(105b) Simultaneous Desulfurization and Denitrification of Flue Gas with Haloalkaliphilic Bacteria

Sulfur dioxide and nitrogen oxides from flue gas are major pollutants in air. Haloalkaliphilic microorganisms are used to treat flue gas in this study.

The process of sulfate reduction by haloalkaliphilic microorganisms was feasible. Compared with lactate, ethanol was a more appropriate electron donor for haloalkaliphilic sulfate-reducing bacteria (SRB). When ethanol was used as sole electron donor with COD/SO₄^2− ratio of 4.0, the optimum HRT was 18 h with a sulfate removal efficiency of 97.8% and a sulfate removal rate of 6.26 kg/m³ d. There was no sulfide inhibition in haloalkaliphilic sulfate-reducing bioreactor. Based on denaturing gradient gel electrophoresis analysis of 16S rRNA, the major SRB was Desulfonatronovibrio sp. and Desulfonatronum sp.

The effects of nitrate and salinity on the performance of haloalkaliphilic sulfate-reducing bioreactors were investigated. It was found that when COD/SO₄^2- and HRT were 2.35 and 24 h, respectively, the addition of nitrate did not affect the performance of sulfate-reducing bioreactor when nitrate concentration was below 1000 mg/L. This result indicated that the process of haloalkaliphilic simultaneous desulfurization and denitrification was feasible. When nitrate concentration reached 1500 mg/L, sulfate reduction was obviously inhibited by nitrate. Activities of other microorganisms were also inhibited by nitrate. It was found that concentration of sulfate reduced at the bottom of bioreactor accounted for 62.1% of total concentration of sulfate reduced in bioreactor.

When HRT was 24 h, the optimum NO₃^−/SO₄^2− ratio was 3.0 with a nitrate removal rate of 6.0 kg/m³ d and a sulfate removal rate of 1.39 kg/m³ d, respectively. There was no sulfide inhibition in bioreactor. Lactate was a more appropriate electron donor for denitrifying bacteria (DB), while SRB preferred to utilize ethanol. Based on denaturing gradient gel electrophoresis analysis of 16S rRNA, the major SRB and DB were Desulfonatronovibrio sp. and Halomonas campisalis, respectively. Decrease in NO₃^-/SO₄^2- ratio led to obvious changes in bacterial community. Although the SRB became dominant, the population of DB also increased.

These results indicated that haloalkaliphilic microorganisms can reduce sulfate and nitrate simultaneously at high salinity with high absorption efficiency and low cost.