| During the twentieth century, experience gained in bioengineering techniques to safeguard the environment augmented tremendously, thus providing more knowledge about the use of microorganisms in environmentally related engineering disciplines. Toward these technological advances, “bio” processes such as biodegradation, biotreatment, and bioencapsulation became focus subjects of intensive research studies in both academic and industrial arenas. Nevertheless, even though application of biopolymers were known in such fields as medicine, pharmaceuticals, food, plastics, and drilling, no systematic approach was ever taken to explore the possibility of using that technology toward its effectual subsurface applications in the complex fields of hazardous waste management, erosion control, and liquefaction mitigation.; The extensive research work undertaken herewith, inquires with the performance of biopolymer producing bacteria and their derivatives, i.e. “biopolymers,” in the underground porous materials. Such investigative efforts are needed, for instance, as one plans to construct an impervious “bio-wall” or bio-liners and bio-cover systems for solid or hazardous waste landfills to completely blockade the flow of hazardous materials to the underground or to the surface environment. The experimental approach in this dissertation therefore concentrates first on the optimum growth of biopolymer producing bacteria, Alcaligenes eutrophus, Alcaligenes faecalis, Alcaligenes viscolactis, and Xanthomonas campestris, and then takes the initiative to question their effects on the two extremely significant parameters of the soil strength and hydraulic conductivity. Alcaligenes eutrophus strains yield intracellular biopolymer, polyhydroxybutyrate(PHB), highly crystalline thermoplastic polyester and the most abundant of PHA's (polyhydroxyalkanoates). The other three species produce extracellular biopolymers, categorized as bacterial polysaccharides. Xanthan gum, for instance, is a high-molecular-weight heteropolysaccharide synthesized by Xanthomonas campestris. The candidate soils are Bonnie silt and Silver sand, symbolizing low and moderate permeability porous materials when they are fairly packed in a column. Upon application of either of the bacteria or their corresponding extracted biopolymers to the soil samples, the hydraulic conductivity decreases tremendously, up to one million fold, whereas the soil strength increases significantly, up to three times. The microscopic level studies prove that biopolymers intertwiningly bind the soil aggregates, that they are being adsorbed at the available surface areas and that they fashion a cross-link network of solid particles with macroscopic effects of complete blockage to any possible fluid flow and of mounting the soil strength. |
