For BOD5 test
1) Why water samples needed dilution?
2)How to check the test accuracy?
3)Under what conditions, the water sample needs "seed"?
anyone can help?please.
Certainly! I can help answer your questions about the BOD5 test.
1) Why are water samples needed dilution?
Water samples in the BOD5 (Biochemical Oxygen Demand) test are often diluted to ensure that the concentration of organic material is within the range that can be accurately measured. If the initial concentration of organic material is too high, it can exceed the capacity of the dissolved oxygen (DO) meter or the incubation bottles to accurately measure the oxygen demand. Diluting the sample helps bring the organic material within a measurable range.
To dilute a water sample for the BOD5 test, you can follow these steps:
a) Measure an appropriate volume, depending on the expected organic content and the dilution factor required.
b) Add this measured volume of water sample to a clean and sterile container.
c) Dilute the sample by adding the required volume of distilled water.
d) Mix the contents thoroughly, either by shaking the container or using a magnetic stirrer.
2) How to check the test accuracy?
To check the accuracy of the BOD5 test, you can perform a quality control procedure known as a "seed control." A seed control involves adding a known amount of a biologically active and stable seed source into a separate BOD5 test bottle, in addition to the water sample. This seed source typically consists of activated sludge or a seed culture.
By using a seed control, you can compare the oxygen uptake of the seed bottle to the oxygen uptake of the sample bottle. Both bottles should be incubated at the same conditions (e.g., temperature) and tested for oxygen uptake after a specific time period. If the seed control produces the expected oxygen uptake, it verifies that the test conditions (such as temperature, pH, and nutrient availability) are adequate, and the results obtained from the sample bottle are accurate.
3) Under what conditions does the water sample need a "seed"?
In some cases, water samples may require the addition of a seed source. The need for a seed arises when the water sample itself lacks a sufficient number and variety of microorganisms that are capable of breaking down the organic material present. This is often the case when testing highly treated effluent samples or samples from sources with very low organic content.
To provide the necessary microbial activity for the BOD5 test in such cases, a seed source, such as activated sludge or a seed culture containing microorganisms, can be added to the water sample. The seed source introduces a microbial population that can consume the organic material and produce measurable changes in dissolved oxygen levels during the incubation period.
It's important to note that the use of a seed source should be justified, and the quantity and characteristics of the seed should be documented to ensure test accuracy and reproducibility.
Remember, when performing BOD5 tests, it is crucial to follow the specific protocols and guidelines provided by the standard methods or regulatory agencies to obtain reliable and accurate results.