Sorption Behavior of Rhamnolipid Biosurfactant on Peat

Surfactants are extensively utilized across agriculture, pharmaceuticals, and environmental remediation due to their ability to modify surface and interfacial properties. In horticulture, wetting agents and synthetic surfactants are commonly employed to mitigate water repellency in organic growing media, particularly peat-based substrates. These agents are known to aid the substrate’s wettability and improve physical and hydraulic properties, optimizing plant growth and productivity. However, environmental persistence and the potential ecotoxicity of synthetic surfactants have raised significant concerns, highlighting the need for sustainable alternatives. Biosurfactants, particularly rhamnolipids, have gained considerable attention for their biodegradability and surface-active properties both at the scientific and commercial levels. Despite their potential, a comprehensive understanding of the interaction between rhamnolipid and peat essential for assessing its environmental fate and behavior is inadequate. In this regard, the main objective of this study is to quantify the sorption and desorption dynamics of rhamnolipid in peat using batch equilibrium and kinetic experiments to evaluate its suitability as a surfactant for horticultural systems, optimize application strategies, and assess the transport behavior and environmental implications of residual surfactants. Kinetic analysis revealed rapid initial adsorption followed by a gradual approach to equilibrium, with the adsorption and desorption kinetics being well described by the Elovich equation, indicating a chemisorption-dominated process. Furthermore, desorption followed both the Elovich and pseudo-first-order models, illustrating a complex and rate-dependent release process likely influenced by heterogeneous retention of rhamnolipid on the peat surface. Equilibrium analysis demonstrated that the adsorption data were best fitted by the Freundlich model, reflecting the heterogeneous nature of the peat surface and the complexity of its adsorption sites. Sequential desorption experiments exhibited notable hysteresis with reduced desorption efficiency, suggesting strong retention of rhamnolipid on the peat particles. These findings highlight the potential of rhamnolipid as a sustainable alternative to synthetic surfactants for mitigating water repellency in peat-based growing media. Equilibrium and kinetic modeling results will be presented with a comprehensive discussion of their practical implications, providing critical insights into their environmental significance and potential applications in horticultural systems.

Keywords: Water repellant peat, sorption, rhamnolipid biosurfactant