Simultaneous removal of NOx and SO2 from flue gas in an integrated FGD-CABR system by sulfur cycling-mediated Fe(II)EDTA regeneration

Chemical absorption-biological reduction (CABR) process is an attractive method for NOx removal and Fe(II) EDTA regeneration is important to sustain high NOx removal. In this study a sustainable and eco-friendly sulfur cycling-mediated Fe(II)EDTA regeneration method was incorporated in the integrated biological flue gas desulfurization (FGD)-CABR system. Here, we investigated the NOx and SO2 removal efficiency of the system under three different flue gas flows (100 mL/min, 500 mL/min, and 1000 mL/min) and evaluated the feasibility of chemical Fe(III)EDTA reduction by sulfide in series of batch tests. Our results showed that complete SO2 removal was achieved at all the tested scenarios with sulfide, thiosulfate and S-0 accumulation in the solution. Meanwhile, the total removal efficiency of NOx achieved similar to 100% in the system, of which 3.2%-23.3% was removed in spray scrubber and 76.7%-96.5% in EGSB reactor along with no N2O emission. The optimal pH and S2-/Fe(III)EDTA for Fe(II)EDTA regeneration and S-0 recovery was 8.0 and 1:2. The microbial community analysis results showed that the cooperation of heterotrophic denitrifier (Saprospiraceae uncultured and Dechloromonas) and iron-reducing bacteria (Klebsiella and Petrimonas) in EGSB reactor and sulfide-oxidizing, nitratereducing bacteria (Azoarcus and Pseudarcobacter) in spray scrubber contributed to the efficient removal of NOx in flue gas.

Automated summary

Chemical absorption-biological reduction (CABR) process is an attractive method for NOx removal, and Fe(II) EDTA regeneration is crucial for sustaining high NOx removal efficiency. In this study, a sustainable and eco-friendly sulfur cycling-mediated Fe(II)EDTA regeneration method was incorporated into an integrated biological flue gas desulfurization (FGD)-CABR system. Complete SO2 removal was achieved at all tested scenarios with sulfide, thiosulfate, and S-0 accumulation in the solution. The total removal efficiency of NOx in the system was close to 100%, with different proportions removed in the spray scrubber and EGSB reactor, accompanied by no N2O emission. Microbial community analysis revealed the cooperation of denitrifying and iron-reducing bacteria in the EGSB reactor, as well as sulfide-oxidizing and nitrate-reducing bacteria in the spray scrubber contributed to efficient NOx removal in flue gas.