purification+process

=Water Purification and Filtration= Water filtration and purification is the process of taking water that is dirty or unsafe and making it drinkable. Water filtration is a blanket of processes which may be more specific depending on the type and quality of water prior to filtration or purification.

Navigation

 * The Process of Filtration
 * Alternatives to Chlorine Disinfection
 * Desalination
 * Distillation
 * Reverse Osmosis
 * Portable Water Filtration
 * Additional Resources

The Process of Filtration
Water filtration is the process of creating safe drinking water by subjecting water to multiple processes to remove pollutants, bacteria, microbes, as well as improve clarity and taste. In most municipalities, water filtration follows this general process:
 * 1) Pre-filtration: involves the removal of large debris from the water supply such as branches and roots.
 * 2) pH adjustment: pure water as a pH of 7, and ocean water has a slightly higher pH of 8.3. In order to adjust the pH of municipal water supplies, cities often add chemicals such as lime, soda ash, or sodium hydroxide to raise the pH if it is too low, or they use a variety of acids to lower the pH if it is too high.
 * 3) Flocculation: is a process used to remove finer particles from the water which may house dangerous microbes, as well as improves the clarity of the water. The process consists of adding usually ammonium hydroxide and calcium chloride to the supply. As the chemicals are agitated, they form a gel precipitate known as floc which sticks to the sand and other particles in the water. After agitation, the water is held in a settling tank and the floc is allowed to float to the top.
 * 4) Sand and coal filtration: After flocculation, the water is often vertically filtered through a filter that contains sand and coal. This filter removes the floc from the water as well as other organic compounds. This step seeks to improve the taste and smell of the water.
 * 5) Chlorine Disinfection: is a process used to kill micro-organisms such as viruses and bacteria. The process often occurs by adding chlorine compounds such as chlorine, chloramine, chlorine dioxide, or sodium hypochlorite. These all react with water to produce calcium hypochlorite, which kills the viruses and bacteria. This step also helps improve the taste of water.

Alternatives to Chlorine Disinfection
The most controversial step to the water filtration process is often the chlorine disinfection step. Chlorine and its various compounds can sometimes be unreliable as international relations and poor roadways in less developed nations prevent the transport of chlorine. Chlorine compounds also have potentially hazardous effects, too, such as the production of poisonous gasses. Therefore, some municipalities employ alternatives to chlorine disinfection, including ozone and UV-C disinfection. Ozone disinfection is the use of Ozone, O 3, to remove the viruses and bacteria from water. This particular method is considered good because it requires a lower concentration to remove bacteria than chlorine disinfection. One major drawback to this method, however, is that it is often only cost-effective at large-scale plants. Despite the cost, it is the most common form of water disinfection used in Europe. Another alternative to chlorine disinfection, UV-C disinfection, is also highly effective at removing bacteria from the water supply and is more cost-effective on smaller scales. The major drawback to both of these alternatives is that they dissapate quickly, leaving the water vulnerable to infection after it has left the water filtration plant and before it reaches its destination. It is therefore necessary in both processes to add small doses of chlorine to the water to protect the water on its way to the consumer. 

[[image:http://glossary.periodni.com/image/distillation.gif width="201" height="221" align="right"]]Desalination
Desalination is an umbrella of processes which seek to remove salt from salt water in order to make it drinkable. The two major processes of desalination include distillation and reverse osmosis. Both of these processes can create drinkable water out of salt water, though they typically come at the cost of high amounts of energy required to undertake both of these processes.

Distillation
Distillation is the process of boiling substances to specific temperatures in order to remove one component of a solution via evaporation while leaving behind other components of the solution. This applies to desalination in the way that boiling salt water to 100 degrees Celsius allows the water component of salt water to evaporate into a gaseous state, leaving solid salt behind. The gaseous water is collected and allowed to condense, turning to pure, liquid water.

[[image:http://images.yourdictionary.com/images/main/A4reosmo.jpg width="156" height="160" align="left"]]Reverse Osmosis
Reverse osmosis is the act of forcing the water through a selective membrane from one side which is pressurized through to a side that is less pressurized. The selective membrane acts as a filter to remove larger molecules and ions from the water supply. This is similar to traditional osmosis used by our own cells which still employs a selective, semi-permeable membrane in order to filter certain solutes from a solvent. However, traditional osmos utilizes natural concentration gradients to separate the solutes and solvents from one another, allowing the solvent to travel more freely through the membrane from a side of more solvent pressure to the side with less solvent pressure.

Point-of-Use Water Filtration
The general theme with most water filtration and purification is that it is a life-saving, though very large-scale, expensive process. Water purification and filtration is a given in many developed countries. However, many of the world's underdeveloped nations are left with water that is riddled with turbidity and microbes which cause diseases such as Typhoid, Dysnetary or other diarrhoeal diseases. It is estimated that 43% of the world's population lacks ready access to safe water piped into their homes. This is especially true in rural areas where there simply isn't the money or resources for traditional water filtration. The answer to this issue lies with how to make water filtration smaller and cheaper.

One possible answer lies with concepts such as point-of-use filtration, which is a means of filtering water at the point of consumption rather than in a centralized set-up. Point-of-use methods can include:
 * boiling
 * ceramic pot filtration
 * chlorination
 * pasteurization
 * cloth filtration

Another more technological example of point-of-use filtration comes in the form of a product called the LifeStraw which is produced by humanitarian entrepreneur Vestergaard Frandsen. The LifeStraw is a small, portable, and relatively cheap device that can be used by one person to purify up to 1,000 gallons of drinking water, which is enough water for one person for one year. The LifeStraw uses human-powered reverse osmosis in a straw format in order to remove up to 99% of bacteria and microbes, successfully purifying drinking water on an individual level.

Additional Resources

 * [|Water Purification - Wikipedia]
 * [|Point-of-Use Water Treatment - Wikipedia]
 * [|LifeStraw - Wikipedia]
 * [|Desalination - Wikipedia]
 * [|Reverse Osmosis - Wikipedia]
 * [|LifeStraw - Vestergaard Frandsen]
 * Water - CSU Wiki

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