Key Takeaways & Executive Findings
- •• • Thermal regeneration technologies (multi-hearth furnace, rotary kiln, superheated steam, microwave, solar) achieve desorption efficiencies up to 90% at temperatures 800–900°C, but each has trade-offs in energy consumption and carbon loss (e.g., 5–10% per cycle). • • Regeneration efficiency is critically dependent on temperature and atmosphere: inert gas (N2) at 850°C restores >95% of original adsorption capacity, while oxidizing atmospheres (air) can cause 10–15% carbon burn-off, reducing yield. • • Purge gas flow rate significantly impacts pollutant removal: optimal flow rates (e.g., 200–400 mL/min) enhance desorption kinetics, but excessive rates (>600 mL/min) lead to thermal gradients and incomplete regeneration. • • Combined regeneration technologies (e.g., ultrasonic-thermal, microwave-steam) show synergistic effects, improving regeneration efficiency by 15–20% compared to single methods, while reducing energy consumption by up to 30%.
Abstract
Activated carbon, characterized by its extensive pore structure, high specific surface area, and superior adsorption capacity, is widely employed in advanced water treatment. However, upon reaching adsorption saturation, its efficacy diminishes, necessitating replacement or regeneration. Thermal regeneration stands out due to its high desorption efficiency, simple equipment requirements, and low energy consumption, making it the predominant industrial method. Despite its prevalence, systematic investigations into the underlying reaction mechanisms and the influence of operational parameters remain insufficient. This review comprehensively examines common thermal regeneration technologies for saturated activated carbon, including multi-hearth furnaces, rotary kilns, superheated steam, microwave, and solar regeneration. It delineates the fundamental principles, process flows, advantages, disadvantages, and current research status of each method. The desorption and reaction mechanisms of pollutants within activated carbon pores during thermal regeneration are discussed in detail, along with the effects of critical conditions such as temperature, atmosphere, and purge gas flow rate on pollutant removal efficiency. Furthermore, the relationship between activated carbon performance parameters and regeneration efficiency is analyzed, and innovations based on conventional thermal regeneration, as well as integration with emerging technologies, are explored. Finally, the challenges facing thermal regeneration are summarized, and future research priorities are proposed, focusing on the treatment of waste gas and liquid byproducts, technology integration, and enhancement of overall regeneration performance. This review aims to provide a scientific foundation for the sustainable recycling of activated carbon in industrial applications.
1. Introduction
The escalating discharge of industrial and municipal wastewater, driven by rapid industrialization and population growth, poses severe threats to ecological safety. Conventional water treatment processes often require advanced polishing steps to meet stringent discharge standards. Among these, activated carbon adsorption is widely adopted due to its high porosity, large specific surface area, and absence of toxic byproduct formation. However, the finite adsorption capacity of activated carbon necessitates periodic replacement once saturation is reached, leading to significant operational costs and environmental burdens associated with disposal. Thermal regeneration has emerged as the most industrially prevalent solution, offering high desorption efficiency, simple equipment, and relatively low energy consumption. Despite its widespread use, the scientific literature lacks a comprehensive synthesis of the underlying reaction mechanisms and the quantitative influence of key operational parameters, such as temperature, atmosphere, and purge gas flow rate, on regeneration performance. This gap hinders the optimization of regeneration protocols and the development of more efficient, sustainable technologies.
This review addresses this bottleneck by systematically analyzing the state-of-the-art in thermal regeneration technologies, including conventional furnaces and emerging methods like microwave and solar regeneration. It critically evaluates the desorption and reaction mechanisms of pollutants within the porous structure of activated carbon, and correlates regeneration efficiency with material performance parameters. Furthermore, it explores innovative combinations of thermal regeneration with other techniques, such as ultrasonic and steam activation, to overcome the limitations of individual methods. By synthesizing current knowledge and identifying key challenges—particularly the treatment of secondary waste streams and the need for integrated approaches—this work provides a strategic roadmap for advancing the circular economy of activated carbon in industrial water treatment, offering both immediate operational insights and long-term research directions.
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ZHOU Yang, HUA Yinfeng, YIN Hang, YAN Lili, RAO Pinhua (2026). Research Progress on Thermal Regeneration Technology for Saturated Activated Carbon. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025042802
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Frequently Asked Questions
What are the primary mechanisms of pollutant desorption and reaction during thermal regeneration of saturated activated carbon, and how do they vary with temperature?
Desorption mechanisms include volatilization, thermal decomposition, and gasification. At temperatures below 300°C, volatile organic compounds (VOCs) primarily desorb via evaporation. Between 300–600°C, chemisorbed species undergo thermal cracking, releasing smaller molecules. Above 600°C, carbon gasification with steam or CO2 occurs, which can restore porosity but also cause carbon loss. For example, studies show that at 850°C in an inert atmosphere, up to 95% of adsorbed phenol is desorbed, while in air, oxidation leads to 10–15% carbon burn-off.
How does the choice of regeneration atmosphere (inert vs. oxidizing) affect the structural integrity and adsorption capacity of regenerated activated carbon?
Inert atmospheres (N2, Ar) minimize carbon oxidation, preserving pore structure and surface area. Regeneration under N2 at 850°C typically restores >90% of the original adsorption capacity. In contrast, oxidizing atmospheres (air, O2) can introduce oxygen functional groups, altering surface chemistry and potentially reducing adsorption capacity for certain pollutants. Additionally, oxidation can lead to pore widening and increased ash content, reducing mechanical strength. For instance, air regeneration at 500°C resulted in a 20% loss in BET surface area due to carbon burn-off.
What are the scalability bottlenecks of microwave and solar thermal regeneration compared to conventional multi-hearth furnaces?
Microwave regeneration offers rapid and volumetric heating, reducing energy consumption by up to 50% and processing time by 70% compared to conventional furnaces. However, scalability is limited by the penetration depth of microwaves, which is only a few centimeters, making uniform heating of large batches challenging. Solar regeneration, while sustainable, is intermittent and requires concentrated solar power systems, which have high capital costs and are geographically dependent. Conventional multi-hearth furnaces, though energy-intensive, offer continuous operation and high throughput, making them more suitable for industrial-scale applications. Hybrid systems, such as microwave-assisted steam regeneration, are being explored to combine advantages.
What is the impact of purge gas flow rate on the efficiency of thermal regeneration, and what is the optimal range?
Purge gas flow rate influences the removal of desorbed pollutants and the heat transfer within the reactor. Insufficient flow rates lead to re-adsorption of volatilized species, reducing regeneration efficiency. Excessive flow rates can cause thermal gradients and incomplete heating, as well as increased energy costs. Studies indicate an optimal flow rate of 200–400 mL/min for lab-scale reactors, achieving >95% desorption of toluene at 800°C. At flow rates above 600 mL/min, efficiency plateaus or slightly decreases due to reduced residence time and potential channeling.
How do combined regeneration technologies (e.g., ultrasonic-thermal, microwave-steam) improve performance over single methods, and what are the trade-offs?
Combined methods leverage synergistic effects to enhance desorption and reduce energy consumption. For example, ultrasonic-thermal regeneration uses ultrasonic waves to disrupt the boundary layer and enhance mass transfer, allowing lower thermal temperatures (e.g., 600°C vs. 850°C) to achieve similar regeneration efficiency, reducing energy use by up to 30%. Microwave-steam regeneration combines rapid volumetric heating with steam gasification, which can restore pore structure more effectively, achieving regeneration efficiencies of 95% with 20% less carbon loss compared to conventional steam regeneration. However, these hybrid systems require more complex equipment and control, increasing capital and maintenance costs, and may not be economically viable for all applications.
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