| A logical approach toward optimizing hazardous-waste treatment using microorganisms is to elucidate rate controlling processes at the cell surface-water interface. This approach has been tested on aqueous bioremediation of nonionic, insoluble petroleum compounds and on biosorption of heavy metals. Related projects described below demonstrate that biotreatment enhancement is associated with cell-surface-contaminant bioavailability.; Enhanced hydrocarbon contact and uptake can promote aqueous-phase-hydrocarbon bioremediation. However, dissolution, dispersion, solubilization, and transport of insoluble hydrocarbon is required to increase the bioavailability of insoluble, petroleum contaminants. Two biodegradable soil-washing surfactants, a microbial rhamnolipid biosurfactant, and an oleophilic fertilizer were assessed for their ability to enhance contaminant availability and promote biodegradation for specific aliphatic and aromatic hydrocarbons with solubilities ranging more than seven powers of ten. Each of the surfactants tested were found to decrease surface tension and to emulsify the petroleum compounds in a concentration-dependent manner. These effects could be correlated with substantial surfactant-dependent enhancement of biodegradation rate and extent. Both the soil washing formulations and the oleophilic fertilizer, Inipol EAP-22, had comparable effects on increasing bioavailability and internalization of insoluble hydrocarbons to those previously reported for the Pseudomonas rhamnolipid. The degree of enhancement was proportional to hydrocarbon insolubility in experiments using either bran-adsorbed microbial consortia or pure bacterial cultures.; Prepared biomass from Gram-negative and Gram-positive bacterial strains were tested for use as aqueous-phase heavy metal biosorbents. Patterns of aqueous biosorption of Cu(II), Co(II), Ni(II) and Cr(II) could be attributed to differences in cell wall composition. Substantial improvement in heavy metal sorption is thought to be due to an increased exposure of potential binding sites resulting from use of partially intact cell surfaces, as compared to intact cells.; The net result of each study was to demonstrate that by utilizing extant fundamental knowledge of the basic physicochemical properties of contaminants and of the microbial cell surface, an improved understanding of the interfacial phenomena that affect the biotreatment of environmental contaminants can result in an optimization of many bioremedial technologies. |
