Chelating Agents and Heavy Metal Phytoextraction

Electrostatic field as an emergent technology in refining crude oils: a review

Vegetable oils and fatty acid esters (FAEs) are commonly used in various industrial and commercial applications. However, the presence of contaminants in these oils can severely affect their functionality and suitability. Conventional refining techniques for vegetable oils typically involve degumming, neutralization, bleaching and deodorization. Meanwhile, refining of FAEs often utilize wet or dry washing processes. These are often resource-intensive, producing substantial waste products, causing neutral oil loss, and can also result in the loss of micronutrients. To address these challenges, researchers have explored the use of nano-adsorbents and electrostatic field (E-field) technologies as alternatives in purifying industrial dielectric oils by removing polar particles and contaminants. Nano-adsorbents demonstrated increased efficiency in removing polar contamination while minimizing neutral oil loss. However, removal of these spent adsorbents can be challenging due to their nano-size, and physicochemical properties. The use of these materials combined with E-field technologies offers a novel and sustainable solution for removing spent nano-adsorbents and contaminants. This review provides an overview of current traditional and novel refining technologies for vegetable oils and FAEs, including their associated limitations. Compared to conventional methods, E-field treatment offers several advantages, making it an attractive alternative to conventional approaches in food processing and oil refining.

Evaluation of soil metal sorption characteristics and heavy metal extractive ability of indigenous plant species in Abeokuta, Nigeria

Heavy metals sorption behavior and phytoremediative potentials of 14 indigenous tropical plants were evaluated with EDTA and Urea as amendments. Order of preferential sorption of metals are: Pb > Cu > Zn > Cd. In competitive sorption, Pb sorption was increased by 4.98, Cu by 4.24, Zn by 1.40, and Cd by -6 units, implying potential Cd pollution. Order of plants' dry matter accumulation was: Panicum maximum > Zea mays > Amaranthus cruentus > Vetiveria zizanoides > Andropogon tectorum > Tithonia diversifolia > Ocimum gratissimum. Andropogon tectorum and O. gratissimum preferentially translocate Cu and Zn, while V. zizanoides and Z. mays translocated Zn, Cu, and Pb. Amaranthus cruentus, P. maximum, and T. diversifolia preferentially translocated Cu, Pb, Cd, and Zn. The plants are preferentially enriched in Cu and Zn, Pb was selected by P. maximum, T. diversifolia and V. zizanoides. Urea and EDTA enhanced the metal uptake in the plants by 130% and 145%, respectively. Tolerance index (TI) of the plants were reduced by the amendments except in A. tectorum, P. maximum, V. zizanoides, and Z. mays. Amaranthus spinosus, Cassia occidentalis, Pennisetum purpureum, Chromolena odorata, Hibiscus sabdariffa, Hibiscus cannabinus, and Cochorus olitorus could not tolerate the metals.

Phytoassessment of Vetiver grass enhanced with EDTA soil amendment grown in single and mixed heavy metal-contaminted soil

Over the years, ethylene-diamine-tetra-acetate (EDTA) has been widely used for many purposes. However, there are inadequate phytoassessment studies conducted using EDTA in Vetiver grass. Hence, this study evaluates the phytoassessment (growth performance, accumulation trends, and proficiency of metal uptake) of Vetiver grass, Vetiveria zizanioides (Linn.) Nash in both single and mixed heavy metal (Cd, Pb, Cu, and Zn)-disodium EDTA-enhanced contaminated soil. The plant growth, metal accumulation, and overall efficiency of metal uptake by different plant parts (lower root, upper root, lower tiller, and upper tiller) were thoroughly examined. The relative growth performance, metal tolerance, and phytoassessment of heavy metal in roots and tillers of Vetiver grass were examined. Metals in plants were measured using the flame atomic absorption spectrometry (F-AAS) after acid digestion. The root-tiller (R/T) ratio, biological concentration factor (BCF), biological accumulation coefficient (BAC), tolerance index (TI), translocation factor (TF), and metal uptake efficacy were used to estimate the potential of metal accumulation and translocation in Vetiver grass. All accumulation of heavy metals were significantly higher (p < 0.05) in both lower and upper roots and tillers of Vetiver grass for Cd + Pb + Cu + Zn + EDTA treatments as compared with the control. The single Zn + EDTA treatment accumulated the highest overall total amount of Zn (8068 ± 407 mg/kg) while the highest accumulation for Cu (1977 ± 293 mg/kg) and Pb (1096 ± 75 mg/kg) were recorded in the mixed Cd + Pb + Cu + Zn + EDTA treatment, respectively. Generally, the overall heavy metal accumulation trends of Vetiver grass were in the order of Zn >>> Cu > Pb >> Cd for all treatments. Furthermore, both upper roots and tillers of Vetiver grass recorded high tendency of accumulation for appreciably greater amounts of all heavy metals, regardless of single and/or mixed metal treatments. Thus, Vetiver grass can be recommended as a potential phytoextractor for all types of heavy metals, whereby its tillers will act as the sink for heavy metal accumulation in the presence of EDTA for all treatments.

Application of manures to mitigate the harmful effects of electrokinetic remediation of heavy metals on soil microbial properties in polluted soils

Ethylenediaminetetraacetic acid (EDTA) used with electrokinetic (EK) to remediate heavy metal-polluted soils is a toxic chelate for soil microorganisms. Therefore, this study aimed to evaluate the effects of alternative organic chelates to EDTA on improving the microbial properties of a heavy metal-polluted soil subjected to EK. Cow manure extract (CME), poultry manure extract (PME) and EDTA were applied to a lead (Pb) and zinc (Zn)-polluted calcareous soil which were subjected to two electric intensities (1.1 and 3.3 v/cm). Soil carbon pools, microbial activity, microbial abundance (e.g., fungal, actinomycetes and bacterial abundances) and diethylenetriaminepentaacetic acid (DTPA)-extractable Pb and Zn (available forms) were assessed in both cathodic and anodic soils. Applying the EK to soil decreased all the microbial variables in the cathodic and anodic soils in the absence or presence of chelates. Both CME and PME applied with two electric intensities decreased the negative effect of EK on soil microbial variables. The lowest values of soil microbial variables were observed when EK was combined with EDTA. The following order was observed in values of soil microbial variables after treating with EK and chelates: EK + CME or EK + PME > EK > EK + EDTA. The CME and PME could increase the concentrations of available Pb and Zn, although the increase was less than that of EDTA. Overall, despite increasing soil available Pb and Zn, the combination of EK with manures (CME or PME) mitigated the negative effects of using EK on soil microbial properties. This study suggested that the synthetic chelates such as EDTA could be replaced with manures to alleviate the environmental risks of EK application.

Enhancement of Cd phytoextraction by hyperaccumulator Sedum alfredii using electrical field and organic amendments

The combined use of organic amendment-assisted phytoextraction and electrokinetic remediation to decontaminate Cd-polluted soil was demonstrated in a laboratory-scale experiment. The plant species selected was the hyperaccumulator Sedum alfredii. Prior to the pot experiment, the loamy soil was treated with 15 g kg^-1 of pig manure compost, 10 g kg^-1 of humic acid, or 5 mmol kg^-1 of EDTA, and untreated soil without application of any amendment was the control. Two conditions were applied to each treatment: no voltage (without an electrical field) and a direct current (DC) electrical field (1 V cm^-1 with switching polarity every day). Results indicated that Cd concentrations in S. alfredii were significantly (p < 0.05) increased by application of the electrical field and soil amendments (pig manure compost, humic acid, and EDTA). By switching the polarity of the DC electrical field, significant pH variation from anode to cathode can be avoided, and no significant impact was observed on shoot biomass production. Electrical field application increased DTPA-extractable Cd in soils and the Cd accumulation in shoots by 6.06-15.64 and 24.53-52.31%, respectively. The addition of pig manure compost and humic acid enhanced shoot Cd accumulation by 1.54- to 1.92- and 1.38- to 1.64-fold because of their simultaneous enhancement of Cd concentration in shoots and biomass production. However, no enhancement of Cd accumulation was found in the EDTA treatment, which can be ascribed to the inhibition of plant growth caused by EDTA. In conclusion, pig manure compost or humic acid addition in combination with the application of a switched-polarity DC electrical field could significantly enhance Cd phytoextraction by hyperaccumulator S. alfredii.

Improving the efficiency of phytoremediation using electrically charged plant and chelating agents

The low efficiency of phytoremediation is a considerable problem that limits the application of this environmentally friendly method on heavy metal-polluted soils. The combination of chelate-assisted phytoextraction and electrokinetic remediation could offer new opportunities to improve the effectiveness of phytoextraction. The current experiment aims to investigate the effects of electrical fields and chelating agents on phytoremediation efficiency. In a pot experiment using mine soil, poultry manure extract (PME), cow manure extract (CME), and ethylenediaminetetraacetic acid (EDTA) were applied to soil as chelating agents (2 g kg(-1)) at the beginning of the flowering stage. A week later, Helianthus annuus (sunflower) was negatively charged by inserting a stainless steel needle with 10 and 30 V DC electricity in the lowest part of the stems for 1 h each day for a 14-day period. At the end of the experiment, the shoot and root dry weight, lead (Pb) concentration in plant organs, translocation factor (TF), metal uptake index (UI), and soil available Pb (diethylene triamine pentaacetic acid (DTPA) extractable) were detected. Results indicated that the application of electrical fields had no significant impact on the shoot and root dry weights, while Pb concentration and UI increased in the 10-V EDTA treatment by 500 % compared to control. There was no significant difference between UI in 30- and 10-V EDTA treatments. Soil available Pb significantly increased in the 30-V treated soil. A positive correlation was observed between the available Pb in soil near the root and Pb concentration in shoot, its TF, and UI. In conclusion, a negatively charged plant along with the application of EDTA significantly increased the phytoremediation efficiency.