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Water Facts

Where and when is UV necessary?

UV is ideal for untreated water sources like ground water, rain water, bore, spring, lake or stream water. A dosage intensity of 30mJ/cm eliminates most living nasties. For instance, E.coli requires a dosage of 10mj/cm while Anthrax spores and Aspergillus Glaucus requires a dosage of about 46mJ/cm.

When used in treated water sources like mains or city water, a UV dosage of 16mJ/cm is ideal. In this case, the UV is used as a backup in case the water supply authority fails. However, UV filtration is not considered necessary for use in chlorine treated water yet chlorine treatment does not eliminate Cryptosporidium that causes diarrhoea.

UV is also very effective when usedin swimming pool water since it eliminates the need to use chemicals and chlorine. When used in hot water return systems, UV controls Legionella at a 12mJ/cm dosage.

Why UV treatment?

UV light water treatment is a proven water disinfection method that offers numerous advantages over disinfection methods like ozonation and chlorination. For instance, UV does not add any chemicals to the water and it does not generate byproducts that may be harmful. It only uses radiation energy to disinfect the water. It is efficient, effective, environmentally friendly, economical and fast.

Moreover, UV water sterilisation systemsare carefully conceived to provide just the correct germicidal dosage in the entire disinfection chamber. The dosage is usually a function of light intensity and time. As such, high flow rates result to low exposure durations and vice versa. Higher flow rates may require higher power output lamps.

The UV Process:

  • Turbid or cloudy water flows through the system filters (filter media customised to address the water issues)is cleaned and then flows into the stainless steel chamber.
  • Micro-organisms are exposed to intense UV rays as the water travels through the chamber and are sterilised.
  • The water that exits the UV Chamber is then clean, clear and safe for drinking.

 

The UV water disinfection/ filtration system only works effectively with visually clear water, hence the need for prefiltration. UV light rays cannot penetrate cloudy water because particles in the water will shield the micro-organisms from UV exposure. Water clarity is successfully achieved by using 5 micron or less filter cartridges. 

Plugged Cartridges:

The role of filter cartridges is to trap and hold contaminants.If the water quality entering the system is poor then filter media will block more quickly.The average replacement for say filters used with rain water is 6 to 9 months. Filter media that requires changing more regularly than this means the water quality is very poor and may need additional prefiltration. Filters should be replaced regularly with the correct quality and type. Do not mix old with new filters and do not use inferior bleach filter media as it can be a health issue. Note that the UV water system is designed to disinfect water as opposed to improving poor water quality. Poor water quality is characterised by the inclusion ofdecayed leaves, seeds, pollen, silt and mud etc.

Water Quality:

Water quality is paramount in the transmission of germicidal UV rays. Experts recommend that water should not exceed concentration levels of:

  • 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% 

UV Dose:

Even at the end of their lamp life, UV systems are required to generate at least 30,000 μW-s/cm2 which is enough to destroy most water microorganisms like yeast, algae and bacteria. Dosage is a product of intensity and time. Effective UV dosage is affected by a number ofdifferent factors;

UV transmittance: this is the effectiveness in which 2537 Angstrom units of UV light are transmitted through water. Higher water transparency results in a more effective UV system. Water optical clarity is determined through performing a test that entails passing light through 1 cm water depth and recording the results against the same test utilising distilled water.This is done because distilled water passes 100% of incident light through a 1 cm depth.

The unit designs take into account typical transmissions at a desiredwavelength. This means that systems designed to flow 24 gallons per minute could have higher flow rates with higher transmissibility and vice versa. Typical UV transmission rates include:

Citywater 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 and filtration systems overview

Most of the water on earth originates from salt seas making it unfit for human consumption without further treatment. Water treatment plants globally release 1.2 trillion raw sewage gallons annually. Much of the raw sewage flows downstream to another person’s water supply. Harmful water organisms are becoming resistant to chlorine disinfection and microbes are becoming resistant to antibiotics. Half the populationof the world have no access to clean drinking water or protection from waterborne diseases.

History:

The use of chlorine to disinfect water was embraced to combat 3 common water bacterial diseases; asiatic cholera, typhoid fever and bacillary dysentery. Chlorine is used to control a myriad of viruses and bacteria present in water as well as infectious diseases like Hepatitis and Polio. However there is more evidence to support the notion that chlorine causes health issues.

It is estimated that 15% of bladder cancer cases in Ontario resulted from drinking water containing high chlorine disinfectant levels. Additionally, there is an increase in rectal and bladder cancer cases in areas where people consume chlorinated groundwater. UV water disinfection techniques are emerging as the best and safest alternative to chlorinefor disinfecting drinking water.

The UV water treatment process is an extremely radical process that triggers molecular re-arrangement of the genetic material known as microorganism DNA. DNA is a self-replicating constituent of organism chromosomes. UV works by blocking themicroorganisms ability to replicate and breed more colonies that cause water borne diseases. Different microorganisms require different UV energy levels for effective disinfection. The required energy level is referred to as dosage. The DNA disruption UV dosage is:

  • the product of Intensity &time
  • DOSAGE = INTENSITY x TIME
  •  = microW/cm2 x time
  •  = microWsec/cm2
  • 1000 microWsec/cm2 = 1 mJ/cm2

 Required dosage

  • 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)

The above dosages represent end-of-lamp life (EOL) figures.

Common microorganisms include;

E. coli

Polio

Bacillus

Cryptosporidium

Cyanobacteria

Shigella

Comparison of bacteria structure

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)

Cryptosporidium Efficacy

Factors Affecting UV

UV treatment is only effective when the full dosage is absorbed by the target. Things that impact this include;

  • Other water particles like tannins, iron and humic acids absorb the UV dosage too.
  • Turbidity which are solid particles that fail to dissolve and appear as cloudy/coloured water. They scatter and absorb UV rays by shielding the target.
  • Fouling of the quartz sleeve caused by biological and chemical deposits like scale.
  • Low lamp temperature resulting to low UV energy levels.
  • Excessive water flow rates which are not consistent to the chamber design and lamp power.
  • UV iridescencerate in water.
  • Water qualityimpacts on the UV performance.

UV application guidelines requires that

  • Iron < 0.3 ppm
  • Manganese < 0.05 ppm
  • Hydrogen Sulphide< 0.05 ppm 
  • Hardness < 7 gpg
  • Suspended Solids < 10 ppm

Advantages of water systems UV filtration systems

  • No handling of dangerous, toxic and potentially corrosive chemicals.
  • It requires simple, inexpensive and quick installation of just one electrical connection.
  • Simple annual lamp replacement maintenance.
  • It does not have moving parts that can break or wear out.
  • Immediate disinfection eliminates the need for longer retention times and retention tanks.
  • You get microbiologically free water without having to use potentially harmful chemicals.
  • UV disinfection does not affect taste, odour, conductivity or pH.
  • You require low power consumption.
  • Automatic and user friendly operation.
  • UV has gained recognition globally and is currently used to treat rural and urban domestic water, surface waters, ground waters at point of POE and point of use POU.
  • It is used in many industries; food and beverage, breweries, diaries and wineries, etc.