Determination of odorous VOCs and the risk of occupational exposure to airborne compounds at the waste water treatment plants.

Concentrations of non methane-VOCs and risk levels of employees' exposure to VOCs were determined at two Finnish waste water treatment plants. The concentration of hydrogen sulphide (H2S) reached the Finnish OEL (occupational exposure limit). The concentrations of styrene, 1,2-dichloroethane, and toluene were found to be elevated at plant A. 328.4 microg/m3 of styrene and 709.8 microg/m3 toluene was found in the sludge dewatering, and 955.8 microg/m3 of 1,2-dichloroethane was detected in the trash rake. TVOC concentrations varied from 149.8 microg/m3 in the Plant B sludge dewatering to 7719.0 microg/m3 in the Plant A sludge dewatering. Most of the detected TVOC concentrations were quite high in comparison to the indoor air regulations or recommendations. The most odorous compounds were determined by combined TD-GC-MS-sniffing analysis. Odour was mainly caused by sulphur-containing compounds, aldehydes, and butanoic acid, in addition to aromatic compounds such as styrene, toluene and 4-methylphenol.