water part 1

7/31/2019 Water Part 1

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WATER


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WATER

Water is a chemical substance with the chemical formulaH2O. Itsmolecule contains one oxygen and twohydrogen atoms connectedby covalent bonds. Water is a liquid at ambient conditions, but itoften co-exists on Earth with its solid state, ice, and gaseous state(water vapor or steam). Water also exists in a liquid crystal state

near hydrophilic surfaces.[1][2]

Water covers 70.9% of the Earth's surface,[3]and is vital for all

known forms oflife.[4] On Earth, it is found mostly in oceans andother large water bodies, with 1.6% of water below groundin aquifers and 0.001% in the air asvapor, clouds (formed of solidand liquid water particles suspended in air),

and precipitation.[5]

Oceans hold 97% of surface water, glaciers andpolar ice caps 2.4%, and other land surface water suchas rivers, lakes and ponds 0.6%. A very small amount of the Earth'swater is contained within biological bodies and manufacturedproducts.
http://en.wikipedia.org/wiki/Chemical_substancehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Chemical_formulahttp://en.wikipedia.org/wiki/H2Ohttp://en.wikipedia.org/wiki/H2Ohttp://en.wikipedia.org/wiki/H2Ohttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressurehttp://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressurehttp://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressurehttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressurehttp://en.wikipedia.org/wiki/Icehttp://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressurehttp://en.wikipedia.org/wiki/Gaseoushttp://en.wikipedia.org/wiki/Gaseoushttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Icehttp://en.wikipedia.org/wiki/Gaseoushttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Hydrophilehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Lifehttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Lifehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Aquiferhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Vaporhttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Aquiferhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Vaporhttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Ice_caphttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Oceanhttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Ice_caphttp://en.wikipedia.org/wiki/Pondhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Pondhttp://en.wikipedia.org/wiki/Pondhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Ice_caphttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Oceanhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Vaporhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Aquiferhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Lifehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Hydrophilehttp://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Liquid_crystalhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Gaseoushttp://en.wikipedia.org/wiki/Icehttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressurehttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/H2Ohttp://en.wikipedia.org/wiki/H2Ohttp://en.wikipedia.org/wiki/H2Ohttp://en.wikipedia.org/wiki/Chemical_formulahttp://en.wikipedia.org/wiki/Chemical_substance


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WATER IS LIFE

Water covers 75% of the Earth's surface. The total amount of water on

Earth remains about the same from one year to the next, as it circulates

between the oceans, land and atmosphere in a cycle of evaporation and

precipitation. This hydrological cycle is fundamental to the functioning of

the Earth as it recycles water, and has a role in modifying and regulating

the Earth's climate.

Nearly 98% of the Earth's water is in the oceans. Freshwater makes up less

than 3% of water on earth, and over two-thirds of this is tied up in polar

ice caps and glaciers. Freshwater lakes and rivers make up only 0.009% of

water on Earth and groundwater makes up 0.28%.

Water is essential for all life forms. For example, it makes up 60 to 70% byweight of all living organisms and is essential for photosynthesis. The

viability of all life on Earth is determined chiefly by the presence of water,

which is not evenly distributed on the planet. If it were, it would cover the

entire surface to a depth of 3 km (nearly five miles).


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It seems that the most relative fact is that while three-quarters of the Earth's

surface is covered with water, less than one percent (0.37% to be exact) of

that water is drinkable. Furthermore groundwater, where we place pumps for

wells, only accounts for 0.28% of freshwater across the globe.


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THE WATER CYCLE

The sun, which drives the water cycle, heats water in oceans and seas. Water

evaporates as water vapor into the air. Ice and snow can sublimate directly into

water vapor. Evapotranspirationis water transpired from plants and evaporated

from the soil. Rising air currents take the vapor up into the atmosphere where

cooler temperatures cause it to condense into clouds. Air currents move water

vapor around the globe, cloud particles collide, grow, and fall out of the sky asprecipitation. Some precipitation falls as snow or hail, sleet, and can accumulate as

ice caps and glaciers, which can store frozen water for thousands of years. Most

water falls back into the oceans or onto land as rain, where the water flows over

the ground as surface runoff. A portion of runoff enters rivers in valleys in the

landscape, with streamflow moving water towards the oceans. Runoff and

groundwater are stored as freshwater in lakes. Not all runoff flows into rivers,much of it soaks into the ground as infiltration. Some water infiltrates deep into

the ground and replenishes aquifers, which store freshwater for long periods of

time. Some infiltration stays close to the land surface and can seep back into

surface-water bodies (and the ocean) as groundwater discharge. Some

groundwater finds openings in the land surface and comes out as freshwater

springs. Over time, the water returns to the ocean, where our water cycle started.
http://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Sublimation_(chemistry)http://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Surface_runoffhttp://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Infiltration_(hydrology)http://en.wikipedia.org/wiki/Aquiferhttp://en.wikipedia.org/wiki/Aquiferhttp://en.wikipedia.org/wiki/Infiltration_(hydrology)http://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Surface_runoffhttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Sublimation_(chemistry)http://en.wikipedia.org/wiki/Air


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THE WATER CYCLE


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THE MAIN PROCESSES OF THE

WATER CYCLE Precipitation

Condensed water vapor that falls to the Earth's surface . Mostprecipitation occurs as rain, but also includes snow, hail, fog drip, graupel,and sleet.[1] Approximately 505,000 km3 (121,000 cu mi) of water falls asprecipitation each year, 398,000 km3 (95,000 cu mi) of it over theoceans.[2]

Canopy interception

The precipitation that is intercepted by plant foliage, eventuallyevaporates back to the atmosphere rather than falling to the ground.

Snowmelt

The runoff produced by melting snow.

Runoff

The variety of ways by which water moves across the land. This includesboth surface runoff and channel runoff. As it flows, the water may seepinto the ground, evaporate into the air, become stored in lakes orreservoirs, or be extracted for agricultural or other human uses.
http://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Rainhttp://en.wikipedia.org/wiki/Hailhttp://en.wikipedia.org/wiki/Fog_driphttp://en.wikipedia.org/wiki/Ice_pelletshttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Rainhttp://en.wikipedia.org/wiki/Hailhttp://en.wikipedia.org/wiki/Fog_driphttp://en.wikipedia.org/wiki/Graupelhttp://en.wikipedia.org/wiki/Ice_pelletshttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Interception_(water)http://en.wikipedia.org/wiki/Snowmelthttp://en.wikipedia.org/wiki/Runoff_(hydrology)http://en.wikipedia.org/wiki/Channel_runoffhttp://en.wikipedia.org/wiki/Channel_runoffhttp://en.wikipedia.org/wiki/Channel_runoffhttp://en.wikipedia.org/wiki/Runoff_(hydrology)http://en.wikipedia.org/wiki/Snowmelthttp://en.wikipedia.org/wiki/Interception_(water)http://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Ice_pelletshttp://en.wikipedia.org/wiki/Graupelhttp://en.wikipedia.org/wiki/Fog_driphttp://en.wikipedia.org/wiki/Hailhttp://en.wikipedia.org/wiki/Rainhttp://en.wikipedia.org/wiki/Precipitation_(meteorology)


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Subsurface flow

The flow of water underground, in the vadose zone and aquifers.

Subsurface water may return to the surface (e.g. as a spring or by being

pumped) or eventually seep into the oceans. Water returns to the land

surface at lower elevation than where it infiltrated, under the force of

gravity or gravity induced pressures. Groundwater tends to move slowly,

and is replenished slowly, so it can remain in aquifers for thousands of

years.

Evaporation

The transformation of water from liquid to gas phases as it moves from

the ground or bodies of water into the overlying atmosphere.[4] The source

of energy for evaporation is primarily solar radiation. Evaporation often

implicitly includes transpiration from plants, though together they are

specifically referred to as evapotranspiration. Total annualevapotranspiration amounts to approximately 505,000 km3 (121,000

cu mi) of water, 434,000 km3 (104,000 cu mi) of which evaporates from

the oceans.[2]

Sublimation

The state change directly from solid water (snow or ice) to water vapor. [5]
http://en.wikipedia.org/wiki/Subsurface_flowhttp://en.wikipedia.org/wiki/Vadose_zonehttp://en.wikipedia.org/wiki/Gravityhttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Sublimation_(chemistry)http://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Sublimation_(chemistry)http://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Gravityhttp://en.wikipedia.org/wiki/Vadose_zonehttp://en.wikipedia.org/wiki/Subsurface_flow


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Advection

The movement of water in solid, liquid, or vapor states

through the atmosphere. Without advection, water that evaporatedover the oceans could not precipitate over land.[6]

Condensation

The transformation of water vapor to liquid water droplets in the

air, creating clouds and fog.[7]

Transpiration

The release of water vapor from plants and soil into the air. Water

vapor is a gas that cannot be seen.
http://en.wikipedia.org/wiki/Advectionhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Advection


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WATER PURIFICATION

Water purification is the process of removing undesirable chemicals,materials, and biological contaminants from contaminated water. The goalis to produce water fit for a specific purpose. Most water is purified forhuman consumption (drinking water) but water purification may also bedesigned for a variety of other purposes, including meeting therequirements of medical, pharmacology, chemical and industrial

applications. In general the methods used include physical processes suchas filtration and sedimentation, biological processes such as slow sandfilters or activated sludge, chemical processes such as flocculation andchlorination and the use of electromagnetic radiation such as ultravioletlight.

The purification process of water may reduce theconcentration of

particulate matter including suspendedparticles, parasites, bacteria,algae, viruses, fungi; and a range of dissolved and particulate materialderived from the surfaces that water may have made contact with afterfalling as rain.
http://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Filtrationhttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Slow_sand_filtershttp://en.wikipedia.org/wiki/Slow_sand_filtershttp://en.wikipedia.org/wiki/Slow_sand_filtershttp://en.wikipedia.org/wiki/Filtrationhttp://en.wikipedia.org/wiki/Activated_sludgehttp://en.wikipedia.org/wiki/Activated_sludgehttp://en.wikipedia.org/wiki/Activated_sludgehttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Flocculationhttp://en.wikipedia.org/wiki/Flocculationhttp://en.wikipedia.org/wiki/Slow_sand_filtershttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/wiki/Activated_sludgehttp://en.wikipedia.org/wiki/Flocculationhttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Particle_(ecology)http://en.wikipedia.org/wiki/Parasitehttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Virushttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Particle_(ecology)http://en.wikipedia.org/wiki/Parasitehttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Virushttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Rainhttp://en.wikipedia.org/wiki/Rainhttp://en.wikipedia.org/wiki/Rainhttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Virushttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Parasitehttp://en.wikipedia.org/wiki/Particle_(ecology)http://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/wiki/Flocculationhttp://en.wikipedia.org/wiki/Activated_sludgehttp://en.wikipedia.org/wiki/Slow_sand_filtershttp://en.wikipedia.org/wiki/Slow_sand_filtershttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Filtrationhttp://en.wikipedia.org/wiki/Drinking_water


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METHODS OF WATER PURIFICATION

Flocculation

Sedimentation

Filtration

pH adjustment

Desalination

Distillation


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THE PURIFICATION PROCESS

Coagulation and Flocculation: The first stage, to collect small particles and

dissolved organic matter, is a complex physical and chemical process. A

coagulant is added to the untreated water and this reacts with the

impurities, forming them into floc particles up to 5mm in diameter.

Sedimentation: After 20 to 30 minutes in the flocculation tanks, the water

and suspended floc particles pass through to sedimentation basins where,

after several hours, most of the floc settles to the bottom of the basins

and forms a sludge. The water, now containing only a small amount of very

fine floc particles, passes on to the filters. The sludge is removed for

further treatment and disposal.


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Filtration: Water from the sedimentation process passes through afiltering media usually a deep bed of sand or sand/anthracite dualmedia. As the water passes through the filter bed, any particles remainingfrom the sedimentation process are trapped in the fine spaces within the

media resulting in clear, clean water.

Disinfection: Disinfection is achieved by adding chlorine, generallybetween the filters and the filtered water storage tank, to destroy anymicro-organisms that are not removed in the flocculation and filtrationstages. In longer water mains such as those in country areas, SA Water

uses chloramination, a combination of chlorine and ammonia, fordisinfecting water. Chloramine is more effective in these longer systemsthan chlorine alone. Both methods of disinfection are widely used acrossAustralia and other parts of the world and have been for many decades.

Storage and distribution: After disinfection the water passes to covered

water storage tanks ready for distribution.


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THE PURIFICATION OF WATER

Flocculation is a process which clarifies the water. Clarifying means

removing any turbidity or colour so that the water is clear and colourless.

Clarification is done by causing a precipitate to form in the water which

can be removed using simple physical methods. Initially the precipitate

forms as very small particles but as the water is gently stirred, these

particles stick together to form bigger particles. Many of the small

particles that were originally present in the raw water adsorb onto the

surface of these small precipitate particles and so get incorporated into

the larger particles that coagulation produces. In this way the coagulated

precipitate takes most of the suspended matter out of the water and is

then filtered off, generally by passing the mixture through a coarse sandfilter or sometimes through a mixture of sand and granulated anthracite

(high carbon and low volatiles coal).
http://en.wikipedia.org/wiki/Flocculationhttp://en.wikipedia.org/wiki/Turbidityhttp://en.wikipedia.org/wiki/Anthracitehttp://en.wikipedia.org/wiki/Volatileshttp://en.wikipedia.org/wiki/Volatileshttp://en.wikipedia.org/wiki/Anthracitehttp://en.wikipedia.org/wiki/Turbidityhttp://en.wikipedia.org/wiki/Flocculation


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Coagulants / flocculating agents that may be used include:

Iron(III) hydroxide. This is formed by adding a solution of an iron (III)compound such as iron(III) chloride to pre-treated water with a pH

of 7 or greater. Iron (III) hydroxide is extremely insoluble and formseven at a pH as low as 7. Commercial formulations of iron saltswere traditionally marketed in the UK under the name Cuprus.

Aluminium hydroxide is also widely used as the flocculatingprecipitate although there have been concerns about possiblehealth impacts and mishandling led to a severe poisoning incident

in 1988 at Camelford in south-west UK when the coagulant wasintroduced directly into the holding reservoir of final treated water.

PolyDADMAC is an artificially produced polymer and is one of aclass of synthetic polymers that are now widely used. Thesepolymers have a high molecular weight and form very stable andreadily removed flocs, but tend to be more expensive in usecompared to inorganic materials. The materials can also bebiodegradable.
http://en.wikipedia.org/wiki/Flocculantshttp://en.wikipedia.org/wiki/Iron%28III%29_hydroxidehttp://en.wikipedia.org/wiki/Iron%28III%29_chloridehttp://en.wikipedia.org/wiki/Aluminium_hydroxidehttp://en.wikipedia.org/wiki/Camelfordhttp://en.wikipedia.org/wiki/Camelford_water_pollution_incidenthttp://en.wikipedia.org/wiki/Camelfordhttp://en.wikipedia.org/wiki/PolyDADMAChttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Inorganichttp://en.wikipedia.org/wiki/Inorganichttp://en.wikipedia.org/wiki/Inorganichttp://en.wikipedia.org/wiki/Inorganichttp://en.wikipedia.org/wiki/Inorganichttp://en.wikipedia.org/wiki/Flocshttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/PolyDADMAChttp://en.wikipedia.org/wiki/Camelfordhttp://en.wikipedia.org/wiki/Camelford_water_pollution_incidenthttp://en.wikipedia.org/wiki/Aluminium_hydroxidehttp://en.wikipedia.org/wiki/Aluminium_hydroxidehttp://en.wikipedia.org/wiki/Aluminium_hydroxidehttp://en.wikipedia.org/wiki/Iron%28III%29_chloridehttp://en.wikipedia.org/wiki/Iron%28III%29_hydroxidehttp://en.wikipedia.org/wiki/Flocculants


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Floc floating at the surface of a basin Mechanical system to push floc out of

the water basin
http://en.wikipedia.org/wiki/Flocculationhttp://en.wikipedia.org/wiki/Flocculation


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SEDIMENTATION

Waters exiting the flocculation basin may enter the sedimentation basin,

also called a clarifier or settling basin. It is a large tank with slow flow,

allowing floc to settle to the bottom. The sedimentation basin is best located

close to the flocculation basin so the transit between 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 layerthat furthest from the sedimentexits. The amount of floc that

settles out of the water is dependent on basin retention time and on basin

depth. The retention time of the water must therefore be balanced against

the cost of a larger basin. The minimum clarifier retention time is normally 4hours. A deep basin will allow more floc to settle out than a shallow basin.

This is because large particles settle faster than smaller ones, so large

particles collide with and integrate smaller particles as they settle. In effect,

large particles sweep vertically through the basin and clean out smaller

particles on their way to the bottom.
http://en.wikipedia.org/wiki/Settling_basinhttp://en.wikipedia.org/wiki/Weirhttp://en.wikipedia.org/wiki/Weirhttp://en.wikipedia.org/wiki/Settling_basin


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As particles settle to the bottom of the basin, a layer of sludge is

formed on the floor of the tank. This layer of sludge must be

removed and treated. The amount of sludge that is generated is

significant, often 3 to 5 percent of the total volume of water that istreated. The cost of treating and disposing of the sludge can be a

significant part of the operating cost of a water treatment plant.

The tank may be equipped with mechanical cleaning devices that

continually clean the bottom of the tank or the tank can be taken

out of service when the bottom needs to be cleaned.


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FILTRATION

After separating most floc, the water is filtered as the final step to remove

remaining suspended particles and unsettled floc using Rapid sand filters,

Membrane filtration or Slow sand filters.

Rapid sand filters

The most common type of filter is a rapid sand filter. Water movesvertically through sand which often has a layer ofactivated 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.
http://en.wikipedia.org/wiki/Rapid_sand_filterhttp://en.wikipedia.org/wiki/Activated_carbonhttp://en.wikipedia.org/wiki/Anthracite_coalhttp://en.wikipedia.org/wiki/Anthracite_coalhttp://en.wikipedia.org/wiki/Activated_carbonhttp://en.wikipedia.org/wiki/Rapid_sand_filter


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To clean the filter, water is passed quickly upward through the filter,opposite the normal direction (called backflushing or backwashing) to

remove embedded particles. Prior to this, compressed air may be blown

up through the bottom of the filter to break up the compacted filter mediato 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.
http://en.wikipedia.org/wiki/Backwashing_%28water_treatment%29http://en.wikipedia.org/wiki/Backwashing_%28water_treatment%29


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Advantages:

Filters out much smaller particles than paper and sand filters can.

Filters out virtually all particles larger than their specified pore sizes.

They are quite thin and so liquids flow through them fairly rapidly.

They are reasonably strong and so can withstand pressure differences

across them of typically 25 atmospheres.

They can be cleaned (back flushed) and reused.


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MEMBRANE FILTRATION

Membrane filters are widely used for filtering both drinking water and

sewage. For drinking water, membrane filters can remove virtually all

particles larger than 0.2 umincluding giardia and cryptosporidium.

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 furtherdownstream. 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 phosphorus,

nitrates and heavy metal ions.
http://en.wikipedia.org/wiki/Membrane_technologyhttp://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Giardiahttp://en.wikipedia.org/wiki/Cryptosporidiumhttp://en.wikipedia.org/wiki/Cryptosporidiumhttp://en.wikipedia.org/wiki/Giardiahttp://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Membrane_technology


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Slow sand filters Slow "artificial" filtration (a variation ofbank filtration) to the ground,

Water purification plant Kran, Czech Republic

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 fordisinfection. 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 pre-treatment is well designed and produces water

with a very low available nutrient level which physical methods oftreatment rarely achieve. Very low nutrient levels allow water to be safely

sent through distribution system 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 eventuallyobstructed by biological growth.
http://en.wikipedia.org/wiki/Bank_filtrationhttp://en.wikipedia.org/wiki/Slow_sand_filterhttp://en.wikipedia.org/wiki/Schmutzdeckehttp://en.wikipedia.org/wiki/Schmutzdeckehttp://en.wikipedia.org/wiki/Slow_sand_filterhttp://en.wikipedia.org/wiki/Bank_filtration


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A specific 'large-scale' form of slow sand filter is the process ofbank

filtration, in which natural sediments in a riverbank are used to provide a

first stage of contaminant filtration. While typically not clean enough to beused 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.
http://en.wikipedia.org/wiki/Bank_filtrationhttp://en.wikipedia.org/wiki/Bank_filtrationhttp://en.wikipedia.org/wiki/Bank_filtrationhttp://en.wikipedia.org/wiki/Bank_filtration

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