[그림 3] 카트리지 여과기(출처 Hayward)

[그림 4] 복합여과기

[그림 5] 부식된 복합여과기 내부모습

[표 2] 다층여과기의 작동 사이클

2. Types of Pool Filters

(1) Cartridge filter

Removable foreign substances of size 10 to 20 μm. It is suitable for home and small swimming pools rather than commercial ones due to its high price and high initial input and maintenance costs. The small filter regenerates the filtering capability by removing and cleaning the cartridge.

[Image 3] Catridge Filter (Source Hayward)

(2) Multi-layered filter

40μm to 100μm particles can be removed. The operating cycle consists largely of a filtration-backwash-rinse-filtration cycle. This is one of typical pool filtration system. Since the filtering area is the surface area of the filter, the size and the volume of the filters increases according to the water volume. Pollutants in small particles should be colloidal with a cohesive agent to enlarge the unit size and then filtered out.

[Image 4] Multilayer Filter

[Image5] Corroded Multilayer Filter Inside

If the filter layer consisting of activated carbon and sand is blocked during filtration, the absorption capacity and the flow rate are gradually reduced. Therefore, the filter layer is raised periodically by passing water in the reverse direction to raise the water to raise the foreign substance, then drain it with water, rinse it with clean water, and resume the filter cycle again. This process is called Backwash.

If backwash is not performed properly, the water quality will deteriorate, as well as the accumulation of biofilm, mud balls, and sludge on the filter tank and pipe walls, corroding the tank and pipes, reducing water flow and stinking. The adsorption capacity of activated carbon is extinguished by chlorine and foreign substances and is not regenerated, and filtering function can be maintained only by periodic replacement.

“Backwash” is an essential process to regenerate the filtration capacity of most swimming pool filtration systems such as sand filters, diatomite filters, cartridge filters, as well as multi-layer filters. In this process, backwash water is indispensably consumed. 

64 KARSE

[Table 2] Operational cycle of multi-layered filters 

Since Korean law does not stipulate a standard for the amount of backwash water sent out it is mostly up to the experience of the operator to determine the appropriate level in the backwash rather than using calculation. At some swimming pools, the amount of water used in the backwash is not even measured.

Korea has a high population density and great fluctuation in rainfall across seasons, leading to a small amount of available water per capita. The total annual rainfall per capita, is 2,546m³ which is only about1/6 of the global average. According to the criteria of the UN’s research center on population dynamics, Korea is classified as a “country under water stress.” (Or “a country lacking water” in laymen’s terms). With economic growth, there has been a drastic increase in demand for water used in leisure facilities such as water parks, swimming pools, children’s swimming pools and spas, but the available water resources in the country has barely changed from 50 years ago. According to some publications, the Water Poverty Index of Korea is ranked 43rd out of 147 countries, or 20th among 23 OECD countries. (Water and the Future, published by K-Water, 2020).

For swimming pools that use a large amount of water to provide services, water is an essential resource. We need to remind ourselves of the recent past, when there was rationing on drinking water, and it had to be supplied by water tank trucks to the regions of Gyeongsangnam-Do, Gangwon-Do and Jeju-Do. If we come into a situation where there is a shortage of drinking water during the dry season, it would be unthinkable to throw out such precious water through the sewage system just for the backwashing of the filter. At a time when the water management system is being upgraded with the lead of the national government and sophisticated equipment are being developed and applied to conserve water resources, there is a growing need for the water treatment system in swimming pools to be upgraded to stay in step with the trends.

(3) Perlitefilter

The pearlite filter can filter out foreign matter of 1㎛~3㎛in size, and comes in various models fit for small or large swimming pools.The filter is compact in size and has a high filtering efficiency. Since the small porosity filters out small particles, high turbidity can be maintainedwithout having to add cohesive agents.