Depth filter

Depth filters are the variety of filters that use a porous filtration medium to retain particles throughout the medium, rather than just on the surface of the medium. These filters are commonly used when the fluid to be filtered contains a high load of particles because, relative to other types of filters, they can retain a large mass of particles before becoming clogged.

Depth filtration typified by multiple porous layers with depth are used to capture the solid contaminants from the liquid phase. Due to the tortuous and channel-like nature of the filtration medium, the particles are retained throughout the medium within its structure, as opposed to on the surface. Depth filters pose the added advantage that they are able to attain a high quantity of particles without compromising the separation efficiency. Depth filters are commonly characterised by the sand filter and have the ability to be used with substantially higher filter rates than in other designs. It is these characteristics that have cemented the use and popularity of depth filters as an effective medium for separation. With ongoing advances in process technologies depth filter designs are continuously adapting and improving to meet the needs of industry.

To accommodate for the variety of applications for depth filters, various designs have been implemented within industry to ensure feasible processes whilst retaining the main objective of depth filters.

Packed into a rectangular frame with a dividing wall.

Chemicals –Manufacturing paints, organic solvents, ink

Petroleum – Wax, kerosene

Winery, cosmetics

Industrial separations for hydrocarbon fuels

The use of deep bed sand filters as the final carrying step in municipal potable water treatment has increased significantly over the past decade, with its application ranging from clarification and processing of drinking water to wastewater treatment plants where the wastewater is required to be polished before being discharged. The main advantage of depth filtration involves the ability to retain particles throughout the medium channels, rather than purely on its surface. This significantly increases the filtration ability of the medium in comparison to other types of filtration processes and allows particles of different sizes to be filtered in the matrix.

The prominent deep bed filtration processes currently used are direct filtration and contact-flocculation filtration. Direct filtration involves a short period of pre flocculation stage followed by the filtration process. In sewage treatment plants, the majority of suspended solids and other contaminates are successfully removed after the primary and secondary treatment stages. To remove the remaining solids and organic compounds from the wastewater stream, direct filtration method is utilised with prior flocculation. As the contaminant separation process takes place in the filter medium, factors such as flocculation time, filtration velocity and flocculent dosage are required to be monitored regularly, as they can directly affect the flocculent size produced. This is vital to the process in order to prevent potential clogging or bioclogging of the filter bed.

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Wikipedia