Public concern over odours from sewage treatment facilities have been increasingly significantly in Brazil in recent years due to urban developments around existing plants or construction of new ones. The city of Sorocaba is an example where the expansion of the sewage collection and treatment system has increased and consequently more people have been exposed to bad odours. Due to this scenario, it was necessary to find a solution for this new challenge, but this is no easy task as people′s response to odours is subjective. In this case, odours must be quantified first in order to be controlled. An electronic sensor (‘nose’) of H2S (hydrogen sulfide) was installed at one selected pumping station and after one month of monitoring H2S levels some chemical products were tested in order to minimize bad odours. Best results were achieved using an iron salt blend (FeII and FeIII) directly to the sewage flow at 30 mg/L (as Fe), which reduced by 83% the H2S levels in the air. Such reduction was adequate for mitigating odour complaints regarding that pumping station.

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