Novel Methanogenic Rotatable Bioelectrochemical System Operated with Polarity Inversion

Abstract

A novel membraneless bioelectrochemical system termed rotatable bioelectrochemical contactor (RBEC) was fabricated and evaluated for its ability to recover useful energy (here methane) from a low organic strength wastewater. We studied the operational characteristics of the RBEC by operating it as a three-electrode electrolysis cell. A stack of conductive disks (each subdivided into two half disks), similar to rotating biological contactors, were rotated with one-half disk immersed in the wastewater and the other into the gas headspace. By carrying out regular half rotations (180° rotation) the anode became the cathode and vice versa. This operation resulted in the build-up of a biofilm that could catalyze both an anodic acetate oxidation and a cathode-driven methanogenesis. Methane production rate was directly proportional to the applied electrical energy. Increase in current density (from 0.16 to 4.1 A m(-2)) resulted in a faster COD removal (from 0.2 to 1.38 kg COD m(-3) day(-1)) and methane production (from 0.04 to 0.53 L L(-1) day(-1)). Of the electrons flowing across the circuit, over 80% were recovered as methane. Such methane production was electrochemically driven by the headspace-exposed cathodic half disks, which released the methane directly to the gas-phase. Energy analysis shows that the new design requires less energy for COD removal than what is typically required for oxygen supply in activated sludge processes. Because the system could operate without wastewater recirculation against gravity; additional pH buffer chemicals; ion-exchange membranes or electrochemical catalysts, it has desirable characteristics for process up-scale. Further, the current report shows the first example of a BES with identical biofilm (due to intermittent polarity inversion) on both electrodes.

Impact of applied voltage on methane generation and microbial activities in an anaerobic microbial electrolysis cell (MEC)

“…Sasaki [5,6,7] found that methane yield has been significantly improved when MEC is used for solid waste treatment. Cheng [8] established a novel methanogenic rotatable BES operated with polarity inversion and they found the methane production rate was directly proportional to the applied electrical energy. Chae [9] studied the inhibition of methanogens in a two-chambered MEC and the results showed that abrupt decrease in temperature and pH had no effects on methanogenesis and exposing the anode biofilm to air was also ineffective in inhibiting specific methanogens.…”

Enrichment of Microbial Electrolysis Cell Biocathodes from Sediment Microbial Fuel Cell Bioanodes

“…Biofilms that develop on electrodes in MFCs under oxic cathode conditions have been shown to sustain current generation when the functions of the electrodes are switched (the cathode, for example, becomes the anode) (7,8,35). This indicates that both exoelectrogenic and electrotrophic microorganisms can be maintained in the electrode biofilms when the cathode is switched from oxic to anoxic conditions.…”

Tetramethylammonium hydroxide production using the microbial electrolysis desalination and chemical-production cell

“…As shown in Eqs. (5)(6)(7), the pH in the anode chamber can be controlled at 7.0 with the synergistic reaction between the BPM and exoelectrogens throughout the experiments, resulting in the high performance of MEDCC. Our MEDCC has better performance in terms of current density and Columbic efficiency than other bioelectrochemical systems, such as MDC and MEDC [15,24].…”

“…Because the exoelectrogens can utilize many kinds of organics and release electrons in the neutral solution at room temperature, the BES is potentially useful in the electrosynthesis field [2]. Many products have been reported to be produced in the BES, such as hydrogen, hydrogen peroxide, methane, and others [3][4][5][6]. However, the application of BES is still limited mainly because of relatively low values of the above products.…”