Diatomaceous earth filtration is a method used to remove tiny particles from liquids. This process uses a layer made from the fossilized remains of microscopic water organisms called diatoms. These diatoms are mined from diatomite deposits, which are found on Earth's surface because they have built up in sediment from moving water bodies. After mining, the diatomaceous earth is purified using acid leaching or liquid-liquid extraction to prepare it for use. The D.E. filtration process has three main steps: pre-coating, body feed, and cleaning.

Because diatomaceous earth filtration can remove very small and harmful particles while working efficiently, it is widely used in aquariums, wastewater treatment, food and beverage filtration, and other applications.

Function

Diatomaceous earth filters are widely considered the best choice for removing pollutants while maintaining high efficiency. When used for pool filtration, DE filters are effective at capturing a wide range of particle sizes, helping to keep water clear. Recent studies show that DE filters can remove particles as small as 1 to 6 micrometers, which improves water quality. This level of filtration helps remove tiny particles, including bacteria, algae, viruses, and other microscopic materials. These particles can come from bodily fluids, fecal matter, and other sources that may contaminate water. While coagulants like chlorine can help remove some particles, certain pollutants, such as cryptosporidium, giardia duodenalis, and pseudomonas aeruginosa, are not efficiently removed by chlorine. These parasites are resistant to chlorine and can survive in water. Despite this, outbreaks of cryptosporidium or giardia are rare. In a study in Atlanta, Georgia, out of 160 pools, 13 (18.1%) tested positive for at least one of these parasites.

Some common contaminants include:
• Hepatitis A
• Norovirus
• E. coli
• Legionella
• Shigella
• Cercariae
• Campylobacter
• Staphylococcus

Filtration is essential for protecting the health of pool users. If a DE filter is properly designed, it can remove nearly 100% of parasites. To do this, the filtration media (diatomaceous earth) must be at least 4 micrometers to remove cryptosporidium and at least 7 micrometers to remove giardia duodenalis (G. lamblia). Research shows that DE filtration reduces parasite oocyst concentrations more effectively than other methods, such as conventional or granular media filtration. In full-scale water treatment simulations, DE filtration achieved a 6-log reduction in parasitic oocysts. A 6-log reduction means the microorganism is reduced by 99.9999% from one million. Because DE filters have a low micron rating, they can trap very small pollutant particles.

DE filters used in surface water and recreational water treatment require regular maintenance. Depending on water volume, maintenance and replacement may be needed more often. To ensure efficiency, water must flow continuously through the filter, and pressure checks should be done regularly. Filters must be backwashed every four to six weeks, and fresh DE media should be added after each backwash. If maintenance is not done properly, bacteria, viruses, and parasites may build up, reducing filter efficiency. It is important to remember that filtration systems do not guarantee complete removal of all contaminants, so some risk of contamination may still exist.

Diatomaceous earth filtration is also used in food and beverage production to remove contaminants like bacteria and microorganisms that can affect product quality. If bacteria and fungi are not removed from liquids, they can cause long-term contamination, harming preservation and quality. For example, brewers must meet specific requirements during alcohol production, such as in making malt beverages (beer, ale, etc.). Beer filtration often removes turbidity, which includes yeast, hops resin, and calcium oxalate. These materials can leave harmful microorganisms and affect the taste of the beverage. By using DE filtration, microbes are removed, improving the beer’s taste and appearance while extending its shelf life. DE filtration is a popular choice for brewers because it uses a natural process without chemicals, and the amount of DE can be adjusted based on brewing needs.

Major components and process

Diatomaceous Earth (D.E.) filters can be adjusted based on their intended use, but all basic D.E. filters have similar parts. The process begins with a direct pipeline connected to a raw water source, where water flow can be controlled continuously. Copper pipes are often used throughout the system because they resist rust and decay.

Water for filtration must come from a direct source, which can vary depending on location and water availability. The materials used to carry water must be rust and corrosion resistant. Copper is a common choice because it is strong and durable. In some cases, copper pipes may be wrapped with special plastic sleeves for extra protection. Other materials, like polyvinyl chloride (PVC), cross-linked polyethylene (PEX), and acrylonitrile butadiene styrene (ABS), are also used. These plastic pipes are strong, flexible, and can handle high pressure without rusting. During filtration, the same type of piping must be used throughout to keep the water pure as it moves through the system.

Fluids, sometimes called slurry, often contain particles of different sizes that may not be fully removed by the main D.E. filter. These particles can build up, increasing pressure and reducing water flow, which can make the filter stop working. To prevent this, filter aids—solid particles that improve water flow—are added. These aids trap small particles while allowing water to pass through. When filter aids collect, they form a porous layer, with about 15% of the material being solid and the rest empty space. This layer, called a precoat, is applied before filtration begins. It is pumped into the filter press, creating a porous layer on the filter cloths. Body feed is another type of filter aid that is added during filtration to help keep the filter working properly. If too much filter material builds up, it can block water flow. The precoat and body feed tanks both help remove large particles that might slow down the filtration process. The amount of precoat or body feed needed depends on how clean the original slurry is.

Filter cake, a layer of collected material, does not form on its own. It needs a support structure, called a septum, which is usually made of plastic or metal. The septum has small openings that let water pass through while allowing diatomaceous earth to collect and block the openings.

Changes in pressure can happen due to long filtration cycles, poor maintenance, a damaged septum, or changes in water flow. Pressure is important for filtration: too much pressure can damage the filter and cause water to pass through too quickly. It is important to monitor water flow, precoat, and body feed to ensure smooth operation without blockages.

Manufactured diatomaceous filter types

A method to remove small particles such as iron, magnesium, mill scale, and other deposits uses a pressure filter. This filter includes a strong container that can handle high pressure, along with a system of pipes for water movement and collection. It may use one or more types of filtering materials. Pressure filters are used in many places, including city water systems, factories, homes with wells, and swimming pools. These diatomaceous earth (D.E.) filters are simple to operate and can be placed vertically or horizontally. They can also be adjusted to use multiple types of filter materials. The filter has an inlet at the top and an outlet at the bottom. Water enters through the inlet and passes through a grid covered with synthetic fabric, which supports a layer of D.E. Gravity helps the water flow through the D.E. layer, removing unwanted particles. The cleaned water then exits through the outlet at the bottom of the filter and moves to another container. Pressure filters are useful in situations where water or other liquids flow steadily, and they require monitoring of the pressure in the filtered liquid.

Additional reading

• Methods used to remove Cryptosporidium and Giardia from drinking water
• Recommended standards for water treatment facilities
• A list of state-specific standards for water turbidity
• Water turbidity benchmarks in California
• Precoat filtration using body feed and variable settings
• Explanation of precoat and body feed filtration techniques
• Handbook of Water and Wastewater Treatment Plant Operations, 4th Edition
• Written report on filtration (Marciano et al., 2011)
• Advanced Physiochemical Treatment Processes Volume 4 (Kang et al., 2006)
• Slow sand and diatomaceous earth filtration for removing cysts and other particles (Schuler et al., 2003)