Enhanced bioremediation of crude oil utilizing lipophilic fertilizers

Bioremediation is being increasingly seen as an affective, environmentally friendly treatment for contaminated shorelines from marine oil spills. Oil bioremediation is limited by the availability of nitrogen and phosphorous, which are needed by the bacteria and are not present in sufficient amounts for the biodegradation of the spilled hydrocarbons. The supply of these two essential elements as water-soluble salts presents several problems. These include the rapid dilution of the salts in the large volumes of polluted sea water as well as their utilization by other bacteria that do not degrade oil. In addition, by increasing the concentration of mobile nitrogen further environmental problems could potentially be created. As an alternative, hydrophobic sources of nitrogen and phosphorous have been used that have a low solubility in water and hence, they can overcome these problems, however, many of these bioremediation agents have proven to be somewhat toxic. The aim of this study was to examine the effects of lipophilic fertilizers of natural origin (uric acid and lecithin) on the degradation of crude oil hydrocarbons in comparison with the degradation that is achieved by commercial bioremediation agents. Biodegradation was quantified by GC/MS analysis of selected components. Petroleum degraders were measured by MPN analysis. From a series of 18 days long experiments it was found that the saturated fraction of the residual oil was degraded more readily and extensively than the aromatic fraction and the bacterial growth of the biostimulated solutions is much greater compared to the control. The results showed that the treatment of oil spills with uric acid and lecithin is very effective in a period of almost 7 days. Uric acid and lecithin can stimulate microbial growth from 3.65 to 1.9×104 MPN/mL within 7 days and thus lead to extensive degradation of oil hydrocarbons in comparison to the control and S200 solutions. Uric acid and lecithin proved to be excellent biostimulant agents in combating oil spills.

This study aimed to evaluate the biodegradation of crude oil that is achieved when natural, lipophilic nutrients are used. A set of chemical and microbiological experiments were run and the observed trend in the chromatographs from the examined solutions showed that lipophilic nutrients enhance the biodegradation of crude oil. The apparent reduction in petroleum hydrocarbons that was achieved with the formulation UL (uric acid– lecithin) over a period of 18 days is very encouraging (with final removal of C19-C34 n-alkanes of 83% as shown in Fig. 6). In comparison, the commercial bioremediation agent S200 eventually was not as effective in degrading petroleum hydrocarbons in crude oil for this particular set of experiments. This contradicts previous studies using S200 to stimulate indigenous hydrocarbon degraders. It should be noted however, that S200 was found to be very effective in combined biostimulation–biaugmentation experiments with isolated hydrocarbon degrading consortia [19]. The GC profiles after 7 and 18 days showed that biodegradation in both resolved and unresolved hydrocarbons in the solutions were nutrients had been applied is more extensive than that in the control solutions. However most of the crude oil fractions were totally utilized after 18 days of treatment. The application of nutrients in the solutions enhanced the growth of the hydrocarbon degraders as was estimated by the MPN method in comparison with the control solution where no nutrients were added. As shown by the chromatographs (Fig. 5), the saturated fraction of the residual oil is degraded more extensively than the aromatic fraction. Lecithin supports the higher biodegradation rate, comparable to that obtained by using soluble phosphates. Both uric acid and lecithin are suitable lipophlic nutrient sources and enhance microbial growth during the first 7 days. The fact that remains however is that in the first week the overall growth is not very high when in real life immediate hydrocarbon degradation is needed. Considering this, besides the use of biostimulation additives (like UL) we may have to supplement with the addition of hydrocarbon degrading consortia (bioaugmentation) particularly when the oil spill approaches near the shore line.