Wastewater Treatment Operator Certification Practice Test

Which method is commonly used to measure the concentration of dissolved oxygen in water?

1. Colorimetric analysis

2. Thymol blue test

3. Winkler titration method

4. Fluorescent microscopy

The correct answer is: Winkler titration method

The Winkler titration method is the standard technique for measuring dissolved oxygen concentrations in water. This method involves a series of chemical reactions that result in the formation of a colored compound, which can then be quantified through titration. The process begins with the addition of manganous sulfate and alkali-iodide-azide reagent to a water sample, where dissolved oxygen reacts with these reagents to form a precipitate. After acidifying the sample, the iodine released can be titrated with a sodium thiosulfate solution. The amount of titrant used is directly proportional to the concentration of dissolved oxygen in the sample. This method is highly regarded for its accuracy and has been a standard in water quality analysis for many years. Its ability to determine low levels of oxygen makes it particularly valuable in assessing the health and quality of aquatic environments. The other methods mentioned, while useful in different contexts, do not serve the same purpose for measuring dissolved oxygen concentration directly.