Water Treatment Plant Process- Chlorination or Ultraviolet Radiation By Shreya Shah
Surface waters necessitate water treatment before consumption to guarantee no health risk is present to the user. Poor quality water which consists of dissolved and suspended particles, can impact and cause health risks to consumers. The most important contamination is the microbiological contamination as it leads to infectious diseases (Water Treatment, 1994). Chemicals such as nitrates and cyanide when contaminate the water cause long-term health risk such as cancer, kidney and liver damages. Physical contamination may also cause a health risk such as eczema as it extends microbial survival (Drinking Water Treatment Chemicals, 2001). The water treatment system is designed to remove the contamination, which includes the suspensions of solids from the water. During the treatment the final process used is disinfection where many types of disinfectants are used, however ultraviolet radiation and chlorination are the most common types used. Chlorination is believed to be a more suitable process compared to ultraviolet radiation. However, ultraviolet radiation also has many positive processes to produce germ-free water. The treatment process involves the removal of contaminants through a number of stages which include: pre- water treatment, suspension, coagulation and flocculation, sedimentation, filtration, and disinfection which include either chlorination or ultraviolet radiation. This is called the multiple barrier principle (Water Treatment, 1994). Figure 1: This shows large objects in the surface water being removed as it is passing through the screen. The flow of water is indicated by the direction of the black arrows. http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html Figure 1: This shows large objects in the surface water being removed as it is passing through the screen. The flow of water is indicated by the direction of the black arrows. http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html The pre-water treatment begins with the process of screening, in which the site of the water intake is covered by large screens (Casiday, RC 1999). The heavier solid particles move slower than the lighter particles which allow the lighter particles to pass through the screen with the force of the water. However, the larger and heavier particles that move slowly are stopped by the screen as they can’t filter through. This leads onto suspension where the small particles that passed through the screen are removed. The water collected is allowed to sit steadily, as the heavy particles settle to the bottom of the tank because they are denser than the water so they sink, while the lighter particles float on top. After the settling is completed the water on top is collected through the outlet on the side of the tank without disturbing the layer of sediment (Casiday, RC 1999).
Figure 3: The structure of a guar gum polymer. http://en.wikipedia.org/wiki/Guar_gum Figure 3: The structure of a guar gum polymer. http://en.wikipedia.org/wiki/Guar_gum The finely dispersed solids that do not settle are known as colloids which are suspended in the water. Colloids dispersed in water are known as hydrocolloids, which take different states such as gel and sol. Hydrocolloids are irreversible or reversible, meaning they can interchange between states or stay in a single state (About Coagulation and Flocculation , 2009). Most hydrocolloids in the water going through treatment are results of natural sources. Main hydrocolloids include: agar-agar, carrageenan, alginate and guar gum. Figure 2: The structure of an algarose polymer. http://en.wikipedia.org/wiki/Agar-agar
Figure 2: The structure of an algarose polymer. http://en.wikipedia.org/wiki/Agar-agar
Figure 4: Negatively charged particles repel each other due to charges on their surface....
Bibliography: Water Treatment, 1994, United Nations, n.p , viewed 12 April 2012, <http://www.who.int/water_sanitation_health/dwq/S12.pdf>.
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