[2] Various designs have been implemented to ensure feasible processes whilst retaining the main objective of depth filters.
[3] Chemicals –Manufacturing paints, organic solvents, ink Petroleum – Wax, kerosene Winery,[4] cosmetics Industrial separations for hydrocarbon fuels [6] The use of deep bed sand filters as the final 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.
To remove the remaining solids and organic compounds from the wastewater stream, direct filtration method is utilised with prior flocculation.
The other advantage of the depth filtration method is the flexibility in the choice of filter arrangement, which allows high solid storage capacities to be obtained, while keeping the energy consumption rate within an acceptable range.
[1] The downside of using direct filtration is that microbes are able to grow within the channels of the filter and hence reproduce throughout long operating runs.
[11] Source:[12] Backwashing is an important operation employed to remove filtered solids as this build up causes resistance to filtration to increase with time.
The operation of depth filters is inherently cyclic due to the necessity of solids removal build up during the process, as such two or more units are typically used so that backwashing does not interfere with the filtration.
[11] Sand, magnetite, coke and anthracite are the most commonly used particle mediums in industry particularly to their wide availability.
Table [1] Process/Design Characteristics of Monomedium Filter Beds for Wastewater treatment (Deep Bed):[13] parameter values Table [2] Design Parameters for Pressure Depth Filters:[13] Depth filtration may be used in pre-treatment, removing suspended particles from a carrying fluid intended to be used as a feed stream or in the context of clarification where particulates are removed to purify a product stream.
Ideally if the medium is too large, filtrate will be of a poor quality as it will fail to collect particulates within its matrix.
Beyond 1.5 indicates that the system may experience a greater pressure drop and as mentioned may result in clogging, seeping of waste flow and reduced filtration rate.
[16] As a guideline it is recommended that the smallest particles used within depth filters should be placed at least 150 mm from the outlet stream to prevent fluidization.
High velocity inlet streams with relatively large particulates will cause possible clogging and wearing down of the filter media.
In situations where the filter media is clogged and pressure drop continually increases it is common that waste particles and streams may seep through the zones within the cartridge and pass through the outlet stream resulting in no purification To minimize the effects of clogging and particle build-up a back flushing system must accommodate approximately 1-5% of the bulk flow as back flush, operating at approximately 6-8 bar.
By convention, depth filters consist of a single outlet stream of a purified liquid retaining the waste particles within its system.
[12] With the ongoing advancements in process technologies, depth filters have been modified to improve its feasibility within a range of industrial sectors.