The generation of compounds that generate unpleasant odours is an undesired consequence of diverse industrial processes. In the case of wastewater plants this happens with the hydrogen sulfide gas (H2S). The emission of the referred gas (in very low concentrations) generates an unpleasant odour that affects those people working at wastewater plants and, depending on the existing atmospheric conditions, it may also affect near populated areas.

In the case of wastewater plants, the emission of hydrogen sulfide gas in concentrations of 1ppm or less generates an odour that is sensed by most of the people.

Existing methods for controlling the odour propagation from a wastewater plant, focus in controlling the emission. They vary from acting upon the industrial process itself for avoiding the emission of the compound responsible for odour, to covering all points of connection between the contaminant and the atmosphere, thus avoiding its emission.

These alternatives are not the only feasible ones and usually they do not result a cost effective solution. In this sense an interesting application field is opened by acting not upon the emission but acting upon the propagation of odour from the wastewater plant to the neighbouring areas. This section introduces the application of the SIS Technology to the control of odour propagation in the terms referred above. This introduction focuses in the case of wastewater plants (probably the most usual case of application), but the application of the SIS Technology to other cases is possible and should be specifically examined.