Electrokinetic remediation of uranium(VI)-contaminated red soil using composite electrolyte of citric acid and ferric chloride

Pilot scale application of 226Ra-contaminated soil leaching remediation

To address the issue of soil contamination caused by associated elements during the extraction and processing of radioactive minerals, this study employed two types of chemical leaching methods, one based on organic acids and the other on carbonates, to remediate radium-contaminated soil. Large-scale soil slurry reactors were used in field experiments to investigate the effects of acidic and alkaline leaching agents on the removal of 226Ra from naturally contaminated soil, and the optimal operational conditions were determined. The combined use of organic acids, salts and solubilizers has demonstrated high removal rates of radionuclide on a laboratory scale. Pilot scales revealed that using FeCl3, oxalic acid, NaClO2, and HEDP, or Na2CO3, NaHCO3, H2O2, and deep eutectic solvent (DES) as leaching agents achieved the best remediation outcomes for radium-contaminated soil. Under optimal conditions, the radium removal efficiencies of the two leaching systems reached 93.02% and 90.66%, respectively. Characterization analyses using X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR), and scanning electron microscope (SEM) demonstrated that the chemical leaching methods are both safe and reliable, effectively removing radium while having minimal impact on the soil's original structure. Additionally, these methods have the potential to replenish soil nutrients and restore its functional use.

Uranium bioprecipitation mediated by a phosphate-solubilizing Enterobacter sp. N1-10 and remediation of uranium-contaminated soil

Uranium (U) pollution in soils is prevalent worldwide and poses a significant health risk that will require remediation approaches. However, traditional U bioreduction by sulfate reducing bacteria (SRB) are sensitive to oxygen and are not suitable for treating aerobic topsoil. Bioprecipitation of U into uranyl phosphate (UP) mediated by phosphate-solubilizing microorganism (PSM) is not affected by oxygen. In this study, PSM strains were isolated and used for U-contaminated soil remediation. Microbial metabolites and the mechanism of PSM bioprecipitation were revealed. The results showed that strain Enterobacter sp. N1-10 had the highest phosphate-solubilizing capacity (dissolved P was 409.51 ± 8.48 mg/L). Uranium bioprecipitation was investigated by culturing the bacterium in the presence of 50 mg/L U and in the cell-free culture supernatant. The results showed that strain N1-10 had a high U removal rate (99.45 ± 0.43 %) after adding 50 mg/L U to the culture medium. A yellow precipitate was immediately formed when uranyl nitrate solution was added to the cell-free culture supernatant. The analysis indicated that bacterium produced lactic acid (37.58 mg/L), citric acid (4.76 mg/L), succinic acid (2.03 mg/L), and D-glucuronic acid (1.94 mg/L); the four organic acids solubilized Ca3(PO4)2 to form stable uranyl phosphate precipitate. The application of strain N1-10 and Ca3(PO4)2 significantly decreased the bioavailability of soil U (43.54 ± 0.52 %). In addition, pot experiments showed that PSM N1-10 and Ca3(PO4)2 promoted plant growth and markedly reduced U accumulation by pakchoi. These results demonstrate that PSM N1-10 and Ca3(PO4)2 exhibit a great potential for U bioremediation.

Challenges and opportunities for low-carbon remediation in the Niger Delta: Towards sustainable environmental management

There is increasing demand for low-carbon remediation strategies for reducing greenhouse gas emissions and promoting sustainable development in the management of environmental contamination. This trend is within the broader context of sustainable remediation strategies that balance environmental, economic, and social aspects. This article critically reviewed existing literature to evaluate and compare various low-carbon remediation methods, such as bioremediation, phytoremediation, in situ chemical oxidation, soil vapour extraction, and electrokinetic remediation, to identify suitable techniques for the remediation of oil-contaminated sites in the Niger Delta region of Nigeria. We analysed the UK sustainable remediation frameworks (SuRF-UK) to glean lessons for the Nigerian context. Our findings indicate that bioremediation and phytoremediation are particularly promising low-carbon remediation technologies for the Niger Delta region due to their cost-effectiveness and adaptability to local conditions. We proposed a framework that deeply considers opportunities for achieving multiple goals including effective remediation and limited greenhouse gas emissions while returning net social and economic benefit to local communities. The proposed framework will help decision makers to implement effective remediation technologies that meet sustainability indices, integrates emissions considerations return net environmental benefit to local communities. There is a need for policymakers to establish and enforce policies and regulations that support sustainable remediation practises, build the capacity of stakeholders, invest in research and development, and promote collaboration among stakeholders to create a regulatory environment that supports sustainable remediation practises and promotes environmental sustainability in the region. This study provides insights for achieving low-carbon remediation in regions addressing land contamination by different contaminants and facilitates the adoption of remediation technologies that consider contextual socio-economic and environmental indices for sustainable development.

Advances in the management of radioactive wastes and radionuclide contamination in environmental compartments: a review

Several anthropogenic activities produce radioactive materials into the environment. According to reports, exposure to high concentrations of radioactive elements such as potassium (⁴⁰K), uranium (²³⁸U and ²³⁵U), and thorium (²³²Th) poses serious health concerns. The scarcity of reviews addressing the occurrence/sources, distribution, and remedial solutions of radioactive contamination in the ecosystems has fueled data collection for this bibliometric survey. In rivers and potable water, reports show that several parts of Europe and Asia have recorded radionuclide concentrations much higher than the permissible level of 1 Bq/L. According to various investigations, activity concentrations of gamma-emitting radioactive elements discovered in soils are higher than the global average crustal values, especially around mining activities. Adsorption technique is the most prevalent remedial method for decontaminating radiochemically polluted sites. However, there is a need to investigate integrated approaches/combination techniques. Although complete radionuclide decontamination utilizing the various technologies is feasible, future research should focus on cost-effectiveness, waste minimization, sustainability, and rapid radionuclide decontamination. Radioactive materials can be harnessed as fuel for nuclear power generation to meet worldwide energy demand. However, proper infrastructure must be put in place to prevent catastrophic disasters.

Online quantitative substrate, product, and cell concentration in citric acid fermentation using near-infrared spectroscopy combined with chemometrics

As a mature platform compound, citric acid (CA) is mainly produced by Aspergillus niger (A. niger) through submerged fermentation. However, the CA fermentation process is still regulated based on experience and limited offline data, so real-time monitoring and intelligent precise control of the fermentation process cannot be carried out. In this study, near-infrared (NIR) spectroscopy combined with different chemometrics methods was used to quantify the substrate, product, and cell concentration of CA fermentation online. The predictive performance of total sugar (TS), CA, and dry cell weight (DCW) concentrations were compared between traditional partial least squares (PLS) and intelligent stacked auto-encoder (SAE) modeling methods. Theresults showed that both PLS and SAE models had good performance in predicting TS and CA. The performance, accuracy, and precision of the PLS models are slightly better than those of the SAE models in predicting TS and CA. SAE model was superior to the PLS model in predicting DCW concentration. The SAE modeling method has advantages in predicting the concentration of complex components. In this study, the multi-parameter online prediction was realized in the complex system of CA fermentation, which provided the basis for real-time intelligent control of the fermentation process.