SUSTAINABLE REMEDIATION OF WATER CONTAMINATED WITH ORGANIC POLLUTANTS BY USING BIOELECTROCHEMICAL SYSTEMS
Date of Award
Master of Science
With increase in population and human activities globally, many of the current technologies for treatment of water contaminated with organic pollutants, which require high energy input, will be difficult to meet the requirement of sustainability. Bioelectrochemical systems (BESs), such as microbial fuel cells (MFCs) and microbial electrolysis cells (MECs), are emerging technologies for sustainable water treatment with renewable energy production or reduced energy consumption. In the first study, low-cost nanomaterials were introduced in two-chambered MFCs to increase the wastewater treatment efficiency and the power production of the system. Ni nanoparticles (NPs), multi-walled carbon nanotubes (MWCNT), and MWCNT/Ni were used to modify the cathode electrode. The overall performance of the MFC was enhanced in the following order: MWCNT> MWCNT/Ni > Ni. The power production increased by 7.9 times to 1.2 W/m3 with 1.5 mg/cm2 of MWCNT. The power density further increased to 1.9 W/m3, and the chemical oxygen demand (COD) of the anode solution maximally decreased by 163.3 mg/L in a 24-h duration with 3.0 mg/cm2 of MWCNT. The internal resistance decreased maximally by 65.2% to 0.4 kΩ with 1.5 mg/cm2 of MWCNT/Ni. Electrochemical impedance spectroscopy (EIS) was conducted to assess the effects of different nanomaterials on the impedance of the MFC. Charge transfer resistance of the cathode was maximally reduced by ~85% to 0.3 Ω with 3.0 mg/cm2 of MWCNT/Ni. In the second study, BES was used for sustainable degradation of trichloroethylene (TCE) contaminated groundwater in the cathode chamber of the system with and without supply of external voltage, simultaneously with wastewater treatment in the anode chamber, to reduce energy consumption. TCE was reduced according to second order reduction for up to 91.3 and 98.4% in MFC and MEC, respectively. It was discovered for the first time that same products were obtained for the TCE reduction under the two different conditions. The primary products obtained were dimethy disulphide and vinyl chloride. Trace amount of chloroform was also detected. In the meantime, COD was reduced from 665 mg/L to 475 mg/L and 272 mg/L without and with voltage supply, respectively, in the anode chamber. Bacterial species responsible for TCE cathodic reduction mostly belonged to phyla of Proteobacteria, Bacteroidetes and Firmicutes in both MFC and MEC. In the third study, a two-chambered MFC was explored for the degradation of groundwater contaminated with emerging contaminant 1,4-dioxane in the anode chamber, with simultaneous power production. Comparative study was carried out with 1,4-dioxane as sole carbon source, or cometabolic degradation with presence of methanol. Cometabolic pathway increased 1,4-dioxane removal by 10% to 52% after 7 days, increased the types of degradation products by 14 to 17, and increased power production of the MFC by 18% to 88.9 mW/m3. Formation of biofilm for 1,4-dioxane degradation on anode surface promoted power production of the MFC. Bacteroidetes, Firmicutes, and Proteobacteria facilitated 1,4-dioxane degradation both without and with methanol, in the anode chamber of the MFC. Rikenella sp. and Solitalea canadensis occupied the highest percentages of 18.8 and 24.0% on the anode surface without and with methanol, respectively.
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