METHANOTROPHIC BACTERIA AND FACILITATED TRANSPORT OF POLLUTANTS IN AQUIFER MATERIAL

In situ stimulation of methanotrophic bacteria has been considered as a methodology for aquifer remediation. Chlorinated aliphatic hydrocarb ons such as trichloroethylene are fortuitously oxidized by the methane monooxygenase produced by methanotrophic bacteria. Experimental resul ts are presented that indicate that both colloidal suspensions contain ing methanotrophic cells and the soluble extracellular polymers produc ed by methanotrophic cells have the potential to enhance the transport and removal of other environmental contaminants such as polynuclear a romatic hydrocarbons and transition metals in aquifer material. Three well-characterized methanotrophic bacteria were used in the experiment s: Methylomonas albus BG8 (a type I methanotroph), Methylosinus tricho sporium OB3b (a type II methanotroph), and Methylocystis parvus OBBP ( a type II methanotroph). Isotherms were obtained for sorption of two r adiolabeled pollutants, [C-14]phenanthrene and Cd-109, onto an aquifer sand in the presence and absence of washed cells and their extracellu lar polymer. Column transport experiments were performed with the wash ed methanotrophic cells and phenanthrene. The distribution coefficient s for Cd with extracellular polymers were of the same order as that ob tained with the aquifer sand, indicating that polymers from the methan otrophic bacteria could act to increase the transport of Cd in a porou s medium. Polymer from BG8 significantly reduced the apparent distribu tion coefficient for Cd with an aquifer sand. [C-14]phenanthrene also sorbed to extracellular polymer and to washed, suspended methanotrophi c cells. The exopolymer of BG8 and OBBP significantly reduced the appa rent distribution coefficient (K-d) for phenanthrene with aquifer sand . The distribution coefficients for phenanthrene with the methanotroph ic cells were an order of magnitude greater than those previously repo rted for other heterotrophic bacteria. Cells of the methanotrophs also significantly reduced the apparent K-d for phenanthrene with an aquif er sand. The three strains of methanotrophs tested displayed mobility in a column of packed sand, and strain OBBP reduced the retardation co efficient of phenanthrene with an aquifer sand by 27%. These data indi cate that both extracellular polymer and mobile cells of methanotrophi c bacteria display a capacity to facilitate the mobility of pollutant metals and polynuclear aromatic hydrocarbons in aquifer material.