How can BOD5 samples be preserved effectively?

BOD5, or Biochemical Oxygen Demand over a period of five days, is a crucial measurement in wastewater treatment that indicates the amount of organic material in water. The preservation of BOD5 samples is essential to ensure accurate results, as various factors like temperature and exposure to light can alter the organic content before analysis.

Storing samples in a refrigerator above freezing and up to 4 degrees Celsius is an effective method of preservation because cooler temperatures slow down the metabolic processes of microorganisms present in the sample. This helps to minimize changes in the biological activity level, ensuring that the BOD value remains stable until the sample can be analyzed. Keeping it at this controlled temperature mitigates any immediate biological reactions that could occur at warmer temperatures.

The other methods of preservation do not provide the same level of reliability. For example, maintaining samples at room temperature could accelerate microbial activity, leading to a potential increase in BOD values that would misrepresent the actual organic content. Similarly, storing samples in an ice bath at 0 degrees Celsius, while it may slow down metabolic reactions, can also lead to potential freezing or damage to the sample. Depending on the preservative chemical used, it may not be appropriate for all BOD tests, and some chemicals could interfere with the