What are the two processes involved in the adsorption of organic pollutants?

It includes adsorption processes such as physical adsorption, electrostatic adsorption and ion exchange adsorption.

Physical adsorption. Physical adsorption is the force of attraction between the adsorbed fluid molecules and the molecules on the surface of the solid, the so-called van der Waals force. Therefore, physical adsorption, also known as van der Waals adsorption, is a reversible process.

When the gravitational force between the molecules on the surface of the solid and the molecules of the gas or liquid is greater than the gravitational force between the molecules inside the gas or liquid, the molecules of the gas or liquid are adsorbed on the surface of the solid. From the point of view of molecular motion, these molecules adsorbed on the surface of the solid will also detach from the surface of the solid and enter the gas (or liquid) due to the molecular movement, without any chemical changes themselves. As the temperature increases, the kinetic energy of gas (or liquid) molecules increases, and the molecules are less likely to remain on the surface of the body, and more and more escape into the gas (or liquid), that is, the so-called "desorption".

This reversible phenomenon of adsorption-desorption exists in physical adsorption. This phenomenon is used in industry to change the operating conditions to desorb the adsorbed substance, so as to achieve the purpose of regenerating the adsorbent and separating the adsorbed substance. The characteristic of physical adsorption is that the adsorbed substance does not undergo any chemical reaction, the adsorption process is carried out very quickly, and the equilibrium between the phases involved in the adsorption can be reached instantaneously.

Electrostatic adsorption. Electrostatic adsorption is the principle that objects have different electrical properties, and opposites attract.

Ion exchange adsorption.

Ion exchange adsorption selects different pseudotiger adsorbents according to different requirements.

1. Operating conditions, temperature and pressure have an impact on adsorption, an appropriate increase in temperature is conducive to chemical adsorption, low temperature is conducive to physical adsorption, and the influence of temperature on adsorption before gas phase width is greater than that on liquid adsorption. For gas adsorption, an increase in pressure is beneficial for adsorption, and a decrease in pressure is conducive to desorption.

2. The properties of the adsorbent, the properties of the adsorbent such as porosity, pore size, particle size, etc. affect the specific surface area.

Thus affecting the adsorption effect.

3. The carrying properties and concentration of adsorbents, for gas-phase adsorption, the critical diameter of adsorbents, and the relative molecular weight.

Boiling point, saturation, etc. affect the amount of adsorption, for liquid phase adsorption, molecular polarity of adsorbate, relative molecular mass, solubility in solvents.

and so on.

4. The activity of the adsorbent, the activity of the adsorbent is a sign of the adsorbent capacity, often based on the adsorption mass adsorbed on the adsorbent and the percentage of all adsorption doses.

The physical meaning is the adsorption mass that can be adsorbed per unit of adsorbent.

5. Contact time, during the adsorption operation, it should be ensured that the adsorbate and the adsorbent have a certain contact time, so that the adsorption is close to equilibrium, and the adsorption capacity of the adsorbent should be fully utilized.

6. Performance of the adsorber.

Chemisorption is characterized by the fact that only monolayer adsorption occurs; Heat of adsorption and heat of chemical reaction.

Fairly; selective; Most of them are irreversible adsorption; The adsorption layer can remain stable at higher temperatures, etc. To determine whether an adsorption is chemisorption, it is mainly based on the heat of adsorption and irreversibility.

Chemical adsorption concept.

Chemical adsorption is the transfer, exchange or sharing of electrons between adsorbate molecules and solid surface atoms or molecules to form adsorption chemical bonds.

adsorption. Due to the existence of an inhomogeneous force field on the surface of the solid, the atoms on the surface often have residual bonding ability, and when the gas molecules collide on the solid surface, electrons will be exchanged, transferred or shared with the surface atoms to form the adsorption of adsorption chemical bonds.

Characteristics of chemisorption.

1. Be selective.

2. The heat of adsorption is approximately equal to the heat of reaction.

3. The force involved in adsorption is comparable to the chemical bonding force, which is better than the van der Waals force.

Much stronger. 4. It is irreversible to temperature and pressure, and in addition, chemical adsorption often requires activation energy.

5. Adsorption is monolayer, so it can be described by Langmuir isotherm and sometimes Freudlich formula.

The migration and transformation of organic pollutants in water bodies is mainly determined by their own physical and chemical properties and water environment properties, in which the interaction with dissolved organic matter plays an important role, and organic pollutants are generally migrated and transformed through adsorption, volatilization, hydrolysis, photolysis, bioaccumulation and biodegradation.

Prokaryotic microorganisms and eukaryotic microorganisms need oxygen to participate in the microbial degradation of polycyclic aromatic hydrocarbons to produce oxidase, which adds oxygen atoms to the C-C bond to form a C-O bond, and then breaks the C-C bond and reduces the number of benzene rings through hydrogenation and dehydration.

The adsorption of inorganic pollutants by soil mainly has the following mechanisms:

1.Ion exchange: Ion exchange in soil is an important adsorption mechanism.

Many inorganic contaminants, such as heavy metal ions, can be dispersed and exchanged with ions on the surface of soil particles. This adsorption mechanism involves positive exchange and negative exchange, where positive exchange refers to the process of ion adsorption to the soil surface, and negative exchange refers to the exchange of dissolved ions in the soil (such as sodium and potassium) with the surface of soil particles.

2.Surface complexation: The surface of soil particles has many active functional groups such as potential and functional hydroxyl groups, which can form complexes with pollutants such as heavy metals. Surface complexation occurs through the interaction of hydrogen bonds, coordination bonds, etc.

3.Precipitation and co-precipitation: Many inorganic contaminants can form precipitation in the soil or co-precipitate with existing precipitation. This adsorption mechanism can be formed by the reaction of dissolved contaminants with some dissolved ions (e.g., iron, aluminum) in the soil.

4.Adsorption:

Physical adsorption: Physical adsorption is mainly achieved by attraction and van der Waals forces, which is a temporary interaction.

Chemical adsorption: Some inorganic contaminants (such as heavy metal ions) can be adsorbed by chemical reactions with the surface of soil particles.

These adsorption mechanisms often occur at the same time and can affect each other. The adsorption mechanism and intensity of different inorganic pollutants are different from soil, and are also affected by soil pH, temperature, organic matter content and other residual factors. Understanding the adsorption mechanism of soil to inorganic pollutants is of great significance for environmental pollution control and soil remediation.

1. The adsorbate is transferred from the fluid body to the outer surface of the solid adsorbent in the form of convective diffusion, and this process is called external diffusion.

2. The adsorbate enters the micropores of the adsorbent from the outer surface of the adsorbent, and then diffuses to the inner surface of the solid infiltrate, which is called internal diffusion.

3. The adsorbate chain is adsorbed by the adsorbent on the inner surface of the adsorbent solid, which is called the surface adsorption process.

The equilibrium between the phases involved in adsorption can be achieved instantaneously and after desorption. The desorption of this type of adsorption is also not easy to carry out, and the kinetic energy of the gas (or liquid) molecules increases, and sometimes both adsorptions occur simultaneously as the temperature rises to a certain extent. Therefore.

The heat of adsorption emitted by chemical adsorption is much larger than that emitted by physical adsorption, and when a thin layer of liquid or gas adheres to a solid substance, it begins to undergo chemical changes and turns into chemical adsorption, which itself does not undergo any chemical changes. Physical adsorption is the force of attraction between the adsorbed fluid molecules and the molecules on the surface of the solid.

Chemical adsorption is often irreversible. From the point of view of molecular motion, the adsorption equilibrium also takes a considerable time to achieve, so it is also called "activated adsorption", the desorption of substances often undergoes chemical changes are no longer the original properties, and will also be separated from the solid surface and enter the gas (or liquid), that is, the so-called "desorption", adsorption can be divided into physical adsorption and chemical adsorption. The heat of adsorption released by physical adsorption is usually similar to the heat of liquefaction of gas, so the process is irreversible.

This phenomenon is exploited in industry, and it is a reversible process. This type of adsorption requires a certain amount of activation energy, and often requires a very high temperature to expel the adsorbed molecules, and it carries out physical adsorption on the adsorbent. With the increase of temperature, and the solid does not react chemically with the adhered substance, at low temperature, physical adsorption, also known as van der Waals adsorption, to achieve the regeneration of adsorbents.

The magnitude of this chemical bond affinity can vary greatly. The characteristic of physical adsorption is that the adsorbed substance does not undergo any chemical reaction, reaching the order of magnitude of the heat of chemical reaction. This reversible phenomenon of adsorption-desorption exists in physical adsorption.

Depending on the forces on the surface of the adsorbent and the adsorbate, more and more of the gas (or liquid) escapes into the same substance, the so-called van der Waals forcesThe rate of chemisorption is mostly slower, but it greatly exceeds the van der Waals force of physical adsorption; Chemical adsorption is the result of the chemical bonding force between the solid surface and the adsorbate, and the adsorption process proceeds extremely quickly. When the gravitational force between the molecules on the surface of the solid and the molecules of the gas or liquid is greater than the gravitational force between the molecules inside the gas or liquid, the molecules adsorbed on the surface of the solid are adsorbed on the surface of the solid due to the movement of the molecules, so that the adsorbed substances are desorbed, and the molecules are not easy to stay on the surface of the body.

It has also been found that increasing the temperature can greatly increase the adsorption rate. Chemical adsorption plays an important role in the catalytic process.

Answer]: The BAB sewage treatment process is the adsorption-biodegration process.