Study on H2S Removal in the Bio-Trickling Filter via Denitrification thiobacillus Under Anaerobic Conditions

Abstract

Denitrification thiobacillus has been used to inoculate a bio-trickling filter packed with volcanic rocks to remove H₂S from mixed gas under anaerobic conditions. A batch experiment was carried out to check the transformed form of element S under Denitrification thiobacillus under anaerobic conditions. The degradation mechanism of H₂S was predicted. Results showed that the removal efficiency of 93 % was obtained at pH of 7, the inlet gas empty bed residence time (EBRT) of 30 s, the inlet H₂S concentration of 500 ppm and the flow rate of the nutrient solution circulating counter-currently of 25 L h^-1. It was inferred that almost all the H₂S was transferred by biodegradation but not chemical absorption. It was found that H₂S was transferred into element S⁰, SO₄^2-, S₂O₃2- and SO₃^2- etc. Calculated results showed that the total amount of element S after H₂S was degraded was equal to the amount before H₂S was degraded. When H₂S concentration was far less than NO₃^- concentration, H₂S was almost completely converted into SO₄^2-. On the contrary, when H₂S oncentration was far more than NO₃^- concentration, the excess H₂S was transferred into S⁰ by the reaction with SO₄^2- under Denitrification thiobacillus. When S^2-/NO₃^- was 1.25/2, nearly half of the H₂S was transferred into S₂O₃^2- and SO₃^2-, 1/4 of the H₂S was transferred into SO₄^2- and element S⁰ production was very little.