chlorination – a way to disinfect drinking waters

05/01/2023Chlorination - A way to disinfect domestic water supplies

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Chlorination – A way to Disinfect domestic water supplies

Presented By- Sumer PankajClass- M.Sc. EST

Semester- 1Year – 2016-17


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Disinfection of water History of chlorination Chlorination – Process of disinfection Chlorine demand Residual chlorine Types of chlorination process Chlorination practice in in India Advantages and disadvantages of

chlorination

Outline


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Water disinfection means the removal, deactivation or killing of pathogenic microorganisms.

Microorganisms are destroyed or deactivated, resulting in termination of growth and reproduction.

When microorganisms are not removed from drinking water, drinking water usage will cause people to fall ill.

FACT Disinfection can be attained by means of physical or chemical disinfectants. The agents

also remove organic contaminants from water, which serve as nutrients or shelters for microorganisms. Disinfectants should not only kill microorganisms. Disinfectants must also have a residual effect, which means that they remain active in the water after disinfection. A disinfectant should prevent pathogenic microorganisms from growing in the plumbing after disinfection, causing the water to be recontaminated.

Disinfection

http://www.lenntech.com/water-pollution-FAQ.htm


4Types of disinfection

Disinfection

Chemical Disinfectants

- Chlorine (Cl2)- Chlorine dioxide (ClO2)

- Hypo chlorite (OCl-)- Ozone (O3)

Fig:- Hypochlorate structure.


5 Why only chlorination ?

Various processes of disinfection

- Costlier process

- Cannot be stored

- Needs skilled persons

- Do not leave ant residual

effect in waters.

Ozonation- Iodine and bromine-

Metals- silver and copper-

Uv and x-rays

Chlorination-


6 Water Treatment plant


7 Chlorination – a process of disinfection Chlorination is the process of adding the

element chlorine to water as a method of water purification to make it fit for human consumption as drinking water.

Chlorine in its various forms is invariable and almost universally used for disinfecting public water supplies. It’s cheap, reliable, easy to handle, easily measurable and above all it is capable of providing residual disinfecting effects for long periods.

It provides complete protection against further contamination of water in the distribution system.

It’s only disadvantage is that when used in greater amounts, it imparts bitter and bad taste to waters.

It is an effective method in water emergency situations as it can eliminate an overload of pathogens relatively quickly.


8 History of Chlorination• Chlorine was first discovered in

Sweden in 1744. At that time, people believed that odors from the water were responsible for transmitting diseases.

• In 1835, chlorine was used to remove odors from the water.

• After 1890, chlorine became a way to reduce the amount of disease transmitted through water.

• chlorination began in Great Britain and then expanded to the United States in 1908 and Canada by 1917.

• Earlier used to kill Bactrian responsible for cholera, typhoid, dysentery, and some viruses like polio virus and hepatitis-A followed by parasitic protozoans.

Fig. :- Disease caused by various means in great Britain

Fig. :- graph showing the decline in no. of deaths of typhoid patients.


9 What happens when Chlorine is added to waters ???

Cl2

Oxidizes organic acids (making DPBs)

Reacts with organic nitrogen

(making Chlora

mines = Combined

Chlorine)

Oxidizes inorganics

(e.g. Iron and

Manganese)

Free Chlorine HOCl

OCl -


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11 Chlorine Chemistry

Total = Free chlorine + Combined chlorine

Free chlorine = Hypochlorous acid + hypochlorite ion

HOCl = Hypochlorous AcidCa(OCl)2 = Calcium hypochlorite

Ca(OH)2 = Calcium Hydroxide NaOCl = Sodium hypochlorite

HOCl ↔ H+ + OCl- [pH dependent reaction]Ca(OCl)2 + 2H2O ↔ 2HOCl + Ca(OH)2

NaOCl + H2O ↔ HOCl+NaOH

FactKilling effiency of HOCl is 40 -

80 times larger than OCl - . Lower pH favors HOCl.


12 Chlorine chemistry conti…

Combined chlorine (chloramines):

HOCl + NH3 ↔ NH2Cl (monochloramine) + H2O

HOCl + NH2Cl ↔ NHCl2 (dichloramine) + H2O

HOCl + NHCl2 ↔ NCl3 (trichloramine) + H2O

Chlorine combined with ammonia or organic nitrogen

(causes chlorine taste and odor)


13 Chlorine demand and its measurement Chlorine demand is the difference between total chlorine added in the water and residual

chlorine. It is the amount which reacts with the substances in water, leaving behind an inactive form of chlorine. Chlorine demand can be caused in a water body due to rain containing ammonia or the addition of fertilizers which can be oxidized by chlorine.

To purify water supplies and make them suitable for purposes like drinking, cooking and swimming, chlorine is added. Chlorine demand from the total chlorine added can be explained using the following equation:

Chlorine demand = Total chlorine – Chlorine residual The purity of water can be determined by monitoring the value of chlorine demand. If the

value is zero, the water is already free of pathogenic microorganisms. If the value is less than the total chlorine, it shows that the amount of chlorine added initially to the water was sufficient.


14 Residual chlorine Residual chlorine is the amount of chlorine that remains in the water after a certain period or

contact time. Testing for residual chlorine is one of the most common tests used by water treatment

plants. Through the residual chlorine test, the remaining chlorine amount is determined in water that has finished testing and is ready to be released in the distribution system.

There are three forms of residual chlorine in water treatment:i. Free - Residual chlorine composed of dissolved hypochlorite ions, hypochlorous acid and

chlorine gasii. Combined - Composed of chloramines that can kill bacteria and oxidize organic matteriii. Total - The sum of free and combined residual chlorine.Hypochlorous acid and other strong acids are used as oxidizing agents for disinfecting drinking water. However, these acids can also react as oxidants, especially with lead, which increases the chances of lead corrosion. Therefore, operators in water treatment and distribution plants must ensure that there is the proper amount of residual chlorine as the water reaches the end of the system.


15 Types of chlorination Chlorination

Plain Chlorination

Pre-Chlorination

Post- Chlorination

Double- Chlorination

Break Point Chlorination

Super Chlorinatio

nDechlorinati

-on

Based on quantity and stage at which

it is added


16 Plain-Chlorination

• This term is used to indicate that only the chlorine treatment and no other treatment has been given to the raw water.

• Under plain chlorination, therefore, raw water is fed into the distribution system after giving chlorine treatment only. This helps in removing Bactria, organic matter and colour from the raw water.

• This technique may be used for treating relatively clearer waters (with turbidity less than 20 to 30 mg/L) obtained from lakes, reservoirs, etc.

• It may also be used during emergencies, when full-fledged treatment cannot given, such as for supplying water to army troop during the war times.

• The quantity of chlorine required for plain chlorination is about 0.5mg/L or more.


17 Pre-Chlorination It is the process of applying chlorine to the

water before filtration or rather before sedimentation coagulation.

It helps in improving coagulation , and reduces the loads on the filters. It also reduces the taste, odour, algae and other organisms.

The chlorine dose should be such that about 0.1 to 0.5mg/L of residual chlorine comes to the filter plant. The normal doses required are as high as 5 to 10mg/L .

Pre-chlorination is, however is always followed by post chlorination, so as to ensure the final safety of water.


18 Post-Chlorination Post chlorination sometimes called as

Chlorination is the normal standard process of applying chlorine in the end, when all other treatment have been completed.

While treating normal public supplies, post chlorination is adapted after filtration and before the water enters the distribution system.

The dosage of chlorine should be such as to have a residual chlorine of about 0.1 to 0.2mg/l, having a contact period of about 30 min.

The residual chlorine will ensure the disinfection of water, it will handle any further recontamination occurs in the distribution system.


19 Double Chlorination / Re - chlorination Double chlorination indicates that

the water had been chlorinated twice. Chlorination and post-chlorination both are used in this process.

Post-chlorination is generally always used but pre-chlorination is used when there is high turbidity and contamination.

The water get both the benefits of pre chlorination and post chlorination.

This is done when the distribution system is large and complex as the contamination can occur at the joints.

Residual chlorine concentration level is 1mg/l.


20 Super chlorination It refers to the excess amount of chlorine

(i.e. 5 to 15 mg/l). This may be required in special cases like highly polluted waters or during the epidemic of the water borne diseases.

The quantity of chlorine added in this process is such as to give about 1 to 2mg/l of residue beyond the breakdown point, in the treated waters.

Sometimes higher dosage of chlorine may be used and the resultant waters to be de chlorinated by using de-chlorinating agents like activated carbon, sodium thyosulphate, sulphur dioxide etc. This ensures the removal of the bad taste and odour causes by presence of excess chlorine.

In such cases, desirable amount of chlorine is added to the waters of about 0.1 to 0.2 mg/l.

This process in generally done when emergency times for providing immediate water supply (having a very less contact period)


21 Break-point chlorination

It is a term which gives an idea of the extent of chlorine added to the water. It represents, that much dose of chlorination, beyond which any further addition of chlorine will appear as free residual chlorine.

When chlorine is added in waters, first it generally reacts with ammonia present in waters to form chloramines. If the residual chlorine is tested at this stage then it can be seen that the amount of residual chlorine keeps on increasing. It is the first stage of breakpoint chlorination (denoted by curve AB).

Resid

ual c

hlor

ine

A

B

C


22 Break-point chlorination Cont… If the chlorine is further added beyond point B, the

organic matter present in the waters gets oxidised and hence, the residual chlorine content suddenly falls down as show by the curve BC. At point B where the oxidation of organic matter starts it gives a bad smell and taste which disappears at Break point (c). This is the second stage of the break point chlorination.

The point “C” is the point beyond which any further addition of chlorine will appear equally as free chlorine, nothing of it will be utilized. This Point “C” is called as breakpoint as any amount of chlorine added beyond this point will appear as residual chlorine. The addition of chlorine be this point is known as break-point chlorination.

Generally the amount of residual chlorine beyond point “C” is 0.2 to 0.3mg/l of free chlorine.

Resid

ual c

hlor

ine

B

A

C


23 De-chlorination It indicates “Removal of the chlorine from the waters”

which is generally done after super chlorination process.

This process can be taken place in 2 ways:-

i. Either by removing the chlorine to such a extent that sufficient amount of residual chlorine remains in water.

ii. Or by completely removing the chlorine from waters and again adding the chlorine to prevent it from further contamination.

This process of dechlorination is done by dechlorinating agents like Activated carbon, sodium thyosulphate, sulphur dioxide gas and ammonia.

Note:- Ammonia is generally used as dechlorinating agent as is economical and easily reacts chlorine to form chloramines.


24 Chlorination practice in India


25 Advantages


26 Disadvantages


27 References… http://www.aboutcivil.org/chlorine-demand.html https://www.corrosionpedia.com/definition/978/residual-chlorine https://

books.google.co.in/books/about/Handbook_Of_Methods_In_Environmental_Stu.html?id=BAJAPgAACAAJ&redir_esc=y

https://books.google.co.in/books/about/Water_Supply_Engineering.html?id=74HYY31zwhQC

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjmqM6n8rHOAhXIRo8KHfxNAzMQFggmMAI&url=http%3A%2F%2F178.62.242.206%2Fdocs~water-supply-engineering-sk-garg.

https://en.wikipedia.org/wiki/Water_chlorination http://www.slideshare.net/AshwaniKumar292/chlorination-n-chlorine-demand?qid=54820

4e4-27b5-4f68-a7dd-39eef9619ecb&v=&b=&from_search=2

http://www.slideshare.net/AshwaniKumar292/disinfection-of-water http://www.slideshare.net/EngineerImtiazRehman/disinfection-and-chlorination-of-potable-

water-lines?qid=36518f6f-614a-4deb-952c-e69a8aeeec3d&v=&b=&from_search=6

http://www.aboutcivil.org/chlorine-demand.html

http://www.aboutcivil.org/chlorine-demand.html

https://www.corrosionpedia.com/definition/978/residual-chlorine

https://www.corrosionpedia.com/definition/978/residual-chlorine

https://books.google.co.in/books/about/Handbook_Of_Methods_In_Environmental_Stu.html?id=BAJAPgAACAAJ&redir_esc=y






https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjmqM6n8rHOAhXIRo8KHfxNAzMQFggmMAI&url=http://178.62.242.206/docs~water-supply-engineering-sk-garg




https://en.wikipedia.org/wiki/Water_chlorination

https://en.wikipedia.org/wiki/Water_chlorination

http://www.slideshare.net/AshwaniKumar292/chlorination-n-chlorine-demand?qid=548204e4-27b5-4f68-a7dd-39eef9619ecb&v=&b=&from_search=2



http://www.slideshare.net/AshwaniKumar292/disinfection-of-water

http://www.slideshare.net/AshwaniKumar292/disinfection-of-water

http://www.slideshare.net/EngineerImtiazRehman/disinfection-and-chlorination-of-potable-water-lines?qid=36518f6f-614a-4deb-952c-e69a8aeeec3d&v=&b=&from_search=6




28 Everything is good in its limit…If it exceeds it becomes toxic in nature.

Thank you…