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A Monviso clone has been applied to promote PCB degradation in a soil historically contaminated by polychlorinated biphenyls (PCBs) and heavy metals (HMs). The multi-contaminated area is located in Southern Italy. PCBs, HMs, and the soil microbial community (abundance, viability, and structure) were analysed in selected plots of the poplar-treated area. At 900 days after poplar planting, chemical analyses showed that PCBs and most of HMs diminished under the Italian legal limits. The overall results suggest that the poplar clone was effective in promoting PCB rhizodegradation and HM phytostabilization. Organic carbon content increased strongly in the rhizosphere of the planted plots. Microbiological results highlighted an overall increase in microbial abundance, cell viability, and the presence of bacterial groups involved in PCB degradation. The poplar-based bioremediation technology is a nature-based solution able to promote the recovery of soil quality in terms of contaminant removal, increase in organic carbon, and stimulation of autochthonous bacterial groups able to transform PCBs.

This paper reports the application of organic amendments, such as biochar (BC) or compost (CMP) in a Plant-assisted bioremediation (PABR) strategy of a soil contaminated by polychlorinated biphenyls (PCBs) and heavy metals (HM). BC and CMP were applied for improving PABR in specific plots where the highest amounts of PCBs were present. Before the organic treatments and six months after it, soil samples and plant tissue (leaves, shoots and roots) were collected from each investigated plot and chemical and microbiological analyses performed. Moreover, micro-X ray fluorescence (µXRF) analysis was performed on soil and biomass (leaves, roots). Preliminary results evidenced different effects of the CMP or BC on promoting PCB and HM removal, depending on the initial pollutant concentrations

Plant-assisted bioremediation (PABR) represents a green technique for the recovery and remediation of contaminated areas. The biomass produced by these crops is generally considered as a contaminated waste product and potentially harmful. Therefore, it is very important to characterize these biomasses aiming at understanding if they can be treated like traditional biomasses and it is possible to use them in energy conversion process (pyrolysis, gasification, etc.). In this work, the energy conversion processes is simulated through an innovative TGA-DTA analysis using PABR poplar pruning and the emissions are characterized to assess the distribution of the contaminants in the effluent. The TGA-DTA system is interfaced with a particulate filter and a bubbling system for capturing metals. To assess the potential of easily repeatable, small scale TGA-DTA analysis in predicting the main aspects of the gasification process, the results of the experiment are compared with those obtained using the same biomass in a lab-scale fluidized bed gasification (FBG) plant. This comparison showed a good agreement between laboratory tests and those conducted on the real system, confirming that the proposed instrumental apparatus represents an interesting predictive tool for determining the fate of the metals contained in biomass. The analysis also showed that Cd is completely concentrated in the bottom ashes, while as for the other metals, such as Mn, Fe, Cu, Zn, not negligible concentrations are found in the fugitive ashes, e.g. bubbling gases, and then specific metal trapping must be considered in case of PABR gasification., Proceedings of the 28th European Biomass Conference and Exhibition, 6-9 July 2020, Virtual, pp. 302-305

Although the use of DDTs has been banned in most Countries over 20 years ago, its residues (DTTr) still persist in the environment. DDE (1,1-dichloro-2,2-bis(4- chlorophenyl)ethylene) is the most toxic DDT metabolite and it is reported to be more persistent than its parental compound (Ortìz and Velasco, 2013). Plant-assisted bioremediation can be a promising and cost-effective clean-up technology to contaminated soil remediation. It relies on synergistic action between plant rhizosphere where microorganisms support toxic substance removal. Solanum lycopersicum is known to be able to accumulate DDTs in roots, owing to exudate production, which make these contaminants more bioavailable for soil microorganisms. Moreover, several natural bacterial strains have been shown to degrade organochlorine pesticide through their enzymes able to break-down complex molecules (Verma et al., 2014; Qu et al., 2015). In this context, a greenhouse experiment was performed to study the effects of tomato plant presence on DDE persistence in an agricultural soil. The experimental set up consisted of pots filled with contaminated soil (1ppm of DDE) in presence/absence of tomato plants and control soils (with/without plant and/or DDE). The plots were sampled 40 days from DDE exposure. The effects of DDE and/or plant presence on the natural microbial community were evaluated in terms of microbial abundance, viability, structure, dehydrogenase activity and DDE residual concentration. The overall results showed that although the plant presence stimulated the soil microbial community activity, it did not increase DDE degradation. On the other hand DDE presence not only did not negatively affect the natural microbial community, but the latter was able to degrade DDE independently from the plant presence, showing a preacquired capability presumably due to a soil previous contact with this pesticide.

Plant-assisted bioremediation is emerging as one of the most effective means by which plants and their associated rhizosphere microorganisms can degrade organic contaminants in soils. Among biostimulation approaches, vegetation of different contaminated matrices with plant species found applications for accelerating the depletion of recalcitrant contaminants comprising Polychlorinated biphenyls (PCBs). This process is mainly due to the stimulation of organic contaminant biodegradation by natural occurring microorganisms through root exudates that can eventually increase the bioavailability of the contaminants and induce a natural selection of the microbial community. However, the efficiency of a phytoremediation process depends mainly on the presence and activity of plant-associated microorganisms carrying degradation genes required for the enzymatic breakdown of contaminants. In case the plant is growing in presence of contaminants, there is an interaction between contaminant, soil, and plant species that determines the structure and the metabolic activity of the plant associated microbial communities. The knowledge of this interaction is far from being complete, even though it is essential for designing an efficient plant based biostimulation of contaminants biodegradation. PCBs are ubiquitous and persistent organic pollutants (POPs), generated exclusively from human sources. They are found in the environment as a mix of several congeners (e.g. Apirolio, produced in Italy and used for electrical transformers). PCB biodegradation can potentially occur through aerobic and anaerobic microbial processes, but their poor bioavailability and the requirement for an inducer in anaerobic conditions may hinder microbial degradation. In this work the results of pot studies conducted in a greenhouse for 8 months for investigating the effect of the forage species Medicago sativa on PCBs degradation are reported. Soil samples were collected from a historically contaminated soil and used for setting-up different microcosms in presence/absence of the plant and/or of municipal solid waste compost. An additional amount of Apirolio was added to half microcosms. Finally, eight different experimental conditions were set-up. Microbiological and chemical analysis were performed at different experimental times in order to evaluate the changes in the structure and functioning of microbial populations in relation to the different experimental conditions and the PCB degradation. The microbial community was studied in terms of abundance (DAPI counts), viability (live/dead methods), diversity (Fluorescent In Situ Hybridization) and activity (dehydrogenase activity). PCBs decreased in all conditions 8 months after the microcosm set-up. Each treatment acted in a different way and times on transformation/degradation of the various congeners. The addition of Apirolio not only did not affect negatively the microbial community, but it also stimulated their degradation activity particularly towards the low chlorinated congeners (28 and 52). Apirolio being freshly added PCBs degraded faster than the pre-existing ones, according with the fact that PCB molecules adsorbed on soil for a long time become progressively less bioavailable. PCB degradation of most congeners analysed (28, 52, 105, 167, 156, 157, 101, 118) was higher in the conditions in which Apirolio was added together with plant and compost. These results are supported by a significant shift at 224 days in the microbial community groups. In particular, Beta-Proteobacteria, initially the dominant group of the bulk soil, decreased significantly while at the same time Alpha-Proteobacteria become the dominant one.

Bioremediation is an increasingly popular alternative to conventional methods for treating waste compounds, in line with environmental sustainability, with the possibility to degrade contaminants using natural microbial activity mediated by different consortia of microbial strains. Among the techniques of so-called green remediation, plant-assisted bioremediation seems to be one of the most promising techniques. Plant-assisted bioremediation is a technology that exploits the synergistic actions that are established in the rhizosphere between plant roots and microorganisms in order to remove, transform or immobilize toxic substances. The presence of plant species through the roots promotes the modification of the physico-chemical properties of contaminated soils as well as the release of root exudates. Organic pollutants may be partially co-metabolic degraded by root enzymes and/or completely biodegraded by microorganisms in the rhizosphere. The phytoremediation effectiveness depend on the use of plant species tolerant to the toxic effects of contaminants in the soil and with roots able to promote the development of a microbial community capable of supporting the degradation of the contaminant in the rhizosphere. This technique is used in preliminary experiments, one in the field and in two in greenhouse, using a soil diffusely contaminated by PCBs in which different plant species were tested. In the field experiment, two tree species (Tamarix gallica and clone Monviso of the genus Populus), were used. At the same time, soil microcosms were set up in greenhouse in order to study in detail the possible PCB degradation processes that occur in the rhizosphere. For this purpose, some microcosms were prepared in the presence/absence of Medicago sativa specie and others in the presence of the Monviso clone, the same used in the field experiment. In this work we describe the various experiments and their main results.