As population grows, drinking water becomes one of the most valuable resources in the world nowadays. The drinking water even becomes an important public health issue in some developing countries such as China and some African countries. During the entire process of drinking water treatment, the step of sterilization is especially important. The reason is that the raw water contains many kinds of microbes, which may results in spread of infectious diseases. This paper will show some sterilization methods for drinking water treatment and their cons and pros.
These methods are chloramine, UV disinfection, solar water disinfection and a combination of simple filtration and low-temperature sterilization. Chloramine is one of the most populated materials for water sterilization. Chlorine can react with the ammonia in the water and produce Chloramine to eliminate bacteria in water. This method can control the reproduction of bacteria effectively without generating smelly gas related to chlorine. In addition, it is very simple to use. However, this process can produce disinfection byproducts.
As mentioned in the article, “In the mid-1970s, byproducts of the chlorination process were discovered, including chloroform and trihalomethanes (THMs) (Lyon, Milsk and DeAngelo 6743). ” Trihalomethanes is formed by the reaction of chlorine and the decayed plants, the salt in the water or other natural organic matters (Lyon, Milsk and DeAngelo 6743), which is toxic to nervous system and it also has oncogenicity and mutability. This is the limitation of chloramine sterilization. Another method is UV sterilization.
A mercury lamp which can emitting 254nm UVC is used as a piece of sterilization equipment (Mori, Hamamoto and Takahashi 1237). Compared with other sterilization process, UV sterilization produces no byproducts to water. As Mori mentioned in their article, “UV sterilization performs effective disinfection without the addition of chemical substances and has recently been in the spotlight as a substitute for chlorination (Mori, Hamamoto and Takahashi 1237). These advantages allows the UV sterilization process becomes more popular than the conventional sterilization like chloramine process.
There also exist limitations for the UV process. Because the traditional lamp is made by mercury, it exits the potential risk because this liquid mental is also dangerous to human life. Mori also talked about this situation. “… the lamp, which contains mercury, must be disposed of at the end of its lifetime or following damage due to physical shock or vibration. (Mori, Hamamoto and Takahashi 1237)” Besides, because of the penetrating ability, the conventional UV lamp can only get through a thin layer of water.
If the water which need to be processed is deep enough, the UV light cannot sterilize the entire water effe The third method is solar water sterilization. This method is simple and low-cost enough for people in developing countries with enough sunlight resource. The unprocessed water just need to be directly placed under where the sunlight is sufficient and consistent for several hours. The result is “it is possible to achieve a complete decontamination of water samples without any danger of bacterial re-growth, if the disinfected water is properly stored for one week (Hindiyeh and Ali 208).
This method is recommend to be used in areas between the latitude 35°N and 35°S (Hindiyeh and Ali 208). As I mentioned before, this process can be only effective in the area with sufficient and consistent sunlight. In addition, if the weather in this area is not good enough, for example, during mostly cloudy days, the required temperatures may not be reached, the effectiveness of solar water sterilization will decrease (Nimbkar and Rajvanshi 519). Therefore, the forth process is created under this situation.
The combination of simple filtration and low-temperature sterilization can do the same work as the solar system do. The experiment shows that “filtration of raw water through four layered cotton-sari cloth (250um) reduced the coliform count and further heating to sub-boiling temperatures (55-60°C) for less than an hour resulted in complete inactivation of coliforms. (Nimbkar and Rajvanshi 519)” The authors also mentioned that this is a “feasible and environmentally sustainable technique of disinfection to obtain clean drinking water. Nimbkar and Rajvanshi 519)”
If the methods is mature enough, it can also solve the water problem in the area without sufficient sunlight. However, water is one of major medium of infectious diseases. The experiment just mentions the inactivity of coliform. The result of other microbes haven’t been mentioned. Thus, it is a major limitation of this process. The sterilization for water is so important because many infectious diseases can transmit through polluted drinking water resource, especially in some developing countries.
However, the human activities and population growth makes the situation more serious. As conclusion, these four methods have their own advantages and limitations. The researches on the sterilization for drinking water continues. For example, some scientists are working on developing a new UV sterilization device which is more suitable for water purification (Mori, Hamamoto and Takahashi 1237). We hope that these processes can grow more mature to adapt to the new situation.
