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 S0 accumulation in the solution. Meanwhile, the total removal efficiency of NOX achieved ∼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 S0 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, nitrate-reducing bacteria (Azoarcus and Pseudarcobacter) in spray scrubber contributed to the efficient removal of NOX in flue gas.

Revealing the role of nitrate on sulfide removal coupled with bioenergy production in Chlamydomonas sp. Tai-03: Metabolic pathways and mechanisms.

Recently, simultaneous sulfide removal and bioenergy production by microalgal treatment have attracted growing attention. However, the response of nitrogen metabolism to the sulfide-removal process has yet to be explored. Here, variable levels of sulfide could be completely removed by Chlamydomonas sp. Tai-03 under both high and low nitrate conditions in synthetic wastewaters. The highest sulfide removal rate of 5.56 mg-S L-1 h-1 was achieved with the addition of 100 mg L-1 sulfide in the presence of high nitrate. Meanwhile, sulfide was chemically oxidized to sulfate and then ingested by microalgae. Interestingly, sulfide-removal efficiency critically depended on nitrate concentration. Sulfide can also enhance the ability of microalgae to assimilate nitrogen. Based on the analysis of sulfur- and nitrogen-related metabolic profiling, serine as a precursor decreased by 94 % under low levels of nitrate, which induced the significant inhibition of cysteine and methionine biosynthesis. The results indicated that nitrogen source played a critical role in the sulfur cycle because of the positive relationship between the aforementioned metabolic processes and nitrate concentration. Additionally, sulfide can improve lipid and carbohydrate productivity under high levels of nitrate. This study enhances our understanding of the mechanisms underlying the simultaneous removal of sulfide and alternative bioenergy production.