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

Biological clogging of aquifers and other porous media during bioremediation, sand filtration, and aquifer recharge is a significant problem that is yet poorly understood and controlled. One major difficulty is the relatively few direct observations of clogging phenomena, which are required to adequately validate numerical models for predicting flow through porous media. Visualization of biological growth with time and accompanying reductions in hydraulic conductivity were obtained using two-dimensional micromodels of porous media. The micromodels were seeded with mixed microbial cultures to allow natural selection of dominant aerobic morphologies following continuous 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 colony morphologies, filaments dominated at pH 3, while biofilms and aggregates dominated at neutral pH. Conductivity decrease correlated with biological growth and morphology, and sudden conductivity recoveries correlated with sloughing events. Periodic chlorine disinfection resulted in temporary increase in conductivity and helped open channels of flow between dense colonies. However, aggregates of organisms exhibited increased resistance to chlorine disinfection with rime, reducing disinfection effectiveness. Continuous, rather than periodic, disinfection is recommended. Models for biological substrate removal and clogging should incorporate different growth morphologies to produce satisfactory simulation results.