IN-SITU BIOREMEDIATION OF TRICHLOROETHYLENE-CONTAMINATED WATER BY A RESTING-CELL METHANOTROPHIC MICROBIAL FILTER

An in situ microbial filter technology is being tested and developed f or remediating migrating subsurface plumes contaminated with low conce ntrations of trichloroethylene (TCE). The current focus is the establi shment of a replenishable bioactive zone (catalytic filter) along expa nding plume boundaries by the injection of a representative methanotro phic bacterium, Methylosinus trichosporium OB3b. This microbial filter strategy has been successfully demonstrated using emplaced, attached resting cells (no methane additions) in a 1.1 m flow-through test bed loaded with water-saturated sand. Two separate 24 h pulses of TCE (109 ppb and 85 ppb), one week apart, were pumped through the system at a flow velocity of 15 mm h-1; no TCE (< 0.5 ppb) was detected on the dow nstream side of the microbial filter. Subsequent excavation of the wet sand confirmed the existence of a TCE-bioactive zone 21 days after it had been created. An enhanced longevity of the cellular, soluble-form methane monooxygenase produced by this methanotroph is a result of th e laboratory bioreactor culturing conditions. Additional experiments w ith cells in sealed vials and emplaced in the 1.1 m test bed yielded a high resting-cell finite TCE biotransformation capacity of about 0.25 mg per mg of bacteria; this is suitable for a planned sand-filled tre nch field demonstration at a Lawrence Livermore National Laborato site .