Transcript LDO in Wastewater Applications

Luminescent Dissolved
Oxygen (LDO) Measurements
for Wastewater Applications
Edward C. Craig, Ph.D.*
Cary B. Jackson, Ph.D.
Christopher P. Fair
Hach Company
Loveland, CO
Purpose of this Talk…

Discuss our effort to add Luminescence
(LDO) to the List of EPA Approved
Methods for Dissolved Oxygen
Measurements
Proposed EPA Method 360.3
Specifically…
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Discuss our In-House Preparation for a
External Nationwide Validation Study
run as Part of a Tier 3 EPA Approval
Process for the Luminescence Method
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Also share some of the results from the
External Validation Study
Current EPA Approved Methods for
Measuring Dissolved Oxygen Conc.
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Winkler Titration (1888)
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EPA Method 360.2
Membrane Electrodes (1959)
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EPA Method 360.1
Winkler Titration
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L.W. Winkler, “The Determination of
Dissolved Oxygen in Water”, Ber. Deut.
Chem. Ges., 21, 2843 (1888)
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EPA “Reference Method” for Dissolved
Oxygen Measurement
Winkler Titration – Reactions

2
Mn  2 OH  Mn(OH ) 2 
1
2 Mn(OH ) 2  O2  H 2 O  2 Mn(OH ) 3
2
2 Mn(OH ) 3  6 H   3 I   2 Mn 2   I 3  6 H 2 O

3
I  I2  I

I 2  2 S 2 O32   2 I   S 4 O62 
Winkler Method – Floc Formation
Winkler Method - Titration
Winkler Titration
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Pros
Direct DO Measurement
 Easy Clean-up
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Cons
Samples must be Analyzed in a Laboratory
 Subject to Several Chemical Interferences
 Very Technique Sensitive
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Membrane Electrode
L.C. Clark
 “Clark Cell”
 Patent Nov. 19, 1959
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Membrane Electrode
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Pros
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In-situ Measurements Possible
Easy to Make Measurements
Cons
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Frequent Maintenance Required
Must be Polarized Before Use
Must be Calibrated Before Use
Consumes Oxygen
Very Sensitive to Sample Flow
Luminescent Dissolve Oxygen (LDO)

Completely New Technology

Measures the Quenching of a
Luminescent Reaction caused by
Oxygen
Luminescent Dissolved
Oxygen (LDO) - Probe
Luminescent Dissolved Oxygen (LDO)
Probe Components
Luminescent Dissolved Oxygen (LDO)
Probe
Photo Diode
Luminescent Dissolved Oxygen (LDO)
Probe
Sensor
Photo Diode
Luminescent Dissolved Oxygen (LDO)
Probe
Sensor
Photo Diode
Luminescent
Indicator
Molecules
Oxygen
Clear, Gas
Impermeable
Substrate
Gas Permeable
Polymer Matrix
Luminescent Dissolved Oxygen (LDO)

Pros
No Maintenance
 Field Measurements Possible
 No Polarization
 Insensitive to Sample Flow
 Rugged
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Luminescent Dissolved Oxygen (LDO)

Pros (cont.)
Accurate
 Precise
 Very Stable Calibrations
 No Chemical Interferrents
 Lower Day-to-Day Cost than Winkler
Titration

Luminescent Dissolved Oxygen (LDO)

Cons
Higher Initial Cost than Winkler Titration
 Not Currently EPA Approved
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External Validation Study…
12 Wastewater Laboratories Nationwide
 Accuracy & Precision (IPR)
 Method Detection Limit (MDL) Determn.
 5 Day BOD
 Side-by-side Comparisons with Other
DO Methods
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In-House Preparation for
External Validation Study…
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Preparation of Replicate DO Standards
Shelf-Life Experiment
Shipping Experiment
Ruggedness Testing
Use Model Comparisons
Accuracy & Precision Determinations
MDL Determination
BOD5 Demonstration
Side-by-side Comparison with Other Methods
Accuracy & Precision
Determinations
Dissolved Oxygen Concentration Measured with LDO
vs. Theoretical Disolved Oxygen Concentration
Dissolved Oxygen Conc. (mg/L) Measured by LDO
12
10
8
y = 1.0048x
2
R = 0.9993
6
4
2
0
0
2
4
6
Theoretical DO Conc. (mg/L)
8
10
12
Comparison of LDO, Clark Electrode, and Winkler Titration DO Measurements
to Theoretical Hitchman Values
12
Clark Electrode
Winkler Titration
LDO
Measured DO Conc. (mg/L)
10
Theoretical
8
6
4
2
0
0
2
4
6
Theoretical DO Conc. (mg/L)
8
10
12
Percent Recovery at 1.69 mg/L
Percent Recovery at 1.69 mg/L
106
104.3
Percent Recovery
104
102
101.5
100.9
100
98
96
94
LDO
Clark Cell
Method Used to Measure DO Conc.
Winkler
Percent Recovery in Air-saturated Water
Percent Recovery in Air-saturated Water (6.91 mg/L)
106
Percent Recovery
104
102
101.2
100.8
100
98
97.2
96
94
LDO
Clark Cell
Method Used to Measure DO Conc.
Winkler
MDL Determination
LDO – In-House Method Detection Limit
In-House MDL Determination for LDO
Avg 0.070 (+/- 0.007) mg/L, MDL ~ 0.023 mg/L
0.10
Measured DO Conc. (mg/L)
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
1
2
3
4
LDO Instrument
5
6
7
Pooled MDL and ML Results (mg/L)
Data Source
Pooled MDL
ML
In-house Study
0.02
0.07
Inter-laboratory Study
0.06
0.18
Pooled
0.05
0.16
BOD5 Demonstration
BOD5 Comparison
BOD's Measured using Different Methods for DO Measurements
250
150
LDO
Membrane
Winkler
100
50
Ef
l lu
en
t#
2
Ef
fl u
en
t#
3
In
fl u
en
t#
1
In
fl u
en
t#
2
In
fl u
en
t#
3
Ef
fl u
en
t#
1
GA
#3
G
GA
#2
G
GA
#1
G
all
Se
ed
Sm
Se
ed
0
Bi
g
Measured BOD (mg/L)
200
Sam ple Description
Comparison of Glucose and Glutamic Acid Quality Control Checks
(correct BOD value 198 mg/L)
250
211.5
Measured BOD (mg/L)
200
191.3 192.0
190.5
198.8
197.5 197.0
192.5
165.0
150
LDO
Membrane Electrode
Winkler Titration
100
50
0
Dilution 1
Dilution 2
Dilution 3
Method Comparison – DO Measurements Influent and
Effluent Samples from 12 Different Wastewater Facilities
10.00
9.00
8.00
Method DO (mg/L)
7.00
6.00
Winkler
Membrane
5.00
LDO Reference
Membrane
4.00
Winkler
3.00
2.00
1.00
0.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
LDO (mg/L)
7.00
8.00
9.00
10.00
What’s Next?
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Report for External Validation Study has been
submitted to EPA
Next the results are opened to the public for
Review and Comments (~ 3 mo.)
Expect Full EPA Approval in 12 to 18 months
Currently Partitioning EPA for Provisional
Approval (6 to 12 mo.)
Soliciting/Helping WW Labs seeking Tier 1
Approvals
Contacts…
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Edward C. Craig, Ph.D.
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Cary B. Jackson, Ph.D.
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Research & Development Chemist
[email protected]
Regulatory Chemist
[email protected]
Christopher Fair
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Wastewater Applications Chemist
[email protected]