Optimization of SO2 and NOx sequential wet absorption in a two-stage bioscrubber for elemental sulfur valorisation

Removal of SO2 and NOX from flue gases has become an important issue in air pollution control. A two-stage bioscrubber based on a sequential wet absorption of SO2 and NOx followed by a two-stage biological process has been proposed in order to valorise SO2 and NOx by elemental sulphur production. Biological process characterization established a maximum sulfate loading rate (5 kg S·m-3·d-1) and an optimal COD/S ratio (5.4 g O2·g S-1) in order to maximize elemental sulfur production and to avoid biological process limitations. Absorption of SO2 and NOx species is highly dependent on the absorption effluents compositions. In this sense, the success of the two-stage bioscrubber process lies in an optimal sequential transfer of pollutants to the liquid. Differences in the solubility of pollutants enable the individual absorption of pollutants in two in-series scrubbers operated under different pH and residence time conditions. In addition, the use of secondary effluents from the reduction-oxidation biological process as absorbent was demonstrated as a key parameter to improve the efficiency and reduce operating costs.