Replacement Parts And Accessories - HACH LANGE BODTrak II Manual Básico Del Usuario

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High oxygen demand

Refer to

Figure 4

on page 10. Samples that are above range (for

example, a BOD over 350 mg/L when a 160-mL sample is taken) will

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 10. 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

Optional reagents

on page 12.

Excessive time lag

Refer to

Figure 4

on page 10. 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 10. 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 10. 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.