Xylem OxiTopIS 12-6 - Handbuch (Seite 29)

BOD
5
determination
Sample preparation
Measurement
28 29
BOD
5
determination
Normally municipal wastewater does not contain toxic or impeding substances.
There are enough nutrient salts and suitable microorganisms. Under these
conditions the BOD
5 determination with the OxiTop â measuring system is possible
in the undiluted sample
Required instruments and accessories
OxiTop â measuring system
Inductive stirring system
Incubator thermostatic box (temperature 20°C ± 1K)
Sample bottles brown (nominal volume 510 ml)
Stirring rods
Stirring rod remover
suitable overflow measuring beakers
Rubber quivers
Sodium hydroxide tablets
Selection of sample volume
Estimate the BOD 5 value to be expected for the wastewater sample:
Expected BOD 5 value »»»» 80 % of the COD value
Look for corresponding measuring range in the following chart and gather correct
values for sample volume and factor.
Sample volume (ml) Measuring range (mg/l) Factor
432 0 - 40 1
365 0 - 80 2
250 0 - 200 5
164 0 - 400 10
97 0 - 800 20
43.5 0 - 2000 50
22.7 0 - 4000 100
Sample preparation
See following WTW application reports:
· WTW Application report 895230:
"BOD measurement in household wastewater"
· WTW Application report 895231:
"BOD measurement in organically heavily contaminated wastewater"
···· WTW Application report 895232:
"BOD measurement with presence of impeding or toxic substances"
Measurement
Information: To measure the sample volume, usually overflow measuring
beakers or measuring cylinders are used.
Chose the volume according to the measured value expected.
Too large measuring ranges will lead to inaccurate results. To
estimate the measured value you can reckon with approx. 80%
of the CBS value.
• Sample preparation and filling of the measuring bottles compare following
instruction: DIN 38409 part 52: "Measurement of the oxygen consumption" as
well as WTW applicationsreports see chapter "Sample preparation and
measurement".
• Rinse measuring bottle with sample. Empty thoroughly.
• Exactly measure the required oxygen-saturated (thoroughly homogenized)
quantity of the sample according to information.
• Put the magnetic stirring rod into the bottle.
• Insert a rubber quiver in the neck of the bottle.
• Put 2 sodium hydroxide tablets into the rubber quiver with a tweezers.
(Caution: The tablets must never come into the sample!)
• Screw OxiTop â directly on sample bottle (tightly close).
Start measurement:
Press S and M simutaneously. (2 seconds) untill the display
shows 00.
Display: Stored values are deleted.
• Keep the measuring bottle with the OxiTop put on for 5 days at 20°C (e.g. in an
incubator). After the meas. temperature has been reached (after 1 hour at the
earliest, after 3 hours at the latest; AutoTemp function), the OxiTop
automatically starts the measurement of the oxygen consumption .
• During the 5 days the sample is continuously stirred. The OxiTop automatically
stores one value every 24 hours for 5 days. To have the current value shown
press the M key.
Display current measured value:
Press M until measured value is displayed (1 second).
• Readout of the stored values after the 5 days have passed.