Are there troubleshooting tips for low GGA results when testing BOD?

Document ID

Document ID TE887

Published Date

Published Date 08/20/2019
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Question
Are there troubleshooting tips for low GGA results when testing BOD?
Summary
BOD GGA too low
Answer
The three most common reasons that results for Glucose and Glutamic Acid (GGA) standards are too low are:
  • The GGA is underseeded
  • The seed contains toxic compounds
  • The GGA is incorrectly prepared
Underseeding: GGA checks are used to determine the amount of seed needed for measurements of Biochemical Oxygen Demand (BOD). Though most users try to achieve a seed depletion of 0.6-1.0 mg/L, this is not always correct. Seed amount should be adjusted until 198 mg/L of GGA BOD is achieved.

Toxicity: Seed that contains compounds which are toxic can inhibit microbiological growth, resulting in less oxygen demand. Seed toxicity can be determined by plotting oxygen demand/uptake versus volume of seed used. This relationship should be linear; if it is not, this indicates that a toxic compound could be present. A different source of seed should be used to confirm the toxicity.

Incorrectly prepared GGA: Standard methods calls for a GGA solution that has 150 mg/L of glucose and 150 mg/L of glutamic acid. The BOD Standard Solution, 300 mg/L, pk/16 - 10-mL Voluette® Ampules (Product # 1486510) contain 300 mg/L of glucose and glutamic acid. When using this standard, one should use half of the amount specified in Standard Methods to achieve the 150 mg/L GGA required.

On a related note, one could use this BOD standard in a Chemical Oxygen Demand (COD) test to validate the standard was made properly. If a COD test is run, using this BOD standard, the results should be 613 +/- 25 mg/L COD.
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