Anaerobic dechlorination of hexachlorobenzene in contaminated sediment

Abstract

Hexachlorobenzene (HCB) is persistent organic pollutant that was found in the sediment from the canal near Bang Poo Industrial Estate, Thailand. Microbial anacrobic dechlorination was investigated to remove HCB from contaminated sediment. The objective of this study was to accelerate the dechlorination rate of HCB by examine the role of various types of carbon-source supplementation and the role of sludge to contaminated sediment quantity. The dechlorination was demonstrated in twenty-ml syringe under anaerobic condition containing HCB-contaminated sediment and homogenized granular sludge from anaerobic digestion, which was maintained at total of ten grams (dry weight of sediment and wet weight of homogenized granular sludge), and ten ml of nutrient media. The experiments were conducted for nine weeks and samples were analyzed every two weeks. The decreasing of HCB at designated time was fitted with first-order equation in order to obtain the comparable dechlorination rate. No significant decreasing of HCB was observed in control set. The dechlorination rate was observed in the range of 0.028 to 0.143 day-1, which glucose provided the highest dechlorination rate as 0.143 day-1. It was found that the rate of dechlorination was increased 5.18 times when carbon-source was added. It was 2.16 times increasing in dechlorination rate when higher sludge to sediment ratio was used. The combined role of carbon source supplementation and sludge to sediment ratio resulted in increasing dechlorination rate of 5.59 times. These results implied that both carbon-source and sludge quantity affect the microbial dechlorination of hexachlorobenzene.