Application of Green Surfactants in the Remediation of Soils Contaminated by Hydrocarbons

Israel Gonçalves Sales Da Silva,Nathália Maria Padilha Da Rocha E Silva,Fabíola Carolina Gomes De Almeida,Joaquim Teodoro Romão De Oliveira,Leonie Asfora Sarubbo,Attilio Converti

doi:10.3390/pr9091666

Israel Gonçalves Sales Da Silva, Nathália Maria Padilha Da Rocha E Silva + Show 4 more

Open Access

https://doi.org/10.3390/pr9091666

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Abstract

Among the innovative technologies utilized for the treatment of contaminated soils, the use of green surfactants appears to be a biocompatible, efficient, and attractive alternative, since the cleaning processes that normally use synthetic surfactants as additives cause other problems due to toxicity and the accumulation of by-products. Three green surfactants, i.e., two biobased (biobased 1 and biobased 2) surfactants produced by chemical synthesis and a microbial surfactant produced from the yeast Starmerella bombicola ATCC 22214, were used as soil remediation agents and compared to a synthetic surfactant (Tween 80). The three surfactants were tested for their ability to emulsify, disperse, and remove different hydrophobic contaminants. The biosurfactant, which was able to reduce the water surface tension to 32.30 mN/m at a critical micelle concentration of 0.65 g/L, was then used to prepare a commercial formulation that showed lower toxicity to the tested environmental bioindicators and lower dispersion capacity than the biobased surfactants. All the green surfactants showed great emulsification capacity, especially against motor oil and petroleum. Therefore, their potential to remove motor oil adsorbed on different types of soils (sandy, silty, and clay soil and beach sand) was investigated either in kinetic (flasks) or static (packed columns) experiments. The commercial biosurfactant formulation showed excellent effectiveness in removing motor oil, especially from contaminated sandy soil (80.0 ± 0.46%) and beach sand (65.0 ± 0.14%) under static conditions, while, in the kinetic experiments, the commercial biosurfactant and the biobased 2 surfactant were able to remove motor oil from all the contaminated soils tested more effectively than the biobased 1 surfactant. Finally, the S. bombicola commercial biosurfactant was evaluated as a soil bioremediation agent. In degradation experiments carried out on motor oil-contaminated soils enriched with sugarcane molasses, oil degradation yield in the sandy soil reached almost 90% after 60 days in the presence of the commercial biosurfactant, while it did not exceed 20% in the presence of only S. bombicola cells. These results promise to contribute to the development of green technologies for the treatment of hydrophobic pollutants with economic gains for the oil industries.

Highlights

The contamination of soils, oceans, and seas has contributed to increased research on environmental remediation
The aim of this work was to investigate the tensioactive properties of three green surfactants, i.e., two commercial biobased surfactants and a formulated microbial surfactant produced from the yeast Starmerella bombicola, and to apply them in the treatment of soils contaminated with hydrocarbons
The biosurfactant production using Starmerella bombicola ATCC 22214 was proven by the reduction of surface tension to 32.30 mN/m in 192 h of fermentation, meaning a 77.6%

Summary

Introduction

The contamination of soils, oceans, and seas has contributed to increased research on environmental remediation. Soil pollution urgently requires the application of a series of physicochemical and biological techniques and treatments to minimize the extent of damage [1,2]. Physical and chemical methods for the removal of hydrocarbons from the environment have some disadvantages compared to biological techniques, including higher cost, lower effectiveness, and toxic effects caused to the environment by chemical compounds such as chemical dispersants. Bioremediation, in turn, arises as a cheaper, more effective, and eco-friendly alternative or complementary technique, which is able to mineralize pollutants or transform them into less toxic substances [3,4,5,6,7]. The choice of the most appropriate and feasible in-situ or ex-situ biological remediation techniques, will depend on preliminary analyses of the environmental conditions, type of pollutant, soil composition, removal costs, and time available for treatment. There are many hydrocarbon-degrading microorganisms in nature, the growth of many of them is hampered by several factors, such as the recalcitrant nature of the substrate and the low availability of organic compounds in aqueous systems, which limits their use as a carbon source [8]

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