Introduction

BOD (Biochemical Oxygen Demand) is an analytical procedure for determining the amount of dissolved oxygen consumed by aerobic biological microorganisms in water. The analysis occurs in a given water sample at a certain temperature over a specific period. It is most commonly expressed in milligrams of oxygen consumed per liter of sample at the constant temperature of 20 °C during 5 days of incubation (BOD5) or monitoring the complete oxidation value after a maximum period of 30 days (BODultimate). BOD determination is widely used as an indication of the organic quality of water and the degree of organic pollution of water.

BOD Test using Control Test Tablets

In order to check the complete RESPIROMETRIC Sensor System, it is possible to use the Control Test Tablets (Code A00000136), performing an oxygen demand experiment analogous to the BOD method. Introducing a tablet, a certain amount of oxygen in the test is chemically absorbed. Thus, inside the bottles a reproducible negative pressure increases which can be used for a system check. Thanks to the software RespiroSoftTM it’s possible to read the test value after 24-48 hours and this value should remain constant for 5 days. In this way, the whole BOD System can be tested, including the stirring system, the incubator, the correct sealing and calibration of the complete pressure measurement system sensor.

Control Test Tablets

Expected value: 293 ± 30 mg/l

Analysis Procedure

1. Set the temperature of the refrigerated thermostat at 20.0 ± 0.5 °C;

2. Verify the cleaning of bottles and stirring rods; 

3. Pour 157 ml of distilled water measured with a graduated cylinder in each BOD bottle and add the stirring rod;

4. Place the 6 bottles in the stirring equipment “RESPIROMETRIC Sensor System 6” and introduce it into the refrigerated thermostat;  

5. Connect the power cable of the equipment to the internal socket

6. The equipment’s thermal equilibrium at 20.0 °C is normally reached in 30-40 minutes;

7. In the software RespiroSoftTM set the following parameters:

Sample name: Tablet

Volume (ml): 157

Type: Standard 2

Sensor N°: from 1 to 6

Scale (mg/l): 600

Duration analysis (d): 5

Sampling time (h): 8 

8. Connect the wireless receiver to the PC and from the software select [Menu], [Service], [Connect receiver].

9. After pre-tempering, without taking the bottles out of the refrigerated thermostat, put one tablet inside each bottle: open tablet strip by tearing the foil sideways in that way, that one could be released completely and directly into a bottle without touching it;

10.Fit the empty alkali holder into the bottleneck without introducing CO2 absorber (different from usual BOD analysis), to prevent deviation from the check value;

11.Screw RESPIROMETRIC Sensor tightly on each bottle;

12.Press two times the key [START] on each RESPIROMETRIC Sensor to start the test.

Results with BOD Control Test Tablets