Continuous Hydrogen Peroxide Production in Microbial Electrochemical Cells

Hydrogen peroxide (H₂O₂) is a commonly used chemical in the water and wastewater industries. H₂O₂ is an oxidizing agent to organic contaminants in water. H₂O₂ is coupled with the Fenton process or UV treatment in advanced oxidation processes to disinfect drinking water. Complex organic contaminants can be oxidized by H₂O₂ to form simpler products that are bioavailable for consumption by microorganisms. Currently, 95% of H₂O₂ is produced using the anthraquinone process, which requires large amounts of energy and uses potentially carcinogenic catalysts. Producing H₂O₂ using microbial electrochemical cells (MECs) may be a more sustainable alternative to these processes. An MEC consists of an anode, where bacteria oxidize wastewater organics and respire electrons to the anode to produce current. The reduction of O₂ is carried out with relatively low-cost catalysts at the cathode. My MEC is a flat plate reactor with two chambers. It includes a carbon fiber, which serves as the anode, an anion exchange membrane and a carbon cloth exposed to catholyte on one side and air on the other. All of these components have areas of 49 cm², and are compressed together to construct the MEC. The MEC is fed continuously at the anode chamber with acetate media. The MEC operates at a set air flow with a chosen electrolyte and a set hourly retention time (HRT). My research objective is to demonstrate continuous H₂O₂ production and optimize operation conditions for H₂O₂ production. This MEC is the first continuously produce H₂O₂, and at concentrations greater than 0.15%_. The cathode chamber was fed continuously for more than two months without downtime.  My MEC produced a maximum H₂O₂ concentration of 0.3076 wt%, using 200 mM NaCl electrolyte with no EDTA stabilizer, 20 ccm air flow rate and 4 hour HRT. Increasing HRT from 1 and 4 hours led to an increase in H₂O₂ production from about 0.12 wt% to 0.3 wt%; 6 hour HRT showed a decrease in H₂O_2. Changes in air flow rate have no significant effect on H₂O₂ production. Including EDTA as a H₂O₂ stabilizer decreased H₂O₂ production from about 0.35 wt% to 0.15 wt%, likely due to its diffusion through the AEM to the anode chamber preventing microbial growth. In future research, I will test other electrolytes for improved H₂O₂ production. I believe that sustainable technologies like MECs have the potential to remediate wastewater and produce H₂O₂ for water disinfection at remote communities that do not have access to clean, running water, like the rural communities on the Navajo and Hopi reservations and military forward operating bases.