Occurrence of synthetic polycyclic and nitro musk compounds in sewage sludge from municipal wastewater treatment plants

Synthetic musk compounds (SMCs) are widely used as fragrances that can be released from different sources and through the sewer system, finally reaching wastewater treatment plants (WWTPs). In this study, 6 synthetic polycyclic and 5 nitro musk compounds were screened in 55 sewage sludge (SS) samples from 43 different WWTPs in the Czech Republic, and the effect of WWTP technology parameters on SMC content in SS was assessed. Galaxolide and Tonalide were predominant synthetic polycyclic musk compounds (SPMCs) detected in all SS tested and accounted for 99.5% of the average content of sludge SMCs (5518 μg/kg dw). The amount of synthetic nitro musk compounds (SNMCs) in SS samples was negligible. The Tonalide content in SS correlated significantly with the WWTP design capacity (r = 0.32, P < 0.05). The significant correlation between chemical oxygen demand (COD) removal efficiency and SMCs (r = −0.37, P < 0.05) partly suggests the recalcitrance of SMCs, mainly of Celestolide, Galaxolide and Tonalide, to biodegradation in WWTPs. A statistically lower SNMC content was found in anaerobically digested sludges than in aerobic ones. There was no significant difference (P > 0.05) between the digestion technology as well as the temperature of anaerobic digestion on the SPMC content in sewage sludge. The wastewater (WW) load percentage or WW hydraulic retention time had no influence on the SMC content in the resulting SS. Musk compounds did not change over time when the SS samples were analysed with a gap of two years, suggesting that sewage sludge for soil applications only needs to be analysed for musk compounds once a year. Our study indicates that the currently common WWTP technologies have only very limited potential to affect the accumulation of musk compounds in sewage sludge.