Changing Filters: Benefits of AFM vs Sand
By Howard Dryden 16 May, 2016
Dr. Dryden, inventor of AFM®, shares how the upcycled glass filter means lower bacteria & costs and a longer life
A sustainable economy depends on a sustainable environment and the provision of high quality water is essential, not only for human consumption but for all industries, food security and protection of the environment.
Sand filtration is the standard process used for the treatment of water, it represents the primary means of treating most of our drinking water, industrial process water, and for polishing waste water for second use in irrigation.
Sand filters are the primary means of treatment but there are bacteria & stability issues
Sand filters work well, but there are performance and stability issues attributed to bacterial fouling of the sand which leads to bio-dynamic instability, and transient channelling of unfiltered water through the filter bed and into the product water.
Typically, a sand filter will channel for 0.01% to 5% of the time, even when the sand is aggressively back-washed, and sterilised using chlorine, a bacterial problem and channelling will still develop. A channelling filter will allow unfiltered water to enter the product water and a channelling rate of 0.01% is sufficient to permit Vibrio Cholera bacteria to enter the water distribution network or parasites such as Cryptosporidium, Giardia as well as heavy metals including lead, arsenic, chromium.
AFM® can replace any sand filter with no need to change existing infrastructure
It prevents bacteria passing through
Activated Filter Media, (AFM®) is a direct replacement for sand in any type of rapid sand filter. Simply replacing the sand with AFM®, will greatly improve performance and stability of the filters. AFM® does not channel, so unfiltered water will never enter the product water, and because of this engineered property the security of the water supply is assured. A solution to a difficult problem achieved with no change to the existing infrastructure, and once AFM® is in the filters, it never needs to be changed.
Our thinking behind AFM®
AFM® is the product of 30 years of research and innovation. The initial research started with zeolite molecular sieve ion exchange sand which developed into the use of glass as the raw material for manufacture of the molecular sieve catalytic filter media AFM®.
AFM® is made from upcycled glass
AFM® is a sustainable cradle-to-cradle (C2C) product in keeping with the circular economy, non-toxic environment and human health agenda.
AFM® is manufactured by upcycling waste glass. Although it will last the lifetime of the filter, AFM® development is ongoing and older product can be reprocessed at any time to incorporate the latest technological advances. Contrast this with sand which at the end of its useful life is dumped into landfill (classed as hazardous waste in some countries) and replaced by new mined sand, further depleting a finite environmental resource.
Our Dryden Aqua factory in Scotland can manufacture more than 30,000 tonnes of AFM® per year, sufficient to provide clean drinking water to 80 million people. This capacity will be increased as required by building new factories nearer to the source of the required raw materials.
Applications are wide from municipal to industrial treatment
AFM® is the chosen filter media in more than 100,000 installations around the world including:
- Municipal drinking water plants, ground water and surface water
- Municipal Sewage Treatment Plants, tertiary treatment of effluent
- Salt water desalination, pre treatment prior to membranes
- Industrial users
- Petrochemical & Chemical , provision of clean water and removal of oil
- Pharma & Bio-chemical
- Food & Beverage producers
- Swimming pools
AFM®’s use prior to reverse osmosis reduces biofouling
The pre-treatment of water with AFM® prior to reverse osmosis membranes offers significant advantages over the more conventional UF or multimedia options. The fact that AFM® will not support bacterial colonies or biofilm, helps reduce biofouling of the membrane.
AFM® will also remove substances such as silica from solution, which UF, in spite its superior mechanical filtration performance, is unable to perform. This helps prevent scaling on the membrane. As both biofouling and scaling involve the use and subsequent disposal of fairly aggressive chemicals AFM® will help to reduced operating costs and increase membrane life.
What makes AFM® so effective?
- We use predominantly green container glass as it has the correct chemical and structural properties for our activation process.
- 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 sub-angular AFM® media, the grains lock together to prevent the solids slipping through.
- 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 electrostatic attraction of the negative zeta potential makes AFM® the best filtration media for potable water treatment.
When we met Dryden Aqua we learnt first-hand about the company, its history and its products. The Scottish-based marine biological company was established in 1980 and specialises in water quality and innovative & sustainable treatment technologies. You can catch Dryden Agua and the AFM® at Aquatech Shanghai in June 2016. For more information see Dryden’s website here.
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