Date of Award

8-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Dr. Sudeep Popat, Committee Chair

Committee Member

Dr. David Freedman

Committee Member

Dr. David Ladner

Abstract

Water and wastewater treatment utilities require large amounts of energy inputs, and new technologies are being sought to reduce the energy costs associated with traditional treatment strategies. For wastewater treatment systems that separate blackwater and greywater, microbial fuel cells may represent a novel treatment technology in which electroactive bacteria are fed energy-rich blackwater to produce electrical power or other valuable coproducts. Microbial peroxide-producing cells are a variation on microbial fuel cells that produce hydrogen peroxide (H2O2), which is a powerful disinfectant that can be combined with advanced oxidation processes to effectively remove chemical oxygen demand as well. This research examines parameters that affect the production of H2O2 at the cathode of a microbial peroxide-producing cell, including carbon catalyst loading and current density. The potential for in situ disinfection of coliforms in the cathode chamber using the electrochemically produced H2O2 is then considered.

Vulcan carbon catalyst loadings of 0.5, 1.5, and 3.33 mg/cm2 on a carbon cloth cathode were compared with a control cathode with no additional catalyst added. The control produced the highest cathodic Coulombic efficiency for H2O2 production, and the 0.5 mg/cm2 catalyst loading produced the next highest efficiencies. Cathodic Coulombic efficiencies decreased with increasing catalyst loading. However, linear sweep voltammograms show that the application of a carbon catalyst is still justified, because the addition of any of the tested catalyst loadings resulted in large decreases in cathodic overpotential. Scanning electron microscope images and X-ray computed tomography showed that increased catalyst loadings corresponded to decreased porosities within the electrodes, which may cause a more tortuous path of diffusion for the electrochemically generated H2O2, causing decreased cathodic Coulombic efficiencies.

The effects of applied current density were then examined using current densities of 0.1, 0.5, and 1 mA/cm2. The lowest current density produced the lowest concentrations of H2O2 and the lowest changes in pH over the four hour experiments. The highest current density produced the highest concentrations of H2O2 and the largest pH changes. At 1 mA/cm2, experiments performed on the 0.5 and 1.5 mg/cm2 cathodes showed linearly increasing concentrations until around 950-1050 mg/L H2O2, where concentrations began to level off. A closer examination of pH data led to the hypothesis that at pH values close to the pKa of H2O2, changes in the relative speciation of H2O2 lead to increased decomposition of H2O2, which caused concentrations to stabilize instead of continuing to increase linearly.

Finally, the potential for in situ disinfection was examined by passing a synthetic greywater containing a representative coliform loading through the cathode at current densities of 0.1 and 1 mA/cm2 for 60 minutes and 10 minutes, respectively. Relatively high levels of coliform inactivation occurred, and were believed to be enhanced by the presence of iron in the synthetic greywater, which may have led to the formation of additional hydroxyl radicals.

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