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Phytoremediation driven energy crops production on heavy metal degraded areas as local energy carrier

Final Report Summary - PHYTO2ENERGY (Phytoremediation driven energy crops production on heavy metal degraded areas as local energy carrier)

Phyto2Energy has formed a strategic multidisciplinary intersectoral partnership to enable transfer of knowledge and mutual training between 3 organizations from research sector and 3 organizations from commercial sector representing complementing skills and expertise in the area of life sciences, environmental engineering, energy, biotechnology and land management. The scientific and technological challenge for this partnership was to develop and validate in field conditions an innovative, complex approach combining phytoremediation of heavy metal contaminated sites with energy crops production and their conversion to energy using gasification. The development and validation of the approach involved research addressing three specific aspects: the use of energy crops for phytoremediation purposes, development of microbiological methods to enhance and monitor the phytoremediation effect and increase the biomass production and the conversion of the produced biomass into energy by a gasification process.
The basis for the project implementation was a 4-year field experiment established at two heavy metal contaminated sites: arable land (Bytom, Poland) and a postindustrial area – a former sewage sludge disposal site (Leipzig, Germany) with a selection of 4 preselected energy crop species: Miscanthus x giganteus, Sida hermaphrodita, Spartina pectinata and Panicum virgatum. The experiment allowed to define which of the species deliver the best results in terms of the biomass production and the phytoremediation effect (phytoextraction for heavy metal contaminated arable land and phytostabilisation for post-industrial sites). Panicum virgatum demonstrated the most promising potential for phytoextraction at sites contaminated with Pb as the main contaminant, whereas Sida hermaphrodita for Cd contaminated sites while both M. x giganteus and P. virgatum turned out to be promising Zn extractors. Due to low accumulation of heavy metals in the aboveground parts Spartina pectinata was identified as the most promising species for metal phytostabilization, at the same time producing high yield of a relatively “clean” biomass for energy production. Very low lead extraction by Miscanthus x giganteus and Sida hermaphrodita from the postindustrial site suggest, that these species could be used for non-contaminated or slightly contaminated biomass yield production. Analyses also showed that the treatment of plants with a commercial bioinoculate EmFarma Plus™ stimulated the uptake of Cd (S. hermaphrodita) and Zn (M. x giganteus). Also conditions that determine the efficiency of these processes were identified and characterized. Physical and chemical properties of the soil (e.g. compaction) and the bioavailability of the heavy metals were identified as the key factors influencing phytoextraction effect. Hight bioavailability significantly reduced the contaminants extraction from soil The results of these investigations advanced the knowledge on the specific properties of energy crop species and their application for the purpose of phytoremediation projects taking into account soil conditions, heavy metal contamination and the desired phytostabilisation or phytoextraction effect respectively of the land management option. These results may find commercial application for engineering large scale phytoremediation projects as well as land management projects related to marginal land. They also create a solid base for new opportunities for the partners in performing application specific research and development of professional carriers in the area of energy crops production combined with remediation which could be implemented in practice for commercial phytoremediation applications.
To improve the biomass production and the phytoremediation effect microbiological methods were investigated which are based on the power of soil microbes to improve plant performance and health on heavy metal contaminated and marginal sites with focus on general plant growth promotion, improved inert immunity of plants, improved plant fitness towards biotic and abiotic stressors as well as nutrient mobilization and transport. As a result of the joint work 3 Pseudomonas putida strains were selected and characterized as plant growth-promoting bacteria out of 144 rhizobacteria strains isolated from rhizosphere soil of the tested plants. They were further characterised using genomic techniques including genome sequencing to define the properties of individual strains with respect to pathogens. The characteristics showed that the selected strains contained genes promoting the growth of the plants as well as heavy metals resistance genes. Due to their unique properties they were selected as candidates for the development of a prototype formula of a plant biostimulator which could be a good starting point for the continuation of the partnership towards development of a commercial product. For the prototype formula a dry-freezing procedure was developed and tested in batch and bioreactor conditions with the use two lypoprotectants: trehalose and inulin. The influence of dry-freezing on the biocontrol agent properties of the strains was carried out that is of importance for determining the function of the potential new plant biostimulant product. To enable assessment of the impacts of bioremediation strategies on soil quality, a framework of methods based on a hierarchical concept has been developed that can be used for the assessment of soil quality depending on the respective on site situation. As significant improvements of soil quality of heavy contaminated sites by bioremediation strategies take longer than the project period, the proposed indicator system was not tested under field conditions, but important steps forward towards the detection of important indicator species were made in greenhouse trials.
The investigations on the ways to convert the biomass produced from the 4 tested energy crops into energy using gasification involved gasification tests at a lab scale fixed bed gasification installation and thermogravimetry (TG) installation were performed. They allowed to provide new knowledge on the characteristics of a gasification process of a heavy metal contaminated biomass in terms of the properties of the biomass produced from the tested energy crop species as gasification feedstock, the influence of these parameters on the efficiency of the gasification process and the quality of the end products as well as the fate of contaminants during the gasification process. Particularly promising results were obtained for Sida hermaphrodita which recently gained an increasing interest as a bioenergy plant. Sida hermaphrodita as a gasification feedstock resulted in the lowest content of ash. The LHV of the produced gas was acceptable taking into consideration the usage of this gas as fuel in engines, gas turbines (as a part of the CHP systems) and boilers. The best air ratio of gasification gas was found for λ = 0.18. In terms of other process parameters, the content of volatile matter and moisture were similar for all 4 tested energy crop species, similarly was the percentage of carbon, hydrogen and oxygen. Considering the parameters of the feedstock resulting from the agrotechnical measures, the test data showed that the gas obtained from NPK fertilized biomass had the highest LHV. The tests also confirmed that the effect can be enlarged by catalyst addition to the fuel e.g. halloysite. Moreover, the produced gasification gas is characterized by higher content of hydrogen and the amount of tar is significantly lower compared with non-catalytic gasification process of biomass. The implications obtained from the investigations allowed to elaborate a set of recommendations concerning the gasification processes of heavy metal contaminated biomass as well as gasification installations that would improve the performance of the process and the quality of the gas while minimizing the generation of by-products. They also allowed to develop tools enabling assessment of the economic feasibility of the gasification and its environmental added value which may find further application for making assessments for small scale power generation projects including agroenergy. The tests on the gasification of the “difficult” biomass that has not been used so far for energy purposes allowed the partners to advance their knowledge that may find application in addressing the gasification challenges related to other refuse derived fuels as well as for commercial services related to design of gasification installations.
The transfer of knowledge and mutual training involved 107.45 months of secondments implemented by 12 experienced researchers and 14 early stage researchers as well as one 24 months external recruitment of an experienced researcher. All the involved researchers benefited from cross-sectorial training implemented by 66 internal seminars and trainings and strengthened thus their expertise and future carrier prospects.
Outreach activities beyond the partnership members were provided by 51 open workshops and seminars organized by project partners. Implementation of joint research programme resulted in 9 articles published in scientific journals of high impact factors, presentation of results at 31 national and international conferences and seminars including 10 posters (three of them were awarded). 28 media interactions including publications in non- scientific press, radio and TV broadcasts allowed to bring the project results to general public . Additionally, the project allowed to develop 8 outputs of potential marketing value.