When the dosage of powdered activated carbon is below 20 mg/L, the effluent tends to have a stronger odor. This occurs because organic matter in the water occupies the adsorption sites on the activated carbon, preventing the removal of odor-causing substances. Additionally, the negative charge of the powdered activated carbon can interfere with coagulation, especially at lower dosages. As a result, turbidity may increase, leading to poorer coagulation and higher odor levels in the treated water.
As the dosage increases from 20 mg/L to 50 mg/L, more adsorption sites become available, allowing the remaining odor compounds to be effectively removed, which gradually lowers the odor value of the effluent. However, beyond this point, further increases in dosage do not significantly improve odor removal, as the adsorption capacity reaches saturation.
When potassium permanganate is used in combination with powdered activated carbon, the results are even more promising. At a fixed dose of 0.5 mg/L of potassium permanganate, when the powdered activated carbon dosage is 20 mg/L, the effluent odor is rated at 25. Increasing the dosage to 40 mg/L reduces the odor to 5, with no detectable smell, showing a much better deodorization effect compared to using either potassium permanganate or activated carbon alone.
Under the condition that the effluent odor threshold remains below 10, the combination of both chemicals can reduce the required amount of powdered activated carbon by approximately 20% compared to using activated carbon alone. This makes the process more cost-effective and efficient.
In cases where the raw water has a high odor threshold (greater than 90), the dosage of powdered activated carbon must be increased to 40 mg/L to ensure the effluent odor threshold drops to 7, achieving a clean and odor-free result that meets national drinking water quality standards.
In real-world applications, factors such as filtration efficiency and economic considerations often lead to a reduction in the dosage of powdered activated carbon. Filters can remove some odorous compounds, reducing the need for higher doses of activated carbon while still maintaining acceptable water quality.
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