Microcosm testing with a mixed trichloroethene (TCE) and 1,1,1- trichloroethane (TCA) degrading culture was performed as part of an enhanced in situ biodegradation (EISB) system optimization program. Field data from a Southeastern Pennsylvania Superfund Site EISB pilot test showed only incomplete degradation of volatile organic compounds (VOCs) occurred after biostimulation with methanol, ethanol and lactate, and bioaugmentation with a commercial preparation of Dehalococcoides. Two potentially inhibitory conditions exist in the site ground water: 1. Compounds with known inhibitory properties such as chloroform and TCA present in the 1 to 20 ppm range; and, 2. Compounds such as cis-1,2-dichloroethene (cis-DCE), not generally known to be inhibitory at low ppm concentrations, but possibly inhibitory at high concentration (i.e. >100 ppm).
A microcosm study was performed via two approaches to rectify the incomplete biodegradation observed in the field. The primary approach was to test bioaugmentation cultures that are resistant to inhibitors in the site ground water. The second approach involved a procedure to gradually acclimate the culture to higher VOC concentrations. The initial microcosm VOC concentrations were CIS-DCE (94.8 PPM), TCE (42.8 PPM), 1,1,1-TCA (15 PPM), 1,1-dichlororethene (1,1-DCE, 2.7 PPM), chloroform (1.7 PPM), and tetrachloroethene (PCE, 1.6 PPM) with 1,2-dichloroethane (1,2-DCA), 1,1-dichlororethane (1,1-DCA) and vinyl chloride present at lower concentrations.
The microcosm study was performed with a bioaugmentation culture unsusceptible to high concentration TCE and TCA inhibition. Unknown was the potential inhibition due to chloroform, high cis-DCE concentrations, and the effect of excess nutrients such as methanol and ethanol present in the site ground water from ongoing electron donor addition activities. We describe our initial approach to solving the problem.