A simple measure of whether the liquid is filterable is useful to enable assessment of filtration as an appropriate process, if so what type of pre-treatment and filter media are required. The use of deep beds of porous granular media to filter liquids to improve their clarity is widespread in municipal and industrial practice. Other liquids are filtered through granular media in the processing of beverages and food products for example. Predominant is the filtration of drinking water and industrial water, although the filtration of sewage as a tertiary stage of treatment is increasing. Although the normal methods of chemical and physical analysis such as suspended solids content, turbidity, color etc. may, with experience, indicate whether a suspension is filterable, they give no direct measure of this property.
The Filter ability Index Unit utilizes a bed of granular material, normally sand, which can be chosen by the investigator to suit his own purposes. The measurements taken with this apparatus enable a filter ability number to be calculated which has significance in deep bed filter performance.
A number of measures of filter ability have been proposed, using woven micromesh, lint pads or membrane filters, which have application where these materials represent, or are identical to, the filter media to be used. However none of them is representative of porous granular filter media, such as sand, consequently they are not applicable to deep bed filtration.
The Filter ability Index Unit is not intended for filter design purposes. That requires pilot filter column equipment such as the Deep Bed Filter Column. However preliminary assessment of pre-treatment processes, and possible filter media with the Filter ability Index Unit will reduce the amount of testing required with pilot filter columns.
