Evaluation of the performance of a Pilot-Scale sewage sludge treatment system and study of PFAS removal

Evaluation of the performance of a Pilot-Scale sewage sludge treatment system and study of PFAS removal A. Koukoura, E. Gkalipidou, G. Gatidou, M. Kostakis, D. T. Gerokonstantis, M. S. Fountoulakis, S. Vakalis, O. I. Kalantzi, N. S. Thomaidis, O. S Arvaniti, A. S. Stasinakis Chania May 2025 Water and Air Quality Laboratory, Department of Environment, University of the Aegean, Mytilene, Greece PFAS (Perand Polyfluoroalkyl Substances) fluorinated substances that contain at least one fully fluorinated methyl (-CF3)or methylene (-CF2) carbon atom Highest electronegativity among all the elements in the periodic table Exceptional chemical and thermal stability due to the strong carbon–fluorine bond High hydrophobicity and oleophobicity properties High capacity to reduce the surface tension of water Low reactivity and non-flammability Wide use in various applications and industries! Exposure to PFAS has been linked to health concerns including cancer, hormone disruption, developmental toxicity, increased cholesterol levels etc. EU Drinking Water Directive (2020/2184) –0.2μg/l for sum concentracion of 20 PFAS US EPA70 ng/l for PFOA and PFOS Sorption of PFAS in suspended solids PFAS resistance to biodegradation Extreme Persistence chemicals Frequent detection worldwide in municipal and industrial wastewater, as well as in leachates from solid waste landfills PFAS accumulation in primary and secondary sludge Arvaniti et. al. (2024) Objective of the project The ZeroPM Project, funded under Horizon 2020, aims to address key knowledge gaps in the literature regarding the behavior of PFAS during sludge treatment. The project focuses on modifying anaerobic digestion processes through the integration of ultrasound and thermal pretreatment,as well as exploring the application of hydrothermal carbonization. Limited information is currently available regarding: The behavior and fate of PFAS in anaerobic digesters The specific mechanisms responsible for PFAS removal The combined effectiveness of technologies such as thermal treatment, ultrasound, and hydrothermal carbonization in removing PFAS https://zeropm.eu/ Lesvos island The pilot system are located in WWTP of Mytilene Sedimentation Tank Secondary sewage sludge Recirculation Manhole Feeding pump Pilot system Side-stream treatment line Influent tank Thermal pretreatment Ultrasound pretreatment Anaerobic digester (CSTR) Effluent tank Main treatment line Hydrothermal carbonization Solar drying hydrothermal carbonization Anaerobic digestion Ultrasound treatment Thermal treatment Pre-treatment WWTP Sewage sludge or Solar drying Experimental phase A Experimental phase B Experimental phase C Anaerobic digester Q: 28 L d-1 HRT: 18 d Hydrothermal carbonization P: 17 bar T: 200 oC Anaerobic digester Q: 28 L d-1 HRT: 18 d Thermal pretreatment T: 80 oC Duration: 2 hr Hydrothermal carbonization P: 17 bar T: 200 oC Anaerobic digester Q: 28 L d-1 HRT: 18 d Ultrasound pretreatment P: 900 Watt F: 20 kHz Hydrothermal carbonization P: 33-48 bar T: 238 oC Continuous monitoring •2 samples per week •2 months of operation •Conventional pollutants Sampling campaign •At the end of each Phase •PFAS Anaerobic digester Thermal pretreatment Ultrasound pretreatment Sewage sludge (Inlet) Anaerobic digester Thermal pretreatment Ultrasound pretreatment Sewage sludge (Inlet) Hydrothermal carbonization Solar drying SCADA + Mobile monitoring ✓Analysis of the samples from the 3rd sampling campaign has been completed - the results are not estimated yet. Results –PFAS removal PFNA PFDA PFDoA PFTrDA PFTeDA PFBS PFPeS PFHxS 4-2FTS 6-2FTS 8-2FTS PFOSAA N-MePFOSAA N-EtPFOSAA 99.9 100.0 76.7 52.1 60.0 85.8 70.0 100.0 100.0 97.9 70.1 99.9 99.5 99.9 0.1 0.0 19.2 25.0 13.7 5.4 25.2 0.0 0.0 1.4 11.5 0.1 0.3 0.3 Removal during HTC (%) •There was no PFAS removal during sludge thermal pretreatment •Most of PFAS were not removed in the anaerobic reactor (CSTR) •Significant removal was observed only for 8:2FTS => 77.7 ±10.9% •14 out of 22 PFAS were removed during HTC •The removal ranged between 52 ±25 % (PFTrDA) and 100 ±0 % (PFDA, PFHxS, 4:2 FTS) Thank you for your attention! This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101036756 Acknowledgments