Bio-nanocrystal Stabilized Biosurfactant Foams for Groundwater and Soil Remediation

Surfactants are crucial for reducing surface tension at liquid interfaces and have diverse applications in various fields. Solutions of surfactants can help remediate contaminated soil and groundwater. Foams, dispersions of gas bubbles within a liquid stabilized by surfactants, exhibit enhanced sweep properties that can improve the cleaning efficiency in groundwater remediation. However, surfactant-stabilized foams are thermodynamically unstable, and this poses challenges to their applications. Utilizing nanoparticles in conjunction with surfactants has shown promise in enhancing foam properties and contaminant recovery. Biosurfactants, which are surfactants naturally produced by microorganisms, offer a promising alternative to synthetic surfactants due to their biodegradability and low toxicity. In this paper, we investigated the use of biosurfactants, specifically rhamnolipids, in combination with bio-nanocrystals, namely cellulose nanocrystals (CNCs), to improve foaming properties and assess contamination recovery through foam flooding tests. The effect of pH and CNCs on the foaming properties of the rhamnolipid solution was also examined. Foam stability and foamability were evaluated using modified bulk foam tests, considering foam stability parameters and maximum foam volume. Constant shear rate and strain amplitude sweep tests were performed on different foams formulated at varying pH levels to assess viscosity and elasticity, and to distinguish the foam exhibiting superior properties. Furthermore, sand pack flooding experiments were conducted to assess the performance of rhamnolipid-stabilized foams in groundwater remediation. The results reveal pH-dependent variations in the foaming properties of the mixture. The findings suggest that an optimal, eco-friendly foam with maximum stability, foamability, and elasticity can be formulated by using 1000 mg/L rhamnolipid together with 1000 mg/L CNCs at a pH value of 10. Additionally, experiments demonstrate that foams with optimal properties can recover approximately 70% of contaminants (n-decane), representing more than three times the recovery achievable through the same amount of water injection.