Ultraviolet 

Ultraviolet irradiation is a powerful technology that has been employed by several diverse industries such as pharmaceutical, semiconductor, power generation, food and beverage, cosmetics, aquaculture, etc. for several decades.  The most common use of ultraviolet radiation is for the disinfection of water.  It is used primarily for the control of water borne microorganisms.

 

The use of ultraviolet technology for water treatment has several advantages.  UV radiation does not add anything to the water.  No chemicals, no undesirable color, no odor, no taste or flavor and it does not generate harmful by-products.  It only imparts energy into the water stream in the form of ultraviolet radiation.  It is a fast, efficient, cost effective and environmentally friendly solution to controlling the growth of bacteria, viruses, molds, and spores in water.

 

Disinfection: This is the most common application of UV radiation in water treatment.  Using a 254 nanometer UV wavelength the radiation penetrates the outer cell wall of the microorganism, passes through the cell body, reaches the DNA of the microorganism and alters the genetic material.  This process inhibits the microorganism's ability to replicate and therefore destroys the microorganism.

 

TOC Reduction: A number of water quality standards include a limitation for "total organic carbon".  USP Purified Water and Water for Injection (WFI) have an upper limit of 500 ppb while ASTM and CLSI standards have varying limitations for TOC.  Total organic carbon levels may be reduced in water by using UV radiation with a 185 nanometer wavelength.  The more powerful 185 nm wavelength, with proper dose, decomposes the organic molecules.  The level of TOC reduction desired dictates the UV dose required.  Typical UV dose is 4X - 10X (120 - 300 mJ/cm2)

 

Ozone Destruction: Ozone is commonly used in the Life Sciences industry for sanitizing storage tanks, vessels, piping, auxiliary equipment, etc.  In some cases ozone is continuously fed on return piping loops to storage tanks and/or occasionally used as a disinfectant.  Ozone can be detrimental to downstream water treatment equipment and can harmful to humans if in a concentrated vapor form.  UV (254 nm), with a proper dose, can be used to destroy residual ozone by breaking down the O3 to O2 (oxygen).  Typical UV dose is 3X or 90 mJ/cm2.

 

Chlorine/Chloramine Destruction: While the addition of chlorine and chloramines to city water may control bacteria levels, they have detrimental effects on the some water treatment equipments such as reverse osmosis membranes.  Popular methods of chlorine/chloramine removal such as activated carbon or sodium metabisulfite injection have sometimes proven to be problematic.  Adding chemicals, such as metabisulfite to a high purity water system is sometimes frowned upon and activated carbon media can be a breeding ground for bacteria.  UV (185 nm) in a proper dose can destroy chlorine and chloramines.  Care must be taken when employing this technology for this application.  Depending upon the level of chlorine and/or chloramines UV doses of 20X - 50X (600 - 1500 mJ/cm2) may be required.

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