Aeration is one of the important factors to produce monoclonal antibodies from Chinese hamster ovary (CHO) cell lines. Compressed air is continuously supplied for 2 weeks with a flow rate of 0.05 m3/min and velocity of 0.31 m/sec into a 2.5 L medium. It is found that the air provided contain 2.8 x 10 5 CFU/m3 of contaminants. Determine the dimension of the filter used, if the X90 value for cotton wool is 1.5 cm.