Diesel-Contaminated Soil Washing by Mixed Nonionic Surfactant Emulsion and Seed Germination Test

Abstract

Petroleum hydrocarbons are applied in various energy activities. If accidents happen, they may result in environmental contamination, especially in soil. Petroleum hydrocarbons have low evaporation rates and are adsorbed on the soil surface, making it necessary to treat contaminated soil before the pollutants spread to other areas. Soil washing with surfactant solution is a method used to treat petroleum hydrocarbon contamination. The process relies on surfactant properties which reduce surface tension and desorb diesel from soil particles prior to flushing out with water. The relationship between efficiency of diesel extraction from contaminated soil and factors of both single surfactants (Span20, Tween20, Tween80, Dehydol LS9) and mixed surfactants (Span20+Tween20, Span20+Tween80, Span20+Dehydol LS9) were investigated including hydrophile-lipophile balance (HLB) and interfacial tension (IFT) to select a suitable surfactant. Diesel was analyzed by GC-FID. Findings revealed that extraction efficiency significantly increased when the HLB of the surfactant increased in every solution pair (p = 0.05). Span20+Dehydol LS9 solution with HLB 12 showed the lowest IFT (17.767 ± 0.013 mN/m) and the highest diesel extraction efficiency (66.2%). The water washing process, repeated twice after washing with 1% (w/v) Span20+Dedydol LS9, resulted in less toxicity on germination and growth of tomato, rice, and green bean compared with diesel washing solution and fresh washing solution. Diesel-contaminated soil washing with mixed surfactant is an interesting alternative as an environmentally friendly soil treatment.