The application of activated carbon in the treatment of domestic wastewater

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Activated carbon is an adsorbent widely used in domestic wastewater treatment, and it comes in two forms: granular and powdered. Powdered activated carbon has a long history in wastewater treatment both domestically and internationally. The raw materials used for producing activated carbon can be found everywhere, including fruit peels, wood, waste materials, and so on. Among these, fruit peels are the best choice as raw materials for activated carbon; however, due to constraints related to their availability, storage, and collection, their price is quite high. At present, our country has been exploring various methods to use waste materials such as garbage and scrap as raw materials for producing activated carbon, and has already utilized waste materials such as walnut shells, bamboo, and cigarette butts as raw materials. Below, the application characteristics and advantages of activated carbon in domestic wastewater treatment are analyzed and studied from several aspects. 2. The importance of activated carbon technology in treating domestic wastewater: With the rapid development of China’s economy, the availability of water resources is becoming increasingly out of balance with population growth. As cities develop, they cause environmental pollution to varying degrees, with water resource pollution being the most severe. The traditional methods currently used in our country, such as chemical processing and physical treatment methods, have limitations to varying degrees when applied in practice. The biological activated carbon adsorption and purification technology is easy to operate, exhibits excellent performance, and has promising prospects for development. In recent years, the pace of urban construction in our country has accelerated, which has led to the direct discharge of large amounts of untreated domestic wastewater, thereby causing water pollution. According to statistics, the volume of urban domestic wastewater discharged in our country is increasing at a rate of 5% per year. Therefore, addressing domestic wastewater management is the top priority in solving environmental problems. The history of using powdered activated carbon for water purification dates back 70 years; since its first application in the United States to eliminate the unpleasant odor caused by chlorophenols, activated carbon purification has remained an effective method for removing impurities from water, and its effectiveness has been recognized by many. 3. Mechanism of action of activated carbon: The process by which activated carbon adsorbs impurities from water is quite complex, involving the combined effects of ionic attraction, molecular forces (van der Waals forces), and chemical interactions. Differences in the processing methods used to produce activated carbon can also result in variations in its adsorption capacity. The activated carbon adsorption method utilizes the porous properties of activated carbon to adsorb one or more impurities in water onto its surface, thereby removing them. Such as removing organic matter, colloidal particles, microorganisms, residual chlorine, and odors from water. Adsorption consists of two types of diffusion rates: rapid diffusion and slow diffusion. Rapid diffusion can achieve 60% to 80% of the total adsorption amount within a few hours; it is a process in which solute molecules diffuse through the large pores of the carbon structure, where there is less resistance. When solute molecules enter the smaller pores connected to these large pores, they encounter significant resistance due to the small pore sizes, resulting in slow diffusion. The adsorption capacity of activated carbon is not only related to its specific surface area but also closely tied to the pore size structure of its pores. The macropores provide pathways for solute molecules to diffuse into the micropores, thereby achieving adsorption; hence, the adsorption force on solute molecules is primarily influenced by the macropores. The organic substances present in water include not only small molecules but also various large molecules; the pores account for more than 95% of the surface area, and the amount of adsorption depends on these pores. Therefore, in the treatment of domestic wastewater, it is necessary to select appropriate activated carbon to meet the different requirements of various adsorbates. The adsorption of solute molecules is primarily driven by intermolecular forces, namely van der Waals forces. Due to the different pore diameters and distribution patterns of activated carbon, different types of activated carbon have varying adsorption capacities for different solute molecules. Physical adsorption is related to factors such as the affinity of activated carbon for solutes, the solubility of solutes, the size of solute molecules, the pore distribution of activated carbon, and its surface area. 4. Application of activated carbon purification technology in domestic wastewater treatment 4.1 Characteristics of activated carbon purification technology for treating domestic wastewater There are several types of adsorption methods using activated carbon, namely fixed-bed, contact adsorption, moving-bed, and fluidized-bed methods. Among them, powdered activated carbon employs only contact adsorption as its method of adsorption, and this is one of its characteristics. When used to treat domestic wastewater, the amount of powdered activated carbon used is increased depending on the conditions of the water quality, which yields particularly good results in cases where there are significant variations in wastewater quality. At the same time, powdered activated carbon can be added either dry or wet, depending on the requirements; wet addition can be used to address certain everyday sewage problems, while dry addition can be utilized for emergency sewage treatment. At the same time, the type of powdered activated carbon must also be determined based on the quality of the raw water, particularly the distribution of molecular weights of the organic substances present in it. In the emergency treatment of domestic wastewater, activated carbon can be added to the raw water before the sedimentation tank to ensure thorough contact and adsorption; once saturated, it can then be removed through sedimentation. Powdered activated carbon is widely used in municipal wastewater treatment in countries such as Europe and the United States. In the early 1980s, the United States used approximately 2.6×105 tons of powdered activated carbon per year for treating domestic wastewater, and this amount has been increasing over the years. Our country began to pay attention to the issues of deodorization and odor removal in water treatment in the late 1960s. Powdered activated carbon has been tried in the treatment of municipal domestic wastewater in Shanghai, Hefei, Harbin, and Guangzhou. In recent years, China has gained a deeper understanding of the research and application of powdered activated carbon. Institutions such as Harbin University of Civil Engineering and Architecture and Tongji University have conducted in-depth studies on activated carbon, achieving many practical results. Since powdered activated carbon is easy to apply, requires less investment in equipment, is inexpensive, and can adsorb solute molecules rapidly, it is more suitable for the renovation of old plants. It offers advantages such as cost savings, reduced space requirements, and strong resilience to short-term or sudden water quality contamination. 4.2 Application of biological activated carbon technology: Activated carbon plays a crucial role in the treatment of domestic wastewater due to its excellent adsorption capacity. Its unique molecular structure, as well as its comprehensive properties such as high specific surface area, resistance to strong acids and bases, and tolerance to high temperatures and pressures, have drawn much attention, and its importance in domestic wastewater treatment is increasing day by day. However, activated carbon also has a number of issues such as easy saturation in adsorption and high regeneration costs. To effectively address these problems, people combined the principle of biodegrading waste with that of activated carbon adsorption, thereby creating bioactivated carbon purification technology. Bioactivated carbon purification technology incorporates both biodegradation and activated carbon adsorption; it not only increases the saturation level of the activated carbon but also enhances its adsorption capacity, which is why it has attracted much attention. Many companies around the world have already adopted this new technology, including some enterprises in our country; those in Europe and the United States are the most prominent among them. 5. Conclusion: As urban wastewater increases year by year due to economic growth in society, activated carbon technology must also continue to be improved and innovated. In China’s current use of activated carbon purification technologies, the issue of treating domestic wastewater has been effectively addressed, and the application techniques related to activated carbon are also constantly being refined. It is hoped that this article can serve as a reference for enterprises in dealing with domestic wastewater treatment.