Water Treatment - Filtration

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Water Treatment

First Water Products




		Filtration is the removal of suspended solids in a liquid or gas by passing it through a medium. For most portable water treatment systems, the medium consists of precision-made ceramics or blown microfibers. Filters may be either depth cartridges or surface membranes. In a depth cartridge filter, water flows through the thick wall of the filter and particles are trapped throughout the complex openings in the medium. With graduating density, coarser particles are trapped toward the outside wall and finer particles toward the inner wall, giving the depth filter a higher dirt-loading capacity and thus useful life. Surface filters are usually membranes or nonwoven fabric materials that trap particles on their surface. They are usually pleated to increase surface area and extend useful life. The ability of a filter to remove microbes is a function of pore size. Portable water filters normally require a pore size of 1 micron to remove cysts, eggs and larvae that may harbor pathogenic parasites or bacteria. Microfilters designed to protect against bacteria normally have a pore size of 0.2 to 0.3 microns. The pore size may be average or "absolute", the latter meaning that no particle in excess of the stated pore size will infiltrate the unit. The usefulness and economy of a filtration system also depends on its ability to be cleaned in the field. Ceramic filters are usually capable of 200-300 cleanings of the outer surface in order to remove sediment and large particles that may obstruct pores and reduce flow. It is important to check the thickness of these ceramic cartridges or "candles" after each cleaning to ensure that they are still of minimum thickness. A gauge is often provided for this purpose. Some membrane filters can be "back washed" by reversing the direction of flow and pumping microbiologically safe water through the system to release accumulated particles.