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A new odor control technology (Bentax) is emerging in the U.S. that conditions make-up air to a working space or odor source with ionized oxygen molecules, for reaction with hydrogen sulfide (H2S) and other odorous compounds. Bentax is the industry standard at wastewater treatment plants (WWTPs) in Switzerland and it has been demonstrated to be effective in the U.S. There are currently two small permanent installations and there are also several large scale systems where Bentax has been selected and is currently being designed in the U.S. The conductivity of air in the odorous air space is increased by passing inlet air across ionization tubes that create a measurable and controllable quantity of positive and negative ions (about 1,000 ions of each per cubic centimeter), which activate clusters of oxygen molecules. The higher energy ions react with odorous molecules in the air space before being exhausted.

Advantages of this Bentax system are that there are no chemicals required, it has very low power consumption, does not generate ozone and it is simple to operate and maintain. A critically important and unique aspect of using oxygen ionization is that it conditions incoming air not exhaust air, thus producing a safe working environment because long term, low-level exposure to H2S can cause deleterious health effects. Ionization tubes use only 50 watts of power for 5 tubes that will condition about 110-140 m3 (4,000-5,000 ft3) of air space. The tubes require cleaning every three (3) months and replacement every three (3) years. Air must be filtered for the Bentax tubes which are mounted directly in make-up air ducts and ionization is adjusted through a simple voltage regulator.

Case studies are presented for WWTPs in Switzerland that the author visited and a full scale design by the author of a system under construction at the Town Branch WWTP in Lexington, Kentucky will be presented. The Lexington-Fayette Urban County Government selected the Bentax system for a 72,000 ft3 belt filter press room that dewaters anaerobically digested sludge. The objective is to significantly reduce H2S from peak levels of 20 ppm in the room to safer working levels and to exhaust air from the room without using existing odor control scrubbers. The system is designed for 12 air changes per hour and there are 80 Bentax tubes in the make-up air plenum. A strict performance guarantee and test are included in the contract.

The information provided in this paper will assist municipalities and industries in evaluation of this odor control technology in other applications through a presentation of: 1) the theory of odor removal by ionization; 2) design criteria and costs for capital and O & M; 3) a cost comparison to other technologies such as scrubbers, carbon adsorbers and biofilters and; 4) a discussion of the best applications of the technology.

Document Type: Research Article


Publication date: 2000-01-01

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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