The objective of this paper is to present evidence for the possibility of enhanced metal precipitation inside denitrifying biofilms. The pH environment surrounding microorganisms growing in biofilms is frequently different than the environment of the bulk liquid because products of metabolic reactions are limited in their ability to diffuse out of the biofilm. In the case of denitrifying biofilms, the interior pH will be higher than the pH in the bulk liquid, creating conditions that favor precipitation of heavy metals. A theoretical model was used to predict pH inside denitrifying biofilms. Copper and nickel solubities were calculated as a function of pH and alkalinity. Results provide evidence to support the theory that higher internal pH can result in greater metal removal by the biofilms.