Is H2S a suitable process indicator for odour abatement performance of sewer odours?

Odour abatement units are typically designed and maintained on H2S concentrations, but operational failures are reported in terms of overall odour removal, suggesting a wide range of malodorous compounds emitted from sewers that may not be efficiently removed by existing odour abatement processes. Towards providing greater insight into this issue, several activated carbon filters and biofilters treating odorous emissions from sewer systems in Sydney (Australia) were monitored by collecting and analysing gas samples before and after treatment. The monitoring studies were conducted by both olfactometric measurements and gas-chromatography- based chemical analysis. Single H2S assessment often failed to indicate the odour abatement performance for treatment systems in the abatement units studied, particularly when the incoming H2S concentrations were in the sub-ppm range (i.e. below H2S odour threshold). Chemical analysis indicated that some non-H2S odorous compounds were not removed efficiently during odour treatment. Additionally, when odour eliminations were correlated with the removal of individual compounds (Pearson's correlations) it was observed that the correlation (with a coefficient of 0.79) was best when the overall removal of all the measured odorous compounds that exceeded their odour threshold values was used for the analysis. These findings may help to further advance the design and operation of odour abatement processes to address the treatment of sewer odour emissions.