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10 things you need to know about monitoring Total Residual Oxidants
WWEM 2014
Who we are?
Palintest manufactures a range of advanced
water and environmental testing equipment,
and from its Tyneside base exports to over
100 countries across the globe. These
products are used in a wide variety of
applications to protect the environment and
safeguard public health. Crucially Palintest are
able to simplify testing for key water quality
parameters, enabling critical water quality
decisions to be made with confidence.
Introduction
Agenda
• Total Residual Oxidants (TRO)
• Guidelines across the globe
• The problems of transient species
Portable methods:
• DPD method
• Lissamine Green B method
• Other colorimetric methods
• Amperometric Sensor
Laboratory methods:
• Amperometric Titration
• Ion Chromatography
• Spectrophotometric method
• Iodometric titration
Implications on DWI guidelines for TRO?
What are they?
Total Residual Oxidants • Usually used in the context of
chlorine dosing
• Can be applied to other oxidants
e.g. Chlorine Dioxide and the
DBP – chlorate and chlorite
• Usually in the context of drinking
water
What are they?
Total Residual Oxidants • Chlorite is the primary DBP
(50 – 70%)
• Chlorate also produced
(dependent on pH conditions)
• Chlorite and Chlorate can be
introduced by the generator
• Most generators use chlorite or
chlorate precursor chemicals
Name Formula Structure
Hypochlorite ClO-
Chlorite ClO2-
Chlorine Dioxide
ClO2
Chlorate ClO3-
10 things you need to know
# 1 – Total Residual Oxidants
mean ClO2, ClO2- and ClO3
-
(Within the context of chlorine dioxide dosing)
(May include chlorine if chlorinated water is being treated with ClO2)
UK Guidelines
Guidelines behind TRO
DWI Guidelines – Guideline 31
BS EN 12671: 2009 – European Standard
Chemicals used for treatment of water intended for human consumption.
Chlorine dioxide generated in situ.
Additional national Conditions:
The combined concentration of chlorine dioxide, chlorite and chlorate
should not exceed 0.5mg l-1 as chlorine dioxide in the water entering
supply.
Guidelines throughout the world
Guidelines behind TRO
USEPA – used as a international surrogate standard
• ClO2 and ClO2- monitored daily
• ClO3- monitored monthly
• Maximum Disinfectant Residual Levels (defined under DBPR: 2002)
0.8mg/l ClO2
1mg/l ClO2-
10 things you need to know
# 2 – DWI requirements are
relatively stringent
What’s the problem?
Transient or Persistent?
• ClO2 is highly volatile
Samples should be taken in amber
glassware
Small headspace
Minimal agitation
Testing must be carried out on site and
carefully
What’s the problem?
Transient or Persistent?
• ClO2- and ClO3
- are persistent
• More suitable for sampling and off site analysis
• Off site analysis issues in real time decision making
10 things you need to know
# 3 – On site analysis is the
best way of complying with
DWI
• DPD
• LGB
• Amaranth
• CPR
• ACVK
• ChlordioX™ Plus
Portable Methods
Portable methods
DPD
• The ‘Palin system’
• Blue Book method
• US EPA approved method
• Widely accepted method, e.g. EA, HSE
• No longer an AWWA Standard Method (21st
edition)
• A general oxidation method, i.e. not selective
Portable methods
DPD
• Determination of ClO2 (and ClO2- possible)
• ClO2- method difficult and time consuming
• Can result in negative values if chlorine
present
A ‘difference’ method
• Concerns over chlorite and chloride
interference
Removal as AWWA Standard method
# 4 – DPD method is no
longer a AWWA standard
method for chlorine dioxide
10 Things you need to know
Portable methods
Lissamine Green (LGB)
• US EPA Approved method
• ClO2 specific
• ClO2- determination possible
with Horseradish peroxidase
(HRP)
Portable methods
Lissamine Green (LGB)
• Dye bleaching method for ClO2
Time and temperature dependence
Operator errors
• Addition of HRP for ClO2-
A ‘difference’ method
• Generally non-standard methods for ClO2
Useful for process optimisation
Not so good for regulatory reporting
No ability to quantify ClO2- (or ClO3
-)
• Amaranth Method
• Chlorophenol Red Method
• ACVK Method
Other Portable Colorimetric Methods Available
• Amaranth Method
- Popular in Europe
- Small test range
- Generally interferent free
- Dye bleaching method
Other Portable Colorimetric Methods Available
• Chlorophenol Red (CPR) Method
- Generally interferent free (ClO2- can be an issue)
- Dye bleaching method
Other Portable Colorimetric Methods Available
• Acid Chrome Violet K (ACVK)
Method
- Generally interferent free
- Dye bleaching method
- Method defined in BS EN
12671:2009
Other Portable Colorimetric Methods Available
10 Things you need to know
# 5 – Other colorimetric
methods are available
10 Things you need to know
# 6 – Colorimetric methods
suffers from difficulties in the
field
10 Things you need to know
# 7 – Photometric dye
bleaching methods can lead
to operator error
• Patented Palintest technology for ClO2
and ClO2-
• US EPA Approved method The ONLY
portable US EPA approved method for
ClO2-
• Enables compliance to US EPA
requirements (daily monitoring of ClO2
and ClO2-, monthly for ClO3
-)
• Uses standard chemistry (similar to
amperometric titration method)
• Not DWI (because of lack of ClO3-)
Portable Amperometric Sensor Method
• Sequential test protocol
• Aims to simplify ClO2 and ClO2- determination
• Can carry out chlorine measurement
• ClO2- is difference method (but not reliant on
user)
Portable Amperometric Sensor Method
ClO2
ClO2 -
10 Things you need to know
# 8 – ChlordioX™ Plus
enables compliance with
most of DWI requirements
Laboratory methods
• Amperometric Titration
• Ion Chromatography
• Iodometric Titration
• Spectrophotometry
Not portable, therefore no ClO2 determination
Laboratory Methods
Amperometric Titration
• Sequential titration method
• Titration with PAO or thiosulphate
with pH control
• ClO2, chlorine (free and combined),
ClO2- and ClO3
- possible
• Requires a skilled technician
(especially for ClO3-)
Laboratory Methods
• The best way to determine
ClO2- and ClO3
-
• No good for ClO2
• Requires specialist equipment
• Requires careful sample
preparation
• Requires skilled technician
Ion Chromatography
Laboratory Methods
Spectrophotometry • UV/Vis (λ = 360nm) spectrophotometry
can be used for ClO2
• If ClO2- present, can lead to
interferences from intermediate
species
• Some manufacturers offer this as a
visible region test (λ = ~420nm)
Interferences more prominent at longer
λ
But portable
• High limit of detection (not suitable for
potable water)
• Really only suitable for standard
solutions (of high concentration)
Laboratory Methods
Iodometric titration
• Same sequential titration
principle as amperometric
titration
• Suffers from interferences
when multiple oxidants are
present
• Requires skilled technician
• Really only suitable for
standard solutions (and how
Palintest standardise
solutions)
10 Things you need to know
# 9 – Laboratory methods are
not conducive to complying
with DWI guidelines
10 Things you need to know
# 10 – Is it possible to comply
with the DWI guidelines?
Implications
Is it possible to comply with the DWI guidelines? Careful monitoring and dosing control at generator Downstream monitoring must incorporate • On line monitors • Sampling for laboratory (IC) assessment • Portable monitoring
Summary
10 Things you now know about TRO: 1. Total residual oxidants include ClO2, ClO2
- and ClO3- (and chlorine)
2. DWI regulations are relatively stringent
3. On site analysis is the only way of complying with DWI regulations
4. DPD is no longer a standard method
5. Other colorimetric methods are available
6. Colorimetric suffers from difficulties in the field
7. Photometric dye bleaching susceptible to operator error
8. ChlordioX™ Plus enables compliance with most of DWI requirements
9. Laboratory methods alone are not conducive to complying with DWI
guidelines
10. It is difficult to comply with the current DWI guidelines
