BRIDGE Projects

Principal Investigator

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Team Members - CEB

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Fellowship Members - CEB

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Abstract

"The multiple roles of soils often go unnoticed. Soils don’t have a voice, and few people speak out for them." José Graziano da Silva, FAO Director-General Mineral oils are one of the main contaminants affecting the quality of soil and groundwater. In Europe, around 342 thousand contaminated sites were identified, and more than 2.5 million may be potentially contaminated [1]. From all the reported incidents of local contamination, mineral oils account for 22-24%, and represent 45% when considered together with BTEX and polyaromatic hydrocarbons [1]. The progress in the management of contaminated sites in Europe was evaluated through the European Environment Information and Observation Network for soil (EIONET-SOIL), but no data was obtained for Portugal. This reflects an important information void in times where soil protection and restoration are worldwide priorities. The importance of targeting a 'land degradation neutral world' was highlighted in the Rio+20 summit, and in December 2013 the UN General Assembly proclaimed 2015 the International Year of Soils. The prevalence of oils in contaminated soil and groundwater calls for increased efforts on research and development, and represent an opportunity for the remediation market. Anaerobic bioremediation techniques present significant potential for ecosystems restoration in the subsurface, where oxygen is scarce. The main objective of this project is to stimulate anaerobic biodegradation of oils in the subsurface through the addition of ferric minerals, assisting in the development of new strategies for improving in situ bioremediation of deep contaminated sites. Anaerobic microorganisms can biodegrade hydrocarbons coupled to the reduction of nitrate, iron(III), sulfate or under methanogenic conditions [2, 3, 4]. Hydrocarbon degrading microorganisms are present in most soils, and may be dominant in oil-polluted ecosystems [5]. However, anaerobic hydrocarbons biodegradation is particularly slow [6]. In previous work developed in our research group, more than 300 days were required for degradation of 1 mM aliphatic hydrocarbons by methanogenic and sulfate-reducing enrichment cultures. Slow microbial growth and low biomass production by the oil-degrading microorganisms, frequently associated with reduced contaminants bioavailability, limit the applicability of in situ bioremediation. Thus, for timely and economically viable regeneration of contaminated sites, stimulation of the microbial processes towards faster and extensive oil degradation is imperative. To tackle this problem, the high potential of ferric minerals will be assessed for stimulating oil components oxidation, as was recently demonstrated for volatile fatty acids, lactate, ethanol, glucose, starch and oleic acid, at mesophilic and thermophilic temperatures [7, 8, 9, 10]. Enhanced oil biodegradation by Fe(III) minerals has been seldom studied, but positive results with BTEX were reported [11, 12, 13]. In our research group, four iron-reducing enriched cultures were developed, in which biodegradation of aliphatic hydrocarbons was coupled to Fe(III)-reduction. This process occurred in less than two months and was significantly faster than sulfate-reduction or methanogenesis-dependent biodegradation. In this project, the effects of five ferric minerals differing in crystallinity and conductivity will be evaluated in laboratory micro- and mesocosms with different microbial communities. Stimulatory effects by selection of Fe(III)-reducing microorganisms, or enhanced interspecies electron transfer in syntrophic processes, will be investigated. Culture-independent approaches will also be used for identification of the main pathways occurring in oil-contaminated soils and detection of the involved microorganisms in the presence of ferric minerals. Sequestration or mobility of hydrocarbons in soil are key issues that will be addressed in the presence or absence of ferric minerals, by performing adsorption/desorption studies. Partition of the different oil components between soil and groundwater, and bioavailability for microbial bioremediation will be evaluated. All the information and knowledge collected during the project will be integrated in a mathematical model, that will allow prediction of the physical-chemical and biological reactions affecting the fate of oil after a subsurface oil spill. This model will be a useful tool for decision making and management of contaminated sites. Future scenarios resulting from different bioremediation techniques can be simulated and compared. Knowledge transfer activities and public outreach will be made for dissemination of project results, including online dissemination in the research group webpage, frequent postings on a Facebook scientific page created for the project, and organization of one symposium. Being this subject of unequivocal international importance, it is also particularly relevant in Portugal, where bioremediation is a relatively new field.

Acknowledgements

Este trabalho é financiado por fundos FEDER através do Programa Operacional Fatores de Competitividade – COMPETE e por Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia no âmbito do projeto PTDC/AAG-TEC/3500/2014.