Resumen de Innovative bioprocesses for siloxanes removal from biogas and gaseous emissions/ bioprocesos innovadores para la eliminación de siloxanos del biogás y de emisiones de gases
Nowadays, environmental problems such as climate change, the formation of tropospheric ozone, the overuse of natural resources or atmospheric pollution constitute one of the greatest concerns worldwide. The policies and strategies currently enforced, such as the European Green Deal, are focused on boosting the efficient use of resources by moving towards a clean and circular economy, resilient to climate change and based on the reduction of harmful waste. This implies the implementation of measures that promote the prevention of environmental pollution by reducing the CO2 footprint and the emissions of hazardous compounds.
Silicon derivatives such as siloxanes are among the harmful compounds emitted into the atmosphere from anthropogenic sources. Siloxanes are essential building block materials employed in several industrial sectors and in the manufacture of a large number of consumer products available in the market. This fact results in the emissions of volatile methyl siloxanes (VMS) to the atmosphere, along with their release into landfills and wastewater treatment plants ending up either in the air or in the biogas produced in anaerobic digestion. The potential toxic effect of these emissions has been proved in the bioaccumulation of VMS, affecting the respiratory tract and reproductive system of some animals. Moreover, they have been recently classified as potential compounds responsible for trophic magnification in aquatic and terrestrial food chains. Beyond their harmful effects, their presence in biogas entails a high economic impact during its valorisation as renewable energy due to the oxidation of VMS to silicon dioxide (SiO2) during biogas combustion, a crystalline deposit that causes corrosion of engines and turbines.
In this context, there is a growing interest to develop efficient, sustainable and cost-effective technologies for the treatment and abatement of VMS emissions. Physical-chemical processes appear nowadays as the most efficient technologies for the removal of VMS from gaseous emissions. However, these technologies are characterized by their high operating and maintenance costs, along with their high carbon footprint. On the contrary, biotechnologies based on the biodegradation of VMS by the biological catalytic activity, represent a low cost and environmentally friendly alternative for the treatment of VMS gaseous emissions. However, the low solubility of these compounds in the aqueous phase of bioreactors, where the microorganisms responsible for their degradation uptake the pollutant, reduces the removal efficiency (RE) of these technologies and therefore limits their implementation. The present thesis focusses on the design and optimization of the operating parameters of novel high mass transfer bioreactors, such as two-phase partitioning biotrickling filter, with the aim of improving the removal of VMS by reducing the limitation of mass transfer associated with VMS. In addition, the microbial community involved in the degradation process were also investigated.
The results obtained in this thesis demonstrated the feasibility of high mass transfer biological technologies, especially two-phase partitioning systems, as an innovative alternative for the removal of VMS. TP-BTFs thus stand as a new platform to abate siloxanes from aerobic atmospheric emissions and biogas due to their reduced environmental impact and their low cost compared to physical-chemical processes.
