Abstract
Soil washing and landfarming processes are widely used to remediate total petroleum hydrocarbon (TPH)-contaminated soil, but the impact of these processes on soil bacteria is not well understood. Four different states of soil (uncontaminated soil (control), TPH-contaminated soil (CS), after soil washing (SW), and landfarming (LF)) were collected from a soil remediation facility to investigate the impact of TPH and soil remediation processes on soil bacterial populations by metagenomic analysis. Results showed that TPH contamination reduced the operational taxonomic unit (OTU) number and alpha diversity of soil bacteria. Compared to SW and LF remediation techniques, LF increased more bacterial richness and diversity than SW, indicating that LF is a more effective technique for TPH remediation in terms of microbial recovery. Among different bacterial species, Proteobacteria were the most abundant in all soil groups followed by Actinobacteria, Acidobacteria, and Firmicutes. For each soil group, the distribution pattern of the Proteobacteria class was different. The most abundant classed were Alphaproteobacteria (16.56%) in uncontaminated soils, Deltaproteobacteria (34%) in TPH-contaminated soils, Betaproteobacteria (24%) in soil washing, and Gammaproteobacteria (24%) in landfarming, respectively. TPH-degrading bacteria were detected from soil washing (23%) and TPH-contaminated soils (21%) and decreased to 12% in landfarming soil. These results suggest that soil pollution can change the diversity of microbial groups and different remediation techniques have varied effective ranges for recovering bacterial communities and diversity. In conclusion, the landfarming process of TPH remediation is more advantageous than soil washing from the perspective of bacterial ecology.
Highlights
Soil pollution attributed to total petroleum hydrocarbons (TPHs) is a worldwide concern [1]
The soil pH was slightly acidic in the control (6.23) and contaminated sites (CS) (6.22), but after the remediation process, it increased to neutral for the landfarming (LF) (6.90) and soil washing processes (SW) (7.23)
This study used metagenomic analysis to examine how bacterial diversity changed in TPH-contaminated soil after soil washing and landfarming remediation processes
Summary
Soil pollution attributed to total petroleum hydrocarbons (TPHs) is a worldwide concern [1]. Various physicochemical and biological techniques, such as stabilization, soil washing, electrokinetic remediation, landfarming, phytoremediation, and biodegradation are used to remediate TPH-contaminated soil [5]. Since the 1980s, soil washing has been extensively researched and applied throughout Europe and North America. This method is a physicochemical process that uses desorption and solubilization to remove contaminants sorbed to the soil and transfers them to the liquid phase [10]. Landfarming is a biological remediation method that promotes aerobic biodegradation of soil bacteria to degrade petroleum hydrocarbons. Supplementing nutrients and water, cultivating the soil, and sometimes adding a bacterial consortia to improve the biodegradability of contaminants are all part of this process [11,12]
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