Experimental study on the reduction of soil hydraulic conductivity by enhanced biomass growth

Clogging of porous media caused by the accumulation of microbial biomass and extracellular polysaccharide (EPS) greatly influences water flow and chemical transport in subsurface environments. A quantitative understanding of the relationship between increase in microbial biomass and reduction in hydraulic conductivity is of critical importance to the simulation of the fate and transport of biologically reactive contaminants in soil and groundwater systems. In this research, soil column experiments were conducted to examine the influence of enhanced biomass production by indigenous soil microbes on the hydraulic conductivity of a river sand. Dextrose-nutrient solution was used to stimulate microbial growth in soil columns. Soil solutions at different locations of the soil columns were sampled to quantify suspended biomass. Destructive sampling was carried out at the end of the percolation runs to determine distributions of attached biomass. About one and one-half orders of magnitude in reduction of hydraulic conductivity was observed 3 weeks after the application of dextrose-nutrient solutions, and different distributions of hydraulic conductivity reduction along the soil columns were obtained from treatments with different dextrose and nitrogen concentrations. A regression equation relating attached microbial biomass and the logarithmic ratio of hydraulic conductivity was obtained. Our experimental results showed no correlation between suspended and attached biomass.