Luminescent Dissolved Oxygen For Water Analysis

Luminescent Dissolved Oxygenfor Water AnalysisMay 14, 2013Sara Simon, Regional Sales Manager1

Today’s Agenda1. Where DO is measured2. BOD Analysis3. Galvanic Dissolved Oxygen Analysis4. Luminescent Dissolved Oxygen Analysis5. Products Available for Measurement6. Time for Q&A2

Where is DO Measured?1EqualizationBasin1PrimaryClarifierPlant Inlet(Influent)1SecondaryClarifierAeration BasinNitrificationBasinReturn Activated Sludge (RAS)Gravity SludgeThickenerFinalFiltrationWaste Activated Sludge (WAS) DO Monitoring Points:SludgeDewatering– Equalization1Aerobic / AnaerobicBasinSludge Digester– Aeration Basin– Nitrification Basin– Aerobic/Anaerobic Digester– Plant Effluent– Lakes/Streams, etc.CentrateDisinfectionSludgeDisposalPlant Effluent13

BOD: What is it? Biochemical Oxygen Demand is a measure of organic pollution A measurement of the oxygen demand impact of effluent into areceiving body; measures all oxygen demand including nitrogenbased oxygen demandIn other words BOD measurements help inmonitoring the effect of effluenton the dissolved oxygenconcentration of the receivingwater body4

What is BOD? Biochemical Oxygen Demand: How much oxygenthe bugs in your sample consume BOD5 is the most common form of US EPA-Basedtesting– “5” is the number of days between initial and finalmeasurements of DO– BOD7 is a similar test that monitors over seven days Required in the US for water discharge: industrialrelease, wastewater treatment, etc. Used globally as a best practice for waterdischarge testing5

BOD: How is it measured? BOD is measured by oxidizing organics using microorganisms (underspecific conditions) and directly measuring the amount of oxygenconsumed in the process. Food Oxygen (O2)(Bacteria)Carbon Dioxide (CO2)Measured DirectlyMeasured Indirectly Changes in dissolved oxygen concentration are used as an indirectmeasure of organic content (food) BOD is the amount of oxygen, expressed in mg/L bacteria take fromthe water when they oxidize organic matter.6

BOD: Why do we do it?Top 5 reasons:1. We have to!2. It’s on our permit3. Week-by-week barometer of how the overall plant isperforming4. Historical data on the plant to know how seasonalityplays into plant performance5. We have to!!7

BOD & cBOD: Any concerns?Average number of hours/week a typicalWW facility spends on BOD?15 hoursAverage number of bottles set per week for BOD? 20 - 40Average number of times per week BOD is run?2 setsPercent of BOD tests that FAIL to meetStandard Methods Guidelines?5-10%8

Is there a better way? Failure of standards can often be traced to issues with membraneelectrodes and calibrations– Oxygen consumptive reduction from an electrolyte and two metallicelectrodes– Oxygen must diffuse through a membrane to be reduced at a cathode Limitations––––Requires high flow across membraneNarrow linearity rangeElectrolyte and electrode degradationMembrane fouling – must be changed frequently9

Outline – Dissolved OxygenDO Measurement Techniques– Luminescence (LDO)– Galvanic10

Galvanic DO Measurement A galvanic cell operatesmuch like a battery!11

Galvanic DO Measurement How does a galvanic sensor measure dissolved oxygen?12

Galvanic DO Measurement Two electrodes of dissimilarmetals are immersed in afilling solution.FeAnodeAgCathode13

Galvanic DO Measurement A spontaneous reactionoccurs between the twometals.FeAnodee-AgCathodeFe2 14

Galvanic DO Measurement Oxygen enters the cell througha membrane.e-FeAnodeAgCathodeFe2 O2O215

Galvanic DO Measurement Oxygen is reduced to hydroxideat the cathode.FeAnodee-AgCathodeFe2 4e-16

Galvanic DO Measurement Flow of current is proportional tothe number of electronsproduced at anode.FeAnodee-AgCathodeFe2 4e-17

Galvanic DO Measurement The more oxygen in the sample:– The greater the current flow(voltage)FeAnodee-AgCathodeFe2 4e-18

Galvanic DO Measurement The Voltage is converted to amg/l, ppm or % saturationreading.FeAnodee-AgCathodeFe2 4e-19

Galvanic DO Measurement The cell reaction destroys theelectrolyte, the anode, andoxygen to complete the reading!FeAnodee-AgCathodeFe2 4e-20

Outline – Dissolved Oxygen DO Measurement Techniques– Luminescence (LDO)– Galvanic21

Luminescence Based OxygenSensors Measures the light emission characteristics of a reversible luminescentreaction In the presence of oxygen the luminescence is quantitatively reducedor quenched Dissolved oxygen concentration is inversely proportional to theluminescence lifetime of the light emitted by the photo-luminescenceprocessProbeSensorPhoto Diode22

Luminescent DO A sensor is coated with aluminescent material. Blue light from an LEDstrikes the luminescentchemical on the sensor.ProbeSensorPhoto Diode The luminescent chemicalinstantly becomes excited.23

Luminescent DO As the excited chemicalrelaxes, it releases redlight. The red light is detectedby a photo diode. The time it takes for thechemical to return to arelaxed state ismeasuredProbeSensorPhoto Diode24

Luminescent DO When oxygencontacts theluminescentchemical, theintensity of the redlight decreases The amount of time ittakes for the materialto relax is reducedProbeSensorPhoto Diode25

Luminescent DO The higher theoxygenconcentration, theless red light thatis given off by thesensor.Red EmissionLightOxygen Concentration26

Luminescent DO A red LED is alsopresent in the probe. Between flashes of theblue LED, a red LED ofknown intensity, isflashed on the sensor. The red LED acts as aninternal standard (orreference) for acomparison to the redlight given off by theluminescent chemical.ProbeSensorPhoto Diode27

Advantages of Luminescent Technology Reduced Maintenance– No anode or cathode No cleaning of anodes No more coating of electrodes– No membrane to replace No more stretching of Teflon and worrying about air bubbles– No Interferences from other chemicals– No electrolyte to foul or poison No H2S poisoning of the electrolyte No more punctured membranes28

Why is this a Big Deal? Accurate and Stable Readings– With nothing to interfere with the readings, LDO produces more stablemeasurements for a longer time Speed!– Turn it on and it’s running!– Response time of less than 30 seconds to 90%! Simple Operation and Maintenance– Only one replacement part– Inexpensive sensor cap is simple to replace quickly29

What about EPA Approval?Green: Approved - No data neededBlue:Approved with Performance Data* - Est. total time 2-8 Lab hrs/30-90 daysOrange: Tier 1 Submissionhttp://www.hach.com/hqdguide-do30

How does LDO help reduce errors? Fast response and no sensor drift– No warm-up time Quick calibration in water saturated air No membrane to replace– No electrolyte to foul or poison– No more punctured membrane No H2S poisoning of the electrolyteMultiple sources of error eliminated fromthe BOD method!31

IntelliCAL LBOD Probe LDO Technology Integrated stirrer Designed for the US EPA-Based Method of BOD5Measurement– Critical Bottle Dimension: 0.625 inches (15.875 mm)– Can be used in any facility testing for BOD For use with the HQ40d Meter32

HQ40d Portable Meter Kit withLBOD101 Luminescent DissolvedOxygen (LDO) Probe for BODMeasurement33

HQ440d Benchtop Meter Package withLBOD101 Dissolved Oxygen Probe for BODMeasurement34

IntelliCAL LDO101 Standard LuminescentDissolved Oxygen (LDO) Probe35

IntelliCAL LDO101 Rugged LuminescentDissolved Oxygen (LDO) Probe36

Dissolved Oxygen:Hach LDO Probe, Model 237

Alternative Laboratory Methods forAnalysis in WWTPsThank you very much!Sara Simon, Regional Sales Managerssimon@hach.com38

Luminescence Based Oxygen Sensors Measures the light emission characteristics of a reversible luminescent reaction In the presence of oxygen the luminescence is quantitatively reduced or quenched Dissolved oxygen concentration is inversely proportional to the luminescence lifeti