Effect of electric fields strength on soil factors and microorganisms during electro-bioremediation of benzo[a]pyrene-contaminated soil

Insight into the effect of electric fields on bioremediation of petroleum-contaminated soil: A micro-ecological response

The voltage gradient plays a crucial role in the process of electro-bioremediation for petroleum-contaminated soil. However, the micro-ecological response mechanisms of relevance have been scarcely documented. This study compared petroleum degradation characteristics, soil physicochemical properties, and bacterial microbiome indicators under 0.5 V cm-1, 1 V cm-1, and 2 V cm-1 conditions to elucidate the interaction mechanism among soil micro-ecological factors. The findings indicated that the treatment at 1 V cm-1 resulted in the most effective synergistic enhancement of electrokinetics and bioremediation, yielding a peak petroleum degradation ratio of 43.54 ± 1.64% over 105 days. The improvement in biodegradation resulted from the direct stimulation of bio-metabolism by higher ratios of "window condition" (RWC, 0.5331) and the indirect sustenance of microbial physiological activity by favorable soil conditions. The 1 V cm-1 voltage gradient either maintained or fostered the soil microbiome's response to the remediation system. The structural equation models (SEMs) demonstrated that variations in microbiome properties across different voltage gradients resulted from the influences of effective current intensity, soil pH, redox potential (Eh), dissolved organic carbon (DOC), and electrical conductivity (EC). Optimizing voltage gradients is a practical approach for developing effective micro-ecosystems to efficiently remediate petroleum-contaminated soil and implement electro-bioremediation in various engineering applications.

Bibliometric analysis and systematic review on the electrokinetic remediation of contaminated soil and sediment

Electrokinetic remediation (EKR) is a proficient, environmentally friendly separation technology for in-situ removal of contaminants in soil/sediment, distinguished for its ease of implementation and minimal prerequisites compared to other remediation technologies. To comprehensively understand the research focus and progress related to EKR of contaminated soil/sediment, a bibliometric analysis was conducted on 1593 publications retrieved from the Web of Science Core Collection (WOSCC) database. This analysis utilized data mining and knowledge discovery techniques through Bibliometrix, VOSviewer, and CiteSpace software. The results revealed a rising trend in annual publication numbers, with China leading in the number of publications. The primary journals in this field included the Journal of Hazardous Materials, Chemosphere, and Separation and Purification Technology. The primary disciplines contributed to this field included "Environmental Sciences", "Engineering, Environmental", "Engineering, Chemical", and "Electrochemistry". Keyword co-occurrence and burst analysis indicated that current EKR-related research mainly focuses on the remediation of soil/sediments contaminated by heavy metals (HMs) and organic pollutants (OPs). Furthermore, the EKR remediation improvement method emerged as the prevailing and future research hotspots and development directions. Future research could integrate numerical simulations and various methodologies to predict and assess the migration of pollutants and the efficiency of remediation efforts. Additionally, these studies could explore the effects of EKR on the physicochemical properties and microbial diversity of soil/sediment to provide a theoretical foundation for applying EKR in soil/sediment remediation.

Advanced oxidation of polycyclic aromatic hydrocarbons in tropical soil: Self-catalytic utilization of natural iron contents in an oxygenation reactor supported with persulfate

The catalysts derived from natural iron minerals in the advanced oxidation process offer several advantages. However, their utilization in soil remediation is restricted due to the presence of soil impurities, which can inhibit the catalytic activity of these minerals. The soils in tropical regions exhibit lower organic matter content, limited cation exchange capacity, and are non-saline, this enhances the efficiency of utilizing natural iron minerals from tropical soil as a catalyst. In this regard, the catalytic potential of naturally iron-bearing tropical soil was investigated to eliminate phenanthrene (PHE), pyrene (PYR), and benzo[α]pyrene (B[α]P) using an oxygenated reactor supported with persulfate (PS). The system showed an efficient performance, and the removal efficiencies under the optimum conditions were 81 %, 73 %, and 86 % for PHE, PYR, and B[α]P, respectively. This indicated that the catalytic activity of iron was working efficiently. However, there were changes in the soil characteristics after the remediation process such as a significant reduction in iron and aluminum contents. The scavenging experiments demonstrated that HO• had a minor role in the oxidation process, SO4•- and O2•- emerged as the primary reactive species responsible for the effective degradation of the PAHs. Moreover, the by-products were monitored after soil remediation to evaluate their toxicity and to propose degradation pathways. The Mutagenicity test showed that two by-products from each PHE and B[α]P had positive results, while only one by-product of PYR showed positive. The toxicity tests of oral rat LD50 and developmental toxicity tests revealed that certain PAHs by-products could be more toxic from the parent pollutant itself. This study represents a notable progression in soil remediation by providing a step forward in the application of the advanced oxidation process (AOP) without requiring additional catalysts to activate oxidants and degrade pollutant PAHs from the soil.

Construction of an effective method combining in situ capping with electric field-enhanced biodegradation for treating PAH-contaminated soil at abandoned coking sites

The simultaneous application of in situ capping and electro-enhanced biodegradation may be a suitable method for ensuring the feasibility and safety of reusing abandoned coking sites. However, the capping layer type and applied electric field pattern may affect the efficiency of sequestering and removing pollutants. This study investigated changes in electric current, soil moisture content and pH, polycyclic aromatic hydrocarbon (PAH) concentration, bacterial number, and microbial community structure and metabolic function during soil remediation at abandoned coking plant sites under different applied electric field patterns and barrier types. The results indicated that polarity-reversal electric field was more conducive to maintaining electric current, soil properties, resulting in higher microbial number, community diversity, and functional gene abundance. At 21d, the mean PAH concentrations in contaminated soil, the capping layer's clean soil and barrier were 78.79, 7.56, and 1.57 mg kg-1 lower than those with a unidirectional electric field, respectively. The mean degradation rate of PAHs in the bio-barrier was 10.12 % higher than that in the C-Fe barrier. In the experiment combining a polarity-reversal electric field and a bio-barrier, the mean PAH concentrations in contaminated soil and the capping layer were 706.68 and 27.15 mg kg-1 lower than those in other experiments, respectively, and no PAHs were detected in the clean soil, demonstrating that the combination of the polarity-reversal electric field and the bio-barrier was effective in treating soil at abandoned coking plant sites. The established method of combining in situ capping with electro-enhanced biodegradation will provide technical support for the treatment and reuse of heavily PAH-contaminated soil at abandoned coking plant sites.