UV Disinfection

UV Disinfection

  • Physical process
  • Rapid and effective microorganisms inactivation
  • Utilizes the germicidal wavelengths of ultraviolet light
  • Stop bacteria, viruses and protozoa from reproducing and infecting through the damage of their nucleic acids
  • Non chemical process
  • Does not leave residuals
  • Does not involve handling of toxic chemicals
  • Carcinogenic free by-products from UV treatments
  • Does not affect the quality of water

UV rays comes from the sun as part of the light. As a water treatment technique, UV is known to have strong germicidal (inactivating) capacity. UV effectively disinfects water containing bacteria and viruses and works also against protozoans.

UV has been used in the pharmaceutical, cosmetic, beverage, and electronics industries. UV disinfection qualified in both municipal and household water treatment and wastewater treatment systems. There are two classes of disinfection systems – Class A and Class B Units.

Class A — these ultraviolet water treatment systems own designs that will allow them to disinfect microorganisms from contaminated water. Affected contaminants include bacteria and viruses, protozoans, from waste water. This class is not intended for the treatment of water that has obvious contamination such as raw sewage, nor intended to convert wastewater to drinking water.

Class B — have designs to deliver additional bactericidal treatment of water already deemed ‘safe’. i.e., no elevated levels of E. coli. Class B UV systems are designed to operate at a minimum dosage and intended to reduce normally occurring non-pathogenic or nuisance microorganisms only, and not intended for the disinfection of microbiologically unsafe water.

Last region of UV radiation’s wavelength is the one with germicidal properties for disinfection. A low-pressure mercury arc lamp contains elemental mercury and an inert gas, such as argon, in a UV-transmitting tube, usually quartz, omit UV radiation at optimum range for nucleic acids absorption. These lamps are called low pressure type, because they operate at relatively low mercury partial pressure, low overall vapour pressure, low external temperature and most importantly low power. Hence preferred for daily household usage. UV lamps that are effective on microorganisms and will also reduce the total organic carbon (TOC) content of the water. For typical UV system, approximately 95 percent of the radiation passes through a quartz glass sleeve and into the untreated water. The water is flowing as a thin film over the lamp. The glass sleeve is designed to keep the lamp at an ideal temperature.

UV radiation disturbs microorganisms by varying the DNA in the cells and obstructing reproduction. In other words, this treatment procedure does not remove organisms from the water, it merely inactivates them. The effectiveness of this process is related to exposure time and lamp intensity as well as general water quality parameters, followed by proper maintenance of the equipment. To make full use of UV treatment, lamp replacement and proper pre-treatment are needed as lamp intensity decreases over time. Operators can also go further by adding a warning device to alert as lamp intensity falls below the germicidal range.

UV radiation does not improve the taste, odour, or clarity of water. There is no residual disinfection in the water to inactivate bacteria that may survive or may be introduced after the water passes by the light source. However, dissolved organic matter, such as natural organic matter, certain inorganic solutes, such as iron, sulphites and nitrites, and suspended matter (particulates or turbidity) will absorb UV radiation or shield microbes from UV radiation, resulting in lower delivered UV doses and reduced microbial disinfection. Again, pre-treatments to reduce these natural organic and inorganic contaminants are essential. Either sediment filtration or activated carbon filtration should take place before water passes through the unit. Particulate matter, colour, and turbidity affect the transmission of light to the microorganisms and must be removed for successful disinfection.

UV is often the last procedure in a treatment train, following reverse osmosis, water softening, or filtration. The UV unit should be located as close as possible to the point-of-use since any part of the plumbing system could be contaminated with bacteria. It is recommended that the entire plumbing system be disinfected with chlorine prior to initial use of a UV system.

UV systems are meant for continuous operation and should be shut down only if treatment is not needed for several days. A few minutes for lamp warm-up is needed before the system is used again following shut-down. In addition, the plumbing system of the house should be thoroughly flushed following a period of no use, using chemical such as chlorine.

UV capacities range from 0.5 gallons per minute (gpm) to several hundred gpm. There is also a limit to the number of bacteria that can be treated. An upper limit for UV disinfection is 1,000 total coliform/100 mL water or 100 fecal coliform/100 mL