Treatment of Chlorinated Solvents by Nitrogen-Fixing and Nitrate-Supplied Methane Oxidizers in Columns Packed with Unsaturated Porous Media

Abstract

This study compares the feasibility of employing nitrogen-fixing and nitrate-supplied methane-oxidizing cultures grown in unsaturated porous media to degrade cis-1,2-dichloroethylene (cDCE) and trichloroethylene (TCE) in gas streams. Both nitrate-supplied and nitrogen-fixing columns (supplied with 10% CH4 and 10% O2) degraded TCE completely at a gaseous concentration of 0.7 mg/L for 8−10 days. However, when columns were supplied with 4% CH4 and 10% O2, nitrate-supplied columns were not able to recover after degrading TCE at a gaseous concentration of 0.13 mg/L for 7 days. In contrast, nitrogen-fixing columns recovered after degrading 0.13−0.4 mg/L TCE for 3−10 days and were capable of repeatedly degrading TCE at gaseous concentrations of 0.03−0.14 mg/L during long-term intermittent operation (lasting from 38 to 84 days) that was punctuated by appropriate microbial recovery periods (7−9 days). Both nitrate-supplied and nitrogen-fixing columns were capable of degrading cDCE at concentrations of 0.7−1.0 mg/L for 5−10 days, but only the nitrogen-fixing columns recovered from cDCE exposure. The operating period for columns treating a mixture of TCE and cDCE was significantly shorter than that for treatment of TCE or cDCE alone. Several operating curves (percent chlorinated solvent removal versus mass of chlorinated solvent loaded per mass of methane consumed) were developed to facilitate comparisons between operating conditions and to aid in predicting chlorinated solvent removals in such systems. Nitrogen-fixing columns consistently outperformed nitrate-supplied columns, and columns inoculated with a mixed culture outperformed those inoculated with Methylosinus trichosporium OB3b for TCE removal but not for cDCE removal.

nifH Sequences and Nitrogen Fixation in Type I and Type II Methanotrophs

“…However, both type I (LW13, LW15, and the thermophilic Methylococcus capsulatus Bath) and type II strains (LW3, LW4, LW8, PW1, and Methylosinus trichosporium OB3b) have been found that can both express sMMO and fix nitrogen (2,4,13,18,21,24,26,27). The correlation between increased capacity for TCE oxidation and nitrogen fixation in methanotrophs suggests that both type I and type II strains may be suitable for the bioremediation of TCE (5,6,7).…”

“…However, in some vadose zone and aquifer environments, fixed nitrogen may be limiting (5), and methanotrophs capable of nitrogen fixation would have an advantage. Evidence also exists that nitrogen-fixing methanotrophs have an increased capacity for TCE oxidation (5,6,7). Because both type I and type II methanotrophs are now known to possess sMMO, both groups may be important in the bioremediation of TCE.…”

Cometabolic degradation of TCE in enriched nitrifying batch systems

“…The aerobic cometabolism of TCE is known to be initiated by a variety of non-specific oxygenase enzymes of microorganisms grown on a variety of substances like methane, propane, toluene, phenol and ammonia. To date, the cometabolic degradation of TCE is most widely studied in the presence of methanotrophs, propane degraders, toluene degraders and phenol degraders [3][4][5][6][7]. The cometabolic degradation of TCE by ammonia oxidizing bacteria in a nitrification system was first demonstrated by Arciero et al [8].…”

Bacterial community composition determined by culture‐independent and ‐dependent methods during propane‐stimulated bioremediation in trichloroethene‐contaminated groundwater

“…Nitrogen fixation may be important for TCE co‐oxidation. TCE removal by a nitrogen‐fixing, methane‐oxidizing mixed community was found consistently to outperform a non‐nitrogen‐fixing, methane‐oxidizing community that was supplied with nitrogen (Chu and Alvarez‐Cohen, 2000).…”