What is dissolved oxygen and what is the significance of measuring dissolved oxygen in water
Dissolved Oxygen (Dissolved Oxygen) refers to the oxygen dissolved in the molecular state of water, that is, O2 in water, represented by DO. Dissolved oxygen is an indispensable condition for the survival of aquatic organisms. One source of dissolved oxygen is when the dissolved oxygen in the water is not saturated, the oxygen in the atmosphere penetrates into the water body; the other source is the oxygen released by the plants in the water through photosynthesis. Dissolved oxygen changes with changes in temperature, air pressure, and salinity. Generally speaking, the higher the temperature, the greater the dissolved salt, and the lower the dissolved oxygen in water; the higher the air pressure, the higher the dissolved oxygen in water.
Dissolved oxygen is closely related to the partial pressure of oxygen in the air, atmospheric pressure, water temperature and water quality. At 20°C and 100kPa, the dissolved oxygen in pure water is about 9mg/L. Some organic compounds biodegrade under the action of aerobic bacteria, consuming dissolved oxygen in water. If the organic matter is calculated by carbon, according to C+O2=CO2, it can be known that every 12g of carbon consumes 32g of oxygen. When the dissolved oxygen value in the water drops to 5 mg/L, some fish have difficulty breathing.
In addition to being consumed by reducing substances such as sulfide, nitrite, and ferrous ions in water, dissolved oxygen is also consumed by the respiration of microorganisms in water and the oxidative decomposition of organic substances in water by aerobic microorganisms. Therefore, dissolved oxygen is the capital of water body and the performance of water body self-purification ability.
The dissolved oxygen value is a basis for studying the self-purification ability of water. The dissolved oxygen in the water is consumed, and it takes a short time to return to the original state, indicating that the water body has a strong self-purification ability, or the water body is not seriously polluted. Otherwise, it means that the water body is seriously polluted, the self-purification ability is weak, or even loses the self-purification ability.
What is the significance of measuring dissolved oxygen in water?
With the rapid development of industry and agriculture in today's world, a large amount of industrial wastewater and farmland drainage are discharged to rivers, lakes and seas. At the same time, about 80% of urban domestic sewage in my country is discharged directly without treatment, and most of the domestic sewage in small towns and vast rural areas In the state of disorderly discharge, the water quality in many places is deteriorating day by day, water pollution and water resource shortage are becoming more and more serious, so it is urgent to monitor and effectively treat sewage in time. Among them, the dissolved oxygen content in water is an important indicator for water quality monitoring.
The dissolved oxygen in natural water is close to the saturation value (9ppm), and the dissolved oxygen content decreases when the algae multiply vigorously. Water bodies polluted by organic matter and reducing substances can reduce dissolved oxygen. For aquaculture, water body dissolved oxygen has a vital impact on the survival of aquatic organisms such as fish. When dissolved oxygen is lower than 4mg/L, it will It will cause fish to suffocate and die. For humans, the dissolved oxygen content in healthy drinking water should not be less than 6mg/L. When the consumption rate of dissolved oxygen (DO) is greater than the rate of oxygen dissolved into the water body, the content of dissolved oxygen can approach 0. At this time, anaerobic bacteria can reproduce and deteriorate the water body, so the size of dissolved oxygen can reflect the water body is affected It is an important indicator of the degree of water pollution and a comprehensive indicator of water quality. Therefore, the measurement of dissolved oxygen content in water is of great significance for environmental monitoring and the development of aquaculture.
There are two methods of measuring dissolved oxygen:
1. Iodometric method: Manganese sulfate and basic potassium iodide are added to the water sample, and the dissolved oxygen in the water will oxidize low-valent manganese to high-valent manganese, forming a brown precipitate of tetravalent manganese hydroxide. After acid addition, the hydroxide precipitate dissolves and reacts with iodide ions to release free iodine. Using starch as indicator, titrate the released iodine with sodium thiosulfate standard solution, and calculate the dissolved oxygen content according to the consumption of the titration solution.
2. Dissolved oxygen meter method: The dissolved oxygen meter consists of two parts: a sensor and a display instrument. The sensing part of the dissolved oxygen analyzer is composed of gold electrode (cathode) and silver electrode (positive) and potassium chloride or potassium hydroxide electrolyte. Oxygen diffuses into the electrolyte through the membrane and the gold electrode and silver The electrodes form the measuring circuit.
product description
Online dissolved oxygen controller is suitable for aquaculture, metallurgy, pharmaceutical, chemical and other industries. The controller mainly performs continuous monitoring of dissolved oxygen/temperature in the solution.
Application field
The instrument is suitable for aquaculture, metallurgy, pharmaceutical, chemical and other industries.
Measuring principle
(1) Calibration and setting setting password protection
(2) Super large dot matrix LCD with backlight
(3) Technical parameters can be set on site with buttons
(4) High stability, high precision; can measure dissolved oxygen, temperature
(5) Anti-interference circuit design, it can be installed and used in strong interference sites, the set parameters and calibration data will not be lost after power off, with manual setting/automatic temperature compensation, process temperature and calibration temperature, when the temperature sensor is damaged by Automatic temperature compensation conversion, switching to manual temperature compensation can verify test data online
(6) Multiple output modes (relay, 4.00...20.00mA. RS485)
(7) Suitable for aquaculture, metallurgy, pharmaceutical, chemical and other industries
