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Contents

  1. Water purification
  2. Purification - Wikipedia
  3. Purification of Bacteriophages Using Anion-Exchange Chromatography.
  4. Water Purification Systems
  5. RELATED CONTENT

Water Testing. Addressing corrosive nature of various water sources. View All.


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Understanding the Clients Requirements. Process Design. After Sales Service. View Process. Thanks for submitting! Visual inspection cannot determine if water is of appropriate quality. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all possible contaminants that may be present in water from an unknown source.


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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 and microbiological analysis , while expensive, are the only way to obtain the information necessary for deciding on the appropriate method of purification. The goals of the treatment are to remove unwanted constituents in the water and to make it safe to drink or fit for a specific purpose in industry or medical applications. Widely varied techniques are available to remove contaminants like fine solids, micro-organisms and some dissolved inorganic and organic materials, or environmental persistent pharmaceutical pollutants.

The choice of method will depend on the quality of the water being treated, the cost of the treatment process and the quality standards expected of the processed water. The processes below are the ones commonly used in water purification plants. Some or most may not be used depending on the scale of the plant and quality of the raw source water.

Pure water has a pH close to 7 neither alkaline nor acidic. Sea water can have pH values that range from 7. Fresh water can have widely ranging pH values depending on the geology of the drainage basin or aquifer and the influence of contaminant inputs acid rain. If the water is acidic lower than 7 , lime , soda ash , or sodium hydroxide can be added to raise the pH during water purification processes. Lime addition increases the calcium ion concentration, thus raising the water hardness. For highly acidic waters, forced draft degasifiers can be an effective way to raise the pH, by stripping dissolved carbon dioxide from the water.

Sufficient alkalinity also reduces the corrosiveness of water to iron pipes. Acid carbonic acid , hydrochloric acid or sulfuric acid may be added to alkaline waters in some circumstances to lower the pH. Alkaline water above pH 7. The ability of water to precipitate calcium carbonate to protect metal surfaces and reduce the likelihood of toxic metals being dissolved in water is a function of pH, mineral content, temperature, alkalinity and calcium concentration.

One of the first steps in most conventional water purification processes is the addition of chemicals to assist in the removal of particles suspended in water. Particles can be inorganic such as clay and silt or organic such as algae , bacteria , viruses , protozoa and natural organic matter. Inorganic and organic particles contribute to the turbidity and color of water. The addition of inorganic coagulants such as aluminum sulfate or alum or iron III salts such as iron III chloride cause several simultaneous chemical and physical interactions on and among the particles.

Water purification

Within seconds, negative charges on the particles are neutralized by inorganic coagulants. Also within seconds, metal hydroxide precipitates of the iron and aluminium ions begin to form. These precipitates combine into larger particles under natural processes such as Brownian motion and through induced mixing which is sometimes referred to as flocculation.

Amorphous metal hydroxides are known as "floc". Large, amorphous aluminum and iron III hydroxides adsorb and enmesh particles in suspension and facilitate the removal of particles by subsequent processes of sedimentation and filtration. Aluminum hydroxides are formed within a fairly narrow pH range, typically: 5.

Iron III hydroxides can form over a larger pH range including pH levels lower than are effective for alum, typically: 5. In the literature, there is much debate and confusion over the usage of the terms coagulation and flocculation: Where does coagulation end and flocculation begin?

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Purification - Wikipedia

In water purification plants, there is usually a high energy, rapid mix unit process detention time in seconds whereby the coagulant chemicals are added followed by flocculation basins detention times range from 15 to 45 minutes where low energy inputs turn large paddles or other gentle mixing devices to enhance the formation of floc. In fact, coagulation and flocculation processes are ongoing once the metal salt coagulants are added. Organic polymers were developed in the s as aids to coagulants and, in some cases, as replacements for the inorganic metal salt coagulants.

Synthetic organic polymers are high molecular weight compounds that carry negative, positive or neutral charges. When organic polymers are added to water with particulates, the high molecular weight compounds adsorb onto particle surfaces and through interparticle bridging coalesce with other particles to form floc.

Purification of Bacteriophages Using Anion-Exchange Chromatography.

Waters exiting the flocculation basin may enter the sedimentation basin , also called a clarifier or settling basin. It is a large tank with low water velocities, allowing floc to settle to the bottom. The sedimentation basin is best located close to the flocculation basin so the transit between the two processes does not permit settlement or floc break up. Sedimentation basins may be rectangular, where water flows from end to end, or circular where flow is from the centre outward.

Sedimentation basin outflow is typically over a weir so only a thin top layer of water—that furthest from the sludge—exits. In , Allen Hazen showed that the efficiency of a sedimentation process was a function of the particle settling velocity, the flow through the tank and the surface area of tank.

Water Purification Systems

Sedimentation tanks are typically designed within a range of overflow rates of 0. In general, sedimentation basin efficiency is not a function of detention time or depth of the basin. Although, basin depth must be sufficient so that water currents do not disturb the sludge and settled particle interactions are promoted.

As particle concentrations in the settled water increase near the sludge surface on the bottom of the tank, settling velocities can increase due to collisions and agglomeration of particles. Typical detention times for sedimentation vary from 1. Inclined flat plates or tubes can be added to traditional sedimentation basins to improve particle removal performance.

Inclined plates and tubes drastically increase the surface area available for particles to be removed in concert with Hazen's original theory. The amount of ground surface area occupied by a sedimentation basin with inclined plates or tubes can be far smaller than a conventional sedimentation basin. As particles settle to the bottom of a sedimentation basin, a layer of sludge is formed on the floor of the tank which must be removed and treated. The amount of sludge generated is significant, often 3 to 5 percent of the total volume of water to be treated.

The cost of treating and disposing of the sludge can impact the operating cost of a water treatment plant. The sedimentation basin may be equipped with mechanical cleaning devices that continually clean its bottom, or the basin can be periodically taken out of service and cleaned manually. A subcategory of sedimentation is the removal of particulates by entrapment in a layer of suspended floc as the water is forced upward.

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The major advantage of floc blanket clarifiers is that they occupy a smaller footprint than conventional sedimentation. Disadvantages are that particle removal efficiency can be highly variable depending on changes in influent water quality and influent water flow rate.

Legislation and compliance

When particles to be removed do not settle out of solution easily, dissolved air flotation DAF is often used. After coagulation and flocculation processes, water flows to DAF tanks where air diffusers on the tank bottom create fine bubbles that attach to floc resulting in a floating mass of concentrated floc. The floating floc blanket is removed from the surface and clarified water is withdrawn from the bottom of the DAF tank. Water supplies that are particularly vulnerable to unicellular algae blooms and supplies with low turbidity and high colour often employ DAF.

After separating most floc, the water is filtered as the final step to remove remaining suspended particles and unsettled floc. The most common type of filter is a rapid sand filter. Water moves vertically through sand which often has a layer of activated carbon or anthracite coal above the sand. The top layer removes organic compounds, which contribute to taste and odour.

The space between sand particles is larger than the smallest suspended particles, so simple filtration is not enough. Most particles pass through surface layers but are trapped in pore spaces or adhere to sand particles. Effective filtration extends into the depth of the filter. This property of the filter is key to its operation: if the top layer of sand were to block all the particles, the filter would quickly clog. To clean the filter, water is passed quickly upward through the filter, opposite the normal direction called backflushing or backwashing to remove embedded or unwanted particles.


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Prior to this step, compressed air may be blown up through the bottom of the filter to break up the compacted filter media to aid the backwashing process; this is known as air scouring. This contaminated water can be disposed of, along with the sludge from the sedimentation basin, or it can be recycled by mixing with the raw water entering the plant although this is often considered poor practice since it re-introduces an elevated concentration of bacteria into the raw water. Some water treatment plants employ pressure filters. These work on the same principle as rapid gravity filters, differing in that the filter medium is enclosed in a steel vessel and the water is forced through it under pressure.

Slow sand filters may be used where there is sufficient land and space, as the water must be passed very slowly through the filters. These filters rely on biological treatment processes for their action rather than physical filtration. The filters are carefully constructed using graded layers of sand, with the coarsest sand, along with some gravel, at the bottom and finest sand at the top. Drains at the base convey treated water away for disinfection. Filtration depends on the development of a thin biological layer, called the zoogleal layer or Schmutzdecke , on the surface of the filter.

An effective slow sand filter may remain in service for many weeks or even months if the pretreatment is well designed and produces water with a very low available nutrient level which physical methods of treatment rarely achieve. Very low nutrient levels allow water to be safely sent through distribution systems with very low disinfectant levels, thereby reducing consumer irritation over offensive levels of chlorine and chlorine by-products.

Slow sand filters are not backwashed; they are maintained by having the top layer of sand scraped off when flow is eventually obstructed by biological growth. A specific "large-scale" form of slow sand filter is the process of bank filtration , in which natural sediments in a riverbank are used to provide a first stage of contaminant filtration. While typically not clean enough to be used directly for drinking water, the water gained from the associated extraction wells is much less problematic than river water taken directly from the major streams where bank filtration is often used.

Membrane filters are widely used for filtering both drinking water and sewage. For drinking water, membrane filters can remove virtually all particles larger than 0. Membrane filters are an effective form of tertiary treatment when it is desired to reuse the water for industry, for limited domestic purposes, or before discharging the water into a river that is used by towns further downstream. They are widely used in industry, particularly for beverage preparation including bottled water. However no filtration can remove substances that are actually dissolved in the water such as phosphates , nitrates and heavy metal ions.

Ultrafiltration membranes use polymer membranes with chemically formed microscopic pores that can be used to filter out dissolved substances avoiding the use of coagulants. The type of membrane media determines how much pressure is needed to drive the water through and what sizes of micro-organisms can be filtered out. Ion exchange : [11] Ion exchange systems use ion exchange resin - or zeolite -packed columns to replace unwanted ions. Ion exchange resins are also used to remove toxic ions such as nitrite , lead , mercury , arsenic and many others. Precipitative softening : [6] : Electrodeionization : [11] Water is passed between a positive electrode and a negative electrode.

Ion exchange membranes allow only positive ions to migrate from the treated water toward the negative electrode and only negative ions toward the positive electrode. Home Purification. Gilson Connect. Mix and Swap Components for Endless Possibilities. Choose Automated or Manual Injection: Manual. Choose Mass Spec: Yes.

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