Pore Occlusion in Compacted Mixtures of Sand and Kaolinite Due to Bioclogging

Biokinetics in engineered soils is a subject of relatively recent interest. In this paper, results are presented from experimental studies to address the bioclogging mechanisms. The primary focus of this study is to assess the relative importance of biomass growth vs. biogas generated in the soil pores. Experiments were conducted using Pseudomonas aeruginosa as the bacterial culture and compacted mixtures of kaolinite and Ottawa sand as porous media. Results indicated about one order-of-magnitude reduction of permeabilities when the bacteria were introduced through a nutrient solution in the influent chamber. Compacted specimens prepared using a bacterial inoculum and permeated with nutrient solution alone showed that growth kinetics prevented the specimens from ever reaching the saturated hydraulic conductivities with respect to distilled deionized water. Bacterial counts in the influent and in the effluent revealed that the kinetic processes were similar in soil media and in the pure nutrient solution medium. Reductions in permeabilities were attributed to the biogas generated during bacteria permeation. Pore-size distributions of bioclogged specimens showed lager pores, which was also consistent with visual observations of specimen cracking and gas bubble accumulation at the surface of the specimens, particularly in the case of specimens prepared with bacteria inoculum.