What is wastewater treatment? by shubhamindia


									                                    Wastewater treatment
Waste-water treatment is becoming ever more critical due to diminishing water resources, increasing

Waste-water disposal costs.

We call water "hard" if it contains a lot of calcium or magnesium dissolved in it. A water softener
reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion
concentration in hard water. These "hardness ions" cause three major kinds of undesired effects.

Most visibly, metal ions react with soaps and calcium-sensitive detergents, hindering their ability to
lather and forming a precipitate-the familiar "bathtub ring". Presence of "hardness ions" also inhibits the
cleaning effect of detergent formulations.

Second, calcium and magnesium carbonates tend to precipitate out as hard deposits to the surfaces of
pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate
ions but also happens to some extent even in the absence of such ions. The resulting build-up of scale
can restrict water flow in pipes. In boilers, the deposits act as an insulation that impairs the flow of heat
into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a
pressurized system, this can lead to failure of the boiler.

Third, the presence of ions in an electrolyte, in this case, hard water, can also lead to galvanic corrosion,
in which one metal will preferentially corrode when in contact with another type of metal, when both
are in contact with an electrolyte. However the sodium (or potassium) ions released during conventional
water softening are much more electrolytic ally active than the calcium or magnesium ions that they
replace and galvanic corrosion would be expected to be substantially increased by water softening and
not decreased. Similarly if any lead plumbing is in use, softened water is likely to be substantially more
plumbo-solvent than hard water

Ion-exchange resin devices

Conventional water-softening devices intended for household use depend on an ion-exchange resin in
which "hardness" ions trade places with sodium ions that are electrostatically bound to the anionic
functional groups of the polymeric resin. A class of minerals called zeolites also exhibits ion-exchange
properties; these minerals were widely used in earlier water-softeners. Water softeners may be
desirable when the source of water is a well, whether municipal or private.

How it works

The water to be treated passes through a bed of the resin. Negatively-charged resins absorb and bind
metal ions, which are positively charged. The resins initially contain univalent hydrogen, sodium or
potassium ions, which exchange with divalent calcium and magnesium ions in the water. As the water
passes through the resin column, the hardness ions replace the hydrogen, sodium or potassium ions
which are released into the water. The "harder" the water, the more hydrogen, sodium or potassium
ions are released from the resin and into the water.

Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and
hydroxyl ions released from the resin. Both types of resin may be provided in a single water softener.


As these resins become loaded with undesirable captions and anions they gradually lose their
effectiveness and must be regenerated. If a cationic resin is used (to remove calcium and magnesium
ions) then regeneration is usually effected by passing concentrated brine, usually of sodium chloride or
potassium chloride, or hydrochloric acid solution through them.

For anionic resins a solution of sodium or potassium hydroxide (lye) is used. If potassium chloride is used
the same exchange process takes place except that potassium is exchanged for the calcium, magnesium
and iron instead of sodium. This is a more expensive option and may be unsuited for people on
potassium-restricted diets.

waste water treatment plant covers the mechanisms and processes used to treat waters that have been
contaminated in some way by anthropogenic industrial or commercial activities prior to its release into
the environment or its re-use.

Most industries produce some wet waste although recent trends in the developed world have been to
minimise such production or recycle such waste within the production process. However, many
industries remain dependent on processes that produce wastewaters.

Water treatment for the production of drinking water is dealt with elsewhere. (See water purification.)
Many industries have a need to treat water to obtain very high quality water for demanding purposes.
Water treatment produces organic and mineral sludges from filtration and sedimentation. Ion exchange
using natural or synthetic resins removes calcium, magnesium and carbonate ions from water, replacing
them with hydrogen and hydroxyl ions. Regeneration of ion exchange columns with strong acids and
alkalis produces a wastewater rich in hardness ions which are readily precipitated out, especially when
in admixture with other wastewaters.

Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from
wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical,
and biological processes to remove physical, chemical and biological contaminants. Its objective is to
produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated
sludge) suitable for disposal or reuse (usually as farm fertilizer). Using advanced technology it is now
possible to re-use sewage effluent for drinking water, although Singapore is the only country to
implement such technology on a production scale in its production of NEWater.

wastewater treatment plant that cannot be discharged to sanitary sewers for treatment at a centralized
wastewater treatment plant must be treated on the site where it originated. Systems for on-site
treatment of wastewater are referred to as “septic systems”, “on-site disposal systems”, subsurface
disposal systems” or “individual sewerage systems”(SSDS) among others.

Sewage flows from the original area into the septic tank where the heavier solids settle to the bottom
forming a sludge deposit. Lighter solids, such as grease, float to the top and form a scum layer. The
liquid flows from the septic tank into an absorption system where it soaks into the soil. This process
provides treatment of the sewage by gravity settling and skimming, biological decomposition and soil
filtration. Proper functioning of an individual sewerage system depends on adequate design, proper
construction, careful use and maintenance.

Today, we need science-based solutions reflecting expertise in environmental engineering, technology,
regulatory issues, design and project management.

The best approach is to find a single source for these services. This streamlines the work process,
maximizes your performance, extends your budget furthest and ensures greater accountability


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