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Dissolved Oxygen Measurement Techniques and Aplications for the Water Quality of the Passaic River

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Dissolved Oxygen Measurement Techniques and Aplications for the Water Quality of the Passaic River

  1. 1. Dissolved Oxygen Measurement Techniques and Applications for the Water Quality Measurements of the Passaic River
  2. 2. What is dissolved Oxygen?  It is the amount of oxygen gas dissolved in water  Water has a molecule of oxygen in its composition, but that is not the oxygen that we are talking about  Think of it as dissolving a spoonful of sugar in a glass of water
  3. 3. How does water gets its dissolved oxygen?  The oxygen dissolved in the water gets in there by contact with the atmosphere, and sometimes through underground water fountains depending on the body of water in question.  Water in constant movement gets more oxygen on it than still water.
  4. 4. Dissolved Oxygen Factors  Temperature: Cold water holds more oxygen than hot water  Salinity levels: Fresh water holds more DO than salt water
  5. 5. Why is this so important?  From keeping your pet fish alive, to keeping healthy ecosystems.  It is important what factors are messing with the dissolved oxygen levels because if they go dangerously low, it will both kill the fish in your tank, or destroy a whole ecosystem in nature.
  6. 6. Examples  Runoff of salt from roads  Runoff of fertilizer from gardes causing eutrophication in lakes  Factories treating waste water and returning it to a body of water warmer than it should be
  7. 7. Methods of Measuring DO  Electrochemical devises  Electrochemical tests Clarck electrochemical probes Optical based sensing methods  Chemical tests  Titrimetric tests  Colorimetric tests
  8. 8. Electrochemical Probes  Clark Electrochemical probes:  They are also known as membrane covered probes  Are called this way in honor to their inventor Doctor Leeland Clark  They worked by using the membrane that is ony permeable to gasses. When there is Oxygen present, it will diffuse trough the membrane at the cathode, the oxygen will get reduced and this will send an electrical signal that will be analyzed by the computer in the device.
  9. 9. Clark Electrochemical Probes  Sources of Error: Calibrating the probes improperly. Improperly installed electrode Weak electrolyte inside the membrane
  10. 10. Titrimetric Tests  They consist on having the dissolved oxygen react, and then titrate with a solution that will react with the fixed oxygen. The amount of oxygen in the sample will correspond to the amount of the titration solution added to the sample until the endpoint is reached.
  11. 11. Titrimetric Tests Sources of error: Human error: corresponding to the level of skill of the person performing the test. Oxygen introduced to the sample at the moment of sample retrieval The titration solution not being in optimal conditions
  12. 12. Colorimetric Tests  These are also chemical tests. The procedure will cause a change in color in the sample. The concentration of DO will correspond on how dark the color obtained is, which will be compared to a chart.
  13. 13. Colorimetric Tests Sources of error: Human error: Low analytical skills, bias while reading the sample color Introduction of oxygen while obtaining the sample: The sample vial is never capped.
  14. 14. Tests Evaluated  Titrimetric:  HACH DO Kit  LaMotte DO Kit  Colorimetric  CHEMetrics DO kit  Profi O2 test  Clark Electrochemical Probes  GSWA probe  CSE probe
  15. 15. Set up The first set up used in lab consisted in a 3500 mL beaker filled with tap water at room temperature. It was then placed over a stirring plate at velocity seven. A funnel connected to a lab air pump was used in order to introduced air to the sample and maintain a steady level of it. This was changed in order to make the experiment more replicable by replacing the lab pump with an aquarium air pump that deliver air at the same rate at all times.
  16. 16. With Lab Pump and aquarium pump
  17. 17. GSWA probe vs CSE probe 6 6.5 7 7.5 8 8.5 9 0 2 4 6 8 10 12 14 16 DO (ppm) vs time (mins) GSWA (ppm) CSE (ppm)
  18. 18. GSWA probe vs CSE probe  The values were compared over a period of 25 minutes.  As we can observe in the graph, the water has around the maximum amount of dissolved oxygen that can be achieved at this temperature, which is around 8 ppm of oxygen. The difference over 15 minutes was measured in order to make sure that the levels of oxygen in the water were not fluctuating too much and that is what was found.  The average difference was of only 6.11%  This may have been because of the errors while calibrating.
  19. 19. Test Comparison at Room Temperature 8 8.95 8.51 88 8.86 8.58 87.9 8.85 8.49 88 8.88 8.53 8 LA MOTTE GSWA METER CSE METER CHEM ETS Test comparison at 20 C Trial 1 Trial 2 Trial 3 Average
  20. 20. Test Comparison at Room Temperature  The difference between the GSWA meter and the LaMotte testing kit was of 5.21%, which is still a small difference. This sort of difference was expected with titrimetric methods. One source for error could have been not closing the sample bottles tightly immediately after retrieving the water sample  CHEMetrics kit. Since this is a color comparison test, it was more vulnerable to human bias. Not only was this a problem, but also the solution that was indicating the color for a sample containing 8ppm of oxygen was lower than the rest, meaning that the dye would be more concentrated. This means that it was even less accurate, so the final color was compared to the color that indicated 6 ppm and the one that indicated 12 ppm of oxygen. Since it was darker than 6 ppm and lighter than 12 ppm, and the other tests had indicated 8 ppm, we simply assume that was the color for 8 ppm
  21. 21. Dissolved Oxygen at low Temperature 10.4 12.33 11.75 12 10 12.9 12.66 12 10 12 12 10.1 12.74 12.13 12 LA MOTTE GSWA METER CSE METER PROFI O2 Dissolved Oxygen at 7 C Trial 1 Trial 2 Trial 3 Average
  22. 22. Dissolved Oxygen at Low Temperatures  As it was to be expected, the lower the temperature, the higher the concentration of DO in the water sample.  However, for some reason the LaMotte kit had a much bigger difference from the electrochemical meters than in past experiments. The difference between the LaMotte and the GSWA meter was of 23%  The same sodium hydrosulfide solution was used to calibrate the samples so that may explain why, in the case an error was made during calibration, the two meters would be skewed similarly.  The Profi O2 test gave an approximate value.
  23. 23. Dissolved Oxygen at High Temperatures 5.2 5.25 5.85 6 5 5.79 5.18 6 5 5.62 5.18 6 5.1 5.55 5.4 6 LA MOTTE GSWA METER CSE METER PROFI O2 Test Comparison at 40 C Trial 1 Trial 2 Trial 3 Average
  24. 24.  It was noticed that at higher temperatures than 40oC the CSE meter would not function properly and it would display error, so in order to keep the equipment from getting harmed, no higher than 40o C was reached for this test  Do not use to measure DO in hot springs.  With the chemical experiments, it was decided to let the sample sit at room temperature after it was collected in the closed bottle because all chemical reactions are faster at higher temperatures Dissolved Oxygen at High Temperatures
  25. 25. Dissolved Oxygen at Different Temperatures 5.1 5.55 5.4 6 10.1 12.74 12.13 12 LA MOTTE GSWA METER CSE METER PROFI O2 DO at Cold vs Warm Water 40 C 20 C
  26. 26.  The difference can be seen clearly. In this experiment, by looking at the most trust worthy instrument which is the GSWA, there was a difference of 78.6 %. This is one of the reasons that the average temperature, as well as dissolved oxygen, is such an important factor when looking at the health of a body of water Dissolved Oxygen at Different Temperatures
  27. 27. Testing in the Passaic River Only four of the prior described procedures to measure dissolved oxygen were employed in the field testing of the Passaic River. In order to get an accurate result, we decided to take three readings for the Profi O2 and the LaMotte Kits
  28. 28. There were five sites: Newark (site#1), Lyndhurst (site #2), Great Falls (site#3), Chattam (site#4), Mendham (site#5) Testing in the Passaic River
  29. 29. 11 11.1 11.2 9.6 10.2 13 12 12 12 1211.7 14.7 14.04 12.3 12.87 14.44 14.39 14.2 12.24 13.42 SITE 1 SITE 2 SITE 3 SITE 4 SITE 5 Chart Title LaMotte Profi O2 GSWA CSE Testing in the Passaic River
  30. 30.  The water for all of the sites had an average temperature of 3.18oC. Since it was so cold, it was expected to see high levels of oxygen, as the results indicate  The lowest amount of oxygen was found in site 4, which was Chattam. The temperature of the water in Chattam was not very different from the rest of the sites, so temperature could not be the reason there is less oxygen  The site of testing was close to a road. Since the field sampling was done in March, and there was still some recent snow, it could be that the salinity of the water was slightly higher than in the other sites Testing in the Passaic River
  31. 31. Biochemical Oxygen Demand  Biochemical oxygen demand, is the measurement of how much oxygen is consumed by microorganisms in the water sample, in a determined amount of time.  This is very important to know because if the biochemical oxygen demand is too high, then water dissolved oxygen levels would get dangerously low in a phenomenon called eutrophication. Eutrophication happens when there are too many nutrients in the water, which causes an algae bloom.
  32. 32. BOD in the Passaic River 4.7 4.2 2.5 3.16 SITE 1 SITE 2 SITE 3 SITE 4 SITE 5 BOD
  33. 33. BOD in the Passaic River  While testing for the biochemical oxygen demand for these sites, a couple of issues were found. First, although we had sterile bottles, the standard LaMotte test that was used was designed for samples of exactly 65 mL and not 265 mL. Site 2 was done a day before, and the data was completely ruined, so it was not included in the chart. In order to test for this, a proportion relationship was calculated, so if for the 65mL bottles 8 drops were needed then for the 265 mL 32.6 drops were needed. This we have to round to 33 drops for each of the reagents. The step of the titration was not changed
  34. 34. BOD in the Passaic River  Another problem with this data is that it was taken seven days after the initial reading, instead of five days which is the necessary to test for the biochemical oxygen demand.
  35. 35. BOD in the Passaic River  In conclusion, this biochemical oxygen demand data is not reliable and should be performed again correcting the mistakes made. First, only 65 mL bottles should be used for the water sample if the LaMotte kit is to be used. These bottles should be autoclaved to assure sterility. Second, the test should be measured after five days, no more and no less so that reliable results can be acquired.
  36. 36. About all the Methods  In conclusion, the most reliable, accurate and easier to use methods are the electrochemical probes. The chemical methods take a minimum of 20 minutes to perform, while the electronic probes will give the readings instantly. Of course, extra care should be taken while calibrating the probes. This accuracy and technology is the reason these probes are so expensive
  37. 37. About all the Methods  The titrimetric methods would be next. They are pretty accurate as we were able to see with the LaMotte kit, but require more time and more care because toxic and corrosive reagents are being used. These can be purchased for less than a hundred dollars
  38. 38. About all the Methods  Next are the low budget aquarium test kits like the Profi O2 test. Tests like these will do the job of approximately displaying the amount of dissolved oxygen, but it will not be very accurate. These are really meant for people who want to make sure that a lack of oxygen is not killing their fish in their ponds or aquariums
  39. 39. If there was more time, the BOD of each of the sites would be repeated. dissolved oxygen at different salinity concentrations since this is also an interesting factor that affects DO. BOD with different cultures of organisms.

Notas del editor

  • Factories that treat water and dump it in the river, the water is clean, but it’s temperature higher, this leads to less DO and therefore problems for the animals in the echosystem.
    After winter, Runoff from roads will get in the water causing higher salinity levels, lowering DO causing the same problem