Pyrolysis processing of PFAS-impacted biosolids, a pilot study

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Environmental Chemistry

Background:

• Per- and poly-fluoroalkyl substances (PFAS) in wastewater biosolids pose environmental risks.
• Pyrolysis offers a thermal treatment to reduce contaminants in biosolids, creating valuable biochar.
• Managing PFAS-contaminated biosolids is a growing global challenge.

Purpose of the Study:

• To evaluate the effectiveness of a commercial pyrolysis system in removing target PFAS from biosolids.
• To analyze PFAS concentrations in biosolids and biochar using independent laboratory analysis.
• To assess PFAS removal efficiencies and investigate gaseous emissions.

Main Methods:

• A commercial pyrolysis system processed biosolid samples.
• Analysis of 41 target PFAS compounds in biosolids and biochar by two independent laboratories.
• Measurement of gaseous emissions using Fourier transform infrared spectroscopy and gas chromatography time-of-flight mass spectrometry.

Main Results:

• Detected target PFAS concentrations in input biosolids ranged from approximately 2 µg/kg to 85 µg/kg.
• No PFAS compounds were detected in the resulting biochar, with concentrations assumed to be at minimum detection limits (MDLs).
• Estimated target PFAS removal efficiencies ranged from >81.3% to >99.9%, with a mean of >97.4%.

Conclusions:

• The commercial pyrolysis process significantly reduced target PFAS levels in biochar.
• Additional research is warranted to fully understand PFAS transformation, emissions, and air pollution control strategies.
• Pyrolysis presents a promising technology for managing PFAS-impacted biosolids.