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Anthracite is a type of coal, and is the coal with the highest carbon content, in excess of 95% by weight. Like most minerals, anthracite is formed over millions of years of deposited plant layers, combined with pressure and temperature.

Of all the carbon materials, this black and rather shiny mineral is the hardest of them all. Long used in water filtration applications, the anthracite used for water filtration is usually specially selected from deeper mines, where, due to higher pressures, the carbon content is typically even greater.

Why Anthracite Is Used as Water Filter Medium ?

In simple terms, filter media are materials that facilitate the passing of raw untreated water through them, while retaining any impure particle matter, allowing now cleaner water to pass through. Each filter medium has specific characteristics such as size, weight, whether they are activated or non activated, gravity and more. All of these characteristics give rise to differing operational performance at certain filtration tasks - oftentimes a compromise between them is sought to provide the most robust system, or a system at a lower price point. Anthracite’s broad tolerance of contaminants and ease of forming it into a filtration grade product make it a popular choice.

For drinking water, wastewater filtration and water for industrial use, anthracite has ideal properties for purifying and clarifying this type of water - especially when utilised in combination with other sand filters, or as a component of a dual- or multi-media filtration system.

Because of its ideal properties, relative ubiquity and ease of use, anthracite as a water filter medium is one of the most widely used around the world.

Why Anthracite Is Used for Deep Bed Water Filtration

Deep bed filtration is a fast and very efficient method for removing small particles from liquid, and works particularly well with Water. This method of particle dispersion in liquids and water are common in a wide range of different industries and in particular the civil purification industries concerning water and wastewater purification.

Anthracite is perfect for this type of industry as the shape of the particles lend themselves extremely well to deep bed filtration uses. Their strength and other properties - as outlined above, make them an ideal source for these applications.

What Exactly Is Multilayer Filtration ?

Multilayer simply means there are a variety of layers in deep beds that provide filtration at different levels. In contrast to methods like cartridge filtration, multi-layer filtration - which includes gravel in various sizes and forms as well as anthracite - represents a deep-bed filtration. Multilayer, also known as dual- or multi-media filtration, and is by far the most robust and effective filtration set up.

With multi-layer filtration, the water passes through various layers of filter material with increasing fineness in the direction of filtration. Gravel filtration or multilayer filtration, in combination with flocculation, is particularly effective in the treatment of river water. When this process is followed, it usually also involves a process stage of sedimentation. Gravel and multi-layer filters are regularly cleaned by back-flushing.

Why Anthracite Media Is Good at Multilayer Water Filtration

Anthracite’s strength and durability has already been mentioned, and how its particle shapes lend themselves well for deep bed filtrations. With multi-layer filtration, any water requiring purification passes through a number and variety of layers of filter material, with increasing fineness of media along the direction of filtration. Having multiple layers allows the extraction of a variety of particle sizes and types passing through the layers. Thereby ensuring a purer outcome at the end of the process. Multilayer filters can cover a large number of solids to be extracted.

Anthracite Use in Multilayer Beds

A technique widely used for the purification of water and wastewater is the use of multilayer beds. The main applications for this area - and for anthracite use within this area tend to be in urban wastewater purification stations, drinking water treatment plants and desalination plants. Desalination plants tend to proceed using a reverse osmosis technique, with anthracite used as a filter system prior to desalination (see later).

Filtration is a process flowing through a single filter bed, or several that overlapping filter beds. In multilayer beds, usually the less dense filter media (like anthracite) is placed on the upper layer of the bed. Before passing through to other layers such as finer sand, coarse sand, fine gravel, and coarse gravel. Each layer plays it’s part to remove particulate matter from the water. To preserve a uniform filtration depth through each layer, the layers are compacted when added to the filter. Additionally, flow and backwashing rates should be optimised so as not to adversely disturb the filter bed.

One of the major reasons that anthracite is used is that it provides reliable improvements in turbidity extraction, mostly due to its capacity to effectively retain solids.

Source: https://mineralmilling.com/anthracite-filter-media/