Dissolved oxygen value in water, how much dissolved oxygen is generally in water

When the speed of oxygen into the water is equal to the speed of oxygen in the water, that is, an equilibrium is reached, under certain conditions, when the oxygen dissolves in the water to reach equilibrium, the content of dissolved oxygen in a certain volume of water is called solubility, and the solubility of oxygen in water is affected by the water temperature, the salt content in the water, and the partial pressure of oxygen.

Oxygen in water is a gas dissolved in water, and its solubility is inversely proportional to the temperature of the air. That is, the higher the temperature, the lower the solubility of oxygen; The lower the temperature, the higher the solubility of oxygen.

For example, when the water temperature is 20, 100 volumes of water can dissolve 3 volumes of oxygen, which is equivalent to milligrams of oxygen per liter of water; At 0, 100 volumes of water can dissolve 5 volumes of oxygen, which is equivalent to milligrams of oxygen per liter of water.

The relationship between the amount of dissolved oxygen and water.

The amount of dissolved oxygen in water is closely related to many factors in water. For example, the deeper the water, the lower the oxygen content. This is because the oxygen in the water penetrates from the atmosphere to the water, and the process of infiltration is naturally from the surface of the water to the deep layer of the water. The size of the surface area of water is also related to the amount of dissolved oxygen in the water, and the area of water is large, and the area in contact with air is naturally large, and the amount of dissolved oxygen is also large.

The dissolved oxygen standard value is the minimum amount of oxygen in the water, which under ideal conditions is typically 5 milligrams of liters (mg L). But in fact, the standard value of dissolved oxygen in various water bodies will vary according to different factors such as temperature, water depth, water flow, pollution degree, etc.

Dissolved oxygen. The molecular oxygen in the air dissolved in water is called dissolved oxygen, and the content of dissolved oxygen in water is closely related to the partial pressure of oxygen in the air and the temperature of the water. Under natural conditions, the oxygen content in the air does not change much, so the water temperature is the main factor, and the lower the water temperature, the higher the dissolved oxygen content in the water.

The molecular oxygen dissolved in water is called dissolved oxygen and is usually denoted as do, expressed in milligrams of oxygen per liter of water. The amount of dissolved oxygen in the water is an indicator of the self-purification ability of the water body.

Dissolved oxygen is closely related to the partial pressure, atmospheric pressure, water temperature and water quality of oxygen in the air, and at kPa, the dissolved oxygen in pure water is about 9mg L. Some organic compounds are biodegraded by aerophilic bacteria, which consumes dissolved oxygen in the water. If the organic matter is calculated as carbon, according to C+O2=CO2, it can be seen that 32g of oxygen is consumed for every 12g of carbon.

When the dissolved oxygen level in the water drops to 5 mg l, some fish have difficulty breathing.

There are usually two dissolved oxygens: one is when the dissolved oxygen in the spring water is not saturated, the oxygen in the atmosphere infiltrates into the water body; The other** is the oxygen released by plants in the water through photosynthesis. As a result, the dissolved oxygen in the water is constantly replenished by the dissolution of oxygen into the air and the photosynthesis of green aquatic plants.

However, when the water body is polluted by organic matter, the oxygen consumption is serious, and the dissolved oxygen is not replenished in time, the anaerobic bacteria in the water body will multiply quickly, and the organic matter will make the water body black and smelly due to corruption.

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 initial state, indicating that the water body has a strong self-purification ability, or that the water body is not seriously polluted. Otherwise, it means that the water body is seriously polluted, the self-cleaning ability is weak, and even the self-purification ability is lost.

The amount of oxygen in water decreases as the temperature increases. Specifically, the higher the temperature, the lower the oxygen content in the water, and the lower the temperature, the higher the oxygen content in the water. For example:

20 liters of water, 100 liters can dissolve 3 liters of oxygen, when the temperature drops to zero, 100 liters of water can dissolve 5 liters of oxygen.

The higher the temperature of the water, the faster the metabolism and respiration rate of fish and aquatic organisms, the more oxygen content is required than usual, and the oxygen content in the water will naturally decrease. If there is less oxygen in the water, the activity of the fish will be weakened, and the fish will directly surface to breathe the oxygen in the atmosphere in order to cope with the low amount of oxygen, which is often called "floating head".

The amount of dissolved oxygen is related to the depth of the water. Because oxygen is infiltrated from the atmosphere through the surface of the water, the slower the penetration rate is, and the internal pressure of the water is not lower than the atmospheric pressure, so the oxygen content that penetrates into the deep layer is very small, which is why the principle that the water is too deep when we raise fish is not beneficial, and it is better to have a water depth of 2 or 3 meters, because the oxygen content in the water at this depth is very high.

The amount of oxygen in the water is related to the area of the water. The larger the surface area of the water, the higher the oxygen content, and the smaller the surface area of the water, the lower the oxygen content. Therefore, under the same conditions, the probability of fish in a small water surface "turning over (pan) pond" is much greater, for example, a large water surface like a lake will not have a "flipping (pan) pond".

Fluctuations in the water surface cause changes in the oxygen content of the water. For example, when the wind blows, the waves on the surface of the water are in contact with the air, and the undulating wave area is larger than the surface area of the normal still water. Therefore, when the wind blows, the oxygen content in the water is higher than usual.

Therefore, people say that "the wind blows the water, and the water moves the fish" refers to the situation at this time.

In fact, the aerator dissolves the air (oxygen) into the water according to the principle that the fluidity of the water and the contact with the air will increase the oxygen content in the water"Waves"and then absorbed into the water body.

The content of dissolved oxygen in the water is closely related to the partial pressure of oxygen in the air and the temperature of the water, if the oxygen content in the water is too low, it will lead to hypoxia, and even the role of high pressure is very large, hyperbaric oxygen can be used for various toxic diseases, sudden deafness, cerebrovascular diseases, traumatic brain injury, anaerobic infection, post-transplantation, as well as poor healing of fractures, malignant tumors and various nerve damage, etc., hyperbaric oxygen can be used to promote the recovery of function. O2ark hyperbaric oxygen chamber recommends that you try it Crushing presence.

The saturation of dissolved oxygen in water is not a fixed value.

At standard atmospheric pressure, it only varies with the water temperature.

The general formula for calculating dissolved oxygen (DO) is:

Considering that pure water is used for dissolved oxygen, the empirical formula for calculating its dissolved amount DO (unit: mg L) is as follows.

Among them, DO is the amount of oxygen dissolved in water, and the unit is mg L

t is the temperature in

P(O2) is the partial pressure of oxygen, the unit is Pa, in a standard atmospheric pressure air, the oxygen content is 21%, take P(O2) = 21270 Pa

The above formula is obtained according to the thermodynamic fitting of the experimental data, which can meet the application requirements in the appropriate range of the freezing point higher than the freezing point of water and lower than the boiling point of water, and the error is about 5%.

The amount of oxygen in water can vary depending on the environment and conditions, so it is not possible to give a fixed value. However, in the natural environment, the concentration of dissolved oxygen in water is usually low, especially in freshwater systems. In general, the concentration of dissolved oxygen in water is affected by the following factors:

Temperature, pressure, salinity and water agitation and gas exchange. For example, the lower the water temperature, the higher the concentration of dissolved oxygen; When water bodies are polluted or eutrophicated, dissolved oxygen concentrations may decrease.

In general, the concentration of dissolved oxygen in water is usually between a few milligrams of liters (milligrams of liters) to a dozen milligrams of liters. This range can provide the level of oxygen suitable for aquatic life to survive and breathe. It should be noted that the concentration of dissolved oxygen in water may have different requirements for different aquatic organisms and water environments.

Some special aquatic organisms may require higher oxygen levels, while certain polluted or eutrophicated water bodies may cause lower dissolved oxygen concentrations, adversely affecting aquatic life.