Ecotoxicological Assessment and Effects of Physicochemical Factors on Biofilm Development in Groundwater Conditions

Abstract

A new concept in groundwater containment is the development of a biobarrier formed by the biostimulation of a microbial population and exopolysaccharides (EPS) production. Although the efficiency of biofilms to clog porous media and biotransform contaminants suggests their ap plication in aquifers, work on groundwater conditions has to be performed to confirm the potential of this technology. To determine the feasibility and the ecotoxic potential of biobarrier development, a groundwater indigenous population was inoculated in semicontinuous reactors. The effects of aeration, carbon source, feeding rate, C:N:P ratio, calcium ions, and pentachlorophenol (PCP) on biomass, EPS, and biofilm production was studied by a statistical design. The ecotoxic effect of soluble microbial products (SMPs) was assessed using two biotests: the Selenastrum capricornutum and Microtox (Vibrio fischeri) tests. Results showed that the carbon source type and its feeding rate had a significant impact on biofilm development leading to a maximum biofilm thickness of 250 μm after only 144 h. The ecotoxicological assessment revealed that S. capricornutum growth inhibition reached 80% while 90% of V. fischeri bioluminescence was affected by the presence of SMPs. Also, a toxic response was induced by the presence of PCP. These results showed the potential use of an indigenous microbial population and suggested that the ecotoxic potential has to be taken into account for in situ biobarrier development.