Choosing The Right Chlorine Analyzer
For Your Application- DPD Verses
Amperometric
Dr. Vadim B. Malkov, Gary R. Visser,
Terry Engelhardt
Hach Company
Presented by
Kevin Menning
Technical Sales Specialist
Overview
• Multiple Available Chlorine Monitoring Technologies
– Colorimetric and amperometric have different strengths
– Different applications drive different priorities
• Case Study: Uncovering the Unexpected – Visser
– Amperometric results compared with existing colorimetric
– New technology revealed unexpected variances in the sample
– Using continuous measurement, a treatment issue was discovered
• Case Studies: Multiple issues - Englehardt
Online Chlorine Monitoring –
Main Characteristics
• Measurement Precision and Accuracy
• Process Control
– Batch analysis
– Continuous analysis
• Influencing Factors
– Cl2 concentration
– Sample pH
– Sample flow = 90% of issues
– Sample temperature
Accuracy and Precision
• Two words that sound a lot alike, but
very important differences
• Precision is how well you can repeat
the answer over and over• HTTC 10 table iron test
• Accuracy is how close to the true
value your answer is.• How do determine if your answer is accurate?
Online Chlorine Monitoring –
Major Technologies
Colorimetric:
measuring intensity of color developed by
reaction of chlorine with indicator DPD .
The deeper color, the higher chlorine
concentration. Beers Law chemistry.
Main Differentiators:
• Independent of major sample parameters
(pH, flow, temperature, hardness),
• Established calibration curve
Colorimetric Chlorine Analyzer -
it automates the lab method
Colorimeter
Pump
Module
KeypadWiring
CL17 CHLORINE ANALYZERSAMPLE INLET SAMPLE VALVE
UNDER
PRESSURE
LIGHT SOURCE TO WASTE
DETECTORGLASS CELL
MAGNETIC STIRRERPINCHERS
INDICATOR
BUFFER SOLUTION
Online Chlorine Monitoring –
Major Technologies
Amperometric:
measuring electrical current generated in
a circuitry by reaction of chlorine with
electrodes The larger current value, the
higher chlorine concentration.
Main Differentiators:
• No chemical reagents required
• Fast response to analyte concentration
changes
•Range 0-20
Online Chlorine Monitoring –
Case Study Setup
Controller
(sc200)
Grab sample
portChlorine
sensor
Optional
pH sensor
Sample
pressure
control kit
Digital controller – local data logging function
Optional pH sensor – additional information about the sample
Online Chlorine Monitoring –
Technologies Comparison
Colorimetric Amperometric
Pros
• Accuracy (no calibration required)
• Unattended operation (up to 30 days)
• Predictable and simple maintenance
• Results independent of changes in
sample pH, temperature, Cl2concentration, etc.
Pros
• Fast response to changes in Cl2concentration
• Reagentless technology
• No waste stream
Cons
• Reagents and waste stream management
• Clean sample cell
Cons
• Greater interference from sample pH,
temperature, flow, pressure, Cl2concentration, etc.
• Have to calibrate
DPD Waste Stream Analysis
11
� No federal regulations (RCRA) for this kind of discharge
� The analyses performed in accordance with EPA Methods for
Drinking Water
� Results compared with Maximum Contamination Levels (MCL)
listed for found chemicals
� Chemicals produced by the reagents and analyzer were
identified
DPD Waste Stream Analysis - Results
12
Online Chlorine Monitoring –
Applications Overview
Application Type and Regulatory
ExpectationsMain Characteristics
Static Applications: Reportable
(finished water), Sometimes Process
Control
Very stable sample conditions (pH,
Temp, Flow, Cl2 concentration): final
water discharge, distribution systems
Quasi-Stable Applications:
Mainly Process Control, Sometimes
Reportable
Relatively stable sample conditions:
pre-treated water at a DWTP
Dynamic Applications:
Mainly Process Control, Possibly
Reportable
Constantly changing sample
conditions: flash mixers, backwash
loops, disinfection loops, etc.
Online Chlorine Monitoring –
Keys to Application Success
Steps to choosing your chlorine analyzer:
1. Look at the instrument's major performance specifications to make your
initial decision.
• Chlorine concentration range
• Sample pH range
2. Next, consider each technology's key differentiators to determine which
is preferred for your application.
• Colorimetric
• Amperometric
3. Finally, consider the treatment process details - key to application
success to make sure that your preferred instrument is right for your
application.
Making a Selection – Step 1
Step 1: Basic Specifications
Colorimetric Amperimetric
Basic Specifications
Chlorine Concentration
Range0 - 5 mg/L 0 - 20 mg/L
Sample pH range NA pH 4 - 9
Making a Selection – Step 2
Step 2: Technology Key Differentiators
Colorimetric Amperimetric
Key Differentiators
Influence of sample pH,
chlorine concentration,
temperature, flow and/or
pressure changes
No impact on readings
Readings may be impacted.
Adjustment to calibration may be
needed
Calibration Calibration not neededRequired. Frequency based upon
the application.
Routine MaintenanceTubing replacement needed
every 6 months
Membrane and electrolyte
replacement every 3-6 months
ReagentsRoutine reagent replacement
needed every 30 daysNone needed
Reagents in Waste Stream Yes No
Multi-parameter, plug-and-
play sc digital controllerNot available. Compatible with some controllers.
Calibration and Verification
• Two words that sound a lot alike, but
very important differences
• Calibration is using standards and
following the procedure in the
manual for calibration.
• Verification is comparing to a
standard or another instrument and
making sure it is with-in a certain %
usually 10%.
Making a Selection – Step 3Step 3: Performance and Applications Specifics
Colorimetric Amperimetric
Additional Instrument Specifications
Response TimeBatch Analysis,
(150 seconds cycle time)
Continuous Analysis,
T CL = 140s
F CL = 100s
Regulatory Method
SM 4500 CL G
40CFR 141.74
EPA Method 334.0
Only EPA Method 334.0
Make sure to read this Method
Keys to application success
Appropriate Applications
(should meet these
requirements)
�Replace reagents
monthly
�A system to manage the
waste stream (if
required).
�Uninterrupted sample flow 1000 O
�Uninterrupted power
�Sample pH should be within ± 0.5 pH unit from
the average value
�Chlorine concentration should be within ± 20%
from the average value
Online Chlorine Monitoring –
Batch vs. Continuous Analysis
0.75
1
1.25
1.5
1.75
2
2.25
0 50 100 150 200 250 300 350 400 450 500 550
Ch
lori
ne
Co
nce
ntr
ati
on
, p
pm
Time, sec
Response of Amperometric vs. CL17 to Process Chlorine Concentration
Change
Dosage, ppm
CL17, ppm
Amp, ppm
CL17 response time = up to 300 s
depending on sampling
What is the priority – high accuracy or immediate response?
How important is 3 or 5 minutes??
colorimetric
Online Chlorine Monitoring –
Case Study Setup
Controller
(sc200)
Grab sample
portChlorine
sensor
Optional
pH sensor
Sample
pressure
control kit
Digital controller – local data logging function
Optional pH sensor – additional information about the sample
Online Chlorine Monitoring –
Case Study Setup
� Both Colorimetric and Amperimetric measuring the same
sample
� Data from both instruments collected to SCADA
� Main goal for implementation of new analyzer – minimize
ongoing maintenance (cost of reagents)
Online Chlorine Monitoring –
Case Study: SCADA results pre-clearwell
Online Chlorine Monitoring –
Case Study: Evaluation
1. Good trending between two analyzers
2. Larger variance in amperometric analyzer readings
3. Root cause:
� Process issues?
? Sample flow
? Sample pH
? Sample temperature
� Analyzer malfunctioning?
4. Next steps:
a) Internal data logging
b) Full data evaluation
Online Chlorine Monitoring –
Case Study: Logged Data
Online Chlorine Monitoring –
Case Study: Observations
1. Observations:
a) Flow is stable
b) Temperature is stable
c) Substantial pH variations (min = 6.46, max = 9.32)
2. Root cause?
� Not the analyzer (pH independent in this range)
� Process - sample pH effecting chloriamination chemistry
3. Next steps:
a) Verify analyzer performance
b) Determine why pH is unstable
Online Chlorine Monitoring –
Case Study: Verification
Online Chlorine Monitoring –
Case Study: Observations
1. Analyzer performs within specifications
2. Water treatment process issues – root cause?
? pH adjustment
? Disinfectants mixing
? Sampling point
3. Next steps:
a) Change sampling point
b) Introduce changes to the chemicals mixing
c) Validate performance
Online Chlorine Monitoring –
Case Study: Validation
Case Study –
Results and Conclusions
�New amperometric total chlorine continuous analyzer helped to reveal issues with finished
water
�The unexpected problem uncovered in this case study may be very common for many drinking
water treatment facilities
�Both laboratory and online methods based on batch analysis provide the customers with great
value of accurate results (regulatory reporting aspect)
�An amperometric-based online instrumentation can provide additional benefits due to the
continuous nature of measurement (fast response to process changes)
�Optional pH monitoring and local data-logging features can provide additional benefits:
� Reserved data storage in case of SCADA malfunctioning
� Better understanding of the process (monitoring multiple sample parameters)
� Enhanced troubleshooting
Finished Water: Final Discharge
30
Dynamic Application: Ground Water Station (Aurora,
CO)
31
� Stable Finished Water Applications
�Suitable application area for amperometric sensors
�Drift and offset due to pH, flow, etc. should be monitored
� Quasi-Stable Applications
�Some suitable applications for amperometric sensors (redundant)
�Requires more frequent calibration/verification
� Dynamic Applications
�Not the target for amperometric sensor (good redundant analyzer)
�Requires frequent calibration/verification
� Colorimetric instrumentation demonstrated to be suitable for ALL investigated applications
Conclusions
32
Which one costs more to operate?
Purchase cost
Reagent Cost vs Probe
Time to calibrate an maintain
Which one would I purchase?
F. O. R. D.
Thank you for your attention!
Questions?
Please contact Kevin Menning at
+1-970-663-1377 x 233