abstract: Microbial electrochemical cells (MxCs) are a novel technology that use anode-respiring bacteria (ARB) to bioremediate wastewaters and respire an electrical current, which can then be used directly to produce value-added products like hydrogen peroxide (H2O2). Ninety-five percent of the world’s H2O2 is currently produced using the anthraquinone process, whose production requires expensive and potentially carcinogenic catalysts and high amounts of electricity. However, the amount of H2O2 that can be produced from these microbial peroxide-producing cells (MPPCs) has not been thoroughly investigated. Predicting potential H2O2 production in MxCs is further complicated by a lack of mathematical models to predict performance utilizing complex waste streams like primary sludge (PS). A reactor design methodology was developed for MPPCs to systematically optimize H2O2 production with minimal energy consumption. H2O2 stability was evaluated with different catholytes, membranes, and catalysts materials, and the findings used to design and operate long-term a dual-chamber, flat-plate MPPC using different catholytes, ferrochelating stabilizers, and hydraulic retention times (HRT). Up to 3.1 ± 0.37 g H2O2 L-1 was produced at a 4-h HRT in an MPPC with as little as 1.13 W-h g-1 H2O2 power input using NaCl catholytes. Attempts to improve H2O2 production by using weak acid buffers as catholytes or ferrochelating stabilizers failed for different reasons. A non-steady-state mathematical model, MYAnode, was developed combinging existing wastewater treatment, anode biofilm, and chemical speciation models to predict MxC performance utilizing complex substrates. The model simulated the large-scale trends observed when operating an MPPC with PS substrate. At HRTs ≥ 12-d, the model demonstrated up to 20% Coulombic recovery. At these conditions, ARB required additional alkalinity production by ≥ 100 mgVSS/L of acetoclastic methanogens to prevent pH inhibition when little influent alkalinity is available. At lower HRTs, methanogens are unable to produce the alkalinity required to prevent ARB inhibition due to washout and rapid acidification of the system during fermentation. At ≥ 100 mgVSS/L of methanogens, increasing the diffusion layer thickness from 500 to 1000 μm improved Coulombic efficiency by 13.9%, while increasing particulate COD hydrolysis rates to 0.25/d only improved Coulombic efficiency by 3.9%. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2018

abstract: Microbial electrochemical cells (MXCs) serve as an alternative anaerobic technology to anaerobic digestion for efficient energy recovery from high-strength organic wastes such as primary sludge (PS). The overarching goal of my research was to address energy conversion from PS to useful resources (e.g. hydrogen or hydrogen peroxide) through bio- and electro-chemical anaerobic conversion processes in MXCs. First, a new flat-pate microbial electrolysis cell (MEC) was designed with high surface area anodes using carbon fibers, but without creating a large distance between the anode and the cathode (<0.5 cm) to reduce Ohmic overpotential. Through the improved design, operation, and electrochemical characterization, the applied voltages were reduced from 1.1 to ~0.85 V, at 10 A m-2. Second, PS conversion was examined through hydrolysis, fermentation, methanogenesis, and/or anode respiration. Since pretreatment often is required to accelerate hydrolysis of organic solids, I evaluated pulsed electric field technology on PS showing a modest improvement of energy conversion through methanogenesis and fermentation, as compared to the conversion from waste activated sludge (WAS) or WAS+PS. Then, a two-stage system (prefermented PS-fed MEC) yielded successful performance in terms of Coulombic efficiency (95%), Coulombic recovery (CR, 80%), and COD-removal efficiency (85%). However, overall PS conversion to electrical current (or CR) through pre-fermentation and MEC, was just ~16%. Next, a single-stage system (direct PS-fed MEC) with semi-continuous operation showed 34% CR at a 9-day hydraulic retention time. The PS-fed MEC also showed an important pH dependency, in which high pH (> 8) in the anode chamber improved anode respiration along with methanogen inhibition. Finally, H2O2 was produced in a PS-fed microbial electrochemical cell with a low energy requirement (~0.87 kWh per kg H2O2). These research developments will provide groundbreaking knowledge for MXC design, commercial application, and anaerobic energy conversion from other high-strength organic wastes to resources. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

abstract: Eighty-two percent of the United States population reside in urban areas. The centralized treatment of the municipal wastewater produced by this population is a huge energy expenditure, up to three percent of the entire energy budget of the country. A portion of this energy is able to be recovered through the process of anaerobic sludge digestion. Typically, this technology converts the solids separated and generated during the wastewater treatment process into methane, a combustible gas that may be burned to generate electricity. Designing and optimizing anaerobic digestion systems requires the measurement of degradation rates for waste-specific kinetic parameters. In this work, I discuss the ways these kinetic parameters are typically measured. I recommend and demonstrate improvements to these commonly used measuring techniques. I provide experimental results of batch kinetic experiments exploring the effect of sludge pretreatment, a process designed to facilitate rapid breakdown of recalcitrant solids, on energy recovery rates. I explore the use of microbial electrochemical cells, an alternative energy recovery technology able to produce electricity directly from sludge digestion, as precise reporters of degradation kinetics. Finally, I examine a fundamental kinetic limitation of microbial electrochemical cells, acidification of the anode respiring biofilm, to improve their performance as kinetic sensors or energy recovery technologies. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2020