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