Effect of carrier gas during pyrolysis on the persistence and bioavailability of polycyclic aromatic hydrocarbons in biochar-amended soil.

In this study the persistence (based on extractable, C) and bioavailability (based on freely dissolved content, C) of polycyclic aromatic hydrocarbons (PAHs) in biochar-amended soil was investigated. Biochar produced at 500 or 700 °C from sewage sludge (BC) or sewage sludge and willow (W) mixture (BCW) in an atmosphere of nitrogen (N) or carbon dioxide (CO) was evaluated. The biochars were applied to the real soil (podzolic loamy sand) at a dose of 2% (w/w). The content of C and C PAHs was monitored for 180 days. The biochar production conditions determined the C and C PAHs in the soil. A change of carrier gas from N to CO caused an increase in C PAH losses in the soil from 19 to 75% for the biochar produced from SL and from 49 to 206% for the co-pyrolyzed biochar. As regards C PAHs, the change from N to CO increased the losses of C PAHs only for the biochar derived from SL at a temperature of 500 °C (by 21%). In the soil with the other biochars (produced at 700 °C from SL as well as at 500 and 700 °C from SL/W), the C increased from 17 to 26% compared to the same biochars produced in an atmosphere of N.