Where & When is UV used?
UV is used for untreated water sources, such as rain and ground water, bore, stream, spring or lake water.
A dosage of around 30mJ/cm2 (intensity) will eliminate the risk from most of the 'living nasties' (for example E.coli only requires a dose of 10).
Both Anthrax spores (death but extremely rare) and Aspergillus Glaucus (a mould that causes ear infection, skin lesions & ulcers) require a higher dosage of 46 mJ/cm2.
UV for treated water sources (for example city or mains water) is generally delivered at a dosage of 16 mJ/cm2 (which is the US Pubic Health standard for municipal water supplies).
This UV is considered a backup in case of a failure of the water supply authority (that normally use chlorine).
Interestingly UV is not considered necessary for (city/mains) chlorine treated water, yet chlorine is not effective against Cryptosporidium (diarrhoea).
And as we know occasionally the local water authorities get the dose wrong and the consequences are not good.
In case of a UV failure, a 1 micron cartridge provides protection against Cysts that are 4 to 6 micron.
UV is very effective for swimming pool water. It can eliminate the need to use chemicals in the water at a dosage of 16mJ/cm2 so is an excellent alternative to chlorination.
UV for hot water return systems can control Legionella and requires a dosage of 12mJ/cm2.
UV is Superior
Ultraviolet (UV) light treatment is a widely recognized and a proven method of disinfection of water and has several advantages over other disinfection methods such as chlorination, ozonation, etc.
UV light does not add anything to the water (such as undesirable chlorine, color, odor, taste or flavor) nor does it generate harmful byproducts.
UV only adds energy (radiation) that disinfects, in a fraction of the contact times required by other disinfection methods. It is fast, efficient, effective, economical and environmentally-friendly.
Your UV water disinfection system design has been carefully conceived to provide adequate germicidal dosage throughout the disinfection chamber.
The dosage is a function of 'time and intensity'. The higher the flow rate, the lower the exposure time. The lower the flow rate, the higher the exposure time.
The intensity is the germicidal lamps output (measured in watts).
Therefore higher flow rates require higher output lamps.
The UV Process
1) Water enters the filters then flows into the stainless steel chamber (the annular space between the quartz sleeve and the chamber wall).
2) The 'living nasties' (micro organisms) suspended in the water are exposed to UV rays as they travel along the chamber.
3) Provided the water is clear, the correct dosage means that the water leaving the chamber is instantly ready for drinking. No further disinfection is required.
The UV water filtration / disinfection system will only work correctly with visually clear water.
If the water is colored / cloudy the UV rays will not be able to penetrate, or the particles in the water will shield the nasties from the UV rays (shadowing).
Clarity (measured as 'turbidity') is achieved using 5 micron (or lower) filter cartridges.
Your filter cartridges are designed to trap contaminants to allow the UV to work its magic (instead of you drinking them).
The greater the concentration of contaminants and/or the greater the water usage, the faster the cartridges will block (become plugged with the trapped contaminants).
It is important to ensure the filter cartridges are replaced regularly with the type and quality as specified.
The UV water disinfection system is NOT intended to rectify poor quality water. The system is designed to disinfect the water.
Poor water quality can be described as having amounts of silt/mud or pollen/decayed leaves/berries/seeds that cause the cartridges to block (plug) in less than 6 months.
UV is used to disinfect the outflow of treated sewage prior to discharge onto land or into a stream, but it is not intended to convert sewage wastewater to microbiologically safe drinking water.
Water quality plays a major role in the transmission of germicidal ultraviolet rays.
It is recommended that the water does not exceed the following maximum concentration levels:
- Iron < 0.3 ppm (0.3mg/L)
- Hardness* < 7 gpg (120 mg/L)
- Turbidity < 1NTU
- Manganese < 0.05 ppm (0.05 mg/L)
- Tannins < 0.1 ppm (0.3 mg/L)
- UV Transmittance > 75%
Effectively treating water with higher concentration levels than listed above can be accomplished, but may require added measures to improve water quality to treatable levels.
If, for any reason, it is believed the ultraviolet transmission is not satisfactory, contact the factory.
The systems are designed to generate a UV dosage of at least 30,000 microwatt-seconds per square centimeter (μW-s/cm2), even at the end-of-lamp life (EOL), which is more than sufficient to destroy most waterborne microorganisms, such as bacteria, yeasts, algae etc…..
DOSAGE is the product of Intensity & Time
DOSAGE = Intensity x Time = micro Watt/cm2 x time = microwatt-seconds per square centimeter (μW-s/cm2)
Note: 1000 μW-s/cm2 = 1 mJ/cm2 ( milli-Joule/cm2)
UV Disinfection is affected by many factors and the following should be looked at prior to the installation of the UV system;
UV Transmission (transmittance)
- Transmittance deals with the effectiveness in which the 2537 Angstrom units (254 nanometers, 254nm) wavelength of ultraviolet light is transmitted through the water.
- The higher the transparency of the water, the more effective the UV system becomes.
- This optical clarity is evaluated by performing a test which passes incident light through a 1 cm depth of water and recording this against the same test using distilled water as a reference.
- Distilled water will pass 100% of the incident light through a 1 cm depth.
- The basic design of the units has taken into account a typical transmission at the desired wavelength. In practical terms this means that a system designed to flow at 24 gallons per minute (around 100 Lpm), at a typical transmissibility could actually have a higher flow rate in liquids with a higher transmissibility and a lower flow rate in liquids with a lower transmissibility.
- As a general guideline, the following are some typical UV transmission rates (UVT):
City water supplies : 85-98%
De-ionized or Reverse Osmosis water : 95-98%
Surface waters (lakes, rivers, etc) : 70-90%
Ground water (wells) : 90-95%
Other liquids : 1-99%
UV Sterilization & Filtration Systems/ Overview
Water, How much do we have?
- The earth holds 1.35 billion cubic kilometers of water.
- Greater than 97% of all the water on earth comes from salt seas making it undrinkable (without further treatment like desalination)
- Of the 1.35 billion km3 available , 29 million km3 lies frozen in glaciers and under the polar ice caps.
- An additional 8 million km3 lie underground in the spaces between grains of sand and gravel of which only a fraction can be tapped by wells.
- Only about 1/100 of 1% of the entire planet’s water is readily available as fresh water.
Is Water Safe?
Water treatment plants worldwide release 1.2 trillion gallons of raw sewage annually, much of which flows downstream into someone else’s water supply. Organisms are growing resistant to Chlorine disinfection, just as microbes infecting the body are becoming resistant to antibiotics. (Popular Science Magazine). Half the world has little or no access to safe drinking water and even fewer people have sanitation to protect them from waterborne diseases, which the World Health Organisation estimates cause 80 percent of the illness on the earth. (Michael Keating, To the Last Drop).
After the turn of the century chlorine started to be used as a disinfectant in water supplies to combat the 3 most common water born bacterial diseases:
- Typhoid Fever (Salmonella typhosa)
- Asiatic Cholera (Vibro comma)
- Bacillary Dysentery (Shigella dysentariae)
Today Chlorine is still being used to control many water born organisms including bacteria & viruses and other infectious diseases like Polio & Hepatitis, but there are plusses and minuses:
- “It has been estimated that 14-16% of bladder cancers in Ontario may be attributable to drinking water containing relatively high levels of chlorination disinfection”
- “There is an increase in bladder and rectal cancers with duration consumption of chlorinated groundwater”
- If chlorine is removed from water supplies, the rate of water borne diseases will increase dramatically
- If water is contaminated with germs, drinking it can cause serious illness, and often death (ex. Cholera & Typhoid)
Ultraviolet Light Disinfection Techniques are emerging as the most acceptable alternative means of disinfecting drinking water supplies.
DISINFECT – “To cleanse so as to destroy or prevent the growth of disease carrying microorganisms”.
As defined by the EPA and WHO, disinfection means to free from infection or harmful microorganisms.
The test is the absence of an indicator bacteria group.
Disinfection reduces the quantity of water carried germs to levels our body can handle safely.
- Chemical Disinfecting: Chlorine / Iodine / Bromine SICAL
- Physical Disinfecting: Boiling / Fine Filtration
- Ultraviolet Light
- Sanitization: a 2-log reduction or 50 - 99% reduction
- Disinfection defined as a 4-log reduction or 99.99% reduction
- Sterilization defined as a 6-log reduction or 99.9999% reduction
Electromagnetic Spectrum The UV Process
The UV treatment process is an extremely rapid physical process, that causes a molecular rearrangement of the genetic material known as the DNA of the microorganism.
DNA is the main constituent of all chromosomes of all organisms, known as deoxyribonucleic acid, and is self replicating.
UV blocks the microorganism’s ability to replicate itself, and consequently its ability to breed colonies that cause disease.
Due to individual cell make-up, different microorganisms require different levels of UV energy for their destruction. This energy level of destruction is known as dosage.
DNA Disruption UV Dose DOSAGE is:
- the product of Intensity & Time
- DOSAGE = INTENSITY x TIME
- = microW/cm2 x time
- = microWsec/cm2
- 1000 microWsec/cm2 = 1 mJ/cm2
What Dose is Required?
- 16 mJ/cm2 US Public Health (NSF 55 Class B)
- 30 mJ/cm2 A common Manufacturers Standard
- 40 mJ/cm2 EPA Requirement (NSF 55 Class A)
Note: these dosages represent end-of-lamp life (EOL) figures
Microorganisms - What Do They Look Like?
Bacteria Structure Comparison
UV / Chlorine / Ozone
UV Inactivation Efficacy
PATHOGENIC BACTERIA (to achieve 4 log inactivation)
Cholera 6.5 mJ/cm2 (6,500 microWs/cm2 )
Dysentary 4.2 mJ/cm2 (4,200 microWs/cm2 )
E. coli 6.6 mJ/cm2 (6,600 microWs/cm2 )
Legionella 3.8 mJ/cm2 (3,800 microWs/cm2 )
Salmonella 10 mJ/cm2 (10,000 microWs/cm2 )
PATHOGENIC VIRUSES (to achieve 4 log inactivation)
Poliovirus 7 mJ/cm2 (7,000 microWs/cm2 )
Hepatitis A 8 mJ/cm2 (8,000 microWs/cm2 )
Disinfectant Activity Est. CT – 99 (mg-min)/L Free chlorine Poor 7,200 + Chloramine Poor 7,200 + Ozone Good 5 - 15 Chlorine Dioxide Good ~80 Mixed Oxidants Fair ~1,000 UV Irradiation Excellent ~2-5 mJ/cm2 Micro Organisms Destruction Chart BACTERIA Agrobacterium tumefaciens 8,500 Bacillus anthracis 8,700 Bacillus megatherium (vegetative) 2,500 Bacillus megatherium (spores) 2,500 Bacillus subtilis (vegetative) 11,000 Bacillus subtilis (spores) 58,000 Clostridium tetani 22,000 Corynebacterium diphtheria 6,500 Dysentery bacilli (diarrhea) 4,200 Escherichia coli (diarrhea) 6,600 Legionella bozemanii 3,500 Legionella dumoffii 5,500 Legionella gormanii 4,900 Legionella micdadei 3,100 Legionella longbeachae 2,900 Legionella pneumophila (legionnaires disease) 3,800 Leptospira interrogans (infectious jaundice) 6,000 Mycobacterium tuberculosis 10,000 Neisseria catarrahalis 8,500 Proteus vulgaris 6,600 Pseudomonas aeruginosa (laboratory) 3,900 Pseudomonas aeruginosa (environmental) 10,500 Rhodospirillum rubrum 6,200 Salmonella (food poisoning) 10,000 Salmonella enteritidis 7,600 Salmonella paratyphi (enteric fever) 6,100 Salmonella typhimurium 15,200 Salmonella typhosa (typhoid fever) 7,000 Saracen lutea 26,400 Serratia marcescens 6,200 Shigella dysentariae (dysentary) 4,200 Shigella flexneri (dysentary) 3,400 Shigella sonnei 7,000 Staphylococcus epidermidis 5,800 Staphylococcus aureus 7,000 Streptococcus faccalis 10,000 Streptococcus heaolyeous 5,500 Streptococcus lactis 8,800 Viridans streptococci 3,800 Vibro comma (cholera) 6,500 MOLD SPORES Aspergillus flavus (yellowish green) 99,000 Aspergillus glaucus (bluish green) 88,000 Aspergillus nigar (yellowish green) 330,000 Mucor ramosissimus (white-grey) 35,200 Penicillium digitatum (olive) 88,000 Penicillium expansum (olive) 22,000 Penicillium roqueforti (green) 26,400 Rhizopus nigricans (cheese mold) 220,000 ALGAE Chlorella vulgaris 22,000 PROTOZOA Nematode eggs 92,000 Paramecium 200,000 VIRUSES Bacteriophage (E. Coli) 6,600 Hepatitis 8,000 VIRUSES Influenza 6,600 Poliovirus (poliomyelitis) 7,000 Rotavirus 24,000 Tobacco mosaic virus 440,000 YEAST Baker’s yeast 8,800 Brewer’s yeast 6,600 Common yeast cake 13,200 Saccharomyces ellipsoideus 13,200 Saccharomyces sp 17,600
Factors Affecting UV
UV can only be effective if the full dosage is absorbed by the target. This cannot happen due to:
- Absorption by other particles dissolved in the water (mainly iron, humic acids and tannins)
- Turbidity - suspended solids are particles not dissolved that show as colored/cloudy water. These scatter and absorb the UV rays, and shield the targets (shadowing)
- Fouling of the quartz sleeve - due to chemical and biological deposits (mainly inorganic staining & scale: iron, magnesium, calcium, aluminum, manganese, sodium, and anionic carbonate, phosphate, sulphate and organic biofilms)
- Low lamp operating temperature (needs to be on for 2 minutes to achieve the optimum 40oC). An increase or decrease of temperature will affect UV energy levels. Quartz sleeves will minimize temperature fluctuations.
- Excessive water flow rate compared to lamp power/chamber design
Fate of UV Irradiance in Water
Water Quality affects The impact of Water Chemistry on UV performance
UV Application Guidelines (Pretreatment required)
- Iron < 0.3 ppm
- Manganese < 0.05 ppm
- Hydrogen Sulphide < 0.05 ppm
- Hardness < 7 gpg
- Suspended Solids < 10 ppm
- Excessive colour, turbidity, iron or organics (ex. Tannins), require additional treatment
- 1,000 total coliforms per 100ml and/or 100 fecal coliform per 100ml
- Note: treated water by any process should be refrigerated and not stored indefinitely
Advantages of Water Systems UV filtration systems
- No need to handle dangerous toxic or corrosive chemicals
- Simple, quick and inexpensive installation with only two water and one electrical connection
- Simple maintenance, only yearly lamp replacement (provided water quality parameters are met)
- No moving parts to wear out or break
- Virtual immediate disinfection eliminates the need for long retention times -- no need for retention tanks
- Microbiologically free water without the use of potentially dangerous chemicals
- UV imparts no change in taste, odor, pH or conductivity
- Very low power consumption -- a 40 watt light bulb effectively treats up to 50 Lpm
- Lower capital investment when compared to chlorine or ozone systems
- Automatic, unattended and user friendly operation
- No trihalomethanes (THM’s) formation
UV has gained worldwide acceptance and is used for:
- urban and rural domestic water applications
- both point of entry POE and point of use POU
- surface waters and ground waters
- industrial products/processes such as food and beverage; pharmaceutical ;bottling plants ;agriculture ; cooling towers ;dairies ;breweries ; electronics/semi-conductor ; wineries ;aquaculture ;Municipal Waste Waters ; secondary treatment of effluents; tertiary effluent treatment for waste water reuse