Treatment of chlorinated solvents by nitrogen-fixing and nitrate-supplied methane oxidizers in columns packed with unsaturated porous media

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% O-2) 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% O-2, 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.