case study swiming pool

8/13/2019 Case Study Swiming Pool

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Swimming pool water disinfection

Case study


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Introduction

When going to the swimming pool are you thinking about water purification method there and

how water quality can affect your health?

Swimming pool situated in London is the object of current case study. Swimmers have

complained about skin and eye irritation and chlorine smell after bathing. Pipe corrosion is an

increasing problem. Pool workers have more sick leaves due to breathing problems. Average

number of bathers is 700 per day. Water is circulated continuously between 6am and 7pm. Three

pools (main, outdoor and pool for teaching) were constructed according one scheme with the

only difference in pool size, scheme is presented in figure 1. Pool specification is presented in

table 1.

Figure 1. Scheme of main, outdoor and teaching pools [1]

Table 1. Swimming pool specification

Main pool (indoor), size: 25 x 13 m

Capacity 490 m3

Duty 198 m3/h

Outdoor pool, size: 2 x 10 m + free form

Capacity 312 m3

Duty 243 m3/h

Teaching pool (indoor), size: 13 x 7 m

Capacity 68 + 6 m3

Duty 105 m3/h


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Table 1. Swimming pool specification

Water treatment

Primary filtration Sand filters

Primary chemical treatment

Disinfection Chlorine gas

pH Control Soda ash

Flocculation Polyaluminium chloride

As it can be seen from the table, water disinfection method is chlorination for main pool, outdoor

pool and teaching pool. Chlorination is the most common method for swimming pool water

treatment due to low costs and quite high efficiency [2]. However, this method has few important

drawbacks such as carcinogenic by-products formation (trihalomethanes, haloacetic acids, etc.).

Formation of trihalomethanes (THMs) in water depends on amount of organic matter in water,

pH, temperature, contact time between water and chlorine, presence of bromide in source water.

Chloroform (CHCl3), bromdichloromethane (CHCl2Br), dibromochloromethane (CHClBr2) and

bromoform (CHBr3) constitute THMs. According to USEPA among these only CHClBr2 is

probable human carcinogen (type C), others are human carcinogens (type B2) [2].

Chloroform which was used in the past for medical purposes (anesthesia) basically caused death

followed by respiratory and cardiac arrhythmias [3]. Those patients who could survive after

chloroform induced anesthesia had other symptoms such as nausea, vomiting, prostration,

jaundice, coma, etc. It was reported that mean lethal oral dose of chloroform for an adult is about

45g however serious health problems can be caused by digestion of 7.5g [3].

Bromoform was used in the past as a sedative for children who suffered from whooping cough.

Bromoform overdosing has lead to several fatal cases. Dwell described the death of 2 years and 9

month girl suffered from whooping cough due to overdosing of bromoform (bromoform

concentration was 445 mg/kg/day and exposure time 1day). [4]

Dibromochloromethane and bromdichloromethane were not sufficiently studied. However there

are some information concerning acute toxicity of dibromochloromethane, it was defined that

LD50 (oral) for rats is 370 mg/kg [5].


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Swimming pool water contaminated by THMs is especially dangerous for swimmers. It was

reported that level at which people would be exposed to THMs during 1h in the pool is 141 times

than having shower for 10 min under tap water [2]. Currently maximum permissible

concentration for THMs in swimming pools does not exist. However, there are some defined

Maximum Contaminant Levels (MCLs) for chlorination by-products including total THMs in tap

water; for instance, WHO published that concentration of these compounds should not be higher

than 100g/Land the Maximum Contamination Levels Goal (MCLG) for THMs in water is less

than 40g/L [2].

Some attempts were made to evaluate level of THMs concentration in swimming pools in

different countries. Thus 114 residential swimming pools in the USA were examined by Sandel

and it was found that mean chloroform concentration was 67.1g/L with maximum level313g/L.According to the WHO investigations level of chloroform in the USA pools was 4-

420g/L [2]. Italian swimming pools THMs pollution level was reported to be 17.8 - 70.8g/L.

According to Chu and Nieuwenhuijsen concentration of total THMs in Londons pools is

125.2g/L and chloroform concentration is 113.3g/L. Linear correlation was defined between

number of people in the pool and THMs concentration in water. More data concerning THMs

concentration in indoor swimming pool water in various countries is represented in table 2. [6]

Table 2. THMs concentration measured in swimming pool water [6]

CountryTrihalomethanes concentration, g/L

Chloroform Bromoform Bromodichloromethane Dibromochloromethane

Poland 35.9-99.7 0.2-203.2 2.3-14.7 0.2-0.8

Italy

25-43 0.1 1.8-2.8 0.5-10

9-179

19-94

USA

4-402


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water intake is higher than that for adult women and constitute 22 ml while for women it is only

12 ml. For boys water intake is also higher (45 ml) than that for girls (30 ml). [6]

However contaminated water is not the only problem associated with THMs. Another important

point is that THMs are volatile compounds and they can be found in the air above the indoor

pools. Basically concentration of THMs in the air of the swimming pool depends on the

concentration in water, temperature, amount of splashing, ventilation system, etc. Data

represented in table 3 gives an idea about THMs concentration level in the air of indoor

swimming pools.

Table 3. THMs concentration in the air above the swimming pool water surface [6]

Country Trihalomethanes concentration, g/m

3

Chloroform Bromoform Bromdichloromethane DibromochloromethaneCanada 597-1630

Italy

66-650 5-1000 0.1-14

49-280 2-58 4-30

39-195 16-24 9-14

USA


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THMs are considered as one of the most dangerous contaminants in bathing water however it is

necessary to consider other pollutants as well. Possible sources of swimming pool water

contamination and some examples of pollutant are presented in figure 2.

Figure 2. Possible sources of swimming pool water contamination

Most obvious problem for swimmers and pool workers is caused by chloramines as they are the

source of chlorine odor. They induce skin, eye and lung irritation and are a big risk factor for

occupational asthma. They are formed when too small amount of chlorine is added to water.

Chloramines are products of free chlorine and nitrogen derived from urine and sweat. [7, 8]

THM measurements

As a response to swimmers complaints, some studies were carried out recently in all pools and

concentration of THMs was measured in the water and in the ambient air 25 cm above the water

surface, data presented in table 5 and 6.

Table 5. Mean THMs concentration in the water of swimming pools, g/L

Pool name Chloroform Bromoform Bromdichloromethane Dibromochloromethane

Main pool 150.2 1.5 15.6 4.8Outdoor 215.6 8.6 5.4 125.8

Teaching 138.8 14.3 20.2 15.5

Table 6. Mean THMs concentration in the ambient air of the swimming pools, g/L

Pool name Chloroform Bromoform Bromdichloromethane Dibromochloromethane

Main pool 215.4 0.5 46.2 19.5

Outdoor 5.1 0.9 0.1 0.6

Teaching 187.5 35.7 36.8 42.7

Results of studies show that THMs concentration in pools water and ambient air is quite high

which could be risky for bathers. Thus acute problem of water treatment technique should be


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solved. Main engineer of the swimming pool should decide if it is reasonable to change water

purification system. There are several commonly used methods for water disinfection to choose

from.

Chlorine disinfection

It is well known that chlorination is widely used for wastewater disinfection since 1914, when it

was applied first time for this purpose in the USA [9]. There are few main components used for

chlorination: chlorine, sodium hypochlorite, calcium hypochlorite and chlorine dioxide. Recently

quite many water treatment plants started to use sodium hypochlorite instead of chlorine due to

safety concern (handling and storage of hypochlorite is much more easy).

Solubility of chlorine in water is moderate. Chlorine is considered to be highly toxic componentand it could be dangerous for treatment plant workers and for public in case if it accidentally

released. By-products of chlorination are known as carcinogens and mutagens, residual chlorine

in water after disinfection is toxic for aquatic life. [9]

Sodium hypochlorite used instead of chlorine allows to avoid many problems related to

transportation, storage and feeding. It is usually presented as a liquid with 12.5 to 17 % available

chlorine at the moment of manufacture. One of the main disadvantages is that solution

decomposition is affected by high temperature and light. For instance solution (16.7%) stored at

26.7C lose 10% in 10 days. Another drawback is relatively high cost. During handling it can

cause some problems because of chlorine fumes presence and corrosiveness. [9]

Some remarks:

Very effective as both primary and secondary disinfectant; Cheap chemical (equipment (piping etc.) maintenance does increase disinfection cost); Easily measurable by residual chlorine; Residual disinfection effect; Harmful byproducts, which cause skin, eye and lung irritation; Chlorine gas is toxic (high risk for workers).

Ozone disinfectionDue to short life of ozone molecule it is not delivered to target unit (in this case swimming pool),

but is produced on site, usually with a high voltage corona discharge or vacuum ultraviolet ozone

generator. Thus safety problem associated with shipping and handling are diminished. Like


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chlorine, ozone is a strong oxidizing agent. It is effective against viruses and bacteria. Ozone has

very short half-life, so there are not residuals to be removed after ozonation.

There is a certain risk of pool operators to be exposed to ozone due to e.g. leakage. Even very

low concentrations of ozone can be harmful to the upper respiratory tract and the lungs. The

severity of injury depends on both by the concentration of ozone and the duration of exposure.

Some remarks:

No harmful residuals; Short contact time; No regrowth of microorganisms; Complex disinfection system; Very corrosive; Toxic; Relatively high cost; No measurable residual to indicate the efficacy of disinfection. [10, 11]

UV disinfection

On contrary to chlorination and ozonation UV disinfection is a physical disinfection method. As

ozone treatment, ultraviolet will not leave any residuals in water. UV radiation will inactivate

any organism in water, there are no resistant species. Inactivation rate is proportional to UV

dose.

UV radiation causes DNA base thymine dimerization, which leads to inactivation of organism.

Most effective wavelength is somewhere between 260-270 nm [12]. Also production of ozone

and hydroxyl radicals occurs, when wavelength is lower than 200 nm. These compounds are

germicidal, but may cause health issues if people are exposed. A typical low pressure Hg-lampproduces wavelengths around 254 nm - possibly bit off the target. Medium pressure Hg-lamp

produces multiple wavelengths, which might be waste of energy. LEDs can produce any narrow

band of wavelength. UV-lamps contain toxic mercury. This harm could be avoided with UV-

LED systems as they arrive to the markets. At present mostly visible LEDs are used and

probably in near future they will totally replace traditional incandescent and fluorescent lamps.

There are no commercial applications using UV LEDs yet, however extensive research is taking

place at the moment and probably it will be a major green water disinfection method.

Some remarks:


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No byproduct formation (no smell or health effects); No risk of overdosing; No resistance; Easy to operate; Turbidity of water can drastically reduce the disinfection effectivity: prefiltering needed

(as applied with chlorination and ozonation methods);

Some microorganisms may be able to repair damage caused by UV-radiation, when theyare exposed to visible light shortly after the ultraviolet treatment: photoreactivation;

There is no significant residual disinfection, so additional disinfection (e.g. small amountof chlorine) possibly needed;

No means for measuring efficiency in various water conditions; No standardized mechanism to measure, calibrate and certify equipment for efficiency

before and after installation;

Lamps contain toxic mercury and are not that durable [13]In tables 7, 8 and 9 disinfection efficiency of UV radiation is presented.

Table 7. UV-doses (253.7 nm) required for inactivation of different microorganisms [14]

Microorganism Log reduction mWs/cm2

Bacillus subtilis3 20-40

4 60-90MS-2 4 87

Hepatitis A 3 30

Rotavirus 4 40

Giardia lambliacysts1 40

2 180

Table 8. Average log reduction of microorganisms using combined carbon block filter with

ultraviolet disinfection unit (>128 mWs/cm2 / 253.7 nm) [15]

Microorganism Log reduction

Poliovirus 4.28

Rotavirus 4.29

HAV 3.92

MS-2 6

Giardia lambila cysts 3.99

Cryptosporidium parvum 4.3

Vibrio cholerae 5.96

Shigella dysenteriae 6.7

Escherichia coli 6.3

Salmonella typhi 6.52


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Table 9. UV-doses required for inactivation of different microorganisms [15]


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Comparison of disinfection methods (effectiveness and cost)

Every disinfection technique has its specific advantages and disadvantages. In the table 10 some

of these are shown. By-products of discussed methods are presented in table 11.

Table 10. Advantages and disadvantages of different methods [16]

Technology

Friendliness

to the

environment

By-

products

formation

Efficiency InvestmentOperational

costsFluids Surfaces

Ozonation + + ++ - + ++ ++

UV* ++ ++ + +/- ++ + ++

Chlorination:

Chlorine gas -- -- - + ++ +/- --

Chlorine

dioxide+/- +/- ++ ++ + ++ --

Hypochlorite -- -- - + ++ +/- --

* Hg-lamps evaluated. Operational costs with LED-lamps should decrease as the energy demand of LEDs is minimal compared

to Hg-lamps. Investment costs on the contrary would be higher due to new technique and more difficult manufacture.

Table 11. Predominant chemical disinfectants used in pool water treatment and their

associated disinfection by-products [6]

Disinfectant Disinfection by-products

Chlorine/hypochlorite trihalomethaneshaloacetic acids

haloacetonitriles

haloketones

chloral hydrate (trichloroacetaldehyde)

chloropicrin (trichloronitromethane)

cyanogens chloride

chlorate

chloramines

Ozone bromate

aldehydes

ketones

ketoacids

carboxylic acids

bromoform

brominated acetic acids

Chlorine dioxide chlorite

chlorate

Bromine/hypochlorite

BCDMH

trihalomethanes, mainly bromoform

bromal hydrate

bromamines

*UV is generally not considered to produce by/products


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Comparative efficiency of considered water disinfection methods are presented in figure 3.

Figure 3. Comparison of water disinfection methods[17]

Estimated total production costs of different disinfection methods according to US

Environmental Protection Agency (USEPA) are presented in table 12. The disinfection facilities

are categorized to 5 classes based on the designed water flow through the facility.


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Table 12. Cost comparison of different disinfection methods [14]

Total production costs ($cents/m3)

USEPA Flow

Category

Design Flow

m3/d

UV dose

40 mJ/cm2

Chlorination dose

5 mg/l

Ozonation dose

1 mg/l

UV dose

140

mJ/cm2

1 91 5 75 93 72 329 2 18 26 5

3 1022 1 6 9 4

4 2461 1 5 6 3

5 6814 1 2 2 3

Task

Results of studies show that THMs concentration in pools water and ambient air is quite high

which could be risky for bathers. Thus acute problem of water treatment technique should be

solved. Main engineer of the swimming pool should decide if it is reasonable to change water

purification system. Final decision should based on economical calculations (investment and

daily expenses), advantages and drawbacks of chosen method, also environmental issues (waste

utilization, etc.) should be considered for all possible pools water treatment methods.

Take the role of main engineer, discuss about following points:

Which disinfection method would be economically most profitable? Which disinfection method would be most environmentally friendly? Which method would have least health issues (swimmer / poolside worker / machine

operator)?

Decide if it is reasonable to change the disinfection system! Which of the alternative methods would be best for the situation? Reason your decision!


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References:

[1] How swimming pools work. Document available at:

http://home.howstuffworks.com/swimming-pool.htmDate of access: 4.01.2012

[2] Panyakapo Mallika, Soontornchai Sarisak, Paopuree Pongsri. Cancer risk assessmentfromexposure to trihalomethanes in tap water and swimming pool water. Journal of

Environmental Sciences 20(2008), p.372-378

[3] Concise International Chemical Assessment Document 58. Chloroform. WHO. 2004.

Document available at: http://www.who.int/ipcs/publications/cicad/en/cicad58.pdf. Date of

access: 22.12.2011

[4] BROMOFORM AND DIBROMOCHLOROMETHANE. Document available at:

http://www.atsdr.cdc.gov/toxprofiles/tp130-c3.pdf Date of access: 12.12.2011

[5] Material Safety Data Sheet. Dibromochloromethane. Document available at:http://www.sigmaaldrich.com/catalog/DisplayMSDSContent.do SIGMA-ALDRICH. Date of

access: 19.12.2011

[6] Guidelines for Safe Recreational-water Environments. Vol.2: Swimming Pools, Spas and

Similar Recreational-water Environments. WHO, 2006. ISBN 92 4 154680 8

[7] Thickett, K.M., McCoach, J.S., Gerber, J.M., Sadhra, S. and Burge, P.S. Occupationalasthma caused by chloramines in indoor swimming-pool air. Eur Respir J 2002 19(5)827-32

[8] Jacobs J.H., Spaan, S., van Rooy, G.B.G.J., Meliefste, C., Zaat, V.A.C., Rooyackers, J.M.and Heederik, D., Exposure to trichloramine and respiratory symptoms in indoor swimming poolworkers, Eur Respir J 2007 29(4)690-698

[9] George Tchobanoglous, Franklin Louis Burton, H. David Stensel, Metcalf & Eddy.

Wastewater Engineering. Treatment and Reuse. MgGraw-Hill, 4thedition, 2002 ISBN: 978-

0070418783

[10] Health Effects of Ozone. Article available at:

(http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ozone/health_ozo.html)Date of

access: 04.01.2012

[11] National Environmental Services Center, Tech Brief Fact Sheet: Ozone Disinfection.

Available at:http://www.nesc.wvu.edu/techbrief.cfm Date of access: 8.01.2012

[12] Chen,R., Craik, S. and Bolton, J., Comparison of the action spectra and relative DNAabsorbance spectra of microorganisms: Information important for the determination of

germicidal fluence (UV dose) in an ultraviolet disinfection of water, Water Research 2009

43(20)5087-5096

[13]National Environmental Services Center, Tech Brief Fact Sheet: Ultraviolet Disinfection.Available at: http://www.nesc.wvu.edu/techbrief.cfm Date of access: 10.01.2012

[14]USEPA 1997, Small System Compliance Technology List for the Surface Water TreatmentRule EPA 815-R-97-002
http://home.howstuffworks.com/swimming-pool.htmhttp://home.howstuffworks.com/swimming-pool.htmhttp://www.atsdr.cdc.gov/toxprofiles/tp130-c3.pdfhttp://www.atsdr.cdc.gov/toxprofiles/tp130-c3.pdfhttp://www.sigmaaldrich.com/catalog/DisplayMSDSContent.dohttp://www.sigmaaldrich.com/catalog/DisplayMSDSContent.dohttp://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ozone/health_ozo.htmlhttp://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ozone/health_ozo.htmlhttp://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ozone/health_ozo.htmlhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.nesc.wvu.edu/techbrief.cfmhttp://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ozone/health_ozo.htmlhttp://www.sigmaaldrich.com/catalog/DisplayMSDSContent.dohttp://www.atsdr.cdc.gov/toxprofiles/tp130-c3.pdfhttp://home.howstuffworks.com/swimming-pool.htm


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[15]USEPA 1996, Ultraviolet light disinfection technology in drinking water application Anoverview EPA 811-R-96-002

[16] Disinfection. Available at:http://www.lenntech.com/processes/disinfection/disinfection.htm

Date of access: 4.01.2012

[17] Muraca, P., Stout, J. and Yu, V. Comparative Assessment of Chlorine, Heat, Ozone, and

UV Light for KillingLegionella pneumophilawithin a Model Plumbing System, Appl. Environ.

Microbiol. 1987 53(2) 447-453
http://www.lenntech.com/processes/disinfection/disinfection.htmhttp://www.lenntech.com/processes/disinfection/disinfection.htmhttp://www.lenntech.com/processes/disinfection/disinfection.htmhttp://www.lenntech.com/processes/disinfection/disinfection.htm

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