Gasification treatments of poplar biomass produced in contaminated area recovered by plant assisted bioremediation

Gasification represents a viable solution for the treatment of biomass aiming at producing a syngas with an overall conversion efficiency reaching the 75% level. Apart the syngas, the process produces solid residuals (ashes and unburned carbon-char) as well as heavy hydrocarbons (tars) that must be separated from the main gas flow. Here we present the outcomes of a gasification treatment conducted on poplar biomass samples collected from a multi contaminated area of Southern Italy restored by plant assisted bioremediation (PABR) aiming at reducing heavy metal (HM) and PCB contents in the contaminated soil. Pruning residues were collected from the poplar treated area located close to Taranto city. HM and PCB analyses were carried out to evaluate the overall content of these contaminants in the biomass. This preliminary evaluation is necessary for assessing the quality of the biomass and estimating the ensuing pollution in comparison with noncontaminated biomass. In fact, at the moment, the PABR residuals are classified by the Italian legislation as wastes and not as biomass usable for energy purposes when they are produced in contaminated areas. Our aim is to indicate the specific additional treatments possibly required for trapping HMs and PCBs in ashes, thus demonstrating that the PABR biomass gasification is not more pollutant than non-contaminated biomass. The gasification process was carried out in a lab-scale gasifier system, designed at the Faculty of Civil and Industrial Engineering at Sapienza University of Rome. Moreover, we investigated the catalytic effect (and its related impact) associated to the presence of HMs in the biomass as well as the distribution of the HMs and PCBs among the ashes, filters and tars.