Which types of wastewater are suitable for treatment with activated carbon?
Activated carbon exhibits excellent adsorption properties for organic matter in water. Due to its well-developed microporous structure and large specific surface area, activated carbon possesses strong adsorption capacity for dissolved organic pollutants in water, such as benzene compounds, phenolic compounds, petroleum and petroleum products. Furthermore, it shows good removal effects on organic pollutants that are difficult to remove using biological or other chemical methods, such as color, odor, methylene blue surfactants, herbicides, pesticides, synthetic detergents, synthetic dyes, amine compounds, and many artificially synthesized organic compounds.
1. Adsorption of Cr(VI) by Activated Carbon
With the rapid development of the electroplating industry, large amounts of electroplating wastewater are causing increasingly serious harm to the human environment. Chromium-containing electroplating wastewater contains large amounts of Cr(VI), and if discharged directly without treatment, it will severely pollute the environment upon which humanity depends for survival. Activated carbon possesses a highly developed microporous structure and a high specific surface area, exhibiting extremely strong physical adsorption capacity, effectively adsorbing Cr(VI) from wastewater. Simultaneously, the surface of activated carbon contains numerous oxygen-containing groups such as hydroxyl (-OH) and carboxyl (-COOH), which possess electrostatic adsorption capabilities, resulting in chemical adsorption of Cr(VI). Therefore, it can be effectively used to treat Cr(VI) in electroplating wastewater. Studies have shown that for wastewater with a pH of 4-5 and a Cr(VI) concentration of 100 mg/L in 50 mL, when 2 g of activated carbon is used, after 1 hour of shaking adsorption, the effluent Cr(VI) concentration is reduced to 0.38 mg/L, meeting the maximum allowable discharge concentration requirement for Cr(VI) in the wastewater discharge standard (GB8978.1996).
2. Activated Carbon Treatment of Cyanide-Containing Wastewater
The electroplating industry, coking industry, blast furnace gas washing, and gold and silver ore beneficiation industries all discharge cyanide-containing wastewater. Cyanide is a highly toxic substance, posing a significant threat to humans and fish. Activated carbon has a large specific surface area, thus exhibiting good adsorption treatment effect on cyanide-containing wastewater. Experiments show that for a gold mine cyanide-containing wastewater with a total cyanide concentration (CN') of 389.90 m²/L, when the treatment volume was 26.3 mL and the activated carbon content was g, the CN' adsorption capacity was 10.24 m²/2, and the effluent CN' concentration was below 0.5 m²/L, achieving an adsorption removal rate of 99.9%. Other studies have shown that soaking activated carbon in 3% copper chloride or 5% copper sulfate, followed by washing and drying before column loading, can increase cyanide removal efficiency by 2-3 times. When the influent pH is controlled between 6 and 9, most CN' is in a complexed state, and activated carbon has a stronger adsorption capacity for complexed cyanides than for simple cyanides.
3. Activated Carbon Treatment of Mercury-Containing Wastewater
In the chlor-alkali industry, mercury is used as the cathode to produce chlorine and caustic soda; the synthesis of polyvinyl chloride, acetaldehyde, and vinyl acetate all use mercury as a catalyst; mercury is also commonly used in the electronics and instrumentation industry, thus these industries all discharge mercury-containing wastewater. Mercury has serious toxic effects on the human body. Methylmercury accumulates in human brain tissue, invades the central nervous system, damages nerve function, and can lead to death in severe cases. Activated carbon can effectively adsorb mercury in wastewater, and some factories have adopted this method to treat mercury-containing wastewater, but this method is more suitable for treating low-concentration mercury-containing wastewater. When wastewater has a high mercury concentration, primary treatment can be performed first to reduce the mercury concentration before activated carbon adsorption. Wastewater with a mercury concentration below 1-2 mg/L can be passed through an activated carbon filter tower, reducing the mercury concentration in the effluent to 0.01-0.05 mg/L. The activated carbon can be regenerated and reused after mercury recovery. For example, in an electrolysis plant, the mercury concentration in wastewater was 5-10 mg/L. During treatment, ferrous sulfate and sodium sulfide were first added for reaction. After separation and precipitation in a sedimentation tank, the mercury concentration in the supernatant decreased to 0.1-1.0 mg/L. Then, the wastewater was passed through a granular activated carbon tank, resulting in a mercury concentration reduction of 0.01-0.05 mg/L. Activated carbon has a higher adsorption and removal capacity for organic mercury than inorganic mercury. The removal rate of mercury by activated carbon increases as the pH value decreases. It has been reported that pretreatment of activated carbon with carbon disulfide solution can significantly improve its mercury removal capacity. Studies have shown that activated carbon impregnated with carbon disulfide can reduce the mercury content in wastewater from an initial 10.0 g/L to 21.0 g/L. The treatment effect of the carbon disulfide system is optimal at pH=10.
4. Activated Carbon Treatment of Phenolic Wastewater
Phenolic wastewater widely originates from petrochemical plants, plastic factories, synthetic fiber plants, coking plants, textile mills, nitrogen plants, and oil refineries. Activated carbon has good adsorption performance for phenol and can successfully treat phenol-containing wastewater. For high-concentration phenol-containing wastewater, when the influent phenol concentration is 1950 mg/L, a three-column series activated carbon adsorption column can reduce the effluent phenol concentration to below 0.1 mL, but the adsorption column is penetrated by phenol within a short time. Therefore, activated carbon is more suitable for treating medium- and low-concentration phenol-containing wastewater. When the influent phenol concentration is between 0.12 m²/L and 44 mg/L, the phenol removal rate can reach over 99%, with the effluent phenol concentration less than 0.1 mg/L. Experiments show that for coking wastewater with an influent phenol concentration of 427 mg/L to 547 mg/L, when the dosage of powdered activated carbon is 4 O2·L, aeration for 2 hours can reduce the phenol content of the coking wastewater to below 0.5 mg/L, meeting discharge standard I. Activated carbon adsorbs phenol under acidic and neutral conditions and regenerates under alkaline conditions.
5. Activated Carbon Treatment of Dye Wastewater
The development of the textile industry has driven the development of dye production. Surveys show that more than 700,000 tons of dye are produced worldwide annually, of which 2% is directly discharged into water bodies as wastewater, and 10% is lost in subsequent textile dyeing processes. Dye wastewater has a complex composition, fluctuates greatly in water quality, has deep color, high concentration, and is difficult to treat. The color in the water affects the photosynthesis of aquatic plants, thus disrupting the ecological balance of the water. Activated carbon's large specific surface area enables it to effectively remove the color of wastewater. Studies have shown that for solutions of methyl orange, crystal violet, direct fast black G, and reactive turquoise blue with an initial concentration of 30 mg/L, at pH=7, an aeration rate of 1 m³/h, a powdered activated carbon dosage of 6 g/L, and an adsorption time of 20 min, the removal rates of all four dyes were 97%-99% [91]. For wastewater containing acid fuchsin, basic fuchsin, and reactive black B-133 dyes with an initial concentration of 250 m²/L, when the dosage of coconut shell activated carbon was 0 g/L, the removal rates were 97%-99%. When the concentrations were 0.8%, 1.0%, and 2.0%, and the adsorption times were 3.5h, 6h, and 17h respectively, the decolorization rate exceeded 97%, the effluent color dilution factor was no greater than 50 times, and the CODdx was less than 50mg/L, meeting the Class I discharge standard of the Integrated Wastewater Discharge Standard (GB8978-1996). Furthermore, "Within the pH range of 7.5–12.5, for a considerable portion of dyes, pH changes do not significantly affect the adsorption rate of activated carbon." Regeneration of activated carbon after dye adsorption is also relatively easy. Experiments show that after drying at 120℃ for 12h and regenerating with a 600W microwave for 10s, the adsorption performance of granular activated carbon and coconut shell activated carbon for treating simulated Reactive Brilliant Red X-3B dye wastewater recovered to 100% of its original value, while the adsorption capacity of activated carbon fiber reached 2.4 times the original value.
6. Activated Carbon Treatment of Pesticide Wastewater
Pesticide production involves numerous steps, with significant differences in raw materials, synthesis processes, and product chemical structures. This process generates large amounts of wastewater, which is characterized by high organic matter concentration, high toxicity, poor biodegradability, and complex composition. Activated carbon can effectively adsorb and treat pesticide wastewater. Studies have shown that activated carbon can be used to treat organochlorine pesticide wastewater, with adsorption capacities of 100 mg/g, 42 mg/g, 30 mR/R, 15 mg/g, and 11 mT/tZ for isodrin, toxaphene, aldrin, dieldrin, and DDT, respectively. For wastewater from the production of the fungicide o-phenylphenol, at a concentration of 100 m²/L, a dosage of 2.5 L of activated carbon can achieve a removal rate of 99.6%. Activated carbon can also adsorb 2,4-dichlorophenol and small amounts of 3,4-dichlorophenol and 2,5-dichlorophenol contained in herbicide wastewater. "Chlorophenols and 2,6-dichlorophenols."
7. Activated Carbon Treatment of COD in Wastewater
Activated carbon is particularly effective at adsorbing organic matter with a relative molecular mass less than 3000, especially those between 500 and 1000. Among various advanced water treatment technologies, activated carbon adsorption is one of the most mature and effective methods for removing organic pollutants from water, complementing conventional treatment processes. Furthermore, activated carbon exhibits strong adaptability to changes in water volume, quality, and temperature. Experiments show that for domestic wastewater with a COD concentration of 50.04 mg/L, at a pH value of [missing value], [missing value], [missing value]. 3. When the activated carbon adsorption time is 1 hour, the COD concentration of the treated wastewater is 12.41 mg/L, and the removal rate reaches 78.6%. For example, the COD of the effluent from the oil separator of a machinery factory's wastewater treatment plant was originally 89.46 mg/L. When the activated carbon dosage was 2.0% and the adsorption time was 1 hour, the COD of the effluent decreased to 21.87 mg/L. Similarly, the COD of the effluent from the grit chamber of a municipal sewage treatment plant was originally 61.36 mg/L. When the activated carbon dosage was 2.0% and the adsorption time was 1 hour, the COD of the effluent decreased to... 8.84 m²/L.
Activated carbon's excellent adsorption properties have led to its widespread application in water treatment technology. It's worth noting that activated carbon produced by different methods will have varying selective adsorption properties and specific applicable ranges. Improper use will result in poor performance. Therefore, for different water qualities, appropriate activated carbon should be selected, or it should be modified using certain methods, or it should be used in combination with other water treatment technologies to achieve good results. With increasingly higher demands for water quality, activated carbon will play an even greater role in water purification and advanced wastewater treatment.