BIOSURFACTANT ENHANCED ATRAZINE TRANSPORT IN SOIL AND MODEL SORBENTS

Microbially produced surfactants offer potential for improved remediation of contaminated soils. Commercial surfactants have recently been shown to enhance both the solubility and the desorption rates of organic contaminants from soil. Biosurfactants have the added advantages for field applications of being naturally occurring and biodegradable. This research examines the impact of rhamnolipid biosurfactants on the transport of atrazine in soil and model sorbents. The influence of sorbent pore size on surfactant-induced contaminant desorption is being investigated using two hydrophobic polymeric resins with known pore-size distributions (XAD 4 and XAD 1180), simulating microporous soil aggregates. Radiolabeled atrazine was applied to sterile soil and model sorbents and aged for 3 days or over 150 days. Repacked columns constructed from the contaminant-applied sorbents were flushed at a rate of 5 pore volumes per day with contaminant-free artificial soil water containing 500 mg/L rhamnolipid biosurfactants and sodium azide to preserve sterility. Biosurfactant-free treatments served as the controls, and each column was flushed for a period of 3-4 weeks. Results from the model solids showed 2.3 to 3 times greater atrazine elution from the rhamnolipid-flushed column treatments compared to the surfactant-free controls. No significant differences in atrazine elution were observed between the aged and unaged treatments of the XAD resins. Narrow pore sizes did not appear to hinder the effectiveness of the biosurfactant, as the sorbent with 4-nm pores showed greater surfactant-induced increase in atrazine recovery than the sorbent with 30-nm pores. A distributed mass-transfer rate model fitted to the elution data adds insight to the effect of rhamnolipids on atrazine desorption rate constants, apart from changes in atrazine solubility. The model-sorbent results compared to parallel soil-column experiments will contrast or inform our model of soil-contaminant interactions within narrow hydrophobic pores.