Subsurface biofilm barriers for contaminated ground water containment

Abstract

Biofilm barriers are developed by injecting large numbers of mucoid bacteria into permeable strata formations. The bacteria are mixed with water and pumped down a series of injection wells. A suitable growth substrate and additional nutrients then are injected to stimulate microbial growth. These mucoid bacteria are capable of forming large quantities of extracellular polymer material (EPS) during their growth phase. Bacterial growth and EPS production form microbial biomass which substantially reduces the free pore space in the formation and consequently reduces the hydraulic conductivity. This zone of reduced hydraulic conductivity serves as a novel barrier technology for controlling off-site migration of mobile contaminants. Biobarrier technology also may be a useful means of funneling contaminated ground water through subsurface treatment systems (i.e., zero-valent iron systems). The main advantages offered by biobarrier technology are: 1) biobarrier construction is achieved without excavation and therefore will be economically attractive at many sites; and 2) there is no obvious depth limitation for biobarrier technology. Traditional subsurface barrier technologies such as slurry walls and grout curtains are not usually cost effective at depths more than 50 feet.