| Using ultraviolet (UV) light to purify drinking water | | | | copied also. When DNA replicates there is a special |
| is a concept that has existed for more than one | | | | protein that travels the length of the DNA and |
| hundred years. Despite its early beginnings, the | | | | splits it in half. Using the ladder analogy, this |
| science behind UV disinfection is complex. | | | | protein travels down the ladder and splits each |
| Understanding the fundamentals of how UV is able | | | | rung. The result is two separate molecules that |
| to purify drinking water requires a relatively deep | | | | each resembles one side of a ladder. In normal |
| understanding of physics, chemistry and biology. | | | | DNA replication the protein travels down the |
| The average consumer of this technology rarely | | | | ladder and as each rung is split each side is quickly |
| has the science background to fully grasp how a | | | | rebuilt. The result is two identical strands of DNA - |
| "light in a pipe" will be able to protect a water | | | | one for each of the resulting cells. UV-C light has |
| supply from dangerous microorganisms. This often | | | | the ability to penetrate through the cell and attack |
| leads to consumer frustration which in many | | | | the DNA. It actually fuses some of the rungs of |
| cases is exacerbated by faulty information | | | | the DNA ladder together. Recall above that during |
| provided by ill-equipped salespeople. Often the | | | | DNA replication a protein travels along the ladder |
| outcome of this frustration is consumer inaction | | | | and splits each rung. When the DNA of a cell has |
| which is unfortunate because UV systems are an | | | | been exposed to enough UV-C light and some |
| extremely effective and relatively inexpensive | | | | rungs have been fused, the protein responsible |
| way to purify drinking water. The goal of this | | | | for splitting the replicating DNA can't do its job. |
| article is to explain, as simply as possible, the | | | | When it encounters a fused rung it just stops, |
| science behind the disinfection of drinking water | | | | and the DNA replication stops with it. This |
| using ultraviolet light. UV light refers to | | | | prevents the cell from being able to reproduce. A |
| wavelengths of light that exist between visible | | | | bacterial or viral cell that cannot reproduce is not |
| light and x-rays on the electromagnetic spectrum. | | | | capable of causing infection. That statement bears |
| UV can be broken into three subcategories: UV-A, | | | | repeating: if a bacterial or viral cell cannot |
| UV-B, and UV-C. UV-A and UV-B are probably the | | | | reproduce, it cannot make us sick. So, UV light |
| best known of the UV wavelengths since they | | | | does not "kill" microorganisms - it simply makes it |
| are responsible for giving us a suntan or sunburn. | | | | impossible for them to reproduce, rendering them |
| UV-C light is a much higher energy and much | | | | harmless to anybody that might ingest them in a |
| more damaging form of UV light. It is UV-C that | | | | drink of water. It is critical that the DNA of the |
| is used in an ultraviolet light water purification | | | | organism is exposed to enough UV light in this |
| system. As mentioned above, UV-C is a very | | | | process. When discussing UV water purification |
| powerful and very damaging form of ultraviolet | | | | systems, the amount of UV light is usually called |
| light. When a living cell is exposed to UV-C, | | | | dose. UV dose is simply the amount of UV light |
| specifically the 254nm (nm = "nanometer") | | | | an organism is exposed to as it travels through |
| wavelength, the light is able to penetrate through | | | | an ultraviolet water purification device. The good |
| the cell and damage the DNA of the organism. | | | | news about UV is that it takes relatively little |
| DNA, or deoxyribonucleic acid, is responsible for | | | | exposure for a microorganism to be inactivated, |
| directing the activities within all living cells. All cells | | | | and it's impossible to over dose UV light. Because |
| must have intact DNA in order to function | | | | of differing water conditions and in order to purify |
| properly. The structure of DNA is very similar to | | | | different water flow rates, UV manufacturers |
| a ladder that has been twisted from both ends | | | | produce different sized models of UV water filter |
| resulting in a spiral staircase appearance. It is | | | | systems. For higher flow rates, a longer UV lamp |
| sometimes referred to as a "double helix" since all | | | | is required. This is simply to ensure that an |
| DNA is actually comprised of two molecules. You | | | | adequate UV dose is being applied. For slower |
| can think of each side of the ladder as one | | | | flow rates a shorter UV lamp can be used since |
| molecule and the rungs of the ladder as the | | | | the water being treated resides in the UV system |
| connection points between the two. When cells | | | | for a longer period of time. |
| reproduce, the end result is two identical cells | | | | C. Reid Thornley is a B.Sc. Biology and a former |
| each with a functional copy of DNA and all of the | | | | research associate for a world class water |
| other necessary structures for the cell to | | | | purification manufacturer. He has been a |
| function. This is true of the cells in humans, other | | | | presenter for the US Water Quality Association |
| animals, plants, and the bacteria and viruses that | | | | and he now owns and operates aQuatell - Water |
| might be found in drinking water. So at some | | | | Purification Made Easy! |
| point in the cell replication cycle the DNA must be | | | | |