TRICHLOROETHYLENE BIODEGRADATION BY MESOPHILIC AND PSYCHROPHILIC AMMONIA OXIDIZERS AND METHANOTROPHS IN GROUNDWATER MICROCOSMS

This study investigated the efficiency of methane and ammonium for sti mulating trichloroethylene (TCE) biodegradation in groundwater microco sms (Basks and batch exchange columns) at a psychrophilic temperature (12 degrees C) typical of shallow aquifers in the northern United Stat es or a mesophilic temperature (24 degrees C) representative of most l aboratory experiments, After 140 days, TCE biodegradation rates by amm onia oxidizers and methanotrophs in mesophilic Bask microcosms were si milar (8 to 10 nmol day(-1)), but [C-14]TCE mineralization (biodegrada tion to (CO2)-C-14) by ammonia oxidizers was significantly greater tha n that by methanotrophs (63 versus 53%). Under psychrophilic condition s, [C-14]TCE mineralization in flask systems by ammonia oxidizers and methanotrophs was reduced to 12 and 5%, respectively, In mesophilic ba tch exchange columns, average TCE biodegradation rates for methanotrop hs (900 nmol liter(-1) day(-1)) were not significantly different from those of ammonia oxidizers (775 nmol liter(-1) day(-1)). Psychrophilic TCE biodegradation rates in the columns were similar with both biosti mulants and averaged 145 nmol liter(-1) day(-1), Methanotroph biostimu lation was most adversely affected by low temperatures. At 12 degrees C, the biodegradation efficiencies (TCE degradation normalized to micr obial activity) of methanotrophs and ammonia oxidizers decreased by fa ctors of 2.6 and 1.6, respectively, relative to their biodegradation e fficiencies at 24 degrees C, Collectively, these experiments demonstra ted that in situ bioremediation of TCE is feasible at the psychrophili c temperatures common in surficial aquifers in the northern United Sta tes and that for such applications biostimulation of ammonia oxidizers could be more effective than has been previously reported.