The microbial vac is a US-Army funded device that existed in prototype at the time that concentrated anthrax samples by a factor of 10 (to a trillion spores) while sequentially filtering the sample. It can only be used for weaponization on a small scale, its inventor tells me. Here is a video explaining the advantages of the Speed Vac which the US DOJ mistakenly thinks was used.
http://www.youtube.com/watch?v=_hvJOZCCm_M
Freeze Dryer vs. Speed Vac
http://www.bio.net/bionet/mm/proteins/2003-March/011065.html