Luminescent Dissolved Oxygen LDO Measurements for Wastewater Applications

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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

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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

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Specifically

• 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
• Also share some of the results from the External
  Validation Study

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Current EPA Approved Methods for Measuring
Dissolved Oxygen Conc.

• Winkler Titration (1888)
• EPA Method 360.2
• Membrane Electrodes (1959)
• EPA Method 360.1

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Winkler Titration

• L.W. Winkler, The Determination of Dissolved
  Oxygen in Water, Ber. Deut. Chem. Ges., 21, 2843
  (1888)
• EPA Reference Method for Dissolved Oxygen
  Measurement

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Winkler Titration Reactions
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Winkler Method Floc Formation
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Winkler Method - Titration
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Winkler Titration

• Pros
• Direct DO Measurement
• Easy Clean-up
• 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

• Pros
• In-situ Measurements Possible
• Easy to Make Measurements
• Cons
• Frequent Maintenance Required
• Must be Polarized Before Use
• Must be Calibrated Before Use
• Consumes Oxygen
• Very Sensitive to Sample Flow

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Luminescent Dissolve Oxygen (LDO)

• Completely New Technology
• Measures the Quenching of a Luminescent Reaction
  caused by Oxygen

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Luminescent Dissolved Oxygen (LDO) - Probe
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Luminescent Dissolved Oxygen (LDO) Probe
Components
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Luminescent Dissolved Oxygen (LDO)
Probe
Photo Diode
LED
LED
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Luminescent Dissolved Oxygen (LDO)
Probe
Sensor
Photo Diode
LED
LED
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Luminescent Dissolved Oxygen (LDO)
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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

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Luminescent Dissolved Oxygen (LDO)

• Cons
• Higher Initial Cost than Winkler Titration
• Not Currently EPA Approved

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Process LDO

• Cost Savings
• Electricity, Labor, and Chemicals
• John Anderson
• City of Longmont, WWTP Superintendent

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Process LDO Longmont WWTP

• Savings Over 3 Month Period
• Electricity ( 28,000)
• Labor ( 15,000)
• Chemicals ( 36,000)
• Total Savings ( 70,000)

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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

• 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

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Accuracy Precision Determinations
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Percent Recovery at 1.69 mg/L
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Percent Recovery in Air-saturated Water
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LDO Histogram Air-saturated Water
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MDL Determination
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LDO In-House Method Detection Limit
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Pooled MDL and ML Results (mg/L)
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BOD5 Demonstration
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BOD5 Comparison
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Method Comparison DO Measurements Influent and
Effluent Samples from 12 Different Wastewater
Facilities
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Whats Next?

• 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

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Contacts

• Edward C. Craig, Ph.D.
• Research Development Chemist
• ecraig_at_hach.com
• Cary B. Jackson, Ph.D.
• Regulatory Chemist
• cjackson_at_hach.com
• Christopher Fair
• Wastewater Applications Chemist
• cfair_at_hach.com