Reversible electrokinetic adsorption barriers for the removal of organochlorine herbicide from spiked soils

An overview of electrokinetically enhanced chemistry technologies for organochlorine compounds (OCs) remediation from soil

In recent years, electrokinetic (EK) remediation technology has gained significant attention among researchers. This technology has proven effective in the remediation of low-permeability polluted soil. Organochlorines (OCs) are highly toxic, persistent, bioaccumulative, and capable of long-distance migration. They can also accumulate through the food chain, posing significant environmental risks. This paper provides a review of the reaction mechanism of combining chemical technology with EK remediation for the removal of several typical OCs. Furthermore, the factors influencing the efficiency of EK remediation, such as pH and ζ potential, voltage gradients, electrode materials, electrolytes, electrode arrangements, and soil types, are summarized. The paper also presents an overview of recent advancements in the methods of combining chemical technology with EK remediation for the treatment of OCs contaminated soil. Specifically, the research progress in surfactants-combined EK technology, chemical oxidation-combined EK technology, chemical reduction-combined EK technology, and chemical adsorption-combined EK technology is summarized. These findings serve as a foundation for ongoing and future research endeavors in the field. Further exploration and investigation in this area are essential for advancing the field and improving environmental remediation strategies.

Cork barriers for the remediation of soils polluted with lindane

The in-situ removal of lindane from spiked soil was studied using cork barriers combined with electrokinetic and ohmic heating soil remediation processes. Both vertical and horizontal cork barriers have been evaluated to retain pollutants mobilized by electro-osmotic flow or volatilized by ohmic heating. Moreover, the addition of surfactant solutions in electrolyte wells has been evaluated to promote the dragging of lindane by electrokinetic fluxes. Results indicated that the drag of lindane by liquid flows is not as important as expected, opposite to what happened with the dragging by gaseous flows. The retention of gaseous lindane was also confirmed in adsorption tests carried out in a column packed with cork granules. The addition of surfactant had a very limited effect on the mobility of lindane, and dragging of this species to the electrode wells or to a permeable reactive barrier. On the contrary, the reactivity of lindane during the electrochemical treatments is relevant due to the electrokinetic basic front promoting the in-situ conversion of lindane into less chlorinated pollutants.

Scale-up of electrokinetic permeable reactive barriers for the removal of organochlorine herbicide from spiked soils

This work aims to shed light on the scale-up a combined electrokinetic soil flushing process (EKSF) with permeable reactive barriers (PRB) for the treatment of soil spiked with clopyralid. To do this, remediation tests at lab (3.45 L), bench (175 L) and pilot (1400 L) scales have been carried out. The PRB selected was made of soil merged with particles of zero valent iron (ZVI) and granular activated carbon (GAC). Results show that PRB-EKSF involved electrokinetic transport and dehalogenation as the main mechanisms, while adsorption on GAC was not as relevant as initially expected. Clopyralid was not detected in the electrolyte wells and only in the pilot scale, significant amounts of clopyralid remained in the soil after 600 h of operation. Picolinic acid was the main dehalogenated product detected in the soil after treatment and mobilized by electro-osmosis, mostly to the cathodic well. The transport of volatile compounds into the atmosphere was promoted at pilot scale because of the larger soil surface exposed to the atmosphere and the electrical heating caused by ohmic losses and the larger interelectrode gap.

Removal of Transition Metals from Contaminated Aquifers by PRB Technology: Performance Comparison among Reactive Materials

The most common reactive material used for the construction of a permeable reactive barrier (PRB) is zero valent iron (ZVI), however, its processing can generate corrosive effects that reduce the efficiency of the barrier. The present study makes a major contribution to understanding new reactive materials as natural and synthetic, easy to obtain, economical and environmentally friendly as possible substitutes for the traditional ZHV to be used as filters in the removal of three transition metals (Zn, Cu, Cd). To assess the ability to remove these pollutants, a series of batch and column tests were carried out at laboratory scale with these materials. Through BACH tests, four of seven substances with a removal percentage higher than 99% were prioritized (cabuya, natural clinoptilolite zeolites, sodium mordenite and mordenite). From this group of substances, column tests were performed where it is evidenced that cabuya fiber presents the lowest absorption time (≈189 h) while natural zeolite mordenite shows the highest time (≈833 h). The latter being the best option for the PRB design. The experimental values were also reproduced by the RETRASO code; through this program, the trend between the observed and simulated values with respect to the best reactive substance was corroborated.

Strategies for powering electrokinetic soil remediation: A way to optimize performance of the environmental technology

The electro-kinetic remediation of soils using different powering strategies has been studied, in order to clarify which is the best strategy to couple solar powering with this remediation technology, in a context of developing more sustainable electrochemical remediation technologies. Direct powering from photovoltaic panels (Case a), application of constant electric fields with the same average value of Case a (Case b) and application of constant specific power with the same average value of Case a (Case c) have been compared. Results show an outstanding influence of the powering strategy on the removal efficiency of clopyralid (model of herbicide used in this work). The direct use of solar power profiles obtained the lowest removal efficiencies, which contrasts with the higher expected sustainability of this powering strategy. Reversion of pollutant transport overnight and extreme electric field values at noon help to explain the lower efficiency of this strategy. Evaporation mechanisms are promoted by operating at extreme large electric fields. In addition, harsher conditions lead to a higher negative soil affectation in terms of regions affected by extreme pHs, water contents and/or conductivities and to lower specific pollutant removals. Therefore, maximum efficiencies were found for Case b (constant electric potential gradient) with a total removal over 110 g kWh^-1 and only a slight affectation into the final soil properties.

Removal of Phenol from Steel Plant Wastewater in Three Dimensional Electrochemical (TDE) Process using CoFe2O4@AC/H2O2

This study investigated the removal of phenol from steel industry wastewater by three dimensional electrochemical (TDE) process using CoFe2O4 nanobiocomposite based activated carbon in the presence of H2O2 (EC-CoFe2O4@AC-H2O2). In this study, CoFe2O4 nanobiocomposite-foundation activated carbon (CoFe2O4@AC) was used as microelectrode, adsorbent, and activator for peroxide hydrogen. The removal efficiency of phenol and COD was investigated through the parameters of pH, contact time, CoFe2O4@AC dosage, current density, and H2O2 concentration. The highest removal rates of phenol and COD were >99% and 98%, respectively. Also, steel plant wastewater under the optimal conditions of pH = 6.5, current density = 15 mA cm−2, contact time = 25 min, H2O2 concentration of 1.0 mM, and CoFe2O4@AC dose = 0.3 g L−1. Kinetic analysis revealed that the adsorption experimental data was best fitted by the pseudo-first-order model.

Electrokinetic remediation of contaminants of emergent concern in clay soil: Effect of operating parameters

The potential of electrokinetic (EK) remediation to remove from soils one particular group of contaminants - contaminants of emergent concern (CECs), remains largely overlooked. The present study aimed to evaluate the efficiency of the EK process for the remediation of an agricultural clay soil containing CECs. The soil was spiked with four CECs - sulfamethoxazole, ibuprofen, triclosan and caffeine - and their status (i.e. residual amounts and spatial distribution) evaluated at the seventh day of EK treatment at a defined current intensity, directionality and duration of void period. The characterization of the soil physicochemical properties was also undertaken. The results showed similar degradation trends in all applied EK strategies, which were suchlike to that of the natural attenuation (biotic control): sulfamethoxazole > ibuprofen ≥ triclosan ≥ caffeine. The removal of the CECs was higher under a 10 mA constant current application than in the natural attenuation (up to 2.8 times higher; from 13 to 85%). Caffeine was the exception with its best removal efficiency being achieved when the ON/OFF switch mode with a void period duration of 12 h was used (36%). The use of electro-polarization reversal mode did not favour the remediation. The soil pH variations resulting from EK application were determinant for triclosan remediation, which increased with soil pH increase. The only EK condition that promoted the removal of all CECs was the ON/OFF switch mode of 12 h (removals between 36 and 72%), in which only minor physicochemical disturbances of the soil were observed. This is in accordance with a potential application of EK in-situ. The last is reinforced by the low estimated electrical cost of the best EK technology - 2.33 €/m³ for the 7 days. Overall the EK remediation processes are a promising technology to stimulate in situ the removal of CECs from agricultural soils.