REDUCTIVE DECHLORINATION OF CHLOROBENZENES IN SURFACTANT-AMENDED SEDIMENT SLURRIES

Microbial anaerobic dechlorination of hexachlorobenzene (HCB) was exam ined in sediment slurries amended with two classes of nonionic surfact ant, polyoxyethylene (POE) sorbitan fatty acid esters (Tweens) and POE alcohols (Brijs). The rationale for surfactant addition was to increa se the bioavailability of highly sorbed organic pollutants to degradin g microorganisms by enhancing their solubility. The solubility of HCB was initially enhanced via micellar partitioning; however, primary deg radation of most surfactants occurred within 10 d. Dechlorination acti vity was significantly reduced at POE alcohol concentrations above the critical micelle concentration (cmc), with or without the occurrence of surfactant degradation. Tween 80 decreased HCB dechlorination at co ncentrations significantly above the cmc (1,500-5,000 mg/L). At concen trations closer to the cmc (300-1,200 mg/L). Tween 80 increased dechlo rination rate constants four- to fivefold in acclimated slurries. Addi tions of Tween 80 at or below the cmc (3, 30, 300, and 911 mg/L) stimu lated dechlorination activity in unacclimated slurries that exhibited very little activity in unamended controls. An average of 89% of HCB w as dechlorinated after 90 d, compared to 20% in unamended sediments. N o effect was observed for POE alcohols at these sub-cmc levels. The la ck of a stimulated response for the POE alcohols suggests that Tween 8 0 may not be acting simply as a source of carbon or energy.