A dissolved oxygen sensor is a sensing device used to measure the amount of oxygen dissolved in water. Continuous measurement of dissolved oxygen concentration in water plays several important roles in the field of water treatment:
1. Measurement and regulation of oxygen in activated sludge tanks of wastewater treatment plants to achieve high efficiency in the biodegradation process.
2. Hydrological monitoring measures the oxygen content in rivers, lakes, and oceans to indicate water quality.
3. Water treatment: Oxygen content measurement, such as detecting the status of drinking water (oxygen abundance/corrosion prevention, etc.).
4. Fishponds: Oxygen content is measured and adjusted to maintain optimal ecological and growth conditions.
The solubility of oxygen in water depends on temperature, pressure, and the amount of salt dissolved in the water. A dissolved oxygen analyzer sensor consists of a gold electrode (cathode), a silver electrode (anode), and a potassium chloride or potassium hydroxide electrolyte. Oxygen diffuses through a membrane into the electrolyte, forming a measurement circuit with the gold and silver electrodes. When a polarization voltage of 0.6–0.8 V is applied to the dissolved oxygen analyzer electrodes, oxygen diffuses through the membrane, the cathode releases electrons, and the anode accepts electrons, generating a current. The entire reaction process is as follows: Anode Ag + Cl → AgCl + 2e-; Cathode O2 + 2H2O + 4e- → 4OH-. According to Faraday's law, the current flowing through the dissolved oxygen analyzer electrodes is directly proportional to the oxygen partial pressure, and at constant temperature, there is a linear relationship between current and oxygen concentration.
Currently, there are no particularly high-quality dissolved oxygen sensors among domestic brands in China. A relatively good one is the KDS-25B dissolved oxygen sensor produced by FIGARO Corporation of Japan. The Yuasa KDS-25B is a unique galvanic cell sensor specifically developed for water quality control. Its most significant feature is its long lifespan and insensitivity to CO2.
The KDS-25B uses a special acidic electrolyte, with an inert gold cathode and lead anode. Oxygen diffuses through a fluoropolymer membrane to participate in the redox reaction, forming an oxygen-lead-acid battery. The internal resistor converts the current generated by the redox reaction into a voltage output. The generated current is directly proportional to the dissolved oxygen concentration, or more precisely, to the oxygen partial pressure (the higher the dissolved oxygen content, the more oxygen molecules participate in the reaction through the fluoropolymer membrane). The KDS-25B is one of the ideal sensors for environmental monitoring and water quality testing.
