Remediation of a diesel-contaminated soil from a pipeline accidental spill: Enhanced biodegradation and soil washing processes using natural gums and surfactants

Purpose: This paper addresses the application of bioproducts produced by plants (locust bean, guar, and mesquite seed gums) to enhance remediation processes of different nature: soil washing and biodegradation methodologies. Materials and methods: These natural gums were tested at laboratory scale to remove total petroleum hydrocarbons-diesel fraction (TPH-diesel) from oil-contaminated volcanic soils sampled from a polluted site in an agricultural area of western Mexico. TPH-diesel removal by natural gums was compared to common synthetic surfactants. Results and discussion: There is a strong evidence of contamination caused by the presence of TPH-diesel at a concentration of 32,100 mg/kg, which is above the legal limit of 1,200 mg/kg for agricultural soils in Mexico. Regarding the surfactant soil washing experiments, ionic surfactants showed removal rates above the control test of about 78. 51 % (Maranil LAB), 71. 27 % (Texapon 40), 60. 13 % (SDS), and 48. 19 % (Surfacpol G). In contrast, some nonionic surfactants showed removal rates below soil-washing background rate (40 %). On the other hand, natural gums showed interesting and promising results. Guar gum and locust bean gum showed efficiencies of 54. 38 % and 53. 46 %, respectively. Biodegradation experiments confirmed the effectiveness of natural gums as biodegradation enhancers in diesel-contaminated soils. Specifically, guar gum showed an excellent performance. An 82 % TPH-diesel removal rate was achieved for a very low gum concentration (2 ppm). In this particular context, reported surfactant concentrations to assist biodegradation are, in general, higher. Conclusions: This work demonstrated the applicability of natural gums as soil remediation enhancers in diesel-contaminated systems. Particularly, guar gum might represent a cost-effective alternative for biodegradation enhancement processes.