THE DISSOLVED OXYGEN ANALYZER
(Weston & Stack Inc., Model 300-B)
METHOD FOR THE DETERMINATION OF THE
BOD OF INCINERATOR QUENCH WATER
A Division of Research and Development
Open-File Report (RS-03-68-17)
l.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
-------
THE DISSOLVED OXYGEN ANALYZER
(Weston & Stack Inc., Model 300-B)
METHOD FOR THE DETERMINATION OF THE
BOD OF INCINERATOR QUENCH WATER
A Division of Research and Development
Open-File Report (RS-03-68-17)
written by
Donald L. Wilson, Research Chemist
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Environmental Health Service
Bureau of Solid Waste Management
1970
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PREFACE
In publishing an analytical method which employs specific brands
of laboratory supplies and instrumentation, the U.S. Public Health Ser-
vice does not imply that other commercial products could not be utilized
with appropriate modifications in the procedure.
111
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INTRODUCTION
The analysis of an aerated, diluted sample for its BOO involves
the determination of its dissolved oxygen content before and after an
incubation period. The difference between the initial dissolved oxygen
and the final oxygen content represents the oxygen demand of the sample.
The oxygen demand of incinerator quench water* (or similarly
polluted water) is exerted by three classes of materials: (a) carbonaceous
organic material usable as a food source by aerobic organisms; (b) oxidiz-
able nitrogen derived from nitrite, ammonia, and organic nitrogen compounds
which serve as food for specific bacteria (e.g. Nitrosomonas and Nitro-
bacter); and (c) certain chemical reducing compounds (e.g. ferrous iron,
sulfite, and sulfide) which will react with molecularly dissolved oxygen.
Since the oxidation of nitrogeneous materials may proceed at a variable
rate, the nitrification process is inhibited, thus restricting the BOD
determination to the organic carbon present. The wfler samnle is acidified
to pH 2 to 3 and subsequently neutralized to accomplish the inhibition of
the nitrification.
Complete stabilization of a given sample may require an overly
long incubation period for practical purposes. The 5-day incubation period
has been accepted as standard. For certain industrial wastes, however, it
may be advisable to determine the oxidation curve . Conversion of data from
one incubation period to another can only be made if such special studies
are carried out. Studies in recent years have shown that the exponential
rate of carbonaceous oxidation at 2OC rarely has a value of 0.1, but may
*Quench water refers to water which has been employed to cool the non-
combustibles after emergence from the furnace.
v
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vary from less than one-half to more than twice this value. This fact
usually makes it impossible to calculate the ultimate carbonaceous demand
of a sample from 5-day GOD values unless the exponential rate value has
been determined on the contaminated water under consideration.
Since incinerator quench water may contain many variables which
affect the Winkler Method of analysis, the Dissolved Oxygen Analyzer
Method is recommended for GOD analysis of all quench water sample. The
Alsterberg (Azide) Modification of the Winkler Method is recommended for
standardization of the Analyzer using the relatively pure dilution water.
Preliminary tests, which show the validity of the Winkler DO value, are
discussed in the section on the Winkler Method.
The sampling location at each site is very important in the
evaluation of the data. The sampling site should be chosen on the basis
of obtaining the most representative sample.
vi
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TABLE OF CONTENTS
DISCUSSION 1
APPARATUS 3
Requirements 3
Preparation and Maintenance 4
Probe 4
Membrane Installation 4
Detection of Membrane Perforation 8
Servicing a Contaminated Probe 10
Glass and Plastic Apparatus 11
Recharging Batteries 11
REAGENTS 12
Chemical Requirements 12
Preparation of Solutions 13
SAFETY PRECAUTIONS 15
CALIBRATION 15
Zero Adjustment of Amplifier 15
Temperature Compensation of the Probe’s Output 16
Temperature Scale 17
Regular Adjustment of the Bridge Potential 17
Special Adjustment of the Bridge Potential 19
Probe 21
Various DO Saturation Levels 21
System of Known DO Depletion Capability 25
ANALYSIS OF SAMPLES 27
Sample Collection 27
Site Collection 27
Sample Size and Container 27
Sample Preservation and Shipment 28
Sample (and Blank) Preparation 28
Adjustment for Nitrification Process 28
vii
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Adjustment for Residual Chlorine 29
Dilution and Aeration 29
Determination of the DO Concentration 31
CALCULATIONS 32
BOD of Dilution Water 32
BOD of Quench Water 33
METHOD EVALUATION 34
Precision 34
Accuracy 34
Sensitivity 34
BIBLIOGRAPHY 36
viii
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DISCUSSION
The Weston and Stack Dissolved Oxygen Analyzer utilizes a speci-
ally designed probe to measure accurately and quickly the amount of
dissolved oxygen in gas streams and liquids. The probe is constructed
of cast-epoxy and is separated from the sample by a semipermeable mem-
brane.
The Analyzer is powered by A.C. or internal batteries and is
ruggedly constructed and moisture-proof to facilitate laboratory or
field use. Interferences in water or gas samples are minimal with this
instrument. Hydrogen sulfide does not interfere, but will eventually
corrode the lead anode. The probe will then require cleaning. Dissolved
or suspended solids will not affect the probe provided the analyzer is
calibrated using a similar type of sample to account for partial pressure
changes. Laboratory tests have reaffirmed that this probe is not
affected by ferrous or ferric iron, sulfite, or nitrite.
Since temperature affects the rate of diffusion of dissolve oxygen
through the Teflor membrane, the probe output for a given concentration
of dissolved oxygen is a function of the temperature. A secondary resis-
tance to oxygen diffusion exists at the Teflo aqueous sample interface.
The interfacial resistance is of minor significance when the sample is
vigorously agitated to produce a high degree of turbulence. Also, a high
degree of turbulence is imperative for the temperature compensation to
function satisfactorily.
—l —
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-2-
Temperature compensation in the Weston and Stack Analyzer is
accomplished by an operational amplifier. A thermistor (resistor whose
resistivity varies intensely with temperature) and resistance network
introduced in the feedback circuit for the amplifier provides suitable
multiplication so that temperature effect on the probe is limited to ÷
2% over the temperature range of 0 to 50C when suitable turbulence is
provided.
The probe must be calibrated by the Winkler Method to enable the
analyst to read the true ppm DO directly off the instruments scale. This
calibration, although normally needed only once a month, preferably
should be checked at the beginning and ending of each 5-day incubation
period.
Although a probe output can be obtained for any element or com-
pound which diffuses through the semipermeable (Teflo ) membrane and is re-
duced at a potential of -0.578 volts or less, interferences of this
nature appear to be infrequent. Sulfite, nitrite, ferrous and ferric
iron, and other reducing and oxidizing substances which normally interfere
with the Winkler Method, apparently do not affect the output of this
probe. There are a few substances, however, which affect the probe’s
sensitivity over a period of time. Hydrogen sulfide and chlorine,
although not detected by the probe, will react with the lead anode and
cause a decline in sensitivity. Greases and oils will coat the semiper-
meable memberane, increase the diffusion resistance and decrease the probe
output. Variations in dissolved solids will alter the partial pressure of
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-3-
oxyqen in the aqueous samples and hence the probe output. The calibration
and utilization of the instrument should be accomplished with these facts
in mind.
APPARATUS
Requi rements
1. Analyzer, Weston and Stack, Model 300-B: 0-15, 0-1.5 ppm, tempera-
ture compensation and temperature readout. A.C. powered with inter-
nal combination power supply battery charger.
2. Probe, Weston and Stack, Model A-30 BOO agitator-thermistor assembly.
3. Accessory Kit: membranes, electrolyte, syringe, manual, recorder, plug.
4. Extra membranes: Tef1ot , 1/2 mu thick, 3” square; 24 per package.
5. Graduates: 50 ml, 1 liter, and 2 liter.
6. Beakers: 250 ml, 2 liter, and 3 liter.
7. Siphon tubinq.
8. Rubber bands.
9. BOD bottles, 300 ml capacity.
10. Analytical balance.
11. Volumetric flasks: 100 ml, 500 ml, and 5 - one liter.
12. pH paper: range 2 through 9.
13. Air incubator or waterbath, thermostatically controlled at 20C + 1C.
14. Carboy, polyethylene nalgene, wide mouth, two - 2 gallon (7 liters
or more).
15. Test tube with 14 mm 1.0.
16. Magnetic stirrer with Teflo - coated stirring bar.
17. Stopwatch or accurate watch with second hand.
18. Pipets, graduated or volumetric, two - 2m1.
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-4—
19. Reagent bottles, resistant glass, narrow mouth with ground glass
stoppers, 1 liter capacity, at least one amber in color,
20. Sample collection bottles, polyethylene (or similar non-breakable
bottle) with narrow mouth and tightly fitting caps, about 1 liter
(or one quart) capacity, sterile.
21. Regulator, 2—stage, with cylinder valve outlet for nitrogen (CGA
No. 580).
22. Ice chest, capable of holding several one liter sample collection
bottles and maintaining a SC temperature for 24 hours,
Preparation and Maintenance
Probe . Membrane Installation. Since the performance of the probe
is dependent upon a properly installed membrane, the analyst should exer-
cise great care in performing the following instructions:
Procedure Comments
1. Remove the probe shield and thermis- 1. See Figure 1 for identifica-
tor housing, electrolyte fill screw, tion of probe components.
and old membrane from the probe,
2. Wrap a rubber band around a test 2.
tube, having a 14 m I.D.
See Figure 2(a-f) for the
diagramatic representation
of steps #2, 6, 7, 9, 10 and 12.
3. The open end of the test tube
should be flush with the fore-
finger.
3. Hold the test tube in an upright
position by encircling it with
the fingers and thumb of one hand.
4. Place one membrane sheet over the
top of the test tube and fist.
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-5—
CORD RESTRAINER SERVICE CAP
Co RD
REMOVABLE PROBE
AND THERMISTOR HOUSING
SERVICE CAP
ELECTROLYTE
FILL SCRE Y
PROBE BODY
Figure 1. THE PROBE.
(Reproduced with the permission
of Weston and Stack, Inc.)
PIN HOUSING
CONNECTOR
PINS
LEAD
PLATINUM CATHOO
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-6-
a. Step #2: Position of the
rubber band on the test
tube.
d. Step #9: Drawing up the
membrane to provide a snuz
fit across the face of the
platinum tip.
b. Step #6:
trolyte i
membrane.
Pouring the elec-
nto the depressed
e. Step #10: Wrapping a second
rubber band around the probe
just above the small holes.
c. Step #7: Pressing the mem-
brane down into the tube
with the probe.
f. Step #12: The probe after
the removal of the upper
rubber band and the trim-
ming of the membrane.
Figure 2. MEMBRANE INSTALLATION PROCEDURE.
(Drawings reproduced with the permission
of Weston and Stack, Inc.)
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—7-
Procedure
5. Gently depress the membrane about
one inch into the tube.
6. Pour electrolyte into the depress-
ion.
7. Press the membrane down into the
tube with the probe.
8. Slip the rubber band off the tube
and over the membrane to a point
1/2 inch above the holes near the
tip of the probe.
9. Carefully draw up the membrane to pro- 9.
vide a snug fit.
10. Wrap a second rubber band as
tightly as possible just above
the holes.
11. Remove the first (top) rubber band.
12. Trim membrane close to and above
the second rubber band.
6. See preparation of electrolyte.
7. Do this carefully so the mem-
brane is not damaged. Keep air
bubbles from being trapped be-
ween the probe and membrane.
8. Remove the tube.
It is necessary to have a close,
smooth fit over the platinum
electrode without stretching
or tearing the membrane.
10. Apply securely to prevent leak-
age of electrolyte from membrane.
Comnien1 s
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-8-
Procedure
13. Use the syringe to completely fill
the cavity in the probe with
electrolyte.
14. Shake and tap the probe so that air
bubbles will escape from the fill
hole.
15. Replace the fill screw and probe
shield.
16. Connect the probe to the readout
instrument and turn the meter to
the “ON” position and the selector
switch to “DO-MULl 1” position.
Hold the probe with platinum
electrode up and shake it
vigorously.
Comments
13. The probe should be held
upright.
14. Thumb is held over fill hole
during shaking.
16. See Figure 3 for the location
of components of the instru-
ment.
17. 17. If the meter needle oscil-
lates, air bubbles are present
and steps #14 through #17 must
be repeated.
Detection of Membrane Perforation. When a hole developes in the mem-
brane, the response rate of the probe decreases as the electrolyte is
diluted and the cathode is poisoned. To assure the proper performance of
the probe, frequent inspections of the membrane should be performed:
Procedure Comments
1. Hold the membrane end of the probe 1. If the membrane was installed
in a beaker containing clear water. recently, the probe should be
rinsed thoroughly to remove
electrolyte which may be trapped
in the folds of the membrane.
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FRONT BACK
PROBE
INPUT
0 • ‘ ‘
0
STO
TU
RAGE
BES
0 0
c
AC PLUG
Figure 3. FRONT AND BACK VIEWS OF THE ANALYZER.
(Reproduced with the permission of Weston and Stack, Inc.)
Ii
0
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- 10 -
2. While looking through the water 2. If a hole is detected a new mem-
towards a light source search for brane must be installed.
a small stream (diffused light)
of electrolyte floating through a
hole in the membrane.
Servicing a Contaminated Probe. Upon setting for a few months with
electrolyte, the inner parts of the probe become contaminate and may not
allow any calibration adjustment to be made or readout needle drifting
downwards. The procedi re for cleaning a probe is as follows:
Procedure Comments
1. Remove the probe shield and ther- 1. See Figure 1 for identification
mistor housing, membrane, electro- of probe parts.
lyte fill screw, and probe service
cap screw (may use quarter coin).
2. Turn probe upside down and shake out
the lead anode.
3. Clean the lead anode by immersing
it in warm 10 percent NaOH (or HC1)
solution, then rinse thoroughly
with distilled water.
4. Clean the platinum electrode and 4.
the inside of the probe body with
6N(l:l)HC1, then rinse thoroughly
with distilled water.
3. All the yellow deposit must be
removed.
The lead anode will not seat
properly or make contact if the
lead ring inside the probe is
not completely clean.
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—11 —
5. Polish the platinum cathode
with a soft tissue.
Reassemble lead anode and probe
service cap.
6. Use a small amount of silicon
grease on the threads and the
“0” ring.
7. Install a new membrane as pre- 7. See section on Membrane Insta-
viously directed. ilation.
Glass and Plastic Apparatus . Sampling bottles, tubing, containers,
and the like must be thoroughly cleaned (sterile) to assure the removal
of materials capable of exerting a BOO. Detergents may be used if clean-
in is followed by thorough rinsing with distilled water.
Recharging Batteries . The Weston and Stack Dissolved Oxygen Analyzer,
Model 300-B, is provided with an internally combined AC power supply and
battery charger. The instrument can be operated in the laboratory directly
on 110 AC or in the field using the rechargeable nickel cadmium batteries.
When the instrument is employed in the field, a record of the hours of
amplifier usage should be maintained. Before each standardization of the
instrument in the laboratory or utilization in the field, the analyst
should then check his record. If the amplifier usage > 20 hours, the
batteries should be recharged, as follows:
Procedure _________
1. While operating the instrument on
110 AC, place the selector switch
in the “DO-Mult 1” position.
2. Turn the power switch to the
“OFF/CHG” position.
Comments
1. See Figure 3 for the location
of the components of the instru-
ment.
6.
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-12-
3. Determine if a charge is coming
from the batteries.
Chemical Requirements
The following chemicals are ACS, Reagent Grade:
1. Potassium iodide
2. Sodium sulfite
3. Sodium hydroxide
4. Hydrochloric acid, concentrated
5. Sulfuric acid, concentrated
6. Phosphate buffer solution, pH 7.2 (or prepared)
7. Potassium phosphate, monobasic
8. Potassium phosphate, dibasic
9. Sodium phosphate, dibasic, heptahedrate, crystal
10. Ammonium chloride
11. Magnesium sulfate, crystal
12. Calcium chloride, anhydrous
3. The meter needle should respond
and possibly oscillate. If no
response occurs check the 12V
batteries and connections. Re-
place components if necessary.
Rechargeable batteries last about
three years.
4. Place selector switch in the 4.
“Transit’ position and recharge the
batteries for a maximum of 10 hours
NOTE: The 30 V battery is not rechargeable and last about six months.
REAGENTS
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-13-
13. Ferric chlroide, lumps
14. Manganese(ous) sulfate, monohydrate
15. Potassium hydroxide
16. Nitrogen, 99.9 percent pure.
Preparation of Solutions
The water employed in the preparation of solutions must be distilled
from a block tin or all-glass still, contains less than 0.01 mg/liter
copper, and be free of chlorine, chloramines, caustic alkalinity, organic
materials, and acids.
Solutions are prepared as follows:
1. Electrolyte solution: Dissolve 50.0 g of potassium iodide in distilled
water and dilute with same to 100 ml. Store solution in a dark brown
bottle. (8 oz. bottles of this solution may be purchased from either
the Weston and Stack Company, 1426 Lewis Lane, West Chester, Pennsyl-
vania, 19380 or their Ohio representative, Henry P. Thompson Co.,
4866 Cooper Road, Cincinnati, Ohio, 45242).
2. Sodium sulfite solution: Dissolve about five grams of sodium sulfite
in 500 ml of distilled water.
3. Sodium hydroxide solution, approximately 1N: Dissolve 41.6 grams NaOH
in distilled water and dilute with same to one liter.
4. Sulfuric acid solution, approximately 1N: Cautiously add 28 ml of con-
centrated H 2 S0 4 to distilled water and dilute with same to one liter.
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-14-
5. “Dilution Water”: To one liter of distilled water at 20C, add 1 ml
of each of the following solutions: Phosphate buffer solution, pH
7.2; magnesium sulfate solution (22.5 g Mg S0 4 7H 2 0 per liter of
solution); calcium chloride solution (27.5 g anhydrous CaC1 2 per
liter of solution); ferric chlroide solution (0.25 g FeCl 3 6H 2 0 per
liter of solution).
6. Sodium hydroxide solution, 10% (w/v): Dissolve 10.0 g NaOH in dis-
tilled water and dilute with same to 100 ml.
7. Phosphate buffer solution, pH 7.2 may be purchased already prepared
or prepared as such: Dissolve 8.5 g KH 2 PO 4 , 21.75 g K 2 HPO 4 , 33.4 g
Na 2 HPO 4 .7H 2 0, and 1.7 g NH 4 C1 in 500 ml distilled water and dilute
with same to one liter. The pH of this buffer should be 7.2 without
further adjustment.
8. Hydrochloric acid solution, 10 percent (v/v): Cautiously add 10 ml
concentrated HC1 (sp. gr. 1.19) to 75 ml distilled water and dilute
with the latter to 100 ml.
9. Hydrochloric acid solution, 5N: Cautiously add 42.8 ml concentrated
HC1 (sp. yr. 1.19) to 40 ml distilled water and dilute with the
latter to 100 ml.
10. Manganous sulfate solution, 0.25 M: Dissolve 21.13 g MnS0 4 H 2 0 in
distilled water and dilute with same to 500 ml.
11. Potassium hydroxide solution, 0.5M: Dissolve 14.03 g KOH in dis-
tilled water and dilute with same to 500 nil.
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-15—
SAFETY PRECAUTIONS
Follow general laboratory safety rules. This method has no pro-
nounced safety hazards.
CALIBRATION
Zero Adjustment of Amplifier
To insure the proper amplification of the temperature-compensated
signal from the probe, the output of the amplifier should first be ad-
justed to zero while the probe is inserted in a solution containing no
dissolved oxygen. The procedure is as follows:
Procedure Comments
1. Set the selector switch to “Transit” 1. See Figure 3 for the location of
and power switch to “OFF/CHG”. components of the instrument.
2. Using the unmarked screw on the 2. Adjustment may not be necessary.
meter face, set the meter needle
to zero.
3. Place the probe in the sodium 3. Use regular BOO bottle to contain
sulfite solution for 2 minutes or the solution.
longer
4. Set the selector switch to 4. The agitator should be employed.
“DO—Mult 1” and turn the Analyzer
“ON” for a period of at least 2
minutes.
5. Adjust the meter reading to zero
using the zero-adjustment screw,
marked “zero”, on the front of the
instrument case.
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—16-
6. Remove the probe from the sulfite 6. Keep the probe in BOD bottle of
solution and rinse the membrane clean distilled water when not
thoroughly with distilled water. in use.
Temperature Compensation of the Probe’s Output
A thermistor (resistor whose resistivity varies intensely with tem-
perature) and resistance network introduced into the feedback circuit of
an operational amplifier provides the temperature compensation of the
probe’s output. The compensation is accurate to ± 2 percent over a sample
temperature range of 0 to 50C. However, an adjustment is necessary if
sample temperature varies more than 5C from the temperature of the probe.
The adjustment is as follows:
Procedure Comments
1 . If the probe and sample are not 1 .a) See Figure 3 for the location
essentially the same temperature of the switch.
(within 5C) then move front—left- b) Analyzer may be used to check
switch (marked >5 & <5) to the temperatures of room and sample.
>5 position. (see Sample Analysis).
2. If the probe and sample are near 2. Normally this step is applied.
the same temperature (within SC)
then move above switch to the <5
position.
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—17—
Temperature Scale
Regular Adjustment of the Bridge Potential . The temperature scale
of the instrument is calibrated at the factory and in normal operation
should not require re-calibration. The thermometer circuit is, however,
designed as an unbalanced bridge, whose potential is supplied by a 30
volt-battery. Regular (each day of use) adjustments of the bridge poten-
tial should, therefore, be performed as follows:
Procedure ________
1. Turn the selector switch to 1.
“Temperature.”
50C.
4. Release the “Temp Test” button.
Comments
See Figures 3 and 4 for the loca-
tion of the switch and other com-
ponents of these instructions.
2. The resistor’s activity is equiva-
lent to the thermistor’s resis-
tance at 50C.
3. If the needle can not be adjusted
to 50C, the probe may need clean-
ing or the 30 volt-battery may
need replacement.
2. Press the “Temp Test” button.
3. While pressing the “Temp Test”
button, adjust the potentiometer
by turning the “Temp Adj. Screw”
until the needle indicates exactly
4. The Analyzer is now indicating
temperature correctly.
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-18-
PROBE
INPUT
RIGHT SIDE
Figure 4. SIDE VIEWS OF ANALYZER.
(Reproduced with the
permission of Weston
and Stack, Inc.)
LEFT SIDE
( iiiiPnS
( u t cAt. )
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-19-
Procedure
1. With the power switch in the
“OFF/CHG” position and the
selector switch in the “Transit”
position, adjust the meter to zero
using the unlabeled screw on the
meter face.
2. Assemble probe and thermistor
housing.
3. Connect the probe cable to con-
nector.
4. Remove the back cover of the
instrument by removing all eight
screws.
5. Locate the three potentiometer
adjustment screws inside the unit.
Comments
I. See Figures 3 and 4 for the loca-
tion of the components of the
instrument.
3. Connector located on right side
of instrument case.
5. Facing the back of the unit, four
small screws, aligned in a hori-
zontal line, are immed 4 ately be-
neath the handle attachment. The
multiplier adjustment screw is
the one on the far left, the others
are the potentiometer screws.
Special Adjustment of the Bridge Potential . When a resistance
component in the temperature bridge is replaced, the temperature scale
must be recalibrated. The special potentiometer adjustments are as
follows:
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-20-
6. Imerse the probe into a 0 C bath 6.a) The temperature of the bath
consisting of distilled water and should be checked with an accu-
finely crushed ice, then agitate rate thermometer.
the probe assembly. b) Equilibrium should be reached
after 5 to 10 minutes.
7. Still agitating the probe, turn the
potentiometer screw which is farthest
to the right (facing the back of the
Analyzer) until a reading of 0 C is
obtained on the meter.
8. Repeat the procedure with a water 8. “Temp Adj” screw is located on
bath at 50C and the meter reading the left side (Figure 4) of the
adjustments with the “Temp Adj.” instrument case.
screw only.
9. While pushing on the “Temp Test”
button, turn the second from right
(facing the back of the Analyzer)
potentiometer screw until the meter
reads 50C.
10. Using a 25C water bath, compare the 10. The third potentiometer adjust-
meter temperature reading to an ment screw, which is located
accurate thermometer. If there is right of the multiplier adjust-
an error, readjust potentiometer ment screw, should never be
adjustment screw farthest to right turned.
(facing the back of the Analyzer).
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-21-
Probe
Various DO Saturation Levels . Before employing the Analyzer and
preferably each day it is used (never longer than three weeks), the
analyst should calibrate the probe with samples whose DO concentration
have been determined by the Alsterberg (Azide) Modification of the
Winkler Method.
The dissolved oxygen probe is a partial pressure device; this means
that the transfer of dissolved oxygen through the semi-permeable rnem-
orane is a function of the ratio of dissolved oxygen concentration to
dissolved oxygen concentration at saturation. For example, when a salt
solution is saturated with oxygen at 20C, it may contain only 3 ppm of
dissolved oxygen; water, however, when saturated with oxygen at 20C will
contain 9.2 ppm of dissolved oxygen. Since the rate of oxygen transfer
through the membrane would be the same in both cases, the probe output
would be the same. The probe must therefore be calibrated using a
liquid similar to the sample to be analyzed. Since “quench water” is
greatly diluted with “dilution water” before analysis, the calibration
of the probe, before analyzing general “quench water” samples, should be
performed with “dilution water”. The probe must be calibrated each day
it is used. If the membrane has been replaced the calibration of the
probe will change slowly for a period of about 24 hours before becoming
stabilized. If the probe is used during the period, frequent calibration
checks will be required.
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-22-P
2. Siphon the aerated water from
the beaker into each of 3 BUD
bottles.
3. Using the Analyzer and probe,
determine the DO and temperature
of one of these aerated samples.
4. Adjust the calibration screw so
the Analyzer reads the same ppm
DO as observed in Table 1 for
the sample temperature.
before the probe
Comments
This may be
water forth
graduate to
three times.
2. During the siphoning, the water
should be continuously stirred
using a magnetic mixer and a
Teflo, —coated magnetic bar.
3. See “Determination of the DO
Concentration.”
4.a) See Figure 3 for the location
of “Cal” screw.
b) An exact DO concentration at
20C and zero chloride concen-
tration is 9.1%.
The probe must be calibrated to the specific turbulence of the
system. Since the Weston & Stack BUD Agitator is used, the agitation is
built into the probe assembly. Therefore, when calibration is performed,
it is applicable for any container or use to which the BUD Agitator may
be applied.
NOTE: The Modified Winkler Method must be established
can be calibrated.
Procedure _________
1. Saturate a liter of “dilution 1. done by pouring the
water” with oxygen. and back from a
a beaker at least
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-23-
Table 1. SOLUBILITY OF OXYGEN IN WATER EXPOSED TO WATER-SATURATED AIR*
Temp.
°C
Chloride
I
Concentration
in Water—mg/I
Difference per
100 mg Chloride
0
5.000
10,000
I
15,000
I
20,000
Diss
olved
Oxygen—ni
g/l (ppm)
0 14.6 13.8 13.0 12.1 11.3 0.011
1 14.2 13.4 12.6 11.8 11.0 0.016
2 13.8 13.1 12.3 11.5 10.8 0.015
3 13.5 12.1 12.0 11.2 10.5 0.015
4 13.1 12.4 11.7 11.0 10.3 0.014
5 12.8 12.1 11.4 10.1 10.0 0.014
6 12.5 11.6 11.1 10.5 9.8 0.014
1 12.2 11.5 10.9 10.2 9.6 0.013
8 11.9 11.2 10.6 10.0 9.4 0.013
9 11.6 11.0 10.4 9.8 9.2 0.012
10 11.3 10.1 10.1 9.6 9.0 0.012
11 11.1 10.5 9.9 9.4 8.8 0.011
12 10.8 10.3 9.7 9.2 8.6 0.011
13 10.6 10.1 9.5 9.0 8.5 0.011
14 10.4 9.9 9.3 8.8 8.3 0.010
15 10.2 9.1 9.1 8.6 8.1 0.010
16 10.0 9.5 9.0 8.5 8.0 0.010
11 9.1 9.3 8.6 8.3 1.8 0.010
18 9.5 9.1 8.6 8.2 1.1 0.009
19 9.4 8.9 8.5 8.0 1.6 0.009
20 9.2 8.1 8.3 1.9 1.4 0.009
21 9.0 8.6 8.1 1.1 1.3 0.009
22 8.8 8.4 8.0 1.6 1.1 0.008
23 8.1 8.3 1.9 1.4 1.0 0.008
24 8.5 8.1 1.7 1.3 6.9 0.008
25 8.4 8.0 1.6 1.2 6.7 0.008
26 8.2 1.8 1.4 1.0 6.6 0.008
21 8.1 1.1 1.3 6.9 6.5 0.008
28 1.9 1.5 7.1 6.8 6.4 0.008
29 7.8 1.4 1.0 6.6 6.3 0.008
30 1.6 1.3 6.9 6.5 6.1 0.008
31 1.5
32 7.4
33 7.3
34 7.2
35 7.1 ‘At a total pressure of 780 mm, Hg. Under any other barometric pressure, P (mm,
36 1.0 or P’ . in.), the solubility, .S’ (mg/I), can be obtained from the corresponding
31 6.9 value in the table by the equation
36 6.8 8
in which S is the solubi lity at 760 mm (29.92 In.) and p is the pressure mm
of saturated water vapor at the temperature of the water. For elevations less
41 6.5 than 3,000 ft and temperatures below 25°C. p can be ignored. The equation then
A becomos
‘ IL U.’. P
43 6.3 8 = 8160 = 2992
44 6.2
Ac 6 1 Dry air is assumed to contain 20.90 per cent oxygen. (Calculations made by
Whipple and Whipple).
46 6.0
41 5.9 (Reproduced from Standa.rd Methods for the Exajncnation of Water and Wastewater,
48 5.8 12th Edition, 1965, p. 409 with the permission of th American Public Health
49 5 7 Association, Inc.. American Water Works Association, and Water Pollution Con-
trol Federation.)
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5. Determine the DO of the same
sample using the Modified
Winkler Method.
6. Using the Analyzer and probe,
determine the DO of the second
aerated sample.
7. Considering the difference be-
tween the Analyzer and Modified
Winkler Method with the first
aerated sample, adjust the cali-
bration screw.
8. Determine the DO of the same sample
using the Modified Winkler Method.
9. The third aerated sample is used
as a re-check of the calibration
point. If the calibration screw
needs more adjustments, then more
aerated sample should be prepared
and analyzed until the calibra-
tion screw does not need adjustment.
5. See Modified Winkler Method
(Bibliography).
9. After calibration the probe should
always be kept in a BOD bottle
filled with distilled water to
prevent air bubbles from entering
the probe.
Having performed the above calibration procedure, the probe has
now been calibrated at the upper and lower (zero adjustment of amplifier)
DO saturation limits. The Analyzer’s DO measurements are linear between
-------
-25-
these limits; however, the analyst may wish to verify the DO readings be-
tween these limits. This may be done by performing the probe calibration
as just described except allowing pure nitrogen to bubble, for about 15
to 30 minutes, through the aerated samples before the DO analysis. This
treatment with nitrogen gas will lower the saturated oxygen concentration
to about 3 to 4 ppm. The nitrogen gas will not interfere with the Modi-
fied Winkler’s DO analysis.
System of Known DO Depletion Capability . The calibration proce-
dures described thus f ar are usually employed only in the laboratory. The
following method is applicable both in the laboratory and in the field
where regular calibration procedures would be difficult to perform. This
method utilizes a system of known oxygen depletion capability to evaluate
indirectly the probe’s response below the saturation level. It is not a
true probe calibration method. The probe or Analyzer must first be cali-
brated by comparison to the Modified Winkler Method then, while being
operated in the field, can easily be checked for performance by the
following method.
Procedure Comments
1. Prepare 3 BOD bottles of aerated
water samples as previously des-
cribed in the probe calibration
procedures.
2. Using the Analyzer and probe, 2. See “Determination of the DO
determine the DO of one of these Concentration.”
aerated samples.
3. Remove the probe and rinse it 3. When the probe is not being used,
with distilled water. keep it in a BOD bottle which is
filled with distilled water.
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-26-
4. To the same BUD bottle, using a
volumetric pipet, add 2 ml of
0.25 M inanganous sulfate solution.
5. Immediately initiate the addition
of 2 ml of 0.5 M potassium hydro-
xide solution; record the exact time
of initiation.
6. After the KOH has been added,
stopper the bottle and mix the
contents by repeated inversions.
7. After not more than 8 minutes have
elapsed, insert the probe into the
BOO bottle.
8. After exactly 10 minutes have
elapsed since the addition of
the KOH solution, record the
DO concentration.
9. Repeat steps #2 through #8 with
the other two prepared BUD
bo t t 1 e s.
10. Determine the depletion of DO for
each sample by substracting the
final ppm DO from the initial
observation.
4. The tip of the pipet should be
placed beneath the surface of
the sample.
5.a) Use a volumetric pipet.
b) Use a stopwatch or other accu-
rate device to measure exactly
the 10-minute reaction period.
7. Equilibrium is attained in about
two minutes.
10. The average depletion should be
3.60 ÷ 0.25 ppm. If the deple-
tion is not this value, re-check
calibrations; the instrument may
have to be returned to the manu-
facturer.
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ANALYSIS OF SAMPLES
Sample Collection
Site Selection . When the BOO of quench water is measured to deter-
mine the amount of oxidizable wastes that will be discharged to a sewerage
system serving an incinerator facility or a drainage system associated with
the residue disposal area, the site of sample collection must be chosen
with due consideration. Settlement tanks, surface pools, sewers, and other
areas immediately adjacent to the sewage or drainage system are preferable
collection sites.
Sample Size and Container . Normally 50 ml of sample is needed to
perform the BOD analysis; however, since various dilutions may be needed
and a larger sample size may be more representative, it is recommended to
collect one liter quench water sample.
The samples should be collected in sterile, non-breakable bottles
with narrow mouths and caps which can be tightly fitted. The sample bot-
tle should be completely filled. All containers must be thoroughly rinsed,
especially if cleaned with a detergent, before they can be reused.
Samples should not be collected on Monday or Tuesday unless the
analysts are to work on Saturday or Sunday (5-day BOD).
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-28-
Sample Preservation and Shipment
If the sample analysis is to be initiated within four hours after
collection, sample preservation measures are not absolutely necessary.
However, if initiation of the analysis will be started after four hours,
samples, soon after collection, should be placed in an ice chest (or
similar container) so that the samples are maintained in the dark at 5C.
The bottle caps must be tightly fitted to prevent an increase in oxygen
solubility with the reduction in temperature.
Sample shipment to the laboratory should be immediate and via air
freight if necessary to insure the initiation of BOO analysis in the labo-
ratory within 24 hours of sample collection. Samples received more than 24
hours old should not be analyzed.
Since the Analyzer requires calibration, the laboratory personnel
should be informed at least two days before the arrival of samples. Be-
cause samples require some preparation before the actual analysis and
the exact dilution requirements may not be known, samples (not at 5C)
should be shipped to the laboratory so that they are received at least
two hours before the end of the normal working day. Samples shipped in
an ice chest (5C) and refrigerated may be analyzed the following day pro-
vided the analysis can be initiated before the samples are 24 hours old.
Sample (and Blank) Preparation
Adjustment for Nitrification Process . Prior to analysis each
sample (and “dilution water” blank) is treated as follows to inhibit the
nitrification process:
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-29-
Procedure Comments
1. Place 50 ml of a thoroughly mixed 1. The exact volume of quench water
quench water sample in a 250 ml sample depends upon the dilution
beaker. requirements. See “Dilution and
Aeration.”
2. Using pH paper, check the pH of 2. Usually the pH is about 11.
the sample.
3. Using iN NaOH or 1N H 2 S0 4 , adjust 3. Omit if the sample already has a
the pH of the sample to a range of pH of 2 to 3.
2 to 3; maintain pH for 15 minutes.
4. Then neutralize the sample to a 4. Em loy the same iN solutions as
pH of 6.5 to 8.3. in step 3.
Adjustment for Residual Chlorine . Chlorine, at concentrations
normally found in chlorinated water and sewage effluent, does not influence
the probe output nor the determination of oxygen. Chlorine will react with
lead and hence cause the probe sensitivity to decrease after long exposure.
Since residual chlorine dissipates when samples stand for 1 to 2 hours or
they are well aerated, no adjustments are therefore recommended.
Dilution and Aeration . Prepared samples must be diluted in order to
obtain a measurable depletion (2 ppm to 7 ppm) of oxygen at the end of the
5-day incubation period. Since incinerator quench water usually has a BOO
of 100-300 ppm, a suitable or applicable dilution is 50 ml of sample
diluted to 2 liters. If the analyst suspects that the BOO of the quench
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-30’- -
water differs from the usual value, he should test various dilutions since
the analysis cannot be repeated upon the same original sample after the
5-day waiting period. To obtain more reliable results, 3 BOO bottles
should be prepared, 3 for the initial DO and the same 3 for the final DO and
the final DO values should never be less than 1.0 ppm.
Since the dilution water, employed in the analysis of each quench
water, may contain a few oxidizable materials capable of exerting a small
BOO, each quench water analysis should include a blank evaluation, i.e.,
a determination of the BOD of the dilution water. The observed BUD of the
qi en h water can then be corrected by substracting the appropriate propor-
tionate fraction of this blank value.
The dilution and aeration procedures
Procedure _________
1. Pour the total prepared sample 1.
from the 250 ml beaker into a 2
liter graduate and dilute to the
mark with “dilution water.”
2. Aerate the sample by pouring it
forth and back from the graduate
into a 3 liter beaker at least 3
times.
3. Siphon the diluted aerated sample
(or blank) from the beaker and
into 3 BOO bottles.
are as follows:
Comments
Solution still represents 50 ml
of original sample.
2. Dilution water blank is aerated
in like manner.
3. The sample should be stirred con-
tinuously using a magnetic stirrer
and a Tef1on coated magnetic bar.
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—31—
4. The DO concentration of the sample
(or blank) in the 3 BOO bottles
should be determined ininediately.
5. Then put the same 3 BOO bottles in
an incubator (or waterbath) and
determine their DO content after a
5-day incubation period at 20C.
Procedure
1. Turn the toggle switch located in
the lower left hand corner of the
front panel to “<5”.
4.a) See “Determination of the
DO Concentration.”
b) Only two reasonable DO results
are needed. See “Precision.”
5.a) During the incubation period
the samples should not be ex-
posed to the light.
b) See “Determination of the DO
Concentration”
c) Only two reasonable DO results
are needed. See “Precision.”
Comments
1. In most cases the entire body of
the probe is essentially at the
temperature of the sample. If
the probe body temperature varies
more than 5°C from the sample
temperature, turn the toggle
switch “>5”.
Determination the DO Concentration
As shipped, the Analyzer has the components necessary for operation.
Before attempting to place the analyzer into service, check to ascertain
that: 1) the membrane is free of holes, 2) the needle zeroes correctly,
3) the temperature reading is correct, and 4) the probe is free of air
bubbles.
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-32--
2. Turn the selector switch to “DO-
Mult 1.1
3. Turn toggle switch located in front
lower right hand corner of case to
“ON”.
4. Insert probe into BOD bottle.
5. Wait 2 minutes for equilibrium
and then read ppm dissolved
oxygen directly on top scale.
6. If temperature of the sample is
desired, turn selector switch to
“Temp” and read temperature (C)
directly on the bottom scale.
7. Turn toggle switch (right hand
corner) to “OFF” and selector
s switch to “TRANSiT”.
4. The agitator should be operating.
5.a) Record value.
b) The absolute value of the dif-
ference between duplicated
readings should not exceed
1.96 r*,or 0.58 ppm, more
than 5% of the time. See
re-.
“P ’cis ion”.
Record value.
Accuracy is ± 1C.
6. a)
b)
7. Perform this step if the meter
is not to be used for several
hours.
CALCULATIONS
BOD of Dilution Water
The following formula should be employed to calculate the BOD of
each individual sample of “dilution water.”
BOD 1 = - D 2
-------
-33-
Where: BUD 1 = The biochemical oxygen demand of dilution water
D 1 = The dissolved oxygen content of initial (before
incubation) dilution water
= The dissolved oxygen content of final (after incuba-
tion) dilution water
BOD of Quench Water
The initial DO concentration minus the final DO concentration equals
BUD of the diluted sample. The BOD of the diluted sample times the dilu-
tion factor equals the BOD of the original sample.
The dilution factor is found by dividing the original amount of
sample taken into the final dilution as: 50 ml of sample diluted into 2
liters gives a factor of 40.
The following formula should be employed to calculate the BOD of each
irididivual sample of quench water.
BOD 2 F [ (D 3 - D 4 ) - P 1 (BOD 1 )]
Where: BOD 2 The biochemical oxygen demand of quench water
F The dilution factor
D 3 The dissolved oxygen content of initial (before
incubation) quench water
D 4 The dissolved oxygen content of final (after
incubation) quench water
P 1 The decimal fraction of dilution water used in the
BOD analysis of the quench water
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-34-
METHOD EVALUATION
Precis ion
After analyzing a number of “quench water” samples, in duplicate
(three determinations were performed to ensure reasonable duplicate results),
the precision of the observations were evaluated by calculating (using
Olivetti Programa 101) the pooled standard deviation of all observations,
except those obtained on samples collected from dump truck drainage.
The results of these calculations are shown in the following table.
Accuracy
There is no standard with which the accuracy of the determination
can be measured. The accuracy of the instrument is 1% of the reading and
is better than ± 0.1 ppm
Sensitivity
This DO Analyzer method is not applicable to samples with a dilution
factor of 40, having a 5-day BOO value of 23.5 ppm or less.
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- 35 -
TABLE 2
PRECISION OF THE DO ANALYSISa
Number of
Determinationsb
Pooled
Deviati
Standard
on(s)C
Confidence Inte val
.t l.961/T (s)
82
0.21
. 0.58
Number of
Determinations
PRECISION
Standard
Deviation(s)e
OF THE BOD
Diluti?n
Factor
ANALYSIS
Confidence Interval
l. 96 ( 4 O)s
20
0.30
40
±23.5
aAssistance in the statistical analysis was provided by the Statistical
Section, Operational Analysis Branch, Division of Technical Operations,
BSWM.
bNll at least two initial and three final determinations were made for
each sample.
CA pooled standard deviation was computed for all determinations. It was
assumed that there was no statistically significant difference between
initial and final variances, i. e. homogeneity of the variances was as-
sumed.
dThe absolute value of the difference between duplicated readings should
not exceed l.96l (s), or 0.58 ppm, more than 5% of the time. The co-
variance between the duplicated readings was ignored.
eThe standard deviati e difference between initial and final DO
readings, (i.e. , S= (s .f- s ) . In this calculation it was assumed that
the initial and final pooled variances were equal and the covariance
term between initial and final readings was ignored.
Di1ution factor may vary, but for calculation purposes the normal dilu-
tion factor is shown here.
g 9570 confidence limits about a single BOD result, assuming a standard
dilution factor of 40 or 2.5 percent dilution.
-------
-36-
BIBLIOGRAPHY
1. American Public Health Association, American Water Works Association,
and Water Pollution Control Federation. Oxygen (Dissolved). In
Standard methods for the examination of water and wastewater.
12th ed. New York, American Public Health Association, Inc.,
165 p. 405-421.
2. Whipple, G. C. and Whipple, M. C., J. American Chem. Soc., 1911,
33, 362.
3. Weston and Stack, Incorporated, Operation Manual, Dissolved Oxygen
Analyzer, Model 300. West Chester, Pennsylvania, 1968.
4. Wilson, Donald L. Report on the Applicability of Existing Methods
for the Determination of the Biochemical Oxygen Demand (BUD) of
Incinerator Quench Water. Bureau of Solid Waste Management. (In
press).
5. Wilson, Donald L. The Alsterberg (Azide) Modification of the
Winkler Method for the Determination of the BUD of Incinerator
Quench Water and the Calibration of the Weston and Stack DO
Analyzer, Model 300-B. Bureau of Solid Waste Manageient. (In
press).
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