Application of Activated Carbon in Water Treatment

According to statistics, the annual industrial wastewater discharged from China is approximately 8×108m3, which contains not only highly toxic components such as cyanide but also metal ions such as chromium, zinc, and nickel. There are many waste water treatment methods, including chemical precipitation, electrolysis and membrane treatment. This article describes activated carbon adsorption. Activated carbon has a large surface area and high physical adsorption and chemical adsorption. Therefore, activated carbon adsorption is widely used in wastewater treatment. And it has high efficiency and good effect.

Activated carbon
Activated carbon is a special treatment of carbon, with numerous small pores, a large surface area, per gram of activated carbon surface area of ​​500-1500 square meters. Activated carbon has a strong physical adsorption and chemical adsorption function, but also has detoxification. Detoxification is the use of its huge area, the poison adsorbed in the pores of activated carbon, thus preventing the absorption of poisons. At the same time, activated carbon can be combined with a variety of chemicals to prevent the absorption of these substances.

Classification of activated carbon
There are many types of activated carbon used in production. Generally made into powder or granules.
Powdered activated carbon has a strong adsorption capacity, is easy to prepare, and has a low price, but it is difficult to regenerate, and generally cannot be reused.
Granular activated carbon is more expensive, but it can be reused after being regenerated, and its working conditions are better when used, and its operation and management are convenient. Therefore, more granular activated carbon is used in water treatment [1].

Activated carbon adsorption
Activated carbon adsorption refers to the use of the solid surface of activated carbon to adsorb one or more substances in water to achieve the purpose of purifying water quality.

Factors Affecting Activated Carbon Adsorption
Adsorption capacity and adsorption rate are the main indicators to measure the adsorption process. The size of adsorption capacity is measured by the amount of adsorption. The adsorption rate refers to the amount of substance adsorbed per unit weight per unit time. In water treatment, the adsorption rate determines the contact time between the wastewater and the adsorbent.
The adsorption capacity of activated carbon is related to pore size and structure of activated carbon. In general, the smaller the particles, the faster the pore diffusion rate and the stronger the adsorption capacity of activated carbon.
The pH and temperature of the sewage also have an effect on the adsorption of activated carbon. Activated carbon generally has a higher adsorption capacity under acidic conditions than under alkaline conditions. The adsorption reaction is usually an exothermic reaction, so a low temperature favors 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 the equilibrium concentration of the adsorbed material.

Application of Activated Carbon in Sewage Treatment
Because activated carbon requires high pretreatment of water, and the price of activated carbon is expensive, activated carbon is mainly used to remove trace contaminants from wastewater in the treatment of wastewater for the purpose of deep purification.

Activated carbon treatment of chromium-containing wastewater
Chromium is a kind of metal raw material with a relatively large amount in electroplating. In the waste water, hexavalent chromium exists in different forms with different pH values.
Activated carbon has a well-developed microporous structure and a high specific surface area, has a strong physical adsorption capacity, and can effectively adsorb Cr(VI) in wastewater. On the surface of activated carbon, there are a large number of oxygen-containing groups such as hydroxyl (-OH), carboxyl (-COOH), etc. They all have electrostatic adsorption function and produce chemical adsorption of Cr(VI). It can be completely used to treat Cr(VI) in electroplating wastewater. The wastewater after adsorption can meet the national emission standards.
The results showed that the Cr(VI) concentration in the solution was 50 mg/L, the pH was 3, and the adsorption time was 1.5 h. The adsorption performance of activated carbon and the removal rate of Cr(VI) all reached the best effect.
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   Therefore, the process of using activated carbon to treat chromium-containing wastewater is the result of comprehensive effects of physical adsorption, chemical adsorption and chemical reduction of activated carbon on Cr(VI) in solution. The activated carbon treatment of chromium-containing wastewater has stable adsorption performance, high treatment efficiency, low operating costs, and certain social and economic benefits.