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Water Filtration

Reuse, Recycle and Reduce: The New Mantra for Water Filtration

| Author / Editor: Nikunj Shah / Dominik Stephan

Activated Glass vs Sand - The Filter Challenge

The health and well-being of everyone depends on the supply of clean potable water. Sand is used to filter more than 99 per cent of all drinking water but issues with parasites (cryptosporidium), disinfection by-products and priority substances such as endocrine disrupters and heavy metals still remain major areas of concern for those involved in water processing. With AFM, a high negative charge means that it is very effective at removing metals and organic particles that have a positive charge.

Iron, Arsenic and Chromium Removal

Iron, arsenic and chromium, which are often found in high concentrations in tube well water, can also be treated with AFM. The recommended first step in water treatment is vigorous aeration to gas strip the volatiles and increase oxidation potential. Through this, the oxidation state of metals changes and they become insoluble and easier to remove with AFM.

For example: iron changes from Fe2+ to Fe3+ and arsenic from AS3+ to AS5+. Dryden Aqua has observed that longer aeration produces larger ferric particles and, in turn, makes it easier for removal by AFM. AFM is twice as efficient as sand or greensand at removing ferric. A vigorous backwash removes the iron and arsenic, and this, of course, means that AFM need not be replaced. Chromium, however, is a little more difficult.

After the gas stripping stage, a second stage involves the addition of ferrous Fe2+ at a high pH to reduce Cr6+ to Cr3+ after which the water can be filtered by AFM. Pre-treatment AFM can also be used as pre-treatment to reverse osmosis (RO) or ultra filtration (UF). In such cases, the silt density index (SDI) is 50 per cent lower than the SDI from a sand filter. Also, it offers by-products free of silica and biofouling. Hence, it becomes an ideal choice for pre-treatment prior to membranes.

Additional Information
 
Less Chemicals, Less Energy, Less Toxic Substances

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