HEXACHLOROBENZENE DECHLORINATION BY ENRICHED MIXED CULTURES FROM THAI CANAL

摘要

After collecting and analyzing the sediments from 10 sites along the Hua-Lum-Poo Canal located in Samut Prakarn, a province of Thailand, hexachlorobenzene (HCB) and 1,3,5-trichlorobenzene (1,3,5-TCB) were found in four sediment samples. 1,3,5-TCB has never been made commercially for industrial and agricultural usage, and most of it was transformed from highly chlorinated benzenes. Therefore, it was suggested that HCB has been dechlori-nated to 1,3,5-TCB in the natural sediment of Hua-Lum-Poo Canal. This study was devoted to investigate the reductive dechlorination of HCB by the anaerobic microorganisms in canal sediments. Indigenous microorganisms from 10 canal sediments were collected and applied to dechlorination experiments. By using anaerobic microbes from pre-enriched natural sediment-water slurries on yeast extract, every set of microorganisms initiated HCB dechlorination after 14 days of incubation and completed the process in a period of 28-42 days. In the sets without yeast extract pre-enrichment, microorganisms also showed dechlorinating activity after 14-28 days of cultivation. Combining the results, it was shown that after 7 days of pre-anoxic and enriched treatment, canal microbes were able to develop HCB dechlorination activity, and completely dechlorinate HCB within 6 weeks. This indicates that the HCB-de-chlorinating microorganisms were prevalent in the sediments along the Hua-Lum-Poo Canal, and possibly remove HCB contamination without any additional nutrient.