What is it, how is it used, and why is it replacing sand, zeolite, and conventional filter glass in modern filtration systems?

AFM® (Activated Filter Media): industrial-grade activated glass, a direct replacement for sand in any filter.

Every water filtration system—be it for a swimming pool, a water treatment plant, or an industrial treatment facility—ultimately relies on a single component: the filter media that fills the filter tank. For decades, silica sand was the default standard, and over time, alternatives like zeolite ("Micro Z") or various crushed filter glass types were added. AFM® (Activated Filter Media) is a filter media developed by Dryden Aqua based on over 30 years of research, and today it is the only filter glass simultaneously certified for swimming pools (NSF/ANSI 50) and drinking water (NSF/ANSI 61).

In this blog, we explain what AFM® is and its applications, its technical advantages over sand, zeolite, and conventional filter glass, the differences between its grades and how they are combined, optimal filtration and backwash speeds depending on the application, how to calculate how much AFM® a filter needs, why it saves water, its lifespan, its pH and temperature ranges, and its filtration levels in microns.

What is AFM® and what are its applications?

AFM® is manufactured from recycled glass (green and amber) subjected to a patented chemical and thermal activation process that modifies its surface at a molecular level. This activation simultaneously achieves three properties that no unprocessed mineral filter media can achieve separately: a self-sterilizing surface that resists biofilm formation, a surface with an active electrostatic charge that adsorbs fine particles and dissolved organic matter, and a mesoporous internal structure that multiplies the available filtration area.

The result is a direct replacement for sand: it can be installed in any existing sand filter—vertical pressure, horizontal, or rapid gravity filter (RGF)—without any mechanical modifications to the filter. Its main applications include:

• Drinking water: surface and groundwater treatment, iron, manganese, and arsenic removal, and pre-filtration before reverse osmosis or ultrafiltration membranes.
• Pools and spas: recreational water filtration, with or without saltwater chlorination systems.
• Municipal wastewater: tertiary treatment to reduce phosphorus, BOD, COD, and bacterial load.
• Process and industrial water: cooling towers, oil, grease, and heavy metal removal.
• Aquaculture and aquariums: recirculating aquaculture systems (RAS) and mechanical filtration prior to biofiltration.

Technical advantages over sand, zeolite, and conventional filter glass

The underlying problem: biofilm

Silica sand has an enormous specific surface area—one cubic meter of sand is equivalent to about 3,000 m² of total surface—making it an ideal substrate for bacterial growth. Within 6 to 12 months of installation, this biofilm has advanced enough for sand grains to agglomerate, forming preferential channels ("channeling") that allow unfiltered water to pass through and make filter performance unpredictable. Biofilm also acts as a breeding ground for pathogens such as Legionella and Pseudomonas, and converts urea from bathers' sweat and urine into chloramines—the compounds responsible for the characteristic "chlorine smell" and irritation of eyes and respiratory tracts in pools.

The three problems of biofilm in a sand filter: bed channeling, pathogen proliferation, and chloramine formation.

AFM®'s activated surface not only better resists biofilm formation: it is genuinely self-sterilizing, so it structurally does not promote its formation. This means that a filter with AFM® does not develop these problems over time, no matter how many years it has been in operation.

Finer filtration and greater adsorption capacity

The independent laboratory IFTS (Institut de la Filtration et des Techniques Séparatives, France) evaluated AFM® alongside silica sand and various filter glasses, at a filtration speed of 20 m/h and without flocculant addition. The results: AFM®ng retains 95% of particles below 1 micron, standard AFM® retains 95% below 4 microns, while sand retains 95% only below 20 microns, and conventional filter glasses above 25 microns.

The difference is not just filtration fineness: AFM®'s activated surface (right) also does not promote biofilm development like sand (left).

In addition to filtering finer, AFM®'s activated surface adsorbs about 50% more dissolved organic matter (oils, lipids) than sand or unprocessed filter glass. In practice, this reduces chlorine consumption and other treatment chemicals by 20% to 30%, and in pools, it reduces the formation of disinfection by-products like chloroform by more than half.

What about zeolite (Micro Z)?

Zeolite offers a finer particle size than sand and some cation exchange capacity, which explains its popularity as an alternative to sand in recent years. However, it is still a natural mineral without any surface activation process: like sand, it does not have a self-sterilizing surface, so it remains exposed to bacterial colonization over time and requires the same conventional backwash regimes. Unlike AFM®, it does not have published independent data on biofilm resistance or 1-micron filtration performance verified by a laboratory like IFTS.

Differences between AFM® Grade 1, 2, and 3, and how they are used

AFM® is manufactured in different grades based on grain size, each with a specific function within the filter bed:

How these grades are combined depends on the filter size and type:

• Small filters (less than 800 mm in diameter) and any filter with a nozzle plate, regardless of its diameter: 50% Grade 1 + 50% Grade 2.
• Filters with a bed larger than 32 in (81 cm) and with laterals: 60% Grade 1 + 20% Grade 2 + 20% Grade 3, where Grade 3 acts as the lower support layer to ensure correct flow through the laterals.

Standard combination of AFM® grades according to filter bed height and type of internal filter distribution.

AFM® is supplied in 21 kg and 25 kg bags, or in 1,000 kg bulk bags, with a density of 1,250 kg/m³.

Optimal filtration and backwash speeds according to application

The recommended filtration and backwash speed is not the same for all applications: it depends on the expected solids load, the type of contaminant to be removed, and how critical it is to prevent unfiltered water from passing through. This table summarizes the recommended ranges:

Application	Filtration speed	Backwash speed
Drinking water (surface / groundwater)	9.8 – 14.7 m/h (max. 49 m/h)	29 – 49 m/h
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