Pyrolysis processing of PFAS-impacted biosolids, a pilot study

ABSTRACT

Concentrations of per- and poly-fluoroalkyl substances (PFAS) present in wastewater treatment biosolids are a growing concern. Pyrolysis is a thermal treatment technology for biosolids that can produce a useful biochar product with reduced levels of PFAS and other contaminants. In August 2020, a limited-scope study investigated target PFAS removal of a commercial pyrolysis system processing biosolid with the analysis of 41 target PFAS compounds in biosolids and biochar performed by two independent laboratories. The concentrations of 21 detected target compounds in the input biosolids ranged between approximately 2 µg/kg and 85 µg/kg. No PFAS compounds were detected in the biochar. The PFAS concentrations in the biochar were assumed to equal the compounds’ minimum detection limits (MDLs). The pyrolysis system’s target PFAS removal efficiencies (REs) were estimated to range between >81.3% and >99.9% (mean >97.4%) with the lowest REs being associated with the lowest detected PFAS concentrations and the highest MDLs. No information on non-target PFAS compounds in influent or effluent media or products of incomplete combustion was considered. Selected gaseous emissions were measured by Fourier transform infrared spectroscopy and gas chromatography time-of-flight mass spectrometry to provide additional information on air emissions after process controls. This limited-scope study indicated that additional research to further understand this process is warranted.Implications: Development of alternative approaches to manage PFAS-impacted biosolids is of emerging international importance. A commercially operating biosolid pyrolysis process was shown to lower target PFAS levels in produced biochar. Additional research is warranted to understand all potential PFAS transformation emission routes and optimal air pollution emissions control strategies for this technology class.

Disclaimer

The research described in this paper was funded in part by the EPA ORD under contract C68HERC20D0018 to Jacobs Technology, with portions of the research conducted by ORD and BFT under a memorandum of understanding for cooperative research. This paper has been subjected to review by the EPA ORD and approved for publication. Approval does not signify that the content reflects the views of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. The authors thank SVCW and individuals with EPA ORD, Montrose, and Bioforcetech assistance in conducting this research.

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No potential conflict of interest was reported by the author(s).

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Additional information

Notes on contributors

Eben D. Thoma

Eben Thoma is a research physical scientist with EPA’s Office Research and Development, Center for Environmental Measurement and Modeling in Durham, NC. His research focuses on characterization of difficult to measure air pollution sources and their impacts using next generation measurement approaches.

Robert S. Wright

Robert S. Wright is a chemist with EPA’s Office Research and Development, Center for Environmental Measurement and Modeling in Durham, NC. He is a quality assurance specialist with interests in PFAS and EPA traceability protocols for gaseous calibration standards.

Ingrid George

Ingrid George is a research analytical chemist with EPA’s Office Research and Development, Center for Environmental Measurement and Modeling in Durham, NC. Her research focuses on characterization of volatile organic compounds in source emissions and development of new instrumentation and analysis methods to characterize near sources impacts.

Max Krause

Max Krause is a research environmental engineer with EPA’s Office Research and Development, Center for Environmental Solutions and Emergency Response in Cincinnati, OH. His research focuses on PFAS, landfills, and waste management topics.

Dario Presezzi

Dario Presezzi is a Co-Founder and Chief Executive Officer of Bioforcetech Corporation in South San Francisco, CA. Since 2012 he has been working on developing and implementing systems to divert organic waste from landfills and transform them into valuable products.

Valentino Villa

Valentino Villa is a Co-Founder and Chief Operating Officer of Bioforcetech Corporation in South San Francisco, CA. Since 2012 he has been working on developing and implementing systems to divert organic waste from landfills and transform them into valuable products.

William Preston

William Preston is a chemist with Consolidated Safety Services in Durham, NC. He specializes in advanced gas chromatography and mass spectrometry for characterization of environmental samples.

Parik Deshmukh

Parik Deshmukh is a Principal Air Quality Engineer with AECOM in Raleigh, NC and was formerly with Jacobs Technology in Durham, NC. His research focuses on the development and implementation of innovative environmental technology and characterization of near-source impacts.

Phil Kauppi

Phil Kauppi is the National Director of FTIR Services for Montrose Air Quality Service. He has 23 years of field experience utilizing Fourier transform infrared spectroscopy for characterization of combustion, chemical and many other air pollution sources and emission control technologies.

Peter G. Zemek

Peter G. Zemek is a Senior Vice President with Montrose’s Research and Development Center for Emerging Technologies and Emerging Compounds in Fuquay Varina, NC and Boston, MA. His research focuses on characterization of difficult to measure air pollution sources, carbon capture technologies, and mitigation of forever chemicals from air, water and soil.