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How Does UV Light Act As a Sterilizing Agent?

Increasing research in the area of drinking water purification has resulted in the invention of ultraviolet disinfection units for purifying water and making it potable. Earlier, ultraviolet disinfection was restricted to waste water decontamination. But today, water purification systems employing ultraviolet disinfection are considered the most economically viable option for disinfecting drinking water.

  1. How It Works

    • The ultraviolet light kills microorganisms by penetrating the cell wall and reaching directly inside the cell where it causes alterations in the DNA strands, thereby leading to disruption of the genetic material. As a result, the cell becomes inactivated and is no longer able to reproduce. All that the ultraviolet radiation does is damage the cellular DNA and prevent multiplication of cells. It does not eliminate organic or inorganic particulate matter from the water, nor does it change the chemical properties of water.

    Ultraviolet Disinfection Units

    • Ultraviolet disinfection units use a mercury vapor lamp for disinfection. A mercury vapor lamp is a special kind of lamp that produces ultraviolet radiation of varying wavelengths. When electricity is supplied to the lamp, the mercury inside the lamp vaporizes and starts emitting ultraviolet radiation. These lamps are never placed in direct contact with water. They can be enclosed in quartz sleeves that have high rate of transmission and then placed inside the water chamber. Alternatively, they can be placed outside the water chamber and the ultraviolet radiations made to pass through water flowing through fine Teflon tubes. Ultraviolet radiations in a wavelength range of 250 to 270 nanometers are considered ideal to achieve maximum disinfection. There are three types of ultraviolet lamps: low-pressure, low-pressure high output, and medium-pressure lamps.

    Water Flow Rate

    • The effectiveness of ultraviolet disinfection process depends not only on the intensity of the ultraviolet light and the period of exposure. It also depends on other factors like flow rate. If the flow rate is too fast, the exposure time to ultraviolet radiations will be insufficient while if the flow rate is too slow, the system tends to get heated up. Hence, it is advisable to use ultraviolet lamps in water supply lines where the water supply is uninterrupted and can be controlled to a medium flow rate to allow sufficient exposure time.

    Water Quality

    • The effectiveness of ultraviolet disinfection process also depends on the water quality. Heavy turbidity and suspended particulate matter in the water can reduce the efficiency of the disinfection process because these suspended materials shield the microorganisms from direct ultraviolet light penetration. As a result, the microorganisms escape the disinfection treatment and remain active and capable of causing infections.

    Type of Microorganisms

    • Consider the type of microorganism present in the water when deciding the wavelength to be used for disinfection with ultraviolet light. While bacteria and viruses can easily be killed, molds and spores require greater intensity of ultraviolet radiations for inactivation.

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