3.3. Time required for the concentration of viruses Sixteen water samples were processed using smaller MF and UF cartridges (CEP-2-E-4MA and UFP-100-C-4MA) with filter surface areas of 420 and 650 cm2 respectively and the rest of the samples were processed using larger cartridges (CFP-2-E-9A and UFP-100-C-9A) with filter surface areas of 8400 cm2 and 1.15 M2.