Biodegradation of biodiesel and toluene under nitrate-reducing conditions and the impact on bacterial community structure
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Biodiesel is a renewable fuel that can be mixed with toluene and be accidentally released into anoxic ecosystems and impact soil microbial communities. Therefore, the aim of the present work was to examine, under nitrate-reduction conditions, the biodegradation of toluene in the presence of two different types of biodiesel (sunflower and rapeseed), and their impact on the bacterial community structure.
Materials and methods
Sediment samples were spiked individually with toluene, biodiesel, and their blends in laboratory-designed microcosms. Sunflower oil biodiesel was produced in the laboratory, while rapeseed oil biodiesel was a commercial product. Degradation of biodiesels and blends was monitored by directly measuring the substrate or indirectly by determining nitrate removal during the course of the experiment. Denitrification rates were estimated with the acetylene inhibition technique. Denaturing gradient gel electrophoresis was used to assess impacts on the bacterial community structure exposed to biodiesels, blends, and toluene.
Results and discussion
The results of this study showed that toluene and biodiesel were completely degraded within 10 days. Biodiesel significantly affected the bacterial community structure at a similar magnitude, independently of its origin. Additionally, toluene impacted the bacterial community and denitrification process to a lower extent than biodiesel and a clear decrease in the relative bacterial richness and diversity was shown in samples with biodiesel and blends. To the best of our knowledge, this is one of the first reports describing degradation of biodiesel alone and blends under nitrate-reducing conditions, and also the effects of these compounds on the denitrification process. In addition, due to the recently discovered “oxygenic denitrification” process, the acetylene inhibition technique and nitrous oxide quantification may not be the most adequate tool to estimate denitrification rates. Further detailed studies are advised to understand whether the identified bacterial community shift impacts ecosystem functions.
Our results help to understand the biodegradation of toluene, biodiesel, and their blends in sediments under nitrate-reducing conditions and might be important in implementing bioremediation strategies in anoxic environments.
KeywordsAcetylene inhibition technique Biodiesel Bioremediation Microbial community structure Soil Toluene
The authors acknowledge the anonymous reviewers and editors for their valuable comments and suggestions, which were helpful in improving the manuscript.
The authors acknowledge the Portuguese Science and Technology Foundation (FCT) for the following financial support: the research grant SFRH/BPD/112485/2015 and other funds within the project PTDC/AAG-TEC/4403/2012, financed by national funds through FCT/MEC (PIDDAC) and co-financed by FEDER through COMPETE (POFC) FCOMP-01-0124-FEDER-027941 and the Project UID/EQU/00511/2013-LEPABE (Laboratory for Process Engineering, Environment, Biotechnology and Energy – EQU/00511) by FEDER funds through Programa Operacional Competitividade e Internacionalização – COMPETE2020. This research was also partially supported by the Structured Program of R&D&I INNOVMAR - Innovation and Sustainability in the Management and Exploitation of Marine Resources (reference NORTE-01-0145-FEDER-000035, Research Line ECOSERVICES).
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