Application of Activated Carbon in Water Treatment

All surfaces tend to spontaneously reduce surface energy. Since solid surfaces cannot shrink freely, they lower surface energy by reducing interfacial tension, which is the fundamental cause of adsorption occurring on solid surfaces. Activated carbon features a highly developed pore structure and ultra-large specific surface area, granting it strong adsorption capacity for dissolved organic matter in water such as benzene compounds, phenolic compounds, petroleum and petroleum derivatives. As a core adsorbent, Activated carbon for wastewater treatment can also efficiently remove organics that are difficult to eliminate via biological and other conventional treatments, including color-causing substances, off-odor compounds, surfactants, herbicides, synthetic dyes, amines and many artificially synthesized organic compounds. Therefore, activated carbon adsorption technology, especially the application of Activated carbon for wastewater treatment, has been widely adopted in water treatment.

 

I. Characteristics of Activated Carbon

Activated carbon is a porous carbonaceous material with well-developed micropore structures and a huge specific surface area. It covers a variety of carbon-based adsorbents capable of capturing numerous chemical substances on its surface. Initially applied in the sugar refining industry, activated carbon has later been extensively used to remove organic and certain inorganic contaminants from wastewater, among which Activated carbon for wastewater treatment stands out due to its targeted performance for complex sewage.

 

1.1 General Properties of Activated Carbon

Activated carbon is dark black in appearance with outstanding adsorption performance. It boasts stable chemical properties, resisting strong acids and strong alkalis, and tolerating water immersion and high temperatures. With a density lower than water, it is classified as a porous hydrophobic adsorbent.

 

 

1.2 Adsorption Mechanism of Activated Carbon

Adsorption on activated carbon originates from the unsaturated atomic force field and surface energy on solid surfaces. The material adsorbs molecules to reduce its surface energy. After a solid adsorbs solute molecules from solution, the solute concentration of the bulk solution decreases, while adsorbed molecules accumulate densely on the solid surface.

During activated carbon production, volatile organic components are eliminated, and inter-lattice voids are formed, generating countless fine pores of diverse shapes and sizes. Pores normally account for 70%–80% of the total volume of activated carbon particles. These pores vary widely in shape and pore size distribution. The total surface area of pore walls, namely the specific surface area, generally reaches 500–1700 m²/g, which is the primary reason for activated carbon's powerful adsorption capacity and high adsorption loading.

The adsorption performance of activated carbon depends not only on the structure and distribution of fine pores, but also on its surface chemical properties. Activated carbon itself is non-polar; its surface functional group content and surface charge vary with raw material composition and activation conditions. Carbon activated at low temperature (< 500°C) generates surface acidic oxides that release H⁺ upon hydrolysis. Weak polarity on the carbon surface enables polar solutes to compete for active adsorption sites, reducing the adsorption capacity of non-polar solutes. Meanwhile, ion exchange adsorption and complexation reactions occur between activated carbon and certain metal ions in water, improving the removal efficiency of metal ions.

In summary, micropore structures dominate adsorption capacity, as micropores constitute nearly all of the total specific surface area. Macropores and transitional pores act as coarse and fine mass transfer channels respectively; their quantity and distribution greatly affect adsorption and desorption rates. Furthermore, surface chemical properties also exert influences on activated carbon adsorption performance.

 

II. Applications of Activated Carbon in Water Treatment

Activated carbon adsorption process is the preferred technology for organic pollutant removal in water. Thanks to abundant raw material sources and large specific surface area, it achieves high removal rates for color, odor, taste and other organic contaminants, leading to expanding application in water treatment.

Powdered activated carbon (PAC) is especially effective for low-molecular-weight dissolved organic carbon (DOC) secreted by algal cells and can efficiently eliminate microcystins in water. Installing an activated carbon filter after conventional slow sand filters removes odor-causing organics such as geosmin and 2-methylisoborneol (MIB), drastically reducing unpleasant taste and odor in effluent. However, activated carbon shows limited adsorption performance for highly hazardous halogenated hydrocarbons, and the regeneration of saturated activated carbon has long failed to achieve satisfactory outcomes. New adsorbents including activated carbon fibers and porous synthetic resins are currently under research and development.

 

 

2.1 Application in Drinking Water Treatment

Rapid biological filters filled with granular activated carbon (GAC) are commonly used as secondary filtration units. Microbes attached to the surface of granular activated carbon degrade biodegradable organic matter (BOM) in water, a process also known as secondary biological activated carbon filtration. Literature has verified its reliable treatment efficiency. To cut operating costs and facilitate popularization in water plants, a dual-layer filter concept of "primary sand filtration + biological activated carbon filtration" has been proposed. The advantages of biological filters for BOM removal are as follows:

1. Reduces nutrient substrates for bacterial growth in water supply pipelines and effectively inhibits bacterial reproduction;
2. Cuts the content of organic matter that reacts with disinfectants, lowering disinfectant dosage and stabilizing residual disinfectant concentration in finished water;
3. Eliminates organic precursors of disinfection by-products, reducing disinfection by-product levels in finished water;
4. Converts organic pollutants into inorganic end products;
5. Residues of aged and detached biofilm are easier to dispose of than chemical precipitation sludge;
6. Biological treatment delivers lower operating costs than standalone activated carbon adsorption.

 

 

2.2 Deodorization of Wastewater by Activated Carbon

Activated carbon adsorption columns can remove a wide range of malodorous substances. Malodorous components such as acetaldehyde and indole are eliminated via physical adsorption, while hydrogen sulfide (H₂S), mercaptans and other sulfur-containing compounds are removed through oxidation reactions on the carbon surface followed by secondary adsorption. Activated carbon performs excellently for hydrogen sulfide and sulfur-containing compounds yet shows limited removal effect on ammonia and nitrogen-containing organics.

Before reaching adsorption saturation, activated carbon maintains a relatively stable removal rate for malodorous substances and exhibits strong resistance to shock loads of gas flow, granting it wide adaptability. Nevertheless, frequent regeneration of the adsorbent is impractical, so the concentration of incoming waste gas must be controlled at a low level.

 

2.3 Decolorization of Printing and Dyeing Wastewater by Activated Carbon

Activated carbon adsorption delivers remarkable treatment performance for complex dye manufacturing wastewater. The standard process flow is listed below:

1. After anaerobic pretreatment followed by coagulation and sedimentation, the COD removal rate reaches approximately 83% and the decolorization rate hits 99.3%, creating favorable inlet conditions for subsequent activated carbon adsorption.
2. Activated carbon possesses superior adsorption capacity. The optimal adsorption parameters for this process are: pH=4, powdered activated carbon dosage of 20 g/L, continuous stirring during adsorption, and adsorption duration of 40 min. After adsorption, the CODCr of effluent drops below 150 mg/L, complying with national discharge standards.
3. Two regeneration methods, alkaline elution and Fenton reagent oxidation, can effectively restore the adsorption performance of saturated activated carbon. After regeneration, the regenerated carbon still achieves a COD removal rate above 77% and a decolorization rate exceeding 97%.

 

Benefiting from extensive raw material sources, large surface energy, powerful adsorption capacity and convenient recyclability, activated carbon adsorption technology has achieved mature development and wide application in wastewater treatment. Our company provides a full series of activated carbon products specially developed for water treatment. Please feel free to contact us for inquiries if you have any interest!

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