Weathered Railroad Diesel Removed From A Loamy Sand Soil By Means Of Mono-Rhamnolipids

The extensive use of diesel as fuel has contributed to the current problem of soil contamination, and the aged diesel is a highly toxic pollutant for the soil microbial flora. The objective of the present work was to determine the ability of mono-rhamnolipid surfactants to solubilize weathered diesel absorbed for decades in a loamy sand soil. The mono-rhamnolipids were produced by P. aeruginosa ATCC 9027, using glycerol as the carbon source. The mono-rhamnolipid characterization revealed that 90% of congeners contained saturated fatty acids of short chains. At its CMC (70.3 mg/L), the mixture of mono-rhamnolipids decreased the surface tension of deionized water (30.3 mNm(-1)) and emulsified complex mixtures of petroleum hydrocarbons (73%). A 0.5% mono-rhamnolipid solution allowed solubilizing the following hydrocarbon fractions identified in the weathered diesel: aliphatics (66 +/- 3%), polycyclic aromatic hydrocarbons (PAHs) (23.16 +/- 11%), and asphaltenes (41.4 +/- 6%). Within the group of PAHs, four PAHs derivatives, well known to be highly carcinogenic and mutagenic to humans, were identified: neutral, methylated, nitrated, and oxydated. The PAHs and the first three derivatives were removed in an average of 20%. However, regarding the oxy-PAHs, the increment of their concentration allowed assuming the biodegradation of the PAHs during the desorption process. Results show that hydrocarbon desorption with mono-rhamnolipid solutions of high content of saturated fatty acids offers an effective and viable alternative for soil bioremediation because of the low concentration of surfactants required (0.2-0.5%), the short treatment times (approximate to 72 h) and above all, because mono-rhamnolipids are biodegradable compounds friendly to the environment.