Ultraviolet disinfection is a means of killing or rendering harmless,microorganisms in a dedicated environment. These microorganisms can range from bacteria and virusesto algae and protozoa. UV disinfection is used in air and water purification, sewage treatment, protection of food and beverages, and 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. The focus of this article will be on water treatment.
Iron and Manganese both are capable of precipitating on the quartz sleeve and preventing the UV energy from transmitting into the water. Iron should not exceed 1.0 ppm. At that level additional maintenance is required to keep the quartz sleeve clean and transparent. It is recommended that both iron and manganese are removed from the water, or at least reduced to levels that eliminate thepossibility of staining.
Total Dissolved Solids (TDS) should not exceed 500 ppm, however due to many factors, this number is nebulous at best. There are many factors that make up this equation, such as the distance between the lamp and the wall of the UV chamber; the particular make-up of the dissolved solids and how fast they absorb the available UV energy; flow rate; output of the lamp; etc. Calcium, in high amounts, has a tendency to build up on the quartz sleeve, again impeding the UV energy from penetrating the water. Contact your supplier for details on the amount of TDS your equipment is capable of handling. The solution could be as simple as running your system slower for a higher dosage.
Turbidity is the inability for light to travel though 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.
The difference between the two types of lamps is the quality of the glass used in their construction. A germicidal lamp is constructed of quartz glass, argon gas, mercury and the filaments used to ignite the mixture. When a lamp is lit and has achieved its ideal operating temperature of 104 degrees F, the mercury changes from its solid state into a gaseous state. While the lamp is in this operating state it imparts particles into the pores of the glass. This process is referred to as solarization. Solarization takes place in the hard glass lamp in about 9,000 hours, due to its smooth and less porous surface (that's four-and-a-half times longer than a soft glass lamp). UV lamps may burn for many years, however the solarization of the lamp will determine the UV energy output.
The purpose of the quartz sleeve is to help the lamp to maintain its ideal operating temperature. It is also to isolate the lamp from the water. For the maximum UV transmission of energy, the quartz sleeve needs to be constructed of the same high-quality materials as the lamp. The quartz sleeve should be wiped down every three to six months which is contingent upon the quality of the water you are dealing with. It is recommended that every UV application is inspected after three month's time. This will give you an opportunity to monitor the effect the water chemistry is having on the quartz sleeve, and your maintenance schedule time frame can be modified from there. The sleeve should be wiped down with a soapy solution each time it is inspected. If there is a residue left you may need to use a non-abrasive cleaner that is formulated to remove iron and scale buildup. Abrasive cleaner could scratch the sleeve and make it unusable.