Overview of activated carbon filtration principle and quality standards
The adsorption capacity of activated carbon has a certain relationship with the level of water temperature and the quality of water. The higher the water temperature, the stronger the adsorption capacity of activated carbon; if the water temperature is above 30 °C, the adsorption capacity reaches the limit and there is a possibility of gradual decrease. When the water quality is acidic, the adsorption capacity of activated carbon for anionic substances is relatively weakened; when the water quality is alkaline, the adsorption capacity of activated carbon for cationic substances is weakened. Therefore, the pH of the water is unstable, which will also affect the adsorption capacity of activated carbon.
The principle of adsorption of activated carbon is: a balanced surface concentration is formed on the surface of the particles, and the impurities of the organic substances are adsorbed into the activated carbon particles, and the initial adsorption effect is high. However, after a long period of time, the adsorption capacity of activated carbon will be weakened to varying degrees, and the adsorption effect will also decrease. If the water in the aquarium is turbid and the organic content in the water is high, the activated carbon will soon lose its filtering function. Therefore, activated carbon should be cleaned or replaced regularly.
The size of the activated carbon particles also has an effect on the adsorption capacity. In general, the smaller the activated carbon particles, the larger the filtration area. Therefore, the powdered activated carbon has the largest total area and the best adsorption effect, but the powdered activated carbon easily flows into the aquarium with water, which is difficult to control and is rarely used. Granular activated carbon is not easy to flow due to particle formation, and impurities such as organic matter in water are not easily blocked in the activated carbon filter layer, and its adsorption capacity is strong, and it is convenient to carry and replace.
The adsorption capacity of activated carbon is proportional to the time of contact with water. The longer the contact time, the better the water quality after filtration. Note: The filtered water should flow out of the filter layer slowly. The new activated carbon should be cleaned before the first use, otherwise black ink will flow out. Before the activated carbon is installed in the filter, it should be spread with 2~3 cm thick sponge at the bottom and top to prevent the penetration of large particles such as algae. After 2~3 months of activated carbon, if the filtration effect is reduced, it should be exchanged. New activated carbon and sponge layers should be replaced regularly.
[Standard number of activated carbon quality indicators]
Activated carbon name national standard number
Wood fine granular activated carbon GB/T13803.1-1999
Activated carbon for wood purification water GB/T13803.2-1999
Activated carbon for sugar liquid decolorization GB/T13803.3-1999
Activated carbon for injection GB/T13803.4-1999
Acetate synthesis of coal-contacted activated carbon GB/T13803.5-1999
Coal granular activated carbon for desulfurization GB/T7701.1-1999
Coal-based granular activated carbon for recycling solvent GB/T7701.2-1999
Coal particle granular activated carbon for catalyst interception GB/T7701.3-1999
Coal-based granular activated carbon for purifying water GB/T7701.4-1999
Coal granular activated carbon for purifying air GB/T7701.5-1999
Coal particle granular activated carbon for protection GB/T7701.6-1999
High-efficiency adsorption coal particle granular activated carbon GB/T7701.7-1999
National Standard for Test Methods of Wood Activated Carbon in China
Indicator name national standard number
Determination of apparent density GB/T12496.1-1999
Determination of particle size distribution GB/T12496.2-1999
Determination of ash content GB/T12496.3-1999
Determination of moisture content GB/T12496.4-1999
Determination of carbon tetrachloride adsorption rate (activity) GB/T12496.5-1999
Determination of strength GB/T12496.6-1999
Determination of PH value GB/T12496.7-1999
Determination of iodine adsorption value GB/T12496.8-1999
Determination of caramel decolorization rate GB/T12496.9-1999
Determination of adsorption value of methylene blue GB/T12496.10-1999
GB/T12496.1-1999 Determination of benzoic acid adsorption value GB/T12496.11-1999
Activated carbon has strong adsorption and catalytic properties, sufficient raw materials and high safety, acid and alkali resistance, heat resistance, insoluble in water and organic solvents, easy to regenerate, etc. It is an environmentally friendly adsorbent. As an excellent adsorbent, activated carbon has been widely used in the field of water treatment, and it is an effective means to remove organic matter, odor, and especially synthetic organic matter in water. The adsorption performance of activated carbon is mainly determined by its special surface structure characteristics and surface chemical properties. At the same time, the electrochemical properties of activated carbon also have a great influence on the adsorption performance.
As the drinking water source in urban areas is increasingly polluted, in order to improve the drinking water quality, it is necessary to renovate the conventional water treatment process of the water plant. The application of ozone-activated carbon deep water treatment technology will become more and more popular, and the selection of activated carbon will directly affect the deep water. The effect of processing and investment in construction funds.
2 activated carbon
Activated carbon is widely used in industrial three waste treatment, solvent recovery, food and beverage purification, carrier, medicine, gold extraction, semiconductor applications, battery and electrical energy storage. Adjusting the pore structure of activated carbon and modifying the surface groups plays an important role in improving its special properties and specific adsorption catalysis [1].
Activated carbon can be prepared from most carbonaceous materials such as wood, sawdust, coal, peat, husk, pit, bagasse and rice husk, petroleum waste, waste plastic, waste leather, waste tires, paper waste, municipal waste. And other waste. At present, it is generally believed that the shell is the best raw material for the preparation of activated carbon, but the nut shell resources in China are very limited, and it is not easy to concentrate, store and expensive. In recent years, various types of wastes with low prices and wide sources have been tested at home and abroad for the preparation of activated carbon [1]. At present, the performance of activated carbon produced from waste is not high, and the practical application is still relatively small, but it is increasingly favored because of its low price, high carbon content, easy availability of materials, sufficient raw materials and green non-toxicity. The effective use of waste to produce activated carbon not only saves resources but also protects the ecological environment.
Among the environmental protection industries, the largest amount of activated carbon is urban water purification projects and sewage treatment projects, accounting for more than 70% of the total amount of activated carbon in the environmental protection industry; followed by air purification, the amount of activated carbon is also increasing year by year. However, there is a certain degree of environmental pollution in the production process of activated carbon. In the case of increasingly strict national environmental protection policies, solving the environmental problems of activated carbon production enterprises is a major issue for the sustainable development of the activated carbon industry. Some experts pointed out that in the next 10-20 years, China's demand for activated carbon will further increase, China's activated carbon industry will develop towards low consumption, low pollution and high quality, high technology [2].
As an excellent adsorbent, activated carbon has a wide range of applications in the purification of drinking water, the advanced treatment of wastewater, purification or storage of gases. Studies have shown that activated carbon mainly has a strong adsorption effect on organic substances with a relative molecular mass of less than 3,000, especially 500-1000. The main factors affecting the performance of activated carbon are specific surface area, pore volume and pore size distribution. Generally, the larger the specific surface area and pore volume, the stronger the adsorption capacity.
3 Application of activated carbon in water purification technology
At present, the urban drinking water treatment process is mainly to remove the suspended matter, turbidity and pathogenic microorganisms from the coagulation→precipitation→filtration→disinfection conventional treatment process, and select the appropriate treatment structure type according to the characteristics of the source water, and combine it into drinking water treatment. Process flow. The disinfection method is mainly based on chlorine disinfection, and a few water plants use chlorine dioxide, ozone or ultraviolet disinfection. The effluent water quality is generally required to meet the national standards for drinking water quality.
For water sources with good water quality, traditional water treatment processes can obtain safe and qualified drinking water. However, with the pollution of source water, the traditional water treatment process can not meet the requirements of the current drinking water needs to be solved for the removal of organic matter and the reduction of the trinitrogen content. [3] Drinking water in most areas has been treated conventionally. However, it still contains a variety of trace organic substances, especially toxic, teratogenic, carcinogenic and mutagenic substances, people will drink, long-term drinking, there will be dizziness, fatigue, hair loss, increased incidence of cancer [4]. With the rapid development of urbanization and industrialization, new pathogenic microbial factors appear in drinking water, and chlorination can not effectively kill pathogens, viruses and anti-chlorine pathogens such as Giardia cysts and hidden in water. Sporozoite oocysts, etc. The emergence of anti-chlorine-type pathogenic microorganisms such as Cryptosporidium has also raised questions about the traditional chlorination process [5].
In order to improve and improve drinking water quality, effective removal of trace organic substances in drinking water and harmful substances such as iron, manganese and heavy metal ions to prevent the production of teratogenic and carcinogenic substances such as THMs, many countries in the world have carried out research in this area. And took the corresponding measures. According to the available data, the deep purification of drinking water mainly adopts measures such as pre-oxidation, activated carbon adsorption and ozone oxidation [6].
Activated carbon not only has good effect on color and odor removal in purifying water supply, but also has high adsorption capacity for synthetic detergent ABS, trihalomethanes (THMs), halogenated hydrocarbons and free chlorine, and can effectively remove almost impossible to decompose. Carbamate insecticides, etc. Activated carbon can effectively remove free chlorine and some heavy metals (such as Hg, Sb, Sn, Cr) in water and is not easy to produce secondary pollution. It is often used in the purification process of domestic water and drinking water [7] in water purification technology. It is generally divided into preprocessing and advanced processing techniques. . The main advantages of activated carbon in wastewater treatment are high degree of treatment and stable effluent quality. Used in combination with other methods to obtain high quality effluent quality, even to drinking water standards.
3.1 Adsorption pretreatment technology
Adsorption pretreatment technology refers to a method of removing contaminants from water by utilizing the adsorption or exchange of substances. Currently used adsorbents for water treatment are activated carbon, diatomaceous earth, silica, activated alumina, zeolite and ion exchange resins [8]. In recent years, some new adsorbent materials have been developed, such as porous synthetic resins and activated carbon fibers. The most used one is the hydrophobic substance-activated carbon which has strong adsorption to organic pollutants and odors in water. However, after the powdered activated carbon participates in the coagulation and sedimentation process, it remains in the sludge. At present, there is no good recycling method, which results in high processing cost and is difficult to popularize and apply. Although the clay mineral adsorbent has sufficient supply and low price and has good adsorption performance, a large amount of clay is added into the coagulant to increase the sludge discharge amount of the sedimentation tank, which brings certain difficulties to the production operation [8][9] .
3.2 Advanced Processing Technology
The following two brief introductions to the advanced treatment technology of activated carbon.
I. Oxygen-activated carbon combined with advanced treatment technology
Activated carbon is a porous material composed of macropores, mesopores and micropores. The removal of organic matter mainly depends on the adsorption of mesopores and micropores. Ozone activated carbon combined with advanced treatment technology adopts the method of adsorption of activated carbon after ozone oxidation, and continues oxidation in the adsorption of activated carbon. The basic principle is to add ozone to the carbon layer, transform the macromolecules in the water into small molecules, change the molecular structure and shape, and provide the possibility that the organic matter enters the smaller pores, so that the organic matter on the surface of the activated carbon in the macropores is oxidatively decomposed. Therefore, the activated carbon can fully adsorb the oxidized organic matter to achieve the purpose of deep purification of water [8], such as ozone may destroy some organic structures and may also produce some toxic and harmful intermediates. The results show that the water source is treated by ozone 2 activated carbon adsorption, and the effluent water quality after chlorination may still be mutagenic. . Of course, ozone activated carbon combined technology also has its limitations.
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