas superficial velocity in the range from 0.0083 to 0.047 sec 1 in a fixed-bed column. The K L a value of the investigated BF is at the lower end of the scale compared with the studies mentioned, but because the treatment efficiency of the investigated BF is rather poor, this is to be expected. RE of MT, DMS, and DMDS The REs of various sulfur-containing gases were measured using the MIMS (Table 3) and compared with those of the model. In 180,000 iteration model simulations (30 min real time), the REs of the gases in Table 3 were examined with the model under the same conditions with the estimated K L a values and air velocity. The MT, DMS, and DMDS oxidation kinetics were described using the type of kinet- ics described in eq 13, and r MT,max was set to an equiva- lent of 33 mol m 3 sec 1 or 4.5 times the loading rate of 6.6 mol MT m 2 sec 1 , corresponding to 37 L of air  • • • 