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Definition and Types of
Chlorination
By: Haseeb Jamal
Definition:
Chlorination serves not only for disinfection, but as an
oxidant for other substances (iron, manganese, cyanide, etc) & for taste
& odor control in water & wastewater.
Other chemical disinfectants include chlorine dioxide,
ozone, bromine, iodine.
The last two chemicals are generally used for personal
application, not for the public water supply.
Types of Chlorination
Plain Chlorination
Chlorination of water relatively free from suspended
matter without any other treatment
Pre-Chlorination
The application of chlorine to raw water before any other
treatment to improve the coagulation & to remove the taste, odor, &
color
Post Chlorination
Application of chlorine to treated water after all the
other treatment. Dosage chlorine range from 0.25-5.0mg/lit in order to obtain
the combine residual chlorine in range of 0.1-0.2mg/lit
Chemical Properties of Chlorine -
Chemistry of Chlorination
Free Available Chlorine
Effective chlorine disinfection depends upon its chemical
form in water.
The influencing factors are pH, temperature, & organic
content in water.
When chlorine gas dissolved in water, it rapidly
hydrolysis to hydrochloric acid (HCL) & hypochlorous acid (HOCL)
Cl2 + H2O ? H+ +
Cl- + HOCL
The equilibrium constant is KH = [H+] [Cl-]
[HOCL]
[Cl2 (aq)] = 4.48 × 10 -
4 at 25 °C
Hypochlorous acid is a weak acid & subject to the
further dissociation to hypochlorite ions & hydrogen ions
HOCL ? OCl- + H+
& its acid dissociation constant Ka is
Ka = [OCl-] [H+]
HOCL = 3.7 × 10-8 at 25 ?C
Combine Available Chlorine
Chlorine reacts with certain dissolved constituent in
water, such as ammonia & amino nitrogen compounds to produce the
chloramines. These are referred as combined chlorine.
In the presence of ammonium ions, free chlorine reacts in
a stepwise manner to form three species.
1.
Monochloramine
NH2Cl
2.
Dichloramine NHCl
3.
Trichloramine NCl3
Haseeb
Jamal. I am a Civil Engineer, graduated from University
of Engineering and Technology, Peshawar, Pakistan in 2010. I also
have a PG-Diploma in Disaster Management and
MS in Urban
Infrastructure Engineering (In Progress). My expertise include civil
related softwares like AutoCAD,
SAP2000, MS Project, Primavera, MS Office and GIS. My technical skills include
project management, monitoring and evaluation, structural assessment, disaster risk
management, Quantity survey, land survey, material testing, site management and
technical writing. I am trained in writing project progress reports as well as
proposals and concept papers. I have also received advanced training on
surveying, proposal writing, Monitoring and Evaluation of projects as well as
organizations.
I have worked as Project
Engineer at National Research and Development Foundation, Peshawar and
CENCON Associates. I also worked with Spectra Engineering Solutions as Senior
Civil Engineer in monitoring of World Bank and UNDP funded projects all
over Khyber Pakhtunkhwa and FATA. Currently, I am working as Deputy
Manager Development at NayaTel, Peshawar.
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