Gasification treatment of poplar biomass produced in a contaminated area restored using plant assisted bioremediation.

Remediation of polluted soils using phytoremediation techniques is an effective strategy. However, the use of the biomass from these soils for energy purposes may raise efficiency and pollution emission problems and there is currently little research on this issue. In this work, the main results of a fluidized-bed gasification treatment conducted on poplar biomass pruning residues from a multi-contaminated area are presented. The samples were collected from an experimental site in which a plant-assisted bioremediation (PABR) technology has been applied since 2013 to reduce the soil heavy metal (HM) and polychlorinated biphenyl (PCB) contents. The main goal of this study was to identify the specific treatment necessary, in addition to conventional tar reforming, for trapping possible residues of HMs and PCBs in ashes during the gasification process. In our study, we demonstrate that gasification of contaminated biomass coming from PABR (where contaminant residues are concentrated mainly in the roots and are insignificant in the shoots) produces syngas whose characteristics are similar to those obtained using non-contaminated biomass. The results showed that contaminant concentrations in the prunings were negligible; the total amount of PCBs was 1.63 ng/g, while HMs ranged from 0.01 to 0.70 mg/kg, except for Cu and Zn (∼20 mg/kg). Furthermore, the presence in the biomass of Ca and traces of other metals showed a possible catalytic effect with an improvement in the tar conversion in the gasifier leading to a reduction of 5-10% in tar content. The overall results suggest that a specific treatment for pollutant capture is necessary only when the roots, the part of the plants where these contaminants are concentrated, are sampled and used for the gasification process. Although energy from biomass produced on a contaminated site is currently considered waste and involves disposal costs, this paper shows that the poplar biomass grown on a multi-contaminated soil can be used for energy purposes without any impact on the environment.

Pyrolysis wastewater treatment by adsorption on biochars produced by poplar biomass.

Pyrolysis is a widely studied thermochemical process, however the disposal of the produced byproducts is an unexplored field. In particular, the acqueous phase, characterized by a high organic load (TOC), must be necessarily treated. Aims of this work is to study the potentiality of biochar as adsorbent material for the treatment of this wastewater. For this aim, pyrolysis wastewater and biochar produced in the same plant were used. Two biochars produced at different temperatures (550 and 750 °C) and an activated biochar produced by chemical activation with NaOH of the raw biomass were tested. The study shows that higher temperature in the biochar production leads to higher sorption capacity of the organic compounds due to an increase of the surface area. The activation process further increases the surface area of the biochar that becomes similar to that of a commercial activated carbon while the sorption capacity exceeds that of commercial activated carbon of 2.5 times.