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Biomolecules from olive pruning waste in Sierra Mágina

By Moussa Dicko, Farida Darkrim Lamari, Gilles Lepesant, Philippe Silar, Clélia Bilodeau and Marianne Cohen


International audienceThe volatility of fossil resources prices, the uncertainty of their long-term availability and the environmental, climatic and societal problems posed by their operation, lead to the imperative of the energy transition, development and use of other alternative and sustainable resources. In Europe, established feedstocks for ethanol and biodiesel have thrived largely under the protection of subsidies but first generation biofuels have triggered a debate within the European Union (EU) over their economic and environmental sustainability. Acknowledging that indirect land-use change can reduce the greenhouse gas emissions savings, the EU has reshaped its biofuel policy. It has a set of sustainability criteria to ensure that the use of biofuels guarantees real carbon savings and protects biodiversity. From a sustainability perspective, biofuels and bioliquids offer indeed both advantages (more secure energy supply, emissions reductions, reduced air pollution, production of high added-value molecules) and risks (monocultures, reduced biodiversity, and even higher emissions through land use change). Approaching economic, environmental and social sustainability at the local level and in an integrated way helps to maximize benefits and minimize risks. This approach has been adopted to assess the relevance of bio-refineries supplied from lignocellulosic biomass and implementing emerging technologies such as pyrolysis process in an olive-growing area (Sierra Mágina). Sierra Mágina is vulnerable to climate change because of its high level of specialization in olive growing and the burning in loco of pruning waste (several kilos per tree) contributes to greenhouse gases (GHG) emissions. Therefore this territory has been selected for the OLIZERO project.The OLIZERO bio-refinery concept is part of an interdisciplinary thinking which aims to optimize the use of biomass available in a specific territory by analyzing local and integrated production of finished and/or intermediate products and higher added-value molecules (from solvents to aroma, flavors and products of medical interest). The final objective is to develop innovative methods for recovering chemicals from the most difficult valuable fractions (lignocellulosic fractions). The project is then about a study of the feasibility of a bio-refinery coupled to existing olive mills. We initially identified and mapped the resource available in a Spanish territory located in Sierra Mágina, Andalucía. We have in a second step associated a Py-GCMS analysis from a sampling of several available olive tree cuttings in this territory. This preliminary study will provide a picture of what kind of chemicals can be obtained from a pyrolysis process. The second on-going step is to perform lab scale pyrolysis experiments with the selected resources. The coupling of the territorial study and physicochemical analysis will optimize the annual output of high-value molecules and associated biochar (fertilizer). It is then necessary to define the geographic data (workflow, localization, mapping etc.) to plan the availability of the biomass according to harvest periods and secondly physicochemical characteristics to assess the nature of bio-molecules that will be extracted (volumes and material flow).ResultsIn this work, social acceptance of such biorefinery project has been evaluated. This evaluation relied on a field survey, with qualitative inquiries, questionnaires and engaging workshops (Benyei, 2015, unpublished). The burning of pruning waste is currently being partly replaced by chipping and composting chips on the soils, a practice with less emission of GHG, but which generates a potential risk of pest contamination, mostly unknown by farmers. Along with this transition, local stakeholders showed their interest for OLIZERO project, but made suggestions that the team took into consideration within a multi-actor approach. The first suggestion was to fully integrate the carbon balance of the innovation (for example the cost of the transport of the pruning waste), the second concern was the economic viability of the innovation, and the possible return for the farmers (who invested in machines and energy for pruning waste chipping). Moreover, according to farmers, chipping pruning waste and composting on the ground bring benefits for the soil, avoiding erosion and fertilizing it. For this reason, we introduced the return of biochar to compensate the “loss” of the compost due to the project (chips will be used in the pre-fungal and pyrolysis process).Geographic analysis showed that the valorization of pruning wastes will have to deal with strong spatial heterogeneities, the quantity of biennal pruning waste varying from 1 to 5, according to the location and age of olive-groves. This evaluation relies on a crossed analysis between field data (pruning waste weight in olive trees of different tree crow sizes) and remote sensing analysis of the olive tree cover all over the Sierra Mágina region Bourrand et al. (2015, unpublished). Further, a crossed analysis between farmers’ field survey and geographical data showed that the choice of waste management depends on the distance to the road: above the threshold of 250 meters between a viable road and the grove, farmers continue burning the pruning residue. The road system and the slope will be major issues for spatial optimization of the wastes collection. Basic data still need to be improved to perform such spatial modelling. Analysis of Endophytic fungi present in pruning residues showed that the major species belonged to the genus Alternaria, a group that is known to contain many strains pathogenic to olive trees. Leaving the pruning materials unattended may therefore facilitate the emergence of opportunistic strains able to infect weakened trees, a condition that may become prominent due to climatic change. Pruning residues should therefore be disposed of in a way that would limit fungal growth. We proposed that in replacement to burning, pyrolysis will be able to dispose in a safe way of pruning residues, in addition to produce high-value-biomolecules and fertilizer.Py-GCMS analysis results are presented. The results show recurrent molecules with high intensity peaks. Target molecules for the construction of a bio-refinery are proposed. Ongoing tests at lab scale should clarify if they can effectively be recovered in sufficient amount.From an European perspective, the OLIZERO project helps to understand the added-value and the shortcomings of the different EU instruments ranging from the financial means provided by the Cohesion policy to the standards set by the legal framework related to renewable energies, air pollution and agricultural policies. Focusing on a specific area, OLIZERO offers an insight on how the EU framework affects governance schemes, rural development practices and business models that are instrumental for the surge of innovative biofuels and bioliquids. ConclusionsThe collaboration between social, biological and chemical engineering sciences brought many advantages: first, we chose a territory with a social demand to improve the waste management, along with a capacity of innovation. This encourages us to improve the agronomical and economic benefits of the proposed innovation. Secondly, the analysis of Endophytic fungi showed the potential risks of the changing practices along with the potential benefit of our innovation. Finally, further investigations are needed to address the technical challenges in the production processes and in the design of appropriate separation technologies. However, knowing that potential molecules of interest could be recovered is encouraging for the future developments of OLIZERO.AcknowledgmentsIdEx Sorbonne Paris Cité and Région Ile de France are acknowledged for their financial support.Pôle image and Coumba Doucouré (Université Paris 13) are acknowledged for their technical support

Topics: pruning waste, pyrolysis, Py-GCMS, biorefinery, waste reduction, low-carbon olive-growing systems, pathogenic strain, EU policy., [ SDE ] Environmental Sciences
Publisher: HAL CCSD
Year: 2016
OAI identifier: oai:HAL:hal-01350824v1
Provided by: Hal-Diderot
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