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The anode activity in a microbial electrolysis cell (MEC) is known to be a limiting factor in hydrogen production. In this study, the MEC was constructed using different anode materials and a platinum-coated carbon-cloth cathode (CC). The anodes were comprised of CC, stainless steel (SS), and a combination of the two (COMB). The CC and SS anodes were also treated with plasma to improve their surface morphology and hydrophilic properties (CCP and SSP, respectively). A combined version of CCP attached to SS was also applied (COMBP). After construction of the MEC using the different anodes, we conducted electrochemical measurements and examination of biofilm viability. Under an applied voltage of 0.6 V (Ag/AgCl), the currents of a MEC based on CCP and COMBP were 11.66 ± 0.1331 and 16.36 ± 0.3172 A m−2, respectively, which are about three times higher compared to the untreated CC and COMB. A MEC utilizing an untreated SS anode exhibited current of only 0.3712 ± 0.0108 A m−2. The highest biofilm viability of 0.92 OD540 ± 0.07 and hydrogen production rate of 0.0736 ± 0.0022 m3 d−1 m−2 at 0.8 V were obtained in MECs based on the COMBP anode. To our knowledge, this is the first study that evaluated the effect of plasma-treated anodes and the use of a combined anode composed of SS and CC for hydrogen evolution in a MEC.

Summary This study focuses on a semi‐single‐chamber microbial electrolysis cell (MEC) based on an anode made of carbon cloth (CCp) combined with stainless‐steel (SS) and encapsulated in a dialysis bag with different molecular weight cut‐offs of 2, 14, and 50 kDa (D2‐, D14‐, and D50‐COMBp, respectively). The encapsulated anode was inoculated with Geobacter sulfurreducens in a small volume directly into the dialysis bag. While the MEC with the non‐encapsulated anode was inoculated into the main chamber volume. The hydrogen evolution rates obtained in the MECs based on D2‐COMBp, D14‐COMBp, and D50‐COMBp anodes were 0.134 ± 0.005, 0.144 ± 0.014, and 0.160 ± 0.009 m3m−2d−1, respectively; while the COMBp led to only 0.122 ± 0.004 m3m−2d−1. When the MEC utilizing D50‐COMBp was fed with wastewater, the current density was only 12.4 ± 0.21 A m−2, compared to feeding with acetate (15.7 ± 0.63 A m−2). The encapsulated anode in the presence of wastewater included 70% of G. sulfurreducens, while the non‐encapsulated included only 58%.

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Microbial electrolysis cells (MECs) are an emerging technology capable of harvesting part of the potential chemical energy in organic compounds while producing hydrogen. One of the main obstacles in MECs is the bacterial anode, which usually contains mixed cultures. Non-exoelectrogens can act as a physical barrier by settling on the anode surface and displacing the exoelectrogenic microorganisms. Those non-exoelectrogens can also compete with the exoelectrogenic microorganisms for nutrients and reduce hydrogen production. In addition, the bacterial anode needs to withstand the shear and friction forces existing in domestic wastewater plants. In this study, a bacterial anode was encapsulated by a microfiltration membrane. The novel encapsulation technology is based on a small bioreactor platform (SBP) recently developed for achieving successful bioaugmentation in wastewater treatment plants. The 3D capsule (2.5 cm in length, 0.8 cm in diameter) physically separates the exoelectrogenic biofilm on the carbon cloth anode material from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. MECs based on the SBP anode (MEC-SBPs) and the MECs based on a nonencapsulated anode (MEC control) were fed with Geobacter medium supplied with acetate for 32 days, and then with artificial wastewater for another 46 days. The electrochemical activity, chemical oxygen demand (COD), bacterial anode viability and relative distribution on the MEC-SBP anode were compared with the MEC control. When the MECs were fed with artificial wastewater, the MEC-SBP produced (at −0.6 V) 1.70 ± 0.22 A m−2, twice that of the MEC control. The hydrogen evolution rates were 0.017 and 0.005 m3 m−3 day−1, respectively. The COD consumption rate for both was about the same at 650 ± 70 mg L−1. We assume that developing the encapsulated bacterial anode using the SBP technology will help overcome the problem of contamination by non-exoelectrogenic bacteria, as well as the shear and friction forces in wastewater plants.