Pyrolysis atmosphere and temperature impact on biochar properties and heavy metals fate

About 250,000 contaminated sites in the European Union are known to require extensive clean up. Phytoremediation, i.e. the cultivation on the contaminated soils of purposely selected plants, is gaining consideration to extract, stabilize and/or detoxify from pollutants contaminated soils. The use of energy crops in phytoremediation of contaminated lands is a fast-developing field since it allows to combine the reduction of soil pollution and the power generation through the biofuels production from pyrolysis of produced biomass. By a proper choice of processing parameters, pyrolysis may be able to concentrate the potential toxic elements (PTEs) in the solid product (biochar) leaving the vapor phase (bio-oil) free of heavy metals thus enabling its use as a fuel. Pyrolysis temperature is the main variable affecting PTEs fate during pyrolysis. However, also the presence of an inert or reacting atmosphere can affect their thermal behavior or chemical transformation. In the present study populus nigra contaminated by Pb is tested under slow pyrolysis conditions, and the effect of temperature (465, 550, 700 °C) and gas carrier (N2 and CO2) are investigated on biochar properties and PTEs behavior. The risk assessment of the biochar was also performed to evaluate the toxicity of the biochars.