Industrial activities have led to a release of many toxic chemicals to the environment. The components released are contained in heavy metals and other organic pollutants which can get into the environment either due to accidental spills or due to improper management. The result of these spills has led to millions of contaminated sites all over the world and has endangered lives of humans and other living organisms. The biggest problem currently haunting the world is toxicities in the soil, ground water, and sediments. As such, the polluted sites need urgent treatment and remediation to protect the living things and in addition guarantee the health of the environment. Despite the need to protect the environment and the environment, the technologies which have been in use for many years have proven to be ineffective and expensive. This mostly affects contaminated sites that have lower permeability, contaminant mixture among others. There is need to develop new technologies that will address these circumstances and overcome issues in such sites while on the other hand reducing the cost of treatment. This dissertation discusses electrochemical remediation technologies in ground water and how these technologies have been used to remedy toxicities in the latter.
Introduction to Electrochemical Remediation Technologies for Chlorinated Solvents
Over the recent past, electrochemical remediation technologies have proven to have a great potential in remediation of toxicities in chlorinated solvents in complex sites. The technology relies on the use of electro-kinetic technologies to remediate soils, sediments, and groundwater by applying low-intensity electric field directly to the solvent in the polluted site. The electromagnetic field mobilizes the ions from the solvents, and these ions are then collected at the electrodes. Consequently, the electric field generates electro-osmotic flow on the cathode by mobilizing interstitial fluid in the solvent. The flow of this component allows for the removal of soluble contaminants from the solvent. The success of managing and extracting toxic components from the chlorinated solvents entirely depends on the efficient extraction of the specified component and its transportation to the electrode where collection and pumping are carried out. The extracted components can then be treated at this stage. The use of electromagnetic remediation technologies is still in their earliest stages. Despite this, the use of these technologies have aided in detoxicating the soil, recognizing a broad range of contaminants and various geochemical components.
The DC employed in the remediation process has two functions. Among these functions is heating the soil to about 100 degrees Celsius which is used to disperse residual phase liquid while on the other hand inducing electroosmosis which moves pore water in the solvent from the anode to the cathode which provides flushing action even in dense clays. The DC has an advantage over the AC due to its ability to provide electroosmotic flow as opposed to AC which has no capability of providing such. The electroosmotic flow of pore water intercepts and even has the ability to degrade contaminants in the solvent. This makes it easy for the extraction and treatment of the contaminated solvent comfortable.
Electrochemical Oxidation
Pesticides and other chemicals are used in agricultural activities and pest control to improve yields. Among the commonly used chemicals are herbicides which are used in killing weeds in the farms. However, a frequent use of these chemicals leads to their accumulation in the environment and the only available natural waste is the water stream. The availability of such components in natural water streams has adverse effects on human and animal health since most of the living things depend on water for various functions. Taking into account the impact of these chemicals on the lives of the living organisms, different methods have been devised to reduce their toxicity on the lives of living organisms.
Electrochemical Oxidation has been studied, and several tests carried out to determine if it is the best alternative for the treatment of toxicity in the ground water and most of the studies carried out indicate that this technique is reliable for the on-site treatment of complex and highly volatile organic compounds. 2,4,5-T an oxidative degradation herbicide as studied by Zaou (2017) using the advanced oxidation processes indicates that the EF process can remove toxic substances from the tested solution efficiently.
In groundwater remediation, the ISCO or the In situ chemical oxidation is often accomplished through the injection of chemical oxidizers to the contaminated groundwater aimed at destroying chemical contaminants from the environment. This process has the ability to treat a wide range of organic compounds which are immune to the natural detoxifiers. The half redox reaction in the ISCO chemical oxidation results in the loss of quite a huge number of electrons. During the process, one of the reactants is oxidized during the reaction making it lose the electrons. Additionally, the other reactant is reduced or gains electrons. In ISCO, the oxidizing compounds or those that participate in oxidization gives away electrodes to the other compounds involved in the reaction. These compounds are the ones used to detoxify the contaminants to harmless compounds. ISCO chemical reaction process occurs in the contaminated site as expressed by the name. Different groundwater contaminants react differently with the ISCO method. These pollutants react either moderately or adversely with the ISCO method. The ISCO method is applicable in the treatment of either saturated or unsaturated ground water making it one of the most preferred remediation techniques for groundwater CITATION Sie14 \l 1033 (Siegrist, 2014). The most common oxidants that are used to detoxify groundwater include potassium permanganate, sodium permanganate and persulfate. The two permanganate variants (sodium and potassium) have nearly the same oxidation capabilities. The only difference comes up with the solubility. While potassium permanganate is less soluble, sodium permanganate is highly soluble. With its crystalline solid nature, potassium permanganate has to be dissolved in water before applying it on the contaminated groundwater, this depends on the temperature. Low temperatures make potassium permanganate to solidify. On the other hand, sodium permanganate is more expensive as compared to potassium but more soluble which makes it more effective than potassium. Pensufate is a newer technology that is used in the treatment of contaminated groundwater. The pensulfate compound in it is highly soluble and has a least effect on the environment.
Electrochemical Reduction
Reduction and oxidation (Redox) state of water has a significant control in the chemical components of water. It influences the stability and solubility of different constituents of water and allows a geochemical control of groundwater constituents. The in situ chemical reduction (ISCR) is a remediation technique that is commonly used for groundwater and soil treatment. It reduces the amount of contaminants groundwater or soil to the acceptable levels which are less toxic to the living things. ISCR is applied in groundwater by injecting reductive components which are in liquid form into the groundwater in contaminated area. ISCR can be used to treat organic compounds that include the compounds that are immune from natural degradation. Like ISCO, ISCR has an ability of detoxifying compounds of varied abilities and can even be more efficient in the remediation of groundwater than ISCO. One-half of a redox results to the component to gaining electrons while the reactants, on the other hand, become oxidized meaning it loses electrons. The reducing compounds in this remediation technique accept electrons provided by the other components in the reaction process (Zazou, 2017). These compounds turn the contaminants into harmless compounds hence remediation of ground water.
ISCR as a remediation technique is still a new technology in ground water treatment but has been there for decades. While it has proven its worth in treatment of ground water and removal of contaminants, there is still a gap that if filled correctly can open new fronts in the eradication of contaminants both in water and contaminated soil. There is need to find a deeper understanding of the chemistry of this technique to open new opportunities in toxin removal and increase reductive capabilities. The most commonly used reductants are Zero valent metal commonly known as ZVMs, iron metals, dithionite, polysulfides and bimetallic materials. The most commonly used zvm metal is iron referred as ZVI or zero valent iron. However, Zinc has shown the highest capability of eradicating contaminants more than zinc can do. Iron is used in creating a soft but permanent barrier under the ground to capture organic compounds such as those in groundwater. These metals have proven to be useful in reduction process and have been in use to remediate soil or groundwater in contaminated areas. Several reductive processes can take place in ISCR. These processes include the elimination of hydrogen, elimination of hydrogen and the transfer of electrons. These processes depend on the type of contaminant present in the ground water after preliminary analysis. Another factor that affects the reductive processes that take place in a contaminated ground water is the natural as well as the biological processes.
Electrolytic reactive barrier for groundwater remediation
The electrolytic reactive barrier or e-barrier is an emerging technology that uses electrochemical principles to remediate groundwater. This e-barrier is made up of closely spaced but permeable electrodes which are usually installed in a trench to intercept groundwater that has toxic substances. The electrodes are supplied with a low voltage direct current (DC) which is sufficient to drive the contaminants of interest to the electrodes. When enough electric current is supplied to the electrode, oxidizing conditions develop which allows the anode to develop oxidizing conditions while the cathode receives reducing conditions. The contaminants are then extracted from the electrodes and treated.
E-barriers are created based on permeable reactive barrier (PRB) where contaminants are moved through a reactive barrier over a natural flow of the groundwater. The most common electrolytic barrier is the titanium screen supplied with low-voltage which degrades the contaminants as they pass through it. The electrolytic reactive barrier has an enormous potential of addressing contaminants with a significantly low cost as compared to other methods of groundwater remediation (Bao, 2017).
Works Cited
Bao, D. Z. (2017). Electrochemical Reduction of N2 under Ambient Conditions for Artificial N2 Fixation and Renewable Energy Storage Using N2/NH3 Cycle. Advanced Materials, 29.
Siegrist, R. L. (2014). In situ chemical oxidation. In Chlorinated Solvent Source Zone Remediation, 253-305.
Zazou, H. O. (2017). Comparative study of electrochemical oxidation of herbicide 2, 4, 5-T: kinetics, parametric optimization, and mineralization pathway. Sustainable Environment Research, 15-23.
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