Application of activated carbon in water treatment

Activated carbon is a kind of microcrystalline carbon material with black appearance, developed internal pore structure, large surface area and strong adsorption capacity. It is a commonly used adsorbent, catalyst or catalyst carrier, widely used in almost all sectors of the national economy and people's daily life.

1 activated carbon

1.1 classification of activated carbon

Due to different sources of raw materials, manufacturing methods, appearance shapes and application occasions, the main varieties are:

1.1.1 according to the source of raw materials, it can be divided into wooden activated carbon (such as coconut shell activated carbon, apricot shell activated carbon, wooden powder carbon, etc.), mineral raw material activated carbon (various kinds of coal and oil and the activated carbon made of processing products as raw materials), and other raw materials activated carbon (such as waste rubber, waste plastic, etc.).

1.1.2 according to the manufacturing method, it can be divided into chemical activated carbon (chemical carbon) and physical activated carbon.

1.1.3 it is divided into powder activated carbon and granular activated carbon according to the appearance and shape.

1.1.4 in addition to the two categories of powdered activated carbon and granular activated carbon, other shapes of activated carbon include activated carbon fiber, activated carbon fiber blanket, activated carbon cloth, honeycomb activated carbon, activated carbon plate, etc. There are many kinds of activated carbon used in production. Generally made into powder or granule. The powdered activated carbon has strong adsorption capacity, easy preparation and low price, but it is difficult to regenerate and cannot be reused. Granular activated carbon is more expensive, but it can be reused after regeneration, and the working conditions are better when it is used, and the operation and management are convenient. Therefore, granular activated carbon is widely used in water treatment.

1.2 adsorption of activated carbon and factors affecting adsorption

1.2.1 activated carbon adsorption refers to the adsorption of one or more substances in water by the solid surface of activated carbon, so as to achieve the purpose of purifying water quality.

1.2.2 factors affecting the adsorption of activated carbon

Adsorption capacity and adsorption speed are the main indicators of adsorption process. Adsorption capacity is measured by adsorption capacity. The adsorption speed refers to the mass of adsorbed substance per unit weight of adsorbent in unit time. In water treatment, the adsorption speed determines the contact time between wastewater and adsorbent. The adsorption capacity of activated carbon is related to its pore size and structure. Generally speaking, the smaller the particles are, the faster the pore diffusion speed is, and the stronger the adsorption capacity of the activated carbon is.

The pH value and temperature of sewage also have influence on the adsorption of activated carbon. In general, the adsorption capacity of activated carbon is higher in acidic condition than in alkaline condition. The adsorption reaction is usually exothermic, so the low temperature is favorable for the adsorption reaction.

Of course, the adsorption capacity of activated carbon is related to the concentration of sewage. At a certain temperature, the adsorption capacity of activated carbon increases with the increase of equilibrium concentration of adsorbed substances. Using powdered activated carbon to remove organic matter, color and odor in water has achieved successful experience and better removal effect.

Study on water purification efficiency of powdered activated carbon

Adsorption of solute molecules in water by powdered activated carbon is a complex process, which is the result of several forces, including ion attraction, van der Waals force, chemical heterozygosity and force. According to the double rate diffusion theory of adsorption, adsorption is a double rate process consisting of two stages of rapid diffusion and slow diffusion. The rapid diffusion is completed in a few hours, and the adsorption capacity of 60-80% activated carbon is developed. The factors that affect the adsorption of PAC involve the polarity, molecular weight and spatial structure of solute molecules, which depends on the characteristics of water quality. Activated carbon has selective adsorption for different substance molecules.

2.1 selection of dosing process

Foreign experts have analyzed the application of powdered activated carbon, and thought that the adsorption and removal of synthetic chemicals by powdered activated carbon mainly depends on the type of the compound. When selecting the dosing point, the mixing degree and treatment contact time must be considered to minimize the interference of water treatment agent on adsorption. When selecting the process of adding powdered activated carbon, the main considerations are as follows:

2.1.1 sufficient mixing conditions shall be provided at the dosing point so that the powdered activated carbon can quickly mix with the treated water in good contact.

2.1.2 try to extend the contact adsorption time between powdered activated carbon and water, make full use of the adsorption capacity of powdered activated carbon, and improve

Adsorption rate.

2.1.3 powder activated carbon with small particle size shall be selected as far as possible to make the adsorption area of activated carbon with the same weight relatively large; wooden activated carbon with developed mesopores shall be selected to improve the adsorption efficiency of activated carbon on organic matters.

2.1.4 minimize the chemical interference during water treatment, such as chlorine, potassium permanganate, coagulant, etc.

2.1.5 dry or wet dosing shall be selected according to the amount of dosing and site conditions.

2.1.6 determine the dosage according to the water pollution status. The addition of powdered activated carbon from 5-30mg / L blocked the light absorption of algae. At the same time, it had a significant coagulation effect in the water source with low turbidity, which was helpful to remove algae in the coagulation sedimentation.

2.2 add powdered activated carbon to improve the effluent quality

2.2.1 adding powdered activated carbon has obvious effect on removing chromaticity. It has been reported that the removal of chromaticity can reach 70%. The low chromaticity indicates that the removal efficiency of organic matter is high, and the removal effect of iron and manganese is good. However, the effect of removing chromaticity is not directly proportional to the amount of activated carbon added. Its complex mechanism remains to be further studied.

2.2.2 adding powdered activated carbon can remove smell