CHAPTER 5 MManaginganaging wwaterater aandnd aairir qqualityuality his chapter builds upon the background provided in Chapters 2, 3 and 4 and Tprovides guidance relating to water and air quality management (risk management specifi c to certain microbial hazards is covered in greater detail in Chapter 3). The primary water and air quality health challenges to be dealt with are, in typical order of public health priority: • controlling clarity to minimize injury hazard; • controlling water quality to prevent the transmission of infectious disease; and • controlling potential hazards from disinfection by-products. All of these challenges can be met through a combination of the following factors: • treatment (to remove particulates, pollutants and microorganisms), including fi ltration and disinfection (to remove/inactivate infectious microorganisms); • pool hydraulics (to ensure effective distribution of disinfectant throughout the pool, good mixing and removal of contaminated water); • addition of fresh water at frequent intervals (to dilute substances that cannot be removed from the water by treatment); • cleaning (to remove biofi lms from surfaces, sediments from the pool fl oor and particulates adsorbed to fi lter materials); and • ventilation of indoor pools (to remove volatile disinfection by-products and radon). Controlling clarity, the most important water quality criterion, involves adequate water treatment, including fi ltration. The control of pathogens is typically achieved by a combination of circulation of pool water through treatment (normally requiring some form of fi ltration plus disinfection) and the application of a chemical residual disinfectant to inactivate microorganisms introduced to the pool itself by, for instance, bathers. As not all infectious agents are killed by the most frequently used residual disinfectants, and as circulation through the physical treatment processes is slow, it is necessary to minimize accidental faecal releases and vomit (and to respond effectively to them when they occur) and to minimize the introduction of bather-shed organ- isms by pre-swim hygiene. Microbial colonization of surfaces can be a problem and is generally controlled through adequate levels of cleaning and disinfection. The control of disinfection by-products requires dilution, selection of source waters without DBP precursors (may include water pretreatment if necessary), pre-swim showering, treat- ment, disinfection modifi cation or optimization and bather education. Figure 5.1 outlines the components and shows a general layout of a ‘typical’ pool treatment system. Most pools have a pumped system and water is kept in continuous 80 GUIDELINES FOR SAFE RECREATIONAL WATER ENVIRONMENTS llayoutayout SSafeafe WWater.inddater.indd 110202 224.2.20064.2.2006 99:57:13:57:13 Plant room Coagulant dosing (5.2) Strainer Pump Filtration (5.4) Water disinfection (5.3) alternative disinfection dosing point pH correction dosing (5.10.3) Surface water off-take Balance tank Swimming pool Treated water Dilution (5.5) and make-up water Bottom off-take Figure 5.1. Water treatment processes in a ‘typical pool’ (relevant section numbers are identifi ed in parentheses) circulation (see Section 5.6), with fresh water being added for dilution of materials that are not effectively removed by treatment and to account for losses (often referred to as make-up water). 5.1 Pre-swim hygiene In some countries, it is common to shower before a swim. Showering will help to remove traces of sweat, urine, faecal matter, cosmetics, suntan oil and other potential water contaminants. Where pool users normally shower before swimming, pool water is cleaner, easier to disinfect with smaller amounts of chemicals and thus more pleas- ant to swim in. Money is saved on chemicals (offset to some extent by the extra cost of heating shower water, where necessary). The most appropriate setup for showers (e.g. private to encourage nude showering, a continuously run or automatic ‘tunnel’ arrangement) will vary according to country, but pool owners and managers should actively encourage showering. Showers must run to waste and should be managed to control Legionella growth (see Chapter 3). The role of footbaths and showers in dealing with papillomavirus and foot infec- tions is under question. However, it is generally accepted that there must be some barrier between outdoor dirt and the pool in order to minimize the transfer of dirt into the pool. A foot spray is probably the best of the alternatives to footbaths. Where outdoor footwear is allowed poolside (e.g. some outdoor pools), separate poolside drainage systems can minimize the transfer of pollutants to the pool water. CHAPTER 5. MANAGING WATER AND AIR QUALITY 81 llayoutayout SSafeafe WWater.inddater.indd 110303 224.2.20064.2.2006 99:57:14:57:14 Toilets should be provided and located where they can be conveniently used before entering and after leaving the pool. All users should be encouraged to use the toilets before bathing to minimize urination in the pool and accidental faecal releases. If babies and toddlers (that are not toilet trained) are allowed in the pool facilities, they should, wherever possible, wear leak-proof swimwear (that will contain any urine or faecal release) and, ideally, they should have access only to small pools that can be completely drained if an accidental faecal release occurs. 5.2 Coagulation Coagulants (or fl occulants) enhance the removal of dissolved, colloidal or suspend- ed material by bringing it out of solution or suspension as solids (coagulation), then clumping the solids together (fl occulation), producing a fl oc, which is more easily trapped during fi ltration. Coagulants are particularly important in helping to remove the oocysts and cysts of Cryptosporidium and Giardia (Pool Water Treatment Advisorz Group, pers. comm.; Gregory, 2002), which otherwise may pass through the fi lter. Coagulant effi ciency is dependent upon pH, which, therefore, needs to be controlled. 5.3 Disinfection Disinfection is part of the treatment process whereby pathogenic microorganisms are inactivated by chemical (e.g. chlorination) or physical (e.g. UV radiation) means such that they represent no signifi cant risk of infection. Circulating pool water is disinfected during the treatment process, and the entire water body is disinfected by the application of a residual disinfectant (chlorine- or bromine-based), which partially inactivates agents added to the pool by bathers. Facilities that are diffi cult or impos- sible to disinfect pose a special set of problems and generally require very high rates of dilution to maintain water quality. For disinfection to occur with any biocidal chemi- cal, the oxidant demand of the water being treated must be satisfi ed and suffi cient chemical must remain to effect disinfection. 5.3.1 Choosing a disinfectant Issues to be considered in the choice of a disinfectant and application system include: • safety (while occupational health and safety are not specifi cally covered in this volume, operator safety is an important factor to consider); • compatibility with the source water (it is necessary to either match the disinfec- tant to the pH of the source water or adjust the source water pH); • type and size of pool (e.g. disinfectant may be more readily degraded or lost through evaporation in outdoor pools); • ability to remain in water as residual after application; • bathing load; and • operation of the pool (i.e. capacity and skills for supervision and management). The disinfectant used as part of swimming pool water treatment should ideally meet the following criteria: • effective and rapid inactivation of pathogenic microorganisms; • capacity for ongoing oxidation to assist in the control of all contaminants dur- ing pool use; 82 llayoutayout SSafeafe WWater.inddater.indd 110404 224.2.20064.2.2006 99:57:14:57:14 • a wide margin between effective biocidal concentration and concentrations re- sulting in adverse effects on human health (adverse health effects of disinfec- tants and disinfection by-products are reviewed in Chapter 4); • availability of a quick and easy measurement of the disinfectant concentration in pool water (simple analytical test methods and equipment); and • potential to measure the disinfectant concentration online to permit automatic control of disinfectant dosing and continuous recording of the values measured. 5.3.2 Characteristics of various disinfectants 1. Chlorine-based disinfectants Chlorination is the most widely used pool water disinfection method, usually in the form of chlorine gas, a hypochlorite salt (sodium, calcium, lithium) or chlorinated isocyanurates. While chlorine gas can be safely and effectively used, it does have the potential to cause serious health impacts, and care must be taken to ensure that health concerns do not arise. When chlorine gas or hypochlorite is added to water, hypochlorous acid (HOCl) is formed. Hypochlorous acid dissociates in water into its constituents H+ and OCl– (hypochlorite ion), as follows: HOCl ↔ H+ + OCl– hypochlorous hydrogen hypochlorite acid ion ion The degree of dissociation depends on pH and (much less) on temperature. Disso- ciation is minimal at pH levels below 6. At pH levels of 6.5–8.5, a change occurs from undissociated hypochlorous acid to nearly complete dissociation. Hypochlorous acid is a much stronger disinfectant than hypochlorite ion. At a pH of 8.0, 21% of the free chlorine exists in the hypochlorous acid form (acting as a strong, fast, oxidizing disin- fectant), while at a pH of 8.5, only 12% of that chlorine exists as hypochlorous acid. For this reason, the pH value should be kept relatively low and within defi ned limits (7.2–7.8 – see Section 5.10.3). Together, hypochlorous acid and OCl– are referred to as free chlorine. The usual test for chlorine detects both free and total chlorine; to determine the effectiveness of disinfection, the pH value must also be known. The chlorinated isocyanurate compounds are white crystalline compounds with a slight chlorine-type odour that provide free chlorine (as hypochlorous acid) when dis- solved in water but which serve to provide a source of chlorine that is more resistant to the effects of UV light.