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DC Field | Value | Language |
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dc.contributor.advisor | de Lannoy, Charles | - |
dc.contributor.author | Elganzoury, Mohamed | - |
dc.date.accessioned | 2022-08-29T17:24:30Z | - |
dc.date.available | 2022-08-29T17:24:30Z | - |
dc.date.issued | 2022 | - |
dc.identifier.uri | http://hdl.handle.net/11375/27769 | - |
dc.description.abstract | Since the industrial revolution of the 18th century, rapid growth occurred in the energy, electronic, fertilizers, pesticides, detergents, pharmaceutical, mining and paper industries, among others. Consequently, wastewaters produced from these various industries is highly contaminated with hazardous pollutants including toxic metals and organic contaminants as well as useful resources such as phosphates and precious metals. It is necessary to remove hazardous pollutants from industrial wastewater to meet the environmental disposal regulations or to enable safe recycling of the treated wastewater in other applications. It is also economically beneficial to separate the valuable resources from the industrial waste solutions. Several technologies have been employed for metal and other contaminants (e.g., organics and minerals) removal from industrial wastewater including chemical precipitation, coagulation and flocculation, membrane separation, ion exchange, adsorption, chemical oxidation, and biodegradation. Chemical precipitation, coagulation and flocculation, and chemical oxidation processes have a high chemical consumption. Adsorption and ion exchange do not require a high chemical consumption while separating pollutants from wastewater, nevertheless acids and chemical reagents are required for the regeneration of sorbents and ion exchange resins for their reuse in subsequent processes. Membrane technologies suffer from membrane fouling and scaling, which require the use of chemical reagents and antiscalants to mitigate these problems. The use of bacteria in biodegradation is a common alternative in many wastewater, but this process requires a toxic-free environment, which is rarely the case in industrial wastewaters due to the presence of toxic metals in most of the industrial effluents. As such, this process is not appropriate for most industrial separations, requiring additional unit operations to remove toxic metals before the biodegradation processes which causes higher operational and capital cost. The objective of this thesis is to substitute metal and associated contaminants conventional removal methods with novel electrochemical approaches to decrease the chemical consumption, lower the environmental impact, extract precious metals and to decrease the overall unit operations during industrial wastewater treatment. In the first part of the thesis, using chemical coagulants was substituted by electrochemically induced in-situ coagulants to remove toxic metals from mixed industrial wastewater. The newly introduced technique utilized the presence of iron in the waste solution and converted it into iron hydroxide coagulants through the reaction of iron with the hydroxyl groups generated via water electrolysis at a stainless-steel cathode. The generated coagulants interacted with the toxic metals (i.e., arsenic, cadmium, lead, nickel, copper, chromium) in the wastewater and separated them from the solution. To decrease the overall unit operations of the mixed industrial wastewater treatment, the associated organic pollutants in the waste solution were simultaneously degraded. A dimensionally stable anode (DSA) was used to oxidize the organic contaminants in the solution simultaneously with the metal coagulation occurring at the cathode. The electrochemical oxidation-in-situ coagulation (ECO-IC) process resulted in a treated solution with a substantially lower heavy metal content, lower organic content, greater effective diameter of the suspended particles, and distinct phases that can be separated for further treatment. In the second part of the thesis, a closed-loop continuous cycle for metal adsorption and electrodesorption using CNT sorbents was invented. In this process, 1) metals are adsorbed onto the surface of CNTs, 2) the metal-saturated CNTs are filtered onto a microfiltration (MF) membrane to form a temporary membrane electrode, 3) the CNT-coated membrane is used as an anode in an electrochemical cell, 4) an applied electric potential desorbs the metals from the CNT-membrane, and 5) the CNTs are separated from the membrane to be reused as adsorbents in a closed-loop process. The closed-loop regenerative cycle allowed recycling the effective but expensive CNT sorbents in subsequent adsorption-electrodesorption cycles. The electrochemical regeneration of CNTs eliminated the need for using acids and chemical reagents for CNTs regeneration. The proposed technique was successfully employed for adsorption and electrodesorption of copper (a model toxic metal) from aqueous solutions and gold (a model precious metal) from acidic chloride solutions mimicking e-waste leachate. The results of this study demonstrate a chemical-free method for metal removal that achieves removal at rates comparable to conventional chemical methods and adsorbent regeneration as high as that achieved with chemical methods. In the third part of the thesis, limitations and sources of error during electrochemical water treatment were identified to be taken into consideration by future researchers. In the first phase of this research, sources of error arising in batch electrochemical cells were illustrated. Batch electrochemical experiments are considered the baseline for testing porous electrodes and electrochemical membranes (ECMs) in water treatment applications (including metal separation and contaminant removal) before being used in continuous processes. It was identified that electrochemical dissolution of metal fasteners holding porous conductive membranes in batch electrochemical cells occur, even when keeping the metal fasteners outside the electrolyte solution. This phenomenon can confound water treatment experimental results in batch cells. The reason for this phenomenon was investigated and a simple solution to prevent it was proposed. In the second phase of this research, limitations on using metal feed spacers as electrodes during gypsum solution (secondary pollutants produced during metal removal from mining wastewater) RO filtration was identified. Using electro-assisted filtration has a lower environmental impact than using antiscalants for preventing gypsum scale formation on RO membranes. Nevertheless, using metal feed spacer electrodes for this purpose was not effective due to low generation of hydrogen gas and the spacers' anodic electro dissolution. Inert electrodes to electro dissolution (i.e., CNTs coated polypropylene feed spacers) are proposed as an effective and economic option for electro-assisted filtration of gypsum solutions. | en_US |
dc.language.iso | en | en_US |
dc.title | Electrochemical Approaches for Water Treatment: Metal Separation and Associated Industrial Contaminant Removal | en_US |
dc.type | Thesis | en_US |
dc.contributor.department | Chemical Engineering | en_US |
dc.description.degreetype | Thesis | en_US |
dc.description.degree | Doctor of Philosophy (PhD) | en_US |
dc.description.layabstract | With rapid industrial development, industrial wastewaters are heavily contaminated with hazardous pollutants and valuable resources. As a result, there are social and economic needs for efficient industrial wastewater treatment to remove harmful contaminants and to extract useful compounds. Metals of particular interest in industrial wastewaters are organized into two categories, toxic metals (e.g., arsenic, zinc, nickel, mercury, and cadmium) and precious metals (e.g., gold, silver, platinum, and palladium). An effective metal separation from industrial waste solutions is a major goal for the sustainable development of industrial processes. Conventional metal removal technologies have intensive chemical consumption producing secondary pollution. Here, we introduce two novel environmental approaches for metal removal with minimal chemical consumption. The first approach replaces chemical coagulants with electrochemically generated in-situ coagulants for toxic metal removal from industrial wastewater. The second approach introduces a closed loop continuous process for adsorption and electro-desorption of toxic and precious metals from aqueous solutions using carbon nano tubes (CNTs) sorbents. The closed-loop continuous regenerative process enables the use of highly effective CNT sorbents for metal removal from waste solutions. The desorption process is based on electrochemical regeneration of CNTs from metals, which avoids the need for acids or other solvents to regenerate the CNT sorbents. | en_US |
Appears in Collections: | Open Access Dissertations and Theses |
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File | Description | Size | Format | |
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Elganzoury_Mohamed_A_202208_PhD.pdf | 7.01 MB | Adobe PDF | View/Open |
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