Water purification processes and methods

Water Purification: Natural, Drinking, And Wastewater

Water can still be found that is purified naturally by the environment. For example, if the source of the groundwater is deep enough, the groundwater may be isolated from chemicals and other impurities, and naturally filtered through the soil and rocks. Springs are often the source of deep ground water, although because of its high mineral content, deep groundwater may taste unpleasant, compared with artificially purified drinking water. But as a precaution: "No water, irrespective of the original source, should be assumed to be completely free of contaminants. The most common process used for treatment of surface water and ground water consists of sedimentation, coagulation, filtration, disinfection, conditioning, softening, fluoridation, removal of tastes and odors, corrosion control, algae control, and aeration" (Robson 2010).

The first process of treating water for drinking purposes is sedimentation, or removal of obvious particles, such as dirt and sand. Then, by adding a chemical such as alum, the water is coagulated and takes the form of flocculent particles. The dangerous particles then settle to the bottom. The filtration process follows, along with disinfection with an agent such as chlorine. This chemical is used to kill harmful organisms and pathogenic bacteria. Softening removes bitter 'hard' minerals such as calcium and magnesium. "In a typical municipal water treatment process, water flows through pumps to a rapid mix basin, then to a flocculation basin, to a settling basin, through filters to a clear well, then after disinfection, to storage tanks, and finally to the end users" (Robson 2010).

Depending on the nature of the water, different purification strategies may be deployed. Aeration, adding oxygen to water, is used to remove carbon dioxide and hydrogen sulfide. Deionization (the substituting of sodium ions for calcium and magnesium ions) or using lime and soda ash to precipitate the calcium and magnesium as carbonate and hydroxide, are used for softening water (Water treatment," Sci-Tech Encyclopedia, 2010).

While filtration of drinking water is similar to the natural filtration of groundwater in that the water passes through a porous substance (artificial filters rather than natural rocks and soil), chemicals are necessary to ensure the water is not harmful for human consumption and will not cause illnesses due to bacteria or pesticides and fertilizes that have seeped into the soil. "Raw water and post-treatment water are tested for bacterial, physical, and chemical standards, particularly pH, color, and turbidity. The Safe Drinking Water Act of 1974 established maximum contaminant levels, which are the national drinking water standards. These apply to any water distribution system that serves at least twenty-five units daily. Standards may vary from state to state, but they cannot be lower than those prescribed by the federal government" (Robson 2010).