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.

Heavy metal pollution in soil can have detrimental effects on soil ecosystems and human health. In situ remediation techniques are widely used to reduce the bioavailable fractions of heavy metals in soil. The main objective of this study was to examine the reduction of the bioavailable fractions of As and Pb in paddy soil with artificial lightweight material (ALM) manufactured from recycled materials. A total of four treatments, including a control (no amendment), ALM10 (10% of ALM in soil), ALM10+L (10% ALM combined with 0.5% lime), and ALM10+FeO (10% ALM combined with 0.5% FeO), were applied to paddy fields, and rice (Oryza sativa L.) was cultivated after 32 weeks. The highest reduction efficiencies for the bioavailable fractions of As and Pb in soil were observed in the ALM10+FeO (52.8%) and ALM10+L treatments (65.7%), respectively. The uptake of As decreased by 52.1% when ALM10+FeO was applied to paddy soil, and that of Pb decreased by 79.7% when ALM10+L was applied. Correlation analysis between bioavailable heavy metals in soil and soil chemical properties showed that soil pH, electrical conductivity (EC), P₂O_5, and soil organic matter (SOM) were the main factors controlling the mobility and bioavailability of As and Pb. Overall, the efficiencies of As and Pb reduction increased synergistically in both soil and plants when FeO and lime were combined with the ALM. In future studies, long-term monitoring is necessary to examine the longevity of soil amendments.

Heavy metal pollution in the environment is a critical issue, engendering ecosystem deterioration and adverse effects on human health. The main objective of this study was to evaluate heavy metal adsorbents by modifying industrial byproducts. The bottom ash was sintered and evaluated for Cd and Pb sorption. Three adsorbents (bottom ash, sintered bottom ash (SBA), and SBA mixed with microorganisms (SBMA)) were tested to evaluate the sorption kinetics and mechanism using a lab-scale batch experiment. The results showed that the highest sorption efficiency was observed for Cd (98.16%) and Pb (98.41%) with 10% SBA. The pseudo-second-order kinetic model (R² > 0.99) represented the sorption kinetics better than the pseudo-first-order kinetic model for the SBA and SBMA, indicating that chemical precipitation could be the dominant sorption mechanism. This result is supported by X-ray photoelectron spectroscopy analysis, demonstrating that -OH, -CO₃, -O, and -S complexation was formed at the surface of the sintered materials as Cd(OH)₂ and CdCO₃ for Cd and PbO, and PbS for Pb. Overall, SBA could be utilized for heavy metal sorption. Further research is necessary to enhance the sorption capacity and longevity of modified industrial byproducts.