Carbon dioxide as a carrier gas and biomass addition decrease the total and bioavailable polycyclic aromatic...

Area of Science:

• Environmental Chemistry
• Materials Science
• Biomass Conversion

Background:

• Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants.
• Biochar production from sewage sludge can immobilize contaminants.
• Optimizing biochar properties for PAH reduction is crucial for environmental applications.

Purpose of the Study:

• To investigate the impact of willow co-firing and carrier gas (N2 vs. CO2) on PAH content in biochar.
• To analyze the effects of pyrolysis temperature on PAH reduction.
• To evaluate the influence of these factors on the PAH profile and biochar's affinity for PAHs.

Main Methods:

• Pyrolysis of sewage sludge and willow mixtures (8:2, 6:4 w/w) at 500, 600, and 700°C.
• Use of nitrogen (N2) and carbon dioxide (CO2) as carrier gases.
• Quantification of organic-solvent extractable (Ctot) and freely dissolved (Cfree) PAHs using US EPA 16 PAHs method.
• Determination of distribution coefficients (log K_TOC) to assess PAH affinity.

Main Results:

• Addition of willow and use of CO2 significantly reduced both Ctot PAHs (7.0-52%) and Cfree PAHs (15-29%).
• Biochars produced with willow and/or CO2 showed a lower percentage of 3-6-ring PAHs.
• Increasing pyrolysis temperature decreased Ctot PAHs in sewage sludge biochar but had no significant effect when willow was present.
• CO2 as a carrier gas increased biochar's affinity for PAHs (log K_TOC).

Conclusions:

• Co-pyrolysis of sewage sludge with willow and the use of CO2 as a carrier gas are effective strategies for reducing PAH content in biochar.
• These conditions also favorably alter the PAH profile, leading to more environmentally benign biochar.
• Willow addition influences the temperature-dependent behavior of PAHs during pyrolysis.