Ultraviolet UV Sterilization System are useful in many water purification systems to disinfect and control bacteria. Ultraviolet or UV energy is found in the electromagnetic spectrum between visible light and x-rays and can best be described as invisible radiation. UV light occurs with a wavelength ranging from 200 to 390 nanometers (nm). The most effective wavelength frequency, from the point-of-view of microbiological disinfection, is 254 nm as this is where the optimum energy intensity is found.
Principle of UV Sterilization System
Typical UV disinfection systems involve the flow of water through a vessel containing a UV lamp . •As the water passes through this vessel, microorganisms are exposed to intense ultraviolet light energy which causes damage to genetic molecules (i.e. nucleic acids: DNA or RNA) needed for reproductive functions.
In order to kill microorganisms, the UV Sterilization System UV rays must actually strike the cell. UV energy penetrates the outer cell membrane, passes through the cell body and disrupts its DNA preventing reproduction. This damage prevents the microorganism from multiplying or replicating in a human or animal host. Because the microorganism cannot multiply, no infection can occur. Disinfection of water is achieved when UV light causes microbial inactivation.
Advantages of UV Sterilization System
UV disinfection does not add chemicals to the water. UV Sterilization System is effective against bacteria and viruses. Cryptosporidium, giardia and other biological pathogens get inactivated, and bacterial regrowth is arrested. Most UV device have audible UV emission detector to notify user when lamp intensity is inadequate.
There are some disadvantages as well like regular maintenance and lamp replacement is essential. UV units only kill bacteria at one point in a watering system and do not provide any residual germicidal effect downstream. The piping in a watering system treated by UV disinfection will need to be periodically sanitized with a chemical disinfectant. Water being treated must not be turbid or cloudy. Any level of color present in water will hinder the ability of UV radiation to penetrate it and destroy the microorganisms within.
Disinfection is generally final treatment process in Water Treatment. The objective of Disinfection is to destroy pathogens in water and provide additional protection against subsequent contamination.
Below is a precise method statement that is useful when someone wants to do testing and commissioning of UV Sterilization System.
System Pre-Commissioning & Construction Completion Checks for Filter
Before commissioning the system the following shall be ensured.
- The system has been checked against the approved installation drawings.
- Check that the upstream pressure at the filter inlet is more than 2.5 bar (38psi) during the rinse cycle.
- Check that the filter is mounted in the correct flow direction.
- Check that all the control tubes are connected properly and that all connections are tight.
- Check that the three-way mini-valve is turned to the automatic position. The arrow on the knob should point to AUTO, and the sticker ο on the filter.
- Check if the pipe installed is as per approved drawing or the nominal diameter should be 3” (75mm).
- If the recommended upstream and downstream isolation valves have been installed, check that they are shut.
System Pre-Commissioning Checks for UV Sterilizer
Check the radiation chamber for leaks and venting according to the following procedure:
- Release (open) vent screw on radiation chamber
- Slowly open shut-off valve upstream of radiation chamber
- Fill radiation chamber until water emerges at the vent screw
- Close vent screw, use only slight force
- Check radiation chamber for leaks
- Open shut-off valve downstream of radiation chamber (necessary only for manual shut-off valve)
Commissioning Phase for UV Sterilization System
Commissioning of the Filter System, the following steps has to be performed:
- Slowly open the isolating valve at the filter inlet. Water will flow into the filter.
- Check for leaks and repair if necessary.
- Check that the minimum inlet pressure remains 2.5bars (38psi) or higher.
- Slowly open the isolating valve at the outlet of the filter.
- If there is a by-pass valve close it slowly.
- Ensure the flow through the filter does not exceed the filter’s published maximum flow rate.
- Start a manual flush by turning the three-way valve to the OPEN position for a few seconds, and then turn it back to AUTO.
- During the self-cleaning cycle, check the pressure at the filter inlet and in the rotor chamber
Note: The minimum pressure in the rotor chamber should be 1.5bar (22psi) lower than the inlet pressure.
Commissioning of the UV filtration System, the following steps has to be performed:
- Switch on master switch or connect power plug
- Check parameters in programming mode of the control system and change if necessary see Operating Status Settings.
- Switch on UV disinfection system with START/STOP key; press the START/STOP key and hold for at least 2 seconds.
- If the control assumes the PAUSE state, operate the pause contact. After being ignited, it can take several minutes for the UV lamps to reach their full UV output.