Analysis of the role of dissolved oxygen sensor

First, in wastewater treatment plants, it helps regulate oxygen levels in the activated sludge tank, which is essential for efficient biological degradation of organic matter. Second, in hydrological monitoring, it measures oxygen content in rivers, lakes, and oceans, serving as an indicator of overall water quality. Third, in water treatment systems, it assists in managing oxygen levels in drinking water, such as for oxygen enrichment or corrosion prevention. Lastly, in aquaculture, it ensures optimal oxygen levels in fish ponds, supporting healthy aquatic ecosystems and growth.

The solubility of oxygen in water is influenced by factors such as temperature, pressure, and the presence of dissolved salts. A typical dissolved oxygen sensor consists of a gold electrode (cathode), a silver electrode (anode), and an electrolyte such as potassium chloride or potassium hydroxide. Oxygen diffuses through a membrane into the electrolyte, creating a measurement circuit between the two electrodes. When a polarization voltage of 0.6 to 0.8 volts is applied, oxygen enters the cell, where it reacts at the cathode, releasing electrons, while the anode accepts them, generating an electric current. This electrochemical reaction can be summarized as follows: at the anode, Ag + Cl⁻ → AgCl + 2e⁻; at the cathode, O₂ + 2H₂O + 4e⁻ → 4OH⁻. According to Faraday’s law, the current produced is directly proportional to the partial pressure of oxygen, and under constant temperature conditions, there is a linear relationship between the current and the dissolved oxygen concentration.

Currently, high-quality dissolved oxygen sensors are not widely available from domestic brands. Among the best options, the KDS-25B from Japan's FIGARO company stands out. This shallow dissolved oxygen sensor is a unique galvanic type designed specifically for water quality control. One of its most notable advantages is its long service life and resistance to interference from carbon dioxide, making it highly reliable in real-world applications.

The KDS-25B uses a special acidic electrolyte, with the cathode made of inert gold and the anode composed of lead. Oxygen passes through a fluororesin membrane to participate in the redox reaction, forming an oxygen-lead storage battery. The internal resistance generates a current, which is then converted into a voltage output. The magnitude of this current is directly proportional to the concentration of dissolved oxygen, more precisely, to the partial pressure of oxygen. The higher the dissolved oxygen level, the more oxygen molecules diffuse through the membrane and contribute to the reaction. As a result, the KDS-25B is considered an ideal sensor for environmental monitoring and water quality testing.