Determination of VOSCs in sewer headspace air using TD–GC–SCD

The management of odorous emissions from sewer networks has become an important issue for sewer operators resulting in the need to better understand the composition of volatile organic sulfur compounds (VOSCs). In order to characterise the composition of such malodorous emissions, a method based on thermal desorption (TD) and gas chromatography coupled to sulfur chemiluminescence detector (GC–SCD) has been developed to determine a broader range of VOSCs, hydrogen sulfide (H₂S), methanethiol (MeSH), ethanethiol (EtSH), dimethyl sulfide (DMS), carbon disulfide (CS₂), ethylmethyl sulfide (EMS), 1-butanethiol (1-BuSH), dimethyl disulfide (DMDS), diethyl disulfide (DEDS), and dimethyl trisulfide (DMTS). Parameters affecting the chromatographic behaviour of the target compounds were studied (e.g., temperature program, carrier gas velocity) as well as the experimental conditions affecting the adsorption/desorption process (temperature, flow and time). Optimised extraction of VOSCs samples was achieved under adsorption temperatures of less than −20 °C, and a desorption flow rate of ~6 ml/min. Active collection on the cold trap enabled a small gas volume of 50–100 ml to be sampled for all analytes without breakthrough. Calibration curves were derived at different TD loading volumes with determined linearity ranging between 0.09 ng and 60.1 ng. The method detection limits (MDLs) were in the range of 0.10–5.26 μg/m³ with TD recoveries higher than 66% and reproducibility (relative standard deviation values) between 1.8% and 6.1% being obtained for all compounds. The VOSCs characterisation at different sewerage collection sites in Sydney, Australia (for seasonal, weekly and diurnal) showed that six of the ten targeted compounds were consistently detected at all sample events. Diurnal patterns of VOSCs investigated were clearly observed with the highest concentration occurring after 12 pm (noon) for H₂S and MeSH. The consecutive 5 day analysis showed no significant difference in the targeted VOSCs concentrations and demonstrated the suitability of the method for routine sewer VOSCs emission measurements.