Bioremediation of crude oil-bearing soil: Evaluation of rhamnolipid addition as for the toxicity and crude oil biodegradation efficiency

This work is aimed at evaluating the potentiality of adding a rhamnolipid biosurfactant in a
petroleum-bearing soil. For this purpose, dehydrogenase activity and seed germination
(Lactuca sativa) testes were performed before the biodegradation assays with different
concentrations of rhamnolipid (1 to 15mg for 1g of soil). The addition of 1 and 15 mg g-1 of
rhamnolipid was harmful to the soil environment. The biodegradation assays were carried out
at room temperature during 45 days in bioreactors containing 450g of a polluted soil with
different rhamnolipid concentrations varying from 1 to 15 mg g-1. The nutrients were corrected
through the addition of NH4NO3 and KH2PO4, in a nutritional ratio of C:N:P=100:15:1. The
humidity was adjusted to 50% of the liquid retention capacity. Besides these assays, a control
test was conducted without adding rhamnolipid. TPH (Total petroleum hydrocarbon) removal
and seed germination were evaluated at the end of these experiments. When 4 mg g-1 of
rhamnolipid were used a TPH removal of about 60% was observed. The biosurfactant
addition improved all treatments, except for the assays with addition of 1 and 15 mg g-1 in
which a decrease of the bioremediations rates was observed in the toxicity tests.