An ultrafiltration filter has a pore size around 0.01 microns. A microfiltration filter has a pore size around 0.1 microns, so when water undergoes microfiltration, many microorganisms & viruses are removed from water. Ultrafiltration would remove these larger particles, and remove some viruses. Neither microfiltration nor ultrafiltration can remove Dissolved substances they are first adsorbed (with activated carbon) or coagulated (with alum or iron salts).