1.
Dissolved Oxygen
Measurement Techniques
and Applications for the
Water Quality Measurements
of the Passaic River

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.
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.
Dissolved Oxygen Factors
 Temperature: Cold water holds more
oxygen than hot water
 Salinity levels: Fresh water holds more DO
than salt water

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.
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.
Methods of Measuring DO
 Electrochemical devises
 Electrochemical tests
Clarck electrochemical probes
Optical based sensing methods
 Chemical tests
 Titrimetric tests
 Colorimetric tests

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.
Clark Electrochemical Probes
 Sources of Error:
Calibrating the probes improperly.
Improperly installed electrode
Weak electrolyte inside the membrane

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.
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.
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.
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.
Tests Evaluated
 Titrimetric:
 HACH DO Kit
 LaMotte DO Kit
 Colorimetric
 CHEMetrics DO kit
 Profi O2 test
 Clark Electrochemical Probes
 GSWA probe
 CSE probe

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.
With Lab Pump and aquarium pump

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.
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.
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.
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.
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.
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.
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.
 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.
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.
 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.
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.
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.
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.
 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.