EFFECT OF BIOMASS ADDITION BEFORE SEWAGE SLUDGE PYROLYSIS ON THE PERSISTENCE AND BIOAVAILABILITY OF POLYCYCLIC AROMATIC HYDROCARBONS IN BIOCHAR-AMENDED SOIL

There is a lack of studies dealing with the effects of co-pyrolyzed biochars produced from different materials on the persistence of polycyclic aromatic hydrocarbons (PAHs). This research aimed to determine the persistence (based on extractable Ctot) and bioavailability (based on freely dissolved content, Cfree) of PAHs in soil amended with biochar derived from sewage sludge (SL) or a mixture of SL and biomass (SLW). Biochars produced at 500, 600, and 700 degrees C were applied to the soil (podzolic loamy sand) at a rate of 2% (w/w) and incubated for 180 days. The content and changes of PAHs differed between the experiment with SL, SL-derived biochar, and SLW-derived biochar. In the soil with the SLW-derived biochar, the losses of Ctot sigma 16 PAHs were lower (between 13 and 38%) than in the soil with the SL-derived biochar (from 27 to 74%). Compared to Ctot, a completely different trend was observed for Cfree PAHs. The decrease of Cfree PAHs in the soil with the SLW-derived biochar was higher than or similar (from 4 to 18%) to the losses of Cfree PAHs in the soil with the addition of the SL-derived biochar. The differences between the individual treatments resulted from the difference in the physical and chemical properties of the biochars, which affected the persistence and bioavailability of the studied compounds.