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- All Subjects: Microbial Electrochemical Cells
- Creators: Torres, Cesar
- Creators: Krajmalnik-Brown, Rosa
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.
Microbial peroxide producing cells (MPPCs) are a type of microbial electrochemical cells that are used to produce hydrogen peroxide (H2O2). Different catholytes were evaluated in biotic and abiotic reactors to determine their impacts on reactor performance. The abiotic reactor produced cathode efficiencies of less than 1%, leading us to investigate the potential causes of the low efficiency. An acid wash of the reactor parts was observed to significantly decrease the degradation rate of peroxide in the reactor, indicating that metal impurities in the catholyte solution was the driving cause of the low peroxide yields in the reactor. Diffusion testing confirmed that peroxide diffused across the anion exchange membrane (AEM) at a rate of 13.3 mg/L/hr, but had no significant impact on the overall peroxide produced in the reactor. We also confirmed that auto-decay of H2O2 was not responsible for the low observed yields.