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 μg/m³ of styrene and 709.8 μg/m³ toluene was found in the sludge dewatering, and 955.8 μg/m³ of 1,2-dichloroethane was detected in the trash rake. TVOC concentrations varied from 149.8 μg/m³ in the Plant B sludge dewatering to 7719.0 μg/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.