Updated: July 2002

1. Outline of the Unit

Sewage treatment plants use large volumes of activated carbon as a deodorizer. However, since replacing carbon results in considerable maintenance and management costs, the development of activated carbon, which readily adsorbs sulfur odors (hydrogen sulfide, methylmercaptan, etc.), the main components of odors generated at sewage treatment plants, is much desired.
Iodic acid activated carbon is created by impregnating activated carbon (palm carbon) with iodic acid (HIO3). The strong oxidation capacity of iodic acid contributes to oxidation of hydrogen sulfide. The decomposed products are adsorbed to the activated carbon.

2. Features

2-1 Effective for composite odors

One Iodic acid activated carbon is sufficient for handling composite odors (see Figure 1), which makes maintenance and management easier. When two layers are stacked, the first layer can be used until it reaches the adsorption equilibrium (see Figure 2). Further, if Iodic acid activated carbon is incorporated in the design of the unit, a compact unit can be created.

2-2 Strong adsorption capability because of strong oxidation capability

Compared to standard impregnated carbon for acid components, Iodic acid activated carbon can adsorb almost twice the hydrogen sulfide, which is the main component of sewage odors.

2-3 Possible introduction to existing activated carbon towers

The handling of Iodic acid activated carbon is the same as that of standard activated carbon, so activated carbon used in existing activated carbon towers can be replaced with Iodic acid activated carbon. Adsorption capability can be improved by simply replacing this activated carbon. Iodic acid activated carbon is also effective at sewage treatment plants where there are problems with odors in excess of those planned for by improving adsorption capability.

3. Performance

According to data from tests utilizing the actual gas of a sewage treatment plant, the adsorption capability (g-adsorption volume/g-activated carbon×100) for hydrogen sulfide is 25 wt% or more and the adsorption capability (g-adsorption volume/g-activated carbon×100) for methylmercaptan is 22 wt% or more. Figure 3 shows a breakthrough curve for hydrogen sulfide using standard gas.

4. Fields of Application and Target Waste

Iodic acid activated carbon is suitable for odors generated during water treatment and odors in pumping areas with high concentrations of hydrogen sulfide and methylmercaptan. Further, Iodic acid activated carbon, which can adsorb almost twice as much hydrogen sulfide as conventional activated carbon, is effective for deodorizing outside of the scope of biological deodorizing for economic reasons, as well as for deodorizing odors generated during sludge treatments in which it is difficult to treat with conventional activated carbon because of high concentrations of hydrogen sulfide.

Figure 1

Figure 2 Adsorption of the activated carbon layer

Figure 3 Breakthrough curve for hydrogen sulfide