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What are the operational precautions for activated carbon filters?
Release Date:
2022-11-21
In water quality pretreatment systems, activated carbon filters adsorb residual chlorine that cannot be removed by upstream filtration, thereby preventing oxidative degradation of reverse osmosis membranes. They also adsorb trace organic compounds and other contaminants that may have leaked during earlier stages of the process, exhibiting significant adsorption and removal capabilities for odors, colloids, colorants, heavy metal ions, and chemical oxygen demand (COD) in the water. So, what are the operational precautions for activated carbon filters?
In water quality pretreatment systems, activated carbon filters adsorb residual chlorine that cannot be removed by upstream filtration, thereby preventing oxidative degradation of the reverse osmosis membrane. They also adsorb trace organic compounds and other contaminants that may have leaked during earlier stages of the process, exhibiting significant removal efficiency for odors, colloids, colorants, heavy metal ions, and chemical oxygen demand (COD) in the water. So, what are the operational precautions for activated carbon filters?
What are the operational precautions for activated carbon filters?
In practical operation, attention should be paid to factors such as the turbidity of the influent water, the backwash cycle, and the backwash intensity.
1. Turbidity of feed water
High turbidity in the influent water can introduce excessive particulate matter into the activated carbon filter bed, where these impurities become trapped, clogging the pores and surface of the activated carbon and thereby impairing its adsorption performance. Prolonged operation allows these retained substances to accumulate between the layers of the activated carbon filter, forming a stubborn sludge film that cannot be removed by backwashing, which accelerates the aging of the activated carbon. Therefore, the turbidity of the water entering the activated carbon filter should be maintained below 5 mg/L to ensure normal operation.
2. Backwash Cycle
The length of the backwash cycle is a primary factor affecting filtration performance. A cycle that is too short results in excessive backwash water consumption, while a cycle that is too long can compromise the adsorption efficiency of the activated carbon. In general, when the influent turbidity is less than 5 mg/L, backwashing should be performed every 4 to 5 days.
3. Backwash Intensity
During backwashing of an activated carbon filter, the expansion ratio of the filter bed has a significant impact on the thoroughness of the wash. If the expansion ratio is too low, the lower layer of activated carbon will not become suspended, and the surface of the carbon cannot be adequately cleaned; if the expansion ratio is too high, carbon fines are prone to be carried away. In general, the expansion ratio is maintained within the range of 40% to 50%.
4. Backwash Time
Typically, when the expansion ratio of the filter bed is 40%–50% and the backwash intensity is 13–15 L/(m²·s), the backwashing time for an activated carbon filter is 8–10 minutes.
What is the adsorption principle of activated carbon?
1. Activated carbon, with its unique pore structure, is a microcrystalline carbon material primarily made from carbon-containing feedstocks. It appears black, boasts a highly developed internal pore network, a large specific surface area, and strong adsorption capacity. The material contains numerous invisible pores; when unfolded, the total surface area of the pores in just 1 gram of activated carbon can reach 800–1,500 square meters, making it exceptionally well suited for specialized applications. In other words, within a single activated-carbon particle of typical crystallite size, the internal surface area of the micropores can be comparable to the floor space of a living room. This highly developed microporous structure, akin to the capillaries in the human body, endows activated carbon with outstanding adsorption performance.
2. The attractive forces between molecules are also known as “van der Waals forces.” Molecular motion is influenced by temperature and the material, but molecules are always in motion within a microenvironment. Due to these intermolecular attractions, when certain molecules become trapped in the micropores of activated carbon and enter those pores, they attract additional molecules until the pores are completely filled.
Keywords:
Activated carbon filter
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