AFMWhat is AFM®?

AFM® is an Activated Filter Media manufactured from green amorphous aluminosilicate to replace sand in all types of sand filter. AFM® offers a revolutionary step change by providing better than a 30% performance improvement over sand. Independent whole life cycle analysis confirms a return in capital from power and chemical savings in less than 8 months.

The activated surface of AFM® is self-sterilizing which prevents bacteria mud-balling, coagulation and channeling of unfiltered water through the filter bed. Activation increases the surface area by 300 times for catalysis and adsorption reactions. Similar to activated carbon, the surface nano-structure adsorbs pollutants from the water but unlike carbon, AFM® is recharged by just back-washing with water. AFM® is a sustainable cradle-to-cradle product in keeping with the circular economy.

  • Lower running costs & better performance - AFM® filters at least 30 % better than sand. A return in capital can be expected in less than 8 months.
  • AFM® will last for the life of the filters - And should never need to be changed.
  • Lower consumption of chlorine - AFM® performs better than sand, so the water has a lower chlorine oxidation demand, up to 50% less chlorine.
  • Lower disinfection by-products - AFM® will reduce disinfection by-products by at least 50% because we use 50% less chlorine.
  • Ferric, arsenic & manganese - AFM® is the perfect filter media for the sustainable control of heavy metals and metalloids.
  • Priority substances - AFM® will effectively remove some priority substances. Pretreatment research is being conducted to enhance the performance and expand the range of priority substances that can be removed.

AFM® to replace sand in all sand filters

AFM® reduces the biological risk from bacteria and parasites as well as the chemical risk. AFM® does not channel so it is an effective barrier against Cryptosporidium and giardia. AFM® does not incubate or discharge bacteria, indeed it will reduce the bacterial load of the product water. Also because of the better filtration performance, there are lower THM concentrations. AFM® provides the potential to remove some priority substances, research is in place to further enhance the product performance and expand the range of priority substances that can be treated.

AFM® is manufactured in a state-of-the-art hygienic factory designed by Dr Howard Dryden to solve all these problems. It contains metal oxide catalysts that dissociate oxygen and water to create a zone of high oxidation potential to prevent bacteria growing on the surface of AFM®. In addition, the huge activated surface area has a strong negative charge for the adsorption of sub-micron particles and dissolved organic molecules. This makes AFM® far superior to any other filtration media because AFM® is recharged by a simple back-wash.

Why is biofilm a problem for Pressure and RGF filters?

Silica sand is a good filtration media but it also makes a perfect home for growing bacteria. Bacteria are required in biofilters and slow bed sand filters but in rapid gravity or pressure filters the bacteria cause a biodynamic mechanical instability of performance. Bacteria like to stick themselves onto the sand by secreting an alginate jelly. The alginate forms a film that provides a home for the bacteria and even protects them from oxidation by chlorine. The problem is that the alginate glues the sand together and blocks the bed, especially during the summer months, AFM® solves this problem.

The bacteria can double in biomass every 30 minutes, the alginates secreted by the bacteria increase the Delta P and can half the length of the run phase. The alginates also glue the sand grains together and promote the development of wormhole channeling.

What makes AFM® so effective?

Dryden Aqua Intellectual Property protects AFM® but we are happy to share some of the key points;

  1. We use predominantly green container glass as it has the correct chemical and structural properties for our activation process.
  2. Particle shape and size distribution are critical for the best fluid hydraulics and solids retention. For example, solids can easily push their way through glass bead filter media but with a subangular AFM® media, the grains lock together to prevent the solids slipping through.
  3. The AFM® activation process increases the surface area available for adsorption by 300 times to over 1‘000‘000 m2/m3. This means 300 times more surface area for the adsorption of dissolved organic pollutants. The huge surface area coupled with the magnetic attraction of the negative zeta potential makes AFM® the best filtration media for potable water treatment.

Dryden Aqua Integrated System

AFM® is a clean product with an excellent uniformity coefficient, low pressure drop and 100% efficiency on backwash. It can be used in any rapid or pressure sand filter with no change to the infrastructure. There is less or no requirement to use anthracite, granular activated carbon or powdered activated carbon with AFM®.

Dryden Aqua also manufacture ZPM zeta potential static mixers in 316 stainless steel and titanium. In addition we manufacture multi-spectrum flocculants and peristaltic pumps.


AFM Instruction for use

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