Full-Scale Evaluation of In Situ Cometabolic Degradation of Trichloroethylene in Groundwater through Toluene Injection

Abstract

Groundwater contaminated with 500−1200 μg/L trichloroethylene (TCE) was treated in situ over a 410-day period by cometabolic biodegradation through injection of 7−13.4 mg/L toluene, oxygen, and hydrogen peroxide in groundwater circulated between two contaminated aquifers through two treatment wells located 10 m apart. One well pumped contaminated groundwater from the 8 m thick upper aquifer to the 5 m thick lower aquifer, while the other pumped contaminated water from the lower to the upper aquifers using flow rates of 25−38 L/min, effecting groundwater circulation between them. Following 18 days of periodic toluene injection to develop an active biological population, continuous pulses of toluene were added. Over 312 days, an average 87 ± 8% TCE removal was obtained in the upper aquifer with each pass through the treatment well. In the lower aquifer, removals were 83 ± 16% over the last 79 days when peroxide addition was reduced. Treatment reduced TCE in the regional groundwater plumes from about 1000 μg/L in new water entering the 480 m2 monitored treatment zone to an average of 18−24 μg/L in groundwater leaving the treatment zone, indicating total TCE removal of 97−98%. Pumping heads for groundwater recirculation were less than 6 m. Toluene was removed by 99.98% through biodegradation to an average of 1.1 ± 1.6 μg/L at the 22 m × 22 m boundaries of the study zone, well below the goal of 20 μg/L maximum.

Unique Kinetic Properties of Phenol-Degrading Variovorax Strains Responsible for Efficient Trichloroethylene Degradation in a Chemostat Enrichment Culture

“…Indeed, TCE is considered to be a potentially serious threat to drinking water sources (26). Considering this, research that has focused on both anaerobic reductive dechlorination and aerobic degradation via cometabolism has been under development (25,33).…”

Characterization of the Adaptive Response to Trichloroethylene-Mediated Stresses in Ralstonia pickettii PKO1

“…In oxic contaminated subsurface environments, TCE can be degraded by means of a cooxidation reaction catalyzed by microbial oxygenases such as ammonia monooxygenase (2), alkene monooxygenase (8,9), methane monooxygenase (12,23), propane monooxygenase (24), toluene dioxygenase (6,14,52), and toluene monooxygenase (11,33,48). Among these, TCE cooxidation by bacteria carrying toluene oxygenase pathways has been of particular interest in environmental microbiology, since studies have shown that aerobic TCE biodegradation is stimulated in situ when toluene is added (15,26).…”

Enhancing bacterial transport for bioaugmentation of aquifers using low ionic strength solutions and surfactants

“…Instead of trying to disperse bacteria over large distances, investigators have chosen to create smaller, bioactive zones of <1 m (McCarty et al, 1998). It is feasible to distribute cells over these smaller distances and the injection of nutrients into smaller bioactive zones can be more carefully controlled than more widespread nutrient additions and therefore are more likely to support the injected microbes than the indigenous community.…”