Enhanced In Situ Bioremediation of Tetrachloroethylene with Electrochemical Injection of Lactate

摘要

A series of experiments evaluated the efficacy of injecting lactate amendment into a low-permeability, silty clay (k_h = 2×10~(-7) cm s~(-1)) using electrochemistry. These experiments mixed Dehalococcoides dechlorinator KB-1~(TM) culture (SiREM, Ontario, Canada) with PCE (20 mg L~(-1) in the pore water) in a clay-water slurry and consolidated the slurry into 40-cm long cells inside a nitrogen filled anaerobic chamber. Duplicate experiments with the PCE/KB-1~(TM) mixture were operated as control (no electricity applied) and duplicate PCE/KB-1~(TM) mixture bioremediation experiments were conducted under 5.3 A m~(-2) and 13.3 A m~(-2) current densities. Results from electrochemical injection experiments show that effective lactate injection was achieved under a current density of 5.3 A m~(-2) with final pore water lactate concentrations as high as 3,000 mg L~(-1) . The ion migration rate was more than 191 times faster than transport under a hydraulic gradient. Biological fouling usually observed in the hydraulic delivery experiments was not observed under these experiments. The PCE and the KB-1~(TM) culture mixed (no electricity) with the clay resulted in partial dechlorination of PCE halting at cis-DCE presumably because of absence of an electron donor. The duplicate PCE and KB-1? culture experiments with lactate injection by electrochemical means completely degraded PCE to ethene within 4 months across the 40 cm long silty clay medium. PCE was transformed to DCE following a zero order rate of 0.0063 to 0.027 mmol L~(-1)d~(-1) and the transformation of DCE to ethane followed a first order rate of 0.0577 to 0.254 d~(-1). The soil pH remained between 7 and 7.5 throughout the experiments.