Table 3.
Microorganism susceptibility to filtration.
| Organism | Approximate aize (μm) | Recommended filter rating (μm) |
|---|---|---|
| Virusesa | 0.03 | Ultrafilter, nanofilter, reverse osmosis |
| Escherichia coli Campylobacter Vibrio cholerae | 0.5 by 3–8 0.2–0.4 by 1.5–3.5 0.5 by 1.5–3.0 | 0.2–0.4 (microfilter) |
| Cryptosporidium oocyst | 2–6 | 1 (microfilter) |
| Giardia cyst Entamoeba histolytica cyst | 6–10 by 8–15 5–30 (average 10) | 3–5 (microfilter) |
| Nematode eggs | 30–40 by 50–80 | 20 (microfilter) |
| Schistosome cercariae Dracunculus larvae | 50 by 100 20 by 500 | Coffee filter or fine cloth, or double thickness closely woven cloth |
a
Microfilters (most filters with pore size of 0.1–0.2 μm) can filter bacteria and protozoan cysts but are not effective for virus removal unless designed to rely on electrostatic trapping of viruses. Hollow-fiber filters with 0.02 μm pores and reverse osmosis filters are capable of filtering viruses.