Florida Wastewater Practice Test

Which preservation method is commonly used for a wastewater sample intended for CBOD5 testing?

1. Heat to 80° C

2. Cool to 4° C

3. Add chemicals

4. Expose to air

The correct answer is: Cool to 4° C

For a wastewater sample intended for carbonaceous biochemical oxygen demand (CBOD5) testing, cooling the sample to 4° C is the commonly used preservation method. This cooling process slows down the metabolic activity of microorganisms present in the sample, thereby preventing any significant changes in the organic matter content before the analysis takes place. By maintaining a lower temperature, the sample remains stable for a longer period, ensuring that the measurements obtained during the testing accurately reflect the conditions and characteristics of the wastewater at the time of collection. Using heat, adding chemicals, or exposing the sample to air may interfere with the microbial processes that the CBOD5 test is designed to measure. Heating the sample could kill or inhibit microorganisms, leading to inaccurate results, while adding chemicals might alter the chemical composition of the sample. Exposing the sample to air could result in oxidation of organic materials, further complicating the reliability of the test results. Thus, cooling the sample is the most effective and appropriate preservation method in this context.