SOIL-ENHANCED AND SURFACTANT-ENHANCED REDUCTIVE DECHLORINATION OF CARBON-TETRACHLORIDE IN THE PRESENCE OF SHEWANELLA-PUTREFACIENS 200

Sorption of organic contaminants to soils has been shown to limit bioa vailability and biodegradation in some systems. Use of surfactants has been proposed to reverse this effect. In this study, the effects of a high organic carbon content soil and a nonionic surfactant (Triton X- 100) on the reductive dechlorination of carbon tetrachloride (CCl4,) w ere examined in anaerobic systems containing Shewanella putrefaciens. Although more than 70% of the added CCl4, was sorbed to the soil phase in these systems, the reductive dechlorination of CCl4, was not dimin ished. Rather, rates of CCl4, dechlorination in systems containing soi l were enhanced relative to systems containing non-sorptive sand slurr ies. This enhancement was also observed in sterile soil slurries to wh ich a chemical reductant, dithiothreitol was added. It appears that th e organic soil used in these experiments contains some catalytic facto r capable of transforming CCl4, in the presence of an appropriate chem ical or microbial reductant. The addition of Triton X-100 to sand and soil slurries containing S. putrefaciens resulted in increased CCl4, d egradation in both systems. The effect of Triton could not be explaine d by: (i) surfactant induced changes in the distribution of CCl4, (i.e . decreased sorption) or the rate of CCl4, desorption; (ii) a direct r eaction between Triton and CCl4,; or (iii) increased cell numbers resu lting from use of the surfactant as a substrate. Rather, it appears th at Triton X-100 addition resulted in lysis of bacterial cells, a relea se of biochemical reductant, and enhanced reductive transformation of CCl4,. These results provide insights to guide the development of more effective direct or indirect bioremediation strategies. (C) 1997 Else vier Science B.V.