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

Sand filters are the primary means of treatment but there are performance & stability issues due to bacterial fouling
AFM® is a direct replacement; channelling doesn't occur so bacteria & heavy metals are prevented from passing
Made from upcycling glass it fits the circular economy; various uses: drinking water, sewage treatment & industrial

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 Glass
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.

Benefits include:

  • Lower running costs & better performance – AFM® filters at least 30% better than sand and 10 times better at removing sub 5 micron particles (independently measured by IFTS). A return in capital can be expected within two years
  • AFM® will last for the life of the filters – should never need to be changed (sand replacement is normal every 3-5 years)
  • Lower consumption of chemicals – AFM® performs better than sand, so less flocculant is needed (up to 40% saving) and the product water has a lower chlorine oxidation demand, (up to 80% less chlorine)
  • Lower disinfection by-products – AFM® will reduce harmful disinfection by-products (THM’s) because we use considerably less chlorine
  • Bacteria removal – AFM® is the only filter media able to consistently and reliably remove Cryptosporidium, Giardia, Vibrio Cholera and Legionella bacteria from water, which are known to be the source of sickness and sometimes death in millions of people worldwide
  • Ferric, arsenic, chromium, lead & 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. Pre-treatment research is being conducted to enhance the performance and expand the range of priority substances that can be removed


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
    • Textile
    • Aquaculture
    • 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?

  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 sub-angular 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 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.

Further Reading

  • Water SMART Blue Buildings For Sustainable Urbanisation – Complete coverage of centralized water & sewage systems may never be possible in China, so what can one do? Ecosoftt’s Stanley Samuel & Marcus Lin share how their Water SMART Blue Buildings Standard can be a valid alternative
  • A New Model In Village Water Management – Water projects in China suffer from sustainability issues. Ivanna Tan from Lien Aid on how their Village Water Management programme overcomes these issues and has delivered clean & sustainable water to more than 72,000 rural villagers
  • Water: Habits & Actions – What are your water habits? Even giving up chocolate for one week can positively impact our waters as Patricia Dwyer, Founder & Director of The Purpose Business Group, tells us. See what other changes you can make
  • Heavy Metals & Agriculture – Check out China Water Risk’s overview of the status of heavy metals discharge into wastewater, priority provinces, overlap with agriculture sown lands, crops exposed and industries targeted for clean-up
  • KAF Bio-Sand Filter: Arsenic Be Gone! – Arsenic contamination affects China’s waters & soil, affecting health. Patrick Cox & Fan Chen tells us about how a bio-sand filter can remove arsenic from any source, be it natural or man-made
  • Water Stewardship: Actions Must Match Risk – Despite acknowledgement of water risks, 58% of companies in CDP’s 2014 Global Water report do not have a public commitment to water. We expand on actions needed in China & globally to match the risk
  • 2014 Investments in Chinese Waters – With the government encouraging public & private sector water spend, check out investments in 2014 from agriculture, wastewater, water infrastructure, drinking water to Israeli cleantech
Howard Dryden
Author: Howard Dryden
Dr. Howard Dryden is the founder of Dryden Aqua Ltd. The company was founded from his PhD research on molecular sieve ion exchange zeolitic sand filtration systems for closed system aquaculture, and development of intensive aquaculture technology. Dr. Dryden has unique knowledge combination of biology, chemistry and technology and is the inventor of the activated, bio-resistant filter media AFM®. Dr. Dryden is one of the world`s leading experts in sustainable water treatment and winner of multiple international awards in innovation and sustainability including: Member of the Scottish Government's Hydro-Nation Forum and Research and Communications Sub-Group, Member of EU Business and Biodiversity Platform, and Member of the CE100 SME group, Foundation for circular economy
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