how do dissolved oxygen meters work

How do Dissolved Oxygen Meters Work?

Dissolved oxygen is an essential factor in aquatic life as well as in many industrial processes that require water quality control. Therefore, dissolved oxygen monitoring is a crucial task in different fields. A dissolved oxygen meter is a device that measures oxygen molecules' concentration in water, in parts per million (ppm), or milligrams per liter (mg/L). In this article, we will discuss how dissolved oxygen meters work, their types, and their uses.

What is Dissolved Oxygen, and Why is it Essential?

Dissolved oxygen (DO) is the amount of molecular oxygen that dissolves in water. The oxygen molecules move from the atmosphere or photosynthesis by aquatic plants to the water. DO is measured in ppm or mg/L. DO is essential in aquatic life as it is the primary source of oxygen for fish, plants, and other marine organisms.

What are Dissolved Oxygen Meters, and How do they Work?

A dissolved oxygen meter is a device that measures dissolved oxygen in water. There are two main types of dissolved oxygen meters, Optical (also called luminescence-based) and electrochemical. Optical meters measure the oxygen's effect on the fluorescence of the sensor dye; electrochemical meters measure the oxygen's effect on a polarographic cathode. Optical meters are becoming more popular due to their precision and simplicity, particularly in low-oxygen areas.

Optical Dissolved Oxygen Meters

Optical dissolved oxygen meters measure the amount of oxygen molecules in water by monitoring the oxygen molecules' excitement state. The device includes an optical sensor made up of an oxygen-sensitive dye that fluoresces when excited. When oxygen molecules enter the sensor chamber, they quench the dye's fluorescence in proportion to the dissolved-oxygen concentration. The quenched fluorescence is measured and correlated to DO concentration.

The optical DO meter has a specific working range of about 0-20 ppm, with an accuracy of ± 0.2 ppm or ± 2% (whichever is greater). Since the optical DO sensors do not consume oxygen during the testing, they are suitable for low-oxygen concentrations and sensitive samples.

Electrochemical Dissolved Oxygen Meters

Electrochemical dissolved oxygen meters measure the oxygen concentration by detecting the absorption of electrons at a polarographic cathode. The cathode is made of a noble metal, typically gold or platinum, that passively absorbs oxygen molecules. A steady flow of oxygen-free water shields the cathode from dissolved oxygen in the water. The cathode produces an electrical potential that varies proportionally to the number of oxygen atoms absorbed.

The polarographic oxygen sensor is suitable for measuring dissolved oxygen concentrations in the range of 0-20 ppm. The accuracy is ± 1.5%. One drawback is that the sensor consumes oxygen during the test, leading to inaccuracies and limitations in measuring low-oxygen concentrations.

Why are Dissolved Oxygen Meters Essential?

Dissolved oxygen meters are essential in different applications that require monitoring water quality. Some applications include:

Aquaculture: The dissolved oxygen level plays a major role in the health and growth of aquatic organisms. An adequate oxygen supply is critical for fish and shellfish to thrive.

Wastewater treatment: The dissolved oxygen concentration affects the bacterial population that breaks down wastewater; thus, it is vital to maintain the optimal temperature in aerobic treatment systems.

Environmental monitoring: Dissolved oxygen monitoring is required for monitoring pollution control and environmental impact assessments; monitoring DO levels help understand the health of an ecosystem and its biological activities.

Conclusion

Dissolved oxygen meters are essential tools in monitoring water quality. The availability of two types of sensors allows users to choose which option will best suit their needs. Optical DO meters provide precision in low-oxygen concentrations, while polarographic sensors offer stability and accuracy in the middle concentration range. Whether you are a scientist, environmentalist, or aquaculturist, dissolved oxygen meters will give you insight into the quality of the water you depend on.