UV – Ultraviolet desinfection
Ultraviolet disinfection is a means of killing or rendering harmless microorganisms in a dedicated environment. These microorganisms can range from bacteria and viruses to algae and protozoa. UV disinfection is used in air and water purification, sewage treatment protection of food and beverages, and many other disinfection and sterilization applications. A major advantage of UV treatment is that it is capable of disinfecting water faster than chlorine without cumbersome retention tanks and harmful chemicals. UV treatment systems are also extremely cost efficient!
Advantages of UV sterilization
How does UV Disinfection Work?
Ultraviolet is one energy region of the electromagnetic spectrum, which lies between the x-ray region and the visible region. UV itself lies in the ranges of 200 nanometers (nm) to 390 nanometers (nm). Optimum UV germicidal action occurs at 260 nm.Since natural germicidal UV from the sun is screened out by the earth’s atmosphere, we must look to alternative means of producing UV light. This is accomplished through the conversion of electrical energy in a low pressure mercury vapor “hard glass” quartz lamp. Electrons flow through the ionized mercury vapor between the electrodes of the lamp, which then creates UV light. As UV light penetrates through the cell wall and cytoplasmic membrane, it causes a molecular rearrangement of the microorganism’s DNA, which prevents it from reproducing. If the cell cannot reproduce, it is considered dead.
What Factors Affect the Effectiveness of UV Disinfection?
Because UV does not leave any measurable residual in the water it is recommended that the UV sterilizer be installed as the final step of treatment and located as close as possible to the final distribution system. Once the quality of your water source has been determined, you will need to look at things that will inhibit the UV from functioning properly (e.g., iron manganese, TDS, turbidity, and suspended solids).
Iron and manganese will cause staining on the quartz sleeve and prevent the UV energy from transmitting into the water at levels as low as 0.03 ppm of iron and 0.05 ppm of manganese. Proper pre-treatment with a sediment filter and Triangular Wave Deposit Control System is required to eliminate this staining problem.
Total Dissolved Solids (TDS) should not exceed approximately 500 ppm (about 8 grains of hardness). There are many factors that make up this equation such as the particular make-up of the dissolved solids and how fast they absorb the available UV energy. Calcium and magnesium, in high amounts, have a tendency to build up on the quartz sleeve, again impeding the UV energy from penetrating the water. A Triangular Wave Deposit Control System will handle TDS before it becomes a problem for the UV system.
Turbidity is the inability of light to travel through water. Turbidity makes water cloudy and aesthetically unpleasant. In the case of UV, levels over 1 NTU can shield microorganisms from the UV energy, making the process ineffective. Suspended Solids need to be reduced to a maximum of 5 microns in size. Larger solids have the potential of harboring or encompassing the microorganisms and preventing the necessary UV exposure. Pre-filtration is a must on all UV applications to effectively destroy microorganisms to a 99.9% kill rate.
An additional factors affecting UV is temperature. The optimal operating temperature of a UV lamp must be near 40 0C (104 0F). UV levels fluctuate with temperature levels. Typically a quartz sleeve is installed to buffer direct lamp-water contact thereby reducing any temperature fluctuations.
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