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Treatment of Wastewater by Carbon Adsorption from Activated Carbon Equipment

July 25, 2019

1 Preface
According to statistics, the annual discharge of industrial wastewater in China is about 8 *108 m3, which contains not only highly toxic components such as cyanide, but also metal ions such as chromium, zinc and nickel. There are many methods to treat wastewater, such as chemical precipitation, electrolysis and membrane treatment. This paper introduces activated carbon adsorption method. Activated Carbon Equipment plays an important role in it. Activated carbon processed by Activated Carbon Production Equipment is to deal with this problem. Activated carbon has a large surface area and high physical and chemical adsorption functions. Therefore, activated carbon adsorption is widely used in wastewater treatment. And it has the characteristics of high efficiency and good effect.
2 Activated Carbon
Activated carbon is a specially treated carbon with numerous small pores and huge surface area. The surface area of each gram of activated carbon is 500-1500 square meters. Activated carbon has strong physical and chemical adsorption functions, and also has detoxification effect. The detoxification effect is to use its huge area to adsorb poisons into the micropore of activated carbon, thus preventing the absorption of poisons. At the same time, activated carbon can combine with a variety of chemicals, thus preventing the absorption of these substances.

Classification of 2.1 Activated Carbon
There are many kinds of activated carbon used in production. Generally made into powder or granular.
Powdered activated carbon has strong adsorption capacity, easy preparation and low price, but it is difficult to regenerate and can not be reused.
Granular activated carbon is expensive, but it can be reused after regeneration, and has better working conditions and convenient operation and management. Therefore, granular activated carbon is often used in water treatment.
2.2 Activated Carbon Production Equipment is Better than Activated Carbon Adsorption
Activated carbon adsorption refers to the adsorption of one or more substances on the solid surface of activated carbon to purify water.
2.3 Factors Affecting Activated Carbon Adsorption
Adsorption capacity and adsorption rate are the main indicators to measure the adsorption process. The adsorption capacity is measured by the amount of adsorption. The adsorption rate is the mass of adsorbent adsorbed per unit weight in a unit time. In water treatment, the adsorption rate determines the contact time between wastewater and adsorbent.
The adsorption capacity of activated carbon is related to the pore size and structure of activated carbon. Generally speaking, the smaller the particle size, the faster the pore diffusion rate, the stronger the adsorption capacity of activated carbon.
The pH and temperature of sewage also affect the adsorption of activated carbon.  Activated carbon generally has higher adsorption capacity in acidic condition than in alkaline condition. Adsorption reaction is usually exothermic reaction, so low temperature is beneficial to 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.
Application of Activated Carbon in Sewage Treatment
Because of the high requirement of activated carbon for water pretreatment and the high price of activated carbon, activated carbon is mainly used to remove trace pollutants in wastewater in order to achieve the purpose of deep purification.
3.1 Activated Carbon Treatment of Chromium-Containing Wastewater
Chromium is a kind of metal material with large amount in electroplating. Hexavalent chromium exists in different forms in wastewater with different pH values.
Activated carbon has very developed microporous structure and high specific surface area. It has very strong physical adsorption capacity and can effectively adsorb Cr (VI) in wastewater. There are many oxygen-containing groups on the surface of activated carbon, such as hydroxyl (- OH), carboxyl (- COOH), etc. They all have electrostatic adsorption function and have chemical adsorption effect on Cr (VI). It can be used to treat chromium (VI) in electroplating wastewater. The adsorbed wastewater can meet the national discharge standard.
Poke me and try.
The results showed that when the concentration of chromium (VI) in solution was 50 mg/L, pH = 3 and the adsorption time was 1.5 h, the adsorption performance of activated carbon and the removal rate of chromium (VI) were the best. sewage
Therefore, the process of treating chromium-containing wastewater with activated carbon produced by Carbonization Furnace and Activation Furnace is the result of physical adsorption, chemical adsorption and chemical reduction of chromium (VI) in solution by activated carbon. Activated carbon treatment of chromium-containing wastewater has stable adsorption performance, high treatment efficiency, low operating costs, and certain social and economic benefits.
3.2 Activated Carbon for Treatment of Cyanide-Containing Wastewater
In industrial production, cyanide or by-product cyanide is used in wet extraction of gold and silver, production of chemical fibers, coking, synthetic ammonia, electroplating, gas production and other industries, so a certain amount of cyanide-containing wastewater must be discharged in the production process.
Activated carbon has been used to purify wastewater for quite a long time, and more and more literatures have been reported to treat cyanide-containing wastewater. However, due to the small adsorption capacity of CN_ and HCN on activated carbon, it is generally 3 mgCN/gAC-8 mgCN/gAC (depending on the variety), which is not cost-effective.
3.3 Activated Carbon for Treatment of Wastewater Containing Mercury

Activated carbon has the capability of adsorbing mercury and mercury compounds, but its adsorptive capacity is limited, so it is only suitable for treating wastewater with low mercury content. If the concentration of mercury is high, it can be treated by chemical precipitation method. After treatment, the mercury content is about 1 mg/L, which can reach 2-3 mg/L at high level. Then activated carbon can be used for further treatment.


3.4 Activated Carbon for Treatment of Phenolic Wastewater
Phenolic wastewater is widely derived from petrochemical plants, resin plants, coking plants and refineries. Experiments show that the adsorption performance of activated carbon on phenol is good, the increase of temperature is not conducive to adsorption, so that the adsorption capacity decreases, but the time to reach adsorption equilibrium is shortened when the temperature is raised. There is an optimum amount of activated carbon and adsorption time. Under acidic and neutral conditions, the removal rate does not change much. Under strong alkaline conditions, the removal rate of phenol decreases sharply, and the stronger the alkalinity, the worse the adsorption effect.
3.5 Activated Carbon Equipment for Treatment of Wastewater Containing Methanol
Activated carbon can adsorb methanol, but its adsorptive capacity is not strong. It is only suitable for treating wastewater with low methanol content. The results of engineering operation show that the COD of mixed liquor can be reduced from 40 mg/L to less than 12 mg/L, and the removal rate of methanol can reach 93.16%~100%. The effluent quality can meet the water quality requirement of water reused to boiler desalination system [9].
3.6 Refinery Advanced Treatment
Oily wastewater from refineries is treated by oil isolation, air flotation and biological treatment, and is further treated by sand filtration and activated carbon filtration. The phenol content in wastewater decreased from 0.1 mg/L (after biological treatment) to 0.005 mg/L, cyanide from 0.19 mg/L to 0.048 mg/L, and COD from 85 mg/L to 18 mg/L.
4 Prospects
With the progress of science and technology and the special requirements of wastewater treatment, the research of activated carbon has gradually developed from its pore structure and specific surface area to the effect of surface functional groups on the adsorption performance of activated carbon.
For example, activated carbon fibers (ACF) have attracted the attention of researchers in wastewater treatment in recent years. Its diameter is generally 5-20 um. The preparation principle of ACF is the same as that of traditional activated carbon, i.e. activated carbon fibers are treated with steam or carbon dioxide at 800 C or above. The pore structure of fibrous activated carbon is mainly microporous, with few mesoporous and almost no macroporous, and its specific surface area can reach 2500 m2/g. It has the characteristics of high adsorption and desorption rate, large adsorption capacity and high conductivity.
The experimental results show that the adsorption capacity of ACF for phenol is 248 mg/g, and the adsorption capacity is almost unchanged after several regeneration after adsorption saturation. The adsorption performance of ACF is better than that of activated carbon. At room temperature, under acidic or neutral conditions, 0.5g activated carbon fibers were added to phenol-containing simulated wastewater with a concentration of 282mg/L at 100mL, and the phenol removal rate could reach 91% after 30 minutes of constant temperature oscillation.
Recently, it has been found that activated carbon not only has adsorption properties, but also exhibits catalytic properties. The catalytic oxidation method developed from this has attracted more and more attention, and its research is also deepening. In order to improve the treatment efficiency, starting from the study of catalytic oxidation mechanism, the surface structure of activated carbon was changed, the ability of activated carbon was improved, and the ideal adsorbent was found.

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