Water Treatment Using UV Rays

7/29/2019 Water Treatment Using UV Rays

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Violet being the colour of the shortest wavelength of visible light.Ultraviolet (UV) light is electromagnetic radiation. UV light has awavelength shorter than that of visible light, but longer than thatof soft X-rays. 22

It is typically divided into near UV (200-380nm) and extreme orvacuum UV (10-200nm)

The sun is the greatest source of UV light . The sun emitsultraviolet light in both near UV and vacuum UV wavelengths, butbecause of absorption in the atmosphere's ozone layer, 99% of theultraviolet light that reaches the Earth's surface is 315-380nm(referred to as UV-A)


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Municipal Wastewater

Municipal Drinking Water

Private Potable Water Industrial Process

Water Industrial Wastewater Consumer Drinking Water

Groundwater Remediation


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Dose= I x RtWhere:

I is the Intensity (quantity of UV light per unit area falling on a

surface)Rt is the Residence Time (contact time in the reaction chamber)UV Dose is expressed in:

Wsec/cm2 (Microwatt seconds/cm2)

mWsec/cm2 (Milliwatt seconds/cm2)

mJ/cm2 (Millijoules/cm2 )

UV DOSE INFLUENCING FACTORS

Fast Flow = Low Dose

Slow Flow = High Dose


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UV Transmittance (UVT) The ratio of light entering the water to that exiting the

water usually reported for a path length of 1 cm. is often represented as a percentage and is related to the

UV absorbance %UVT = 100 x 10-A

DI/RO Water = 99%

UVT Fresh Water (Post AGC) = 95% UVT

Municipal Tap Water = 85-95% UVT The higher the % value the greater the UV dose will be.

As the UV absorbance increases, the UV transmittancedecreases.


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Performance is highly dependent on howclear ( transmissive ) the water is to UV

light UVT has a cumulative effect, reducing the UV

intensity based on the thickness of the waterlayer that UV light must pass through

Sizing and lamp spacing is very sensitive to

UVT of the water

Proper system design and sizing is dependenton accurate water sample analysis


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http://www.sswm.info/sites/default/files/toolbox/CAWST%202009%20UV%20Tube%20Design%20Concept%20Fundacion%20Cantaro%20Azul.jpg


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Turbidity (NTU)

Turbidity is a measurement of suspended matter in

water. Turbidity is normally reported in Nephelometric

Turbidity Units (NTU) which represent the lightscattering and absorbing properties of the suspendedmatter present in a given sample of water.

Turbidity is an important consideration becausesuspended matter can shield pathogens fromdisinfection treatment


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Turbidity (NTU)Dose can be significantly influenced by turbidity

Turbidity may harbour pathogens and impede theeffectiveness of disinfection

Higher levels of turbidity means more uncertaintyin disinfection process

Turbidity can be influential on system design and

sizing


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Sleeve Fouling can affect UV transmittance (%UVT) and disinfection

performance. Many variables (water quality, lamp technology, flow, etc.)

can contribute to sleeve fouling Iron content in source wateris often a factor in sleeve fouling Sleeve cleaning systemsoffer a means to treat fouling but also have variability(system type, wiper design, wiper frequency, maintenanceschedule, water quality, etc). An effective system with anappropriate cleaning schedule is critical


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Disinfection, in terms of microorganisms, is a reduction of at least3 log (or 99.9%) .Disinfection is not sterilization .

Typical Disinfection Applications

Point of entry Post activated carbon Pre-reverse osmosis (RO)system

Post RO storage tank Post demineralization Prior to process and distribution loops

Point of use Anywhere there is biofilm potential or a bio-contamination problem Simple syrup up to 67 brix.


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UV light at the 254 nm wavelength penetrates the cell wall ofthe microorganism

Above and below this wavelength, the drop-off in effectiveness

is quite rapid

Intensity The amount of UV delivered to the organism Thymine dimerization

The UV energy permanently alters the DNA structure of themicroorganism

The microorganism is inactivated and rendered unable to

reproduce or infect


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Disinfection UV Oxidation

Destruction of bacteria, viruses and otherpathogens through DNA disruption by UV photons

Destruction of chemical contaminants via UVphotolysis and UV light- induced activation ofhydrogen peroxide


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The UVtube is basically the same as a commercial fluorescent bulb,except that it lacks the phosphor coating and the glass exterior isreplaced by fused quartz.

UVlight is generally defined to be wavelength of electromagneticradiation shorter than 400 nm and is further divided into UV-A (315-400nm), UV-B (280-315nm) and UV-C (200-280 nm).

The bulbs are suspended inside a larger tube in a covered channel.Water enters at one end and flows through the outlet at the otherend. While the water flows through the tube, the UVlight emittedfrom the bulb inactivates the microorganism.


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Large quantities of disinfected water can be obtained quickly Minimum behaviour change required Can be constructed with locally available material Highly effective on broad range of pathogens, including E. Coli,

Guardia and Cryptosporidium No risk for DBP formation (e.g. trihalomethanes) Inactivation independent of pH and temperature No unpleasant taste or odour (as it can appear for chemical

treatments) No transportation, storage or handling of chemicals


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Higher cost of equipment when compared with chlorine solution Requires regular power source for operation Lamp tube needs replacement every 6-12 months Some investment for installation is required UV lamp needs to be cleaned regularly and handled with care

because of their mercury content Only effective for microbial pollution No residual disinfection effect and risk of re-growth or

recontamination Iodine


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Water Treatment Using UV Rays