How it works
The Odab is designed to allow the manhole to safely vent treated odourless air, whilst capturing the hydrogen sulphide from that air through absorption in a replaceable activated carbon cartridge, which can be safely disposed of at a landfill once saturated.
Treating Peak Flow
Some authorities have tried suspending an absorbing media, such as an activated carbon bed in the chamber. As soon as the chamber lid is closed, the top layer of carbon media is exposed to H2S gas continuously and is saturated in a matter of days, rendering the media and its ability to remove odour completely useless.
The concept of the bellows and associated valve arrangements is to ensure that ONLY peak H2S flow is treated. This concept has been well-proven in the US by multiple studies on the sister product: the Manhole Odor Eliminator MOE.
One such independent study conducted in 2012 by the University of the Pacific, Stockton California, inserted a H2S meter both above and below the pan in a chamber, measuring values at 5s intervals of H2S in the chamber above and below the manhole cover. Results over 96 hours show the effectiveness of the bellows valve system, the media bed is only exposed to approximately 1/30th of the mean average H2S in the chamber, preserving the media to only treat peak gas flows.