title: Rhamnolipid surface thermodynamic properties and transport in agricultural soil.
abstract: Rhamnolipid is a biosurfactant produced by several Pseudomonas species, which can wet hydrophobic soils by lowering the cohesive and/or adhesive surface tension. Because of its biodegradability, rhamnolipid applications bring minimal adverse impact on the soil and groundwater as compared with that of chemical wetting agents. Subsequently, rhamnolipid applications have more advantages when used to improve irrigation in the agricultural soil, especially under draught conditions. In the presence of rhamnolipid, water surface tension dropped linearly with the increase of rhamnolipid concentration until the rhamnolipid critical micelle concentration (CMC) of 30 mg/L was reached. Below the CMC, rhamnolipid had linear adsorption isotherms on the soil with a partition coefficient of 0.126 L/kg. Rhamnolipid transport breakthrough curves had a broad and diffuse infiltration front, indicating retention of rhamnolipid on the soil increased with time. Rhamnolipid transport was found to be well represented by the advection-dispersion equation based on a local equilibrium assumption. When applied at concentrations above the CMC, the formed rhamnolipid micelles prevented rhamnolipid adsorption (both equilibrium adsorption and kinetic adsorption) in the soil. It was discovered in this research that rhamnolipid surface thermodynamic properties played the key role in controlling rhamnolipid transport. The attractive forces between rhamnolipid molecules contributed to micelle formation and facilitated rhamnolipid transport.
authors.affiliation: Department of Civil and Environmental Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310, United States.
authors.forename: Tyler Dillard
authors.initials: TD
authors.lastname: Renfro
authors.affiliation: Department of Civil and Environmental Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310, United States.
authors.forename: Weijie
authors.initials: W
authors.lastname: Xie
authors.affiliation: Department of Chemical Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310, United States.
authors.forename: Guang
authors.initials: G
authors.lastname: Yang
authors.affiliation: Department of Civil and Environmental Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310, United States. Electronic address: gchen@eng.fsu.edu.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
mesh_terms: D000327:Adsorption; D000383:Agriculture; D006017:Glycolipids / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*; D013499:Surface Properties; D013500:Surface Tension; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D006017:Glycolipids; D012987:Soil; C418382:rhamnolipid; D014867:Water
keywords: Critical micelle concentration (CMC); Deposition; Lewis acid/base interaction; Retardation; Rhamnolipid; van der Waals interaction