Degradation of Petroleum Hydrocarbons Using Rhamnolipids with Lignosulfonates and Biochar in Louisiana Wetland Sediments.

Biosurfactants are microbial generated amphipathic glycolipids produced by various bacterial species. Rhamnolipids are some of the most studied biosurfactant glycolipids regarding bioremediation of crude oils in upland soils since their presence stimulates in-situ microbial consortia to degrade both polar and non-polar compounds. However, the general effects of rhamnolipid biosurfactants on the remediation of crude oil-contaminated wetlands soils are not yet known. The objective of the present study is to investigate the impacts of rhamnolipids along with two soil conditioners, sugarcane residue biochar and lignosulfonates, on oil contaminated coastal wetland sediments from Louisiana, USA. Different combinations of treatments of biochar and lignosulfonates and rhamnolipids with crude oil-contaminated wetland soils under sufficient N levels were incubated in a series of microcosm experiments, and monitored for soil respiration and changes in total petroleum hydrocarbons (TPH).  The TPH recovery in each was measured using gas chromatography/mass spectroscopy following solvent extraction with dichloromethane and hexane. Gas fluxes in each treatment sample were monitored daily through the first week and then every 72 hours for the remaining weeks. Initial incubation results indicate a significant difference between rhamnolipid-remediated and rhamnolipid with soil conditioner samples. The reduced TPH concentration due to the addition of rhamnolipids may be correlated to the degradation of hydrocarbons by in-situ chemotrophs. The results of this study and their implications on Louisiana coastal wetland soils will be discussed.