Aim Water purification

Transcription

1 Aim : To develop a water purifier using ozone that is portable and less power consuming As Ozone is better than chlorine and has a lesser contact time for purification,it is preferred over chlorine for disinfection purposes. Ozone is prepared by using an electric discharge in which the high electric field breaks down the ozygen molecules to form ozone. Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption (drinking water) but water purification may also be designed for a variety of other purposes, including meeting the requirements of medical, pharmacology, chemical and industrial applications. In general the methods used include physical processes such as filtration and sedimentation, biological processes such as slow sand filters or activated sludge, chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light. The purification process of water may reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi; and a range of dissolved and particulate material derived from the surfaces that water may have made contact with after falling as rain. The standards for drinking water quality are typically set by governments or by international standards. These standards will typically set minimum and maximum concentrations of contaminants for the use that is to be made of the water. It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water considered safe for all practical purposes in the 19th century must now be tested before determining what kind of treatment, if any, is needed. Chemical analysis, while expensive, is the only way to obtain the information necessary for deciding on the appropriate method of purification. According to a 2007 World Health Organization report, 1.1 billion people lack access to an improved drinking water supply, 88% of the 4 billion annual cases of diarrheal disease are attributed to unsafe water and inadequate sanitation and hygiene, and 1.8 million people die from diarrheal diseases each year. The WHO estimates that 94% of these diarrheal cases are preventable through modifications to the environment, including access to safe water.simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in safe containers could save a huge number of lives each year. Reducing deaths from watverborne diseases is a major public health goal in developing countries. The most common disinfection method involves some form of chlorine or its compounds such as chloramine or chlorine dioxide. Chlorine is a strong oxidant that rapidly kills many harmful microorganisms. Because chlorine is a toxic gas, there is a danger of a release associated with its use. This problem is avoided by the use of sodium hypochlorite, which is a relatively inexpensive solution that releases free chlorine when dissolved in water. Chlorine solutions can be generated on site by electrolyzing common salt solutions. A solid form, calcium hypochlorite exists that releases chlorine on contact with water. Handling the solid, however, requires greater routine human contact through opening bags and pouring than the use of gas cylinders or bleach which are more easily automated. The generation of liquid sodium hypochlorite is both inexpensive and safer than the use of gas or solid chlorine. All forms of chlorine are widely used despite their respective drawbacks. One drawback is that chlorine from any source reacts with natural organic compounds in the water to form potentially harmful chemical by-products trihalomethanes (THMs) and haloacetic acids

2 (HAAs), both of which are carcinogenic in large quantities and regulated by the United States Environmental Protection Agency (EPA) and the Drinking Water Inspectorate in the UK. The formation of THMs and haloacetic acids may be minimized by effective removal of as many organics from the water as possible prior to chlorine addition. Although chlorine is effective in killing bacteria, it has limited effectiveness against protozoa that form cysts in water (Giardia lamblia and Cryptosporidium, both of which are pathogenic). Ozone disinfection O 3 is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe. It is an effective method to inactivate harmful protozoa that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and added to the water by bubble contact. Some of the advantages of ozone include the production of fewer dangerous by-products (in comparison to chlorination) and the lack of taste and odour produced by ozonisation. Ozone has been used in drinking water plants since 1906 where the first industrial ozonation plant was built in Nice, France. The U.S. Food and Drug Administration has accepted ozone as being safe; and it is applied as an anti-microbiological agent for the treatment, storage, and processing of foods. Previous circuits have, almost without exception, been split into three stages. First of all, the main voltage is reduced to 12V or so, then rectified and smoothed. Next there is an oscillator driving a transformer to step the voltage back up to a few hundred volts again. Finally, there will be a ladder of rectifiers and capacitors to step the voltage up to a few kv. The justification for this cumbersome process appears to be little more than the reduction in size of the ladder capacitors, achieved by running the oscillator at a fairly high frequency. In the present design, the ladder runs directly from the mains. This cuts out the first two stages of the usual Ionizer circuit. Larger capacitors are needed -1 0nF as opposed to 100pF or so but they are not much bigger in physical size. As the circuit uses no active components at all, it is almost certain to work first time, testing is easy, and the final circuit can be run continuously for years without problems. Rectifiers Another advantage of running the circuit at 50Hz Instead of 50kHz or so is that 1 N4007 rectifiers can be used. Ordinary rectifiers are not too keen to work at high frequencies, the main reason being their painfully slow reverse recovery time, which begins to degrade circuit performance at frequencies as low as 2 khz in the case of a 1 N4007. Readers may be interested in the results of applying a sine wave of increasing frequency to the circuit shown in Fig. 1

3 Construction The 1N4007 rectifiers are mounted vertically on the board in the-four central rows of holes and the capacitors are mounted in the _ outer rows as shown in the component overlay (Fig. 2). Figure 3a is an end-on view of the board with the first rectifier and capacitor in each row shown. All the rectifiers are mounted the same way around. When putting in the capacitors, you will find it easier to put them all in place at once and hold them with a rubber band while soldering, rather than trying to solder them in one at a time. Although some of the benefits of air ionization may be exaggerated, the action itself is real enough. One consequence of using an Ionizer is that the Ions attach themselves to any dust, dirt or pollen particles that happen to be floating around. The dust then becomes charged and will be attracted to the nearest natural surface. If you intend to run the Ionizer within a foot or so of a wall, cover the wallpaper in some way.

4 Otherwise, try to position the Ionizer towards the centre of the room where any charge dust will end up on the floor and be swept up during normal household cleaning.the action of precipitating particles from the air is of immediate benefit to asthma and hay fever sufferers, no matter how beneficial the ions themselves may be.improvements in health due to ionization occur over several days, rather than at the first breath of ionized air. The best position for an Ionizer is by the bedside, where you will breathe in the icons for eight hours or so at a time. This design is easily portable and you can move the device into the living room, or take it to work with you during the day.the circuit is a standard Cockroft - Walton ladder network which steps up the mains voltage to 10kV. T. The idea is that charge is transferred backwards and forwards from one row of capacitors to the other on each mains cycle, but always moving further up the chain because of the action of the rectifiers. When all the capacitors are fully charged, there will be a voltage across each of them equal, in theory, to the peak-tot-peak voltage of the mains. In practice, the regulation of this type of circuit is very poor, and the full voltage will never be measured because of leakage, corona discharge, and so on.

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