Emissions of SOx and NOx from flue gases require treatment before release into the atmosphere according to the current legislation. Available physical-chemical treatments used industrially are expensive and generate effluents that require further processing. Developing a comprehensive treatment process for flue gases by economical, robust and environmentally friendly, biological methods is still challenging. However, the multistage bioscrubber concept developed by UAB and UPC groups in a former project funded by the Spanish Ministry (SONOVA, CTQ2015-69802-C2) has been proven as technically feasible for SOx treatment and points out at a reasonable economical viability for a wide range of scenarios. The proposed process is based on a sequential absorption step for SOx and NOx coupled to a first biological stage catalyzed by sulfate-reducing microorganisms (SRB) for reducing the sulfate/sulfite mixture from the first absorption stage to hydrogen sulfide. A second biological stage catalyzed by sulfide-oxidizing microorganisms (SOB) oxidizes hydrogen sulfide to elemental sulfur for its subsequent recovery.
The ENSURE project basically develops the SONOVA concept to be applicable in practice by pursuing: i) the removal of NOx, which has been shown inefficient with conventional technologies, ii) sulfidogenesis, which must be improved to ensure process stability and to maximize bioreactors capacities, and iii) process monitoring, which needs of further development of analytical techniques to improve current knowledge. NOx removal will be achieved by testing different approaches from enhanced mass transfer bioreactors to new absorption drivers such as ionic liquids. Sulfidogenesis will be improved by further reactor testing and promoting the growth of acetotrophic SRB. Monitoring will be addressed both through the development of microfluidic systems for S and N species and the use of inkjet printing and the development of biofilm-based microelectrodes for volatile fatty acids analysis. Previous aspects will be complemented with the use of modeling techniques and a range of tools such as batch tests and flat plate bioreactors to determine the activity of SRB. Finally, all stages of the proof of concept will be integrated to practically assess the viability of the SOx and NOx removal process with valuable by-products generation.