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 Wiring

Colorimeter

Pump Module

Keypad

CL17 CHLORINE ANALYZER SAMPLE INLET

SAMPLE VALVE

UNDER PRESSURE

LIGHT SOURCE

GLASS CELL PINCHERS INDICATOR BUFFER SOLUTION

TO WASTE

DETECTOR

MAGNETIC STIRRER

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)

Chlorine sensor

Optional pH sensor

Grab sample port

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

Pros

• Accuracy (no calibration required) • Unattended operation (up to 30 days)

• Fast response to changes in Cl2 concentration

• Predictable and simple maintenance

• Reagentless technology

• Results independent of changes in sample pH, temperature, Cl2 concentration, etc.

• No waste stream

Cons • Reagents and waste stream management • Clean sample cell

Cons • Greater interference from sample pH, temperature, flow, pressure, Cl2 concentration, etc. • Have to calibrate

DPD Waste Stream Analysis 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

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DPD Waste Stream Analysis - Results

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Online Chlorine Monitoring – Applications Overview Application Type and Regulatory Expectations

Main 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 Range

0 - 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 Key Differentiators

Amperimetric

Influence of sample pH, chlorine concentration, temperature, flow and/or pressure changes

No impact on readings

Calibration

Calibration not needed

Routine Maintenance

Tubing replacement needed every 6 months

Reagents

Routine reagent replacement needed every 30 days

None needed

Reagents in Waste Stream

Yes

No

Multi-parameter, plug-andplay sc digital controller

Not available.

Compatible with some controllers.

Readings may be impacted. Adjustment to calibration may be needed Required. Frequency based upon the application. Membrane and electrolyte replacement every 3-6 months

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 3 Step 3: Performance and Applications Specifics Colorimetric

Amperimetric

Additional Instrument Specifications Response Time

Batch 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 2.25

Response of Amperometric vs. CL17 to Process Chlorine Concentration Change

Chlorine Concentration, ppm

2

1.75

Dosage, ppm CL17, ppm colorimetric

1.5

Amp, ppm

1.25

1

CL17 response time = up to 300 s depending on sampling

Time, sec

0.75 0

50

100

150

200

250

300

350

400

450

What is the priority – high accuracy or immediate response? How important is 3 or 5 minutes??

500

550

Online Chlorine Monitoring – Case Study Setup Controller (sc200)

Chlorine sensor

Optional pH sensor

Grab sample port

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

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Dynamic Application: Ground Water Station (Aurora, CO)

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Conclusions 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

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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