Hach-Lange BODTRACK II User Manual - Manual (Page 23)

cause results as shown in Curve 1. Dilute the sample or use a higher
BOD range and a different sample volume. Refer to the Sample dilution,
Simplified procedure, Hach GGA procedure or the Hach Standard
method procedure for more information.
When the BOD range of a sample is unknown:
• Use the results from the Chemical Oxygen Demand (COD test).
Multiply the COD by 0.68 to get an estimated BOD value.
• Use the results from a series of BOD tests that use the same sample
but different volumes.
• Use dilution ratios to select an applicable BOD range.
Typically, effluent is in the 0–70 mg/L range while influent is in the
0-700 mg/L range. when the BOD of the sample is more than 700 mg/L,
prepare a sample dilution. Refer to the Sample dilution section in the
expanded version of this manual for more information.
Nitrification
Refer to Figure 4 on page 20. The condition shown by Curve 2 is an
example of nitrification. Deviation from the typical curve (shown as the
dashed line) is apparent by the concave increase near the end of the
test period.
Biological oxidation of organic nitrogen usually occurs after 5 days with
typical domestic waste. Nitrifying bacteria develop more slowly than
other types of bacteria.
Some samples contain a high concentration of nitrifying bacteria and
nitrification results can occur sooner. Control nitrification problems with
Hach Nitrification Inhibitor. Dispense the inhibitor powder into an empty
sample bottle and then add the sample. With the Hach Dispenser cap,
dispense 6 shots (approximately 0.48 grams) into the empty bottle. Refer
to
Optional reagents on page 22.
Excessive time lag
Refer to Figure 4 on page 20. Curve 3 shows a test that did not start with
sufficient bacteria during the incubation period. To do a test on a sample
without sufficient bacteria, seed the sample. Refer to the Seed the
sample section in the expanded version of this manual for more
information.
Bacteria acclimation also causes conditions that can cause curve 3. This
sometimes occurs with standards and added seed. Add more seed or
select a different seed source.
Sample temperature
Refer to Figure 4 on page 20. The initial negative results of Curve
4 show that the initial sample temperature was below the specified range
of 20 ±1 ºC. A sample supersaturated with oxygen will also show this
type of curve. Refer to the Sample temperature and Supersaturation
sections in the expanded version of this manual for more information.
Bottle leak
Refer to Figure 4 on page 20. Curve 5 shows a bottle leak. A bottle leak
makes the system unresponsive. If such a condition occurs, examine the
seal cup and bottle cap for contamination or damage.
Replacement parts and accessories
Replacement parts
Description Quantity Item no.
BODTrak ™ II instrument, 115/230 VAC 1 2952400
Bottle, BODTrak II, amber 6 714421
Power cord, 18/3 SVT 7.5 ft, 10A,125 VAC
for North American 115 VAC use
1 2959200
Power Cord, 8 ft, with continental
European plug for 230 VAC use
1 2959100
Power supply 1 2952500
Computer cable for data transfer to PC 1 2959300
Seal cup 1 2959500
Spatula scoop 1 1225700
Stir bar, magnetic, BODTrak II 1 2959400
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