Ultrasound-assisted extraction of biosurfactants from water hyacinth for enhanced soil washing of diesel-contaminated soils: performance evaluation and phytotoxicity assessment

Soil washing with surfactants is a promising technique for remediating petroleum hydrocarbon-contaminated soils. This study evaluates a biosurfactant extracted from Eichhornia crassipes (water hyacinth), an abundant aquatic weed in Thailand, using ultrasound-assisted extraction for diesel-contaminated soil remediation. The biosurfactant extract (Extract WH) was characterized for its surface tension reduction, critical micelle concentration (CMC), emulsification capacity with diesel, and phytotoxicity. Extract WH exhibited a CMC of 0.9443% w/v and showed enhanced emulsifying properties when combined with Dehydol LS9, as demonstrated by contact angle measurements. A surfactant formulation containing Extract WH, Dehydol LS9, and NaCl in equal proportions (1.35% w/v total) achieved 73.50% ± 5.65% diesel removal from soil contaminated at 20,000 mg/kg in 30 min. Phytotoxicity tests using rice and tomato seeds indicated improved germination rates in treated soils compared to untreated controls, although plant growth remained lower than in uncontaminated soils, possibly due to nutrient leaching. These results demonstrate the potential of water hyacinth-derived biosurfactants as an environmentally friendly and effective alternative for soil remediation.