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Swimming Pool Sanitation

Typical filtration equipment used in private swimming pools

Water pump

An electrically operated water pump is the prime motivator in recirculating the water from the pool. Water is forced through a filter and then returned to the pool. A typical pool pump uses 500 watts to 2,000 watts. Commercial and public pool pumps usually run 24 hours a day for the entire operating season of the pool. Residential pool pumps are typical run for 4 hours per day in winter (when the pool is not in use) and up to 24 hours in summer. To save electricity costs most people run for between 6 hours and 12 hours in summer with the pump being controlled by an electronic timer. Commercial pools require a minimum 4 hour circulation of the total water volume.

Some pool pumps have two motor speeds to reduce power consumption at times when full power is not needed. Other pump manufacturers (typically Italian or other European) have redesigned their units to use a smaller electric motor with heavier windings, therefore consuming less energy, to power a larger pump impeller. Variable-speed pumps reduce power consumption even more. These pumps run slowly 24 hours a day. The slow speed typically cleans better because smaller particles can be filtered. At the slow speed, minimal resistance in the pipes reduces the energy needed to move the water.

Pool pumps typically are "self priming": they may be positioned above the mean water level of the pool yet still start up and function after a timed rest period. Pumps that do not "self prime" are termed "flooded suction" and must be gravity fed by the pool by being located below the mean level of the pool water.

Most pool pumps available today incorporate a small filter basket termed a "hair and lint strainer" or "lint pot" as the last effort to avoid leaf or hair contamination reaching the close-tolerance impeller section of the pump.

Filter Unit

A pressure-fed filter is typically placed in line immediately after the water pump. The filter typically contains a media such as graded sand (called '14/24 Filter Media' in the UK system of grading the size of sand by sifting through a fine brass-wire mesh of 14 to the inch to 24 to the inch). A pressure fed sand filter is termed a 'High Rate' sand filter, and will generally filter turbid water down to 10 micrometers in size. The rapid sand filter type are periodically 'back washed' as contaminants reduce water flow and increase back pressure. Indicated by a pressure gauge on the pressure side of the filter reaching into the 'red line' area, the pool owner is alerted to the need to 'backwash' the unit. The sand in the filter will typically last five to seven years before all the "rough edges" are worn off and the more tightly packed sand no longer works as intended. Recommended filtration for public/commercial pools are 1 ton sand per 100,000 liters water.

Introduced in the early 1900s was another type of sand filter; the 'Rapid Sand' filter, whereby water was pumped into the top of a large volume tank (3' 0" or more cube) containing filter grade sand, and returning to the pool through a pipe at the bottom of the tank. As there is no pressure inside this tank, they were also known as 'gravity filters'. These type of filters are not greatly effective, and are no longer common in home swimming pools, being replaced by the pressure-fed type filter.

Other filter media

Other filters use diatomaceous earth to help filter out contaminants. Commonly referred to as 'D.E.' filters, they exhibit superior filtration capabilities. Often a D.E. filter will trap water-borne contaminants as small as 1 micrometer in size. D.E. filters are banned in some states, as they must be emptied out periodically and the contaminated media flushed down the sewer, causing a problem in some districts' sewage systems.

Other filter media that have been introduced to the residential swimming pool market since 1970 include sand particles and paper type cartridge filters of 50 to 150 square feet (14 m2) filter area arranged in a tightly packed 12" diameter x 24" long (300 mm x 600 mm) accordion-like circular cartridge. These units can be 'daisy-chained' together to collectively filter almost any size home pool. The cartridges are typically cleaned by removal from the filter body and hosing-off down a sewer connection. They are popular where backwashed water from a sand filter is not allowed to be discharged or goes into the aquifer.

Skimmers

Water is typically drawn from the pool via a rectangular aperture in the wall connected through to a device fitted into one (or more) wall/s of the pool. The internals of the skimmer are accessed from the pool deck through a circular or rectangle lid, about one foot in diameter. On lifting the lid (if the pool is operational) you will see water being drawn from the pool, over a floating weir (operating from a vertical position to 90 degrees angle away from the pool, in order to stop leaves and debris being back-flooded into the pool by wave action), and down into a removable "skimmer basket", the purpose of which is to entrap leaves and other floating debris. The aperture visible from the pool side is typically 1' 0" wide by 6" high, which intersects the water midway though the center of the aperture. Skimmers with apertures wider than this are termed "wide angle" skimmers and may be as much as 2' 0" wide (600 mm). Floating skimmers have the advantage of not being affected by the level of the water as these are adjusted to work with the rate of pump suction and will retain optimum skimming regardless of water level leading to a markedly reduced amount of bio-material in the water. Skimmers should always have a leaf basket or filter between it and the pump to avoid blockages in the pipes leading to the pump and filter.

Overflow channel pools

An overflow channel is a gutter that surrounds the pool, covered by a removable grille. Surface water flows over the edge of the pool and runs by gravity to the filtration plant, usually via a catchment and top-up tank. Often the exterior pool wall is higher than the overflow channel, eliminating the possibility of pool water overflowing onto the adjacent pool surround. Other designs may not have this feature, relying instead on a wider drainage system to trap any overflowing water.

Overflow channels allow faster turnover of the surface water than is possible with simple weir skimmers, which is why they are commonly found in public pools. They can also be attractive designs, particularly when transformed into a total "vanishing edge" pool. This design has been used to great effect in prize winning contemporary home design, notably in Southern California and the surrounding desert states.

Pool water returns

The final link in the pool recirculation system: skimmer-pump-filter-returns are the water returns. Typically these are referred to as "eyeballs" as they incorporate a swiveling nozzle that can be locked down to point in the desired direction and are reminiscent of a swiveling human eyeball. The directional adjustment is usually a 360 degree radius circle of 45 degrees away from the pool wall. Most home pools would incorporate at least two such "eyeballs". One recent development in skimmers was the 1970s "Aquagenie(TM)" which differers considerably operationally from conventional skimmersost of which are quite similar in operation, if not appearancey both drawing the pool water and returning it to the same location through a submerged slot which diverts the water downwards and in a wide fan shape. The concept incorporates a reservoir system to contain saturated trichor tablets which the resulting high strength chlorinated water dribbles back into the recirculation system, so it doubles up as a chlorine feeder as well as a normal skimmer. Arguably an "improvement" in skimmer design, patents on the device expired in 2003 and the system is now available from several US manufacturers.

Other equipment

Other equipment which may be optioned in the recirculation system include heat pumps/gas heaters, saline chlorination units, electronic oxidation systems,[[ionization system]], Tri-Chlor Feeders, diversions to solar panels, etc. are in most cases required to be placed after the filtration plant, and are the last item before the water is returned to the pool.

Outdoor structure

Most swimming pool installations incorporate an outdoor structure designed to house the pool filtration equipment as a protective measure against premature deterioration from sunlight and rain. Typically, these structures range in size from a simple flip-lid three-sided sound-insulated box set against a convenient house wall, the lid being constructed on a 15 to 20 degree slope and the interior large enough to hold the filter plant, pump, and whatever chlorination system has been includedp to a full-size Pool House (AKA "Pool Shed") with separate pool equipment area, bathroom, shower, changing areas, and in some cases even a rumpus-room type entertainment area. As pool-side parties are common amongst pool owning families, the Pool House forms the focal point for adult attendees, while the pool itself remains the realm of the children. (Vigilance for the safety of young children swimmers must be observed at all times, and a designated adult should be present at the poolside in a supervisory capacity)

Consecutive dilution

A pool filtration system as described (above) is termed a "consecutive dilution" system, as a constant and consecutive stream of fresh, chlorinated, and filtered water is being continually returned to the pool as part of a process that could ultimately result in a pool with 100% newly introduced fresh water over a period of time. Of course this goal is never achieved, as there is also a constant stream of new contaminants entering the pool as subsequent sections of this page will indicate.

Potential of contamination in bodies of water used for swimming & bathing

Transmission of disease from unfiltered/untreated swimming pool and spa water which may have become contaminated by micro-organisms from infected swimmers, incoming water from an unsanitary source, airborne contamination from rainfall, and droppings from birds, is possible. Contaminated water can lead to a variety of diseases including diarrhea and skin, ear, and upper respiratory infections, particularly if the swimmer's head is submerged or the water swallowed.

Illness or infections associated with swimming pools, spas, and other recreational-water environments has been linked to fecal contamination of the water due to feces released by bathers or even contaminated source water. Many of the outbreaks related to public swimming pools have occurred because disinfection was poorly maintained - or not introduced at all. The solution for private swimming pools owners is to maintain the filtration and sterilization system in satisfactory working order.

The majority of reported swimming pool-related outbreaks have been caused by viruses; recently, however, reported outbreaks have been more frequently associated with bacteria and protozoa.

Non-fecal human shedding (e.g., from mucus, saliva, skin) in the swimming pool, spa or similar recreational-water environments is a source of potential non-enteric pathogenic organisms. Mucus, saliva and skin of infected users can directly contaminate pool or spa waters and the surfaces of objects or materials at a facility with sufficient numbers of primary pathogens (notably viruses or fungi), which can consequently lead to infections in other swimmers who come in contact with the contaminated water or surfaces.

Opportunistic pathogens (notably bacteria) can be shed from users and transmitted via contaminated water in pools or spas. In addition, certain free-living aquatic bacteria and amoeba can grow in pool or spa water, in pool or spa components or facilities (including heating, ventilation and air conditioning (HVAC) systems) or on other wet surfaces within the facility to a point at which some of the opportunistic pathogens may cause a variety of respiratory, dermal or central nervous system infections or diseases.

Persons with diarrhea are likely to contaminate the water but may not be common in pools due to the effect of their illness on their desire to go swimming. On the other hand, children wearing diapers or youngsters just learning to control their bowels are more likely to have fecal accidents, which may lead to other swimmers swallowing fecal-contaminated water.

Chlorine resistant micro-organisms such as Cryptosporidium (crypto) may come in the municipal piped water supply (mainly in countries with bad sanitation conditions), and are not easily killed by chemical disinfectants in the pool. Alternative pool sanitation technologies such as electronic oxidation combined with copper ionisation provides a 100% protection against Cryptosporidium. The advent of molecular techniques has conducted to characterize different species and genotypes of Cryptosporidium infecting humans. The vast majority of human cases of cryptosporidiosis in the world are caused by both species, Cryptosporidium hominis and Cryptosporidium parvum. However other species including Cryptosporidium felis can infect humans too. To date this (felis) emerging protozoan disease is present in humans around the world, except in Australia and Oceania.

Potential diseases in poorly maintained public swimming pools

See more details in Waterborne diseases

Although extremely rare in Western society, the most frequently reported illnesses in countries that do not enforce a strict code of health compliance in public pools, are caused by micro-organisms such as Cryptosporidium (crypto), Giardia, E. coli O157:H7 (E. coli), and Shigella. Some of these outbreaks may affect thousands of swimmers, although it is not common to see such outbreaks in the daily press or TV.

Crypto is the most common micro-organism to cause outbreaks in public swimming pools and public spas, where its extreme chlorine resistance and small size make it a difficult problem for even the best equipped and well-maintained pools. Major outbreaks associated with Giardia have reportedly occurred in systems that do not use filtration/recirculation systems or have an undetected defect in the filtration system.

Some rural or back-country pools may use a "continuous replacement" system instead of proper filtration, whereby a source of new water is introduced at one end of the pool, and allowed to drain away at the other. An example would be a public access pool using a rural creek or spring which has been dammed to form a "swimming hole", and thus may be included in the description "artificial pool". A swimming pool filtration system which utilizes pump-fed sand (or other) filter media in a closed loop recirculation system is termed a "continuous dilution" system, as freshly filtered and chlorinated water is continually fed into the pool, thus diluting the turbidity and bacteria levels.

E. coli and Shigella are relatively sensitive to chlorine or bromine so most outbreaks have occurred in locations where no disinfectants are added, such as hot pools or spas that are filled with underground thermal waters. In certain countries, fatal primary amoebic meningoencephalitis (caused by Naegleria fowleri) has occurred following swimming in warm dirty thermal water, where the bather has immersed his/her head under the water. Other non enteric pathogens that may be found in swimming pools and hot tubs are Legionella spp., Pseudomonas aeruginosa, Mycobacterium spp., Staphylococcus aureus, Leptospira interrogans, Molluscipoxvirus, human papilloma virus, Acanthamoeba spp., Trichophyton spp., and Epidmermophyton floccosum, that usually produce dermic or respiratory infections.

While not typically spread in pools from one person to another, several other illnesses can also develop with poor sanitation or improper personal hygiene. Commonly infections or physical trauma of the ear canal (for example due to the use of ear buds to dry or clean the ear canal) result in the symptoms of otitis externa - inflammation of the outer ear. Otitis externa can be caused by a number of micro-organisms, including Pseudomonas aeruginosa (mentioned above) which requires special mention and can be spread from human to human in swimming pool water. However, it is generally not a problem for most people unless they are also suffering from immuno-deficiencies such as hepatitis or Human immunodeficiency virus or HIV infection. Pregnant women are also at high risk. Others may experience a rash or other skin irritation. If suspected, at risk individuals who have been exposed should be tested and local health officials should be contacted.

Most modern public swimming pools now use a flocculate, generally Polyaluminium Chloride (PAC), which, when added to the pool circulation, before filter, provides another defense against pathogens such as Cryptosporidium. It lines the top of the filter bed, capturing tiny bacteria and allowing them to be removed as part of backwashing (normal cleaning procedure for pool filters). This is the only way to properly manage the risk of contamination from such micro-organisms and is now fairly standard in the leisure industry.

Prevention of diseases in swimming pools and spas

Disease prevention should be a part of every water quality management program for pool operators, just like the prevention of drowning, injuries, and sunburn. People are less likely to be exposed to polluted water at swimming pools and spas that are monitored regularly and audited for health hazards. The pool water has to be continuously disinfected by disinfectants so that the concentrations set by standards are maintained throughout the pool water, and also the pH, the clarity and the total alkalinity of the water has to be maintained in accordance with the requirements set by standards.

The education of parents of small children and other people with regard to good hygienic behavior at swimming pools is also important for improving health safety at swimming pools and spas. People should also be cautioned about swimming in pools if they are suffering from gastroenteritis or other illnesses where viral pathogens might be transmitted from swimmer to swimmer via pool water.

Since most swimmers are exposed to pathogens by swallowing the water, people will be less likely to get sick if they swim without submerging their head.

Conventional halogen-based oxidizers such as chlorine and bromine are convenient and economical primary sanitizers for swimming pools and provide a residual level of sanitizer that remains in the water. There are, however, conditions in heavily-used commercial and/or public swimming pools whereby supplemental oxidation is warranted. In these instances Advanced Oxidation Processes (AOPs) can be employed whereby water contaminants are oxidized by one or more of four different precursors: ozone, hydrogen peroxide, oxygen, and air in combination with UV radiation and in some instances a catalyst such as titanium dioxide (TiO2). These AOPs react with water (H2O) to produce powerful oxidants such as hydroxyl radical (OH), singlet oxygen (O) and molecular oxygen (O2).

Chlorine, bromine and ozone can all be generated on site by passing an electrical current through either the pool water itself, in the case of chlorine and bromine, or through air, in the case of ozone. Chlorine may be supplied as a hypochlorite solution (bleach), powdered calcium hypochlorite ("cal hypo"), chlorinated cyanurate compounds ("stabilized" chlorine such as dichlor or trichlor), or by dissolving chlorine gas directly in water. Maintaining a safe concentration of disinfectant is critically important in assuring the safety and health of swimming pool users. When any of these pool chemicals are used, it is very important to keep the pH of the pool in the range 7.2 to 7.6; higher pH drastically reduces the sanitizing power of the chlorine due to reduced oxidation-reduction potential (ORP), while lower pH causes bather discomfort, especially to the eyes. Chlorine reacting with urea in urine from bathers can create nitrogen trichloride, which has a teargas-type effect.

Where the water is sanitized by means of oxidizers, some suppliers of electronic monitoring equipment recommend that the efficacy of the oxidizer be measured by the oxidation-reduction potential of the water, a factor measured in millivolts, where the minimum acceptable ORP level in public pools is 650 millivolts. This is supposed to ensure a 1-second kill rate for microorganisms introduced into the water. Unfortunately, a commonly used non-chlorine supplemental oxidizer, potassium monopersulfate, can produce measured 650 mV levels even in the absence of all sanitizing residuals. Cyanurated ("stabilized") chlorinators can give falsely high chlorine readings when tested with OTO (ortho-tolidene, a yellow indicator dye used in inexpensive test kits), since the chlorine indicated by the dye is mostly in a combined form instead of free, and does not contribute to ORP. ORP test cells are available as hand-held instruments, and as probes for mounting permanently in the pool circulation plumbing to control automatic chlorine feeders.

Test kits to make basic measurements of free chlorine and pH from a sample of pool water, which are the most important items to control in a swimming pool, are packaged with small dropper bottles of reagents. These reagents are typically OTO for chlorine and phenol red for pH. OTO has been phased out in most countries due to a connection with the production of cancer cells in test rats. More commonly DPD tablets replaced OTO since 1980. The kits include vials for mixing a water sample with the test reagents, and color charts for reading the indicated levels. These kits are termed "Comparator" kits as the test is "compared" to a known color value. Besides chlorine and pH, which should be checked frequently, more sophisticated reagent kits provide tests for acid demand and base demand, total alkalinity (TA), calcium hardness, and cyanurate ("stabilizer") concentration. These additional tests tend to vary only over weeks or months in a well-maintained pool, and thus need not be checked as frequently as chlorine and pH.

In the 1970s the Taylor Watergram introduced the relationship between the compounds and chemicals desired to be present in pool water. When the requirements of relationship were met, the pool was considered to be "balanced". A residential pool that is in proper "balance" would have a pH of 7.6, Calcium Hardness of 200 ppm (parts per million), Sodium Bicarbonate level of 120 ppmnd a residual chlorine level of 1.0 to 2.0 ppm.

Residential swimming pools generally rely on "breakpoint chlorination" i.e. the amount of residual chlorine present in the water is sufficient to combat the daily introduction of nitrogenous based matter and yet leave a positive residual. This is generally arrived at by a process of experimentation on the part of the pool owner.

Below ground, outdoor, irregularly shaped salt water pool. Automated pool cleaner visible at far end.

Pool sanitation, which necessarily involves toxic or mechanical means of killing microbes, can sometimes unintentionally irritate the swimmers, especially if poorly maintained and especially if too high level of chlorine and/or too low pH. Non-chlorine sanitizing chemicals and devices are promoted as being less harsh, but any sanitizer is harsh if overused. Water circulating through a pipe can be sterilized with UV light instead of chemicals, but some level of chemical sanitizer is still needed, because only a small portion of the pool water passes through the circulation system at any given time, and the circulation system typically only runs for a few hours each day. UV sterilization also does not inhibit algae from growing on pool surfaces, and it does not break down dissolved nitrogenous nutrients that feed algae growth, so some type of oxidizing sanitizer is still needed to check these trends, although it need not be dosed during bathing hours for this purpose.

"Chlorine smell" is misunderstood. While chlorine is a slightly yellowish, gas with a suffocating odor, the so-called "chlorine smell" is not that of pure chlorine. The characteristic odor occurs when an insufficient amount of chlorine is used to disinfect a contaminated pool. In the incomplete reaction that follows, by-products called "chloramines" are produced, and chloramines are responsible for the smell. The way to remove these chloramines is to "super-chlorinate" (commonly called "shocking") the pool with a dose of 10ppm of Cal-Hypo. Regular superchlorination (every two weeks in summer) will eliminate these unpleasant odors in the pool.

Generally, a well managed pool will have no smell or taste, be scrupulously clean, and have crystal clear water. Most people would not want to swim in a pool that appears dirty even if germs were under control. A pool pump circulates water through a strainer and filter to remove dirt and other suspended particles. The plumbing circuit may also include a gas or electric heater, solar panels, and chemical injector.

The proper management of a backyard swimming pool can be a difficult and time-consuming task. The chemical balance of the water has to be monitored carefully to make sure that it does not become fouled with algae or bacteria. Either of these will make the water smell and look unpleasant and can be a serious health hazard. The water must also be kept clear of debris such as fallen leaves and sticks, as these encourage fouling and become very slippery and dangerous as they start to decompose. Most people keep their pool either covered over or drained entirely during the months of the year in which it is not in use, as this is the easiest way to keep it sanitary (draining however can be a serious safety hazard with deeper pools and re-filling can be fairly expensive in areas where water is scarce). Public and competitive swimming pools are therefore often, especially in colder climates, indoor poolsovered with a roof and heatedo enable their use all year round.

Chlorine generators (salt systems)

Chlorine may be generated on site, such as in saltwater pools. A device from New Zealand, the Aquatech IG450 home pool saline chlorinator, was introduced to the residential swimming pool industry when the first commercially manufactured units for home use were shown at the 1973 Chicago Trade Fair. In the following years, many US, Australian and South African companies duplicated the device, as the process of creating chlorine from saline water - a process that occurs in nature when lightning strikes the ocean - was not patentable. This process generates chlorine by low-voltage electrolysis of dissolved salt (NaCl) using an electrode incorporated in the pool plumbing, eliminating the requirement of manually dosing the pool daily with powder chlorine. Chlorine generators avoid the need for constant handling of dangerous sanitizing chemicals, and can generate sanitizing power at a lower cost than equivalent chemicals, but they have a significant up-front cost for the apparatus and initial salting of the pool. Annual rainfall contributes to dilution of the pool water, which will require regular "topping up" with several 50Lb (20 kg) bags of salt for the average size pool.

Another issue is the production of equal amounts of sodium chloride and sodium hydroxide which causes the pool water pH to rise to levels that render the production of useful chlorine HOCl to levels as low as 15% while the balance of the chlorine produced converts to OCl. OCl still maintains some bactericidal properties, but is only effective in concentration of 25,000ppm, so in effect is useless. This dramatic swap occurs in water where the pH is exceeds 8.0. This renders the saline system less effective unless a close watch is kept on pH levels. Some saline units in production (2007) have incorporated an acid demand test, and the pH is maintained at the correct level by periodic shots of acid into the system. The downside of these units is the need to store large quantities of hydrochloric acid on the pool site which must be secured for safety if young children are present.

Modern units use around 2000 ppm to 4000 ppm and the salt cannot be detected by taste. Pool water that splashes and evaporates, such as on a pool deck, leaves a salt residue. Being closer to isotonic salinity (0.9%) than fresh water, saltwater pools have an easier feel on the eyes, and a touch typically characterized as "silky", not unlike bath salts. Nevertheless, due to the reactive nature of chlorine gas that comes off the salt chlorinator, salt chlorinated pools have been found to generate unacceptably high levels of carcinogenic disinfection byproducts, the predominant form being bromoform.

Ozone generators

Ozone use is becoming more prolific as a booster device that will reduce the requirement for Chlorine to be used in both commercial & residential swimming pools. Highly bacteriostatic, pools equipped with ozone units report a 75% reduction in chlorine demand. Ozone is short-lived, generally completely depleted within five minutes of introduction into the pool, but is highly effective in killing all unwanted pathogens in the water which passes through the unit. It is over 1000 times more effective at oxidizing bather waste than chlorine.

There are two basic types of ozone generators: UV bulb & Corona Discharge. In the UV bulb system, ambient air is drawn through a cylinder that contains a specific light wave emitting light bulb(s). The results are a longer lasting and more reliable form of ozone gas for residential pool and spa needs.

The Corona Discharge device is more effective, able to generate sufficient quantities of ozone gas for commercial uses. It is used in almost every bottled water facility in the United States to treat the water, as it leaves no residual chemical, heavy metal or aftertaste. Almost all of the water used to rinse & wash farm produce in the United States is also treated with ozone prior to coming into contact with food, again due to the lack of any residual effects.

High humidity (moisture/water) in the ambient air that is drawn into the CD generation chamber, will result in the formation of nitric acid, which will eventually corrode the CD "chip" rendering them inoperable after a relatively short time. This is not the case for UV Ozone systems as they are not affected by humidity. Higher end commercial systems include an "air dryer" which removes the moisture from the incoming air, thereby eliminating the potential for corrosion. The mid-range systems may utilize non-corrosive tubing, such as TPFE (teflon), to eliminate the corrosion potential.

Since there is no residual sanitizer left in the water after the ozone generator shuts off, a minute quantity of a halogen (e.g. chlorine, bromine, hydrogen peroxide) must be maintained in the water. Some ozone generators are designed to operate 24/7, thereby, further reducing the demand for a residual halogen.

Most mid-range ozone generators have a contact chamber, wherein the ozone in introduced into an off-line tank, where the water velocity has been reduced in order to increase the"contact time." Contact time is the amount of time the ozone is in direct contact with the pool water. From the contact chamber spent & excess ozone is vented into an "ozone destruct" unit. The destruct unit can be a simple activated carbon charcoal filter, or on the higher end units, an electronic active catalytic destruct.

In high quantities, ozone is hazardous to breathe. However, in most swimming pool applications, there is no residual ozone being returned to the swimming pool, as the "contact" occurred at the equipment pad. Additionally, no ozone is vented into the environment, as it is destroyed before being released.

Circuit treatment with ultrafiltration

For more details on this topic, see Ultrafiltration.

The polluted water will flow from the channel into the balance tank. The useful volume of the tank must be dimensioned such that the displacement and splash water can be stored. Storage of a certain backwash water quantity can be omitted to a great extent.

The circulating pump will suck the raw water out of the balance tank and will press it through the pre-filter and the ultrafiltration back into the basin. The pre-filter comprises one or several plastic filters with integrated automatic valves. The pre-filter serves to hold back any major or coarse pollutions which could damage or block the ultrafiltration membranes.

Injection of flocculating agent will for example be done upstream of the circulating pump in order to achieve optimum mixing of the flocculating agent. The rules and requirements for conventional gravel or multi layer filters are also valid for the flocculating agent injection.

The system will treat the water by means of ultrafiltration. The membranes are made of polyethersulfone hollow fibres, also called capillary membranes. These have pores in the size of < 0.05 m (in comparison: a human hair has a diameter of approx. 50 m 5000 times as much), this is so fine that neither bacteria nor viruses can pass the membrane. With this type of filtration the filter openings are so tiny that the water temperature or the viscosity respectively of the water plays a decisive role. The water leaving ultrafiltration is absolutely germ-free. All dissolved matters e.g. salts will remain in the filtrate.

The ultrafiltration modules of the treatment plant consist of several thousand hollow fibres which are placed orderly in a plastic pressure pipe. The ultrafiltration modules are arranged in parallel treatment lines.

The membrane modules are mounted compactly in a rack. The piping is executed in PVC. Pneumatic fittings guarantee automatic and safe operation.

A differential pressure measurement is foreseen for the transmembrane pressure and a volume flow measurement for the flow rate.

Backwashing will be done fully automatic in regular intervals. In addition, instead of the normal water backwashing, a chemical cleaning and disinfection with chlorine will be done regularly.

The filtrate of the ultrafiltration, e.g. a partial quantity, will be led over activated carbon in or-der to remove undesired dissolved matters such as bound chlorine and trihalogenmethanes. Further possibilities are dosing of activated carbon powder upstream of the ultrafiltration or a downstream UV system.

The water will be heated, the pH value will be adjusted to the set value and the water will be mixed with chlorine in order to reach the chlorine values as set out in German DIN 19643 or other similar rules and regulations.

The chlorinated water will be fed into the basin as treated water through the inlet system.

Sphagnum Moss

Sphagnum moss is used as an environmentally-friendly alternative to chlorine in swimming pool sanitation. The moss inhibits the growth of microbes and reduces or eliminates the need for chlorine in swimming pools.

Use of UV

Ultraviolet light technology can assist the primary sanitizer in providing an additional layer of protection against potentially harmful organisms like bacteria, viruses, cysts and protozoa. A UV system improves bather safety from chlorine-resistant organisms such as cryptosporidium and giardia. Passing through the unit, contaminated water is exposed to the UV light, disrupting the genetic material within the cell and rendering it inactive. A UV system will not affect the balance of the pool and reduces the amount of chloramines within the water, allowing the residual chlorine to work more effectively. There are units available for traditional chlorine pools only and ones that can be installed in pools equipped with saline generators.

Biguanides

Other more recent sanitizers have also been introduced as of the early 1990s and are referenced as Biguanides. Biguanides were originally developed for the medical industry and utilize the polymer PHMB (polyhexamethylene biguanide). Biguanides are generally less harsh and more stable in the pool water, but are also more expensive and require the periodic addition of extra strength hydrogen peroxide and can react very harshly with chlorine or other sanitizers.

See also

Filter (water)

Waterborne diseases

Water purification

References

^ "Guidelines for safe recreational waters". who.int. World Health Organization. 2006. http://www.who.int/water_sanitation_health/bathing/bathing2/en/. Retrieved 2 December 2009. 

^ "Healthy Swimming". cdc.gov. Centers for Disease Control and Prevention. 30 November 2009. http://www.cdc.gov/healthyswimming/index.htm. Retrieved 2 December 2009. 

^ Types of Filters

^ National Center for Environmental Health: Healthy Housing Reference Manual - Residential Pool and Spa Filters

^ Podewils LJ, Zanardi Blevins L, Hagenbuch M, et al. (July 2007). "Outbreak of norovirus illness associated with a swimming pool". Epidemiol Infect. 135 (5): 82733. doi:10.1017/S0950268806007370. PMID 17076938. 

^ "Prevalence of parasites in fecal material from chlorinated swimming poolsnited States, 1999". MMWR Morb Mortal Wkly Rep. 50 (20): 4102. May 2001. PMID 11400955. http://www.cdc.gov/MMWR/PREVIEW/MMWRHTML/mm5020a4.htm. 

^ Totkov A, Klobusick M, Valent M, Tirjakov E (September 1994). "[Helminth and protozoan findings in the water of school swimming pools]" (in Slovak). Epidemiol Mikrobiol Imunol 43 (3): 1306. PMID 7953088. 

^ Service de Parasitologie et Mycologie medicales, Faculte de Medecine et Centre hospitalier universitaire d'Amiens, Universite de Picardie Jules Vemrne, 80054 Amiens, France. raccurt.christian@chu-amiens.Fr

^ Crypto Facts | CDC Healthy Swimming

^ Verma, M.; Ghaly, A.E. (2008). "Treatment of Remazol Brilliant Blue Dye Effluent by Advanced Photo Oxidation Process in TiO2/UV and H2O2/UV reactors". American Journal of Engineering and Applied Sciences 1 (3): 230-240. http://www.scipub.org/fulltext/ajeas/ajeas13230-240.pdf. 

^ CDC Healthy Swimming: Chlorine and pH

^ http://www.silsens.ch/pdf/SILSENS_Chlorine_Info_v02.pdf

^ Moss Proving An Alternative To Chlorine In Pools. WCCO. 15 Aug. 2008.

^ Hill, Catey. Time to fire the pool boy? Moss helps pools stay clean. Daily News. 29 Oct. 2009.

External links

ICS 13.060.01 Water quality in general - A series of ISO standards

ICS 07.100.20 Microbiology of water

The Association of Pool & Spa Professionals (APSP) - leading trade association of the pool/spa and hot tub industry

Pool and Spa water treatment software using the APSP tech manual recommendations

UltraPure Water Quality, Inc. - The industry leader for Residential Pool & Spa Ozone Generators

Categories: Water treatment | Water technologyHidden categories: Articles lacking reliable references from January 2008 | Wikipedia articles that are too technical
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