Can BOD test of water samples collected be done within 3-4 days to a week if water samples are preserved in deep freeze at temperature -19 degrees Celsius or ice box?
And what are the technical issues or errors or accuracy issues faced if BOD are taken of water samples, kept in deep freeze?
It is possible to carefully preserve samples for BOD both by freezing and storing on ice for a few days. I suggest storing on ice is preferable if you can analyze within a week.
Freezing samples can cause partial loss of volatile compounds (ammonia and acetate) but in practice it sems to be insignificant. After freezing a fraction of bacteria are inactivated so it can be good to use an inoculum from activated sludge to ensure there are enough heterotrophic bacteria.
Some technical issues are that you should ensure that cooling is fast to avoid biological activity eat some BOD before the sample is cooled and likewise then the sample is restored to 20 °C it should be reasonable fast. Make sure the sample is at 20 °C then the analysis as the analysis is sensitive to being started a low temperature.
According to guidelines samples should be analyzed within 48 hrs of collection. Because storing it for more than that could lead to alteration in microbial activity and loss of volatile, semi volatile compounds.
Sample preservation for BOD testing:
- Freezing at -19°C is not recommended: it kills the microorganisms required for the test, alters organic matter, and leads to inaccurate results.
- Storage in a cooler at 4°C is acceptable, but only for a maximum of 6 to 24 hours.
- Beyond 24 hours, BOD results may be underestimated due to biological or chemical degradation of organic compounds.
Recommendation:
- Analyze samples within 6 to 24 hours after collection, without freezing.
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