ABSTRACT
Background This study investigated the potential application of two biosurfactants for enhanced removal capability and biodegradation of motor oil contaminated sand under laboratory conditions. The biosurfactants were produced by the yeast Candida sphaerica and by the bacterium Bacillus sp. cultivated in low-cost substrates. The ability of removing motor oil from soil by the two biosurfactants was identified and compared with that of the synthetic surfactants Tween 80 and Triton X-100. Results Both crude and isolated biosurfactants showed excellent effectiveness on motor oil removal from contaminated sand under kinetic conditions (70-90%), while the synthetic surfactants removed between 55 and 80% of the oil. A contact time of 5-10 min under agitation seemed to be enough for oil removal with the biosurfactants and synthetic surfactants tested. The crude and the isolated biosurfactant from C. sphaerica were able to remove high percentages of motor oil from packed columns (around 90%) when compared to the biosurfactant from Bacillus sp. (40%). For the degradation experiments conducted in motor oil contaminated sand enriched with sugar cane molasses, however, oil degradation reached almost 100% after 90 d in the presence of Bacillus sp. cells, while the percentage of oil degradation did not exceed 50% in the presence of C. sphaerica. The presence of the biosurfactants increased the degradation rate in 10-20%, especially during the first 45 d, indicating that biosurfactants acted as efficient enhancers for hydrocarbon biodegradation. Conclusions The results indicated the biosurfactants enhancing capability on both removal and rate of motor oil biodegradation in soil systems.