wrapped in an electronically controlled heating jacket. High RH was achieved by adding humid

dilution air to the system.

Viable Removal Efficiency

 The VRE of the test filter was calculated by enumerating bacterial growth in agar plates

of two impactors, one downstream of the test filter and the other for control, which has no test

filter. The VRE was determined by using Eq. (2-1).


 VRE (%)= 1- N x100 (2-1)
 SNt)

where Nt is the total number of viable spores collected in the control and Np is the number of

viable spores collected downstream of the test filter. The entering bioaerosol concentration was

measured by collecting spores at all six stages of the impactor with no test filter for the first and

last 5 mins of an experimental run. The run time of 5 mins was chosen to prevent overloading of

spores on the agar. The average number CFU of the two measurements was used to determine

the entering bioaerosol concentration for 2 hrs of experimental run. Due to the expected low

penetration of spores through the test filter, the impactor downstream of the test filter contained

only the sixth-stage agar plate. The agar plate was replaced with a fresh one every 20 mins for

2-hrs to avoid overloading and dehydration of the agar. Five 2-hr trials were conducted-the

total evaluation time for each filter was 10 hrs-and three filters were tested (i.e., 15 trials).

However, due to the stability of results seen at RT/LRH and time constraints, only two iodine-

treated filters were tested for two 2-hr runs in other environmental conditions (i.e., four trials).

Agar plates containing more than 300 colonies were counted following the positive hole method

recommended by the manufacturer (Thermo Electron Corporation 2003).

Viability of microorganisms on the filter