Why chemically watertreatment

Chemicals are used during wastewater treatment in an array ofprocesses

to expedite disinfection. These chemical processes, which inducechemical

reactions, are called chemical unit processes, and are used alongsidebiological

and physical cleaning processes to achieve various water standards.There

are several distinct chemical unit processes, including chemicalcoagulation,

chemical precipitation, chemical oxidation and advanced oxidation, ion

exchange, and chemical neutralization and stabilization, which can beapplied

to wastewater during cleaning.

Types of chemical water treatment

1. Chlorination 2. Ozonation  3. Oxidation4. Coagulation  5. Precipitation6. Ion Exchange

1. Chlorination:

Water chlorination is the processof adding chlorine (Cl2) or hypochlorite to water. This methodis used to kill certain bacteriaand other microbes in tap water aschlorine is highly toxic.Chlorination also refers to the treatment of water to kill microorganisms and oxidize several organic contaminates.

Or

In this process, chlorine - a strong oxidizing chemical, is used to kill the bacteria which lead to decomposition of water and Destabilisation of colloid particles by the addition of chemicals(coagulant)

Chlorination Advantages:

-low cost & effective

–Easy to use method of chemical purification of water

–Effective at killing bacteria and viruses

Inexpensive Disadvantages:

-chlorine residue could be harmful to environment

–Not effective at killing all parasites.

–Complex compounds can form with organic material which over time can be hazardous to health.

–It is best to use the water in a shorter period of time and store it in a plastic container in a cool and shaded place.

2. Ozonation: The formation of oxygen into ozone occurs with theuse of energy. This process is carried out by anelectric discharge field as in the CD-type ozonegenerators (corona discharge simulation of thelightning), or by ultraviolet radiation as in UV-type ozone generators (simulation of the ultra-violet rays from the sun). In addition to thesecommercial methods, ozone may also be made throughelectrolytic and chemical reactions.

Ozone is a naturally occurring component of freshair. It can be produced by the ultraviolet rays ofthe sun reacting with the Earth's upper atmosphere(which creates a protective ozone layer), bylightning, or it can be created artificially with an ozone generator. 

The ozone molecule contains three oxygen atoms whereas the normal oxygen molecule contains only two.  Ozone is a very reactive and unstable gas with a short half-life before it reverts back to oxygen. Ozone is the most powerful and rapid acting oxidizer man can produce, and will oxidize all bacteria, mold and yeast spores, organic materialand viruses given sufficient exposure.  

Or

This is a chemical water treatment method, wherein oxidizing agents - such as ozone, are used to treat polluted water. These oxidizing agents make water reusable by hampering the biological growth process of bacteria which happens to be the main cause of decomposition of water.

The advantages of using Ozone include:

Ozone is primarily a disinfectant that effectively kills biological contaminants. 

Ozone also oxidizes and precipitates iron, sulfur, and manganese so they can be filtered out of solution.  

Ozone will oxidize and break down many organic chemicals including many that cause odor and taste problems.

Ozonation produces no taste or odor in the water.

Since ozone is made of oxygen and reverts to pure oxygen, it vanishes without trace once it has been used.  In the home, this does not matter much, but when water companies use ozone to disinfect the water there is no residual disinfectant, so chlorine or another disinfectant must be added to minimize microbial growth during storage and distribution.

The disadvantages of using Ozone include:

Ozone treatment can create undesirable by products that can beharmful to health if they are not controlled (e.g., formaldehyde and bromated).  

The process of creating ozone in the home requires electricity.  In an emergency with loss of power, this treatment will not work.

Ozone is not effective at removing dissolved minerals and salts.

3. Oxidation and AdvancedOxidation :

With the introduction of an oxidizing agentduring chemical oxidation,

electrons move from the oxidant to thepollutants in wastewater. The

pollutants then undergo structuralmodification, becoming less destructive

compounds. Alkaline chlorination uses chlorineas an oxidant against cyanide.

However, alkaline chlorination as a chemicaloxidation process can lead to

the creation of toxic chlorinated compounds, and additional steps maybe

required. Advanced oxidation can help remove any organic compoundsthat

are produced as a byproduct of chemical oxidation, through processessuch as

steam stripping, air stripping, or activated carbon adsorption.

Or

● Oxidants are used in wastewater treatment as a first step in the removal of heavy metals to oxidize organics or as a last step in a treatment process, to oxidize odoriferous compounds such as hydrogen sulphide or to oxidize inorganics such as cyanide and for disinfection.

● Common oxidation agents used in wastewater treatment:

-Oxygen(O2).

-Chlorine (Cl2).

-Sodium hypochlorite (NaClO).

-Calcium hypochlorite (Ca(ClO)2).

-Potassium permanganate(KMnO4).

-Hydrogen peroxide(H2O2).

Or

a method by which wastewater is treated by using oxidizing agents.

Generally, two forms viz.

• Chemical oxidation and

• UV assisted oxidation using chlorine, hydrogen peroxide, fenton’sreagent, ozone, or potassium permanganate are used for treating the effluents, especially those obtained from primary treatment (sedimentation)

• Rapid and efficient process

• High energy cost, chemicals required

Or

Oxidation and reduction in terms of electron transfer

• This is easily the most important use of the terms oxidation andreduction at A' level.

Definitions

• Oxidation is loss of electrons.

• Reduction is gain of electrons.

OIL RIG à oxidation is loss, reduction is gain

CuO + Mg à Cu + MgO

Cu2+ + Mg à Cu + Mg2+

Advantages:

•Constant process performance

•No disposal of concentrates or solids (compared with AC sorption or membrane filtration)

safer than chlorination fewer disinfection by-product Complete mineralization of pollutants possible Staff savings and increased reliability No increase in salinity, which enables recirculation No disinfection by-products – in particular no halogenated

compounds Less handling of hazardous chemical agents Little or no sludge formed Hygienic outflow water Robust process – discharge criteria can be met reliably Available quickly – standby operation possible Suitable for varying quantities and qualities of wastewater Rapid reaction rates Small foot print Potential to reduce toxicity of organic compounds Mineralization of organics, i.e. conversion to salt and CO2 Does not concentrate waste for further treatment, such as membranes Does not produce "spent carbon" such activated carbon absorption Easily Automated and Controlled Reduced Labor Input Does not create sludge as with physical chemical process or

biological processes (wasted biological sludge)

Major Disadvantages of Adsorption process are

high cost• Product recovery possibly requiring a special, expensive distillation (or extraction)• Adsorbent progressively deteriorating in capacity as number of

cycles increases• Adsorbent regeneration requiring a steam or vacuum source• Relatively high capital cost• Prefiltering of gas stream possibly required to remove any particles capable ofplugging adsorbent bed• Cooling of gas stream require to get usual range of operation temp (below 50C°)• Relatively high steam requirements to desorb high-molecular-weight pollutants• Spent adsorbent may be considered a hazardous waste• Some contaminants may undergo violent exothermically with adsorbent (explosion danger).

Capital Intensive Complex chemistry must be tailored to specific application For some applications quenching of excess peroxide is required

4. Chemical Coagulation :

This chemical process involves destabilizing wastewater particles sothat

they aggregate during chemical flocculation. Fine solid particles dispersed

in wastewater carry negative electricsurface charges (in their normal stable

state), which prevent them from forming larger groups and settling. Chemical

coagulation destabilizes these particles by introducing positively charged

coagulants that then reduce the negative particles’ charge. Once the charge is

reduced, the particles freely form larger groups. Next, an anionic flocculant is

introduced to the mixture. Because the flocculant reacts against the positively

charged mixture, it either neutralizes the particle groups or creates bridges

between them to bind the particles into larger groups. After larger particle

groups are formed, sedimentation can be used to remove the particles from

the mixture.

Or

Coagulation is a safe and effective method of treating

water, which improves its quality by reducing levels of

organic compounds, dissolved phosphorus, colour, iron

and suspended particles.

Or

In coagulation, we add a chemical such as alum which produces positivecharges to neutralize the negative charges on the particles. Then the particles can stick together, forming larger particles which are more easily removed.

The coagulation process involves the addition of the chemical (e.g. alum) and then a rapid mixing to dissolve the chemical and distribute it evenly throughout the water.

Or

● It takes place in rapid mix, or flash mix basins which are very rapid. The primary function of rapid mix basin is to disperse the coagulant so that it contacts all of the wastewater.

● Over the years a number of different substances have been used asprecipitants. The most common ones

-Alum(Al2(SO4)3.18H2O).

-Ferrous Sulfate(FeSO4.7H2O).

-Lime Ca(OH)2.

-Ferric Chloride (FeCl3).

-Ferric Sulfate (Fe2(SO4)3).

Advantages:

–Proven reduction of viruses, bacteria, protozoa

–Pesticide and heavy metal removal

–Simple technology and use

Disadvantages:

–May be toxic if used improperly

–Could be more expensive and complicated than other methods due to increased number of required materials and skill –Requires multiple steps

5. Chemical Precipitation :

Removal of metal ions from solution by changing the solution composition,thus causing the metal ions to form insoluble metal complexes.

or

Chemical precipitation is the most common method for removing dissolved

metals from wastewater solution containing toxic metals. To convert the

dissolved metals into solid particleform, a precipitation reagent is added

to the mixture. A chemical reaction,triggered by the reagent, causes the

dissolved metals to form solid particles. Filtration can then be used to remove

the particles from the mixture. How well the process works is dependent

upon the kind of metal present, the concentration of the metal,and the kind

of reagent used. In hydroxide precipitation, a commonly used chemical

precipitation process, calcium or sodium hydroxide is used as the reagent to

create solid metal hydroxides. However, it can be difficult to create hydroxides

from dissolved metal particles in wastewater because many wastewater

solutions contain mixed metals.

Or

● Chemical precipitation in wastewater treatment involves the additionof chemicals to alter the physical state of dissolved and suspended solids and facilitate their removal by sedimentation.

Chemical Precipitation

ADVANTAGES AND DISADVANTAGES OF PRECIPITAION:

Look at the definitions I gave and figure it out! But I will help u start:

Advantages: (1) Simple to do (2) Cost effective (3) Doesnot need great expertise but some skill and practice. (4) Instruments are easily avaliable (5) Common used method and one of the oldest

Disadvantages: (1) Needs skill and practise for effecive results (2) Instruments have to be properly calibrated since it will give affected the final result. (3) Reactivity of the elements to be titrated should be well researched since this may affect the end point. (4) Time consuming if done manually

6. Ion Exchange

When water is too hard, it is difficult to useto clean and often leaves a grey

residue. (This is why clothing washed in hard water often retains a dingy

tint.) An ion exchange process can be used to soften the water. Calcium and

magnesium are common ions that lead to water hardness. To soften the water,

positively charged sodium ions are introduced in the form of dissolvedsodium

chloride salt, or brine. Hard calcium and magnesium ions exchange places

with sodium ions, and free sodium ions are simply released in the water.

However, after softening a large amount of water, the softening solution

may fill with excess calcium and magnesium ions, requiring the solution be

recharged with sodium ions.

Or

Ion exchange is basically a reversible chemical process wherein an ionfrom solution is exchanged for a similarly charged ion attached to an immobile solid particle.

Removal of undesirable anions and cations from solution through the use of ion exchange resin

• Consists of an organic or inorganic network structure with attached functional group

• Synthetic resin made by the polymerisation of organic compounds into a porous three dimensional structure

• Exchange capacity is determined by the number of functional groups per unit mass of resin

Advantages

• Remove dissolved inorganic effectively

• Re-generable (service deionization)

• Relatively inexpensive initial and capital investment

Disadvantages

• Does not effectively remove particles, pyrogens or bacteria

• De-ionized bed can generate resins particles and culture bacteria

• High operating costs over long term