Impact of colony morphologies and disinfection on biological clogging in porous media

Biological clogging of aquifers and other porous media during bioremediatio n, sand filtration, and aquifer recharge is a significant problem that is y et poorly understood and controlled. One major difficulty is the relatively few direct observations of clogging phenomena, which are required to adequ ately validate numerical models for predicting flow through porous media. V isualization of biological growth with time and accompanying reductions in hydraulic conductivity were obtained using two-dimensional micromodels of p orous media. The micromodels were seeded with mixed microbial cultures to a llow natural selection of dominant aerobic morphologies following continuou s feed of culture media containing 1.36-1.69 mM acetate flowing at 0.9-3.6 m/day specific discharge velocity. Of the several different resulting colon y morphologies, filaments dominated at pH 3, while biofilms and aggregates dominated at neutral pH. Conductivity decrease correlated with biological g rowth and morphology, and sudden conductivity recoveries correlated with sl oughing events. Periodic chlorine disinfection resulted in temporary increa se in conductivity and helped open channels of flow between dense colonies. However, aggregates of organisms exhibited increased resistance to chlorin e disinfection with rime, reducing disinfection effectiveness. Continuous, rather than periodic, disinfection is recommended. Models for biological su bstrate removal and clogging should incorporate different growth morphologi es to produce satisfactory simulation results.