Reductive Dehalogenation of Trichloroethene Vapors in an Anaerobic Biotrickling Filter

Abstract

Until now, it has not been possible to use biofiltration to treat trichloroethene (TCE) from waste gases generated by soil vapor extraction or dual-phase extraction at remediation sites because aerobic biodegradation of TCE is possible only via cometabolism, which is difficult to engineer on a large scale. This study looks at the possibility of conducting anaerobic gas-phase biotreatment of TCE vapors. The vision is that nitrogen sparging could be substituted for air sparging, resulting in TCE contaminated oxygen-free gas streams which require treatment A lab-scale anaerobic biotrickling filter inoculated with a mixed culture containing multiple Dehalococcoides strains was used for the proof of concept TCE vapors were removed via reductive dechlorination and converted to ethene, cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC). Sodium lactate, a fermentable substrate, was provided to the reactor through the recirculating liquid as a source of hydrogen, the electron donor for Dehalococcoides strains. The biotrickling filter was able to remove >90% TCE at loadings of up to 4 g m(bed)(-3) h(-1) and sustained performance for over 200 days. The distribution of the intermediates of TCE biological reduction was found to be affected by the pH of the recirculating liquid. At pH 8.3, the primary accumulating productwas cis-DCE (approximately 92% of the TCE removed); while at pH 6.85-6.9, conversion to ethene, the intended end product, was 50-67% of the TCE removed. Kinetic determinations using batch biotrickling filter operation showed that VC reduction and not cis-DCE reduction was the sloweststep. Overall, the study shows that sustained anaerobic biotreatment of TCE vapors in biotrickling filters is possible.