Bath water treatment
To treat water for a swimming pool , the water goes through various stages of purification to remove dirt and bacteria.
In addition to the chemical engineering processes, there are also natural treatments in swimming ponds , but these are not suitable for meeting the requirements of German DIN 19643 (treatment of swimming and bathing pool water).
A distinction is made between private and public pools . According to DIN 19643 Part 1 Paragraph 1, only single-family bathrooms are considered private. All others, including baths owned by house communities, are public baths.
Chlorine smell as an indicator
Chlorine as a disinfectant in bath water is odorless. The typical indoor pool smell comes from the bound chlorine, the so-called chloramine . Urea, creatinine, amino acids and other nitrogenous compounds, which primarily come from sweat and urine, react chemically with the chlorine dissolved in the pool water. Approx. 95% of the urea content is brought into the water through urine. Approximately 25 to 30 ml urine is expected per bather. 40 bathers release about as much urea through their skin as a person urinating in water.
A 400,000 liter basin (20 m by 10 m by 2 m basin) contains around 26.5 liters of urea. Showering beforehand removes up to 97% of the skin's urea.
conditions
In Germany, the principle of the Infection Protection Act applies , according to which swimming or bathing pool water in public facilities must be of such a nature that there is no risk of damage to human health , in particular from pathogens . In the absence of further legal provisions, DIN 19643 is used as a subordinate regulation. The standard differentiates between microbiological, chemical and physical requirements.
In Switzerland, the requirements for swimming or bathing pool water are defined in SIA 385/9, in Austria there is ÖNORM M 6215.
Microbiological requirements
| Pure water | Pool water | |
|---|---|---|
| CFU (Colony Forming Units) | Limit value: 20 CFU / ml | Limit value: 100 CFU / ml |
| E. coli | not detectable in 100 ml | not detectable in 100 ml |
| Pseudomonas aeruginosa | not detectable in 100 ml | not detectable in 100 ml |
| Legionella pneumophila | not detectable in 100 ml | not detectable in 1 ml |
Chemical and physical requirements
The following table is an extract from the standard.
| PH value | 6.5 to 7.2 (with flocculation with Al or Al-Fe products) |
| Nitrate concentration in difference to the filling water | ≤ 20 mg / l |
| free chlorine | 0.3 to 0.6 mg / l (hot tub 0.7 to 1.0 mg / l) |
| combined chlorine | maximum 0.2 mg / l |
| clarity | perfect view of the entire pool floor |
| Oxidisability above the value of the fill water | maximum 0.75 mg / l |
Cleaning stages
First, the water runs out of the basin via the overflow channel and flows into a raw water reservoir , from which it is pumped out again as raw water with the help of a circulation pump.
A flocculant is inoculated into this raw water , which binds dirt particles so that they can be filtered out more easily. In addition, with the flocculation, the phosphate , which algae need for their growth, is retained in the filter as poorly soluble aluminum or iron phosphate, thus preventing algae growth. The raw water then flows through one or more filters. Gravel, sand and hydroanthracite, for example, can serve as filter material.
The wastewater from the filter rinsing can be processed by a rinsing wastewater treatment so that it can be returned to the circuit as fill water.
The water, now referred to as the filtrate, is now disinfected; this is done by means of chlorination with chlorine gas , sodium hypochlorite or calcium hypochlorite in order to achieve a depot effect in the swimming pool. After adding chlorine, the filtrate is called pure water.
Additional process steps are required to reduce bound chlorine and trihalomethanes. Bound chlorine can be broken down using an activated carbon filter, UV lamp or powdered charcoal metering.
The pH value is then regulated. According to DIN 19643, this should be at least pH 6.5, the upper value depends on whether and which flocculants are used and whether it is sea or fresh water . A partial flow of the water flows through the heat exchanger before chlorination , where it is heated. The water can be heated in different ways. For example, this can take place by means of a direct-flow boiler without additional heat exchangers and pumps. At higher powers the direct flow to boilers in cascade are provided. The now heated water flows back into the water circuit via a return and mixes with the water flowing there. As pure water, it now flows into the swimming pool via inlet nozzles. The water cycle now starts all over again.
The water quality is monitored using chemical and physical parameters. These are the content of freely effective chlorine, bound chlorine , the redox voltage and the pH value. Pool water is taken from a measuring water pipe and flows through an automated measuring and control unit. In this measuring and control unit there are measuring electrodes whose output values are transmitted to a control computer. This control unit controls the servomotors. Here, the chlorine flow rate is automatically increased or decreased as required.
Chlorination
Chlorine gas is delivered in gray steel gas cylinders (with 65 kg content) or chlorine barrels (with 500 kg or 1000 kg). This leaves the bottle via a vacuum regulator and the dosing regulator . It is mixed with the filtrate water from the treatment process via an injector nozzle. The water pressure of approx. 5 bar required for the injection is generated by a pressure booster pump. The dosing controller regulates the amount of chlorine gas required.
Other common types of chlorination are the dosage of sodium hypochlorite , also known as sodium hypochlorite , from commercially available containers, or produced on site from sodium chloride using an electrolysis system. Granulated calcium hypochlorite is also dissolved and metered in via metering pumps. In-situ electrolysis is a new process. A salt content of around 1% is kept in the circuit and free chlorine is generated via electrodes as required.
The German DIN 19643 in Germany requires between 0.3 and 0.6 mg / l (hot spring pool 0.7-1.0 mg / l) of free chlorine in pool water.
In Switzerland, the chlorine values are between 0.2 and 0.8 mg / l (hot tub 0.7-1.5 mg / l) according to SIA 385/9.
In Austria, ÖNORM M 6215 specifies the following values from pH 6.5 to 7.4 at least 0.3 mg / l free chlorine, from pH 7.4 to 7.8 at least 0.5 mg / l, with a maximum concentration of 1.2 mg / l for indoor pools and 2.0 mg / l for outdoor pools.
For comparison: For the safe disinfection of drinking water, the WHO requires a chlorine value of ≥ 0.5 mg / l to a maximum of 5.0 mg / l, with a minimum chlorine content of 0.2 mg / l for the consumer.
Load capacity factor
The load capacity factor, known as the k-value, provides information on the efficiency of the treatment process in bathers per treated cubic meter of pure water.
In the ozone process, the k-value is 0.6 · 1 / m³. With the sand or multi-layer filter, a k-value of 0.5 · 1 / m³ is calculated, which corresponds to 2 m³ of pure water per bather. A k value of 1.0 x 1 / m³ is given for ultrafiltration.
Water treatment with ozone
Benefits
A bath water treatment process that has been tried and tested for decades, but which causes higher investment costs, is a process with an ozone stage . Apart from ultrafiltration, it is the only process that is considered suitable in Germany for treating water for therapy pools.
effect
Ozone removes the precursors that form disinfection by-products (DNP) such as chloramines and trihalomethanes . “Indoor pool odor” caused by chloramines does not exist in pools with ozone levels. The so-called indoor pool smell cannot be completely ruled out due to the retention time in the pool, as the urea or ammonia decomposition already takes place in the pool. As soon as the hypochlorous acid of the disinfectant reacts with the compound, the odor nuisance occurs.
There is no limit value for the nitrate content in the pool water in a treatment process with an integrated ozone stage, as the ozone forms nitrogen oxides through reaction with atmospheric nitrogen , which in turn form nitrates in the pool water and compliance with the nitrate limit value in the water is therefore not possible.
Procedure
Unused ozone decomposes relatively quickly without residue and without the formation of disruptive side reaction products. The values for pool water treatment with ozone are specified in DIN 19643 Part 3. According to DIN 19643 Part 3, the water to be treated is mixed with ozone after a pre-filtration of the water through a sand or multi-layer filter. The water is then passed through an activated carbon filter , whereby the residual ozone content is removed. In the method according to DIN 19643 Part 3, Variants C and D, the function of the prefilter is coupled with the sorption filtration by an additional pumice coating on the activated carbon layer.
dosage
When treating pool water at normal temperature, a chlorine value between 0.3 and 0.6 mg / l free chlorine should be set in the pool water. If the water is treated with ozone, the value may be between 0.2 and 0.5 mg / l. Ozone may only be present in the pool water up to a maximum of 0.05 mg / l.
Additional oxidation
Treating bathing water with ozone in an additional oxidation stage is recommended wherever many people bathe with different defenses. This is why ozone levels can be found in hospitals and special schools in particular, where many therapy and exercise pools are operated, but also in many modern leisure pools and higher-category hotels.
DIN 19643 prescribes a procedure with ozone for therapy pools; such a procedure is recommended for exercise pools.
Ozone generation and introduction
In swimming pools, dried air is used to produce ozone. The air flows through a macroporous drying material that has to be regularly regenerated by heating. The ozone is generated in ozone generating elements with three coaxially arranged tubes. The inner metal tube is the high-voltage electrode, the outer metal tube is the grounded opposite pole, the glass tube in between serves as a dielectric . With a high voltage of up to 15 kV, the oxygen molecules are dissociated into oxygen atoms by a silent electrical discharge , some of which then combine to form ozone. For this, including air drying, around 20 Wh / g ozone is required.
The transport of the ozone-air mixture to the injector takes place under negative pressure, so that an ozone outbreak is excluded. Thick-walled PVC and stainless steel have proven themselves as piping materials.
The ozone is introduced into the water by a liquid jet pump . To operate the injector, water is taken from the filtrate line and brought to around 2 bar using a booster pump. The injector sucks in the ozone-air mixture through the negative pressure generated and mixes it with the water. The air-water mixture is introduced into the raw water line in front of the reaction vessel.
Other water additives
Private pools
In the private swimming pool can u. Under certain circumstances, further chemicals can be dispensed with entirely, especially if the circulation capacity and the pH value are maintained. Additional disinfectants may be required depending on the frequency of use, dirt entry from the environment and lighting conditions. A sand filter is often used as a filter in private pools to mechanically pre-filter small dirt particles with a size of around 20 to 120 µm. If chlorine is not used, a sand filter can also have a biological filter effect, as a microbial coating then forms on the sand grains. As an alternative to (quartz) sand in a sand filter system, so-called " filter balls" can also be used.
Public pools
In public areas, due to the high frequency of bathers, at least 0.3 mg / l of chlorine must be added for a depot effect, even if an ozone level is in operation. Since ozone is poisonous, it may only have a maximum concentration of 0.05 mg / l in drinking and bathing pool water. A sufficient depot effect in the bath water is not possible with this concentration. The ozone has a strong oxidizing effect and thereby destroys all biological substances in water, deactivates viruses and oxidizes metals contained in water.
Ultrafiltration
The ultrafiltration (UF) in the swimming pool is a relatively new procedure. The first system was put into operation in 2002 in Bad Steben. In the meantime, more than 200 (as of 12/2012) additional UF systems with outputs of up to 800 m³ / h are in operation. The currently largest systems are in the Bad Aibling thermal baths with five circuits with a total of 800 m³ / h circulation capacity. Most of the UF systems are designed with a k-factor of 1.0, i.e. H. half the amount circulated is enough to maintain the water quality in the pool. The revised DIN 19643 was published in 2012 and ultrafiltration was included as part 4.
Process description
The bathed water flows from the channel into the raw water storage tank. The useful volume of the storage tank must be dimensioned so that the displacement and surge water can be absorbed. There is largely no need to store a quantity of flushing water.
The circulation pump sucks the raw water out of the storage tank and pushes it back into the basin through the pre-filter and ultrafiltration. The pre-filter consists of one or more plastic filters with built-in automatic valves . The purpose of the pre-filter is to hold back any coarse contamination that can damage or clog the ultrafiltration membranes.
The flocculant is added either before or after the circulation pump. The injection point must be at least 10 m in front of the filter so that the flocculant has time to react and to achieve optimal mixing of the flocculant. For the addition of flocculants, the same rules and regulations apply as for conventional gravel or multilayer filters.
The ultrafiltration membranes consist of polyethersulfone hollow fibers and are called capillary membranes. These have pores in the range smaller than 50 nm. This is so fine that neither bacteria nor viruses can pass through the membrane. With this type of filtration, the filter openings are so small that the water temperature and thus the viscosity of the water play a very important role. The water that leaves the ultrafiltration is absolutely sterile. Dissolved substances such as B. Salts are retained in the filtrate. Ultrafiltration is carried out in dead-end filtration in swimming pools .
The ultrafiltration modules of the processing plant consist of several thousand hollow fibers that are neatly housed in a plastic pressure pipe. The ultrafiltration modules are arranged in parallel in streets. For flushing, the filtrate from one or more lines can be used to flush another line, or a flushing pump and an external flushing water tank are used. The rinsing takes place fully automatically at regular intervals of around 2 to 4 hours. Instead of normal water rinsing, chemical cleaning and disinfection with chlorine is carried out regularly .
The membrane modules are mounted on a frame. Pneumatic fittings ensure automatic operation.
A differential pressure measurement for the transmembrane pressure and a volume flow measurement for the flow rate are normally provided as measurements .
The filtrate from the ultrafiltration is passed in a partial flow over activated carbon in order to remove unwanted dissolved substances such as bound chlorine and trihalomethanes. Further options are the addition of powder activated carbon before the ultrafiltration or a UV system afterwards.
Precoat filtration
The precoat filtration process is described in DIN 19624. The water is conveyed through a layer of diatomite , perlite or cellulose a few millimeters thick . B. was washed ashore on a fabric-related filter candle or filter plate. This layer takes over the actual filtration.
Powdered activated carbon is also added to break down bound chlorine and trihalomethanes. The powdered activated carbon is only added according to the needs of the swimming pool, depending on the water values. The addition of flocculants is not necessary in this process, but it is possible.
Different variants are built. In the pressure variant, the water is pressed through the filtration layer in closed steel containers. With the suction variant, the water is sucked through the filtration layer in open or closed containers made of steel or plastic.
With precoat filtration, there is no rinsing as with other filter systems. With pressure precoat filters, the direction of flow is regularly reversed and the filtration layer with the dirt, the so-called filter cake, is blown off the fabric. The vacuum precoat filters are cleaned with a hose or a cleaning device. Vacuum precoat filters do not require any backwashing water or a backwashing water reservoir. The water requirement is therefore low.
After cleaning, there is a new coating with diatomite, perlite or cellulose. The filter cake remains in the filter until it is cleaned at regular intervals.
Precoat filters are also used in wine and beer filtration .
Web links
- Pool magazine online - background knowledge and specialist articles on water treatment in swimming pools, published by the Bundesverband Schwimmbad & Wellness e. V.
- FIGAWA worksheet: Ultrafiltration in the circulation treatment of swimming and bathing pool water
- FIGAWA worksheet: Use of UV devices for swimming and bathing pool water treatment
Individual evidence
- ↑ Wolfgang Legrum: Fragrances, between stink and fragrance , Vieweg + Teubner Verlag (2011) p. 163− # 164, ISBN 978-3-8348-1245-2 .
- ↑ Garmisch-Partenkirchen Health Department .
- ^ BR Knowledge: What the disgusting smell of chlorine in the outdoor pool reveals (Video 1,1 ')
- ↑ Hygiene Institute of the Ruhr Area: The new DIN 19643 ( Memento of the original from June 12, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.8 MB).
- ↑ Guidelines for Drinking-water Quality Third Edition incorporating the first and second addenda Volume 1 Recommendations Geneva 2008.
- ↑ Dirk Lindemann: Mathematics for the pool area: Basics and applications for schools and businesses . Litho-Verlag, Wolfhagen 2014, ISBN 978-3-941484-07-8 ( limited preview in Google book search).
- ↑ Extract from DIN 19643 .
- ↑ Teichbau-Profi.de: Explanations on sand filters for private swimming pools .
- ↑ The filter balls for pool sand filter systems as a replacement for filter sand / glass. In: pool information. December 21, 2017, accessed June 3, 2019 (German).
