Prioritisation of odorants emitted from sewers using odour activity values

Volatile sulfur and volatile organic compound (VSC and VOC, respectively) emissions were measured over a 3.5 year period from 21 field monitoring sites across Australia to determine their potential contribution to sewer odours and support the evaluation of odour abatement processes used to treat sewer emissions. Measured VOC concentrations were generally less than 250 μg/m(3), although some VOCs (toluene, trimethylbenzene and cymene) were present at higher concentrations. In general, sewer headspace VOCs are unlikely to be a significant contributor to sewer odours and VOC monitoring is only recommended for sites with a history of significant trade waste discharges or where odour character descriptors are typical of VOCs. A range of VSCs were identified, including hydrogen sulfide, ethyl mercaptan, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, carbon disulfide, and carbonyl sulfide. From a concentration perspective, the VSCs were dominated by hydrogen sulfide, followed by methyl mercaptan, and then a range of sulfides. Significant variations in VSC concentration and relative importance were observed between the cities and all identified VSCs were potentially odorous. An odorant prioritisation methodology to identify key and high priority odorants was developed and successfully demonstrated. While some high priority VOCs were identified, VSCs (hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide) were the dominant priority odorants. A wider range of VSCs should be assessed in addition to hydrogen sulfide to improve the evaluation of odour abatement processes.