UV disinfection

Difference between ozone and UV

—Ozone disinfect via air/ozone injected into water
—UV Disinfect by exposing water to UV light

How does UV work

—UV means ultraviolet
—UV wave has high energy in its envelop
—UV waves has various wave length, hence different applications
—UV for disinfection has specific wave length of 254 angstrom

UV 254 wave length

This typical wavelength and high energy allows the wave to penetrate the DNA of bacteria and disable it

Disinfection mechanism

—UV-C rays will destroy a minimum of 99.99% of harmful microorganisms, including E. coli, Cryptosporidium and Giardia.
—Unlike chemical disinfection the organisms are unable to develop any immune mechanism against UV light.
—The degree of UV inactivation of pathogens is directly proportional to the UV dose applied to the water

UV Intensity

—UV dose is the product of UV light intensity and exposure time and is expressed in mJ/cm2.
—NSF International has established a UV dose of 40 mJ/cm2 as the minimum UV dose required to ensure that all bacteria, viruses, Giardia and Cryptosporidium are killed or inactivated to a safe level.
—Other standard allows 30mj/cm2. As per WHO

The Advantages of UV Disinfection

—More effective against viruses than chlorine
—Environmentally and user friendly, no dangerous chemicals to handle or store, no risks of overdosing
—Low initial capital cost as well as reduced operating expenses when compared with similar technologies such as ozone, chlorine, etc.
—Immediate treatment process, no need for holding tanks, long retention times, etc.
—Extremely economical, hundreds of gallons may be treated for each penny of operating cost
—No chemicals added to the water supply – no byproducts, (i.e. chlorine + organic compounds = trihalomethanes)
—No change in taste, odor, pH, conductivity, nor the general chemistry of the water
—Automatic operation without special attention or measurement, operator friendly
—Simplicity and ease of maintenance, periodic cleaning, (if applicable), and annual lamp replacement, no moving parts to wear out
—No handling of toxic chemicals, no need for specialized storage requirements
—Easy installation, only two water connections and a power connection
—Compatible with all other water purification processes, (i.e. reverse osmosis, filtration, water conditioning and softening)

Pre treatment  before UV

To maximize the efficiency of the UV unit, pre-treatment is advisable. The most common pre-treatment methods are:

—Sediment filters to remove silt that shelters microbes and scatters or absorbs the UV. Silt can drastically cut the effectiveness of a UV unit.
—Carbon filtration to remove organic materials that absorb UV.
—A water softening unit to remove minerals that coat the UV lamp sleeve and cut down transmitted light.

What affects UV performance

—The effectiveness of a UV system in eliminating microbiological contamination is directly dependent on the physical qualities and/or clarity of your water supply.
—Suspended Solids,Particulate matter can cause shielding problems, in which a microbe may pass through the UV chamber without actually having any direct UV penetration.
—Iron/Manganese ,Will cause staining on the quartz sleeve that houses the UV bulb, at levels as low as 0.3 PPM of iron and 0.05 PPM of manganese. In this case, we recommend the installation of a Water Softener and/or an automatic Iron Filter system, as a proper step towards pretreatment which will help eliminate this staining problem. Note: not all UV systems will require the use of a softener if there is iron or manganese present, contact us for details.

More factors

—Calcium/Magnesium, Hardness in your water will cause possible scale formation on the lamp protecting the quartz sleeve. Scaling problems will be especially magnified during low flow or no flow times when the calcium and magnesium ions tie up with carbonates and sulfates to form hard scale buildup inside the chamber and quartz sleeve.
—Temperature is a determining factor, The optimal operating temperature of the UV lamp must be near 40 degrees C.UV levels will fluctuate with excessively high or low temperature levels.

Critical Parameters for performance

—Flow rate
—How does flow rate affects UV efficiency
—Contact time
—Optimum UV intensity
—Doping of heavy metals