Rhamnolipid For Remediation Of Heavy Metals And PAHs Combined Contaminated Soil

Contamination of soil environment by toxic metals and organic compounds is widely recognized as one of the major concern because of the potential health hazard they may pose for humans. The presence of these contaminants can destroy the balance in the natural habitat. Therefore, there is a need for remediation to mitigate these effects on humans and the environment at large. This paper presented laboratory batch and column experiments to evaluate the ability of tipical biosurfactant rhamnolipid to simultaneously remove heavy metals and low-polarity organic compounds US EPA's 16 priority-pollutant PAHs (polycyclic aromatic hydrocarbon) from contaminated soil.The contaminated soil was obtained from the outlet of Jingzhu highway contained 86% sand, 8% fines, 0.42% organic matter and high concentrations of total PAHs (1573mg/kg), lead (395.2 mg/kg), zinc (282.6 mg/kg) and copper (98.5mg/kg).Batch leaching tests were conducted at different concentrations and pH to determine the mechanisms controlling heavy metals and PAHs release and optimize the conditions of removing pollutants. The combination of SDS (sodium dodecyl sulfate) and EDTA(ethylenediamine tetra acetic acid), HPCD (hydroxypropyl-β-cyclodextrin ) were investigated to compare with rhamnolipid. The results showed that different concentrations were significantly influenced removal efficiencies. The maxium tatal PAHs remval efficiency (66.8%) was obtained with 4% rhamnolipid; in addition, the maxium removal efficiency on lead (66.7%), zinc (50.5%) and copper (48.5%) was also obtained with 4% rhamnolipid. The maxium zinc remival (20.5%) was obtained with 2%rhamnolipid at pH 8.0; highest lead (79.5%) and copper (35.5%) and total PAHs ( 60.3%) removal was obtained with 2% rhamnolipid at pH 10.0. It was observed that HPCD was less effective than rhamnolipid; the combination SDS (sodium dodecyl sulfate) with EDTA was found to be more effective than rhamnolipid in removing of heavy metals.According to batch leaching tests, column experiments carried out with 2% rhamnolipid at pH 8.0. The results showed that after a series of three washings of the soil using biosurfactant; the highest removal of lead, zinc and copper was 85.6%, 74% and 63.7%, respectively. As for PAHs, from 70% to 98% of PAHs were removed in three-stage solvent washing. The desorption effiency of high rings of PAHs was higher than the lower rings. Desorption ratio in the first stage was increased and the desorption ratio in the second; third stages were decreased with the increasing of the rings of PAHs. PAHs desorption ratio associated with octanol-water partition coefficient (Kow).The results of the experiments showed that rhamnolipid could greatly enhance the simultaneous desorption and elution of the model organic compound (PAHs) and the model heavy metal (lead, zinc and copper) from the soil examined.