a b s t r a c tThe present work aims to use a two-stage biotrickling filters for simultaneous treatment of hydrogen sulphide (H 2 S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). The first biofilter was inoculated with Acidithiobacillus thiooxidans (BAT) and the second one with Thiobacillus thioparus (BTT). For separate feeds of reduced sulphur compounds (RSC), the elimination capacity (EC) order was DMDS > DMS > MM. The EC values were 9.8 g MM-S /m 3 /h (BTT; 78% removal efficiency (RE); empty bed residence time (EBRT) 58 s), 36 g DMDS-S /m 3 /h (BTT; 94.4% RE; EBRT 76 s) and 57.5 g H2S-S /m 3 /h (BAT; 92% RE; EBRT 59 s). For the simultaneous removal of RSC in BTT, an increase in the H 2 S concentration from 23 to 293 ppmv (EBRT of 59 s) inhibited the RE of DMS (97-84% RE), DMDS (86-76% RE) and MM (83-67% RE). In the two-stage biofiltration, the RE did not decrease on increasing the H 2 S concentration from 75 to 432 ppmv.

Alkaliphilic sulfur-oxidizing bacteria were isolated from an alkaliphilic microbial consortium used to treat H2S at pH>9 in a laboratory scale biofilter. Nineteen isolates were obtained. These isolates could be grouped based on their colonial morphology on a solid medium containing thiosulfate as sole energy source. Half of the isolates presented yellow colonies (group I). This yellowish colonial morphology is typically found in the genus Thioalkalivibrio. For the rest of the isolates, the colonies were white (group II) or transparent (group III). The isolates of each group were characterized by ribosomal intergenic spacer analysis and restriction analysis of their 16S rRNA genes. One of the yellow isolates presented 85% of homology with Thioalkalivibrio jannaschii by partial sequencing of its 16S rRNA gene. The genus Thioalkalivibrio comprises extremely haloalkaliphilic sulfur-oxidizing bacteria that have been proposed as suitable biocatalysts for natural gas desulfurization.