Determination of volatile organic sulfur compounds in the air at sewage management areas by thermal desorption and gas chromatography–mass spectrometry

The concentrations of seven volatile organic sulfur compounds (VOSCs) in air samples were determined by active collection on multisorbent tubes followed by two-stage thermal desorption and gas chromatography–mass spectrometry. The compounds studied were ethyl mercaptan (CH3CH2SH), dimethyl sulfide ((CH3)2S), carbon disulfide (CS2), propyl mercaptan (C3H8S), butyl mercaptan (C4H10S), dimethyl disulfide ((CH3)2S2) and 1-pentanethiol (C5H12S). Active collection on SilcoSteel multisorbent tubes enabled an air volume of 3000 ml to be sampled without observing breakthrough. This study focused on an exhaustive sampling of several process steps or sections from sewage management plants. A wide range of concentrations was observed. Dimethyl sulfide, carbon disulfide and dimethyl disulfide were the most abundant compounds in all samples, the highest concentrations being 608.5 μg m−3, 658.5 μg m−3 and 857.8 μg m−3, respectively. The less appearing compound was ethyl mercaptan, which was only detected in the sludge digestion process at a maximum concentration of 14.8 μg m−3. The remaining compounds were detected and measured in about half the samples. The sections with the maximum values of VOSCs involved sludge processes such as mixing, thickening and digestion. The results were also strongly influenced by the design characteristics of the sampling point, e.g. whether the sample was taken at a confined site or in the open air.