Reliable Ultraviolet Water Treatment Process

microelectronicsIn Microelectronics, Aquafine’s ultraviolet water treatment process provides an enhanced, synergistic approach, towards the reduction of trace organics and microbial contamination for ultra pure water.

Aquafine recognises the challenges faced by water systems professionals in the design and construction of water purification equipment for the microelectronics industry. Aquafine ultraviolet water purification equipment commonly performs four functions in producing pure water – disinfection, TOC (Total Oxidizable Carbon) reduction, ozone destruction and chlorine/chloramines destruction.

Being well versed in how all components of a pure water system interrelate, ensures optimum performance. The Aquafine water treatment process eliminates microbial contamination in the system by utilizing UV’s 254nm energy. This process destroys the DNA which prevents microbial proliferation.

In ultra pure systems, ultraviolet water treatment in combination with ozone provides an enhanced synergistic approach toward the reduction of trace organics. Organics are among the most difficult contaminants to control in a pure water system. As critical dimensions for integrated circuits continue to decrease and transistor capacities continue to increase, contaminants in the parts per trillion ranges can produce yield-impacting defects. Organics are polar and weakly ionize in ultra pure water. This poses a considerable challenge to ion exchange resins. To prevent TOC leakage from polishing deionizers, silica and/or boron levels are typically monitored to determine when regenerations should be performed.

Aquafine TOC reduction units complement the organic scavenger resins of the polishing loop by oxidizing trace organics into free radicals (R -OH-) and carbon dioxide, which are more readily removed by ion exchange resins and/or degasifiers. Should continuous ozone be a process requirement, Aquafine water purification equipment can be used to protect both product and costly microelectronic manufacturing equipment by the dissociation of ozone into dissolved oxygen.  If dissolved oxygen (DO) is a concern, Aquafine engineers can provide assistance for reducing or eliminating DO as well. For these reasons, more manufacturers around the world trust Aquafine for their UV water purification equipment, application assistance and support.

Applicable Ultraviolet Water Treatment Applications

Disinfection

This is the most common UV water treatment process. A pharmaceutical water system could have several locations where UV water purification equipment would be installed. Some typical locations of installation would be post-carbon filter and pre-RO. When installed downstream of the carbon bed and/or directly upstream of the RO unit, a UV system can significantly reduce the microbial counts by destroying at least 99.9% of the bacteria present in the influent stream. Disinfection is also recommended for the process distribution loop and pre storage tank.

Toc Reduction

Ultraviolet water treatment is also used for the effective reduction of organics, commonly referred to as TOC (total oxidizable carbon).  Reduction of TOC is accomplished by incorporating 185nm UV system appropriately designed and sized as well as strategically located in conjunction with other equipment. Carbon dioxide is a typical by-product of TOC reduction process, resulting in a drop in the resistivity of water. While most organic molecules are oxidized into carbon dioxide and water molecules, other more resistant species become weakly ionized or charged, after absorbing the UV. This is why polishing deionization (DI) beds are typically placed downstream of the TOC reduction units, so that they not only remove the charged/ionized organics, but also restore the resistivity to the water.

Ozone Destruction

Ozone is commonly used in the pre treatment area of a water system, as well as for sanitising and re-circulating systems. Prior to the point-of-use, the residual ozone needs to be destroyed to ensure the process water is not compromised.  Because it is a non-chemical, fast acting mechanism, a UV water treatment process is the preferred method for this application. After considering the appropriate variables, a properly sized UV unit can be guaranteed to destroy the ozone to non-detectable limits, insuring the integrity of the process and the product. A dosage of 90mJ/cm2 is recommended for destruction of ozone residuals of 1.0ppm.

Chlorine/Chloramine Destruction

While the addition of chlorine and chloramines to city water may control bacteria levels, they have undesirable effects on the degradation of membrane filtration or RO. Popular methods of removal, such as carbon beds or chemical injection, have proven to be problematic. Sodium metabisulfite involves replacing one chemical with another and creates food for micro-organisms, while carbon beds can be inefficient, vulnerable to channelling and provide breeding grounds for micro-organisms. Aquafine Corporation pioneered the technology of chlorine and chloramines so with local help from KK Water we can provide UV systems for pre-membrane filtration and/or RO make-up water systems.

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