Activated carbon has a huge specific surface area, high porosity, and good physical and chemical properties. Its internal pore structure is well-developed, and it has strong adsorption capacity for molecules. Since its birth, activated carbon has been widely used in the field of pollution control. It can be used for treating domestic sewage, organic wastewater, and industrial flue gas, and It is also commonly used in industries such as solvent recovery, food and beverage purification, air purification, environmental protection, pharmaceuticals, chemical engineering, biotechnology, nanomaterials, and high-efficiency catalysts.
Activated carbon saturated with adsorption will lose its adsorption capacity and become waste activated carbon. If the waste activated carbon is not properly treated, it will result in resource waste and secondary pollution, greatly limiting the application of activated carbon. Therefore, the regeneration technology of activated carbon to reactivate waste activated carbon has important environmental and economic benefits. Through continuous research, various activated carbon regeneration technologies covering physical, chemical, and biological principles have become increasingly mature. These activated carbon regeneration methods have their own characteristics. This article will introduce 9 activated carbon regeneration methods in recent years and compare their advantages and disadvantages.
What Is Activated Carbon Regeneration?
Activated carbon regeneration, or activated carbon reactivation, refers to the use of physical, chemical, or biochemical methods to restore the adsorption performance of saturated activated carbon that can adsorb various pollutants without damaging its original structure, in order to achieve the goal of being reused in the adsorption process. Generally, the following methods are used to disrupt its adsorption equilibrium state and reactivate waste carbon: changing the chemical properties of the adsorbate; Extract with solvents with strong affinity for adsorbates; Replace the adsorbate with a substance that has a higher affinity for activated carbon than the adsorbate, and then desorb the replaced substance; Decompose or oxidize the adsorbate; Reduce solute concentration or pressure in the solvent; Externally heated to high temperature to change the equilibrium conditions.
Activated Carbon Regeneration Methods
Thermal Regeneration Method
The thermal regeneration method is currently the most widely used and mature activated carbon regeneration method in the industry, with the characteristics of high regeneration efficiency and wide application range. The thermal regeneration method is to desorb the adsorbate in the saturated activated carbon under high-temperature conditions, so as to open the originally blocked pores of the activated carbon and restore its adsorption performance. The thermal regeneration process of activated carbon is generally divided into three stages: drying, pyrolysis, and activation. Commonly used equipment includes rotary kilns and multiple hearth furnaces (MHF). Thermal regeneration can decompose various adsorbates, demonstrating good universal performance, and the regeneration is thorough without producing any waste liquid.
The activated carbon regeneration solution provided by GEMCO Energy mainly adopts the thermal regeneration method. The direct heating rotary kiln technology designed by the company for the field of activated carbon regeneration is mature, easy to operate, scientifically designed, and environmentally friendly. It can be used for the regeneration and activation of various granular, powdery, and columnar activated carbons.
Biological Regeneration Method
The biological regeneration method utilizes microorganisms that proliferate on the surface of activated carbon to degrade the adsorbates on the carbon, oxidizing and breaking them down into carbon dioxide and water, thereby achieving the regeneration of activated carbon. This method of using microbial degradation to achieve desorption and regeneration of activated carbon offers unique advantages such as simplicity of operation, low cost, and low energy consumption, making it irreplaceable by other regeneration methods. The biological regeneration process includes ex-situ biological regeneration and in-situ biological regeneration (which includes biologically activated carbon treatment and fixed-bed reactor biological regeneration processes).
Ex-situ biological regeneration refers to adding saturated adsorbed activated carbon into a regeneration bacterial solution for desorption and regeneration. When microorganisms are present, the substances desorbed from the activated carbon into the liquid phase are continuously consumed by the metabolic processes of the microorganisms, allowing the treated substances to keep transferring from the activated carbon to the liquid phase. In recent years, many researchers have used the surface of activated carbon as a site for microbial proliferation. As activated carbon adsorbs organic matter from water, microorganisms simultaneously perform biodegradation. This synergistic water treatment technology, combined with the relatively simple adsorption function of activated carbon, can extend the usage cycle of the activated carbon.
Wet Oxidation Regeneration Method
The wet oxidation regeneration method involves using air or pure oxygen as an oxidizing agent to oxidize and decompose the organic matter adsorbed on activated carbon in a liquid phase under high temperature and high pressure conditions, thereby restoring its adsorption capacity. By adding an appropriate catalyst to the wet oxidation system, the decomposition temperature of the organic adsorbates on the activated carbon can be significantly reduced, effectively achieving low-temperature regeneration and reducing energy consumption.
Chemical Reagent Regeneration Method
The chemical reagent regeneration method can be divided into inorganic reagent regeneration and organic solvent extraction regeneration. Inorganic reagent regeneration uses inorganic acids or bases to alter the pH of the solution for desorption. This process does not require additional regeneration equipment, making the investment relatively low and the process simple. However, the regenerated activated carbon can only be partially restored, making it difficult to achieve complete regeneration. Organic solvent extraction regeneration involves using solvents to extract the adsorbed organic matter from the activated carbon, thereby restoring its adsorption capacity. This method allows for the recovery of useful adsorbates, but the regeneration efficiency is low, and it can easily lead to micropore blockage.
Microwave Radiation Regeneration Method
Microwaves are electromagnetic waves with frequencies between infrared and radio waves, ranging from 0.3 to 300 GHz (wavelengths from 1 mm to 1 m). The frequencies used in heating technology are fixed at 2450 MHz or 900 MHz. Microwave radiation regeneration of activated carbon is an emerging method in which organic matter is desorbed, carbonized, and activated under high-temperature conditions, thereby restoring the adsorption capacity of the activated carbon.
Microwave heating differs from traditional heating methods by providing uniform and rapid heating and the ability to apply energy locally, which significantly improves processing efficiency and reduces energy consumption. An orthogonal experiment with three factors and four levels was conducted to explore the relationship between the regeneration effect of activated carbon and factors such as microwave power, irradiation time, and the amount of adsorption by the activated carbon. The results showed that with low microwave power and short irradiation time, the iodine value did not change significantly; however, with high microwave power and prolonged irradiation time, there was evidence of carbon loss in the activated carbon.
Ultrasonic Regeneration Method
The ultrasonic regeneration method works by generating high-energy “cavitation bubbles” in the regeneration liquid. These bubbles expand in the solution and then collapse into smaller bubbles, producing high-pressure shock waves that act on the surface of the activated carbon, causing the desorption of adsorbates. Experiments have shown that ultrasonic regeneration is feasible for treating powdered activated carbon saturated with adsorbates from coke plant wastewater. Using an ultrasonic generator as the regeneration equipment, experiments were conducted to study the effects of ultrasonic duration, temperature of the regeneration liquid, and the type of regeneration liquid on the ultrasonic regeneration of phenol-saturated activated carbon. The optimal conditions were determined to be a 20-minute ultrasonic treatment at 30°C with a 0.25 mol·L⁻¹ sodium hydroxide solution, significantly improving the regeneration efficiency.
Electrochemical Regeneration Method
The electrochemical regeneration method is primarily used for regenerating granular activated carbon. This method involves placing the spent activated carbon between two main electrodes in an electrolyte solution and applying a direct current electric field. Under the influence of the electric field, the activated carbon becomes polarized, forming a micro-electrolytic cell. Regeneration occurs partly through desorption caused by electrophoretic forces and partly through the oxidation and decomposition of adsorbates by electrolysis products or their transformation into flocculent substances.
Supercritical Fluid Regeneration Method
A supercritical fluid is a state of matter where a substance’s temperature and pressure are above its critical temperature and critical pressure. Due to the unique properties of supercritical fluids, such as high density, low surface tension, high solubility, and excellent diffusion, this method has garnered increasing attention from researchers. Currently, carbon dioxide is the most commonly used supercritical fluid, and studies have shown that it is effective in regenerating activated carbon. Even after multiple regeneration cycles, the activated carbon maintains a high adsorption capacity. However, the broad applicability of this method remains unproven. The theoretical foundation is not deeply established, and the lack of fundamental data limits its research to experimental studies, with no applications at pilot or industrial scales.
Photocatalytic Regeneration Method
The photocatalytic regeneration method involves using a photocatalyst that, under light within a specific wavelength range, generates reactive species with strong oxidizing abilities. These reactive species oxidize and decompose the organic matter adsorbed on activated carbon into carbon dioxide, water, and other inorganic substances, thereby restoring the adsorption capacity of the activated carbon. TiO₂ photocatalysis technology, which has rapidly developed in recent years, is a promising, environmentally friendly advanced oxidation technology. If photocatalytic technology can be applied to activated carbon regeneration, it would offer a novel regeneration method. This approach enhances the purification capability of activated carbon, accelerates the photocatalytic reaction rate, and allows the adsorption of reaction by-products, achieving complete purification of pollutants.
Activated Carbon Regeneration Methods Comparison
| Method | Advantages | Disadvantages |
| Thermal Regeneration | High regeneration efficiency, short regeneration time, universal energy source, no waste generation, high regeneration depth, good selectivity for adsorbate types | Significant damage to the pore structure and surface properties of activated carbon during regeneration, reduced adsorption capacity. Complex equipment, high costs. |
| Biological Regeneration | Simple operation, low cost, less environmental pollution | Long regeneration time, efficiency affected by water and temperature. Limited to specific microorganisms, regeneration efficiency is lower. |
| Wet Oxidation Regeneration | Suitable for a wide range of objects, effective for adsorbates difficult to regenerate, stable regeneration efficiency, does not require additional external heating after regeneration starts | Difficult to break down certain organics, possible production of more toxic intermediates. Equipment is prone to corrosion, requires high standards. |
| Chemical Regeneration | Minimal damage to activated carbon, can recover adsorbed substances, high recovery rate | Potential for secondary pollution during processing, incomplete regeneration, and easy to cause pollution. Some chemicals may corrode activated carbon, damaging its structure. |
| Microwave Regeneration | Uniform heating, high efficiency in temperature control, low energy consumption, effective in removing adsorbates, good regeneration efficiency | Uncertainty regarding the production of other toxic intermediates during regeneration, lack of professional microwave regeneration equipment. |
| Ultrasonic Regeneration | Small energy consumption, easy to set up, minimal damage to activated carbon, suitable for localized regeneration | Small pore size makes it difficult for regeneration efficiency, low overall regeneration efficiency. |
| Electrochemical Regeneration | High regeneration efficiency, minimal pollution, capable of multiple regenerations | High energy consumption, not yet industrially feasible. |
| Supercritical Fluid Regeneration | Does not change the physical properties of adsorbed substances, minimal damage to activated carbon, high recovery rate | The most common supercritical fluids are only effective for CO2, regeneration efficiency is affected by process conditions. Currently only in the research phase. |
| Photocatalytic Regeneration | Simple regeneration process, easy operation, low pollution, energy-efficient | Long regeneration time, low efficiency, stringent requirements for light conditions. |