ENHANCED REMOVABILITY OF ODOROUS SULFUR-CONTAINING GASES BY MIXED CULTURES OF PURIFIED BACTERIA FROM PEAT BIOFILTERS

Four bacteria isolated from peat biofilters, Thiobacillus thioparus DW44, Thiobacillus sp. HA43, Xanthomonas sp. DY44 and Hyphomicrobium sp. I55, were selected to enhanced the removal ratios of hydrogen sulfide (H2S), methanethiol (MT) and dimethyl suflide (DMS) in a mixed gas system. Two bacteria, DW44 and I55, which degrade H2S, MT, DMS and dimethyl disulfide (DMDS), were mixed with DY44 or HA43 which degrade only H2S and MT. Although DMS removal was significantly inhibited by the presence of H2S and MT in a peat biofilter inoculated with the single bacterium, enhanced removability of H2S, MT and DMS was observed by mixing Hyphomicrobium sp. I55 either with Thiobacillus sp. HA43 or Xanthomonas sp. DY44. The removal rate (g-S.Kg-dry peat-1.d-1) by I55 after 8 d was 0.664 in total sulfur load, 0.827 g-S.kg-dry peat-1.d-1, but the rates by the mixed cultures of I55 plus HA43, and I55 plus DY44 were 0.760 and 0.801, respectively. In particular, DMS removability in mixed gases by a mixed culture of I55 and DY44 was almost equivalent to that by I55 when only DMS was supplied, suggesting that removal of H2S and MT, which inhibited DMS removal, was preferentially conducted by DY44 and led to improved DMS removability by I55.