TCE REMEDIATION USING IN-SITU, RESTING-STATE BIOAUGMENTATION

A field test has demonstrated that an in situ biofilter using resting- state cells effectively remediated groundwater with about 425 ppb of t richloroethene (TCE) as the sole contaminant species. About 5.4 kg (dr y weight equivalent) of a strain of methanotrophic bacteria (Methylosi nus trichosporium OB3b) was suspended in 1800 L of groundwater (5.4 x 10(9) cells/mt) and injected into an aquifer through a single well at a depth of 27 m, several meters below the water table. The injected gr oundwater was devoid of TCE and growth substrates but was amended with a phosphate solution (10 mM) to buffer the pH a nd phenol red (20 mu m) to act as a tracer. Approximately 50% of the injected bacteria atta ched to the sediments, forming an in situ, fixed-bed bioreactor of unk nown geometry. Contaminated groundwater was subsequently withdrawn thr ough the biofilter region by extracting at 3.8 L/min for 30 h and then at 2.0 L/min for the remaining 39 days of the field experiment. TCE c oncentrations in the extracted groundwater decreased from 425 to less than 10 ppb during the first 50 h of withdrawal, which is equivalent t o a 98% reduction. TCE concentration extracted through the biofilter g radually increased to background values at 40 days when the experiment was terminated.