Water purification is the process of removing contaminants from a raw water source. The goal is to produce water for a specific purpose with a treatment profile designed to limit the inclusion of specific materials; most water is purified for human consumption (drinking water). Water purification may also be designed for a variety of other purposes and water purified to meet the requirements of medical, pharmacology, chemical and industrial applications. Methods include, but are not limited to: ultra violet light, filtration, water softening, reverse osmosis, ultrafiltration, molecular stripping, deionization, and carbon treatment.
Water purification may remove, particulate sand; suspended particles of organic materal; Parasites, Giardia; Cryptosporidium; bacteria; algae; virus; fungi; etc. Minerals calcium, silica, magnesium, etc., and Toxic metals lead; copper; chromium; etc. Some purification may be elective in its inclusion in the purification process; examples, smell (hydrogen sulfide remediation), taste (mineral extraction), and appearance (iron incapsulation).
Governments usually dictate the quality standards for drinking water water quality, these standards will require minimum / maximum setpoints for the extraction of contaminants and the inclusion of control elements that produce potable drinking water. Quality standards in the United States require specific amounts of disinfectant (example, residual chlorine content) in the water after it leaves the WTP (Water Treatment Plant), at the end of the treatment process to reduce the risk of re-contamination while the water is in the distribution system.
Ground water (usually supplied as well water) is typically a more economical choice than surface water as a source for drinking water, as it is inherently pre-filtered, by the aquifer from which it is extracted. Over large areas of the world, aquifers are recharged as part of the hydrologic cycle, and their water is a renewable resource. In more arid regions, water from an aquifer will have a limited output and can take thousands of years to recharge. Surface water; (rivers, lakes, streams) is locally more abundant where subsurface formations do not function as aquifers; however, ground water is far more abundant than the more-visible surface water. Surface water is a typical raw water source used to make drinking water where it is abundant, ground water is unavailable or poor quality, however, it is much more exposed to human activity and its byproducts. As a water source it is carefully monitored for the presence of a variety of contaminants by the WTP operators.
It is not possible to tell whether water is safe to drink just by looking at it. Simple procedures such as boiling or the use of a household charcoal filter are not sufficient for treating all the possible contaminants that may be in water from an unknown source. Even natural spring water; considered safe for all practical purposes in the 1800s; and must now be tested before determining what kind of treatment is needed. Laboratory analysis will define the contaminants in the water sample, with both qualitative and quantitative measurements. Lab analysis, while expensive, it is the only way you will be able to obtain the bench mark information necessary for establishment of a purification process, methodology for purification.
Reverse osmosis is a separation process that uses pressure to force a solvent through a membrane that retains the solute on one side and allows the pure solvent to pass to the otherside. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute.
Water is a good solvent and picks up impurities easily. Pure water -- tasteless, colorless, and odorless -- is often called the universal solvent. When water is combined with carbon dioxide to form very weak carbonic acid, an even better solvent results. As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water "hard." The degree of hardness becomes greater as the calcium and magnesium content increases and is related to the concentration of multivalent cations dissolved in the water..
One class of impurity that is of special interest is "hardness". This refers to the presence of dissolved ions, mainly of calcium Ca 2+ and magnesium Mg 2+ which are acquired through contact with rocks and sediments in the environment. The positive electrical charges of these ions are balanced by the presence of anions (negative ions), of which bicarbonate HCO 3 – and carbonate CO 3 2– are most important. These ions have their origins in limestone sediments and also from carbon dioxide which is present in all waters exposed to the atmosphere and especially in groundwaters.
Iron is an objectionable constituent of a drinking water. Appreciale amounts of Iron in water impart a bitter characteristic, metallic taste and cause oxdized precipitate.Coloration of water which may be yellowish brown to reddish brown and renders the water objectionable or unsuitable for domestic purpose. In addition Iron stain everything with which it come in contact. In hotels,hospitals, clubs, Institutions, office buildings and homes, Iron-bearing water stain wash basins, toilets, urinals, bath tubs, showers, tiled floors and walls.Iron tolerances for municipal or house hold use should not exceed 0.3 ppm. Concentration of Iron in excess of 0.2 to 0.3 mg/l may cause nuisance even though its presence does not affect the hygienic quality of water.
Iron exists in water in two levels.One as the bi-valent , Ferrous Iron ( Fe ++) and the second one as the tri-valent, Ferric Iron (Fe+++). The Ferric Iron generally occuring in the precipitated form. Iron forms complexes of hydroxides and other in-organic complexes in solution with substantial amounts of bi-carbonate, sulphate, Phosphate, Cyanide or Halides. Presence of organic substances induces the formation of organic complexes which increase the solubility of Iron. The waters of high alkalinity have lower iron than waters of low alkalinity.
The commonest form in which Iron is found in water supplies is as Ferrous bi-carbonate which is a soluble, colourless salt and exists only in solution. Its solubility is increased by increasing the free Carbon-di-oxide content of the water. The unaerated water is clear and colourless. It develops a slight whitish haze, which on longer standing turns yellowish and then forms yellowish brown to reddish brown deposits of hydrated Ferric oxide after aeration..
Oxidation by aeration or use of chemicals like chlorine, chlorine di-oxide or potassium permanganate followed by filtration alone or by settling and filtration can bring about the precipitation of iron and its removal. Use of zeolites as well as catalytic oxidation also serve the purpose.
Water quality is the physical, chemical and biological characteristics of water, characterized through the methods of hydrometry. The primary bases for such characterization are parameters which relate to drinking water, safety of human contact and for health of ecosystems. The vast majority of surface water on the planet is neither potable nor toxic. This remains true even if sea water in the oceans (which is too salty to drink) isn't counted. Another general perception of water quality is that of a simple property that tells whether water is water pollution or not. In fact, water quality is a very complex subject, in part because water is a complex medium intrinsically tied to the ecology of the Earth. Industrial pollution is a major cause of water pollution, as well as runoff from agricultural areas, urban stormwater runoff and discharge of untreated sewage (especially in developing countries).
Contaminants that may be in untreated water include microorganisms such as viruses and bacteria; inorganic contaminants such as salts and metals; pesticides and herbicides; organic chemical contaminants from industrial processes and petroleum use; and radioactive contaminants. Water quality depends on the local geology and ecosystem, as well as human uses such as sewage dispersion, industrial pollution, use of water bodies as a heat sink, and overuse (which may lower the level of the water).
The Environmental Protection Agency prescribes regulations that limit the amount of certain contaminants in the water provided by public water systems for tap water. Food and Drug Administration (FDA) regulations establish limits for contaminants in bottled water that must provide the same protection for public health. Drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants. The presence of these contaminants does not necessarily indicate that the water poses a health risk.
Some people use water purification technology to remove contaminants from the municipal water supply they get in their homes, or from local pumps or bodies of water. For people who get water from a local stream, lake, or aquifer, their drinking water is not filtered by the local government.
Toxic substances and high populations of certain microorganisms can present a health hazard for non-drinking purposes such as irrigation, swimming, fishing, rafting, boating, and industrial uses. These conditions may also impact wildlife which use the water for drinking or as a Habitat.
Interest by individuals and volunteer groups in making local water quality observations is high, and an understanding of the basic chemistry of many water quality parameters is an essential first step to making good measurements. Most citizens harbor great concern over the purity of their drinking water, but there is far more to water quality than water treatment for human consumption.
Statements to the effect that "uses must be preserved" are included within water quality regulations because they provide for broad interpretation of water quality results, while preserving the ultimate goal of the regulations. Technical measures of water quality—that is, the values obtained when making water quality measurements—are always subject to interpretation from multiple perspectives. Is it reasonable to expect a river to be pristine in a landscape that no longer is? If a river has always carried sediment, is it polluted even if the cause is not man induced? Can water quality be maintained when water quantity can not? The questions that arise from consideration of water quality relative to human uses of the water become more complex when consideration must also be given to conditions required to sustain aquatic biota. Yet inherent in the concept of preserving uses is a mandate that waterways must be much more than conduits for a fluid we might want to drink, fill our swimming pool with, or carry our wastes out of town.