Advances in bioremediation techniques for the degradation of hydrocarbons in soils

Abstract

Nowadays, one of the most important problems to be solved as a society is environmental pollution. Special attention has been received to the decontamination of water and air, but there are more contaminated sites where the soil is in a very poor condition and can cause significant damage, which in many cases is already irreversible. Although different pollutants are appearing in the soil, and in many cases mixtures of them, one of the main pollutants to be treated are petroleum hydrocarbons, their complexity and recalcitrant nature make them very difficult to degrade and involve a very high economic cost. Therefore, the main objective of this doctoral thesis was to improve existing bioremediation methods, in a soil highly contaminated with long chain hydrocarbons and other pollutants such as heavy metals, to carry out an effective, sustainable, and economically viable restoration of the areas contaminated with this type of pollutants. Throughout this research, an exhaustive analysis of the application of biostimulation, bioaugmentation and bioelectrochemical technologies is showed, evaluating the optimisation of these technologies, the effectiveness in the degradation of pollutants, the improvement with the incorporation of additives or organic amendments, and environmental sustainability. In addition, this work addresses the limitations and challenges associated with the application of bioremediation techniques, with particular emphasis on the need for further research and development of these techniques to optimise their effectiveness. Firstly, an analysis is made of the importance of the soil and the contamination present in it, as well as all the existing technologies that are commonly used for the mitigation of hydrocarbons, to conclude with the objectives. Following with the background that led us to the development of this research and the scope of the application techniques, putting in context the development of this doctoral thesis through the European Project GREENER H2020. Secondly, and as a central part, three chapters are developed corresponding to three experiments, two at laboratory scale and one at pilot scale, in which different solutions are developed to optimise the degradation mainly of petroleum hydrocarbons, showing the importance of the selection of soil conditions to improve the effectiveness of the techniques. In addition, for the improvement of the biostimulation and bioaugmentation techniques tested during the development of these experiments, different organic amendments and additives, nutrient solutions and a passive bioelectrochemical system were tested. Finally, a review is made not only of the above mentioned, but also an overview of all the experiments developed throughout the period in which this doctoral thesis has been developed, emphasising the development of technologies from laboratory scale, to pilot scale, and as a last step to real scale, being able to understand more precisely the operation of the techniques and the improvement in their optimisation and effectiveness. The results obtained contribute to the advancement of bioremediation of soils contaminated with petroleum hydrocarbons and other xenobiotic pollutants and to the development of integrated approaches for sustainable soil management. This thesis provides valuable insights into the potential of bioremediation techniques to address soil contamination and the need for further research to develop more effective techniques.