This study evaluates hexachlorobenzene (HCB) dechlorination in pre-treated sediment-water slurries and untreated fresh sediment water slurries. Sediment and water samples were collected from 5 different sites along the Hua-Lum-Poo Canal in Samut Prakarn Province of Thailand. In HCB dechlorination experiments of pre-treated slurries, a variety of natural sediment-water slurries were used as sole cultural media without any supplement and extra nutrient. Sediment-water slurries were prepared in different methods, including the sediment to water ratio of 1:2 and 1:4, with or without sterilization, with or without filtration, and with 3 or 7 days of pre-anoxic treatments. Afterwards, 5 ml of inoculation was added into slurries and spiked with HCB in a serum bottle. The results showed that HCB was dechlorinated more effectively in the sediment to water ratio of 1:2 than in the ratio of 1:4. In the sterilization bottles without inoculation, dechlorination did not happen. With inoculation, HCB dechlorination was observed both in the filtrated and non-filtrated sediment slurry bottles. In addition, HCB dechlorination was better in slurries with 7 days of pre-anoxic treatment than those with 3 days of treatment. For experiments of non-treated fresh slurries, the sediment-water slurries were prepared with sediment to water in the ratio of 1:1 and 1:2. Without any inoculation and extra nutrient put into these bottles, most of the fresh slurries completed HCB dechlorination in a remarkably speed within 8 weeks. The results suggested that the indigenous microbes of the canal were active in HCB de-chlorination and also showed the possibility of natural attenuation and bioremediation of HCB-contamination in these sites.
