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Understanding Filter Efficiency - Virus Removal in Depth Filtration

Zeta potential, as the indicator for surface charge, helps to predict and to tune the efficiency of filter materials.

Potable water production requires an efficient and cost-effective technology of drinking water treat-ment. Depth filters based on diatomaceous earth (DE) are widely used for bacteria removal.

Bacteria are unable to penetrate the pores of a microporous DE filter, whereas the 10 times smaller viruses can easily pass the filter and harm the consumer. These contaminants can only be completely removed by electrostatic attraction of the virus on the filter pore surface.

DE filters and many common viruses possess a negative surface charge in the typical pH range of water. Due to the resulting electrostatic repulsion viruses can easily pass through the microporous DE filter.

Modification of the DE filter surface with a heavy metal oxide like ZrO2 shifts the isoelectric point (IEP) of the filter surface to higher pH.
This change can be monitored by pH dependent zeta potential studies of the untreated DE ceramic filter and the DE filter coated with Zr(OH)x (The IEP of MS2 bacteriophages as a representative virus is shown for reference).

The surface of the filter and the contaminants become oppositely charged and efficient virus removal takes place.

M. Wegmann, B. Michen, T. Luxbacher, J. Fritsch, T. Graule, Water Res. 42 (2008) 1726-1734

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