BOD ANALYSISSCHEMATIC DIAGRAM

Janine V. SameloBSChem4Cental Luzon State University

samples Pre-treatment

Satisfy requirements?

adjustmentsadjustments

Proceed to the analysis

yes

Check Laboratory DO to determine the % dilution needed for each sample

ACheck pH B

Check if chlorinated

C

Asamples

Check Laboratory DO to determine the % dilution needed for each sample

Shake at least 20 times

Fill BOD bottles with sample up to the neck

Add 1 ml manganese solution 1 mL alkali potassium iodide azide

Discard 100 mL

Add starch and titrate

Remarks: the higher DO, make more dilutions

vv

Add 1 mL sulfuric acidshake

samplesCheck the pH

Add 1 N NaOH until pH becomes 7.0 or near

Add 1 N H2SO4 until pH becomes 7.0 or near

6.5-7.2?

No change in color

no

yes

Proceed to the analysis

B

Transfer at least 50 mL sample in a small beaker Check pH at 20 C

< 6.5

> 7.2

7.0?

no

yes

Note the volume needed to neutralize the aliquot and using ratio, compute the volume needed for the whole sample

samples

Check if chlorinated

Pipet out 100 mL sample

+ 10 mL 1-> 50 H2SO410 mL KI and 4 drops starchBlue/black

colorchlorinated

not chlorinated

Titrate until the blue color disappears

Note the volume needed to neutralize the 100 mL aliquot and using ratio, compute the volume needed for the whole sample

Neutralized?

No change in color

no

yes

Proceed to the analysis

C

ANALYSIS PROPER

Add nutrientsPrepare dilution water

Aerate for 30 minutes using vacuum air pump

Prepare 2 sets of BOD bottles, usually 3 for each sample (depending upon the number of dilution). Include some for blank ,seed correction and Quality control. One is for the initial measure of Do and the other for the final reading of DO

Fill the ¾ of the bottles with the dilution water

Add volume of sample in each dilution , 3 mL seed and dilute to the mark. Stopper the bottles

Add 1 ml manganese solution 1 mL alkali potassium iodide azide

Discard 100 mL of the liquid Shake at least 20

times

Add 1 mL sulfuric acidshake

Add starch and titrate with sodium thiosulfate

Incubate the 2nd set of BOD Bottles covered with stopper and aluminum foil at 20 C

Calculations* *via worksheet program of computer

The endpoint is marked with color change from blue to clear