Abstract
Volatile methylsiloxanes are wastewater organic pollutants originating from industrial and personal care products. They accumulate in sewage sludge and hamper biogas production through the formation of silicon dioxide on the surfaces of gas engines and turbines, yet there is few knowledge on their fate in sludge treatment systems. Here we studied the occurrence and removal of seven volatile methylsiloxanes along the solid treatment line of an urban wastewater treatment plant. We analyzed 75 sludge samples from seven locations using ultrasound-assisted solid–liquid extraction followed by gas chromatography-mass spectrometry. Results show that volatile methylsiloxanes occur in all samples with a predominance of cyclic homologues, particularly decamethylcyclopentasiloxane. Total siloxane levels reach 6087 ng/g dry weight in the secondary sludge, average at 3575 ng/g in digested sludge, and 5703 ng/g in the dewatered sludge, the latter being likely due to the addition of a polyelectrolyte. Overall, these levels call for measures to reduce methylsiloxane levels before the biogas production step.
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Funding
This work was financially supported by: (i) Base Funding—UIDB/00511/2020 of the Laboratory for Process Engineering, Environment, Biotechnology and Energy—LEPABE—funded by national funds through the FCT/MCTES (PIDDAC); (ii) Projects PTDC/ASP-PLA/29425/2017—POCI-01–0145-FEDER-029425 and PTDC/CTA-AMB/32084/2017—POCI-01–0145-FEDER-032084 funded by FEDER funds through COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI) and by national funds (PIDDAC) through FCT/MCTES; (iii) Vera Homem thanks national funds through FCT—Fundação para a Ciência e a Tecnologia, I.P., under the Scientific Employment Stimulus—Individual Call—CEECIND/00676/2017; (iv) Nuno Ratola thanks FCT for the financial support of his work contract through the Scientific Employment Stimulus—Institutional Call—[CEECINST/00049/2018].
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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Joana Silva and Fábio Bernardo. The first draft of the manuscript was written by Vera Homem and Nuno Ratola, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Silva, J., Bernardo, F., Jesus, M. et al. Levels of volatile methylsiloxanes in urban wastewater sludges at various steps of treatment. Environ Chem Lett 19, 2723–2732 (2021). https://doi.org/10.1007/s10311-021-01191-1
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DOI: https://doi.org/10.1007/s10311-021-01191-1