Effects of biologically produced surfactants on the mobility and biodegradation of petroleum hydrocarbons
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A laboratory investigation was conducted to determine the effects of biologically produced surfactants (biosurfactants) on petroleum hydrocarbons and their potential for the removal of hydrocarbons from groundwater systems. Bioaurfactanta have been found to be produced by microorganisms during growth on insoluble substrates for the purpose of increasing substrate solubility so as to promote biological degradation. In this study, three types of biosurfactants were produced by microorganisms grown on gasoline and a mixture of glucose with vegetable oil. Solubilization and biodegradation of selected gasoline compounds in the presence of bioeurfactante were measured in both static batch and flow through column systems. Batch experiments were conducted in culture tubes, using only liquid phases. A clean sand was used in the column system to monitor physical and chemical interactions yet minimize adsorption effects. A mixed culture of gasoline degrading microorganisms along with isolated cultures grown on selected compounds were used in the biodegradation studies. The biosurfactants produced and used in this study acted similarly to synthetic surfactants and increased, to various degrees, the solubility of the monitored gasoline compounds. Biosurfactants produced from growth on glucose and vegetable oil were very effective surfactants, markedly increasing solubility of the gasoline compounds, but inhibiting biological degradation of these same compounds.
Biosurfactants produced by microorganisms from growth on gasoline were effective surfactants, but they did not inhibit biodegradation of the gasoline compounds. This indicated that the biosurfactants may be substrate or microorganism specific, produced for growth on a particular insoluble substrate by a specific microorganism. Biosurfactants produced from growth on gasoline or an insoluble hydrocarbon could therefore be used to enhance solubility and subsequent biodegradation of that same hydrocarbon.
The effectiveness of the biosurfactants during application by injection or recirculation for groundwater remediation would be limited by the adsorption and removal of the biosurfactant to the soil. The surfactant demand (by adsorption) of the soil would have to be met before the effects of the biosurfactants would become apparent. Biosurfactanta added to groundwater could also create an additional oxygen demand in a system already low in oxygen.
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