Chlorination
From Free net encyclopedia
- This article is about a water treatment process. For chlorination in organic chemistry, see Halogenation.
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water. Water which has been treated with chlorine is effective in preventing the spread of disease.
The chlorination of public drinking supplies was originally met with resistance, as people were concerned about the health effects of the practice. The use of chlorine has greatly reduced the prevalence of waterborne disease as it is effective against almost all bacteria and viruses.
Chlorination is also used to sterlize the water in swimming pools and as a disinfection stage in sewage treatment. It can also apply to the addition of chlorine to other elements, such as gold in the formation of gold chloride.
Contents |
Drawbacks
Disinfection by chlorination can be problematic, in some circumstances. Chlorine can react with naturally occurring organic compounds found in the water supply to produce dangerous compounds, known as disinfection byproducts (DBPs). The most common DBPs are trihalomethanes (THMs), which include chloroform. However, the World Health Organization has stated that the "[r]isks to health from DBPs are extremely small in comparison with inadequate disinfection."[1]
There are also other concerns regarding chlorine including its volatile nature which causes it to disappear too quickly from the water system, and aesthetic concerns such as taste.
Alternatives
Several alternatives to traditional chlorination exist, and have been put into practice to varying extents. Ozonation is used by some municipalities in the United States, including Milwaukee, Wisconsin. Because ozone breaks down quickly, smaller amounts of chlorine are still added to these systems to ensure that water downstream from the treatment facility continues to be safe.
Purification with chloramine is also becoming increasingly common. Unlike chlorine, chloramine does not disapate from water quickly and cannot be removed from water by boiling it.
Water treated by slow sand filtration may not need further disinfection as a very high proportion of pathogens are removed by microorganisms in the filter bed.
The advantage of chlorine is that the residual stays in the water for a period of time, as it travels through the water supply system, in order to prevent reinfection. In a large system this may not be adequate, and so chlorine levels may be boosted at points in the distribution system, or chloramine may be used, which remains in the water for longer before reacting or dissipating.