Choosing Impregnated Carbon for H₂S and NH₃ Removal: KOH or Iodine?

Hydrogen sulfide (H₂S) and ammonia (NH₃) are the most common odor sources at wastewater lift stations, sludge dewatering and industrial plants. Standard activated carbon offers limited capacity for these gases, so impregnated carbons are used. The right impregnation depends on the chemistry of the gas you need to remove.

For H₂S: Caustic (KOH / NaOH) Impregnation

Caustic-impregnated carbon neutralizes acidic H₂S with its alkaline surface, providing very high removal capacity. It is preferred for high and steady H₂S loads. Drawbacks: performance can drop at low humidity, the exothermic reaction requires attention to temperature/fire safety, and it usually cannot be regenerated.

For H₂S: Iodine / Catalytic Impregnation

Iodine- or catalytic-metal-impregnated carbons catalytically convert H₂S into elemental sulfur. They may not offer capacity as high as caustic, but they work over a wider humidity range, have a better safety profile, and some types offer longer life. They suit moderate H₂S levels and enclosed spaces where safety is a priority.

For NH₃ and Acidic Gases: Acidic Impregnation

Ammonia is basic; acidic impregnation (for example phosphoric or sulfuric acid) is used to capture it. The caustic carbon that is right for H₂S is wrong for NH₃ — you must match the chemistry to the character of the gas. In mixed odor streams, layered beds (successive different impregnations) are sometimes used.

How to Choose

• Target gas(es): H₂S, NH₃, mercaptans, VOCs — each requires different chemistry.
• Concentration and flow rate — determine capacity and bed size.
• Humidity and temperature — affect the caustic vs. catalytic choice.
• Safety and space constraints — catalytic can be safer in enclosed/occupied spaces.