Reena Amatya Shrestha

Removal of hexachlorobenzene from soil by electrokinetically enhanced chemical oxidation

This study investigates the feasibility of enhanced electrokinetic Fenton process for the remediation of hexachlorobenzene (HCB) in low permeable soil. Laboratory scale experiments were carried out in two different type of experimental setup to evaluate the influence of electrode positions in the system. Kaolin was artificially contaminated with HCB and treated by electrokinetic Fenton process. beta-Cyclodextrin was used to enhance the solubility of HCB in pore fluid. Results show that the position of electrodes in the system and the way in which Fentons reagent was added to the system has a significant influence on the treatment efficiency.

Effect of ultrasound on removal of persistent organic pollutants (POPs) from different types of soils.

A new and promising technology is utilization of sonochemistry on decontamination of polluted soil. The feasibility of this technology on treatment of contaminated soils (synthetic clay, natural farm clay, and kaolin) was studied by using two target persistent organic pollutants (POPs): hexachlorobenzene (HCB) and phenanthrene (PHE). The soils were highly contaminated in 500 mg/kg. The laboratory experiments were conducted with various conditions (moisture, power, and time duration). The effects of these parameters on ultrasonication (as well as the removal of contaminants) were examined. The reasonable moisture ratio of the slurry could be in range of 2:1-3:1. The process did not change pH values of soils. Experimental results showed that ultrasonication has a potential to reduce the high concentrations of these POPs.

Remediation of hexachlorobenzene in soil by enhanced electrokinetic Fenton process

The feasibility of enhanced electrokinetic Fenton process for the remediation of Hexachlorobenzene (HCB) in low permeability soil was investigated. Kaolin was artificially contaminated with HCB and treated by electrokinetic and electrokinetic Fenton processes. β -Cyclodextrin was used to enhance the solubility of HCB in pore fluid. Three tests were carried out, of which two were electrokinetic experiments to observe the suitability of β -cyclodextrin as a flushing solution for these processes. The third experiment was the electrokinetic Fenton test using β -cyclodextrin as an enhancing agent. Results show that the removal efficiency depends on the choice of a suitable flushing solution and physical parameters like pH, electric current and electro-osmotic flow.

INVESTIGATIONS ON DIFFERENT POSITIONS OF ELECTRODES AND THEIR EFFECTS ON THE DISTRIBUTION OF CR AT THE WATER SEDIMENT INTERFACE

In most mining areas, significant concentrations of metals such as Pb, Cu, Cr, Zn, Cd, Fe, Mn, Co, Ni, Hg, Ar, halogenated organic compounds and radionuclides are found. Of those, Cr is one of the well-known heavy metals that forms toxic species. It is necessary to study the mobilization and accumulation of Cr at the sediment water interface in an electric field at varying different positions and conditions of the electrode arrangement. The tests were carried out with a natural sediment containing heavy metals from the river Weisse Elster (Germany). The electrokinetic experiments have been performed in columns filled with sediment using electrodes made of conductive polymers (polyethylene with carbon black) at a maximum current density of 0.5 mA/cm2. The experimental results suggest that the mobilization and accumulation of Cr highly depends on chemical factors for e.g., pH value, redox potential, respectively redox status and the content of Fe, A1 and organic matter in the soil or sediment. The sorption of Cr (III, VI) is very high in the pH range > 4.5. As expected, a high mobilization of Cr (III, VI) was seen in the case of the experiments with the anode at the sediment, because the pH value was lower than mentioned above. On the opposite, the best conditions for the Cr (III, VI) immobilization is high pH values (cathode at the sediment).

Ultrasound Technology in Green Chemistry

As part of a new and rapidly growing field of study, the applications of ultrasound in green chemistry and environmental applications have a promising future. Compared to conventional methods, ultrasonication can bring various benefits, such as environmental friendliness (no toxic chemicals are used or produced), cost efficiency, and compact, on-site treatment. Besides an overview of the ultrasonic background, this paper summarizes the main findings and innovations of recent studies that have been using ultrasound in environmental analysis, water and sludge treatment, and soil and sediment remediation, as well as air purification.

Electrokinetic and Ultrasonic Treatment of Kaolin Contaminated by POPs

Abstract Three tests were conducted using ultrasound alone, ultrasound as an enhancement for electrokinetic test and electrokinetic test alone to compare the removal performance of the three persistent organic pollutants, hexachlorobenzene, phenanthrene, and fluoranthene from low permeability kaolin. Results show that the removal efficiency in ultrasonically enhanced electrokinetic test was the highest among experiments, though the removal rates improved were small only. The assistance of ultrasound in electrokinetic remediation can help reduce these hydrophobic organic compounds by increasing their mobility, desorption for electroosmotic migration, and also by degrading them through free radical oxidation forming during cavitation process.

Recent studies in environmental applications of ultrasoundA paper submitted to the Journal of Environmental Engineering and Science.

As a young, new, and rapidly growing science, the applications of ultrasound in environmental technology hold a promising future. Compared with conventional methods, ultrasonication can bring sever...

Removal of Hexachlorobenzene and Phenanthrene from Clayey Soil by Surfactant- and Ultrasound-Assisted Electrokinetics

Removal of nonpolar contaminants such as most organic compounds are transported primarily by electroosmosis in electrokinetic remediation, thus the process is effective only if the contaminants are soluble in pore fluid. Hydrophobic organic compounds such as hexachlorobenzene (HCB) and phenanthrene (PHE) can adsorb strongly to clayey soil. Therefore, in this study, enhancements were done by adding 2-hydroxylpropyl-β-cyclodextrin surfactant and ultrasonication comparably to assist the electrokinetic treatment in improving the mobility of these hydrophobic compounds. The results show that HCB and PHE were mobilized and removed in both cases. But HCB is more difficult to remove than PHE, because of its highly stable nature and low water-solubility property. Ultrasound-assisted test performed better PHE reduction than surfactant-assisted test, because ultrasound can degrade the contaminant through oxidation by free radicals.

Electrically induced displacement transport of immiscible oil in saline sediments.

Electrically assisted mitigation of coastal sediment oil pollution was simulated in floor-scale laboratory experiments using light crude oil and saline water at approximately 1/10 oil/water (O/W) mass ratio in pore fluid. The mass transport of the immiscible liquid phases was induced under constant direct current density of 2A/m(2), without water flooding. The transient pore water pressures (PWP) and the voltage differences (V) at and in between consecutive ports lined along the test specimen cell were measured over 90days. The oil phase transport occurred towards the anode half of the test specimen where the O/W volume ratio increased by 50% over its initial value within that half-length of the specimen. In contrast, the O/W ratio decreased within the cathode side half of the specimen. During this time, the PWP decreased systematically at the anode side with oil bank accumulation. PWP increased at the cathode side of the specimen, signaling increased concentration of water there as it replaced oil in the pore space. Electrically induced transport of the non-polar, non-conductive oil was accomplished in the opposing direction of flow by displacement in absence of viscous coupling of oil-water phases.

Electrochemical Soil Stabilization and Verification

ElectroChemical treatment (ECT) has been applied for the in situ chemical stabilization soft clay soils. A possibility during ECT is mineral dissolution and re-deposition which can cause micro-structural changes affecting the engineering behavior of clay soils. Additionally, during ECT the success of depositing the stabilizing chemicals in the tight clay matrices may be hindered by process parameters, such as electrode reactions. A simple monitoring method was tested in the laboratory to track the evolution of intended ECT stabilization for quick assessment and potential control of the process. Calcium and phosphate ions were injected separately and then together into kaolin clay under a constant voltage gradient at varying durations. Calcium hydroxide and phosphoric acid were used as the feed electrolytes in the anolyte and catholyte, respectively. The ECT triggered stabilization was diagnosed by monitoring the evolution of clay soil stiffness. The shear wave velocity (Vs) and the small strain modulus (Gmax) of the treated specimens were monitored using bender elements (i.e., piezoelectric transceivers). Finally, changes in the microstructure of the clay were analyzed using comparative XRD and SEM scans of pre- and post-treatment specimens. The analysis showed that electro-migration of calcium ions occurred but did not result in the expected cementation within the clay soil because of low pH hindering formation of calcium hydrates. In contrast, the Gmax of the samples treated with phosphate ions increased at the cathode and the middle sections of the clay specimens by 10 and 20%, respectively. While SEM results did not reveal discernible micro-structural changes in the treated clay matrix, the XRD result showed discernable changes in some elemental peaks, indicating chemical accumulation. The nondestructive diagnostic method was beneficial and showed promise for possible field application for transient assessment of the efficacy of ECT stabilization of clay soils.