How much COD can one ton of activated carbon adsorb?
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Granular activated carbon
Granular activated carbon is often used in the continuous treatment system of industrial wastewater due to its good stability and easy regeneration.
Adsorption capacity: The dynamic adsorption capacity of granular activated carbon is generally around 10%.
Adsorption capacity: One ton of granular activated carbon can adsorb approximately 0.1 ton of COD.
2. Powdered activated carbon
Powdered activated carbon is widely used in PACT systems due to its large specific surface area and fast adsorption rate.
Adsorption capacity: The dynamic adsorption capacity of powdered activated carbon is usually between 10% and 35%.
Adsorption capacity: One ton of powdered activated carbon can adsorb and remove 0.1 to 0.35 tons of COD. The specific value depends on the water quality conditions and process parameters.
Ii. Key Factors Affecting the COD Adsorption Capacity of Activated Carbon
The adsorption effect of activated carbon on COD is restricted by various internal and external factors. The following are the main influencing factors:
1. Indicators of activated carbon
Iodine value: The iodine value is an important indicator for measuring the adsorption capacity of activated carbon. Generally, the higher the iodine value, the stronger the ability to adsorb COD.
Pore size structure: The ratio of micropores to mesopores determines the adsorption effect of activated carbon on pollutants of different molecular weights.
2. Wastewater quality
COD concentration: The higher the initial concentration of COD in the raw water, the lower the adsorption efficiency per unit mass of activated carbon.
Impurity components: Wastewater containing oil and complex organic matter will occupy the adsorption sites of activated carbon, reducing its ability to adsorb COD.
3. Adsorption conditions
pH value: The optimal adsorption pH is usually in weakly acidic conditions. Extreme pH can weaken the adsorption capacity of activated carbon.
Temperature: A moderate increase in temperature can enhance the adsorption efficiency, but excessively high temperatures may lead to a decline in adsorption performance.
Stirring intensity: Moderate stirring helps enhance the contact between activated carbon and wastewater, thereby improving the adsorption efficiency.
Iii. Variation Law of Adsorption Efficiency
The diminishing effect of unit adsorption efficiency
With the increase of the dosage of activated carbon, the removal rate of COD will gradually improve, but the adsorption efficiency per unit mass of activated carbon shows a decreasing trend. This phenomenon stems from:
The pores of activated carbon are gradually occupied, and the adsorption capacity of the remaining pores for COD weakens.
The remaining COD concentration in the wastewater gradually decreases, and the adsorption driving force reduces (activated carbon cannot adsorb COD to 0mg/L).
2. Applicable COD concentration range
The adsorption capacity of activated carbon is suitable for wastewater with a COD concentration below 600 mg/L. When the COD concentration is too high, relying solely on activated carbon is difficult to achieve the ideal removal effect. Usually, it is necessary to combine other processes (such as coagulation sedimentation, biological degradation, etc.).
Iv. Dosage and Effect Analysis in Practical Applications
The following takes the common coal-based powdered activated carbon (iodine value 800 mg/g) as an example to analyze its practical application under different water quality conditions:
The initial COD concentration is ≤ 400 mg/L
Dosage: The dosage concentration of powdered activated carbon is 400-600 ppm.
Treatment effect: After treatment, the COD of the effluent can be reduced to below 200 mg/L.
The initial concentration of COD is 400 to 600 mg/L
Dosage: It should be appropriately increased to 600-800 ppm.
Treatment effect: The COD of the effluent can generally be reduced to below 300 mg/L.
3. High-concentration wastewater (COD > 1000 mg/L
Suggested process: Adopt a combined process of "pretreatment + activated carbon adsorption". Pretreatment is used to reduce the COD concentration to a range suitable for activated carbon adsorption.
V. How to Optimize the Adsorption Effect of Activated Carbon
To fully leverage the adsorption performance of Shufang activated carbon and enhance the COD removal efficiency, the following aspects can be considered:
1. Choose the type of activated carbon reasonably
Select granular or powdered activated carbon based on the characteristics of the wastewater. For instance, granular activated carbon is suitable for continuous treatment systems, while powdered activated carbon is more appropriate for intermittent treatment or in combination with other processes.
2. Control the dosage
Adjust the dosage according to the water quality and treatment goals to avoid excessive dosage, which may lead to resource waste or incomplete adsorption.
3. Replace or regenerate the activated carbon in a timely manner
The adsorption performance of activated carbon gradually declines with the extension of usage time, so it needs to be replaced or regenerated regularly to maintain the treatment effect.
4. Application of combined processes
For high-concentration COD wastewater, a combined process of "activated carbon + biochemical treatment" or "activated carbon + physicochemical treatment" can be adopted to enhance the overall removal efficiency.
Vi. Comprehensive Analysis
The amount of COD that one ton of activated carbon can adsorb depends on the combined effect of multiple factors. It is best to conduct experiments to test the optimal dosage before adding it. Selecting the type of activated carbon, optimizing the treatment process and reasonably controlling the dosage can significantly improve the removal effect of COD. It can also achieve the best economic solution for the wastewater treatment of enterprises.
