Activated carbon fiber is a new type of adsorption functional material. It is made of lignin, cellulose, phenolic fiber, polypropylene fiber, asphalt fiber, etc. as raw materials, and is made by carbonization and activation. Compared with activated carbon, it has a unique microporous structure, higher external surface and specific surface area, multiple functional groups, and a smaller average pore diameter. It has been applied in wastewater, waste gas treatment, and water purification under specific conditions through physical adsorption and physical and chemical adsorption, but the cost is high, so it is used less. The micropore volume of fibrous activated carbon accounts for about 90% of the total pore volume, and most of its micropore diameters are around 1nm, with no excessive pores or macropores.

A. Adsorption and adsorption forms

The action of gathering solutes on the solid surface is called adsorption. The surface of activated carbon has adsorption. Adsorption can be regarded as a surface phenomenon, so adsorption is closely related to the surface characteristics of activated carbon. Activated carbon has a huge internal surface and pore distribution. The effect of its external surface area and surface oxidation state is relatively small, and the external surface provides many channels that communicate with the internal pores. The main function of surface oxides is to make the hydrophobic carbon skeleton hydrophilic, so that activated carbon has affinity for many polar and non-polar compounds. Activated carbon has surface energy, and its adsorption is caused by the unbalanced force of carbon atoms constituting the surface of the pore wall, which causes surface adsorption.

B. Application of activated carbon adsorption technology in water treatment

1 Overview of activated carbon adsorption technology in water treatment

Practice has proved that activated carbon is an ideal adsorbent for water and wastewater treatment. The research on activated carbon for water and wastewater treatment has a history of ten years. In the past two decades, due to the relatively satisfactory solution to the regeneration problem of activated carbon and the reduction of the manufacturing cost of activated carbon, activated carbon adsorption technology has been gradually promoted and used at home and abroad. At present, the most widely used are tertiary wastewater treatment and water deodorization. In the early 1960s, European and American countries began to use activated carbon adsorption as an effective means of water source purification. In the 1960s, my country used activated carbon for carbon disulfide wastewater treatment. Since the early 1970s, granular activated carbon has developed rapidly in the treatment of industrial wastewater, both in terms of technology and in terms of application scope and treatment scale. In the treatment of oil refining wastewater, explosive wastewater, printing and dyeing wastewater, chemical wastewater, electroplating wastewater, etc., large-scale applications have been formed in production and satisfactory results have been achieved.

2 Application of activated carbon in wastewater treatment

Activated carbon has different forms. At present, granular and powdered forms are still the main forms in water treatment. Powdered carbon is used for intermittent adsorption, that is, powdered carbon is added to the treated water in a certain proportion, mixed evenly, and carbon and water are separated by precipitation or filtration. This method is also called static adsorption. Granular carbon is used for continuous adsorption. The treated water passes through the carbon adsorption bed to purify the water. This method is exactly the same as the fixed bed in form and is also called dynamic adsorption. There are many substances that can be adsorbed by activated carbon, including organic or inorganic, ionic or non-ionic. In addition, the surface of activated carbon can also play a catalytic role, so it can be used in many different occasions.

Activated carbon has a strong adsorption capacity for soluble organic matter in water and is effective in removing most organic pollutants in water, such as phenol and benzene compounds, petroleum and many other synthetic organic matter. Some organic pollutants in water are difficult to remove by biochemical or oxidation methods, but are easily adsorbed by activated carbon.

Because the cost of activated carbon adsorption treatment is higher than other general treatment methods. Therefore, when the concentration of organic matter in water is high, other more economical methods should be used to reduce the content of organic matter to a certain extent before treatment. In wastewater treatment, the activated carbon adsorption process is usually placed after the biochemical blowing, which is called activated carbon tertiary wastewater treatment, to further reduce the content of organic matter in wastewater, remove those pollutants that are not easy to decompose by microorganisms, so that the water treated with activated carbon can meet the requirements of emission standards, or the treated water can be returned to the production process for reuse, so as to achieve the purpose of closed circulation of production water.

The ability of activated carbon to adsorb organic matter is very large. In tertiary wastewater treatment, the COD adsorbed by each gram of activated carbon can reach 40% of its own mass. Adding tertiary wastewater treatment to the wastewater treatment plant can achieve a BOD removal effect of 95%. Activated carbon removes organic matter in water in the form of physical adsorption. The properties of the adsorbed matter do not change before and after adsorption. If an appropriate desorption method can be used, valuable substances in the water can also be recovered. If powdered activated carbon is put into the aeration equipment, the carbon powder and microorganisms form a coagulant, which can make the treatment effect exceed the general secondary biological treatment method, and the effluent water quality is close to the tertiary treatment.

In addition, it can also make the activated carbon sludge dense and solid, reduce the turbidity of the effluent, and increase the hydraulic load of the secondary treatment. Powdered carbon can be added intermittently, and for existing secondary treatment plants, the treatment effect can be improved without increasing the investment in tertiary treatment.

3 Application of powdered activated carbon in water treatment

The application of powdered activated carbon in water treatment has a history of about 70 years. Since the United States first used powdered activated carbon to remove the odor produced by chlorophenol, activated carbon has become one of the effective methods for removing color, smell, taste and organic matter in water treatment. A large number of foreign studies on the adsorption properties of powdered activated carbon have shown that powdered activated carbon has a good adsorption effect on trichlorophenol, organic matter contained in pesticides, trihalomethanes and precursors, and disinfection by-products such as trichloroacetic acid, dichloroacetic acid and dihaloacetonitrile, and the removal effect on color, smell and taste has been recognized.

Powdered activated carbon is widely used in Europe, the United States, Japan and other places. In the early 1980s, the United States used about 250,000 tons of powdered activated carbon in water treatment every year, and there is a trend of increasing year by year. In the late 1960s, my country began to pay attention to the deodorization and taste removal of polluted water sources. Powdered activated carbon has been tried in Shanghai, Harbin, Hefei and Guangzhou.

The main features of powdered activated carbon application are low equipment investment, low price, fast adsorption speed, and strong adaptability to short-term and sudden water pollution. The application of powdered activated carbon adsorption technology in water plants is a very promising technology. However, due to the failure to solve the limitations of the application of this technology, it is still difficult to give full play to the advantages of powdered activated carbon technology, resulting in the inability of the application of this technology to achieve actual results.

The application in water plants must solve two major problems: theoretical basis and application. Theoretically, the main problems that should be solved are as follows:

1. According to the water quality of the water plant's raw water, especially the distribution of the molecular weight of organic matter, determine the type of carbon added to the powdered activated carbon and the effect of activated carbon of different carbon types on the removal of organic matter;

2. According to the actual water quality of the water plant, determine the appropriate and reasonable addition point and addition method to solve the contradiction between the adsorption competition between powdered activated carbon and coagulant and improve the use efficiency of powdered activated carbon.

It is recommended that users consult high-quality manufacturers, purchase high-quality water treatment activated carbon, and obtain technical support to ensure worry-free use.