Dissolution of aquifer-associated mineral solids such as silica may affect the natural bioattenuation of organic compounds by altering their chemical speciation and thus their biodegradability. A study was conducted to evaluate the effect ofdissolved silica on the rates of biodegradation of a cationic surfactant, octylamine, by Rhodococcus erythropolis. The presence of dissolved silica or a surrogate added by dissolving sodium metasilicate significantly enhanced the biodegradation rates ofoctylamine. Microbial kinetic studies based on the Monod/Haldane equation indicated that the rate enhancement was caused by a decrease in the inhibitory properties of octylamine, rather than by an improvement in buffering of the medium. In the presence of dissolved silica, μ{sub}max and K{sub}s remain virtually unaffected, but the inhibition constant, K{sub}i, increased several orders of magnitude (from K{sub}i = 1.32 mM in the silica-free system to K{sub}i > 10{sup}6 mM in the silica system). Surfacetension studies suggested that the presence of dissolved silica significantly decreased the surface-activity of octylamine.
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