Chlorine is widely used in disinfection
of swimming pool.
Chlorine combines with water to form hypochlorous
acid (HOCl) and hydrochloric
acid (HCl).
| Cl2+ H2O |
 |
HOCl + HCl |
Effective
Chlorination in Swimming pool:
It is the hypochlorous acid produced in the reaction that
provides the disinfecting and potent oxidising characteristic
of chlorine solution.
The amount of hydrochlorous acid produced
in chlorinated water is highly dependent upon the pH value
of the solution.
HOCI
=H+ + OCI-
The HOCI is in equilibrium with hydrogen ion and the hypochlorite
ion. Any changes in pH of the solution with cause the equilibrium
to change. As depicted by curve below, HOCl decreases and
OCl- increases as pH increases. At low pH,almost all the free
chlorine is of the molecular form HOCI and at a pH of around
7.5, the ratio between HOCI and OCI- is 50:50.
Hypochlorite ion (OCl-) is a slow acting
sanitizer while the molecular form of HOCl is a fast acting
sanitizer. Since HOCl acts 80 to 100 times faster than OCl-
, it is of more important than its counterpart OCl-.
How do
we measure the effectiveness of pool disinfection?
There has always been a misconception that
measuring the amount of chlorine will be equated to the effectiveness
of pool disinfection. The most effective
way to measure disinfection is to measure the reactions chlorine
produces. Many studies had shown that the rate of killing
the bacteria of E. coli organisms in swimming pool water is
dependent on Oxidation Reduction Potential (ORP or REDOX )
and not the free residual chlorine level.
ORP
ORP (Oxidation-Reduction Potential) or REDOX is a measure
of the oxiding properties of the sanitizer in water i.e. the
activity strength of HOCI.
With a value of 600mV, the kill time of E.Coli bacteria is
30 seconds. Above 700mV, the bacteria is killed within a few
seconds.
To ensure good water quality, it is necessary
to maintain a REDOX level of 650mV to 750mV. We have our very
own Senz Redox. This
instrument is a handy, pocket size tester, which is very simple
to use. Just dip the sensor in the water and read the display
after stabilized.
ORP value also depends on the pH of the pool
water. Normal pH values for pool water is 7.4 to 7.6pH with
a tendency to increase to around 8.0 to 9.0pH depending on
the level of contamination. The pH of the pool water has to
be maintained with the appropriate chemical dosing. REDOX
readings are affected by fluctuations in pH; therefore it
is important to check pH level first before using Eco Redox
tester. pH must be between 7.4 to 7.6 to obtain an accurate
reading.
Total
Dissolved Solids (TDS)
Total Dissolved Solids refers to the amount of dissolved substances
or mineral within the pool which are actually charged ions.
These substances enter the pool either through the original
water supply or by additions of treatment chemicals. As the
water evaporates, total dissolved solids remain behind and
over time become greater and greater.
High TDS readings may produce cloudy water
and could cause corrosion. Total dissolved solids should be
kept under 2000 parts per million. If TDS exceeds this amount,
part of the pool should be drained and replaced with fresh
(low TDS) water.
Since it is the dissolved minerals in water
which conduct electricity, a total dissolved solids probe
or instrument can be effectively used to measure TDS in parts
per million. Trans's Senz
TDS and Senz TDS-2,
are self-contained digital pocket size conductivity meters
with cell and automatic temperature compensator. It provides
quick and accurate reading. All you need to do is to turn
the tester on and dip into sample solution. Any irregularities
of the conductivity can be corrected by adding water. |
