Activated carbon is a non-polar adsorbent activated by carbonaceous materials such as wood, nutshell, coal, petroleum, etc. under high temperature and anoxic conditions. It has a large specific surface area and a developed microporous structure. The specific surface area of ​​activated carbon can be Up to 500 ~ 1700m2 / g.
Generally, in gas phase adsorption, the adsorption capacity mainly depends on the micropores, and the transition pores play a major role in the wastewater treatment adsorption process. At the same time, some oxygen-containing functional groups are formed on the amorphous portion of the activated carbon surface, and thus have the properties of chemical adsorption, catalytic oxidation and catalytic reduction. The finished activated carbon has a black appearance. It is usually used in powder or granules. In addition to mainly carbon (about 92%), it also contains a small amount of oxygen (5%), hydrogen (1%) and sulfur (O. 05%) and other elements and some moisture and ash.
What are the functions of activated carbon in wastewater treatment systems? What are the two ways of activated carbon adsorption?
In addition to removing the odor caused by phenol, petroleum, etc., and the color or organic pollutants formed by various fuels, and the chromaticity of iron, manganese, etc., activated carbon can also be used to remove heavy metal ions such as mercury and chromium, and synthetic washing. Agents and radioactive materials, etc., also have good removal effects on pesticides, insecticides, chlorinated hydrocarbons, aromatic compounds and other difficult biodegradable organic substances.
Activated carbon adsorption is divided into static and dynamic methods. Static adsorption is used less, mainly for primary treatment of small-water industrial wastewater. Static adsorption is to put a certain amount of activated carbon into a certain amount of waste water to be treated, stir it, reach the adsorption equilibrium, and then separate the waste water and activated carbon by precipitation or filtration. If the effluent quality after a single adsorption cannot meet the requirements, multiple static adsorptions can be used. Dynamic activated carbon adsorption is an adsorption operation carried out under continuous flow of wastewater. There are many successful technologies and processes that can be used for the treatment of large-scale industrial wastewater or domestic sewage. The dynamic activated carbon adsorption method is mainly applied in the last step of the wastewater treatment system and the advanced treatment system for wastewater reuse to ensure that the effluent is finally discharged to the standard or meets the requirements for reuse.
In order to improve the treatment capacity of the aeration tank, the powder activated carbon is added to the aeration tank to improve the performance of the activated sludge and increase the biomass of the aeration tank to avoid sludge swelling in the secondary settling tank. A large number of pores of powdered activated carbon adsorb microorganisms, organic matter and oxygen in water, which can make biodegradable organic matter biodegradable, which is a synergistic effect of adsorption and microbial oxidative decomposition. This treatment method is effective and stable, and can be adapted to sewage with complex composition and water quality: variable water content.
What are the activated carbon equipment and devices?
(1) Fixed bed: According to the direction of filtered water flow, it is divided into two types: upflow type and downflow type.
(2) Moving bed: This method can fully exert the adsorption capacity of activated carbon, and the head loss is small.
(3) Fluidized bed: It is suitable for treating wastewater with high suspended solid content.
How many methods of regeneration of activated carbon are there?
(1) Heating regeneration method. The activated carbon used in water treatment is usually regenerated by heating desorption after it has failed.
(2) Chemical washing regeneration method. It is easy to operate and operate at room temperature.
(3) Chemical oxidation regeneration method. It can be further divided into: 1 wet oxidation method; 2 electrolytic oxidation method; 3 ozone oxidation method, using strong oxidant ozone to decompose the organic matter adsorbed on the activated carbon.
(4) Biological regeneration method. It is a method of oxidative decomposition of an organic substance adsorbed on activated carbon by the action of microorganisms.
(5) Microwave regeneration. The microwave is irradiated with microwaves with a frequency of 900-4000 MHz, so that the temperature of the activated carbon is rapidly increased to 500-550 ° C, and then the temperature is maintained for 20 minutes to achieve the regeneration requirement.
What is the process of heating and regeneration of activated carbon?
Heating regeneration, dehydration, drying, carbonization, activation, and cooling are carried out in five steps:
(1) Dehydration: The activated carbon is separated from the conveying water stream.
(2) Drying: heating to 100 to 1.50%, evaporating the water adsorbed in the pores of the activated carbon, and simultaneously evaporating part of the low-boiling organic matter.
(3) Charring: heating to 300-700 ° C, the low-boiling organic matter is volatilized, the high-boiling organic matter is thermally decomposed, and some organic matter is carbonized and left in the pores of the activated carbon.
(4) Activation: heating is continued to 700 to 1000 ° C, and the residual carbon remaining in the pores of the activated carbon is activated by steam, CO 2 or the like to achieve the purpose of re-forming the pores.
(5) Cooling: To prevent oxidation, the activated activated carbon is rapidly cooled by water.
What are the precautions for the operation and management of activated carbon?
(1) When using activated carbon, it is necessary to comprehensively consider various indexes such as adsorption performance, mechanical strength, price, and regeneration performance, and generally cannot be biased toward only one of the properties. The nature of the wastewater is different and the types of activated carbon used are often different. For example, the effect of treating activated carbon on papermaking wastewater is better than using activated carbon, and the effect of treating waste water with activated carbon is better than that of lignite-based activated coke.
(2) The surface of the activated carbon is mostly alkaline, and heavy metal ions in the water may precipitate on the surface of the hydroxide, thereby degrading the adsorption performance of the activated carbon. Therefore, when using activated carbon adsorption to treat wastewater, the lower the inorganic salt content, especially the heavy metal ion content in water, the better (the system of specifically adsorbing heavy metals with activated carbon is another matter).
(3) In order to give full play to the role of activated carbon, avoid excessive saturation of activated carbon to reduce operation and reduce operating costs, it must be ensured that the water quality of the activated carbon adsorption method cannot exceed the design value. Generally, the influent CODc does not exceed 50-80 mg/L. When the concentration of organic matter in the influent water is high, it is necessary to strengthen the management of pretreatment measures such as physical law, chemical method and biological method, and try to improve the treatment effect. When the wastewater contains a large amount of suspended solids or colloids, the coagulant must be added for pretreatment by filtration or air flotation.
(4) For the treatment process of advanced treatment of sewage or some pollutants whose concentration exceeds the standard, the activated carbon treatment process must be set up to bypass or bypass the pipeline. When the influent water quality changes greatly, the activated carbon treatment unit is stopped in time to save the adsorption capacity of the activated carbon bed and effectively prolong the regeneration or replacement cycle.
(5) Since the contact of activated carbon with ordinary carbon steel can cause severe electrochemical corrosion, the equipment or components in contact with activated carbon should use reinforced concrete structures or materials such as stainless steel and plastic. If it must be made of ordinary carbon steel, it must be treated with anti-corrosion treatment. When epoxy resin lining is used for corrosion protection, the thickness of the lining should be greater than 1.5mm.
(6) When using powdered activated carbon, all operations must be considered for fire and explosion protection, and all electrical equipment used must comply with explosion-proof requirements.
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