MODELING OLIGOTROPHIC BIOFILM FORMATION AND LEAD ADSORPTION TO BIOFILM COMPONENTS

Mechanisms governing trace metal interactions with biogenic materials in oligotrophic freshwater aquatic environments were investigated with a laboratory biofilm reactor system using lead as a model compound. U se of controlled laboratory conditions, including a chemically defined medium and an axenic bacterial culture, permitted the development of a mechanistic model to describe lead distribution via the integration of biological models, lead adsorption isotherms, and a chemical specia tion program. Concentrations of suspended and attached cells and their extracellular polymers were accurately modeled by defining the proces ses of growth, cell attachment, and polymer production. Specific extra cellular polymer production rates were observed to be similar for susp ended and attached cells, but the polymer produced by attached cells a ppeared to remain in the biofilm matrix, while the dissolved polymer p roduced by suspended cells washed out of the reactor. Extracellular po lymer constituted up to 80% of the total biofilm organic material (bas ed on chemical oxygen demand), and its specific binding capacity for l ead was three times higher than that of bacterial cells. Thus, predict ed lead binding to extracellular polymer overshadowed lead binding to cells in the biofilms. The integrated model overpredicted lead binding to biofilms by about 30%, indicating the possibility of some masking of available adsorption sites in the biofilm.