Confident Control of

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Confident Control of Sodium Hypo chlorite
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IL AWWA Springfield, IL
Presenter Warren Searles
Copies of the presentation maybe downloaded from
the ILAWWA Website www.isawwa.org
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• Desired Discussion Outcomes
• Understand the degrading of Sodium Hypo
  chlorite,
• 2. Understanding pH (potential of Hydrogen,) and
  oxidation / reduction Potential
• 3. Demonstrating the relationship of pH to the
  redox equation, and to the assurance of
  significant free chlorine,
• 4. Control of the Dosing system.

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Sodium Hypo Chlorite in Concentrated
Aqueous Solution
The Commonly Accepted Deterioration
Reaction is NaClO2 ? 2NaCl O2 ?
pH is of the concentrate is critical, at a higher
pH, Chlorine stays in solution. That is the
reason why suppliers provide concentrate
solutions at elevated pHs. These solutions are to
37 by weight active chemical or Chlorine.
However, viscosities above the typical 15
commercial grade may be difficult to pump
economically.
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Reagent grade RO/DI water should be used for
solution makeup of NaClO23H2O, Other supply
water may contain organic material depending on
the source of that water. Also, metallic ion
contaminates may be present depending on mix tank
material and supply water piping material. All
such contaminants cause sodium hypochlorite
solutions to disassociate faster. Of particular
importance are the presents heavy metals,
particularly iron. Consult The chemical supply
vendor concerning his process if problems
persist.
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All sodium hypochlorite products contain some
salt from the production process. Several
suppliers have determined that if they add a
neutral salts at about a 16.5 per cent by weight
to change the ionic strength of the solution the
addition of the salt changes the equilibrium of
the breakdown reaction (NaClO2 ? NaCl O2?)
which results in a more stable solution.
Suppliers also attempt to control the
deterioration due to biological contaminates in
the blend water by chemical additions or starting
with biological free reagent grade water. Again
consult the supplying vendor!
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Oxygen evolution is to be considered at all
temperatures. At cooler temperatures the more
Oxygen the water will hold. The more oxygen held
in the water the less likely hood of
decomposition of the NaClO2. Summer verses Winter
temperatures are critical -- During the summer
the kinetics of the solution change increase
evolution of oxygen.
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Discussion of pH (potential of Hydrogen,) and
Oxidation / Reduction Potential
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Definition of pH

• The pH unit measures the degree of acidity or
  basicity of a solution.

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To be more exact, pH is the measurement of the
hydrogen ion concentration, H. Every aqueous
solution can be measured to determine its pH
value. This value ranges from 0 to 14 pH. Values
below 7 pH exhibit acidic properties, and values
above 7 pH exhibit basic (also known as caustic
or alkaline) properties. Since 7 pH is the center
of the measurement scale, it is neither acidic
nor basic and is, therefore, called "neutral."
pH is defined as the negative logarithm of the
hydrogen ion concentration. This definition of pH
was introduced in 1909 by the Danish biochemist,
Soren Peter Lauritz Sorensen. It is expressed
mathematically (Next Slide)
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pH -log H where H is hydrogen ion
concentration in mol/L.
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In a neutral solution, the H 1 x 10-7 mol/L.
This represents a pH of 7. pH -log (1 x
10-7) -(log 1 log 10-7) -(0.0
(-7)) 7.0
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As shown in the following slide, pH is a
logarithmic function. A change of one pH unit
represents a 10-fold change in concentration of
hydrogen ion.
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Oxidation Reduction Potential -- Redox --
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Oxidation-Reduction Potential (ORP) or Redox
potential measurements are used to monitor
chemical reactions, to quantify ion activity, or
to determine the oxidizing or reducing properties
of a solution. ORP is a measurement of the
electrical potential of a redox reaction and
serves as a yardstick to judge how much oxidation
or reduction takes place under existing
conditions. 
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ORP electrodes measure the voltage across a
circuit formed by the measuring metal half-cell
and the reference half-cell. When the ORP
electrode is placed in the presence of oxidizing
or reducing agents, electrons are constantly
transferred back and forth on its measuring
surface, generating a tiny voltage. The ORP
measurement can be made using the volt meter
reading in mille volts (mV, 1/1000 of a volt).
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Typical ORP Paired Electrode
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ReDox is a classification category of chemical
reactions. The helpful acronym OILRIG, Oxidation
Is Losing, Reduction Is Gaining losing and
gaining what? Electrons. ReDox reactions are
fewer and slower by comparison to acid/base
reactions where a neutral salt is produced. In
reduction-oxidation reactions one chemical
species loses, another gains electrons. Oxidation
is one chemical borrowing an electron form an
other. Reduction is one chemical lending an
electron to an other.
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ReDox potential is a value (number) defining how
much borrowing or lending an aquatic system
might execute an oxidizing environment (the one
we want) has a positive value. Redox is measured
indirectly as the ability of an aquatic system to
conduct electricity. Hence the term redox
potential, or, if you will, ORP for,
Oxidation-Reduction Potential.
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EXAMINATION OF THE RELATIONSHIP BETWEEN
BIOLBICAL DISINFECTION AND ORP
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ORP technology is gaining recognition worldwide
and is found to be a reliable indicator of
bacteriological water quality for sanitation or
determine the free chlorine parameter. In
swimming pool application, the ideal ORP value is
approximately 700 mV where the Kill Time of
E.Coli bacteria is the fastest to ensure good
water quality. HOWEVER, ORP value also depends on
the pH of the water, which is typically between
7.2 and 7.6 pH in municipal systems. 
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Determining the relationship of pH to
the redox equation,
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To illustrate the dependency of ORP measurements
on pH, consider the measurement of residual
chlorine. In the absence of other oxidizing or
reducing agents, ORP electrodes give good
indications of residual chlorine concentrations.
Over the usual range of residual chlorine
concentration, the output of the ORP electrode
will be 500 to 700 mV. The graph below
illustrates the influence of pH on the residual
chlorine ORP.
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Three Dimensional Graph contrast pH to ORP as
relating to ppm of free Chlorine.
ORP
Graph Shows a target of 0.5 mg/l of free chlorine
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OK, How to control the Nonlinear Relationship
Between pH ORP
ORP
Graph Shows a target of 0.5 mg/l of free chlorine
along the changes in pH and ORP as interpolated
by the engineer.
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Control of the Dosing system.
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One Method Automatic of Control
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Control of dosing pumps is achieved by

• Selecting the appropriate pump required to dose
  to the specified service water flow,
• Select a pump that uses the from 50 to 70 of
  its controlled output to dose the NaClO23H2O,
• Pump to be controlled by a 4 to 20 milli-amp
  signal from a either a dedicated controller or a
  centralized network,
• Contact your dosing pump vendor for proper
  selection.

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Mr. George Clifford writes in the Hand Book of
Chlorination, fifth addition If you can smell or
taste chlorine in our drinking water, there isnt
enough chlorine residual in it. If the residual
falls below the free chlorine minimum, the
reforming chlororganics and chlorinamines (the
taste and order producing part of the
disinfection process) takes the place as a
results of increased contamination (Chlorine
demand). Chlororganics and chlorinamines are a
result of chlorine combining with Ammonia and
Nitrates which are waste byproducts of bacteria
in a non-ammoniated system!
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Open the Subject to Discussion!
For Further Information, contact Warren
Searles HydroTec Systems Company,
Inc. 815.624.6644 or 708.447.7481 warsea_at_purehts.c
om
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Reference Listings
1.0 Opflow Volume 27, Number 6, June 2001. 2.0
Global Environment Center Foundation,
Technology of Water Pollution Continuous
Monitoring in JAPAN principles of Analyzers for
Water Pollution Continuous Monitoring
1999. 3.0 Sensorex, Reduction Oxidation
measurement, Technical Publication
1999. 4.0 Redox, Reduction-Oxidation Potential,
ORP 5.0 Eutech Instruments, Tech Tips,
Introduction to ORP, 1999. 6.0 LMI Milton
Roy, Metering Pumps Rev. C 12/99