3. Perlite Filter Media

Perlite is produced by taking rocks of silicic acid that were generated from volcanic activity and heating them for a short period at a temperature of 850°C~1200°C.

 

[Table3] Diagram of the operational cycle of perlite filters (PilotSystem)

The rock is then expanded like popcorn, with many fine pores inside. This ensures the mass is very small. Perlite that is expanded to approximately 20 times the size of its original rock takes on the form of white or off-white inactive powder which is harmless to the human body. It is non-inflammable and has great efficacy in absorbing noise and moisture, as well as a high adsorptive power, making it ideal to be used as construction material or fine filtering material in the manufacturing of beverages, wine, beer or pharmaceutical products.

Perlite has been listed as a safe food additive under the U.S. Food Chemicals 'CODEX' as well as its Korean equivalent. It does not cause changes in the taste, odor or color of the food, nor does have any toxicity, nor is it considered a heavy metal. This has allowed it to be widely used in various fields worldwide.

Perlite is produced in granule grade according to its use. Due to the numerous fine pores, it can filter out matters as small as 0.1 ㎛ to meet the water quality requirements. For those used in swimming pools, a water permeability of 2.1 ~ 3.4 in Darcy value and approximately 44 ㎛ ~ 150 ㎛(Wet Sieve Method) infineness are applied to offer a filtering level of  1 ㎛.

Perlite is an inactive mineral that has been treated at a high temperature and does not dissolve in water or in chemical solutions.  Nor can it be compressed, which prevents the filter film from solidifying and enables easy detachment.

 

 
[Image 6] Perlite Media

[Image 7] Microscopic image of perlite. Source:Perlite Institute.org

4. Perlitefilter

(1) Classification of perlite filters 

Perlite filters fall into the category of pre-coat filters. Other pre-coat filters include filters using diatomaceousearth or D.E.,polyesterfiber, or cellulose. Perlite filters stand apart from other pre-coat filters in that it is in the sub-category of media regenerative filters. 

This is because unlike other pre-coat filters that throw away the filtering material and refill it, filters using perlite can regenerate the filtering material multiple times.

(2) Comparison of perlite filters and other multi-layered filters

In the case of perlite filters, the surface of hundreds of, or more than a thousand filter tubes serve as the filtering surface. This allows the area needed for installation to be only a quarter of that for multi-layered filters with the same filtering capacity. This saves costs of constructing the machinery room and conserves water, chemicals and thermal energy by more than 70%.

[Image 8] Multi-layered filter that has been installed

[Image 9] After replacing it with a perlite filter

Perlite filters have a useful life that is twice as long as multi-layered filters, which helps save the costs of replacing filters. This offers an advantage in long-term repair and maintenance planning, too.

This is easily verified by cases where an obsolete multi-layered filter is removed and replaced by a perlite filter. 

 

First, the huge steel tank is removed, making the machine room to become more pleasant and roomy. It also reduces the route of movement for the manager. The operational status of each equipment is displayed on the touch screen and is easily manipulated with a simple touch. This makes it easy to train personnel and maintain the equipment.

Each perlite filter has a separate control system to have the steps of filtering, pre-coating and regeneration done automatically. Depending on the season or day of the week, a different program can be applied to let out an appropriate amount of water, dramatically reducing the amount of water thrown out, and thus saving chemicals and thermal energy.

 

[Image10&11] The flex tube of a perlite filter

/ After the filter film has been formed for the perlite filter 

(3) The filtering mechanism of perlite filters 

As water passes through the perlite filter layer that is formed with hundreds of flex tubes wrapping around as shown in the image above, foreign matter in the water is filtered out.

 

[Image12] Cross section of the perlite filter layer 

 

 
[Image13] Cross section of the perlite filter layer

In the perlite filter system, instead of ‘backwashing’, there is a ‘bumping’ step that occurs once or twice a day for regeneration.  The bumping unit has tube sheets attached to the top part, and the tube sheets consist of multiple filter tubes. The bumping unit is moved vertically to dust off the coated layer of the perlite to recoat it for the regeneration. During the regeneration process, no water is consumed, making it environment-friendly and innovative for its energy conservation properties.

One of the most common questions concerning this step is, “Where does the filtered foreign matter go?” The foreign matter adsorbed by the perlite detaches with the filtering material during the bumping process, then becomes a part of the filtering material with the perlite during the pre-coat step. Since the foreign matter, once filtered, cannot backflow into the pool, there are no concerns of water becoming re-contaminated.

When the foreign matter adsorbed into the perlite filtering material accumulates and makes the pores saturated, it should be assumed that the perlite’s life as a filtering material has come to an end. When this happens, the degree of contamination on the filtering film can be checked through the inspection window. Whether the differential in pressure after the bumping step is improved also needs to be checked. When the differential does not decrease, the perlite filtering material must be replaced.

The U.S. CDC noted that “The filtering system of swimming pools do not filter out organic or inorganic contaminants dissolved in the water. Therefore, it is essential that the operator has a plan to remove a certain amount of concentrated water and replenish it with fresh water according to a plan.”If the swimming pool becomes crowded more contaminants accumulate in the water and thus filter circulation is not sufficient to maintain water quality that is clean and safe. As such, replenishing with fresh water is essential.

[Image14] Perlite filter system

The body oil, saliva, sweat and urine from the human body that is dissolved into the water cannot be filtered by the filtering system for swimming pools and sometimes combines with chlorine molecules to generate chloramine. When chloramine evaporates, it generates an unpleasant odor and irritates the skin, eyes and respiratory system. It also corrodes the air purification system and metal pipes in the swimming pool(HealthHazard evaluationreport2008, published by CDC).

The perlite filter system prepares solutions to such issues in advance by having a program automatically discharge an appropriate amount of water from the swimming pool and replenish it.

[Image15] The automatic water discharge program for the perlite filter system 

 

The objective of this water replenishing program is to achieve the highest efficiency in maintaining the highest water quality by proactively managing the replenishing of an appropriate amount of water, instead of a manual replenishing that occurs in proportion to the amount of backwashing water discharged, and thus minimize waste of water.

(4) Application of the perlite filter

Perlite filters are adopted by numerous large-scale water parks, resorts and swimming pools and have proven to be of superior quality. They have also been exported to various establishments in Russia, the Philippines, China and Vietnam requiring water treatment.

The case of a large-scale water park in Vietnam that has recently opened confirms the water treatment function of the perlite filter. Given that the water park is located on an island, water supply is limited. The perlite filter was chosen to address the water shortage. A desalinization facility was run at full steam before the opening of the water park to provide water to the swimming pool. But in the process the desalinization facility broke down, making it impossible to further supply water. Faced with this urgent situation, the client went so far as to purchase and ship water from the mainland to fill the swimming pool. But to add insult to injury, rainfall made soil to flow into the pool.

If the pool had been located on the mainland, it would have been natural to remove all the existing water and replenish it with fresh water. But there was no time to do so with the short deadline. The desalinization facility was still out of order, so the only alternative was to filter water.They first decided to operate the filter for the water that had been mixed with soil and wait and see. Within 48 hours, the water was completely purified, which led to the filtering system gaining complete trust from the client.

 

[Image16] Perlite filter installed and operated in a Vietnamese water park

[Image17] A pool that has completed water purification