Simultaneous bio-reduction of trichloroethene, trichloroethane, and chloroform using a hydrogen-based membrane biofilm reactor

Abstract

The contamination of water by chlorinated solvents is recognized as a serious and widespread problem throughout the industrialized world. Here, we focus on three chlorinated solvents that are among those most commonly detected and that have distinct chemical features: trichloroethene (TCE), trichloroethane (TCA), and chloroform (CF). Because many contaminated waters contain mixtures of the chlorinated solvents, a treatment technology that detoxifies all of them simultaneously is highly desirable. The membrane biofilm reactor (MBfR) is a recent technological advance that makes it possible to deliver H2 gas to bacteria efficiently and safely, despite hydrogen's low water solubility and risk of forming a combustible atmosphere when mixed with air. The objectives of this work are to document whether or not the three chlorinated compounds can be dechlorinated simultaneously in a H2-based MBfR and to determine if competitive or inhibitory interactions affect bio-reduction of any of the solvents. The main finding is a demonstration that directly using H2 as the electron donor makes it possible to bio-reduce combinations of different chlorinated solvents. This finding supports that the H2-based MBfR can treat multiple chlorinated solvents in one step, addressing a common groundwater situation. We saw possible evidence of inhibition by CF at a concentration greater than about 1 μM, competition for H2 from sulfate and nitrate reductions, and possible inhibition of TCE reduction from the accumulation of chloroethane (CA) or chloromethane (CM).