POTABLE WATER TREATMENT
General
Recent research finds UV light can inactivate crypto and giardia.

Small water systems (<1MGD) may find low pressure (LP) lamps work well. Low pressure lamps are less expensive than medium pressure (MP) lamps, with twice the life of a medium pressure UV lamp.

UV is typically a disinfection process, with no additional side benefits when compared to utilizing ozone and chlorine for disinfection.

Impacts
The effectiveness of the disinfection process is impacted by turbidity, total suspended solids, UV absorbance (ie: color, organic matter right), dissolved ions, hardness, alkalinity, and temperature.

As turbidity increases, design and UV dosage must also increase.

Higher organic manner, requires greater ultraviolet intensity as the ultraviolet light is absorbed by organic matter.

UV is generally more cost effective if upstream processes remove all organic matter, turbidity, etc. rather than increasing the UV dosage for comparable kills.

Water temperature (lower or greater that optimal design) will reduce inactivation value for low pressure lamps. Medium pressure operate at a much greater lamp temperature, and are therefore not affected nearly as much by temperature ranges outside of the optimal design range.

Cleaning
It is critical that operators clean the lamp sleeves on a routine basis to maximize UV light transmittance.

Remember, scaling of the quartz sleeves reduces light transmittance in the proper wavelength. Adjust the water pH to minimize scale.

Other Considerations
Age of lamps: as the lamps age, there is a loss of UV light intensity.

As water hardness increases, carbonate scale on quartz sleeves increases. The scale is hard to eliminate - high hardness waters are problematic for cleaning.

Remember, UV is classified as a "physical process."

Optimization of upstream processes will more often than not produce favorable reductions in disinfection costs. This is especially true when using UV as a disinfection process.

Maintenance
Require redundancy-keep the process fully operational! Many installations recognize the critical nature of this process and have enacted " required overtime" to insure complete operation of the process.

Safety
Lockout - blockout - tag out is required on the electrical systems as a safety precaution. Enact and adhere to safety procedures to avoid over exposure to UV light.

Cleaning
The most cited cause for UV systems not meeting disinfection requirements is the lack of proper cleaning of the sleeves.

Chemical cleaning: citric acid, vinegar, sodium hydrosulfite solutions are usually used.

Sodium hydrosulfite is often used for non-contact cleaning systems.

Insure proper operation of mechanical wipers, or ultrasonic cleaning systems.

References:
"Wastewater Engineering, 3rd Edition;" Metcalf & Eddy c 1991 McGraw Hill, Inc

"Handbook of Chlorination & Alternative Disinfectants" 4th Edition; c 1999, Geo. Clifford White, John Whiley & Sons, Inc.

"USEPA Design Manual: Municipal Wastewater Disinfection." 1986. EPA office of research in development, Cincinnati, OH

Water Environment Federation. Wastewater Disinfection. WEF Manual of Practice FD-10. Alexandria, VA: WEF. 1996.

"UV Disinfection Costs For Inactivating Cryptosporidium," Cotton et al, AWWA Journal, June 2001

"USEPA, Wastewater Technology Fact Sheet," UV EPA 832-F-99-064 Sep 1999

"Impacts of a wastewater quality on UV disinfection of reclaimed wastewater," Carins, et al

National Water Research Institute. UV Disinfection Guidelines for Wastewater Reclamation in California and UV Disinfection Research Needs Identification. Fountain Valley, CA: NWRI. 1993.

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