Hydrogen evolution is not a spontaneous reaction, so current electrochemical H 2 systems either require an external power supply or use complex photocathodes. We present in this study that by using electrical decoupling, H 2 can be produced spontaneously from wastewater. A power management system (PMS) circuit was deployed to decouple bioanode organic oxidation from abiotic cathode proton reduction in the same electrolyte. The special PMS consisted of a boost converter and an electromagnetic transformer, which harvested energy from the anode followed by voltage magnification from 0.35 V to 2.2–2.5 V, enabling in situ H 2 evolution for over 96 h without consuming any external energy. This proof-of-concept demonstrated a cathode faradaic efficiency of 91.3% and a maximum overall H 2 conversion efficiency of 28.9%. This approach allows true self-sustaining wastewater to H 2 evolution, and the system performance can be improved via the PMS and reactor optimization.
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Evaluation of gas and carbon transport in a methanogenic bioelectrochemical system (BES)
Bioelectrochemical systems (BESs) may be used to upgrade anaerobic digester biogas by directly converting CO2to CH4. The objective of this study was to evaluate gas (N2, CO2, CH4, and H2) and carbon transport within a methanogenic BES. Four BES configurations were evaluated: abiotic anode with abiotic cathode (AAn‐ACa), bioanode with abiotic cathode (BAn‐ACa), abiotic anode with biocathode (AAn‐BCa), and bioanode with biocathode (BAn‐BCa). Transport of N2, a gas commonly used for flushing anoxic systems, out of the anode headspace ranged from 3.7 to 6.2 L/d‐atm‐m2, normalized to the proton exchange membrane (PEM) surface area and net driving pressure (NDP). CO2was transported from the cathode to the anode headspace at rates from 3.7 to 5.4 L/d‐atm‐m2. The flux of H2from cathode to anode headspace was 48% greater when the system had a biocathode (AAn‐BCa) than when H2was produced at an abiotic cathode (BAn‐ACa), even though the abiotic cathode headspace had 75% more H2than the AAn‐BCa biocathode at the end of 1 day. A 7‐day carbon balance of a batch‐fed BAn‐BCa BES showed transient microbial carbon storage and a net transport of carbon from anode to cathode. After a 7‐day batch incubation, the CH4production in the biocathode was 27% greater on a molar basis than the initial CO2supplied to the biocathode headspace, indicating conversion of CO2produced in the anode. This research expands the current understanding of methanogenic BES operation, which may be used in improving the assessment of BES performance and/or in the development of alternative BES designs and mathematical models. Biotechnol. Bioeng. 2017;114: 961–969. © 2016 Wiley Periodicals, Inc.
- PAR ID:
- 10236348
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Biotechnology and Bioengineering
- Volume:
- 114
- Issue:
- 5
- ISSN:
- 0006-3592
- Page Range / eLocation ID:
- p. 961-969
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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