Petroleum bioremediation―a multiphase problem

Since petroleum is a complex mixture of many different classes of hydrocarbons, of which any particular microorganism has the potential to degrade only part, it follows that the microorganisms must also have a mechanism for desorbing from 'used' oil droplets. The major limitations in bioremediation of hydrocarbon-contaminated water and soil is available sources of nitrogen and phosphorus. The usual sources of these materials, e.g. ammonium sulfate and phosphate salts, have a high water solubility which reduces their effectiveness in open systems because of rapid dilution. We have attempted to overcome this problem by the use of a new controlled-release, hydrophobic fertilizer, F-1, which is a modified urea-formaldehyde polymer containing 18% N and 10% P as P sub(2)O sub(5). Microorganisms were obtained by enrichment culture that could grow on crude oil as the carbon and energy source and F-1 as the nitrogen and phosphorus source. The microorganisms and the F-1 adhered to the oil/water interface, as observed microscopically and by the fact that degradation proceeded even when the water phase was removed and replaced seven times with unsupplemented water - a simulated open system. Strains which can use F-1 contain a cell-bound, inducible enzyme which depolymerizes F-1. After optimizing conditions in the laboratory for the use of F-1 and the selected bacteria for degrading crude oil, a field trial was performed on an oil contaminated sandy beach between Haifa and Acre, Israel, in the summer of 1992. The sand was treated with 5 g F-1 per kg sand and inoculated with the selected bacteria; the plot was watered with sea water and plowed daily. After 28 days the average hydrocarbon content of the sand decreased from 5.1 mg per g sand to 0.6 mg per g sand. Overall, there was an approx. 86% degradation of pentane extractables as demonstrated by dry weight, I.R. and GLC analyses. An untreated control plot showed only a 15% decrease in hydrocarbons. During the winter of 1992, the entire beach (approx. 200 tons of crude oil) was cleaned using the F-1 bacteria technology. The rate of degradation was 0.06 mg/g sand/day (10 degree C) compared to 0.13 mg/g sand/day during the summer (25 degree C).