Standard Solution for BOD Determination

In biochemical oxygen demand (BOD) analysis, a standard solution is a solution with a precisely known oxygen demand value, used primarily for quality control and method validation. Its purpose is to verify the accuracy and reliability of the entire BOD testing procedure.

The most widely recognized BOD standard solution is the glucose-glutamic acid (GGA) solution. It is composed of equal masses of glucose and glutamic acid. According to Standard Methods for the Examination of Water and Wastewater, adding 6 mL of GGA standard to a 300 mL seeded BOD bottle yields a BOD? of 198 ± 30.5 mg/L-19-23. 

This specific formulation is required because glucose alone has a highly variable oxidation rate, while the combination with glutamic acid stabilizes the oxidation process, making it comparable to many municipal wastewaters-23.

For preparation, glucose and glutamic acid are dried at 103 °C for one hour and then dissolved in phosphate buffer solution. Standard solutions are commercially available in single-use ampules or bulk quantities and must be used under strictly controlled conditions, including proper seeding and incubation at 20 ± 1 °C for five days-15.

In practice, GGA standard is employed as a control check. A laboratory running BOD tests must analyze a GGA control weekly (or once per 20 samples) to ensure that its measured BOD? falls within the specified acceptance range; failure to do so indicates a problem with the test procedure, such as poor seed quality or contamination-19. 

Thus, the standard solution serves as an essential quality assurance tool, confirming that the entire analytical system—including reagents, seeding microorganisms, and incubation conditions—is functioning properly.