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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.〔Shukla, A. A. and Kandula, J. R., 2008, Harvest and recovery of monoclonal antibodies from large-scale mammalian cell culture. BioPharm International, May 2008, p. 34-45.〕 Depth filtration typified by multiple porous layers with depth are used to capture the solid contaminants from the liquid phase.〔Derek B Purchas and Ken Sutherland, Handbook of Filter Media (2nd Edition), Elsevier Advanced Technology (2002).〕 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. ==Designs available== 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. Applications of Depth filters and advantages 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.〔Derek B Purchas and Ken Sutherland, Handbook of Filter Media (2nd Edition), Elsevier Advanced Technology (2002).〕 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.〔Ben Aim R., Shanoun A., Visvanathan C., and Vigneswaran S. (1993). New filtration media and their use in water treatment. Proceedings, World Filtration Congress, Nagoya, 273–276〕 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 of the filter bed. The advantages associated with this process include the ability to produce large flocculent, which can then be filtered. 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.〔Derek B Purchas and Ken Sutherland, Handbook of Filter Media (2nd Edition), Elsevier Advanced Technology (2002).〕 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. This reproduction of organisms within the filter matrix can result in the contamination of the filtrate. Depth filtration is also widely used for the clarification of cell culture clarification. The cell culture systems can contain yeast, bacterial and other contaminant cells and hence, an efficient clarification stage is vital to separate the cells and other colloidal matter to produce a particle free cell system (). Most depth filters used in pharmaceutical processes such as cell system harvesting are composed of cellulose fibres and filter aids. The direct flow design in depth filters provides a financially suitable solution by trapping the contaminants within the filter channel while ensuring the maximum recovery rate of the product. The other advantages of this system includes its low power costs, since the pumps utilised in depth filters require minimal power input due to the small pressure within the system. Depth filtration is also flexible in terms of being able to scale up or down the system while outputting a high rate of yield (>95%) Thomas P.O’brien, Large-scale, Single use of depth filration systems for mammalian cell culture clarification, 2012. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Depth filter」の詳細全文を読む スポンサード リンク
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