Improved remediation of co-contaminated soils by heavy metals and PAHs with biosurfactant-enhanced soil washing

Xu Zhang,Shuguang Wang,Xiaodong Zhang,Shan Zhao

doi:10.1038/s41598-022-07577-7

Xu Zhang, Shuguang Wang + Show 2 more

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https://doi.org/10.1038/s41598-022-07577-7

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Journal: Scientific Reports	Publication Date: Mar 8, 2022
Citations: 13	License type: open-access

Affiliation: Shandong University

Abstract

Due to the huge toxicity of co-contaminated soil with PAHs and heavy metals and the complexity of their remediation, it is thus critical to take effective remediation actions to remove heavy metals and PAHs simultaneously from the co-contaminated soil. Biosurfactant-enhanced soil washing (BESW) were investigated in this study for remediation of soil co-contaminated with phenanthrene (PHE) and cadmium (Cd). The co-existence of PHE and Cd caused the change of the structure of soil and rhamnolipid micelle, which lead to different removal rate of PHE and Cd from co-contaminated soil compared with single contaminated soil. The results of FT-IR and NMR showed that PHE entered micelles of rhamnolipid and Cd formed the complexation with the external carboxyl groups of rhamnolipid micelle. We also found that pH, concentration of rhamnolipid solution, temperature and ionic strength had influence on co-contaminated soil remediation. The effects of above mentioned four factors on co-contaminated soil remediation in BESW processes were analyzed by using Taguchi design of experiment method. Taguchi based Grey Relational Analysis was conducted to identify the optimal remediation conditions, which included pH = 9, concentration of rhamnolipid = 5 g/L, temperature = 15 °C and ionic strength = 0.01 M. Under the optimal conditions for BESW, removal rates of cadmium and phenanthrene reached 72.4% and 87.8%, respectively in co-contaminated soil.

Highlights

Due to the huge toxicity of co-contaminated soil with polycycle aromatic hydrocarbons (PAHs) and heavy metals and the complexity of their remediation, it is critical to take effective remediation actions to remove heavy metals and PAHs simultaneously from the co-contaminated soil
To determine optimal operational conditions for Biosurfactant-enhanced soil washing (BESW), we explored the influence of these factors on the removal rates of heavy metals and PAHs
Co-existence of PHE and Cd in BESW could affect the removal of the two contaminants due to their interactions as well as their simultaneous entry into rhamnolipid solutions affecting the structure of rhamnolipid micelles

Summary

Introduction

Due to the huge toxicity of co-contaminated soil with PAHs and heavy metals and the complexity of their remediation, it is critical to take effective remediation actions to remove heavy metals and PAHs simultaneously from the co-contaminated soil. It is critical to take effective remediation actions to remove heavy metals and PAHs simultaneously from the co-contaminated soil. In order to improve the remediation performance, various washing agents have been developed and used in soil washing, such as humic acids[22,23], vegetable o ils[24,25], chelating agents[26,27], water-miscible co-solvents[28], and surfactants[29–33]. Chelating agents such as [S,S]-ethylene diamine disuccinate (EDDS) and Ethylene Diamine Tetraacetic Acid (EDTA) were effective for removal of heavy metals, they encountered difficulties in removing organic compounds[34]. In order to remediate PAHs and heavy metals co-contaminated soil, synthetic surfactants were frequently combined with chelating a gents[35–39]

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