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The Role Of Activated Carbon In Mineral Water Production Line

22 10 月, 2021

Activated carbon has a large surface energy, a wide range of sources, and a low price. It is a commonly used adsorption material. Based on these advantages, the activated carbon adsorption process has also become the current process for removing water. This article describes the properties of activated carbon as a solid adsorbent, and also introduces the application and prospects of activated carbon in water pollution treatment.
Characteristics of activated carbon: activated carbon is a porous carbon-containing material with a developed microporous structure and a huge specific surface area. It includes many kinds of carbon-based substances with adsorption capacity, which can adsorb many chemical substances on its surface. Activated carbon was first used in the sugar industry, and later widely used to remove certain inorganic substances in sewage.

1. General properties of activated carbon

Activated carbon is dark black in appearance, has good adsorption performance, stable chemical properties, can withstand strong acids and alkalis, can withstand water immersion, high temperature, and has a density lower than water. It is a porous, hydrophobic adsorbent.

2. Mechanism of action of activated carbon

The main reason for the adsorption of activated carbon is that the atomic force field on the solid surface is not saturated and has surface energy, so it can adsorb certain molecules to reduce the surface energy. After the solid adsorbs solute molecules from the solution, the concentration of the solution will decrease, and the adsorbed molecules will concentrate on the solid surface.
During the manufacturing process of activated carbon, its volatiles are removed, voids are formed between the crystal lattices, and many pores of different shapes and sizes are formed. Generally, the pores in the activated carbon particles account for 70% to 80% of the total volume of the particles. These pores have various shapes and a wide range of pore size distribution. The total surface area of ​​the pore wall, that is, the specific surface area, is generally as high as 500-1700 m2/g. This is the main reason why activated carbon has strong adsorption capacity and large adsorption capacity.
The adsorption characteristics of activated carbon are not only related to the pore structure and distribution, but also related to the surface chemistry of activated carbon. Activated carbon itself is non-polar, and its content and charge vary with the composition of raw materials and activation conditions. Low-temperature activated carbon (<500℃) can generate surface acidic oxides, which can release H+ after hydrolysis. Due to the weak polarity of the activated carbon surface, other polar solutes compete for the active position of the activated carbon surface, resulting in a decrease in the amount of non-polar solute adsorption, and the exchange adsorption or complexation reaction of some metal ions in the water increases the effect of activated carbon on metal ions. The adsorption effect.
In short, in the adsorption process, it is the microporous structure that really determines the adsorption capacity. Almost all specific surfaces are made of micropores. Coarse pores and transition pores play the role of coarse and fine adsorption channels respectively, and their existence and distribution affect the adsorption and desorption rate to a considerable extent. In addition, the adsorption properties of activated carbon are also affected by the chemical properties of the activated carbon surface.

3. Application of activated carbon in water treatment

Activated carbon adsorption process is the current process for removing substances in water. Due to the rich source of raw materials and large surface area, it has a good removal rate for color, smell, taste and other substances. Activated carbon is increasingly widely used in water treatment processes. Among them, powder activated carbon is particularly effective in removing low molecular weight DOC produced by algae cell secretions in the water, and can effectively remove microcystins in the water. Adding an activated carbon filter after the classic slow sand filter can remove the water odor. Flavoring substances, such as geosmin and 2-methyl isoborneol (MIB), effectively reduce the odor of the effluent. However, the adsorption effect of activated carbon on the more harmful halogenated hydrocarbons is not very good, and the regeneration problem after activated carbon adsorption has been difficult to be solved satisfactorily. Currently, new adsorption materials such as activated carbon fibers and porous synthetic resins are being developed.
3.1 Application of activated carbon in drinking water treatment
The rapid biological filter with granular activated carbon as the filter material is usually used as a second-stage filtration, through the activity of bacteria growing on the surface of the granular activated carbon, to remove BOM in the water. This process is also called secondary biological activated carbon filtration. There are literature reports on the effectiveness of this process. In order to reduce costs and facilitate promotion in water plants, people put forward the concept of “graded sand” and “biological activated carbon double-layer filter”. The application of biological filter to remove BOM from water has the following advantages:
(1) It reduces the nutrients required for the growth of bacteria in the water supply system, which can effectively control the reproduction of bacteria;
(2) Reduce the amount of substances that react with the disinfectant, thereby reducing the amount of disinfectant required for drinking water treatment and stabilizing the content of the remaining disinfectant in the factory water;
(3) By removing some of the precursors of disinfection by-products, the content of disinfection by-products in the water of the water plant is reduced;
(4) Converting substances into inorganic end products;
(5) The aging and shedding biofilm residue is easier to handle than chemical sedimentation sludge;
(6) The cost of the biological treatment method is lower than that of the activated carbon adsorption method.
3.2 The deodorizing effect of activated carbon in the wastewater treatment process
Activated carbon adsorption column can remove many malodorous substances. Malodorous components such as acetaldehyde and indole are removed by physical adsorption, while H2S and mercaptans are further adsorbed and removed by oxidation reaction on the surface of activated carbon. Activated carbon is ideal for the removal of hydrogen sulfide and sulfur-containing compounds, but it is not ideal for the removal of ammonia or nitrogen-containing compounds alone. Before the activated carbon reaches saturation, its removal rate of malodorous substances remains relatively stable and it is less affected by the impact of gas load changes, so it has a wide range of adaptability, but the adsorbent is inconvenient to regenerate frequently, so the concentration of the adsorbed gas is required Can’t be too high.
3.3 The decolorization ability of activated carbon in the treatment of printing and dyeing wastewater
The use of activated carbon adsorption to treat the complex dye production wastewater has a good effect. The basic workflow is as follows
(1) After coagulation and precipitation of the anaerobic pretreated effluent, the COD removal rate is about 83%, and the decolorization rate reaches 99.3%, which creates good conditions for subsequent adsorption.
(2) Activated carbon has good adsorption performance. The adsorption conditions of this process: pH=4, the amount of powdered activated carbon is 20g/L, the adsorption process needs to be stirred, the adsorption time is 40min, and the CODCr of the effluent after adsorption is 150mg/L or less. Meet the national emission standards.
(3) The two regeneration methods of alkaline elution and Fenton reagent oxidation can better restore the adsorption performance of activated carbon. By adsorbing the regenerated activated carbon, the CODCr removal rate can still reach more than 77%, and the decolorization rate can reach more than 97%.

4. Application and development of combined process of activated carbon adsorption and other water treatment technologies

4.1 Potassium permanganate-activated carbon combined process
Some water plants in China use the combined process of potassium permanganate and activated carbon in the treatment of micro-polluted water sources to improve the ability to remove odor and color from degradation products, and the effect is significant. At the same time, this combined process reduces turbidity and saves alum consumption.
4.2 Biological activated carbon method
Biological activated carbon method is a water treatment technology developed on the basis of activated carbon adsorption technology. The biological activated carbon method is a new method that uses activated carbon as a biofilm carrier and uses the adsorption effect of activated carbon and the degradation of the biofilm to remove pollutants in the water.
4.3 “Powder activated carbon-activated sludge process (PACT)
In this method, powdered activated carbon is added to the activated sludge aeration tank to form biological activated carbon, which uses the synergistic effect of adsorption and degradation to remove pollutants. Due to the inherent mechanism of biological activated carbon, it can remove the substances that are difficult to remove by the activated sludge method and improve the removal efficiency of activated sludge. On the other hand, activated sludge has stable and good compactness, thereby overcoming sludge expansion. Because of its advantages in economy and treatment efficiency, it has been widely used in industrial wastewater treatment.

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