UV Treatment of Swimming Pool Water

Transcription

1 UV Treatment of Swimming Pool Water

2 Dechloramination

3 Chlorine in Pool Water Free chlorine (= residual chlorine) exists as hydrochloric acid, hypochlorous acid and the hypochlorite ion; ideally, free chlorine should be mg/l. Combined chlorine (= bound chlorine) is chlorine that has reacted with other substances; in a pool it mostly exists as monochloramine - NH 2 Cl, dichloramine - NHCl 2, and trichloramine - NCl 3. Total chlorine = free chlorine + combined chlorine. Free and total chlorine usually measured by a reagent + photometer system (e.g. Palintest pool tester) and combined chlorine by subtraction.

4 Combined Chlorine in Pools A 2009 survey by the Water Quality and Health Council (WQHC) in the United States revealed that: 17% of bathers urinate in swimming pools. 83% of bathers do not shower before swimming. 63% are unaware of illnesses associated with swallowing, breathing or having contact with contaminated pool water.

5 Combined Chlorine in Pools Bathers in pools introduce substances to the pool water such as urine, sweat and skin cells. These contaminants contain high levels of uric acid, urea, ammonia, histidine and creatinine. These compounds react with chlorine to form a number of byproducts, notably chloramines. Chloramines cause red eye, headaches, unpleasant odours, skin irritation and have been linked to asthma.

6 Stress Corrosion Cracking In people were killed in Uster, Switzerland when the concrete roof of a swimming pool collapsed after only thirteen years of use. The roof was supported by stainless steel rods in tension, which failed due to stress corrosion cracking. In 2001, the suspended ceiling of a municipal swimming pool in the Netherlands collapsed due to a similar cause. Chloramines are thought to be the most important factor in the corrosion of stainless steel in a swimming pool environment. A photomicrograph shows the transgranular nature of chloride stress corrosion cracking.

7 Legislated Maximum Chloramine Concentrations Germany Denmark France Italy Sweden Norway UK USA 0.2 ppm 0.2 ppm 0.6 ppm 0.3 ppm 0.4 ppm 0.5 ppm 0.25ppm (guidance) 0.5 ppm (NSF)

8 Removing Combined Chlorine from Pools Traditional methods of reducing chloramines are: superchlorination (or breakpoint chlorination), activated carbon and dilution with fresh water. The polychromatic emission of medium pressure lamps breaks the bonds within chloramine molecules and destroys them.

9 Optimum Wavelengths for Chloramine Photolysis Monochloramine: Dichloramine: Trichloramine: 245 nm 297 nm 260 nm & 340 nm

10 Chloramine Reduction Photochemical Mechanism UV Hydrochloric Acid Nitrogen Oxygen

11 New Plymouth Aquatic Centre Main Pool Chlorination Chlorine mg/l UV system commissioned East West North /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 / /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 / st Qtr 2nd Qtr Date 3rdFACQtrCombined 4th Qtr TAC

12 Primary Disinfection

13 Cryptosporidium Cryptosporidium is a protozoan which causes Cryptosporidiosis, a diarrhoeal disease. It was first identified in 1983 and is now the third most common cause of diarrhoea in the UK. The parasite is protected by an outer shell that makes it very resistant to chlorine disinfection.

14 Cryptosporidium & Giardia Cryptosporidium and Giardia are gastrointestinal parasites spread through the faecal-oral route. 18 outbreaks of Cryptosporidiosis associated with swimming pools are known to have occurred in the UK between 1989 and In the USA from 2003 to 2004, these parasites were responsible for 61.2% (Cryptosporidium spp. 55.6%; Giardia sp. 5.6%) of gastroenteritis outbreaks associated with swimming pools.

15 Inactivation of Cryptosporidium by Chemicals Disinfectant Effectiveness Estimated Ct-99 Free chlorine Poor 7200 mg-min/l Chloramine Poor 7200 mg-min/l Mixed oxidants Fair ~1000 mg-min/l Ozone Good 5-15 mg-min/l Chlorine dioxide Good ~80 mg-min/l Ct-99 is the concentration x time needed for a 99% reduction.

16 Extract of Application of UV in North America and USEPA Guidance Manual for UV Disinfection, Robert A. Hueslay & Black & Veatch Corporation

17 Non-tuberculous Mycobacteria Mycobacterium avium infection of human lung Most Non-tuberculous Mycobacteria (NTMs) rarely cause disease, but increasing reports of NTM infecting humans. Mycobacteria are resistant to chlorine. 32% of pools in Lisbon area are contaminated with Mycobacterium species. (R. Santos, Instituto Superior Técnico, Lisboa)

18 Fungal Contamination Dermatomicoses Professional swimmers are susceptible to fungal infections due to heat, sweating and friction + exposure to fungi in pools, showers and changing rooms. Tinea pedis Onychomycosis

19 Viral outbreaks through Chlorination Failure

20 Infection Risk in Pools and Spas

21 Pseudomonas aeruginosa

22 Photo-oxidation

23 Photo-oxidation by UV Medium pressure UV oxidises organic molecules in the pool water, resulting in reduced TOC levels. Water clarity improves UV transmittance improvements (T10) from 75% to 95% have been reported. THMs (trihalomethanes) decrease partly due to direct photo-oxidation and partly due to reduced chlorine dosing and removal of organics (WRK study).

24 Gert Holm Kristensen and Morten Møller Klausen, DHI

25 Gert Holm Kristensen and Morten Møller Klausen, DHI

26 Hanovia UV Design

27 UV vs. Chlorine & Ozone

28 UV & Sodium Hypochlorite Residual (free) chlorine is still required, but using Ultraviolet leads to reduced residual requirements, typically between 0.5 and 0.8mg/l. This results in: Lower Chemical Costs Less ph Correction Lower Combined Chlorine formed Lower TOC (Total Organic Carbon).

29 UV or Ozone? UV and O3 systems produce similar quality water, but UV systems have: Lower capital costs Lower running costs Lower maintenance requirements (ozone systems require specialized technicians) Smaller space requirements Lower head loss UV is the most cost-effective solution available

30 National Swimming Centre, Beijing (Water Cube) m3/hr Ozone generators total power = 46 kw 2 contact tanks + 3 carbon filters

31 Southern Cross University, Lismore NSW m3/hr UV System total power = 14 kw

32 Pool Schematic with UV POOL BALANCE TANK ph INJECTION CHLORINE INJECTION CALORIFIER FLOCCULANT INJECTION CIRCULATING PUMPS STRAINER ULTRAVIOLET CHAMBER UV STRAINER BY PASS FILTER FILTER BACK WASH PUMP CUT-OFF SIGNAL (VFC)

33 Benefits of a UV System Increased Bather Comfort Increased Employee Comfort Reduced Need for Expensive Dilution Reduced Maintenance Reduced Corrosion of Steel Structures Protection Against Cryptosporidium and Giardia Reduced health risk to Bathers and Employees

34 Hobart Aquatic Centre Tasmania Leisure Pool: 400 m3/hr

35 Piscinas do Estádio Universitário de Lisboa Olympic Size Pool - UV installed 1997; Combined Chlorine < 0.2 ppm; Transmittance 99.7% (T10)

36 Nirvana Spa, Wokingham, UK Multi-use pool with twenty-eight stations, providing all-round body conditioning for treating sports injuries, or for people simply wishing to relax and unwind. The water temperature is kept at a constant 36 C, which is higher than in leisure pools.

37 Port Aventura s Costa Caribe Aqua Park, Costa Dorada, Spain Five Hanovia UV Systems

38 AQUAPark Poprad, Eight UV systems supplied Slovakia

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