Efficient Removal of Organic and Inorganic Suspended Solids

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Courtesy of Amiad Filtration Systems Ltd.

ABSTRACT

The Romans used sand as a filter media to treat their drinking water 2000 years ago. Centuries ago water was poured through layers of cloth to remove visible impurities in drinking water with fabric bags and paper cartridges soon following. Darcy employed sand beds in Dijon, France over 200 years ago to conduct his experiments for developing his famous equation to describe fluid flow through a porous medium. Since ancient times man has observed that water left quiescent for a period of time becomes clarified, and thus clarifiers were born. For millennia, man has known that certain visible impurities were displeasing in drinking water with entities invisible to the naked eye and harmful to health making their way known with the invention of the microscope. About one hundred years ago the practice of disinfection began. Soon to follow were treatments of softening, deionization, reverse osmosis and other membrane technologies and now we are looking at the removal of radiation and naturally occurring toxic elements. The future will assuredly hold many other treatment technologies. However, the need to remove suspended solids as a pretreatment step will always be necessary for surface and reuse-water sources. A very cost saving alternative to present-day pretreatment clarifiers and sand filters is the use of automatic self-cleaning screen filters to remove a large portion of the suspended solids before traditional water treatment systems receive the raw water. These filters present an impassable barrier to any particle larger than the filtration degree selected for each particular case. And because the differential pressure across the screen is kept to a low maximum level, particles can be hard inorganic in nature or soft organics. This type of filter utilizes a weavewire screen woven from 316-L stainless steel. Such filters are PLC controlled and automatically clean themselves based on a preset differential pressure threshold across the screen. Units with a footprint of four square feet are capable of filtering thousands of gallons per minute. Because there is only one moving part during the short cleaning cycle and no mechanism comes in contact with the screen element, maintenance and repairs are minimal. Installation requires only bringing power to the filter unit and bolting the filter's inlet and outlet flanges into the piping system. No pneumatic or hydraulic lines are required. Another great advantage of this technology is the fact that filtered water is continuously supplied to the downstream system even during the twelve to thirty second cleaning cycle, without redundant filter units. Self-cleaning pre-filtration drastically reduces the operational costs of water treatment systems giving the treatment process constant water quality year-round even from seasonally varying rivers and streams.

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