Activated carbon is one of the widely used adsorbents in water treatment. It is a kind of carbon by specially treated with countless fine pores and a large surface area. The surface area of each gram of activated carbon is 500 square meters ~ 1500 square meters.
Activated carbon has strong physical adsorption and chemical adsorption functions, it also has detoxification effect. The detoxification effect is by using its big surface area to adsorb the poison from activated carbon, thereby it can prevent the absorption of the poison.
Activated carbon is usually divided into powdered activated carbon and granular activated carbon, the former usually use suspension contact adsorption for wastewater treatment. The latter use the filtration-adsorption method for wastewater treatment.
There are two types of treatment systems, one is using activated carbon to treat the secondary treatment effluent directly, the other is using granular activated carbon to adsorb the secondary treatment effluent after chemical clarification, removal of nutrients and filtration.
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Activated carbon has obvious advantages in treating sewage
1. Activated carbon has excellent adsorption characteristics for organic matter in water. Due to activated carbon has a well-developed fine pore structure, it has a strong adsorption capacity for organic pollutants dissolved in water, such as benzene compounds, phenolic compounds, petroleum and petroleum products, and it has a good removal effect on organic pollutants that are difficult to remove by biological methods and other chemical methods, such as color, odor, methylene blue surfactants, herbicides, pesticides, pesticides, synthetic detergents, synthetic dyes, amine compounds and many synthetic organic compounds.
2. Activated carbon has strong adaptability for changes in water quality, water temperature and water quantity. For the same organic pollutant sewage, activated carbon has a good removal effect at high or low concentrations.
3. The activated carbon water treatment device occupies a small area, it is easy to automatically control and has simple operation and management.
4. Activated carbon also has strong adsorption capacity for certain heavy metal compounds. Such as mercury, lead, iron, nickel, chromium, zinc, cobalt, etc. Therefore, activated carbon also has a good effect on the treatment of electroplating wastewater and smelting wastewater.
5. Saturated activated carbon can be reused after regeneration without secondary pollution.
6. It can recover useful substances, such as treating high-concentration phenol-containing wastewater, and recovering sodium phenolate after regeneration with alkali.
Specific treatment methods of activated carbon for wastewater
Wastewater activated carbon treatment is one of the wastewater adsorption treatment methods.
It is a method to remove various pollutants in wastewater by utilizing the properties of activated carbon such as physical adsorption, chemical adsorption, oxidation, catalytic oxidation and reduction.
For example, powdered activated carbon treatment method, which is also known as bio-physical treatment method, feeding aeration method. It is to put powdered activated carbon into the aeration tank, which not only makes full use of the wastewater treatment equipment, but also improves the treatment effect.
The removal of pollutants by this method is generally considered to be a synergistic effect of adsorption and microbial oxidative decomposition. The large number of micropores of activated carbon adsorbs oxygen in organic matter and wastewater, it provide a high concentration of nutrient source for the growth and reproduction of microorganisms, and the enzymes and coenzymes produced in the process of microbial metabolism are adsorbed and enriched in the micropores of activated carbon. In addition, the contact time between microorganisms and organic matter on the carbon is longer, which makes the organic matter that is difficult to degrade may also be decomposed by biological oxidation.
The powdered activated carbon treatment method generally includes three steps:
Intense mixing, so that the charcoal is quickly dispersed into the sewage.
Contact adsorption and oxidation, so that the carbon is suspended in the sewage for suspension adsorption and oxidation.
Liquid-solid separation, in which carbon is separated from the effluent and then regenerated.
The technology of powdered activated carbon for wastewater treatment is a single-stage contact system, that is, mixing, contact reaction, gravity precipitation are completed in the same equipment, and the residence time of activated carbon in the equipment is 2~5 days. This facilitates microbial activity and improves treatment results.
Adding a certain amount of powdered activated carbon to the sludge digestion tank can accelerate the sludge precipitation, purify the supernatant returned to the water treatment system, and improve the efficiency of the water treatment system. In addition, it can also promote the decomposition of sludge solids, eliminate foul odors, and improve the production capacity of equipment.
Application of activated carbon in sewage treatment
Activated carbon treats COD in wastewater
Activated carbon has a strong adsorption effect on organic matter with a relative molecular mass of less than 3000, especially 500~1000. Among the various advanced treatment technologies to improve water quality effects, activated carbon adsorption is one of the most mature and effective methods to improve the conventional treatment process to remove organic pollutants in water, and activated carbon has strong adaptability to changes in water quantity, water quality and water temperature in use.
The data showed that for domestic wastewater with a COD concentration of 50.04mg/L, when the pH value was 3 and the adsorption time of activated carbon was 1h, the COD concentration of the treated wastewater was 12.41 mg/L, and the removal rate reached 78.6%.
Activated carbon treats mercury-containing wastewater
In the chlor-alkali industry, mercury is used as the cathode electrode to produce chlorine gas and caustic soda. The synthesis industry of polyvinyl chloride, acetaldehyde, and vinyl acetate all use mercury as a catalyst. The electronic instrument industry is also commonly used in mercury, so these industries all emit mercury containing mercury waste water.
Activated carbon can effectively adsorb mercury in wastewater. Some factories have used this method to treat mercury-containing wastewater, but this method is more suitable for treating low-concentration mercury-containing wastewater. When the mercury concentration in wastewater is high, primary treatment can be performed first to reduce the mercury concentration in the wastewater before adsorption by activated carbon.
The adsorption and removal capacity of activated carbon for organic mercury is higher than that of inorganic mercury. The adsorption of mercury on activated carbon will increase the removal rate when the pH value is lowered.
Activated carbon treatment of phenol-containing wastewater
Phenol-containing wastewater is widely sourced from petrochemical plants, plastic plants, synthetic fiber plants, coking plants, textile plants, nitrogen plants, and refinery and chemical plants. Activated carbon has good adsorption performance for phenol and can successfully treat phenol-containing wastewater.
For high-concentration phenol-containing wastewater, when the phenol concentration in the influent is 1950 mg/l, the phenol concentration in the effluent can be reduced to less than 0.1 ml through a three-column series-connected activated carbon adsorption column, but the adsorption column will be phenolic in a short time. penetrated. Therefore, activated carbon is more suitable for the treatment of medium and low concentrations of phenol-containing wastewater.
